WO2023050833A1 - Positive electrode material and preparation method therefor, secondary battery, battery module, battery pack and electric device - Google Patents

Abstract

A positive electrode material and a preparation method therefor. The positive electrode material comprises an inner core (11) as well as a first coating layer (12) and a second coating layer (13) which are sequentially arranged on the surface of the inner core (11). The inner core (11) comprises a compound of formula I having a spinel structure as follows: Li1+xMn2-yMyO4-zAz (formula I), where 0≤x≤1, 0≤y≤0.5, 0≤z≤0.5, x, y and z are not zero at the same time, M is selected from one or more of Al, Mg, Ga, Ti, Fe, Nb, Zn, Ni, Sn and Cr, and A is selected from one or more of F, S and Cl. The first coating layer (12) comprises a first polymer containing an electron withdrawing group, the electron withdrawing group being selected from at least one of an ester group or a nitrile group, and the second coating layer (13) contains a polysaccharide.

Description

A kind of positive electrode material and preparation method thereof, secondary battery, battery module, battery pack and electrical device

Cross References to Related Applications

This application claims the priority of the Chinese patent application 202111155957.X entitled "A positive electrode material and its preparation method, secondary battery, battery module, battery pack and electrical device" filed on September 29, 2021, The entire content of this application is incorporated herein by reference.

technical field

The present application relates to the technical field of lithium batteries, in particular to a positive electrode material and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electrical device.

Background technique

In recent years, with the increasing demand for clean energy, lithium-ion batteries have been widely used in energy storage power systems such as water power, fire power, wind power, and solar power stations, as well as in power tools, vehicles, military equipment, aerospace, etc. field. Lithium-ion batteries provide great opportunities for the development of clean energy, but at the same time they also face enormous technical challenges. As a power source for large-scale devices or equipment, people have higher and higher requirements for the energy density and stable performance of lithium-ion batteries.

Lithium manganate material is a type of manganese-based lithium metal oxide with a spinel structure. Because it is suitable for high-voltage systems and has a higher capacity, it has become a key development direction for lithium-ion battery cathode materials. However, a large number of experiments have found that when lithium manganese oxide is used as the positive electrode material in lithium-ion batteries, although the energy density of the battery can be improved, its storage performance and cycle performance are poor.

Therefore, how to effectively improve the storage performance and cycle performance of the lithium manganese oxide battery system has become an urgent technical problem to be solved.

Contents of the invention

The present application is carried out in view of the above-mentioned problems, and its purpose is to provide a positive electrode material and a manufacturing method thereof, a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device, by performing a lithium manganate positive electrode material Double-layer coating to alleviate the Mn dissolution problem in the lithium manganese oxide battery system, so that the secondary battery containing the material has good storage performance and cycle performance.

In order to achieve the above purpose, the present application provides a positive electrode material and a manufacturing method thereof, a positive electrode sheet, a secondary battery, a battery module, a battery pack and an electrical device.

The first aspect of the present application provides a kind of cathode material, it comprises:

an inner core, and a first cladding layer and a second cladding layer sequentially arranged on the surface of the inner core,

The inner core includes a compound of formula I having a spinel structure:

Li _1+x Mn _2-y M _y O _4-z A _z Formula I

Among them, 0≤x≤1, 0≤y≤0.5, 0≤z≤0.5, x, y, z are not zero at the same time, M is selected from Al, Mg, Ga, Ti, Fe, Nb, Zn, Go , one or more of Ni, Sn, Cr, A is selected from one or more of F, S, Cl;

The first coating layer includes a first polymer containing electron-withdrawing groups, and the electron-withdrawing groups are selected from at least one of ester groups or nitrile groups; the second coating layer contains polysaccharides.

The present application arranges the first cladding layer containing the first polymer on the surface of the lithium manganese oxide core with a spinel structure, because the electron-withdrawing group in the first polymer transfers the electrons of Mn ³⁺ to the electron-withdrawing group The deviation increases the average valence of manganese, which can effectively stabilize the Mn ³⁺ on the surface of lithium manganese oxide, and at the same time ensure that the inner lithium manganate material has good electronic conductivity. In addition, on the basis of the first coating layer, a second coating layer containing polysaccharides is further provided to combine with Lewis acids such as phosphorus pentafluoride (PF5) by utilizing the characteristics of the surface of polysaccharides rich in oxygen elements. On the one hand, it can effectively inhibit the production of hydrofluoric acid (HF); on the other hand, because the -CO ether bond in polysaccharides can chelate with the manganese ions dissolved from the inner core, it helps to further inhibit the lithium manganate inner core. Dissolution of manganese ions in the medium. In this application, by setting the above-mentioned double-layer coating structure on the core of lithium manganate, while realizing the physical isolation between the electrolyte and the core of lithium manganate, the generation of HF in the electrolyte is greatly reduced, and the lithium manganate core is effectively suppressed. The dissolution of Mn ions in the medium can also ensure that the positive electrode material has both good electron conductivity and ion conductivity, which helps to improve the cycle performance and storage performance of lithium manganate batteries.

In any embodiment, the mass percentage of electron-withdrawing groups in the first polymer is 20%-65%. In some embodiments, the mass percentage of electron-withdrawing groups in the first polymer is 33%-65%. In this application, by selecting the first polymer with the mass percentage of electron-withdrawing groups within the above range as the first cladding layer of the inner core, it is beneficial to stabilize the Mn ³⁺ on the surface of lithium manganate in the inner core and relieve the Mn 3+ of the lithium manganate material. Dissolution problem, which is beneficial to improve the storage performance and cycle performance of the battery.

In any embodiment, the first cladding layer and/or the second cladding layer are continuously distributed on the surface of the inner core. In some embodiments, in the positive electrode material, the covering ratio of the second covering layer is not lower than that of the first covering layer. In this application, while the second coating layer reacts with PF5 and reduces the generation of HF in the electrolyte, it can also effectively isolate the contact between the electrolyte and the inner core to prevent the inner core from being corroded by the electrolyte. When the coating rate is higher, The better the isolation effect, the higher the coverage rate of the second cladding layer can be selected; at the same time, the electron-withdrawing group of the first cladding layer also gathers a large number of electrons when stabilizing the manganese ions in the inner core, which strengthens the interaction between the inner core and the second cladding layer. The electron transmission between the two coating layers improves the cycle performance of the battery, but when the coating rate of the first coating layer is too high, it will increase the conduction path of lithium ions, resulting in an increase in the ionic impedance of the battery, which will instead make the battery The cycle performance and storage performance are reduced. Therefore, in this application, the covering ratio of the optional second coating layer is not lower than that of the first coating layer.

In any embodiment, based on the mass of the inner core, the mass percentage of the first cladding layer is 0.15%-2.5%. In some embodiments, the mass percentage of the first cladding layer is 0.4%-2%. Further optionally, the mass percentage of the first cladding layer is 0.4%-1.6%. And/or, based on the mass of the inner core, the mass percentage of the second cladding layer is 0.1%-2%. Optionally, the mass percentage of the second cladding layer is 0.3%-1.8%. Further, in some embodiments, the mass percentage of the second cladding layer is 0.3%-1.5%. In this application, by controlling the mass percentage of the first cladding layer and the second cladding layer in an appropriate range, it is beneficial to stabilize the Mn ³⁺ on the surface of the lithium manganese oxide material, and at the same time combine with Lewis acids such as PF5 in the electrolyte, Mn dissolution can be alleviated, and at the same time, it can ensure that the positive electrode material has both good lithium ion conductivity and electron conductivity.

