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

Abstract

The invention provides a negative electrode material which is characterized by comprising a tin phosphide compound, the tin phosphide compound comprises a compound with a general formula shown in the following formula I, a is more than 0 and less than or equal to 4, and b is more than 0 and less than or equal to 3; and the porosity of the tin phosphide compound is 11%-20%, and can be 5%-15% optionally. SnaPb is shown as formula I.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and particularly to a negative electrode material, a preparation method thereof, a negative electrode sheet, a secondary battery, and an electrical device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the great development of secondary ion batteries, higher requirements have also been put forward for their energy density, cycle performance, safety performance, etc. In addition, the selection of negative electrode active materials has become more and more limited, and tin-based negative electrode active materials have gradually attracted attention because they can achieve a higher battery capacity. Summary of the Invention

[0003] The present application is made in view of the above problems, and its purpose is to provide a negative electrode material, a preparation method thereof, a negative electrode sheet, a secondary battery, and an electrical device, wherein the negative electrode material has a high specific capacity, self-healing ability, and fast two-dimensional lithium ion channels, and can improve the cycle stability of the battery.

[0004] The first aspect of the present application provides a negative electrode material, which comprises a tin phosphide compound, and the tin phosphide compound comprises a compound represented by the general formula shown in Formula I.

[0005] Sn a P b Formula I

[0006] wherein, 0 < a ≤ 4, 0 < b ≤ 3; the porosity P of the tin phosphide compound is 11% - 20%, and may be optionally 5% - 15%.

[0007] The negative electrode material of the embodiment of the present application contains stannic phosphide compounds. Phosphorus and tin in the stannic phosphide compounds can have different ratios, whereby stannic phosphide compounds with different compositions can be formed. For stannic phosphide compounds, when the proportion of phosphorus element increases, it helps to improve the specific capacity and energy density of the overall material. However, during the insertion and extraction of lithium ions, it will cause a large volume change in the negative electrode material, thereby destroying the particle structure and causing rapid capacity decay of the battery. On the other hand, when the proportion of tin element increases, it helps to reduce the energy gap of the material and improve the conductivity. At the same time, during the cycling process, the unreacted tin on the one hand accelerates the ion transport ability, and on the other hand can effectively relieve the volume expansion of stannic phosphide. By making the ratio of the stannic phosphide compound within the above range, it can have different physical and chemical properties and can be applied to different scenarios; by making the porosity of the stannic phosphide compound within the above range, it is beneficial to the infiltration of the electrolyte, promotes the improvement of the battery cycle stability and charging rate. In addition, by making the porosity of the stannic phosphide compound within the above range, the coating amount of the stannic phosphide compound when used as the negative electrode material can be achieved, thereby improving the energy density of the battery.

[0008] In any embodiment, the stannic phosphide compound includes Sn 3 P 2 、Sn 4 P 3 、SnP 3 、SnP、SnP 0.94 Among at least one of them, optionally including Sn 3 P 2 、Sn 4 P 3 Among at least one of them.

[0009] By selecting the above specific types of stannic phosphide compounds, the ratio of phosphorus and tin elements can be further optimized, so as to better achieve the above technical effects of the present application.

[0010] In any embodiment, the specific surface area of the stannic phosphide compound is 60m 2 / g to 100m 2 / g, and can be optionally 75m 2 / g to 95m 2 / g.

[0011] By controlling the specific surface area of the stannic phosphide compound within the above range, the number of sites on the surface of stannic phosphide that can accommodate lithium ions can be increased, which is beneficial to the insertion or extraction of lithium ions, thereby improving the cycle stability and charging rate of the battery.

[0012] In any embodiment, the Dv50 of the stannic phosphide compound is 10μm - 25μm, and can be optionally 12μm - 18μm.

[0013] By controlling the Dv50 of the tin phosphide compound within the above range, the specific surface area of the particles can be within an appropriate range. Without affecting the kinetic performance of the material, the number of active sites on the anode material can be increased, thereby improving the Coulombic efficiency of the material and preventing excessive consumption of active lithium.

[0014] The second aspect of the present application provides a method for preparing an anode material, the anode material comprising a tin phosphide compound, and the preparation method comprising: adding raw materials including a tin source and a phosphorus source to an amine solvent for reaction to obtain the tin phosphide compound.

