Negative active material, method for preparing the same, negative electrode sheet, secondary battery, and electric device

Abstract

The application provides a negative electrode active material and a preparation method thereof, a negative electrode sheet, a secondary battery and an electric device. The negative electrode active material comprises: a core, wherein the core comprises SnSe2; and a coating layer covering at least part of the surface of the core, wherein the coating layer comprises carbon containing a graphite layer. The negative electrode active material provided by the application can improve the rapid charging performance of the secondary battery.

Description

Technical Field

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

[0002] Secondary batteries, represented by lithium-ion batteries, have the characteristics of high capacity and long life, and are therefore widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools.

[0003] As battery applications become increasingly widespread, the performance requirements for rechargeable batteries are becoming more stringent. To improve the performance of rechargeable batteries, materials such as the negative electrode material are typically optimized and improved. However, even with current improvements, the rechargeable batteries still suffer from poor fast-charging performance during use. Summary of the Invention

[0004] The purpose of this application is to provide a negative electrode active material and its preparation method, a negative electrode sheet, a secondary battery, and an electrical device, which can improve the fast charging performance of the secondary battery.

[0005] To achieve the above objectives, a first aspect of this application provides a negative electrode active material comprising a core comprising SnSe2; and a coating layer covering at least a portion of the surface of the core, the coating layer comprising carbon containing a graphite layer.

[0006] The negative electrode active material provided in this application is a composite material in which a coating layer is formed on the surface of a SnSe2 core. The SnSe2 in the core of the negative electrode active material has a larger interlayer spacing, which can improve the shuttle migration speed of active ions (such as lithium ions) between the layers and increase the insertion rate of active ions in the negative electrode active material, thereby improving the fast charging performance of the battery. The carbon containing graphite layers in the coating layer of the negative electrode active material can reduce the irreversible capacity loss caused by the insertion of active ions during the first charge and discharge cycle of the pure SnSe2 negative electrode, and at the same time improve the stability of the SEI film, thereby improving the cycle performance and service life of the battery.

[0007] In some embodiments of this application, the core is SnSe2 and the coating layer is a carbon layer containing a graphite layer.

[0008] When the core of the negative electrode active material is SnSe2 and the coating layer is a carbon layer containing a graphite layer, it has essentially the same performance or effect as the negative electrode active material described in the first aspect of this application, and will not be repeated here.

[0009] In some embodiments of this application, the core is a hexagonal nanosheet, and the hexagonal nanosheet satisfies at least one of the following conditions:

[0010] (1) The thickness of the hexagonal nanosheet is 20 nm to 40 nm;

[0011] (2) The side length of each of the hexagonal nanosheets is 100nm to 200nm.

[0012] 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 layers of the negative electrode active material, improve the insertion rate of active lithium ions, and thus improve the fast charging performance.

[0013] In some embodiments of this application, the thickness of the coating layer is 5nm to 15nm, and can be selected as 8nm to 12nm.

[0014] When the thickness of the coating layer is within the above range, it helps to suppress the formation of Li. x While enabling the irreversible reaction of SnSe2, reducing irreversible capacity loss, improving charge and discharge efficiency, and providing overall conductivity and structural stability of the negative electrode active material, it also helps to further improve the shuttle migration speed of active lithium ions between the layers of the negative electrode active material, thereby further improving the fast charging performance of the battery.

[0015] In some embodiments of this application, the coating layer accounts for 5% to 50% of the mass of the negative electrode active material, and may be 5% to 10%.

[0016] The mass ratio 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 fast charging performance are at a relatively high level.

[0017] In some embodiments of this application, the coating layer contains functional groups. Optionally, the functional groups include one or more of carboxyl, hydroxyl, and epoxy groups.

[0018] The aforementioned functional groups contained in the coating layer help to enhance the reactivity of the negative electrode active material and promote the formation of the SEI film during cycling.

[0019] A second aspect of this application also provides a method for preparing the negative electrode active material of the first aspect of this application, comprising:

[0020] A tetravalent tin source, a selenium source, and a carbon source are mixed in a solvent to obtain a mixed solution.

[0021] The mixture is heat-treated to form a core and a coating layer covering at least a portion of the surface of the core, to obtain a negative electrode active material, wherein the core comprises SnSe2 and the coating layer comprises carbon containing a graphite layer.

[0022] By heat-treating the mixture, a tetravalent tin source and a selenium source can react to form a core containing SnSe2, and a coating layer including a graphite layer of carbon can be formed on at least a portion of the surface of the core, thereby obtaining the negative electrode active material of the first aspect of this application.

[0023] In some embodiments of this application, the core is SnSe2 and the coating layer is a carbon layer containing a graphite layer.

