Secondary battery, preparation method thereof, modified conductive agent and power utilization device

Abstract

The invention discloses a secondary battery and a preparation method thereof, a modified conductive agent and an electric device. The secondary battery comprises a positive pole piece, the positive pole piece comprises a current collector and a positive active layer loaded on the surface of the current collector, the positive active layer comprises a positive active material and a modified conductive agent, the modified conductive agent comprises a conductive agent and a chelating agent, and the chelating agent is connected with the surface of the conductive agent through a chemical bond. The chelating agent comprises a transition metal ion chelating functional group, and the transition metal ion chelating functional group comprises a phosphate group and / or a phosphate group. The chelating agent adopted by the invention can be combined with the transition metal ions dissolved out from the positive electrode active layer through coordination, and the dissolution and diffusion of the transition metal ions in the battery are inhibited, so that the cycle performance of the battery is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to secondary batteries and their preparation methods, modified conductive agents, and electrical devices. Background Technology

[0002] Secondary batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles and electric cars, as well as in military equipment and aerospace and other fields.

[0003] Improving the cycle performance of rechargeable batteries has always been an industry goal. However, during the cycle of a rechargeable battery, metal ions such as Ni, Co, and Mn will dissolve from the positive electrode. These dissolved metal ions will enter the electrolyte and diffuse through the separator to the negative electrode, where they will be reduced and deposited on the surface of the negative electrode. This will cause the reversible cycle capacity of the battery to decay, thus reducing the cycle performance. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery and its preparation method, a modified conductive agent, and an electrical device, which aims to solve the problem of reduced battery cycle performance caused by the dissolution of metal ions in the positive electrode of the battery during battery cycling.

[0005] To achieve the above objectives, in a first aspect, this application provides a secondary battery, including a positive electrode sheet, the positive electrode sheet including a current collector and a positive electrode active layer loaded on the surface of the current collector, the positive electrode active layer including a positive electrode active material and a modified conductive agent, wherein the modified conductive agent includes a conductive agent and a chelating agent, the chelating agent is connected to the surface of the conductive agent by chemical bonds, the chelating agent includes a transition metal ion chelating functional group, the transition metal ion chelating functional group including a phosphate group and / or a phosphate group.

[0006] In the secondary battery of this application, the modified conductive agent used in the positive electrode includes a chelating agent connected to the surface of the conductive agent. The transition metal ion chelating functional group contained in the chelating agent can combine with the dissolved transition metal ions in the positive electrode active layer through coordination. That is, phosphate groups and / or phosphate groups can fix the dissolved transition metal ions in the positive electrode active layer through coordination, inhibiting the dissolution and diffusion of transition metal ions in the battery, thereby hindering the transition metal ions from shuttling to the negative electrode, and thus improving the problem of reduced battery cycle performance.

[0007] In any embodiment, the chelating agent comprises an organophosphate. The organic groups contained in the organophosphate are more conducive to the chelating agent attaching to the surface of the conductive agent via chemical bonds.

[0008] In any embodiment, the number of phosphate groups and / or phosphate groups in the chelating agent is n≥2. This suitable number of phosphate groups and / or phosphate groups is beneficial for capturing and immobilizing transition metal ions dissolved in the positive electrode active layer.

[0009] In any embodiment, the secondary battery includes a lithium-ion secondary battery, and the chelating agent includes a lithium organophosphate salt; or, the secondary battery includes a sodium-ion secondary battery, and the chelating agent includes a sodium organophosphate salt. The use of lithium organophosphate salts in lithium-ion secondary batteries facilitates the release of lithium ions during battery use, acting as a lithium replenishment agent, thereby increasing battery capacity and further improving battery cycle performance. Similarly, the use of sodium organophosphate salts in sodium-ion secondary batteries facilitates the release of sodium ions during battery use, acting as a sodium replenishment agent, thereby increasing battery capacity and further improving battery cycle performance.

[0010] In any embodiment, the chelating agent comprises an alkyl backbone and a transition metal ion chelating functional group as shown in Formula I, wherein at least one hydrogen atom in the alkyl backbone bonded to a carbon atom is replaced by a transition metal ion chelating functional group as shown in Formula I.

[0011] -PO3H x M y Formula I

[0012] Where M includes sodium or lithium; x is 0 or a positive integer, y is a positive integer, and x+y=2;

[0013] The alkyl backbone includes any one of alkyl groups having 1-8 carbon atoms, alkyl alcohols having 1-8 carbon atoms, and alkylamines having 1-8 carbon atoms and 1-2 nitrogen atoms.

[0014] In the transition metal ion chelating functional group shown in Formula I of the chelating agent, the oxygen atom bonded to the phosphorus atom contains a lone pair of electrons, which can chelate with the transition metal ions, thereby inhibiting the dissolution and diffusion of transition metal ions such as Co, Ni, and Mn in the battery, thus hindering the transition metal ions from shuttling to the negative electrode and improving the battery cycle performance.

[0015] In any embodiment, the number n of transition metal ion chelating functional groups of Formula I in the chelating agent is 2-6, and the alkyl backbone of the chelating agent includes any one of alkyl groups with 1-5 carbon atoms, alkyl alcohols with 1-4 carbon atoms, and alkylamines with 2-6 carbon atoms and 1-2 nitrogen atoms. A suitable number of transition metal ion chelating functional groups is beneficial for capturing and immobilizing transition metal ions dissolved in the positive electrode active layer. Using the above-mentioned groups with suitable carbon and nitrogen numbers in the alkyl backbone helps control the spatial configuration of the chelating agent, thereby facilitating the capture of transition metal ions.

[0016] In any embodiment, the chelating agent comprises at least one of the compounds shown in Formula I-1 to Formula I-6:

[0017]

[0018] In the technical solution of this application, in the structural formulas shown in I-1 to I-6, phosphate groups are used as transition metal ion chelating functional groups. The oxygen atoms in the phosphate groups that are connected to phosphorus atoms contain lone pairs of electrons, which can chelate with transition metal ions, thereby inhibiting the dissolution and diffusion of transition metal ions such as Co, Ni, and Mn in the battery, and thus hindering the transition metal ions from shuttling to the negative electrode and improving the battery cycle performance.