[0015] In the above method for preparing the anode material of the present application, various raw materials and the amine solvent are directly mixed and then reacted. The reaction steps are few, the reaction process is simple, and the elemental ratio between phosphorus and tin is easy to control. The obtained tin phosphide compound material is porous and loose, and the specific surface area, porosity, etc. of the material are within a suitable range. Thus, the number of lithium ion insertion sites on the anode increases, which is beneficial to improving the battery charging rate and charging rate.

[0016] In any embodiment, the tin source includes at least one of metallic tin and organotin compounds, optionally including metallic tin; the organotin compounds include at least one of monobutyltin, dibutyltin, tributyltin, tributyltin oxide, trimethyltin, triphenyltin, dioctyltin. In any embodiment, the phosphorus source includes at least one of red phosphorus and organophosphorus compounds, and the phosphorus-containing compounds include at least one of phosphorous acid, hydrocarbon phosphonous acid, hydrocarbon hypophosphonous acid, phosphite, ethyl hypophosphite, hydrocarbon phosphite.

[0017] By using the above-mentioned elemental tin and organotin compounds as the tin source, and using the above-mentioned elemental phosphorus (red phosphorus) or organophosphorus compounds as the phosphorus source, the reaction can be made simpler and there are fewer side reactions, and the above-mentioned tin phosphide compounds of the present application can be obtained better. In particular, by using elemental tin as the tin source and elemental phosphorus (red phosphorus) as the phosphorus source, since both phosphorus and tin are in the 0 valence state, the direct redox reaction between the two can make the reaction simpler and there are fewer side reactions, and the above-mentioned tin phosphide compounds of the present application can be obtained better.

[0018] In any embodiment, the amine solvent includes at least one of ethylenediamine, aniline, cyclohexylamine, monoethanolamine, diethanolamine, diisopropanolamine, N-methyldiethanolamine, N,N-dimethylformamide, and can be ethylenediamine.

[0019] In the above preparation method of the present application, during the reaction process, based on the high-pressure environment provided by the reaction solvent heat, the above-mentioned specific amine solvent is easily brought to the boiling or supercritical state. Therefore, the reactants are dispersed in the solvent and become more active. As the temperature rises and during the heat preservation process, the product is slowly formed. In addition, the above product has good dispersibility and uniform particle size. In addition, the amino group in the above-mentioned amine solvent of the present application will decompose at high temperature to generate nitrogen gas, which helps to form a pore structure on the surface of the product particles and increase the specific surface area. This porous structure is beneficial to alleviating the influence of particle volume expansion on the cycle performance during the charge and discharge cycles of the battery.

[0020] In any embodiment, the temperature of the reaction is 150°C - 250°C, optionally 180°C - 220°C, and the reaction time is 12h - 30h, optionally 18h - 24h.

[0021] By making the reaction temperature and reaction time of the preparation method of the present application within the above ranges, it is possible to prevent the structure of the material from being damaged due to too high a reaction temperature or too long a reaction time while ensuring that the reaction proceeds thoroughly, or to prevent the aggregation of product particles.

[0022] In any embodiment, the molar ratio of the tin source to the phosphorus source is 0.8∶1 - 8∶1, optionally 1.3∶1 - 5.6∶1.

[0023] By making the molar ratio of the tin source to the phosphorus source in the above range in the tin phosphide material, the ratio of the two elements can be made more excellent, so that the obtained tin phosphide compounds have different physical and chemical properties and can be applied to different scenarios. Moreover, through the above molar ratio range, it helps to improve the specific capacity per gram of the tin phosphide compounds as the overall anode material. In addition, the tin element in the above molar ratio range helps to reduce the energy gap of the material, improve the conductivity, and the unreacted tin during the cycle process, on the one hand, accelerates the ion transport ability, and on the other hand, can also effectively alleviate the volume expansion of tin phosphide.

[0024] The third aspect of the present application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, and the negative electrode film layer includes the above-mentioned tin phosphide compounds of the embodiments of the present application or the tin phosphide compounds prepared by the preparation method of the present application.