[0024] In some embodiments of this application, the heat treatment includes hydrothermal treatment and / or solvent heat treatment.

[0025] The method provided in this application has a relatively simple preparation process, which can achieve the preparation of nanomaterials and carbon coating with graphite layers in one step. Furthermore, 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.

[0026] In some embodiments of this application, the mixture satisfies at least one of the following conditions:

[0027] (1) The mass ratio of the tetravalent tin source to the selenium source is (3.8:6.2) to (6.8:3.2);

[0028] (2) In the mixture composed of the tetravalent tin source, the selenium source and the carbon source, the carbon source accounts for 3% to 50% by mass.

[0029] When the mass ratio of tetravalent tin source, selenium source and carbon source is within the above range, the precipitation of elemental selenium in the subsequent reaction process can be reduced, thereby increasing the yield of the negative electrode active material.

[0030] In some embodiments of this application, the heat treatment satisfies at least one of the following conditions:

[0031] (1) The temperature of the heat treatment is 150℃~200℃;

[0032] (2) The heat treatment time is 12h to 24h.

[0033] By controlling 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 that generates the negative electrode active material.

[0034] In some embodiments of this application, the method satisfies at least one of the following conditions:

[0035] (1) The selenium source includes NaHSe;

[0036] (2) The tetravalent tin source includes one or more of SnCl4, SnBr4, SnI4, SnF4, SnO2, and SnS2;

[0037] (3) The carbon source includes one or more of natural graphite, artificial graphite, soft carbon, and hard carbon.

[0038] Optionally, the volume average particle size Dv50 of the carbon source is 3 μm to 25 μm.

[0039] In this application, the Dv50 of the carbon source is within the aforementioned range, which is beneficial for further promoting the coating process.

[0040] A third aspect of this application provides a negative electrode sheet, comprising the negative electrode active material of the first aspect of this application or the negative electrode active material prepared by the method of the second aspect of this application.

[0041] A fourth aspect of this application provides a secondary battery, including the negative electrode sheet of the third aspect of this application.

[0042] The fifth aspect of this application provides an electrical device including the secondary battery of the fourth aspect of this application.

[0043] The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery. Attached Figure Description

[0044] Figure 1 Li is generated during the first discharge cycle of a pure SnSe2 anode. x Schematic diagram of the SnSe2 reaction process.

[0045] Figure 2 This is a schematic diagram of the reaction process during the first discharge cycle of the negative electrode active material according to an embodiment of this application.

[0046] Figure 3 This is a schematic diagram illustrating the principle of fast charging achieved by the negative electrode active material according to one embodiment of this application.

[0047] Figure 4 The images show the morphology of the pure SnSe2 material in Comparative Example 1(a), and the negative electrode active materials in Examples 1(b) and 21(c).

[0048] Figure 5 This is a transmission electron microscope (TEM) image of the negative electrode active material of Example 1.

[0049] Figure 6 The first-cycle volt-ampere curves are for the lithium-ion batteries of Comparative Example 1 and Example 1.

[0050] Figure 7 The graph shows the rate performance of the lithium-ion battery in Example 1.

[0051] Figure 8 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0052] Figure 9 yes Figure 8 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0053] Figure 10 This is a schematic diagram of a secondary battery according to another embodiment of this application.

[0054] Figure 11 This is a schematic diagram of a secondary battery according to another embodiment of this application.

[0055] Figure 12 yes Figure 11 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0056] Figure 13 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0057] Explanation of reference numerals in the attached figures:

[0058] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0059] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode active material, its manufacturing method, negative electrode sheet, secondary battery, battery module, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0060] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way may or may not include end values ​​and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0061] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0062] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0063] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0064] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0065] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0066] Currently, rechargeable 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 significant challenges. Achieving longer driving range and faster charging speeds has become a crucial indicator for evaluating the performance of power lithium batteries. The negative electrode is the part of a rechargeable battery, represented by lithium-ion batteries, that stores active ions (such as lithium ions) after charging. The specific capacity of the negative electrode material and the shuttle speed of active ions within it greatly affect the overall capacity and fast-charging capability of the battery.

[0067] Graphite, a commonly used anode material in commercial lithium-ion batteries, has a layer spacing of 0.336 nm and is primarily a hexahedral graphite crystal structure with anisotropic orientation between individual crystallites, allowing lithium ions to reversibly intercalate into the coating layers. However, due to the small layer spacing, at high charging current densities, the migration rate of lithium ions is slower than the reaction rate, making it difficult for the inner graphite layers to achieve lithium intercalation, thus significantly reducing its fast-charging capacity.

