CN118630152A - Negative electrode active material and preparation method thereof, negative electrode sheet, secondary battery and electric device - Google Patents

Abstract

The present application provides a negative electrode active material and a preparation method thereof, a negative electrode plate, a secondary battery and an electric device, wherein the negative electrode active material comprises: a core body, the core body comprises SnSe ₂ ; and a coating layer covering at least a portion of the surface of the core body, the coating layer comprises carbon containing a graphite layer. The negative electrode active material provided by the present application can improve the fast charging performance of the secondary battery.

Description

Negative electrode active material and preparation method thereof, negative electrode sheet, secondary battery and electric device

Technical Field

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

Background Art

Secondary batteries represented by lithium-ion batteries have the characteristics of high capacity and long life, so they are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric airplanes, electric boats, electric toy cars, electric toy boats, electric toy airplanes and electric tools, etc.

As the application range of batteries becomes wider and wider, the requirements for the performance of secondary batteries are becoming increasingly stringent. In order to improve the performance of secondary batteries, the materials in the secondary batteries, such as the negative electrode materials, are usually optimized and improved. However, when the improved negative electrode materials are currently applied to secondary batteries, the secondary batteries still have the problem of poor fast charging performance during use.

Summary of the invention

The purpose of the present application is to provide a negative electrode active material and a preparation method thereof, a negative electrode plate, a secondary battery and an electrical device, which can improve the fast charging performance of the secondary battery.

To achieve the above object, the first aspect of the present application provides a negative electrode active material, including a core body, the core body including SnSe ₂ ; and a coating layer covering at least a portion of the surface of the core body, the coating layer including carbon containing a graphite layer.

The negative electrode active material provided in the present application is a composite material with a coating layer formed on the surface of the core of SnSe _2. The SnSe ₂ in the core of the negative electrode active material has a larger interlayer spacing, which can increase the shuttle migration speed of active ions (such as lithium ions) between layers, and increase the embedding rate of active ions in the negative electrode active material, thereby improving the fast charging performance of the battery. The carbon containing the graphite layer in the coating layer of the negative electrode active material can reduce the irreversible capacity loss caused by the embedding of active ions in the first week of charging and discharging of the pure SnSe ₂ negative electrode, and can also improve the stability of the SEI film, thereby improving the cycle performance and service life of the battery.

In some embodiments of the present application, the core is SnSe ₂ , and the coating layer is a carbon layer containing a graphite layer.

When the core of the negative electrode active material is SnSe ₂ and the coating layer is a carbon layer containing a graphite layer, it has substantially the same performance or effect as the negative electrode active material described in the first aspect of the present application, and will not be described in detail here.

In some embodiments of the present application, the core is a hexagonal nanosheet, and the hexagonal nanosheet satisfies at least one of the following conditions:

(1) The thickness of the hexagonal nanosheets is 20 nm to 40 nm;

(2) The side lengths of the hexagonal nanosheets are each independently 100 nm to 200 nm.

The thickness and side length of the hexagonal nanosheets are within the above range, which is beneficial to further improve the shuttle migration speed of active lithium ions between the negative electrode active material layers, improve the embedding rate of active lithium ions, and thus improve the fast charging performance.

In some embodiments of the present application, the thickness of the coating layer is 5 nm to 15 nm, and can be optionally 8 nm to 12 nm.

The thickness of the coating layer is within the above range, which not only inhibits the irreversible reaction of generating Li _x SnSe ₂ , reduces irreversible capacity loss, improves charge and discharge efficiency, and provides the overall conductivity and structural stability of the negative electrode active material, but also helps to further improve the shuttle migration speed of active lithium ions between the negative electrode active material layers, thereby further improving the fast charging performance of the battery.

In some embodiments of the present application, the coating layer accounts for 5% to 50% by mass in the negative electrode active material, and can be optionally 5% to 10% by mass.

The mass proportion of the coating layer in the negative electrode active material is within the above range, which is conducive to achieving a balance between the capacity and fast charging performance of the negative electrode active material, so that both the capacity and the fast charging performance are at a relatively high level.

In some embodiments of the present application, the coating layer contains functional groups. Optionally, the functional groups include one or more of carboxyl, hydroxyl and epoxy groups.

The above-mentioned functional groups contained in the coating layer are helpful to improve the reaction activity of the negative electrode active material and can promote the formation of the SEI film during the cycle process.

The second aspect of the present application also provides a method for preparing the negative electrode active material of the first aspect of the present application, comprising:

Mixing a tetravalent tin source, a selenium source and a carbon source in a solvent to obtain a mixed solution;

The mixed solution is heat-treated to form a core body and a coating layer covering at least a portion of the surface of the core body, thereby obtaining a negative electrode active material, wherein the core body includes SnSe ₂ and the coating layer includes carbon containing a graphite layer.

By heat treating the mixed solution, the tetravalent tin source and the selenium source can react to form a core body including _SnSe2 , and a coating layer including a carbon containing a graphite layer is formed on at least part of the surface of the core body to obtain the negative electrode active material of the first aspect of the present application.

In some embodiments of the present application, the core is SnSe ₂ , and the coating layer is a carbon layer containing a graphite layer.