[0025] By making the negative electrode sheet of the embodiment of the present application have the above-mentioned tin phosphide compounds of the present application, for the reasons detailed above, it is possible to promote the improvement of the cycle stability and charging rate of the battery. In addition, by making the porosity of the tin phosphide compounds within the above range, the coating amount of the tin phosphide compounds as the anode material can be realized, thereby improving the energy density of the battery.

[0026] In any embodiment, the negative electrode sheet satisfies the following conditions: the porosity of the tin phosphide compound is 5% - 15%, optionally 8% - 12%; the weight content of the tin phosphide compound in the negative electrode film layer is 93% - 98%, optionally 95% - 97%; the thickness of the negative electrode film layer is 50 μm - 100 μm, optionally 60 μm - 80 μm.

[0027] By controlling the porosity, weight content of the tin phosphide compound in the negative electrode sheet, and the thickness of the negative electrode film layer within the above ranges, the negative electrode sheet of the embodiment of the present application can better achieve the negative electrode function, and promote the improvement of battery cycle stability and charging rate.

[0028] In any embodiment, based on the total weight of the negative electrode film layer, the weight content W of the tin phosphide compound is 93% - 98%, optionally 95% - 97%.

[0029] By making the weight content of the tin phosphide compound above the above lower limit value, the loading amount of the negative electrode material can be within a suitable range, thereby ensuring the energy density of the battery; by making the weight content of the tin phosphide compound below the above upper limit value, the usage amount of the binder can be within a suitable range, preventing the preparation of the negative electrode sheet from being affected due to too little binder usage amount.

[0030] In any embodiment, the thickness of the negative electrode film layer is 50 μm - 100 μm, optionally 60 μm - 80 μm.

[0031] By making the thickness of the negative electrode film layer above the above lower limit value, the amount of the active material can be within a suitable range to prevent the reduction of the energy density of the battery caused by too low content of the negative electrode material; by making the thickness of the negative electrode film layer below the above upper limit value, it helps to reduce the lithium ion transmission path, thereby improving the rate performance of the battery.

[0032] In any embodiment, the tap density of the negative electrode film layer is 1.5 g / cm 3 -2.8 g / cm 3 Optionally 1.8 g / cm 3 -2.5 g / cm 3 .

[0033] By making the tap density of the negative electrode film layer above the above lower limit value, the energy density of the battery can be improved; by making the tap density of the negative electrode film layer below the above upper limit value, an appropriate gap can be left between the negative electrode particles, preventing the negative electrode particles from being broken due to the expansion of the negative electrode and too small gaps between the negative electrode particles during the cycling process, thus affecting the battery life.

[0034] The fourth aspect of the present application provides a secondary battery, which includes the negative electrode sheet of the third aspect of the present application.

[0035] The fifth aspect of the present application provides an electrical device, which includes the secondary battery of the fourth aspect of the present application. Description of the Drawings

[0036] Figure 1 It is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0037] Figure 2 is Figure 1 The exploded view of the secondary battery according to an embodiment of the present application shown in the figure.

[0038] Figure 3 It is a schematic diagram of a battery module according to an embodiment of the present application.

[0039] Figure 4 It is a schematic diagram of a battery pack according to an embodiment of the present application.

[0040] Figure 5 is Figure 4 The exploded view of the battery pack according to an embodiment of the present application shown in the figure.

[0041] Figure 6 It is a schematic diagram of an electrical device using the secondary battery according to an embodiment of the present application as a power source.

[0042] Description of the Reference Numerals:

[0043] 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Embodiments

[0044] Hereinafter, embodiments of the stannous phosphide compound, its preparation method, negative electrode sheet, secondary battery, and electrical device of the present application will be described in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent 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 description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0045] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, 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, ranges of 60-110 and 80-120 are also contemplated. 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 ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0046] If there is no special instruction, all implementation manners and optional implementation manners of this application can be combined with each other to form a new technical solution.

[0047] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0048] If there is no special instruction, all steps of this application can be carried out in sequence or randomly, and preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0049] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended or can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can only include or comprise the listed components.

[0050] 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, 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) while B is true (or exists); or both A and B are true (or exist).