[0068] When tin-based materials are used as the negative electrode in secondary batteries, high battery capacity can be achieved through reversible displacement and alloying reactions. Many tin-based materials, such as SnSe2, SnS2, and SnO, have a two-dimensional crystal structure, and the larger interlayer spacing facilitates faster shuttle movement of active ions. Among them, SnSe2 has a relatively large interlayer spacing (0.614 nm) and a narrow band gap (E... g A tin-based two-dimensional material with a voltage rating of 1.0V to 1.5V. As a negative electrode for lithium-ion batteries, its theoretical capacity is 813 mAh / g.

[0069] However, in two-dimensional anode materials like SnSe2, during the initial lithium intercalation process, lithium ions irreversibly intercalate into the material, initiating a phase transition and forming Li. x SnSe2. This irreversible reaction reduces the reversible capacity exhibited by the battery. In addition, the SEI film (solid electrolyte interphase) formed in the first cycle of SnSe2 is not dense enough and has low strength. As cycling progresses, the SEI film will continuously break down and reform, which on the one hand causes the continuous consumption of active lithium, resulting in a decrease in capacity; on the other hand, it will cause the SnSe2 structure to collapse, causing a sharp drop in battery capacity.

[0070] To address the aforementioned technical problems, this application proposes a negative electrode active material that utilizes a carbon coating layer including a graphite layer to coat a SnSe2 core. The core enhances the shuttle migration speed of active ions (such as lithium ions) between material layers, increasing the active ion insertion rate and thus improving fast charging performance. The coating layer reduces irreversible capacity loss due to active ion insertion during the first charge / discharge cycle of the SnSe2 negative electrode, while also improving the stability of the SEI film. The solution will be described in detail below.

[0071] Negative electrode active materials

[0072] A first aspect of this application provides a negative electrode active material comprising a core comprising SnSe2; and a coating layer covering at least a portion of the surface of the core, the coating layer comprising carbon containing a graphite layer.

[0073] It should be noted that the carbon containing graphite layers described in this application refers to carbon materials composed of graphite layers in terms of crystal structure. That is, carbon materials composed of sp2 hybridized carbon atom layers forming graphite layers, and then graphite layers forming carbon materials. The graphite layers can be arranged in a regular or irregular manner. Specifically, they can include, for example, natural graphite, artificial graphite, soft carbon, and hard carbon.

[0074] Not intended to be limited by any theory, the pure SnSe2 anode comes into direct contact with the electrolyte during cycling. During this process, active ions such as lithium ions intercalate into the SnSe2 and undergo an irreversible reaction at a reaction potential of approximately 1.7V to form Li. x SnSe2, and this reaction occurs only during the first discharge cycle. As a non-limiting illustration, such as... Figure 1 As shown, when pure SnSe2 material is used as the negative electrode, Li will first occur. x The irreversible reaction that generates SnSe2 occurs before an SEI film forms on the SnSe2 surface. This process leads to some active lithium ions participating in the formation of Li. x SnSe2 cannot be extracted during subsequent cycles, resulting in irreversible capacity loss. Simultaneously, the SEI film formed by the pure SnSe2 anode is not dense or stable enough. During subsequent discharge, a substitution reaction to form Li2Se and Sn occurs at potentials of 0.5V–0.8V, and an alloying reaction between Sn and Li occurs below potentials of 0.3V. These two reactions lead to significant volume expansion, easily damaging the SEI film structure during subsequent cycles. This, in turn, leads to the co-intercalation of solvent molecules in the electrolyte, ultimately causing battery failure.

[0075] The negative electrode active material provided in this application, after coating the surface of the SnSe2 core with a carbon coating including a graphite layer, is illustrated as a non-limiting example, as shown below. Figure 2 As shown, the surface coating layer is in direct contact with the electrolyte. Since the main voltage range for SEI film formation is around 0.8V to 1.0V, which is much lower than that of Li... x The formation voltage of SnSe2 means that active lithium ions preferentially participate in the formation of a dense SEI film on the surface of the coating layer. In other words, they form the SEI film before Li. x Before the SnSe2 formation reaction, an SEI film had already formed on the surface of the coating layer, thereby inhibiting Li x The irreversible SnSe2 reaction proceeds. The formation of this SEI film has 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 solvent molecules cannot pass through this passivation film, thus effectively preventing the co-intercalation of solvent molecules and avoiding damage to the negative electrode material caused by solvent molecule co-intercalation. Therefore, it can improve the cycle performance and service life of the negative electrode.