In some embodiments of the present application, the heat treatment includes hydrothermal treatment and/or solvent thermal treatment.

The preparation process of the above method provided in the present application is relatively simple, and the preparation of nanomaterials and carbon coating containing graphite layers can be achieved in one step. Moreover, by controlling the heat treatment, the performance of the obtained negative electrode active material can be regulated, which is beneficial to reducing the preparation cost.

In some embodiments of the present application, the mixed solution satisfies at least one of the following conditions:

(1) The mass ratio of the tetravalent tin source to the selenium source is (3.8:6.2) to (6.8:3.2);

(2) In the mixture consisting of the tetravalent tin source, the selenium source and the carbon source, the mass proportion of the carbon source is 3% to 50%.

When the mass ratio of the tetravalent tin source, the selenium source and the carbon source is within the above range, the precipitation of elemental selenium in the subsequent reaction process can be reduced, thereby improving the yield of the negative electrode active material.

In some embodiments of the present application, the heat treatment satisfies at least one of the following conditions:

(1) The temperature of the heat treatment is 150°C to 200°C;

(2) The heat treatment time is 12h to 24h.

By adjusting the temperature and time of the heat treatment within the above range, it is beneficial to provide a suitable high-pressure environment, thereby further promoting the coating process and the reaction of generating the negative electrode active material.

In some embodiments of the present application, the method satisfies at least one of the following conditions:

(1) The selenium source includes NaHSe;

(2) The tetravalent tin source includes one or more of SnCl ₄ , SnBr ₄ , SnI ₄ , SnF ₄ , SnO ₂ , and SnS ₂ ;

(3) The carbon source includes one or more of natural graphite, artificial graphite, soft carbon, and hard carbon.

Optionally, the volume average particle size Dv50 of the carbon source is 3 μm to 25 μm.

In the present application, the Dv50 of the carbon source is within the above range, which is beneficial to further promote the coating process.

The third aspect of the present application provides a negative electrode plate, comprising the negative electrode active material of the first aspect of the present application or the negative electrode active material prepared by the method of the second aspect of the present application.

The fourth aspect of the present application provides a secondary battery, comprising the negative electrode sheet of the third aspect of the present application.

A fifth aspect of the present application provides an electrical device, comprising the secondary battery of the fourth aspect of the present application.

The electric device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of the reaction process of generating Li _x SnSe ₂ during the first cycle of discharge of pure SnSe ₂ negative electrode.

FIG. 2 is a schematic diagram of the reaction process of the negative electrode active material during the first cycle of discharge according to an embodiment of the present application.

FIG3 is a schematic diagram showing the principle of fast charging of the negative electrode active material according to one embodiment of the present application.

FIG. 4 is a morphology diagram of the pure SnSe ₂ material of Comparative Example 1 (a), and the negative electrode active materials of Example 1 (b) and Example 21 (c).

FIG. 5 is a transmission electron microscope image of the negative electrode active material of Example 1.

FIG6 is a first-cycle cyclic voltammetry curve of the lithium-ion batteries of Comparative Example 1 and Example 1.

FIG. 7 is a graph showing the rate performance of the lithium-ion battery of Example 1.

FIG. 8 is a schematic diagram of a secondary battery according to an embodiment of the present application.

FIG. 9 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 8 .

FIG. 10 is a schematic diagram of a secondary battery according to yet another embodiment of the present application.

FIG. 11 is a schematic diagram of a secondary battery according to another embodiment of the present application.

FIG. 12 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 11 .

FIG. 13 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

Description of reference numerals:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly.

DETAILED DESCRIPTION

Below, the negative electrode active material and its manufacturing method, negative electrode pole piece, secondary battery, battery module, battery pack and electric device of the present application are described in detail with appropriate reference to the drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are 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.

"Scope" disclosed in the present application is defined in the form of lower limit and upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope defined in this way includes end values or does not include end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "a-b" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended and closed-ended forms. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": 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).

At present, secondary batteries represented by lithium-ion batteries are widely used in portable electronic devices, electric vehicles and other fields. However, in recent years, the field of power lithium batteries has encountered huge challenges. How to achieve higher driving range and faster charging speed has become an important indicator for measuring the performance of power lithium batteries. The negative electrode is the part of the secondary battery represented by lithium-ion batteries that stores active ions (such as lithium ions) after charging. The gram capacity of the negative electrode material and the speed at which the active ions shuttle in it greatly affect the overall capacity and fast charging capability of the battery.

Graphite material, as one of the commonly used negative electrode materials for commercial power lithium batteries, has an interlayer spacing of 0.336nm, and is mainly a hexahedral graphite crystal plane ordering structure. The orientation between individual microcrystals is anisotropic, and lithium ions are reversibly embedded in the coating interlayer. However, due to the small interlayer spacing of graphite, when the charging current density is high, the migration speed of lithium ions will be slower than the reaction speed, making it difficult to embed lithium in the inner layer of graphite, which greatly reduces its fast charging capacity.