[0019] In any embodiment, the mass ratio of the conductive agent to the chelating agent is 1:(1.5-18). This suitable ratio facilitates the capture and fixation of transition metal ions by the chelating agent without affecting the conductivity of the conductive agent.

[0020] In any embodiment, the mass ratio of the conductive agent to the chelating agent is 1:(3-10). This suitable ratio is more conducive to leveraging the chelating agent's ability to capture and immobilize transition metal ions without affecting the conductivity of the conductive agent.

[0021] In any embodiment, the conductive agent includes at least one of carbon nanotubes, graphene, carbon nanofibers, conductive graphite, and conductive carbon black. Using the aforementioned conductive agent with excellent conductivity is beneficial for maximizing its conductive properties.

[0022] In any embodiment, the mass ratio of the modified conductive agent to the positive electrode active material in the positive electrode active layer is (5-10):(85-90). This suitable ratio is beneficial in two ways: firstly, it allows the chelating agent to effectively capture and immobilize transition metal ions; secondly, it allows the conductive agent itself to effectively conduct electricity.

[0023] Secondly, this application provides an electrical device including the secondary battery provided in the first aspect.

[0024] Thirdly, this application provides a modified conductive agent, comprising a conductive agent and a chelating agent, wherein the chelating agent is connected to the surface of the conductive agent by chemical bonds, and the chelating agent comprises a transition metal ion chelating functional group, wherein the transition metal ion chelating functional group comprises a phosphate group and / or a phosphate group.

[0025] The modified conductive agent used in this application includes a chelating agent connected to the surface of the conductive agent. The transition metal ion chelating functional group contained in the chelating agent can combine with the dissolved transition metal ions in the positive electrode active layer through coordination. That is, phosphate groups and / or phosphate groups can fix the dissolved transition metal ions in the positive electrode active layer through coordination, inhibit the dissolution and diffusion of transition metal ions in the battery, thereby hindering the transition metal ions from shuttling to the negative electrode, and thus improving the problem of reduced battery cycle performance.

[0026] In any embodiment, the chelating agent comprises an organophosphate. The organic groups contained in the organophosphate are more conducive to the chelating agent attaching to the surface of the conductive agent via chemical bonds.

[0027] In any embodiment, the number of phosphate groups and / or phosphate groups in the chelating agent is n≥2. This suitable number of phosphate groups and / or phosphate groups is beneficial for capturing and immobilizing transition metal ions dissolved in the positive electrode active layer.

[0028] In any embodiment, the chelating agent comprises an alkyl backbone and a transition metal ion chelating functional group as shown in Formula I, wherein at least one hydrogen atom in the alkyl backbone bonded to a carbon atom is replaced by a transition metal ion chelating functional group as shown in Formula I.

[0029] -PO3H x M y Formula I

[0030] Where M includes sodium or lithium; x is 0 or a positive integer, y is a positive integer, and x+y=2;

[0031] The alkyl backbone includes any one of alkyl groups having 1-8 carbon atoms, alkyl alcohols having 1-8 carbon atoms, and alkylamines having 1-8 carbon atoms and 1-2 nitrogen atoms.

[0032] In the transition metal ion chelating functional group shown in Formula I of the chelating agent, the oxygen atom bonded to the phosphorus atom contains a lone pair of electrons, which can chelate with the transition metal ions, thereby inhibiting the dissolution and diffusion of transition metal ions such as Co, Ni, and Mn in the battery, thus hindering the transition metal ions from shuttling to the negative electrode and improving the battery cycle performance.

[0033] In any embodiment, the number n of transition metal ion chelating functional groups of Formula I in the chelating agent is 2-6, and the alkyl backbone of the chelating agent includes any one of alkyl groups with 1-5 carbon atoms, alkyl alcohols with 1-4 carbon atoms, and alkylamines with 2-6 carbon atoms and 1-2 nitrogen atoms. A suitable number of transition metal ion chelating functional groups is beneficial for capturing and immobilizing transition metal ions dissolved in the positive electrode active layer. Using the above-mentioned groups with suitable carbon and nitrogen numbers in the alkyl backbone helps control the spatial configuration of the chelating agent, thereby facilitating the capture of transition metal ions.

[0034] In any embodiment, the chelating agent comprises at least one of the compounds shown in Formula I-1 to Formula I-6:

[0035]

[0036] In the technical solution of this application, in the structural formulas shown in I-1 to I-6, phosphate groups are used as transition metal ion chelating functional groups. The oxygen atoms in the phosphate groups that are connected to phosphorus atoms contain lone pairs of electrons, which can chelate with transition metal ions, thereby inhibiting the dissolution and diffusion of transition metal ions such as Co, Ni, and Mn in the battery, and thus hindering the transition metal ions from shuttling to the negative electrode and improving the battery cycle performance.

[0037] In any embodiment, the mass ratio of the conductive agent to the chelating agent is 1:(1.5-18). This suitable ratio facilitates the capture and fixation of transition metal ions by the chelating agent without affecting the conductivity of the conductive agent.

[0038] In any embodiment, the mass ratio of the conductive agent to the chelating agent is 1:(3-10). This suitable ratio is more conducive to leveraging the chelating agent's ability to capture and immobilize transition metal ions without affecting the conductivity of the conductive agent.

[0039] In any embodiment, the conductive agent includes at least one of carbon nanotubes, graphene, carbon nanofibers, conductive graphite, and conductive carbon black. Using the aforementioned conductive agent with excellent conductivity is beneficial for maximizing its conductive properties.

[0040] Fourthly, this application provides a method for preparing a secondary battery according to the first aspect, including a positive electrode preparation step, wherein the preparation step includes:

[0041] A positive electrode slurry is obtained by mixing positive electrode active material, modified conductive agent, binder and solvent;

[0042] The positive electrode slurry is coated onto the current collector to prepare a positive electrode sheet;

[0043] The modified conductive agent includes a conductive agent and a chelating agent that is chemically bonded to the surface of the conductive agent. The chelating agent includes a transition metal ion chelating functional group, which includes a phosphate group.

[0044] The preparation method provided in this application is simple and conducive to industrial application.

[0045] In any embodiment, the modified conductive agent is prepared by the following steps:

[0046] The conductive agent is treated with acid;

[0047] The modified conductive agent is obtained by mixing the acid-treated conductive agent with a solution containing a chelating agent.