[0076] Following this, the relative potential of the negative electrode active material (relative to Li / Li) + It is already far lower than Li x The voltage range at which SnSe2 is formed can suppress the formation of Li. x The irreversible reaction of SnSe2 proceeds. As a result, more active lithium ions participate in the formation of a dense and robust SEI film, thus helping to reduce irreversible capacity loss. Simultaneously, the formation of the SEI film on the coating surface provides a channel for the diffusion of active lithium ions, improving ionic conductivity; and the carbon containing the graphite layer in the coating itself possesses excellent electrical conductivity, which also enhances the overall electronic conductivity of the negative electrode active material. Furthermore, the formation of the coating layer helps mitigate the volume expansion caused by the SnSe2 redox reaction, improving the structural stability of the negative electrode active material.

[0077] Therefore, the negative electrode material provided in this application is a composite material in which a coating layer is formed on the surface of the SnSe2 core, as shown in the attached figure. Figure 3 As shown, the SnSe2 in the core of the negative electrode active material has a larger interlayer spacing, which can improve the shuttle migration speed of active ions (such as lithium ions) between layers and increase the insertion rate of active ions in the negative electrode active material, thereby improving the fast charging performance of the battery. Meanwhile, the carbon containing graphite layers in the coating layer of the negative electrode active material can reduce the irreversible capacity loss caused by the insertion of active ions during the first charge-discharge cycle of the pure SnSe2 negative electrode, and also improve the stability of the SEI film, thereby improving the cycle performance and lifespan of the battery.

[0078] In some embodiments, the core is SnSe2, and the coating layer is a carbon layer containing a graphite layer. When the core of the negative electrode active material is SnSe2 and the coating layer is a carbon layer containing a graphite layer, it has essentially the same performance or effect as the embodiments described above, and will not be repeated here.

[0079] In some embodiments, the core is a hexagonal nanosheet. Optionally, the hexagonal nanosheet is a regular hexagonal shape.

[0080] It is understood that the hexagonal nanosheets described in this application refer to nanosheets with a certain thickness along two planes perpendicular to each other.

[0081] The hexagonal nanosheet core is determined by the crystal structure of the SnSe2 contained within it. This hexagonal nanosheet core has a layered structure with a wide interlayer spacing, which is beneficial for improving the migration rate of active lithium ions. Especially at high charging current densities, it facilitates the rapid migration of active lithium ions and allows them to quickly embed into the inner layers of the negative electrode active material, thereby increasing fast charging capacity and improving the battery's fast charging performance.

[0082] 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 any range of the above values.

[0083] The thickness of a hexagonal nanosheet refers to the thickness along two opposing planes perpendicular to the hexagon, and can be measured using methods known in the art. For example, it can be measured using a transmission electron microscope (TEM, model FEI Titan80–300KV microscope).

[0084] In some embodiments, the side lengths of the hexagonal nanosheets are each independently 100 nm to 200 nm. For example, the side lengths of the hexagonal nanosheets may be 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, or within any range of the above values.

[0085] The side length of a hexagonal nanosheet refers to the side length of each of the two opposite hexagonal planes of the hexagonal nanosheet, and can be measured using methods known in the art. For example, it can be measured using a transmission electron microscope.

[0086] 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 layers of the negative electrode active material, improve the insertion rate of active lithium ions, and thus improve the fast charging performance.

[0087] In some embodiments, the thickness of the coating layer is 5 nm to 15 nm. For example, the thickness of the coating layer can be 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, or within any range of the above values. Optionally, the thickness of the coating layer is 8 nm to 12 nm.

[0088] The thickness of the coating layer has a meaning known in the art and can be measured using methods known in the art. For example, it can be measured using transmission electron microscopy (TEM).

[0089] When the thickness of the coating layer is within the above range, it helps to suppress the formation of Li. x While enabling the irreversible reaction of SnSe2, reducing irreversible capacity loss, improving charge and discharge efficiency, and providing overall conductivity and structural stability of the negative electrode active material, it also helps to further improve the shuttle migration speed of active lithium ions between the layers of the negative electrode active material, thereby further improving the fast charging performance of the battery.

[0090] In some embodiments, the coating layer comprises 5% to 50% of the negative electrode active material by mass. For example, the mass percentage of the coating layer in the negative electrode active material can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any range thereof. Optionally, the coating layer comprises 5% to 10% of the negative electrode active material by mass. More preferably, the coating layer comprises 10% of the negative electrode active material by mass.

[0091] The mass percentage of the coating layer in the negative electrode active material is a term known in the art and can be tested using methods known in the art. For example, transmission electron microscopy can be used for testing.

[0092] When the mass percentage of the coating layer in the negative electrode active material is within the aforementioned range, it is beneficial to achieve a balance between the capacity and fast charging performance of the negative electrode active material, resulting in relatively high levels of both capacity and fast charging performance. If the content of the coating layer is relatively high, it may reduce the overall capacity of the negative electrode active material; if the content of the coating layer is relatively low, it may make the structure of the SnSe2 core relatively unstable, making it prone to structural collapse during fast charging.