When tin-based materials are used as the negative electrode of secondary batteries, higher battery capacity can be achieved through reversible substitution and alloying reactions. Many tin-based materials, such as SnSe ₂ , SnS ₂ , SnO, etc., have a two-dimensional crystal structure, and a larger interlayer spacing is conducive to faster shuttling of active ions. Among them, SnSe ₂ is a tin-based two-dimensional material with a larger interlayer spacing (0.614nm) and a narrow band gap (E _g = 1.0V ~ 1.5V). As the negative electrode of a lithium-ion battery, its theoretical capacity is 813mAh/g.

However, in the first cycle of lithium insertion in two-dimensional negative electrode materials such as _SnSe2 , lithium ions will be irreversibly intercalated into the material, causing _a phase change and forming _LixSnSe2 . The occurrence of this irreversible reaction reduces the reversible capacity of the battery. In addition, the SEI film (solid electrolyte interface film) formed in the first cycle of _SnSe2 is not dense enough and has low strength. As the cycle progresses, the SEI film will continue to break and re-form, which will cause the continuous consumption of active lithium and reduce the capacity on the one hand; on the other hand, it will cause the _SnSe2 structure to collapse, causing the battery capacity to plummet.

In order to solve the above technical problems, the present application proposes a negative electrode active material, which uses a coating layer including a carbon containing a graphite layer to coat a core body including SnSe ₂ , wherein the core body can increase the shuttle migration speed of active ions (such as lithium ions) between material layers, increase the embedding rate of active ions, and thus improve the fast charging performance; while the coating layer can reduce the irreversible capacity loss of active ions embedded in the first cycle of charging and discharging of the SnSe ₂ negative electrode, and at the same time improve the stability of the SEI film. The scheme will be described in detail below.

Negative electrode active material

The first aspect of the present application provides a negative electrode active material, comprising a core body, wherein the core body comprises SnSe ₂ ; and a coating layer coated on at least a portion of the surface of the core body, wherein the coating layer comprises carbon containing a graphite layer.

It should be noted that the carbon containing graphite layers described in the present application refers to a carbon material composed of graphite layers in terms of crystal structure, that is, a carbon material composed of graphite layers composed of sp2 hybridized carbon atom layers, wherein the graphite layers can be arranged regularly or irregularly. Specifically, for example, it can include natural graphite, artificial graphite, soft carbon and hard carbon, etc.

Without intending to be limited by any theory, the pure SnSe ₂ negative electrode will be in direct contact with the electrolyte during the cycle process. During this process, active ions such as lithium ions will be intercalated into SnSe ₂ and undergo an irreversible reaction at a reaction potential of about 1.7V to form Li _x SnSe ₂ , and this reaction only occurs during the first cycle of discharge. As a non-limiting illustration, as shown in Figure 1, when pure SnSe ₂ material is used as the negative electrode, an irreversible reaction of Li _x SnSe ₂ generation will occur first, and then the SEI film will be formed on the surface of SnSe _2. This process will cause some active lithium ions to participate in the formation of Li _x SnSe ₂ , which cannot be deintercalated in subsequent cycles, resulting in irreversible capacity loss. At the same time, the SEI film formed by the pure _SnSe2 negative electrode is not dense and stable enough. In the subsequent discharge process, a substitution reaction of _Li2Se and Sn will occur at a potential of 0.5V to 0.8V, and an alloying reaction of Sn and Li will occur at a potential below 0.3V. These two reactions will cause a large volume expansion, which is easy to destroy the structure of the SEI film in the subsequent cycle, and then lead to the co-embedding of solvent molecules in the electrolyte, which may eventually lead to battery failure.

The negative electrode active material provided by the present application, after the surface of the core body including SnSe ₂ is coated with a coating layer including carbon containing a graphite layer, as a non-limiting illustration, as shown in FIG2, the coating layer on the surface will be in direct contact with the electrolyte. Since the main voltage range for the formation of the SEI film is about 0.8V to 1.0V, which is much lower than the formation voltage of Li _x SnSe ₂ , the active lithium ions will preferentially participate in the formation of a dense SEI film on the surface of the coating layer. In other words, before the reaction of the generation of Li _x SnSe ₂ , the SEI film has been formed on the surface of the coating layer, thereby inhibiting the irreversible reaction of Li _x SnSe _2. The formation of the SEI film will have a crucial impact on the performance of the negative electrode active material. Specifically, the SEI film is insoluble in organic solvents, can exist stably in organic electrolyte solutions, and the solvent molecules cannot pass through the passivation film, thereby effectively preventing the co-embedding of solvent molecules, avoiding the damage to the negative electrode material caused by the co-embedding of solvent molecules, and thus improving the cycle performance and service life of the negative electrode.

After this, the relative potential (relative Li/Li ⁺ ) of the negative electrode active material is much lower than the voltage range of Li _x SnSe ₂ formation, which can inhibit the irreversible reaction of Li _x SnSe _2. As a result, active lithium ions will participate more in the formation of a dense and firm SEI film, which is conducive to reducing irreversible capacity loss. At the same time, the formation of the SEI film on the surface of the coating layer provides a channel for the diffusion of active lithium ions and improves the ion conductivity; and the carbon containing the graphite layer included in the coating layer itself has excellent conductivity, which can also improve the overall electronic conductivity of the negative electrode active material. In addition, the formation of the coating layer is also conducive to alleviating the volume expansion caused by the redox reaction of SnSe ₂ and improving the structural stability of the negative electrode active material.