In any embodiment, based on the mass of the inner core, the total mass percentage of the first polymer and the polysaccharide is ≦3.8%. In some embodiments, the total mass percentage of the first polymer and the polysaccharide is ≦3.5%. Further, in some embodiments, the total mass percentage of the first polymer and the polysaccharide is ≤3%. In this application, by controlling the total mass percentage of the first polymer and polysaccharide in an appropriate range, on the premise of effectively suppressing the dissolution of Mn in the core of lithium manganate, it is beneficial to keep the impedance of the battery low, and further improve the cycle performance and storage of the battery. performance.

In any embodiment, the first polymer is selected from polymethyl acrylate, polyethyl acrylate, polymethyl methacrylate, polyethylene terephthalate, polybutyl methacrylate, polymethacrylic acid One or more of ethyl ester, polyacrylonitrile, polynitrile acrylate, nitrile rubber, acrylonitrile copolymer. In the present application, by selecting a polymer containing an electron-withdrawing group as the first polymer, the Mn ³⁺ on the surface of lithium manganate can be stabilized, and the problem of Mn dissolution in the lithium manganate battery system can be alleviated.

In any embodiment, the molecular structure of the polysaccharide is composed of multiple repeating units containing oxygen atoms, and in the repeating units, the mass proportion of oxygen element is not less than 25%. The present application selects polysaccharides whose oxygen content is within the above range. Due to its high oxygen content, it can effectively combine with the Lewis acid in the electrolyte, reduce the generation of HF in the electrolyte, and effectively relieve the lithium manganate positive electrode. The dissolution of Mn ions in the material can further improve the storage performance and cycle performance of the battery.

In any embodiment, the weight average molecular weight of the polysaccharide ranges from 20,000 to 270,000. In some embodiments, the weight average molecular weight of the polysaccharide ranges from 30,000 to 220,000. In the present application, if polysaccharides within the range of the above-mentioned weight average molecular weight are used, it can ensure that the polysaccharides have a high oxygen content, and by complexing Lewis acids such as PF5 in the electrolyte, the generation of HF in the electrolyte can be reduced, thereby alleviating the manganese in the positive electrode material. Dissolution problem, thus playing a role in improving battery cycle performance.

In any embodiment, the polysaccharide is selected from one or more of sodium alginate, potassium alginate, guar gum, kale gum, carrageenan, and agar. In this application, the above-mentioned substances are polysaccharides rich in oxygen atoms, which can be combined with Lewis acids such as PF5 in the electrolyte to reduce the generation of HF in the electrolyte and alleviate the Mn dissolution problem of the lithium manganate cathode material, thereby further improving the performance of the battery. storage and cycling properties.

In any embodiment, the positive electrode material has a specific surface area of 0.15 m ² /g to 1.5 ^{m 2} /g. In some embodiments, the positive electrode material has a specific surface area of 0.2m ² /g˜0.8m ² /g. In the present application, by controlling the specific surface area of the positive electrode material within a reasonable range, the contact area between the electrolyte solution and the positive electrode material can be reduced, which is beneficial to reduce interface side reactions and ensure the improvement effect of Mn dissolution.

The second aspect of the present application provides a method for preparing a positive electrode material, at least including the following steps:

(1) core is provided, and core comprises formula I compound with spinel structure:

Li _1+x Mn _2-y M _y O _4-z A _z Formula I

Among them, 0≤x≤1, 0≤y≤0.5, 0≤z≤0.5, x, y, z are not zero at the same time, M is selected from Al, Mg, Ga, Ti, Fe, Nb, Zn, Go , one or more elements in Ni, Sn, Cr; A is selected from one or more elements in F, S, Cl;

(2) Provide the first coating solution containing the first polymer, the first polymer contains electron-withdrawing groups, the electron-withdrawing groups are selected from at least one of ester groups or nitrile groups; the inner core is placed in the first coating In the covering liquid, the first polymer is attached to the surface of the inner core to obtain the primary product;

(3) A second coating solution containing polysaccharide is provided, and the primary product is placed in the second coating solution, so that at least a part of the surface of the primary product has a second coating layer attached to obtain a positive electrode material.

In the present application, through the above-mentioned method, the positive electrode material can be prepared simply and easily, which has the advantages of low energy consumption, low cost, and high synthesis efficiency, and is conducive to large-scale production; in addition, the positive electrode material prepared by the above-mentioned method is available in The binding force between the two cladding layers and between the first cladding layer and the inner core is good, and the coverage of the first cladding layer and the second cladding layer on the surface of the material can be flexibly adjusted.

In any embodiment, in step (2), in the first coating liquid, the mass percentage of the first polymer is 0.05%-20%. In some embodiments, the mass percentage of the first polymer is 0.1%-12%. And/or, the mass percentage of the inner core and the first coating liquid is 0.05%-70%. In some embodiments, the mass percentage of the inner core and the first coating liquid is 0.1%˜60%. In the present application, if the mass percentage of the first polymer in the first coating liquid, or the mass percentage of the inner core and the first coating liquid is too high, the inner core is prone to agglomeration in the coating liquid. Therefore, by controlling the first The mass percentage of the first polymer in the coating liquid, or the mass percentage of the inner core and the first coating liquid, is in an appropriate range, which is conducive to achieving uniform coating of the first coating layer on the surface of the inner core.

In any embodiment, in step (3), the mass percentage of polysaccharide in the second coating solution is 0.05%-12%. In some embodiments, the mass percentage of polysaccharide is 0.1%-8%. The mass percentage of the primary product and the second coating solution is 0.05%-70%. In some embodiments, the mass percentage of the primary product and the second coating solution is 0.1%-60%. In the present application, if the mass percentage of the polysaccharide in the second coating liquid, or the mass percentage of the primary product and the second coating liquid is too high, the primary product is prone to agglomeration in the second coating liquid. Therefore, by controlling the The mass percentage of the polysaccharide in the second coating solution, or the mass percentage of the primary product and the second coating solution is in an appropriate range, which is beneficial to realize the uniform coating of the second coating layer on the surface of the inner core.

The third aspect of the present application provides a positive electrode sheet, which includes the positive electrode material of the first aspect of the present application or the positive electrode material obtained according to the preparation method of the second aspect of the present application.

A fourth aspect of the present application provides a secondary battery, including the positive electrode sheet of the third aspect of the present application.

A fifth aspect of the present application provides a battery module including the secondary battery of the fourth aspect of the present application.

A sixth aspect of the present application provides a battery pack, including the battery module of the fifth aspect of the present application.

A seventh aspect of the present application provides an electric device, including at least one of the secondary battery of the fourth aspect of the present application, the battery module of the fifth aspect of the present application, or the battery pack of the sixth aspect of the present application.