[0093] In some embodiments, the coating layer contains functional groups. Optionally, the functional groups include one or more of carboxyl, hydroxyl, and epoxy groups.

[0094] The functional groups contained in the coating layer can be measured by infrared spectroscopy. These functional groups help improve the reactivity of the negative electrode active material and promote the formation of the SEI film during cycling.

[0095] The second aspect of this application provides a method for preparing the negative electrode active material of the first aspect of this application, which may include the following steps:

[0096] S10. The tetravalent tin source, selenium source and carbon source are mixed in the liquid phase to obtain a mixed solution;

[0097] S30. The mixture is heat-treated to form a core and a coating layer covering at least a portion of the surface of the core, thereby obtaining a negative electrode active material, wherein the core comprises SnSe2 and the coating layer comprises carbon containing a graphite layer.

[0098] By heat-treating the mixture, a tetravalent tin source and a selenium source can react to form a core containing SnSe2, and a coating layer including a graphite layer of carbon can be formed on at least a portion of the surface of the core, thereby obtaining the negative electrode active material of the first aspect of this application.

[0099] In some embodiments, the heat treatment includes hydrothermal treatment and / or solvent heat treatment.

[0100] Understandably, hydrothermal treatment involves placing the mixture in a closed container and heating the container to continuously evaporate the mixture into high-temperature steam. This increases the pressure within the container, providing a high-pressure environment for the reaction between the tetravalent tin, selenium, and carbon sources. This high-pressure environment promotes the reaction of the tetravalent tin, selenium, and carbon sources, facilitates the formation of SnSe2, and accelerates the coating process. This results in the formation of a carbon coating layer, including a graphite layer, on at least a portion of the SnSe2 surface, thus obtaining the negative electrode active material. This method is relatively simple, allowing for the one-step preparation of nanomaterials and the carbon coating with a graphite layer. Furthermore, by controlling the heat treatment, the performance of the obtained negative electrode active material can be regulated, which helps reduce preparation costs.

[0101] As a non-limiting example of preparing a negative electrode active material, SnCl4·5H2O can be added to deionized water and stirred. Then, a prepared NaHSe solution is mixed with artificial graphite and stirred to obtain a mixture. Finally, the mixture is transferred to a polytetrafluoroethylene reaction vessel and placed in a stainless steel high-pressure reactor, where it is heated in an oven. After cooling to room temperature, the product is collected by centrifugation, washed several times with deionized water and ethanol, and dried under vacuum.

[0102] 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 within any range of the above values.

[0103] In some embodiments, the heat treatment time is 12h to 24h. For example, the heat treatment time can be 12h, 14h, 16h, 18h, 20h, 22h, 24h, or within any range of the above values.

[0104] By controlling 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 that generates the negative electrode active material.

[0105] It should be noted that in the above preparation process, parameters such as the solubility and concentration of the selenium source in the mixture, as well as the hydrothermal treatment time, all affect the size of the core. The thickness of the coating layer is mainly related to parameters such as the mass ratio of the carbon source in the mixture and the hydrothermal treatment time. Therefore, by adjusting these parameters, the size of the core and the thickness of the coating layer can be controlled within a suitable range, thereby improving the electrochemical performance of the negative electrode active material and the battery, including its fast charging performance and capacity.

[0106] In some embodiments, the selenium source includes NaHSe. The NaHSe provided in this application can be used as a selenium source for selenides, which can prepare selenides with uniform morphology at lower temperatures; and the selenium source has relatively stable chemical properties, which helps to reduce the safety hazards caused by using unstable reducing agents (such as N2H4·H2O or oleylamine) during the preparation process, while reducing the energy consumption required for high-temperature reactions.

[0107] In some embodiments, the method for preparing the selenium source NaHSe may include the following steps:

[0108] S110. Prepare deionized water and put it in a test tube. Insert the gas tube into the deionized water and seal it. Continuously fill it with nitrogen or alkaline gas (such as ammonia) to remove oxidizing gases such as dissolved oxygen in the water.

[0109] S120. Dissolve the reducing agent in the above-mentioned deionized water, slowly shake and add 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. Use this solution as a selenium source for preparing negative electrode active materials.

[0110] The reaction process for preparing the selenium source described above is shown in equation (1):

[0111] 4NaBH4+2Se+7H2O=2NaHSe+Na2B4O7+14H2(1)

[0112] It should be noted that in the preparation process of the selenium source, the reducing agent can be in excess. This allows the Se powder to dissolve completely. Furthermore, in the subsequent preparation of the negative electrode active material, the reducing agent can effectively disperse the carbon source, remove oxygen-containing groups from the carbon source, reduce the particle size of the carbon source (such as Dv50), and promote the coating process.