Therefore, the negative electrode material provided by the present application is a composite material with a coating layer formed on the surface of the core of SnSe _2. As shown in Figure 3, the SnSe ₂ in the core of the negative electrode active material has a larger interlayer spacing, which can increase the shuttle migration speed of active ions (such as lithium ions) between layers, and increase the embedding rate of active ions in the negative electrode active material, thereby improving the fast charging performance of the battery. The carbon containing the graphite layer in the coating layer of the negative electrode active material can reduce the irreversible capacity loss caused by the embedding of active ions in the first week of charging and discharging of the pure SnSe ₂ negative electrode, and can also improve the stability of the SEI film, thereby improving the cycle performance and service life of the battery.

In some embodiments, the core is SnSe ₂ and the coating is a carbon layer containing a graphite layer. When the core of the negative electrode active material is SnSe ₂ and the coating is a carbon layer containing a graphite layer, it has substantially the same performance or effect as the above embodiment and will not be described in detail.

In some embodiments, the core is a hexagonal nanosheet. Optionally, the hexagonal nanosheet is a regular hexagonal shape.

It can be understood that the hexagonal nanosheets described in the present application refer to nanosheets having a certain thickness along two opposite plane directions perpendicular to the hexagonal nanosheets.

The core body is a hexagonal nanosheet, which is determined by the crystal structure of SnSe ₂ included in the core body. The hexagonal nanosheet core body is a layered structure with a wide interlayer spacing, which is conducive to improving the migration rate of active lithium ions; especially when the charging current density is large, it is conducive to the rapid migration of active lithium ions and enables the active lithium ions to be quickly embedded in the inner layer of the negative electrode active material, thereby increasing the fast charging capacity and improving the fast charging performance of the battery.

In some embodiments, the thickness of the hexagonal nanosheet is 20 nm to 40 nm. For example, the thickness of the hexagonal nanosheet can be 20 nm, 22 nm, 24 nm, 26 nm, 28 nm, 30 nm, 32 nm, 34 nm, 36 nm, 38 nm, 40 nm or within a range consisting of any of the above values.

The thickness of the hexagonal nanosheet refers to the thickness along two opposite planes perpendicular to the hexagon, which can be measured by methods known in the art, for example, by using a transmission electron microscope (TEM, model FEI Titan80-300KV microscope).

In some embodiments, the side lengths of the hexagonal nanosheets are independently 100 nm to 200 nm. For example, the side lengths of the hexagonal nanosheets can be independently 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm or within the range of any of the above values.

The side length of the hexagonal nanosheet refers to the side lengths of two opposite hexagonal planes of the hexagonal nanosheet, and can be measured using methods known in the art, such as a transmission electron microscope.

The thickness and side length of the hexagonal nanosheets are within the above range, which is beneficial to further improve the shuttle migration speed of active lithium ions between the negative electrode active material layers, improve the embedding rate of active lithium ions, and thus improve the fast charging performance.

In some embodiments, the coating layer has a thickness of 5 nm to 15 nm. For example, the coating layer has a thickness of 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, or any range thereof. Optionally, the coating layer has a thickness of 8 nm to 12 nm.

The thickness of the coating layer is well known in the art and can be measured by methods known in the art, for example, by using a transmission electron microscope (TEM).

The thickness of the coating layer is within the above range, which not only inhibits the irreversible reaction of generating Li _x SnSe ₂ , reduces irreversible capacity loss, improves charge and discharge efficiency, and provides the overall conductivity and structural stability of the negative electrode active material, but also helps to further improve the shuttle migration speed of active lithium ions between the negative electrode active material layers, thereby further improving the fast charging performance of the battery.

In some embodiments, the coating layer accounts for 5% to 50% by mass in the negative electrode active material. For example, the coating layer accounts for 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% by mass in the negative electrode active material or in the range of any of the above values. Optionally, the coating layer accounts for 5% to 10% by mass in the negative electrode active material. Further optionally, the coating layer accounts for 10% by mass in the negative electrode active material.

The mass ratio of the coating layer in the negative electrode active material is well known in the art and can be tested by methods known in the art, for example, by using a transmission electron microscope.

The mass proportion of the coating layer in the negative electrode active material is within the above range, which is conducive to achieving a balance between the capacity of the negative electrode active material and the fast charging performance, so that both the capacity and the fast charging performance are at a relatively high level. If the content of the coating layer is relatively high, the overall capacity of the negative electrode active material may be reduced; if the content of the coating layer is relatively low, the structure of the _SnSe2 core may be relatively unstable, which may easily cause structural collapse during the fast charging process.

In some embodiments, the coating layer contains functional groups. Optionally, the functional groups include one or more of carboxyl, hydroxyl and epoxy groups.

The functional groups contained in the coating layer can be measured by infrared spectroscopy. The functional groups help to improve the reactivity of the negative electrode active material and promote the formation of the SEI film during the cycle.