[0048] The surface of the acid-treated conductive agent has active oxygen-containing functional groups, which facilitates its combination with the carbon-containing functional groups in the chelating agent through chemical bonds.

[0049] In any embodiment, in the step of acid treatment of the conductive agent, the acid used for acid treatment includes at least one of sulfuric acid and nitric acid; the concentration of the acid used for acid treatment is 12-18 mol / L; and the acid treatment time is 2-5 hours. These suitable acid treatment conditions are beneficial for the conductive agent surface to have active oxygen-containing functional groups, thereby facilitating the bonding of the conductive agent with the carbon-containing functional groups in the chelating agent through chemical bonds.

[0050] In any embodiment, the chelating agent comprises an organophosphate lithium salt or an organophosphate sodium salt, and the chelating agent is prepared by the following steps: mixing an organophosphate with a lithium salt or a sodium salt to undergo a substitution reaction to prepare the chelating agent. The substitution reaction can yield organophosphates with different lithium or sodium atom substitutions. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0052] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0053] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0054] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0055] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0056] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0057] Figure 7 This is a comparison chart of the charge-discharge curves of Embodiment 1 and Comparative Example 1 of this application.

[0058] Figure 8 This is a comparison chart of the cycle performance of Embodiment 1 and Comparative Example 1 of this application.

[0059] Explanation of reference numerals in the attached figures:

[0060] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0061] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, its preparation method, modified conductive agent, and electrical 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 for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0062] 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 article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated 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.

[0063] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0064] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0065] 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.

[0066] 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.

[0067] Improving the cycle performance of rechargeable batteries has always been an industry goal. However, during the cycling process, metal ions dissolve from the positive electrode. Taking lithium-ion rechargeable batteries as an example, the positive electrode material of current lithium-ion batteries is mainly composed of Li-containing transition metal oxides. During the Li+ extraction and insertion process, the transition metal elements undergo valence changes, thus maintaining the overall electroneutrality of the positive electrode material. Ni, Co, and Mn are three common transition metal elements in lithium-ion batteries. However, during the cycling process of lithium-ion batteries, the dissolution of transition metal elements is a very common phenomenon. The dissolved transition metal ions enter the electrolyte and diffuse through the separator to the negative electrode, where they are reduced and deposited on the surface of the negative electrode. This leads to a decrease in the reversible cycle capacity of the battery, thereby reducing the cycle performance.

[0068] Based on this, in a first aspect, embodiments of this application provide a secondary battery, including a positive electrode sheet, the positive electrode sheet including a current collector and a positive electrode active layer loaded on the surface of the current collector, the positive electrode active layer including a positive electrode active material and a modified conductive agent, wherein the modified conductive agent includes a conductive agent and a chelating agent, the chelating agent is connected to the surface of the conductive agent by chemical bonds, the chelating agent includes a transition metal ion chelating functional group, the transition metal ion chelating functional group including phosphate groups and / or phosphate groups.

[0069] In this article, "transition metal ion chelating functional group" refers to a group that can form a stable complex with transition metal ions through coordination bonds.

[0070] In this article, "phosphate group" refers to the group shown in the following formula.

[0071]

[0072] In this article, "phosphate group" refers to the group shown in the following formula, where M represents a metal ion.

[0073]

[0074] It should be noted that in this article, the chelating agent is connected to the surface of the conductive agent through chemical bonds, which may include covalent bonds, etc.

[0075] Phosphate groups and / or phosphate groups can be qualitatively or quantitatively detected using equipment and methods known in the art. Relevant detection methods can refer to domestic and international testing standards and enterprise standards. Furthermore, those skilled in the art can adapt certain detection steps / instrument parameters to obtain more accurate results from the perspective of detection accuracy. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination. For example, infrared spectroscopy analysis of the positive electrode in a secondary battery can be performed using instruments and methods known in the art, such as an infrared spectrometer, like the Nicolet IS10 Fourier transform infrared spectrometer, according to GB / T6040-2002 General Rules for Infrared Spectroscopic Analysis, to test the infrared spectrum of the positive electrode of this application.

[0076] For example, a fresh battery cell can be fully charged to approximately 0% SOC and then disassembled to extract the positive electrode sheet, or a used battery cell can be fully charged to approximately 0% SOC and then disassembled to extract the positive electrode sheet. A positive electrode active layer powder sample is obtained using a scraping method, and phosphate groups and / or phosphate groups can be qualitatively or quantitatively detected using an infrared spectroscopy instrument. In the embodiments of this application, a fresh battery cell can be a battery cell that has just left the factory (not yet subjected to charge-discharge cycles after formation).

[0077] In the secondary battery of this application, the modified conductive agent used in the positive electrode includes a chelating agent connected to the surface of the conductive agent. The transition metal ion chelating functional group contained in the chelating agent can combine with the dissolved transition metal ions in the positive electrode active layer through coordination. That is, phosphate groups and / or phosphate groups can fix the dissolved transition metal ions in the positive electrode active layer through coordination, inhibiting the dissolution and diffusion of transition metal ions in the battery, thereby hindering the transition metal ions from shuttling to the negative electrode, and thus improving the problem of reduced cycle performance of the battery.

[0078] In some embodiments, the chelating agent includes an organophosphate. The organic groups contained in the organophosphate are more conducive to the chelating agent attaching to the surface of the conductive agent through chemical bonds.

[0079] In this article, organophosphates may include only phosphate groups, or they may include both phosphate groups and phosphate groups. Organophosphates can refer to compounds formed by the bonding of phosphorus elements in phosphate groups with organic groups.

[0080] It should be noted that, under normal circumstances, organophosphonates have poor conductivity, and if they are mixed directly in the positive electrode active layer by physical mixing, it will be difficult for them to gain electrons and thus fail to play their role in capturing transition metal ions. In this application, a chelating agent is used to connect with a conductive agent with good conductivity through chemical bonds, which can effectively enable organophosphonates to capture transition metal ions.

[0081] In some embodiments, the number of phosphate groups and / or phosphate groups in the chelating agent is n≥2. This suitable number of phosphate groups and / or phosphate groups is beneficial for capturing and immobilizing transition metal ions dissolved in the positive electrode active layer.