[0113] In some embodiments, the reducing agent in step S120 may include KBH4 and / or NaBH4.

[0114] In some embodiments, the tetravalent tin source includes one or more of SnCl4, SnBr4, SnI4, SnF4, SnO2, and SnS2.

[0115] In some embodiments, the carbon source includes one or more of natural graphite, artificial graphite, soft carbon, and hard carbon.

[0116] In some embodiments, the mass ratio of the tetravalent tin source to the selenium source in the mixture 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 any range of the above values.

[0117] In some embodiments, the carbon source comprises 3% to 50% by mass in the mixture consisting of the tetravalent tin source, the selenium source, and the carbon source. For example, the mass percentage of the carbon source may be 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any of the above values.

[0118] In this application, when the mass ratio of tetravalent tin source, selenium source, and carbon source is within the aforementioned range, the precipitation of elemental selenium during subsequent reactions can be reduced, thereby increasing the yield of the anode active material. Simultaneously, the mass ratio of tetravalent tin source, selenium source, and carbon source affects the size of the core and the thickness of the coating layer. Therefore, by controlling the mass ratio of the three within the aforementioned range, the size of the core and the thickness of the coating layer can be controlled within a suitable range, thereby improving the electrochemical performance of the anode active material and the battery, such as its fast charging performance and capacity.

[0119] It should be noted that, although hard carbon cannot be graphitized from the perspective of the material itself, from the perspective of crystal structure, all of the above-mentioned carbon sources are composed of graphite layers. That is, they are all composed of sp2 hybridized carbon atom layers forming graphite layers, which in turn form the carbon source. However, in artificial graphite, natural graphite, and soft carbon, the graphite layers can be arranged in a regular pattern, while in hard carbon, the graphite layers are arranged irregularly. Therefore, in the negative electrode active materials prepared from the above-mentioned carbon sources, a carbon coating layer including graphite layers can be formed on the surface of the core.

[0120] 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 any range of the above values. A Dv50 of the carbon source within the above range is beneficial for further facilitating the coating process.

[0121] The volume average particle size (Dv50) of a carbon source is a well-known concept in the art and can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0122] This application achieves a carbon coating layer including a graphite layer on the surface of a SnSe2 core, primarily through physical adsorption and chemical reactions. The physical adsorption is mainly manifested in the selection of a small and suitable carbon source (such as artificial graphite), while a reducing agent (such as NaBH4) has a certain exfoliating effect on the carbon source, further reducing its particle size. During the reaction, the carbon source can adsorb onto the surface of the SnSe2 nanosheets, thereby forming the aforementioned coating layer. Furthermore, the chemical reaction is mainly manifested in the use of Sn from the tetravalent tin source. 4+It is a weakly acidic particle. The reducing agent (NaBH4) modifies the surface of the carbon source (such as artificial graphite), forming functional groups containing hydroxyl and oxygen. The weakly acidic and weakly basic groups attract each other, promoting the uniform coating of carbon source particles on the surface of the core, forming a carbon coating layer including a graphite layer. Simultaneously, during heat treatment, the particle size of the carbon source further decreases, which is beneficial for promoting the coating of the carbon source on the core surface and for forming a denser SEI film, without consuming excessive lithium source, thus balancing stability and kinetics. Moreover, the surface of the coating layer forms more abundant functional groups (such as carboxyl, hydroxyl, and epoxy groups), which help increase reactivity, better achieve coating and SEI film formation, and the graphite layer structure of the carbon source becomes thinner.

[0123] The descriptions of the various implementation methods above tend to emphasize the differences between them. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0124] Secondary batteries

[0125] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0126] In one embodiment of this application, a secondary battery is provided.

[0127] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0128] [Positive electrode plate]

[0129] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0130] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0131] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0132] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0133] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0134] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0135] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0136] The positive electrode sheet of this application does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and a binder) sandwiched between the positive current collector and the positive electrode film layer and disposed on the surface of the positive current collector. In other embodiments, the positive electrode sheet of this application further includes a protective layer covering the surface of the positive electrode film layer.

[0137] [Negative electrode plate]

[0138] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0139] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0140] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0141] In some embodiments, the negative electrode active material is the negative electrode active material provided in this application. Simultaneously, the negative electrode active material may also include other negative electrode active materials known in the art for use in batteries. As an example, other negative electrode active materials may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0142] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0143] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0144] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0145] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0146] The negative electrode sheet of this application does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) 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 sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0147] [Electrolytes]

[0148] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0149] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0150] 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 difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0151] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0152] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0153] [Isolation membrane]

[0154] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0155] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0156] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0157] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0158] In some embodiments, the outer packaging of a secondary battery includes a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of a secondary battery also includes a soft pack, such as a pouch-type soft pack. The material of the soft pack includes plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0159] This application does not impose any particular limitation on the shape of the secondary battery, which may include cylindrical, square, or other arbitrary shapes. For example, Figure 7 This is an example of a square-structured secondary battery 5.