Thus, although the mechanism is not yet clear, the applicant unexpectedly found that: the present application arranges the first cladding layer containing the first polymer on the surface of the lithium manganate core having a spinel structure, due to the first polymer The electron-withdrawing group in the Mn ³⁺ deviates the electrons of Mn 3+ to the electron-withdrawing group, so that the average valence of manganese increases, which can effectively stabilize the Mn ³⁺ on the surface of lithium manganate, and at the same time ensure the electron-conducting ability of the inner lithium manganate material good. Moreover, on the basis of the first coating layer, a second coating layer containing polysaccharides is further provided, and the surface of the polysaccharides is rich in oxygen to make it react with Lewis acids such as phosphorus pentafluoride (PF ₅ ) Combining, on the one hand, effectively inhibit the production of hydrofluoric acid (HF); on the other hand, because the -CO ether bond in polysaccharides can chelate with the manganese ions dissolved from the inner core, it helps to further inhibit lithium manganate Dissolution of manganese ions in the core. In this application, by setting the above-mentioned double-layer coating structure on the core of lithium manganate, while realizing the physical isolation between the electrolyte and the core of lithium manganate, the generation of HF in the electrolyte is greatly reduced, and the lithium manganate core is effectively suppressed. The dissolution of Mn ions in the medium can also ensure that the positive electrode material has both good electron conductivity and ion conductivity, which helps to improve the cycle performance and storage performance of lithium manganate batteries.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the accompanying drawings that need to be used in the embodiments of the present application. Obviously, the accompanying drawings described below are only some embodiments of the present application. Those of ordinary skill in the art can also obtain other drawings based on the accompanying drawings on the premise of not paying creative efforts.

FIG. 1 is a schematic structural view of a positive electrode material according to an embodiment of the present application.

FIG. 2 is the 45° C. cycle performance test results of the secondary batteries made of positive electrode materials obtained in Example 1 and Comparative Examples 1-4.

FIG. 3 is a schematic diagram of a secondary battery according to an embodiment of the present application.

FIG. 4 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG. 3 .

FIG. 5 is a schematic diagram of a battery module according to an embodiment of the present application.

FIG. 6 is a schematic diagram of a battery pack according to an embodiment of the present application.

FIG. 7 is an exploded view of the battery pack according to one embodiment of the present application shown in FIG. 6 .

FIG. 8 is a schematic diagram of an electrical device in which a secondary battery is used as a power source according to an embodiment of the present application.

Explanation of reference signs:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery;

11 lithium manganese oxide core; 12 the first cladding layer; 13 the second cladding layer;

51 shell; 52 electrode assembly; 53 cover plate.

Detailed ways

Hereinafter, embodiments of the positive electrode material and its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack, and electrical device of the present application will be specifically disclosed in detail with reference to the accompanying drawings. However, unnecessary detailed description may be omitted. For example, detailed descriptions of well-known items and repeated descriptions of substantially the same configurations may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

A "range" disclosed herein is defined in terms of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive and may be combined arbitrarily, ie any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are contemplated. Additionally, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, 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 "a-b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article, and "0-5" is only an abbreviated representation of the combination of these values. In addition, when expressing that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If there is no special description, all the implementation modes and optional implementation modes of the present application can be combined with each other to form new technical solutions.

If there is no special description, all the technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

If there is no special instruction, all the steps of the present application can be performed sequentially, or randomly, or sequentially. For example, a method comprising steps (a) and (b) means that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially. For example, mentioning that the method may also include step (c) means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), and may also include step (a) , (c) and (b), may also include steps (c), (a) and (b) and the like.

If there is no special description, the "comprising" and "comprising" mentioned in this application mean open or closed. For example, "comprising" and "comprising" may indicate that other components not listed may also be included or contained, or only listed components may be included or contained.

In this application, the term "or" is inclusive unless otherwise stated. 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 either of the following: 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).

Lithium manganese oxide is an important type of positive electrode material. Due to its high relative content of Mn element, there is a problem of high Mn dissolution, which leads to a certain degree of attenuation in the cycle performance of the battery system. In order to improve the Mn dissolution problem of lithium manganese oxide materials, it is more effective to coat, dope, or add HF scavenger on the surface of the material. However, how to coat and modify the ionic conductivity of the lithium manganate material without reducing the ionic conductivity of the lithium manganate material, and at the same time avoid the increase of the polarization degree of the lithium manganate material and the decrease of the available capacity still needs further improvement and exploration.

Positive electrode

The application proposes a positive electrode material comprising:

an inner core, and a first cladding layer and a second cladding layer sequentially arranged on the surface of the inner core,

The inner core includes a compound of formula I having a spinel structure:

Li _1+x Mn _2-y M _y O _4-z A _z Formula I

Among them, 0≤x≤1, 0≤y≤0.5, 0≤z≤0.5, x, y, z are not zero at the same time, M is selected from Al, Mg, Ga, Ti, Fe, Nb, Zn, Go , one or more of Ni, Sn, Cr, A is selected from one or more of F, S, Cl;

The first coating layer includes a first polymer containing electron-withdrawing groups, and the electron-withdrawing groups are selected from at least one of ester groups or nitrile groups; the second coating layer contains polysaccharides.

In the present application, the first cladding layer containing the first polymer is arranged on the surface of the lithium manganese oxide core with a spinel structure, because the electron-withdrawing group in the first polymer transfers the electrons of Mn ³⁺ to the electron-withdrawing group. The group deviation increases the average valence of manganese, which can effectively stabilize the Mn ³⁺ on the surface of lithium manganese oxide, and at the same time ensure that the inner lithium manganate material has good electron conductivity. In addition, on the basis of the first coating layer, a second coating layer containing polysaccharides is further provided to combine with Lewis acids such as phosphorus pentafluoride (PF5) by utilizing the characteristics of the surface of polysaccharides rich in oxygen elements. On the one hand, it can effectively inhibit the production of hydrofluoric acid (HF); on the other hand, because the -CO ether bond in polysaccharides can chelate with the manganese ions dissolved from the inner core, it helps to further inhibit the lithium manganate inner core. Dissolution of manganese ions in the medium. In this application, by setting the above-mentioned double-layer coating structure on the core of lithium manganate, while realizing the physical isolation between the electrolyte and the core of lithium manganate, the generation of HF in the electrolyte is greatly reduced, and the lithium manganate core is effectively suppressed. The dissolution of Mn ions in the medium can also ensure that the positive electrode material has both good electron conductivity and ion conductivity, which helps to improve the cycle performance and storage performance of lithium manganate batteries.

In some embodiments, the mass percentage of electron-withdrawing groups in the first polymer is 20%-65%. In some embodiments, the mass percentage of electron-withdrawing groups in the first polymer is 33%-65%. In the present application, when the mass percentage of the electron-withdrawing group in the first polymer is within the above range, the stabilization effect of the first polymer on the Mn ions in the inner core is more significant, which can further alleviate the Mn ³⁺ dissolution problem, thereby having It helps to improve the cycle performance and storage performance of the battery.