The second aspect of the present application provides a method for preparing the negative electrode active material of the first aspect of the present application, which may include the following steps:

S10, mixing a tetravalent tin source, a selenium source and a carbon source in liquid phase to obtain a mixed solution;

S30, heat-treating the mixed solution to form a core body and a coating layer covering at least a portion of the surface of the core body, to obtain a negative electrode active material, wherein the core body includes SnSe ₂ and the coating layer includes carbon containing a graphite layer.

By heat treating the mixed solution, the tetravalent tin source and the selenium source can react to form a core body including _SnSe2 , and a coating layer including a carbon containing a graphite layer is formed on at least part of the surface of the core body to obtain the negative electrode active material of the first aspect of the present application.

In some embodiments, the thermal treatment comprises hydrothermal treatment and/or solvothermal treatment.

It can be understood that the hydrothermal treatment can be to place the mixed solution in a closed container, heat the closed container, and make the mixed solution evaporate continuously to form high-temperature water vapor, so that the pressure of the closed container is continuously increased, and a high-pressure environment is provided for the reaction between the tetravalent tin source, the selenium source and the carbon source; the high-pressure environment is conducive to promoting the reaction of the tetravalent tin source, the selenium source and the carbon source, and is conducive to the formation of _SnSe2 , and promotes the coating process, so that a coating layer including a carbon containing a graphite layer is formed on at least part of the surface of _SnSe2 , and then a negative electrode active material is obtained. The preparation process of this method is relatively simple, and the coating of the carbon containing the graphite layer can be prepared in one step, and by controlling the heat treatment, the performance of the obtained negative electrode active material can be regulated, which is conducive to reducing the preparation cost.

As a non-limiting example of preparing the negative electrode active material, SnCl ₄ ·5H ₂ O can be added to deionized water and stirred, and then the prepared NaHSe solution is mixed with artificial graphite and stirred to obtain a mixed solution. Finally, the mixture is transferred to a polytetrafluoroethylene reaction container, placed in a stainless steel autoclave, and heated in an oven. After cooling to room temperature, the obtained product is collected by centrifugation, washed several times with deionized water and ethanol, and dried in a vacuum.

In some embodiments, the heat treatment temperature is 150° C. to 200° C. For example, the heat treatment temperature can be 150° C., 160° C., 170° C., 180° C., 190° C., 200° C. or any range thereof.

In some embodiments, the heat treatment time is 12 h to 24 h. For example, the heat treatment time can be 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h or within the range of any of the above values.

By adjusting the temperature and time of the heat treatment within the above range, it is beneficial to provide a suitable high-pressure environment, thereby further promoting the coating process and the reaction of generating the negative electrode active material.

It should be noted that in the above-mentioned preparation process, parameters such as the solubility and concentration of the selenium source in the mixed solution and the time of the hydrothermal treatment will affect the size of the core body. The thickness of the coating layer is mainly related to parameters such as the mass ratio of the carbon source in the mixed solution and the time of the hydrothermal treatment. Therefore, by regulating the above-mentioned parameters, the size of the core body and the thickness of the coating layer can be controlled within a more suitable range, thereby improving the electrochemical properties such as the fast charging performance and capacity of the negative electrode active material and the battery.

In some embodiments, the selenium source includes NaHSe. The NaHSe provided in the present application can be used as a selenium source for selenide, which can prepare selenide with uniform morphology at a relatively low temperature; and the _selenium source has relatively stable chemical properties, which is conducive to reducing the safety hazards caused by the use of unstable reducing agents (such as _N2H4 · _H2O or oleylamine, etc.) during the preparation process, while reducing the energy consumption required for high-temperature reactions.

In some embodiments, the method for preparing the selenium source NaHSe may include the following steps:

S110, prepare deionized water and put it in a test tube, insert the air tube into the deionized water and seal it, and continuously fill it with nitrogen or alkaline gas (such as ammonia) to remove oxidizing gases such as oxygen dissolved in the water;

S120, dissolving the reducing agent in the above-mentioned deionized water, slowly shaking and adding Se powder, a large amount of gas is generated during the process, shaking the test tube until the Se powder is completely dissolved, and obtaining a transparent NaHSe solution, which is used as a selenium source for preparing negative electrode active materials.

The reaction process of preparing the selenium source is shown in the following formula (1):

4NaBH ₄ +2Se+7H ₂ O＝2NaHSe+Na ₂ B ₄ O ₇ +14H ₂ (1)

It should be noted that, in the preparation process of the above-mentioned selenium source, the reducing agent can be in excess, so that, on the one hand, the Se powder can be completely dissolved; on the other hand, the reducing agent can also disperse the carbon source well in the subsequent preparation process of the negative electrode active material, remove the oxygen-containing groups in the carbon source, reduce the particle size of the carbon source (such as Dv50), and promote the coating process.

In some embodiments, the reducing agent in the above step S120 may include KBH ₄ and/or NaBH ₄ .

In some embodiments, the tetravalent tin source includes one or more of SnCl ₄ , SnBr ₄ , SnI ₄ , SnF ₄ , SnO ₂ , and SnS ₂ .

In some embodiments, the carbon source includes one or more of natural graphite, artificial graphite, soft carbon, and hard carbon.