[0051] When used as the negative electrode of a lithium battery, tin-based materials can achieve a relatively high battery capacity through reversible displacement and alloying reactions. Many tin-based materials themselves have a two-dimensional crystal structure, and the relatively large interlayer spacing is conducive to the faster shuttling of lithium ions. Among these tin compounds, tin phosphide has a relatively high specific capacity, and its constituent elements, phosphorus and tin, are both electrochemically active elements (elemental phosphorus has a theoretical capacity as high as 2596 mAh·g -1 and elemental tin has a theoretical capacity of 994 mAh·g -1 ); at the same time, tin phosphide has a variety of different element ratios, such as Sn 4 P 3 、Sn 3 P 2 、SnP 3 、SnP、SnP 0.94 etc.; in addition, most of these tin phosphide materials have a two-dimensional structure, such as Sn 4 P 3 、Sn 3 P 2 、SnP 3 etc. The two-dimensional layered structure provides a two-dimensional channel for lithium ion transport, enabling it to have the ability of fast charge and discharge.

[0052] However, when the existing tin phosphide compounds are used as the negative electrode material of the battery, there are still areas that need to be improved in their morphological characteristics such as the element ratio between tin phosphides and the existing manufacturing methods.

[0053] Based on this, this application provides a tin phosphide compound, its preparation method, a negative electrode sheet, a secondary battery, and an electrical device. The following will be described in detail.

[0054] [Tin phosphide compound]

[0055] The negative electrode material of the embodiment of this application includes a tin phosphide compound, and the tin phosphide compound includes a compound represented by the general formula shown in Formula I,

[0056] Sn a P b Formula I,

[0057] where 0 < a ≤ 4 and 0 < b ≤ 3; the porosity of the tin phosphide compound is 11% - 20%, and can be optionally 5% - 15%.

[0058] In some embodiments, the porosity of the tin phosphide compound may be 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, or in the range between any two of the above values.

[0059] In the tin phosphide compounds of the embodiments of the present application, phosphorus and tin can have different ratios, thereby forming tin phosphide compounds with different compositions. For tin phosphide compounds, when the proportion of phosphorus element increases, it helps to improve the specific capacity and energy density of the overall material. However, during the process of lithium ion insertion and extraction, it will cause a large volume change in the negative electrode material, thus destroying the particle structure and causing rapid capacity decay of the battery. On the other hand, when the proportion of tin element increases, it helps to reduce the energy gap of the material and improve the conductivity. At the same time, during the cycling process, the unreacted tin on the one hand accelerates the ion transport ability, and on the other hand can effectively relieve the volume expansion of tin phosphide. By making the ratio of the tin phosphide compound within the above range, it can have different physical and chemical properties and can be applied to different scenarios. By making the porosity of the tin phosphide compound within the above range, it is beneficial to the infiltration of the electrolyte, promotes the improvement of the battery cycle stability and charging rate. In addition, by making the porosity of the tin phosphide compound within the above range, the coating amount of the tin phosphide compound when used as the negative electrode material can be achieved, thereby improving the energy density of the battery.

[0060] In any embodiment, the tin phosphide compound includes Sn 3 P 2 、Sn 4 P 3 、SnP 3 、SnP, SnP 0.94 and at least one of them, and optionally includes Sn 3 P 2 、Sn 4 P 3 and at least one of them.

[0061] By selecting the above specific types of tin phosphide compounds, the ratio of phosphorus and tin can be further optimized, so as to better achieve the above technical effects of the present application.

[0062] In any embodiment, the specific surface area of the tin phosphide compound is 60 m 2 / g to 100 m 2 / g, and may be 75 m 2 / g to 95 m 2 / g.