In some embodiments, the first cladding layer and/or the second cladding layer are continuously distributed on the surface of the inner core. In some embodiments, in the positive electrode material, the covering ratio of the second covering layer is not lower than that of the first covering layer. In this application, while the second coating layer reacts with PF5 and reduces the generation of HF in the electrolyte, it can also effectively isolate the contact between the electrolyte and the inner core to prevent the inner core from being corroded by the electrolyte. When the coating rate is higher, The better the isolation effect, the higher the coverage rate of the second cladding layer can be selected; at the same time, the electron-withdrawing group of the first cladding layer also gathers a large number of electrons when stabilizing the manganese ions in the inner core, which strengthens the interaction between the inner core and the second cladding layer. The electron transmission between the two coating layers improves the cycle performance of the battery, but when the coating rate of the first coating layer is too high, it will increase the conduction path of lithium ions, resulting in an increase in the ionic impedance of the battery, which will instead make the battery The cycle performance and storage performance are reduced. Therefore, in the present application, the coverage rate of the second coating layer is not lower than that of the first coating layer.

In some embodiments, based on the mass of the inner core, the mass percentage of the first cladding layer is 0.15%-2.5%. In some embodiments, the mass percentage of the first cladding layer is 0.4%-2%. Further, in some embodiments, the mass percentage of the first cladding layer is 0.4%-1.6%. And/or, based on the mass of the inner core, the mass percentage of the second cladding layer is 0.1%-2%. In some embodiments, the mass percentage of the second cladding layer is 0.3%˜1.8%. Further, in some embodiments, the mass percentage of the second cladding layer is 0.3%-1.5%. If the mass percentage of the first coating layer is within the above range, it is beneficial to stabilize the Mn ³⁺ on the surface of the lithium manganese oxide material, alleviate the dissolution of Mn, and at the same time ensure the transmission of lithium ions. If the mass percentage of the second coating layer is within the above range, it is beneficial to combine with Lewis acid such as PF5 in the electrolyte to alleviate the dissolution of Mn, and at the same time, it can ensure that the positive electrode material has both good lithium ion conductivity and electron conductivity characteristics.

In some embodiments, based on the mass of the inner core, the total mass percentage of the first polymer and the polysaccharide is ≦3.8%. In some embodiments, the total mass percentage of the first polymer and the polysaccharide is ≤ 3.5%. Further, in some embodiments, the total mass percentage of the first polymer and the polysaccharide is ≤3%. In this application, by controlling the total mass percentage of the first polymer and polysaccharide in an appropriate range, on the premise of effectively suppressing the dissolution of Mn in the core of lithium manganate, it is beneficial to keep the impedance of the battery low, and further improve the cycle performance and storage of the battery. performance.

In some embodiments, the first polymer is selected from polymethyl acrylate, polyethyl acrylate, polymethyl methacrylate, polyethylene terephthalate, polybutyl methacrylate, polymethacrylic acid One or more of ethyl ester, polyacrylonitrile, polynitrile acrylate, nitrile rubber, and acrylonitrile copolymer. By selecting a polymer containing an electron-withdrawing group as the first polymer, the Mn ³⁺ on the surface of the lithium manganate can be stabilized, and the Mn dissolution problem of the lithium manganate battery system can be alleviated.

In some embodiments, the molecular structure of the polysaccharide is composed of multiple repeating units containing oxygen atoms, and in the repeating units, the mass proportion of oxygen element is not less than 25%. The present application selects polysaccharides whose oxygen content is within the above range. Due to its high oxygen content, it can effectively combine with the Lewis acid in the electrolyte, reduce the generation of HF in the electrolyte, and effectively relieve the lithium manganate positive electrode. The dissolution of Mn ions in the material can further improve the storage performance and cycle performance of the battery.

In the present application, the mass proportion of oxygen in the repeating unit of the polysaccharide molecular structure can be tested by methods known in the art. As an example, an organic elemental analysis method can be used, for example, a Vario EL III elemental analyzer from German Elementar Company can be used for testing.

In some embodiments, the weight average molecular weight of the polysaccharide ranges from 20,000 to 270,000. In some embodiments, the weight average molecular weight of the polysaccharide ranges from 30,000 to 220,000. By using polysaccharides within this weight average molecular weight range, the present application can ensure that the polysaccharides have a high oxygen content, and reduce the generation of HF in the electrolyte by complexing Lewis acids such as PF5 in the electrolyte, thereby alleviating the dissolution of manganese in the positive electrode material. , so as to improve the battery cycle performance.

In this application, the weight average molecular weight of polysaccharides can be tested by methods known in the art. As an example, gel permeation chromatography can be used for determination, such as Agilent's PL-GPC50, PL-GPC220 and other instruments.

In some embodiments, the polysaccharide is selected from one or more of sodium alginate, potassium alginate, guar gum, kale gum, carrageenan, and agar. Wherein, the polysaccharide is composed of one or more of uronic acid, mannose and galactose. By selecting polysaccharides rich in oxygen atoms and combining with Lewis acids such as PF5 in the electrolyte, the generation of HF can be reduced, thereby alleviating the Mn dissolution problem in the lithium manganate battery system, and improving the storage and cycle performance of the battery.

In some embodiments, the positive electrode material has a specific surface area of 0.15 square meters per gram (m ² /g) to 1.5 ^{m 2} /g. In some embodiments, the positive electrode material has a specific surface area of 0.2m ² /g˜0.8m ² /g. When the specific surface area of the positive electrode material is too large, the contact area between the electrolyte and the positive electrode material may be excessively increased, resulting in a poor effect on the improvement of Mn dissolution; the positive electrode material within the above specific surface area can effectively alleviate the Mn dissolution problem, thereby It is beneficial to improve the cycle performance and storage performance of the positive electrode material.

In this application, the specific surface area of the positive electrode material can be tested by methods known in the art. As an example, the nitrogen adsorption specific surface area analysis test method can be used to test, and the gas adsorption method (BET method) can be used to calculate, wherein the nitrogen adsorption specific surface area analysis test can be carried out by the Tri Star ii3020 type specific surface area and pore analyzer of the Micromeritics company in the United States.

Preparation method of cathode material

In one embodiment of the present application, the present application also provides a method for preparing a positive electrode material, at least including the following steps:

(1) core is provided, and core comprises formula I compound with spinel structure:

Li _1+x Mn _2-y M _y O _4-z A _z Formula I

Among them, 0≤x≤1, 0≤y≤0.5, 0≤z≤0.5, x, y, z are not zero at the same time, M is selected from Al, Mg, Ga, Ti, Fe, Nb, Zn, Go , one or more elements in Ni, Sn, Cr; A is selected from one or more elements in F, S, Cl;

(2) Provide the first coating solution containing the first polymer, the first polymer contains electron-withdrawing groups, the electron-withdrawing groups are selected from at least one of ester groups or nitrile groups; the inner core is placed in the first coating In the covering liquid, the first polymer is attached to the surface of the inner core to obtain the primary product;

(3) A second coating solution containing polysaccharide is provided, and the primary product is placed in the second coating solution, so that at least a part of the surface of the primary product is attached with a second coating layer to obtain a positive electrode material; wherein, the second coating The coating contains polysaccharides.

In the present application, through the above-mentioned manufacturing method of the positive electrode material of the present application, the preparation of the positive electrode material can be carried out simply and easily, and has the advantages of low energy consumption, low cost, and high synthesis efficiency, which is conducive to large-scale production; in addition, through the above The positive electrode material prepared by the method has good bonding force between the two cladding layers and between the first cladding layer and the inner core, and can flexibly control the coverage of the first cladding layer and the second cladding layer on the surface of the material .