In some embodiments, in the mixed solution, the mass ratio of the tetravalent tin source to the selenium source is (3.8:6.2) to (6.8:3.2). For example, the mass ratio of the tetravalent tin source to the selenium source can be 3.8:6.8, 3.8:6.0, 3.8:5.5, 3.8:5.0, 3.8:4.5, 3.8:4.0, 3.8:3.5, 3.8:3.2, 6.2:6.8, 6.2:6.5, 6.2:6.0, 6.2:5.5, 6.2:5.0, 6.2:5.5, 6.2:5.0, 6.2:4.5, 6.2:4.0, 6.2:3.5, 6.2:3.2 or within the range of any of the above values.

In some embodiments, in the mixture consisting of the tetravalent tin source, the selenium source and the carbon source, the mass proportion of the carbon source is 3% to 50%. For example, the mass proportion of the carbon source can be 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or within the range of any of the above values.

In the present application, when the mass ratio of the tetravalent tin source, the selenium source and the carbon source is within the above range, the precipitation of elemental selenium in the subsequent reaction process can be reduced, and the yield of the negative electrode active material can be improved. At the same time, the mass ratio of the tetravalent tin source, the selenium source and the carbon source will affect the size of the core body and the thickness of the coating layer. Thus, by controlling the mass ratio of the three within the above range, the size of the core body and the thickness of the coating layer can be controlled within a more suitable range, thereby improving the electrochemical properties of the negative electrode active material and the battery, such as the fast charging performance and capacity.

It should be noted that among the above carbon sources provided by the present application, although hard carbon cannot be graphitized from the material itself, from the perspective of crystal structure, the above carbon sources are all composed of graphite layers, that is, they are all composed of sp2 hybridized carbon atom layers to form graphite layers, and then the above carbon sources are composed of graphite layers, but in artificial graphite, natural graphite and soft carbon, the graphite layers can be arranged regularly, while in hard carbon, the graphite layers are arranged irregularly. Therefore, in the negative electrode active materials prepared from the above carbon sources, a coating layer including carbon containing a graphite layer can be formed on the surface of the core.

In some embodiments, the volume average particle size Dv50 of the carbon source is 3 μm to 25 μm. For example, the volume average particle size Dv50 of the carbon source can be 3 μm, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm, 21 μm, 23 μm, 25 μm or within the range of any of the above values. The Dv50 of the carbon source within the above range is conducive to further promoting the coating process.

The volume average particle size Dv50 of the carbon source is well known in the art and can be measured using instruments and methods well known in the art. For example, it can be conveniently measured using a laser particle size analyzer with reference to GB/T 19077-2016 particle size distribution laser diffraction method, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd., UK.

The present application realizes the coating of the coating layer of carbon containing graphite layer on the surface of the core body including SnSe ₂ , which mainly includes physical adsorption and chemical action, wherein the physical adsorption effect is mainly reflected in: the present application selects a carbon source (such as artificial graphite) with a small particle size and suitable, and at the same time, the reducing agent (such as NaBH ₄ ) has a certain stripping effect on the carbon source, which can further reduce the particle size of the carbon source. During the reaction, the carbon source can be adsorbed on the surface of the SnSe ₂ nanosheet to form the above-mentioned coating layer. In addition, the chemical action is mainly reflected in: the Sn ⁴⁺ contained in the tetravalent tin source is a weak acid particle, and the reducing agent (NaBH ₄ ) will modify the surface of the carbon source (such as artificial graphite) to form some functional groups containing hydroxide and oxygen; the weak acid and weak basic groups attract each other, which can promote the carbon source particles to be evenly coated on the surface of the core body to form a coating layer of carbon containing graphite layer. At the same time, during the heat treatment process, the particle size of the carbon source will be further reduced, which is conducive to promoting the coating of the carbon source on the surface of the core body, and is also conducive to forming a denser SEI film without consuming too much lithium source, which is conducive to taking into account both stability and kinetic capacity. Moreover, the surface of the coating layer will form more abundant functional groups (such as carboxyl, hydroxyl and epoxy groups, etc.), which help to increase the reaction activity, better achieve coating and form SEI film, and at the same time, the graphite layer structure of the carbon source becomes thinner.

The above description of various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced to each other, and for the sake of brevity, they will not be repeated in this article.

Secondary battery

In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

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

Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[Positive electrode]

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, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

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

In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. 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 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries 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 oxide (such as LiCoO ₂ ), lithium nickel oxide (such as LiNiO ₂ ), lithium manganese oxide (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (also referred to as NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (also referred to as NCM ₂₁₁ ), LiNi _0.6 Co 0.2 Mn _0.2 O ₂ (also referred to as NCM ₆₂₂ ), LiNi 0.8 Co _0.1 Mn 0.1 O 2 (also referred to as NCM 811 ), and LiNi _0.8 Co _0.2 Mn _0.2 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and modified compounds thereof. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder 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 collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

The positive electrode sheet of the present application does not exclude other additional functional layers in addition to the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of the present application also includes a conductive primer layer (for example, composed of a conductive agent and a binder) sandwiched between the positive electrode collector and the positive electrode film layer and disposed on the surface of the positive electrode collector. In other embodiments, the positive electrode sheet of the present application also includes a protective layer covering the surface of the positive electrode film layer.