[0082] In some embodiments, the secondary battery includes a lithium-ion secondary battery, and the chelating agent includes lithium organophosphate; or, the secondary battery includes a sodium-ion secondary battery, and the chelating agent includes sodium organophosphate. The use of lithium organophosphate in lithium-ion secondary batteries facilitates the release of lithium ions during battery use, acting as a lithium replenishment agent, thereby increasing battery capacity and further improving battery cycle performance. Similarly, the use of sodium organophosphate in sodium-ion secondary batteries facilitates the release of sodium ions during battery use, acting as a sodium replenishment agent, thereby increasing battery capacity and further improving battery cycle performance.

[0083] In this article, organolithium phosphate salts and organosodium phosphate salts may include only phosphate groups, or they may include both phosphate groups and phosphate groups.

[0084] In some embodiments, the chelating agent comprises an alkyl backbone and a transition metal ion chelating functional group as shown in Formula I, wherein at least one hydrogen atom in the alkyl backbone bonded to a carbon atom is replaced by the transition metal ion chelating functional group as shown in Formula I.

[0085] -PO3H x M y Formula I

[0086] Where M includes sodium or lithium; x is 0 or a positive integer, y is a positive integer, and x+y=2;

[0087] The alkyl backbone includes any one of alkyl groups having 1-8 carbon atoms, alkyl alcohols having 1-8 carbon atoms, and alkylamines having 1-8 carbon atoms and 1-2 nitrogen atoms.

[0088] In this document, "alkyl group with 1-8 carbon atoms" refers to a straight-chain or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, without any unsaturation, having 1 to 8 carbon atoms, and attached to the rest of the molecule by a single bond. Suitable examples include, but are not limited to: methyl (-CH3), ethyl (-CH2CH3), 1-propyl (-CH2CH2CH3), 2-propyl (-CH(CH3)2), 1-butyl (-CH2CH2CH2CH3), 1-pentyl (-CH2CH2CH2CH2CH3), 1-hexyl (-CH2CH2CH2CH2CH2CH3), 1-heptyl (-CH2CH2CH2CH2CH2CH2CH3), and 1-octyl (-CH2CH2CH2CH2CH2CH2CH2CH3).

[0089] In this document, "alkyl alcohols with 1-8 carbon atoms" refers to a straight-chain or branched hydrocarbon chain group composed of carbon and hydrogen atoms, in which at least one hydrogen atom is replaced by a hydroxyl group, the group is not unsaturated, has 1 to 8 carbon atoms, and is attached to the rest of the molecule by a single bond. Suitable examples include, but are not limited to: 1-hydroxymethyl (-CH2OH), 1-hydroxyethyl (-CH2CH2OH), and 1-hydroxypropyl (-CH2CH2CH2OH).

[0090] In this document, "alkylamines having 1-8 carbon atoms and 1-2 nitrogen atoms" refers to a straight-chain or branched hydrocarbon chain group composed of carbon and hydrogen atoms, in which at least one carbon atom is replaced by a nitrogen atom, the group is not unsaturated, has 1 to 8 carbon atoms, and is attached to the rest of the molecule by a single bond. Suitable examples include, but are not limited to: ethylamine (-CH2CH2NH2), trimethylamine (-CH2N(CH3)2), methyl ethylamine (-CH2NHCH2CH3), and tetramethylethylenediamine (-CH2N(CH3)CH2CH2N(CH3)2).

[0091] x is 0 or a positive integer, y is a positive integer, and x + y = 2. x can be 0 and y can be 2. In this case, both hydrogen atoms in the two hydroxyl groups connected to the phosphorus atom are replaced by metal ions. x can be 1 and y can be 1. In this case, one hydrogen atom in the two hydroxyl groups connected to the phosphorus atom is replaced by a metal ion.

[0092] In the transition metal ion chelating functional group shown in Formula I of the chelating agent, the oxygen atom bonded to the phosphorus atom contains a lone pair of electrons, which can chelate with the transition metal ions, thereby inhibiting the dissolution and diffusion of transition metal ions such as Co, Ni, and Mn in the battery, thus hindering the transition metal ions from shuttling to the negative electrode and improving the battery cycle performance.

[0093] In some embodiments, the number n of transition metal ion chelating functional groups of Formula I in the chelating agent is 2-6, and the alkyl backbone of the chelating agent includes any one of alkyl groups with 1-5 carbon atoms, alkyl alcohols with 1-4 carbon atoms, and alkylamines with 2-6 carbon atoms and 1-2 nitrogen atoms. A suitable number of transition metal ion chelating functional groups is beneficial for capturing and immobilizing transition metal ions dissolved in the positive electrode active layer. Using the above-mentioned groups with suitable carbon and nitrogen numbers in the alkyl backbone helps control the spatial configuration of the chelating agent, thereby facilitating the capture of transition metal ions.

[0094] In some embodiments, the chelating agent includes at least one of the compounds shown in Formulas I-1 to I-6:

[0095]

[0096] In the technical solution of this application, in the structural formulas shown in I-1 to I-6, phosphate groups are used as transition metal ion chelating functional groups. The oxygen atoms in the phosphate groups that are connected to phosphorus atoms contain lone pairs of electrons, which can chelate with transition metal ions, thereby inhibiting the dissolution and diffusion of transition metal ions such as Co, Ni, and Mn in the battery, and thus hindering the transition metal ions from shuttling to the negative electrode and improving the battery cycle performance.

[0097] In some embodiments, the mass ratio of the conductive agent to the chelating agent is 1:(1.5-18). At this suitable ratio, it is advantageous to utilize the chelating agent's ability to capture and immobilize transition metal ions without affecting the conductivity of the conductive agent. The mass ratio of the conductive agent to the chelating agent can be 1:1.5, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, or any range of two of the above values.

[0098] The mass ratio of chelating agent to conductive agent can be qualitatively or quantitatively determined using equipment and methods known in the art. Relevant testing methods can refer to domestic and international testing standards and enterprise standards. Furthermore, those skilled in the art can adapt certain testing steps / instrument parameters to obtain more accurate results from the perspective of testing accuracy. For example, a fresh battery cell can be fully charged to approximately 0% SOC and then disassembled to extract the positive electrode sheet, or a used battery cell can be fully charged to approximately 0% SOC and then disassembled to extract the positive electrode sheet. A positive electrode active layer powder sample can be obtained using a scraping method, and the mass ratio of conductive agent to chelating agent can be determined by thermogravimetric analysis. In the embodiments of this application, a fresh battery cell can be a battery cell that has just left the factory (not yet subjected to charge-discharge cycles after formation).