In some embodiments, in step (2), in the first coating solution, the mass percentage of the first polymer is 0.05%-20%. In some embodiments, the mass percentage of the first polymer is 0.1%-12%. And/or, the mass percentage of the inner core and the first coating liquid is 0.05%-70%. In some embodiments, the mass percentage of the inner core and the first coating liquid is 0.1%˜60%. In the present application, if the mass percentage of the first polymer in the first coating liquid, or the mass percentage of the inner core and the first coating liquid is too high, the inner core is prone to agglomeration in the coating liquid. Therefore, by controlling the first The mass percentage of the first polymer in the coating liquid, or the mass percentage of the inner core and the first coating liquid, is in an appropriate range, which is conducive to achieving uniform coating of the first coating layer on the surface of the inner core.

In some embodiments, in step (2), the first coating solution contains an organic solvent, and the organic solvent is selected from acetone, tetrahydrofuran, dimethylacetamide, dimethyl sulfoxide, dichloromethane, and chloroform, One or more of dichloroethane, trifluoroacetic acid, N,N-dimethylformamide. Selecting a suitable organic solvent as the solvent of the first coating solution can better dissolve the first polymer and achieve a better coating effect.

In some embodiments, in step (3), the mass percentage of the polysaccharide in the second coating solution is 0.05%-12%. In some embodiments, the mass percentage of polysaccharide is 0.1%-8%. And/or, the mass percentage of the primary product and the second coating liquid is 0.05%-70%. In some embodiments, the mass percentage of the primary product and the second coating solution is 0.1%-60%. In the present application, if the mass percentage of the polysaccharide in the second coating liquid, or the mass percentage of the primary product and the second coating liquid is too high, the primary product is prone to agglomeration in the second coating liquid. Therefore, by controlling the The mass percentage of the polysaccharide in the second coating solution, or the mass percentage of the primary product and the second coating solution is in an appropriate range, which is beneficial to realize the uniform coating of the second coating layer on the surface of the inner core.

In some embodiments, for example, the stirring temperature is optionally 25° C. (Celsius) to 100° C., and the stirring time is optionally 4 h (hours) to 24 h.

In some embodiments, for example, the drying temperature is optionally 8°C-150°C, and the drying time is optionally 6h-24h.

In some embodiments, for example, the gaseous atmosphere is an inert non-oxidizing gas, optionally nitrogen or argon.

In addition, the secondary battery, the battery module, the battery pack, and the power consumption device of the present application will be described below with appropriate reference to the accompanying drawings.

secondary battery

In one embodiment of the present application, a secondary battery is provided.

Typically, a secondary battery includes a positive pole piece, a negative pole piece, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are intercalated and extracted back and forth between the positive electrode and the negative electrode. The electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece. The separator is arranged between the positive pole piece and the negative pole piece, which mainly plays a role in preventing the short circuit of the positive and negative poles, and at the same time allows ions to pass through.

[Positive pole piece]

The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector. The positive electrode film layer includes the positive electrode material according to the first aspect of the application or the positive electrode material obtained according to the preparation method of the second aspect of the application.

As an example, the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposing surfaces of the positive electrode current collector.

In the secondary battery of the present application, a metal foil or a composite current collector can be used as the positive electrode current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector can be formed by forming metal materials (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalic acid It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In the secondary battery of the present application, the positive electrode material is a double-layer coated positive electrode material obtained by the preparation method of the present application. At the same time, positive electrode materials for batteries known in the art can be used for mixed use. The positive electrode material may include at least one of the following materials: olivine-structured lithium-containing phosphates, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery cathode materials can also be used. These positive electrode materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium manganese oxides (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium cobalt manganese oxides, lithium nickel cobalt oxides, lithium nickel cobalt manganese oxides (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ for short), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (also referred to as NCM ₅₂₃ for short), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (also referred to as NCM ₂₁₁ for short), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (also called NCM ₆₂₂ for short), LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (also called NCM ₈₁₁ for short), lithium-rich oxides and their modified compounds, etc. At least one of. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP for short)), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate ( For example, at least one of LiMnPO ₄ ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium manganese iron phosphate and carbon.

In the secondary battery of the present application, the positive electrode film layer may also optionally include a binder. As examples, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of meta-copolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

In the secondary battery of the present application, the positive electrode film layer may also optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In the secondary battery of the present application, the positive electrode sheet can be prepared in the following manner: the above-mentioned components for preparing the positive electrode sheet, such as positive electrode material, conductive agent, binding agent and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[Negative pole piece]

The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

As an example, the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposing surfaces of the negative electrode current collector.

In the secondary battery of the present application, the negative electrode current collector can adopt metal foil or composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a base layer of polymer material and a metal layer formed on at least one surface of the base material of polymer material. Composite current collectors can be formed by metal materials (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyethylene terephthalic acid It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In the secondary battery of the present application, negative electrode active materials known in the art for batteries can be used as the negative electrode active material. 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 material, tin-based material, lithium titanate, and the like. The silicon-based material may be selected from at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can be selected from at least one of simple tin, tin oxide and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials of batteries can also be used. These negative electrode active materials may be used alone or in combination of two or more.

In the secondary battery of the present application, the negative electrode film layer may also optionally include a binder. The binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethyl At least one of acrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

In the secondary battery of the present application, the negative electrode film layer may also optionally include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In the secondary battery of the present application, the negative electrode film layer may optionally include other additives, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.

In the secondary battery of the present application, the negative electrode sheet can be prepared in the following manner: the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binding agent and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[Electrolyte]

The electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece. The present application has no specific limitation on the type of electrolyte, which can be selected according to requirements. For example, electrolytes can be liquid, gel or all solid.

In the secondary battery of the present application, an electrolytic solution is used as the electrolyte. The electrolytic solution includes electrolyte salts and solvents.

In the secondary battery of the present application, the electrolyte salt can be selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonyl imide, At least one of lithium fluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium difluorooxalate borate, lithium difluorodifluorooxalatephosphate and lithium tetrafluorooxalatephosphate.

In the secondary battery of the present application, the solvent can be selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene propylene carbonate ester, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, butyl At least one of ethyl acetate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

In the secondary battery of the present application, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performances of the battery, such as additives that improve battery overcharge performance, additives that improve high-temperature or low-temperature performance of batteries, and the like.

[Isolation film]

Secondary batteries using an electrolyte, and some secondary batteries using a solid electrolyte, also include a separator. The present application has no particular limitation on the type of the isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.

In the secondary battery of the present application, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multilayer composite film, the materials of each layer may be the same or different, and there is no particular limitation.

In the secondary battery of the present application, the positive pole piece, the negative pole piece and the separator can be made into an electrode assembly through a winding process or a lamination process.

In the secondary battery of the present application, the secondary battery may include an outer package. The outer package can be used to package the above-mentioned electrode assembly and electrolyte.

In the secondary battery of the present application, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, and the like. The outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag. The material of the soft case may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

The present application has no special limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. For example, FIG. 3 shows a square-shaped secondary battery 5 as an example.