[Negative electrode]

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

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

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

In some embodiments, the negative electrode active material adopts the negative electrode active material provided by the present application. At the same time, the negative electrode active material may also include other negative electrode active materials for batteries known in the art. As an example, other negative electrode active materials may also include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, 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, the present application is not limited to these materials, and other traditional 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.

In some embodiments, the negative electrode film layer may further 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).

In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder 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 collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

The negative electrode plate of the present application does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the present application also includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode plate of the present application also includes a protective layer covering the surface of the negative electrode film layer.

[Electrolytes]

The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt may be a lithium salt. As an example, the lithium 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorobis(oxalatophosphate), and lithium tetrafluorooxalatophosphate.

In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[Isolation film]

In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

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

In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

In some embodiments, the outer packaging of the secondary battery includes a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery also includes a soft package, such as a bag-type soft package. The material of the soft package includes plastic, and as the plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed.

The present application has no particular limitation on the shape of the secondary battery, which includes cylindrical, square or any other shapes. For example, FIG7 is a secondary battery 5 of a square structure as an example.

In some embodiments, referring to FIG. 8 , the outer package may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The 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 some embodiments, the secondary battery also includes a battery module assembled from a plurality of battery cells. The battery module may include a plurality of battery cells, and the specific number can be adjusted by those skilled in the art according to the application and capacity of the battery module.

FIG9 is a battery module 4 as an example. Referring to FIG9 , in the battery module 4, a plurality of secondary batteries 5 are arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

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

In some embodiments, the battery cells mentioned above may also be directly assembled into a battery pack, and the number of battery cells contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

FIG10 and FIG11 are battery packs 1 as an example. Referring to FIG10 and FIG11 , 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, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may 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 are not limited to these.

As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

FIG12 is an example of an electric 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 electric device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.

Another example of a device includes a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

Example

Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not indicate the manufacturer are all conventional products that can be obtained commercially.

Example 1

Preparation of negative electrode active materials

8.8 g SnCl ₄ ·5H ₂ O was added to 80 mL deionized water and stirred for 10 min, then 80 mL of the prepared NaHSe solution and 0.8 g of artificial graphite were added, mixed and stirred for 30 min to obtain a mixture. Finally, the mixture was transferred to a 200 mL polytetrafluoroethylene reaction container (filling amount was 160 mL), placed in a stainless steel autoclave, and heated in an oven at 180° C. for 24 hours. After cooling to room temperature, the obtained product was collected by centrifugation, washed several times with deionized water and ethanol, and vacuum dried at 60° C. for 12 hours to obtain a negative electrode active material.

Wherein, the above-mentioned NaHSe solution can be prepared by the following method:

Prepare 80mL of deionized water in a test tube, insert a nitrogen gas tube into the deionized water and seal it, and continue to fill with nitrogen for 5 minutes to remove oxidizing gases such as oxygen dissolved in the water. Dissolve 8g of _NaBH4 in deionized water, shake slowly and add 4g of Se powder. A large amount of gas is generated during the process. Shake the test tube until the Se powder is completely dissolved and a transparent NaHSe solution is obtained.

Preparation of negative electrode

The negative electrode active material, carbon black (Super P) and PVDF binder were mixed in a weight ratio of 8:1:1, added to NMP, and mixed evenly to obtain a homogeneous slurry. The slurry was then evenly coated on the copper current collector and dried in a vacuum oven at 80°C for 24 hours to obtain a negative electrode sheet.

Preparation of electrolyte

1M LiPF ₆ was dissolved in a solvent with a volume ratio of 1:1:1 of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as the electrolyte.

Preparation of isolation membrane

Celgard 3501 microporous membrane was used as the isolation membrane.

Preparation of lithium-ion half-cells

The lithium metal sheet, the negative electrode sheet and the isolation film are assembled in a glove box to prepare a lithium ion half-cell.

Embodiments 2 to 15

The preparation method of the lithium ion half-cell is similar to that of Example 1, except that the negative electrode active material and the related parameters in the preparation process are adjusted, and the specific parameters are shown in the following Table 1. Wherein, "/" indicates that the corresponding parameter does not exist.

Comparative Example 1

The preparation of the lithium-ion half-cell is similar to that of Example 1, except that when preparing the negative electrode plate, an equal mass of pure _SnSe2 material is used to replace the negative electrode active material.

Comparative Example 2

The preparation of the lithium-ion half-cell is similar to that of Example 1, except that when preparing the negative electrode plate, an equal mass of conventional artificial graphite is used to replace the negative electrode active material.

Comparative Example 3

The preparation of the lithium ion half-cell is similar to that of Example 1, except that when preparing the negative electrode active material, an equal mass of SnCl ₂ is used instead of SnCl ₄ .

Table 1

In addition, the negative electrode active materials and lithium ion batteries obtained in the above Examples 1 to 15 and Comparative Examples 1 to 3 were subjected to relevant performance tests, and the test results are shown in Table 2 below.

Test Section

(1) Negative electrode active material morphology test

The morphology of the negative electrode active material was tested using a scanning electron microscope (model: FEI Nova Nano 630) and a transmission electron microscope (model: FEITitan 80～300KV).