[0099] In some embodiments, the mass ratio of the conductive agent to the chelating agent is 1:(3-10). At this suitable ratio, it is more advantageous to leverage the chelating agent's ability to capture and immobilize transition metal ions without affecting the conductivity of the conductive agent.

[0100] In some embodiments, the conductive agent includes at least one of carbon nanotubes, graphene, carbon nanofibers, conductive graphite, and conductive carbon black. Using the aforementioned conductive agents with excellent conductivity is beneficial for maximizing their conductive properties.

[0101] In some embodiments, the mass ratio of the modified conductive agent to the positive electrode active material in the positive electrode active layer is (5-10):(85-90). This suitable ratio is beneficial for both the chelating agent's ability to capture and immobilize transition metal ions and the conductive agent's own conductivity. The mass ratio of the modified conductive agent to the positive electrode active material in the positive electrode active layer can be 5:90, 6:90, 7:90, 8:90, 9:90, 10:90, 5:85, 10:85, or any range of two of the above values.

[0102] The mass ratio between the modified conductive agent and the positive electrode active material can also be obtained, for example, by thermogravimetric analysis.

[0103] In addition, the secondary battery, battery module, and battery pack of this application will be described below with appropriate reference to the accompanying drawings.

[0104] In one embodiment of this application, the secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator is disposed between the positive and negative electrodes, primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing ions to pass through.

[0105] [Positive electrode plate]

[0106] 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, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0107] 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.

[0108] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0109] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0110] In some embodiments, when the secondary battery is a sodium-ion battery, the positive electrode active material may further include positive electrode active materials known in the art for sodium-ion batteries. For example, the positive electrode active material is selected from one or more of layered transition metal oxides, polyanionic compounds, and Prussian blue analogues. In layered transition metal oxides, the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Layered transition metal oxides are, for example, Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0111] Polyanionic compounds can be those containing sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state. Polyanionic compounds can also have sodium ion, transition metal ion, or tetrahedral (YO4) valence states. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl, and Br. Polyanionic compounds can also have sodium ions, tetrahedral structure (YO4). n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n-The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl, and Br. In some embodiments, the polyanionic compound is, for example, NaFePO4, Na3V2(PO4)3, NaM'PO4F (M' is one or more of V, Fe, Mn, and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0112] In some embodiments, the Prussian blue analogue may be a compound containing sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue analogues include, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0113] In some embodiments, the specific positive electrode active material is, for example, NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, Na4Fe3(PO4)2P2O7, NaFePO4, Na3V2(PO4)3, NaMnFe(CN)6, but there are no particular restrictions, so conventional positive electrode active materials used in sodium-ion batteries can be selected.

[0114] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0115] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0116] [Negative electrode plate]

[0117] 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.

[0118] 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.

[0119] 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.).

[0120] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. 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 batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0121] 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).

[0122] 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.

[0123] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0124] 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.

[0125] [Electrolytes]

[0126] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0127] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0128] In some embodiments, when the secondary battery is a lithium-ion battery, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0129] In some embodiments, when the secondary battery is a sodium-ion battery, the electrolyte salt may be selected from the sodium salt electrolyte, which is selected from at least one of sodium hexafluorophosphate (NaPF6), sodium difluorooxalate borate (NaDFOB), sodium tetrafluoroborate (NaBF4), sodium bis(oxalate borate) (NaBOB), sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide (NaFSI), sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI).

[0130] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0131] In some embodiments, the electrolyte may optionally include 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 battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0132] [Isolation membrane]

[0133] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0134] 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.

[0135] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0136] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0137] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0138] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0139] 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. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0140] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0141] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3In battery module 4, multiple secondary batteries 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 secondary batteries 5 can be fixed in place using fasteners.

[0142] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0143] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0144] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 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.

[0145] Secondly, embodiments of this application provide an electrical device, including the secondary battery provided in the first aspect of embodiments of this application.

[0146] The electrical device includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for 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.

[0147] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0148] 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 the secondary battery for this device, a battery pack or battery module can be used.

[0149] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0150] Thirdly, this application provides a modified conductive agent, comprising a conductive agent and a chelating agent, wherein the chelating agent is connected to the surface of the conductive agent by chemical bonds, and the chelating agent comprises a transition metal ion chelating functional group, wherein the transition metal ion chelating functional group comprises a phosphate group and / or a phosphate group.

[0151] The modified conductive agent used in this application includes a chelating agent connected to the surface of the conductive agent. The transition metal ion chelating functional group contained in the chelating agent can combine with the dissolved transition metal ions in the positive electrode active layer through coordination. That is, phosphate groups and / or phosphate groups can fix the dissolved transition metal ions in the positive electrode active layer through coordination, inhibit the dissolution and diffusion of transition metal ions in the battery, thereby hindering the transition metal ions from shuttling to the negative electrode, and thus improving the problem of reduced battery cycle performance.

[0152] In some embodiments, the chelating agent includes an organophosphate. The organic groups contained in the organophosphate are more conducive to the chelating agent attaching to the surface of the conductive agent through chemical bonds.

[0153] In some embodiments, the number of phosphate groups and / or phosphate groups in the chelating agent is n≥2. This suitable number of phosphate groups and / or phosphate groups is beneficial for capturing and immobilizing transition metal ions dissolved in the positive electrode active layer.

[0154] In some embodiments, the chelating agent comprises an alkyl backbone and a transition metal ion chelating functional group as shown in Formula I, wherein at least one hydrogen atom in the alkyl backbone bonded to a carbon atom is replaced by the transition metal ion chelating functional group as shown in Formula I.

[0155] -PO3H x M y Formula I

[0156] Where M includes sodium or lithium; x is 0 or a positive integer, y is a positive integer, and x+y=2;

[0157] The alkyl backbone includes any one of alkyl groups having 1-8 carbon atoms, alkyl alcohols having 1-8 carbon atoms, and alkylamines having 1-8 carbon atoms and 1-2 nitrogen atoms.