In the secondary battery of the present application, referring to FIG. 4 , the outer package may include a case 51 and a cover plate 53 . Wherein, the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening to close the accommodating cavity. The positive pole piece, the negative pole piece and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. Electrolyte is infiltrated in the electrode assembly 52 . The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

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

FIG. 5 is a battery module 4 as an example. Referring to FIG. 5 , in the battery module 4 , a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 . Of course, it can also be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by fasteners.

In some embodiments, the battery module 4 may further include a case having an accommodation space in which a plurality of secondary batteries 5 are accommodated.

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

6 and 7 show the battery pack 1 as an example. Referring to FIGS. 6 and 7 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3 , the upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery module 4 . Multiple battery modules 4 can be arranged in the battery box in any manner.

In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. A secondary battery, a battery module, or a battery pack can be used as a power source of a power consumption device, and can also be used as an energy storage unit of the power consumption device. Electric devices can include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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., but not limited thereto.

As an electrical device, secondary batteries, battery modules, or battery packs can be selected according to their usage requirements.

FIG. 8 is an example of an electrical device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the electric device for the secondary battery, a battery pack or a battery module may be used.

As another example, a device may be a cell phone, tablet, laptop, or the like. The device is usually required to be light and thin, and a secondary battery can be used as a power source

Example

Hereinafter, examples of the present application will be described. The embodiments described below are exemplary and are only used for explaining the present application, and should not be construed as limiting the present application. If no specific technique or condition is indicated in the examples, it shall be carried out according to the technique or condition described in the literature in this field or according to the product specification. The reagents or instruments used were not indicated by the manufacturer, and they were all commercially available conventional products.

Example 1

Dissolve 1.2g (grams) of nitrile rubber in 100g of toluene, and stir at room temperature until the nitrile rubber dissolves completely to form the first coating solution;

Put 100 g of LiMn ₂ O ₄ with a volume average particle diameter Dv50 of 24.3 μm and the above-mentioned first polymer coating solution in a wet packer, and dry them while stirring in a nitrogen atmosphere at 120° C. to obtain the first polymer coating solution. coated solid powder;

Dissolve 1 g of sodium alginate with a weight average molecular weight of 12,000 in 100 g of deionized water, and stir until the sodium alginate is completely dissolved to form a second coating solution;

The above solid powder and the above second coating liquid were placed in a wet packer, dried at 100°C while stirring in an air atmosphere, and then ground, crushed and sieved to obtain both the first coating layer and the second coating layer. It is a positive electrode material with continuous distribution and a specific surface area of 0.336m ² /g.

Example 2

Except that the nitrile rubber is replaced by polymethyl methacrylate, and the solvent is replaced by N,N-dimethylformamide, other conditions are the same as in Example 1, thus obtaining the first coating layer, the second coating layer Both are continuously distributed, and the specific surface area is a positive electrode material of 0.245m ² /g.

Example 3

Except that the nitrile rubber is replaced by polyethylene terephthalate, and the solvent is replaced by a mixed solvent of trifluoroacetic acid and dichloromethane, other conditions are the same as in Example 1, thus obtaining the first cladding layer, the second The two coating layers are continuously distributed, and the specific surface area is a positive electrode material of 0.273m ² /g.

Example 4

Except that the nitrile rubber is replaced by polyacrylonitrile, and the solvent is replaced by N, N-dimethylformamide, other conditions are the same as in Example 1, so that the first coating layer and the second coating layer are continuous Distribution, a positive electrode material with a specific surface area of 0.261m ² /g.

Example 5

Except that the nitrile rubber is replaced by polymethyl acrylate, and the solvent is replaced by dichloroethane, other conditions are the same as in Example 1, thus obtaining the first coating layer and the second coating layer are continuous distribution, and the specific surface area The positive electrode material is 0.253m ² /g.

Example 6

Except that the nitrile rubber is replaced by polyacrylonitrile-based acrylate, and the solvent is replaced by acetone, other conditions are the same as in Example 1, so that the first coating layer and the second coating layer are continuously distributed, and the specific surface area is 0.490 m ² /g of positive electrode material.

Example 7

Except that the amount of polyacrylonitrile used was adjusted to 0.10 g, other conditions were the same as in Example 4, thus obtaining a positive electrode with a continuous distribution of the first coating layer and the second coating layer and a specific surface area of 0.255 m ² /g Material.

Example 8

Except that the amount of polyacrylonitrile used was adjusted to 0.15 g, other conditions were the same as in Example 4, thereby obtaining a positive electrode with a specific surface area of 0.253 m ² /g, in which both the first coating layer and the second coating layer were continuously distributed. Material.

Example 9

Except that the amount of polyacrylonitrile used was adjusted to 0.40 g, other conditions were the same as in Example 4, thus obtaining a positive electrode with a specific surface area of 0.241 m ² /g in which both the first coating layer and the second coating layer were continuously distributed. Material.

Example 10

Except that the amount of polyacrylonitrile used was adjusted to 1.20 g, other conditions were the same as in Example 4, thereby obtaining a positive electrode with a specific surface area of 0.261 m ² /g in which both the first coating layer and the second coating layer were continuously distributed. Material.

Example 11

Except that the amount of polyacrylonitrile used was adjusted to 2.00 g, other conditions were the same as in Example 4, thereby obtaining a positive electrode with a specific surface area of 0.271 m ² /g in which both the first coating layer and the second coating layer were continuously distributed. Material.

Example 12

Except that the amount of polyacrylonitrile used was adjusted to 2.50 g, the other conditions were the same as in Example 4, thus obtaining a positive electrode with a specific surface area of 0.310 m ² /g in which both the first coating layer and the second coating layer were continuously distributed. Material.

Example 13

Except that the amount of polyacrylonitrile used was adjusted to 3.00 g, the other conditions were the same as in Example 4, thus obtaining a positive electrode with a specific surface area of 0.309 m ² /g in which both the first coating layer and the second coating layer were continuously distributed. Material.

Example 14

Except that sodium alginate was replaced by carrageenan, the other conditions were the same as in Example 4, thereby obtaining a positive electrode material with a specific surface area of 0.283 m ² /g, in which both the first coating layer and the second coating layer were continuously distributed.

Example 15

Except that sodium alginate was replaced by agar, the other conditions were the same as in Example 4, thereby obtaining a positive electrode material with a specific surface area of 0.291 m ² /g in which both the first coating layer and the second coating layer were continuously distributed.

Example 16

Except that sodium alginate was replaced by guar gum, other conditions were the same as in Example 4, thus obtaining a positive electrode material with a continuous distribution of the first coating layer and the second coating layer and a specific surface area of 0.279 m ² /g .

Example 17

Except that the amount of sodium alginate used was adjusted to 0.05g, the other conditions were the same as in Example 4, thus obtaining a positive electrode with a specific surface area of 0.338m ² /g in which both the first coating layer and the second coating layer were continuously distributed. Material.

Example 18

Except that the amount of sodium alginate used was adjusted to 0.10 g, other conditions were the same as in Example 4, thereby obtaining a positive electrode with a specific surface area of 0.272 m ² /g, where both the first coating layer and the second coating layer were continuously distributed. Material.

Example 19

Except that the amount of sodium alginate used was adjusted to 0.30 g, other conditions were the same as in Example 4, thereby obtaining a positive electrode with a continuous distribution of the first coating layer and the second coating layer and a specific surface area of 0.297 m ² /g Material.