[0160] In some implementations, refer to Figure 8 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0161] In some embodiments, the secondary battery also includes a battery module assembled from multiple battery cells. The number of battery cells in the battery module can be multiple, and the specific number can be adjusted by those skilled in the art according to the application and capacity of the battery module.

[0162] Figure 9 This is battery module 4, used as an example. (See reference...) Figure 9 In battery module 4, multiple secondary batteries 5 are arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple secondary batteries 5 can be fixed in place using fasteners.

[0163] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0164] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0165] In some implementations, the aforementioned battery cells can also be directly assembled into a battery pack, and the number of battery cells contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0166] Figure 10 and Figure 11 This is battery pack 1 as an example. (See reference...) Figure 10 and Figure 11 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0167] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0168] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0169] Figure 12 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0170] Other examples of such devices include mobile phones, tablets, and laptops. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0171] Example

[0172] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0173] Example 1

[0174] Preparation of negative electrode active materials

[0175] 8.8 g of SnCl4·5H2O was added to 80 mL of deionized water and stirred for 10 min. Then, 80 mL of 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 vessel (filling volume 160 mL) and placed in a stainless steel high-pressure reactor, and heated in an oven at 180 °C for 24 hours. After cooling to room temperature, the product was collected by centrifugation, washed several times with deionized water and ethanol, and vacuum dried at 60 °C for 12 hours to obtain the negative electrode active material.

[0176] The NaHSe solution described above can be prepared by the following method:

[0177] Prepare 80 mL of deionized water in a test tube. Insert a nitrogen gas tube into the deionized water and seal it. Continuously purge with nitrogen for 5 minutes to remove dissolved oxygen and other oxidizing gases from the water. Dissolve 8 g of NaBH4 in the deionized water, gently shake, and add 4 g of Se powder. A large amount of gas will be generated during this process. Shake the test tube until the Se powder is completely dissolved, obtaining a clear NaHSe solution.

[0178] Preparation of negative electrode sheet

[0179] 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 uniformly coated onto a copper current collector and dried in a vacuum oven at 80°C for 24 hours to obtain the negative electrode sheet.

[0180] Preparation of electrolyte

[0181] 1M LiPF6 was dissolved in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1 as the electrolyte.

[0182] Preparation of the separating membrane

[0183] Celgard 3501 microporous membrane was used as the separator.

[0184] Preparation of lithium-ion half-cells

[0185] A lithium metal sheet, the aforementioned negative electrode sheet, and a separator are assembled in a glove box to produce a lithium-ion half-cell.

[0186] Examples 2-15

[0187] The preparation method of the lithium-ion half-cell is similar to that in Example 1, except that the negative electrode active material and related parameters in the preparation process were adjusted. Specific parameters are detailed in Table 1 below. " / " indicates that the corresponding parameter does not exist.

[0188] Comparative Example 1

[0189] The preparation of the lithium-ion half-cell is similar to that in Example 1, except that when preparing the negative electrode sheet, an equal mass of pure SnSe2 material is used instead of the negative electrode active material.

[0190] Comparative Example 2

[0191] The preparation of the lithium-ion half-cell is similar to that in Example 1, except that when preparing the negative electrode sheet, conventional artificial graphite of equal mass is used instead of the negative electrode active material.

[0192] Comparative Example 3

[0193] The preparation of the lithium-ion half-cell is similar to that in Example 1, except that SnCl2 is used instead of SnCl4 in the preparation of the negative electrode active material.

[0194] Table 1

[0195]

[0196] In addition, the negative electrode active materials and lithium-ion batteries obtained in 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.

[0197] Test section

[0198] (1) Morphology testing of negative electrode active materials

[0199] The morphology of the negative electrode active material was tested using a scanning electron microscope (FEI Nova Nano 630) and a transmission electron microscope (FEITitan 80-300KV).

[0200] (2) First-week cyclic voltammetry curve test

[0201] Using a Biologic VMP3 electrochemical workstation, the following parameters were measured: 0.005V–2.5V (V vs Li / Li). + Within the range, a scan is performed at a scan rate of 0.2 mV / s.

[0202] (3) Ratio Performance Test

[0203] The assembled battery was subjected to charge-discharge tests on a new button cell tester. The voltage range of the test was 0.005V to 2.5V, and constant current charge-discharge tests were performed at charge-discharge rates of 0.1C, 0.2C, 0.3C, 0.5C, 1C, 3C and 5C.