[0158] In the transition metal ion chelating functional group shown in Formula I of the chelating agent, the oxygen atom bonded to the phosphorus atom contains a lone pair of electrons, which can chelate with the transition metal ions, thereby inhibiting the dissolution and diffusion of transition metal ions such as Co, Ni, and Mn in the battery, thus hindering the transition metal ions from shuttling to the negative electrode and improving the battery cycle performance.

[0159] In some embodiments, the number n of transition metal ion chelating functional groups of Formula I in the chelating agent is 2-6, and the alkyl backbone of the chelating agent includes any one of alkyl groups with 1-5 carbon atoms, alkyl alcohols with 1-4 carbon atoms, and alkylamines with 2-6 carbon atoms and 1-2 nitrogen atoms. A suitable number of transition metal ion chelating functional groups is beneficial for capturing and immobilizing transition metal ions dissolved in the positive electrode active layer. Using the above-mentioned groups with suitable carbon and nitrogen numbers in the alkyl backbone helps control the spatial configuration of the chelating agent, thereby facilitating the capture of transition metal ions.

[0160] In some embodiments, the chelating agent includes at least one of the compounds shown in Formulas I-1 to I-6:

[0161]

[0162] In the technical solution of this application, in the structural formulas shown in I-1 to I-6, phosphate groups are used as transition metal ion chelating functional groups. The oxygen atoms in the phosphate groups that are connected to phosphorus atoms contain lone pairs of electrons, which can chelate with transition metal ions, thereby inhibiting the dissolution and diffusion of transition metal ions such as Co, Ni, and Mn in the battery, and thus hindering the transition metal ions from shuttling to the negative electrode and improving the battery cycle performance.

[0163] In some embodiments, the mass ratio of the conductive agent to the chelating agent is 1:(1.5-18). At this suitable ratio, it is advantageous to utilize the chelating agent's ability to capture and immobilize transition metal ions without affecting the conductivity of the conductive agent. The mass ratio of the conductive agent to the chelating agent can be 1:1.5, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, or any range of two of the above values.

[0164] In some embodiments, the mass ratio of the conductive agent to the chelating agent is 1:(3-10). At this suitable ratio, it is more advantageous to leverage the chelating agent's ability to capture and immobilize transition metal ions without affecting the conductivity of the conductive agent.

[0165] In some embodiments, the conductive agent includes at least one of carbon nanotubes, graphene, carbon nanofibers, conductive graphite, and conductive carbon black. Using the aforementioned conductive agents with excellent conductivity is beneficial for maximizing their conductive properties.

[0166] Fourthly, embodiments of this application provide a method for preparing a secondary battery, including a positive electrode preparation step, wherein the preparation step includes:

[0167] A positive electrode slurry is obtained by mixing positive electrode active material, modified conductive agent, binder and solvent;

[0168] The positive electrode slurry is coated onto the current collector to prepare a positive electrode sheet;

[0169] The modified conductive agent includes a conductive agent and a chelating agent that is chemically bonded to the surface of the conductive agent. The chelating agent includes a transition metal ion chelating functional group, which includes a phosphate group.

[0170] The preparation method provided in this application is simple and conducive to industrial application.

[0171] In some embodiments, the modified conductive agent is prepared by the following steps:

[0172] The conductive agent is treated with acid;

[0173] The modified conductive agent is obtained by mixing the acid-treated conductive agent with a solution containing a chelating agent.

[0174] The surface of the acid-treated conductive agent has active oxygen-containing functional groups, which facilitates its combination with the carbon-containing functional groups in the chelating agent through chemical bonds.

[0175] In some embodiments, the acid treatment step of the conductive agent includes at least one of sulfuric acid and nitric acid; the concentration of the acid used in the acid treatment is 12-18 mol / L; and the acid treatment time is 2-5 hours. These suitable acid treatment conditions are beneficial for the conductive agent surface to possess active oxygen-containing functional groups, thereby facilitating the bonding of the conductive agent with the carbon-containing functional groups in the chelating agent through chemical bonds. The concentration of the acid used in the acid treatment can be 12 mol / L, 13 mol / L, 14 mol / L, 15 mol / L, 16 mol / L, 17 mol / L, 18 mol / L, or any combination of two of the above values. The acid treatment time can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, or any combination of two of the above values.

[0176] In some embodiments, the chelating agent comprises an organophosphate lithium salt or an organophosphate sodium salt, which is prepared by the following steps: mixing an organophosphate with a lithium salt or a sodium salt to undergo a substitution reaction, thereby preparing the chelating agent. The substitution reaction can yield organophosphates with different lithium or sodium atom substitutions.

[0177] Understandably, the amount of lithium or sodium ions substituted in the chelating agent can usually be adjusted by regulating the molar ratio of lithium or sodium salt to organophosphoric acid. For example, when the molar ratio of lithium salt to organophosphoric acid is relatively larger, more lithium ions will replace the hydrogen atoms in the hydroxyl groups of organophosphoric acid that are linked to phosphorus atoms.

[0178] Example

[0179] 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.

[0180] Example 1

[0181] A lithium-ion secondary battery, the preparation method of which includes the following steps:

[0182] Synthesis of lithium ethylenediaminetetramethylenephosphonate:

[0183] 755g of phosphoric acid was added to 1.2L of concentrated hydrochloric acid (12M concentration) and stirred until dissolved. After the solution temperature dropped to 0℃, 271g of ethylenediamine hydrochloride was added, and the mixture was heated and stirred to obtain a mixed solution. The temperature was raised, and when the temperature of the mixed solution reached 100℃, formaldehyde solution (37%, 902mL) was added dropwise over 20 hours. The solution was then refluxed and cooled for 4 hours. The suspension was filtered under vacuum, washed with 100-600mL of distilled water, and dried to obtain ethylenediaminetetramethylenephosphonic acid powder.

[0184] Lithium hydroxide was dissolved in water and heated and stirred. When the temperature reached 60°C, ethylenediaminetetramethylenephosphonic acid was added and stirring was continued for 1 hour, so that the molar ratio of lithium hydroxide to ethylenediaminetetramethylenephosphonic acid was 4:1. After cooling, lithium ethylenediaminetetramethylenephosphonate (EDTMPLi) solution was obtained.