Example 20

Except that the amount of sodium alginate used was adjusted to 1.50 g, other conditions were the same as in Example 4, thus obtaining a positive electrode with a continuous distribution of the first coating layer and the second coating layer and a specific surface area of 0.428 m ² /g Material.

Example 21

Except that the amount of sodium alginate used was adjusted to 1.80 g, other conditions were the same as in Example 4, thereby obtaining a positive electrode with a continuous distribution of the first coating layer and the second coating layer and a specific surface area of 0.537 m ² /g Material.

Example 22

Except that the amount of sodium alginate used was adjusted to 2.00 g, other conditions were the same as in Example 4, thereby obtaining a positive electrode with a specific surface area of 0.601 m ² /g in which both the first coating layer and the second coating layer were continuously distributed. Material.

Example 23

Except that the amount of sodium alginate used was adjusted to 2.50 g, other conditions were the same as in Example 4, thereby obtaining a positive electrode with a specific surface area of 1.290 m ² /g in which both the first coating layer and the second coating layer were continuously distributed. Material.

Example 24

Except that sodium alginate with a weight average molecular weight of 12,000 is replaced by sodium alginate with a weight average molecular weight of 20,000, other conditions are the same as in Example 4, so that the first coating layer and the second coating layer are continuously distributed. , a positive electrode material with a specific surface area of 0.319m ² /g.

Example 25

Except that sodium alginate with a weight average molecular weight of 12,000 is replaced by sodium alginate with a weight average molecular weight of 30,000, other conditions are the same as in Example 4, thus obtaining the continuous distribution of the first coating layer and the second coating layer , a positive electrode material with a specific surface area of 0.307m ² /g.

Example 26

Except that sodium alginate with a weight-average molecular weight of 12,000 is replaced by sodium alginate with a weight-average molecular weight of 270,000, other conditions are the same as in Example 4, so that both the first coating layer and the second coating layer are continuously distributed. , a positive electrode material with a specific surface area of 0.729m ² /g.

Example 27

Except that sodium alginate with a weight average molecular weight of 12,000 is replaced by sodium alginate with a weight average molecular weight of 300,000, the other conditions are the same as in Example 4, thus obtaining the continuous distribution of the first coating layer and the second coating layer , a positive electrode material with a specific surface area of 1.520m ² /g.

Comparative example 1

LiMn ₂ O ₄ with a specific surface area of 0.267m ² /g was put into the test.

Comparative example 2

Dissolve 1.2g of polyacrylonitrile in 100g of N,N-dimethylformamide and stir until the polyacrylonitrile is completely dissolved to form the first coating solution.

Put 100g of LiMn ₂ O ₄ and the above-mentioned first polymer coating solution in a wet packer, and dry them while stirring in a nitrogen atmosphere at 120°C to obtain only the first polymer coating with a specific surface area of 0.229m ² /g of cathode material.

Comparative example 3

Dissolve 1 g of sodium alginate in 100 g of deionized water, and stir at room temperature until the sodium alginate is completely dissolved to form a second coating solution.

Put 100g of LiMn ₂ O ₄ and the above-mentioned second coating solution in a wet packer, and dry them while stirring in an air atmosphere at 100°C to obtain a solid material with a specific surface area of 0.275m ² /g coated only with polysaccharides .

Comparative example 4

Dissolve 1 g of sodium alginate in 100 g of deionized water, and stir at room temperature until the sodium alginate is completely dissolved to form a second coating solution.

Put 100g of LiMn ₂ O ₄ and the above-mentioned second coating solution in a wet packer, and dry at 100° C. while stirring in an air atmosphere to obtain a polysaccharide-coated solid material.

Dissolve 1.2g of polyacrylonitrile in 100g of N,N-dimethylformamide and stir until the polyacrylonitrile is completely dissolved to form the first coating solution.

Put the above-mentioned solid material and the above-mentioned first polymer coating solution in a wet packer, and dry them while stirring in a nitrogen atmosphere at 120°C to obtain a coating opposite to that of the inner and outer layers of Example 1, with a specific surface area of 0.259 m ² /g of cathode material.

The relevant parameters of the positive electrode materials of the above-mentioned Examples 1-27 and Comparative Examples 1-4 are shown in Table 1 below.

In addition, the positive electrode materials obtained in the foregoing Examples 1-27 and Comparative Examples 1-4 were respectively prepared into secondary batteries as shown below, and performance tests were performed. The test results are shown in Table 2 below.

(1) Preparation of secondary battery

The finished positive electrode material in each of the above examples and comparative examples is used as the positive electrode material, and the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) are mixed in the N-methylpyrrolidone solvent system at a weight ratio of 94:3:3 After being fully stirred and mixed evenly in the medium, it is coated on an aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet.

Artificial graphite as negative electrode active material, conductive agent acetylene black, binder styrene-butadiene rubber (SBR) and thickener sodium carbon methyl cellulose (CMC) were removed according to the weight ratio of 90:5:2:2:1. After fully stirring and mixing uniformly in the ionic water solvent system, coating on the copper foil, drying and cold pressing to obtain the negative electrode sheet.

A porous polymer film made of polyethylene (PE) is used as the separator.

The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrodes to play the role of isolation, and the bare cell is obtained by winding. The electrolyte is 1mol/L (mole per liter) LiPF ₆ /(ethylene carbonate (EC)+diethyl carbonate (DEC)+dimethyl carbonate (DMC)) (volume ratio 1:1:1). Putting the bare cell in the outer package, injecting the above-mentioned electrolyte solution and packaging to obtain a secondary battery.

(2) Cycle performance test of secondary battery at 45°C

Charge the secondary battery prepared above to 4.3V (volt) at 1C in a constant temperature environment of 45°C, then charge at a constant voltage at 4.3V to a current ≤ 0.05C (coulomb), and let it stand for 5min (minutes). Then discharge to 3V according to 1C, and record the number of turns when the capacity decays to 80%.

(3) Mn Dissolution Test of Cathode Material

Each secondary battery prepared above was charged to 4.3V at 0.33C, then charged at a constant voltage at 4.3V to a current ≤0.05C, and finally discharged to 3.82V at 0.33C, and stored at a constant temperature of 60°C. Then the capacity was measured every 15 days. When the capacity decayed to 80%, the secondary battery was disassembled, and the amount of Mn dissolved on the negative pole piece was measured using a thermo ICAP 7000 plasma emission spectrometer and inductively coupled plasma emission spectrometry.

Table 2: Performance test results of Examples 1-27 and Comparative Examples 1-4

According to the above results, it can be seen that the positive electrode materials obtained in Examples 1-27 adopt a double coating layer structure on the surface of the inner core, and further select polymers containing electron-withdrawing groups and polysaccharides with high oxygen content as coatings in turn. The material alleviates the Mn dissolution problem in the lithium manganese oxide battery system, and also improves the cycle performance of the battery.

In contrast, the positive electrode material obtained in Comparative Example 1 was not coated, and its Mn dissolution amount was large, and its cycle performance was poor.

The positive electrode material obtained in Comparative Example 2 was only coated with the first coating layer containing the first polymer, and the positive electrode material obtained in Comparative Example 3 was only coated with the second coating layer containing polysaccharide. Compared with uncoated (Comparative Example 1), there is a slight improvement in cycle performance and Mn dissolution, but the improvement in cycle performance and Mn dissolution is not as good as that of double-layer coating due to the failure to achieve the synergistic effect exhibited by double-layer coating (Example 4) is obviously improved.