[0063] In some embodiments, the specific surface area of the tin phosphide compound may be 60 m 2 / g, 61m 2 / g, 62m 2 / g, 63m 2 / g, 64m 2 / g, 65m 2 / g, 66m 2 / g, 67m 2 / g, 68m 2 / g, 69m 2 / g, 70m 2 / g, 71m 2 / g, 72m 2 / g, 73m 2 / g, 74m 2 / g, 75m 2 / g, 76m 2 / g, 77m 2 / g, 78m 2 / g, 79m 2 / g, 80m 2 / g, 81m 2 / g, 82m 2 / g, 83m 2 / g, 84m 2 / g, 85m 2 / g, 86m 2 / g, 87m 2 / g, 88m 2 / g, 89m 2 / g, 90m 2 / g, 91m 2 / g, 92m 2 / g, 93m 2 / g, 94m 2 / g, 95m 2 / g, 96m 2 / g, 97m 2 / g, 98m 2 / g, 99m 2 / g or 100m 2 / g, or a range between any two of the above values.

[0064] By controlling the specific surface area of the tin phosphide compound within the above range, the number of sites on the surface of the tin phosphide that can accommodate lithium ions can be increased, which is beneficial to the insertion and extraction of lithium ions, thereby improving the cycle stability and charging rate of the battery.

[0065] In any implementation, the Dv50 of the tin phosphide compound is 10 μm - 25 μm, and can be optionally 12 μm - 18 μm.

[0066] In this text, the term "Dv50" refers to the particle size corresponding to when the cumulative volume particle size distribution percentage in the particles reaches 50%. The measurement of the Dv50 can be carried out using the measurement method described in the examples.

[0067] In some embodiments, the Dv50 of the stannous phosphide compound can be optionally 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm or 25μm, or the range between any two of the above values.

[0068] By controlling the Dv50 of the stannous phosphide compound within the above range, the specific surface area of the particles can be within an appropriate range. Without affecting the kinetic performance of the material, the number of active sites on the negative electrode material can be large, thereby improving the Coulombic efficiency of the material and preventing excessive consumption of active lithium.

[0069] [Preparation method of stannous phosphide compound]

[0070] This application also provides a preparation method of a stannous phosphide compound. The stannous phosphide compound obtained according to this preparation method is the above stannous phosphide compound of this application. This preparation method includes: adding raw materials including a tin source and a phosphorus source to an amine solvent for reaction to obtain the stannous phosphide compound.

[0071] In the preparation method of the above stannous phosphide compound of this application, various raw materials and the amine solvent are directly mixed and then reacted. The reaction steps are few, the reaction process is simple, and it is easy to control the element ratio between phosphorus and tin. The obtained stannous phosphide compound material is porous and loose, and the material specific surface area, porosity, etc. are within a suitable range. Thus, the embedding sites of lithium ions on the negative electrode increase, which is beneficial to improving the battery charging rate and charging rate.

[0072] In any embodiment, the tin source includes at least one of metallic tin and organotin compounds, and optionally includes metallic tin; the organotin compounds include at least one of monobutyltin, dibutyltin, tributyltin, tributyltin oxide, trimethyltin, triphenyltin, dioctyltin. In any embodiment, the phosphorus source includes at least one of red phosphorus and organophosphorus compounds, and the phosphorus-containing compounds include at least one of phosphorous acid, hydrocarbon phosphinic acid, hydrocarbon hypophosphinic acid, phosphite, ethyl hypophosphite, hydrocarbon phosphite.

[0073] By using the above-mentioned elemental tin and organotin compounds as the tin source, and using the above-mentioned elemental phosphorus (red phosphorus) or organophosphorus compounds as the phosphorus source, the reaction can be made simpler with fewer side reactions, and the above-mentioned tin phosphide compounds of the present application can be better obtained. In particular, by using elemental tin as the tin source and elemental phosphorus (red phosphorus) as the phosphorus source, since both phosphorus and tin are in the 0 valence state, the direct redox reaction between the two can make the reaction simpler with fewer side reactions, and the above-mentioned tin phosphide compounds of the present application can be better obtained.

[0074] In any embodiment, the amine solvent includes at least one of ethylenediamine, aniline, cyclohexylamine, monoethanolamine, diethanolamine, diisopropanolamine, N-methyldiethanolamine, and N,N-dimethylformamide, and may be ethylenediamine.