[0185] In this embodiment, the structural formula of EDTMPLi is:

[0186]

[0187] Preparation of modified conductive agents:

[0188] 100g of conductive carbon black was added to 20L of 12mol / L sulfuric acid solution, stirred at room temperature for 2h, filtered, and washed three times with water to obtain the first precipitate.

[0189] Take a 50 g / L lithium ethylenediaminetetramethylenephosphonate (EDTMPLi) solution to obtain the first solution; add 10 g of the first precipitate to the first solution so that the mass ratio of EDTMPLi to conductive carbon black in the modified conductive agent is 4.87:1. After thorough stirring, filter to obtain the modified conductive agent.

[0190] Preparation of the positive electrode sheet:

[0191] LiNi0.8Co0.1Mn0.1O2 positive electrode active material, modified conductive agent, polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) were mixed evenly in a weight ratio of 90:5:5:30 to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto the positive electrode current collector, and after drying, cold pressing, and slitting, a positive electrode sheet was obtained.

[0192] Preparation of negative electrode sheet:

[0193] The active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water at a weight ratio of 90:8:0.8:1.2 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is uniformly coated onto the negative electrode current collector copper foil once or multiple times, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0194] Electrolyte preparation:

[0195] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed evenly at a volume ratio of 3 / 7. 12.5% ​​LiPF6 lithium salt is added and dissolved in the organic solvent and stirred evenly to obtain the electrolyte.

[0196] Separating membrane

[0197] Polypropylene film is used as the separator.

[0198] Preparation of lithium-ion batteries:

[0199] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. They are then wound to obtain a bare cell. Tabs are welded onto the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product.

[0200] Examples 2-12 and Comparative Examples 1-2 of this application prepared secondary batteries according to each preparation step in Example 1. For differences, please refer to the parameters in Table 1.

[0201] The difference between Comparative Example 2 and Example 1 is that the modified conductive agent is obtained by directly mixing lithium ethylenediaminetetramethylenephosphonate (Formula I-2) with conductive carbon black, i.e., by physical mixing.

[0202] Performance testing:

[0203] The secondary batteries of Examples 1 to 12 and Comparative Examples 1 to 2 were tested as follows:

[0204] (1) Determination of the molecular structure of lithium ethylenediaminetetramethylenephosphonate (EDTMPLi):

[0205] Molecular structure was determined by phosphorus nuclear magnetic resonance spectroscopy (31P-NMR): The analyte was extracted with Na2EDTA-NaOH extractant at a ratio of 1:10, centrifuged after shaking, and the supernatant was collected for analysis. The freeze-dried sample needed to be reconstituted before 31P-NMR detection.

[0206] (2) Discharge specific capacity test:

[0207] Under constant temperature conditions of 25℃, the electrode was discharged to 2.8V at a rate of 1C under a voltage range of 2.5-4.4V, allowed to stand for 5 minutes, charged to 4.4V at a rate of 1C, and then charged at a constant voltage of 4.2V until the current was ≤0.05C. After standing for 5 minutes, the electrode was discharged to 2.8V at a rate of 1C. The discharge capacity was recorded. The discharge specific capacity was obtained by dividing the discharge capacity by the mass of LiNi0.8Co0.1Mn0.1O2 in the positive electrode.

[0208] See Figure 7 Comparing the charge-discharge curves of Example 1 and Comparative Example 1, the charge-discharge curve of Example 1 of this application shows no new plateau and no significant difference in voltage. Furthermore, the charge-discharge capacity of Example 1 and Comparative Example 1 is basically the same, indicating that the modified conductive agent used in Example 1 of this application does not affect the normal charge-discharge behavior of the battery and has no effect on the polarization and capacity of the battery.

[0209] Please refer to Table 1 for other embodiments and comparative data.

[0210] (3) Cyclic performance test:

[0211] Under a constant temperature environment of 25℃, the capacitor is charged to 4.2V at a rate of 1C at a voltage of 2.8-4.2V, then charged at 4.2V at a constant voltage until the current is ≤0.05C. After resting for 5 minutes, it is discharged to 2.8V at a rate of 1C, and the discharge capacity is recorded. The preceding process is repeated to obtain the capacity retention rate after a specified number of cycles. The capacity retention rate is calculated as: discharge capacity at the specified number of cycles / discharge capacity in the first cycle × 100%. In this embodiment, the specified number of cycles is 500.

[0212] See Figure 8 By comparing the cycle performance graphs of Example 1 and Comparative Example 1, it can be seen that, compared with Comparative Example 1, Example 1 of this application exhibits slower decay and higher cycle stability in the early stage of 500 cycles.

[0213] Please refer to Table 1 for other embodiments and comparative data.

[0214]

[0215] Referring to Table 1, compared to Comparative Example 1, the batteries of Examples 1-12 of this application exhibit higher 500-cycle capacity retention rates, indicating better cycle performance. Examples 1-12 of this application utilize modified conductive agents, including conductive agents and chelating agents. The chelating agents can bind with dissolved transition metal ions in the positive electrode active layer through coordination, inhibiting the dissolution and diffusion of transition metal ions within the battery, thereby improving battery cycle performance. Furthermore, the discharge specific capacity of the batteries of Examples 1-12 is close to that of Comparative Example 1, indicating that the modified conductive agents used in Examples 1-12 have minimal impact on normal charge-discharge behavior and have no effect on battery polarization or capacity.

[0216] Compared to Comparative Example 1, Comparative Example 2 shows a higher 500-cycle capacity retention rate for the batteries of Examples 1-12 of this application, indicating better cycle performance. Comparative Example 2 uses a physical mixing method between the conductive agent and the chelating agent, meaning the chelating agent is not chemically bonded to the surface of the conductive agent. This demonstrates that the bonding mode between the conductive agent and the chelating agent affects the improvement effect of the modified conductive agent on battery cycle performance.

[0217] As can be seen from Examples 1-8, the battery cycle performance can be further improved by adjusting the mass ratio between the chelating agent and the conductive agent.