(2) Cyclic voltammetry curve test in the first week

A Biologic VMP3 electrochemical workstation was used to scan in the range of 0.005 V to 2.5 V (V vs Li/Li ⁺ ) at a scan rate of 0.2 mV/s.

(3) Rate performance test

The assembled batteries were subjected to charge and discharge tests on a new VELCRO instrument, the test voltage range was 0.005V to 2.5V, and constant current charge and discharge tests were performed at charge and discharge rates of 0.1C, 0.2C, 0.3C, 0.5C, 1C, 3C and 5C.

(4) Cyclic performance test

The cycle test temperature is 25℃, the voltage range is 0.005V～2.5V, and the battery is charged and discharged at a constant current of 0.1C in the first cycle to ensure the formation of a more stable SEI film. After the first cycle, the battery is charged and discharged at a constant current of 5C, and the capacity of the second cycle is taken as the initial capacity, recorded as D0. After that, a 5C charge/5C discharge cycle test is performed, and the capacity after 100 cycles is recorded as D1, and the capacity after 1000 cycles is recorded as D2.

The capacity retention rate of a lithium-ion battery after 1000 cycles = D2/D0×100%.

(5) First-cycle Coulomb efficiency test

Since half-cells are used for testing, the coulombic efficiency is the first-cycle charge capacity/discharge capacity.

Table 2

As can be seen from the above table, compared with the pure SnSe ₂ in Comparative Example 1, the embodiment still has a higher capacity retention rate at a 5C charging rate and after 1000 cycles, indicating that the negative electrode active material of the present application can improve the fast charging performance and cycle stability of the battery. In addition, compared with the graphite negative electrode in Comparative Example 2, the embodiment still has a higher cycle capacity at a 5C charging rate and after 100 cycles, indicating that the negative electrode active material of the present application can improve the fast charging capacity of the battery. In addition, it can be seen from Comparative Example 3 that when the tin source is a divalent tin source, the SnSe ₂ nucleus cannot be formed, so the present application needs to use a tetravalent tin source.

It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims (15)

1. A negative electrode active material, characterized by comprising:

A nucleus, the nucleus comprising SnSe ₂; and

A cladding layer overlying at least a portion of the surface of the core body, the cladding layer comprising carbon comprising a graphite layer.

2. The anode active material according to claim 1, wherein the core body is SnSe ₂, and the coating layer is a carbon layer containing a graphite layer.

3. The anode active material according to claim 1 or 2, wherein the core is a hexagonal nanoplatelet that satisfies at least one of the following conditions:

(1) The thickness of the hexagonal nano-sheet is 20 nm-40 nm;

(2) The side length of the hexagonal nano-sheets is 100 nm-200 nm independently.

4. The anode active material according to claim 1 or 2, wherein the thickness of the coating layer is 5nm to 15nm, optionally 8nm to 12nm.

5. The anode active material according to claim 1 or 2, wherein the mass ratio of the coating layer in the anode active material is 5% to 50%, optionally 5% to 10%.

6. The negative electrode active material according to claim 1 or 2, wherein the coating layer contains a functional group,

Optionally, the functional groups include one or more of carboxyl, hydroxyl, and epoxy groups.

7. A method for producing a negative electrode active material, characterized by comprising:

Mixing a tetravalent tin source, a selenium source and a carbon source in a solvent to obtain a mixed solution;

the mixed liquor is subjected to a heat treatment to form a core body and a coating layer on at least a portion of a surface of the core body, wherein the core body comprises SnSe ₂ and the coating layer comprises carbon comprising a graphite layer.

8. The method of claim 7, wherein the core is SnSe ₂ and the cladding layer is a carbon layer comprising a graphite layer.

9. The method according to claim 7 or 8, wherein the heat treatment comprises a hydrothermal treatment and/or a solvothermal treatment.

10. The method of claim 7 or 8, wherein the mixed liquor satisfies at least one of the following conditions:

(1) In the mixed solution, the mass ratio of the tetravalent tin source to the selenium source is (3.8:6.2) - (6.8:3.2);

(2) In the mixture consisting of the tetravalent tin source, the selenium source and the carbon source, the mass ratio of the carbon source is 3-50%.

11. The method according to claim 7 or 8, wherein the heat treatment satisfies at least one of the following conditions:

(1) The temperature of the heat treatment is 150-200 ℃;

(2) The heat treatment time is 12-24 hours.

12. The method according to claim 7 or 8, wherein at least one of the following conditions is met:

(1) The selenium source comprises NaHSe;

(2) The tetravalent tin source comprises one or more of SnCl ₄、SnBr₄、SnI₄、SnF₄、SnO₂、SnS₂;

(3) The carbon source comprises one or more of natural graphite, artificial graphite, soft carbon and hard carbon, and optionally, the volume average particle diameter Dv50 of the carbon source is 3-25 μm.

13. A negative electrode sheet comprising the negative electrode active material according to any one of claims 1 to 6 or the negative electrode active material produced according to the method of any one of claims 7 to 12.

14. A secondary battery comprising the negative electrode tab of claim 13.

15. An electric device comprising the secondary battery according to claim 14.