[0075] In the above preparation method of the present application, during the reaction process, based on the high-pressure environment provided by the reaction solvent heat, the above-mentioned specific amine solvent easily reaches the boiling or supercritical state. Therefore, the reactants are dispersed in the solvent and become more active. With the increase in temperature and the heat preservation process, the product is slowly generated. In addition, the above product has good dispersibility and uniform particle size. In addition, the amino group in the above amine solvent of the present application will decompose at high temperature to generate nitrogen, which helps to form a pore structure on the surface of the product particles and increase the specific surface area. This porous structure is beneficial to alleviating the influence of particle volume expansion on the cycle performance during the charge and discharge cycle of the battery.

[0076] In any embodiment, the temperature of the reaction is 150°C - 250°C, preferably 180°C - 220°C, and the reaction time is 12h - 30h, preferably 18h - 24h.

[0077] In some embodiments, the reaction temperature may be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C or 250°C, or the range between any two of the above values. In some embodiments, the reaction time may be 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h, 25h, 26h, 27h, 28h, 29h or 30h, or the range between any two of the above values.

[0078] By making the reaction temperature and reaction time of the preparation method of the present application within the above range, it is possible to prevent the structure of the material from being damaged due to too high a reaction temperature or too long a reaction time while ensuring that the reaction proceeds thoroughly, or prevent the aggregation of product particles.

[0079] In any embodiment, the molar ratio of the tin source to the phosphorus source is 0.8:1 to 8:1, and may be optionally 1.3:1 to 5.6:1.

[0080] In some embodiments, the molar ratio of the tin source to the phosphorus source may be optionally 0.8:1, 0.9:1, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4:1, 4.2:1, 4.4:1, 4.6:1, 4.8:1, 5:1, 5.2:1, 5.4:1, 5.6:1, 5.8:1, 6:1, 6.2:1, 6.4:1, 6.6:1, 6.8:1, 7:1, 7.2:1, 7.4:1, 7.6:1, 7.8:1 or 8:1, or a range between any two of the above values.

[0081] By making the molar ratio of the tin source to the phosphorus source in the tin phosphide material within the above range, the ratio of the two elements can be made more excellent, so that the obtained tin phosphide compounds have different physical and chemical properties and can be applied to different scenarios. Moreover, through the above molar ratio range, it helps to improve the specific capacity per gram of the tin phosphide compounds as the overall anode material. In addition, the tin element in the above molar ratio range helps to reduce the energy gap of the material, improve the conductivity, and the unreacted tin during the cycling process, on the one hand, accelerates the ion transport ability, and on the other hand, can effectively relieve the volume expansion of the tin phosphide.

[0082] The third aspect of the present application provides a negative electrode tab, which includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, and the negative electrode film layer includes the above-mentioned tin phosphide compounds of the embodiments of the present application or the tin phosphide compounds prepared by the preparation method of the present application.

[0083] By making the negative electrode tab of the embodiment of the present application have the above-mentioned tin phosphide compounds of the present application, for the reasons detailed above, it can promote the improvement of the battery cycle stability and the charging rate. In addition, by making the porosity of the tin phosphide compounds within the above range, the coating amount of the tin phosphide compounds as the anode material can be realized, thereby improving the energy density of the battery.

[0084] In any embodiment, the negative electrode tab satisfies: the porosity of the tin phosphide compounds is 5% - 15%, and may be optionally 8% - 12%; the weight content of the tin phosphide compounds in the negative electrode film layer is 93% - 98%, and may be optionally 95% - 97%; the thickness of the negative electrode film layer is 50 μm - 100 μm, and may be optionally 60 μm - 80 μm.

[0085] In some embodiments, the weight content of the stannous phosphide compound in the negative electrode film layer is 93%, 94%, 95%, 96%, 97% or 98%, or a range between any two of the above values.

[0086] By controlling the porosity, weight content of the stannous phosphide compound in the negative electrode sheet and the thickness of the negative electrode film layer within the above ranges, the negative electrode sheet of the embodiments of the present application can better achieve the negative electrode function and promote the improvement of battery cycle stability and charging rate.

[0087] In any embodiment, based on the total weight of the negative electrode film layer, the weight content W of the stannous phosphide compound is 93% - 98%, and can be optionally 95% - 97%.

[0088] By making the weight content of the stannous phosphide compound above the above lower limit value, the loading amount of the negative electrode material can be within a suitable range, thereby ensuring the energy density of the battery; by making the weight content of the stannous phosphide compound below the above upper limit value, the usage amount of the binder can be within a suitable range, preventing the preparation of the negative electrode sheet from being affected due to too little usage amount of the binder.