[0218] 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 secondary battery, characterized in that, The device includes a positive electrode sheet, which comprises a current collector and a positive active layer loaded on the surface of the current collector. The positive active layer comprises a positive active material and a modified conductive agent. The modified conductive agent includes a conductive agent and a chelating agent. The chelating agent is connected to the surface of the conductive agent by chemical bonds. The chelating agent includes transition metal ion chelating functional groups, which include phosphate groups and / or phosphate groups.

2. The secondary battery according to claim 1, characterized in that, The chelating agent includes organophosphates.

3. The secondary battery according to claim 1 or 2, characterized in that, The number of phosphate groups and / or phosphate groups in the chelating agent is n≥2.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The secondary battery includes a lithium-ion secondary battery, and the chelating agent includes lithium organophosphate salts; or... The secondary battery includes a sodium-ion secondary battery, and the chelating agent includes an organophosphate sodium salt.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The chelating agent comprises an alkyl backbone and a transition metal ion chelating functional group as shown in Formula I, wherein at least one hydrogen atom in the alkyl backbone bonded to a carbon atom is replaced by a transition metal ion chelating functional group as shown in Formula I. -PO3H x M y Formula I Where M includes sodium or lithium; x is 0 or a positive integer, y is a positive integer, and x+y=2; The alkyl backbone includes any one of alkyl groups having 1-8 carbon atoms, alkyl alcohols having 1-8 carbon atoms, and alkylamines having 1-8 carbon atoms and 1-2 nitrogen atoms.

6. The secondary battery according to claim 5, characterized in that, The number n of the transition metal ion chelating functional groups shown in Formula I in the chelating agent is 2-6, and / or; The alkyl backbone of the chelating agent includes any one of the following: alkyl groups having 1-5 carbon atoms, alkyl alcohols having 1-4 carbon atoms, and alkylamines having 2-6 carbon atoms and 1-2 nitrogen atoms.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The chelating agent comprises at least one of the compounds shown in Formula I-1 to Formula I-6:

8. The secondary battery according to any one of claims 1 to 7, characterized in that, The mass ratio of the conductive agent to the chelating agent is 1:(1.5-18).

9. The secondary battery according to any one of claims 1 to 7, characterized in that, The mass ratio of the conductive agent to the chelating agent is 1:(3-10).

10. The secondary battery according to any one of claims 1 to 9, characterized in that, The conductive agent includes at least one of carbon nanotubes, graphene, carbon nanofibers, conductive graphite, and conductive carbon black.

11. The secondary battery according to any one of claims 1 to 10, characterized in that, The mass ratio of the modified conductive agent to the positive electrode active material in the positive electrode active layer is (5-10):(85-90).

12. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1 to 11.

13. A modified conductive agent, characterized in that, It includes a conductive agent and a chelating agent, wherein the chelating agent is connected to the surface of the conductive agent by chemical bonds, and the chelating agent includes a transition metal ion chelating functional group, wherein the transition metal ion chelating functional group includes a phosphate group and / or a phosphate group.

14. The modified conductive agent according to claim 13, characterized in that, The chelating agent includes organophosphates.

15. The modified conductive agent according to claim 13 or 14, characterized in that, The number of phosphate groups and / or phosphate groups in the chelating agent is n≥2.

16. The modified conductive agent according to any one of claims 13 to 15, characterized in that, The chelating agent comprises an alkyl backbone and a transition metal ion chelating functional group as shown in Formula I, wherein at least one hydrogen atom in the alkyl backbone bonded to a carbon atom is replaced by a transition metal ion chelating functional group as shown in Formula I. -PO3H x M y Formula I Where M includes sodium or lithium; x is 0 or a positive integer, y is a positive integer, and x+y=2; The alkyl backbone includes any one of alkyl groups having 1-8 carbon atoms, alkyl alcohols having 1-8 carbon atoms, and alkylamines having 1-8 carbon atoms and 1-2 nitrogen atoms.

17. The modified conductive agent according to claim 16, characterized in that, The number n of the transition metal ion chelating functional groups shown in Formula I in the chelating agent is 2-6, and / or; The alkyl backbone of the chelating agent includes any one of the following: alkyl groups having 1-5 carbon atoms, alkyl alcohols having 1-4 carbon atoms, and alkylamines having 2-6 carbon atoms and 1-2 nitrogen atoms.

18. The modified conductive agent according to any one of claims 13 to 17, characterized in that, The chelating agent comprises at least one of the compounds shown in Formula I-1 to Formula I-6:

19. The modified conductive agent according to any one of claims 13 to 18, characterized in that, The mass ratio of the conductive agent to the chelating agent is 1:(1.5-18).

20. The modified conductive agent according to any one of claims 13 to 19, characterized in that, The mass ratio of the conductive agent to the chelating agent is 1:(3-10).

21. The modified conductive agent according to any one of claims 13 to 20, characterized in that, The conductive agent includes at least one of carbon nanotubes, graphene, carbon nanofibers, conductive graphite, and conductive carbon black.

22. A method for preparing a secondary battery according to any one of claims 1 to 12, characterized in that, The preparation steps include the preparation of the positive electrode sheet, wherein the preparation steps include: A positive electrode slurry is obtained by mixing positive electrode active material, modified conductive agent, binder and solvent; The positive electrode slurry is coated onto the current collector to prepare a positive electrode sheet; The modified conductive agent includes a conductive agent and a chelating agent that is chemically bonded to the surface of the conductive agent. The chelating agent includes a transition metal ion chelating functional group, which includes a phosphate group.

23. The preparation method according to claim 22, characterized in that, The modified conductive agent is prepared by the following steps: The conductive agent is treated with acid; The modified conductive agent is obtained by mixing the acid-treated conductive agent with a solution containing a chelating agent.

24. The preparation method according to claim 22 or 23, characterized in that, In the step of acid treatment of the conductive agent, the acid used for acid treatment includes at least one of sulfuric acid and nitric acid; and / or, The acid concentration used in the acid treatment is 12-18 mol / L; and / or, The acid treatment time is 2-5 hours.

25. The preparation method according to any one of claims 22 to 24, characterized in that, The chelating agent comprises an organophosphate lithium salt or an organophosphate sodium salt, and the chelating agent is prepared by the following steps: The chelating agent is prepared by mixing organic phosphoric acid with lithium or sodium salts to undergo a substitution reaction.

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