[0204] (4) Cyclic performance test

[0205] The cycle test temperature was 25℃, and the voltage range was 0.005V to 2.5V. In the first cycle, the battery was charged and discharged at a constant current of 0.1C to ensure the formation of a more stable SEI film. After the first cycle, it was charged and discharged at a constant current of 5C. The capacity of the second cycle was taken as the initial capacity and recorded as D0. Subsequently, 5C charge / 5C discharge cycle tests were performed, and the capacity after 100 cycles was recorded as D1, and the capacity after 1000 cycles was recorded as D2.

[0206] The capacity retention rate of a lithium-ion battery after 1000 cycles = D2 / D0 × 100%.

[0207] (5) First-lap coulomb efficiency test

[0208] Since the test was conducted using a half-cell, the coulombic efficiency is the first-week charge capacity / discharge capacity.

[0209] Table 2

[0210]

[0211]

[0212] As can be seen from the table above, compared with pure SnSe2 in Comparative Example 1, the embodiment still exhibits a higher capacity retention rate after 1000 cycles at a 5C charging rate, indicating that the negative electrode active material of this application can improve the fast charging performance and cycle stability of the battery. Furthermore, compared with the graphite negative electrode in Comparative Example 2, the embodiment still exhibits a higher cycle capacity after 100 cycles at a 5C charging rate, indicating that the negative electrode active material of this application can improve the fast charging capacity of the battery. In addition, as can be seen from Comparative Example 3, when the tin source is a divalent tin source, SnSe2 nuclei cannot be formed; therefore, this application requires the use of a tetravalent tin source.

[0213] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A negative electrode active material, characterized by, Comprising: a core comprising SnSe2; and a coating layer comprising carbon containing a graphitic layer, the coating layer covering at least part of a surface of the core, the core being a hexagonal nanoplatelet.

2. The negative electrode active material according to claim 1, characterized by The core is SnSe2, and the coating layer is a carbon layer containing a graphitic layer.

3. The negative electrode active material according to claim 1 or 2, characterized by, The hexagonal nanoplatelet satisfies at least one of the following conditions: (1) the thickness of the hexagonal nanoplatelet is 20 nm to 40 nm; (2) the length of each side of the hexagonal nanoplatelet is independently 100 nm to 200 nm.

4. The negative electrode active material according to claim 1 or 2, characterized by The thickness of the coating layer is 5 nm to 15 nm.

5. The negative electrode active material according to claim 4, characterized by The thickness of the coating layer is 8 nm to 12 nm.

6. The negative electrode active material according to claim 1 or 2, characterized by The mass ratio of the coating layer in the negative electrode active material is 5% to 50%.

7. The negative active material according to claim 6, characterized in that, The mass ratio of the coating layer in the negative electrode active material is 5% to 10%.

8. The negative electrode active material according to claim 1 or 2, characterized by, The coating layer contains a functional group.

9. The negative electrode active material according to claim 8, characterized by The functional group comprises one or more of a carboxyl group, a hydroxyl group, and an epoxy group.

10. 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; subjecting the mixed solution to a heat treatment to form a core and a coating layer covering at least part of a surface of the core, wherein the core comprises SnSe2, the coating layer comprises carbon containing a graphitic layer, and the core is a hexagonal nanoplatelet.

11. The method of claim 10, wherein, The core is SnSe2, and the coating layer is a carbon layer containing a graphitic layer.

12. The method according to claim 10 or 11, characterized in that, The heat treatment comprises a hydrothermal treatment and / or a solvothermal treatment.

13. The method of claim 10 or 11, wherein, The mixed solution 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) to (6.8:3.2); (2) in a mixture composed of the tetravalent tin source, the selenium source, and the carbon source, the mass ratio of the carbon source is 3% to 50%.

14. The method of claim 10 or 11, wherein, 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 time of the heat treatment is 12 h to 24 h.

15. The method of claim 10 or 11, wherein, Satisfying at least one of the following conditions: (1) the selenium source comprises NaHSe; (2) the tetravalent tin source comprises one or more of SnCl4, SnBr4, SnI4, SnF4, SnO2, and SnS2; (3) the carbon source comprises one or more of natural graphite, artificial graphite, soft carbon, and hard carbon.

16. The method of claim 15, wherein, The volume average particle size Dv50 of the carbon source is 3 μm to 25 μm.

17. A negative electrode sheet characterized by comprising: The negative electrode active material of any one of claims 1 to 9 or prepared according to the method of any one of claims 10 to 16.

18. A secondary battery characterized by comprising: The negative electrode sheet of claim 17.

19. An electrical device, comprising: The secondary battery of claim 18.

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