[0089] In any embodiment, the thickness of the negative electrode film layer is 50 μm - 100 μm, and can be optionally 60 μm - 80 μm.

[0090] In some embodiments, the thickness of the negative electrode film layer can be optionally 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm or 100 μm, or a range between any two of the above values.

[0091] By making the thickness of the negative electrode film layer above the above lower limit value, the amount of the active material can be within a suitable range to prevent the reduction of the energy density of the battery caused by too low content of the negative electrode material; by making the thickness of the negative electrode film layer below the above upper limit value, it helps to reduce the lithium ion transmission path, thereby improving the rate performance of the battery.

[0092] In any embodiment, the tap density of the negative electrode film layer is 1.5 g / cm 3 - 2.8 g / cm 3 and can be optionally 1.8 g / cm 3 - 2.5 g / cm 3 .

[0093] In some embodiments, the tap density of the negative electrode film layer is 1.5 g / cm 3 、1.6 g / cm 3 、1.7 g / cm 3 、1.8 g / cm3 , 1.9 g / cm 3 , 2.0 g / cm 3 , 2.1 g / cm 3 , 2.2 g / cm 3 , 2.3 g / cm 3 , 2.4 g / cm 3 , 2.5 g / cm 3 , 2.6 g / cm 3 , 2.7 g / cm 3 or 2.8 g / cm 3 , or the range between any two of the above values.

[0094] By making the tap density of the negative electrode film layer above the above lower limit value, the energy density of the battery can be improved; by making the tap density of the negative electrode film layer below the above upper limit value, an appropriate gap can be left between the negative electrode particles, preventing the negative electrode particles from breaking due to the expansion of the negative electrode and the too small gap between the negative electrode particles during the cycling process, thereby affecting the battery life.

[0095] [Negative electrode plate]

[0096] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer includes the above negative electrode material of the present application.

[0097] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0098] 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 can 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 can be formed by forming a metal material (such as 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.).

[0099] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery well-known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery may also be used. These negative electrode active materials may be used alone, or two or more of them may be used in combination.

[0100] In some embodiments, the negative electrode film layer may also 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).

[0101] In some embodiments, the negative electrode film layer may also 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.

[0102] In some embodiments, the negative electrode film layer may also optionally include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0103] In some embodiments, the negative electrode plate can be prepared in the following manner: dispersing the components for preparing the negative electrode plate, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0104] [Positive electrode plate]

[0105] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector. The positive electrode film layer includes the lithium iron phosphate salt particles of the first aspect of the present application as the positive electrode material. When the lithium iron phosphate salt particles of the present application are applied to secondary batteries, they have large particle sizes and also have excellent kinetic properties when used as the positive electrode material.

[0106] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, as the metal foil, the battery aluminum foil of the present application is used. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming the battery aluminum foil of the present application on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0107] In some embodiments, the positive electrode material may be a positive electrode material for batteries well-known in the art. By way of example, the positive electrode material may include at least one of the following materials: lithium phosphate with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode materials may also be used. These positive electrode materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium 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 (which may also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which may also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which may also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (which may also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (which may also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al0.05 O 2 ) and at least one of its modified compounds, etc. Examples of the lithium-containing phosphate with olivine structure may include but are not limited to lithium iron phosphate (such as LiFePO 4 (which may also be simply 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 manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0108] In some embodiments, the positive electrode film layer may further 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 fluorinated acrylate resin.

[0109] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0110] In some embodiments, the positive electrode plate can be prepared by the following method: dispersing the components for preparing the positive electrode plate, such as the positive electrode material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0111] [Electrolyte]

[0112] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. There is no specific limitation on the type of the electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0113] In some embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0114] In some embodiments, the electrolyte salt can 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 bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluorooxalate phosphate.

[0115] In some embodiments, the solvent may 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, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0116] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives capable of improving certain battery performance, such as additives for improving battery overcharge performance, additives for improving battery high-temperature or low-temperature performance, and the like.