Although the positive electrode material obtained in Comparative Example 4 adopts a double coating layer structure, the sequence of the inner and outer coating layers is opposite to that of Example 4. Therefore, the electron-withdrawing groups in the first polymer cannot play the role of Mn ³⁺ charge transfer on the surface of the positive electrode material, and the polysaccharide rich in oxygen in the second coating layer cannot play the role of reducing HF generation, so Neither the amount of manganese dissolution nor the cycle performance has been effectively improved.

Compared with Examples 9-12 in Examples 7 and 13, and compared with Examples 18-22 in Examples 17 and 23, it can be seen that although these Examples have achieved good results in the improvement of cycle performance and manganese dissolution effect, but because the mass percentage of the first coating layer in Examples 7 and 13 is too large, and the mass percentage of the second coating layer in Examples 17 and 23 is too large, resulting in an increase in impedance, which has a certain impact on the cycle performance of the positive electrode material .

Exemplarily, in Example 4, polyacrylonitrile is used as the first polymer, and sodium alginate is used as the selected polysaccharide. On the one hand, polyacrylonitrile has a certain ion conductivity, which has little effect on the transmission of lithium ions; on the other hand, the nitrile group in polyacrylonitrile has strong electron-withdrawing properties, which can better stabilize the surface of lithium manganate. The trivalent manganese ions on the surface can alleviate the problem of Mn dissolution. Compared with other polysaccharides, sodium alginate has higher oxygen content and -COONa group, which is beneficial to combine with Lewis acid. Therefore, in terms of manganese dissolution and cycle performance, Example 4 has achieved good improvement.

It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solutions of the present application, embodiments that have substantially the same configuration as the technical idea and exert the same effects are included in the technical scope of the present application. In addition, without departing from the scope of the present application, various modifications conceivable by those skilled in the art are added to the embodiments, and other forms constructed by combining some components in the embodiments are also included in the scope of the present application. .

Claims (18)

1. A positive electrode material, comprising:

   an inner core, and a first cladding layer and a second cladding layer sequentially arranged on the surface of the inner core,

   The inner core comprises a compound of formula I having a spinel structure:

   Li _1+x Mn _2-y M _y O _4-z A _z Formula I

   Among them, 0≤x≤1, 0≤y≤0.5, 0≤z≤0.5, x, y, z are not zero at the same time, M is selected from Al, Mg, Ga, Ti, Fe, Nb, Zn, Go , one or more of Ni, Sn, Cr, A is selected from one or more of F, S, Cl;

   The first coating layer includes a first polymer containing electron-withdrawing groups, and the electron-withdrawing groups are selected from at least one of ester groups or nitrile groups; the second coating layer contains polysaccharides.
2. The positive electrode material according to claim 1, wherein the mass percentage of the electron-withdrawing group in the first polymer is 20% to 65%; optionally, the electron-withdrawing group is in the The mass percentage of the first polymer is 33%-65%.
3. The positive electrode material according to claim 1 or 2, wherein the first cladding layer and/or the second cladding layer are continuously distributed on the surface of the inner core;

   Optionally, in the positive electrode material, the covering ratio of the second covering layer is not lower than that of the first covering layer.
4. The positive electrode material according to any one of claims 1-3, wherein, based on the mass of the inner core, the mass percentage of the first cladding layer is 0.15% to 2.5%, optionally 0.4% to 2% %, further optionally 0.4% to 1.6%; and/or,

   Based on the mass of the inner core, the mass percentage of the second cladding layer is 0.1%-2%, optionally 0.3%-1.8%, further optionally 0.3%-1.5%.
5. The positive electrode material according to any one of claims 1-4, wherein, based on the mass of the inner core, the total mass percentage of the first polymer and the polysaccharide is ≤ 3.8%, optionally ≤ 3.5%, Further optionally ≦3%.
6. The positive electrode material according to any one of claims 1-5, wherein the first polymer is selected from polymethyl acrylate, polyethyl acrylate, polymethyl methacrylate, polyethylene terephthalate One or more of alcohol ester, polybutyl methacrylate, polyethyl methacrylate, polyacrylonitrile, polynitrile acrylate, nitrile rubber, acrylonitrile copolymer.
7. The positive electrode material according to any one of claims 1-6, wherein the molecular structure of the polysaccharide is composed of a plurality of repeating units containing oxygen atoms, and in the repeating units, the mass ratio of the oxygen element is not less than 25%.
8. The positive electrode material according to any one of claims 1-7, wherein the polysaccharide has a weight average molecular weight of 20,000-270,000, optionally 30,000-220,000.
9. The positive electrode material according to any one of claims 1-8, wherein the polysaccharide is selected from one or more of sodium alginate, potassium alginate, guar gum, kale gum, carrageenan, and agar .
10. The positive electrode material according to any one of claims 1-9, wherein the specific surface area of the positive electrode material is 0.15m ² /g-1.5m ² /g, optionally 0.2m ² /g-0.8m ² /g.
11. A method for preparing a positive electrode material, at least comprising the following steps:

    (1) providing an inner core comprising a compound of formula I with a spinel structure:

    Li _1+x Mn _2-y M _y O _4-z A _z Formula I

    Among them, 0≤x≤1, 0≤y≤0.5, 0≤z≤0.5, x, y, z are not zero at the same time, M is selected from Al, Mg, Ga, Ti, Fe, Nb, Zn, Go , one or more of Ni, Sn, Cr, A is selected from one or more of F, S, Cl;

    (2) providing the first coating solution containing the first polymer, the first polymer contains an electron-withdrawing group, and the electron-withdrawing group is selected from at least one of an ester group or a nitrile group; The inner core is placed in the first coating solution, so that the first polymer is attached to the surface of the inner core to obtain a primary product;

    (3) providing a second coating solution containing polysaccharide, placing the primary product in the second coating solution, so that the second coating layer is attached to at least a part of the surface of the primary product, to obtain Cathode material.
12. The method for preparing positive electrode materials as claimed in claim 11, wherein, in the step (2), in the first coating liquid, the mass percentage of the first polymer is 0.05% to 20%, which can be Optionally 0.1% to 12%; and/or,

    The mass percentage of the inner core and the first coating liquid is 0.05%-70%, optionally 0.1%-60%.
13. According to the preparation method of any positive electrode material in claim 11 or 12, wherein, in said step (3), in said second coating liquid, the mass percentage of said polysaccharide is 0.05%～12%, optional 0.1% to 8%; and/or,

    The mass percentage of the primary product to the second coating solution is 0.05%-70%, optionally 0.1%-60%.
14. A positive electrode sheet, comprising the positive electrode material according to any one of claims 1-10 or the positive electrode material obtained by the preparation method according to any one of claims 11-13.
15. A secondary battery comprising the positive pole piece according to claim 14.
16. A battery module including the secondary battery according to claim 15.
17. A battery pack comprising the battery module according to claim 16.
18. An electric device, comprising at least one of the secondary battery according to claim 15, the battery module according to claim 16, or the battery pack according to claim 17.

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