[0117] [Separator membrane]

[0118] In some embodiments, a secondary battery further includes a separator membrane. The present application does not particularly limit the type of the separator membrane, and any publicly known porous structure separator membrane with good chemical stability and mechanical stability can be selected.

[0119] In some embodiments, the material of the separator membrane may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0120] [Secondary battery]

[0121] In one embodiment of the present application, a secondary battery is provided, which includes the positive electrode sheet.

[0122] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator membrane. During the charging and discharging process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator membrane is disposed between the positive electrode sheet and the negative electrode sheet, mainly serving to prevent short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0123] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator membrane can be made into an electrode assembly by a winding process or a stacking process.

[0124] In some embodiments, the secondary battery may include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte.

[0125] In some embodiments, the outer packaging of the secondary battery can be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The outer packaging of the secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed, etc.

[0126] The present application has no particular limitation on the shape of the secondary battery, and it can be cylindrical, square, or any other shape. For example, Figure 1 is a secondary battery 5 with a square structure as an example.

[0127] In some embodiments, referring to Figure 2 , the outer packaging can include a housing 51 and a cover plate 53. Among them, the housing 51 can include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator can be formed into an electrode assembly 52 through a winding process or a stacking 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 included in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0128] In some embodiments, the secondary batteries can be assembled into a battery module. The number of secondary batteries included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0129] Figure 3 is a battery module 4 as an example. Referring to Figure 3 , in the battery module 4, a plurality of secondary batteries 5 can be 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.

[0130] Optionally, the battery module 4 can further include a housing with a receiving space, and a plurality of secondary batteries 5 are accommodated in the receiving space.

[0131] In some embodiments, the above battery module can also be assembled into a battery pack. The number of battery modules included in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0132] Figure 3 and Figure 4 is a battery pack 1 as an example. Referring to Figure 4 and Figure 5, a battery pack 1 may include a battery box and a plurality of battery modules 6 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can 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.

[0133] [Power-consuming device]

[0134] In addition, the present application also provides a power-consuming device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack can be used as the power supply of the power-consuming device or as the energy storage unit of the power-consuming device. The power-consuming 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, satellites, energy storage systems, etc., but is not limited thereto.

[0135] As a power-consuming device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0136] Figure 6 is a power-consuming device as an example. The power-consuming device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for this power-consuming device, a battery pack or battery module can be used.

[0137] Another example of the device can be a mobile phone, tablet computer, laptop computer, etc. This device usually requires thinning and can use a secondary battery as the power supply.

[0138] Embodiment

[0139] Hereinafter, 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 a limitation of the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0140] Embodiment 1

[0141] 1) Negative electrode tab

[0142] Preparation of tin phosphide compounds: Add metallic tin and red phosphorus to ethylenediamine in a mass ratio of 5.6:1, stir for 10 minutes, and obtain a mixture. Transfer the mixture to a polytetrafluoroethylene reaction vessel, place it in a stainless steel autoclave, and heat it in an oven at 200°C for 24 hours. After cooling to room temperature, collect the product by centrifugation, wash it several times with deionized water and ethanol, and vacuum dry it at 60°C for 12 hours to obtain Sn 3 P 2 .

[0143] Preparation of negative electrode: 3 P 2 , carbon black (Super P) and PVDF binder were mixed in a weight ratio of 8:1:1, added into N-methylpyrrolidone (NMP), and mixed evenly to obtain negative electrode slurry. Then the negative electrode slurry was evenly pasted on the copper current collector, dried at 80°C in a vacuum oven for 24 hours, and cold pressed to obtain a negative electrode sheet.

[0144] 2) Preparation of positive electrode

[0145] The positive electrode active material is lithium iron phosphate LiFePO 4 The conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an N-methylpyrrolidone solvent system in a weight ratio of 97:1:2 to obtain a positive electrode slurry with a solid content of 65%; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained after drying and cold pressing.

[0146] 3) Electrolyte

[0147] In an argon atmosphere glove box (H 2 O content <10ppm, O 2 The first solvent vinylene carbonate and the second solvent ethylene carbonate and dimethyl carbonate (EC and DMC mass ratio is 1:1) are mixed, and 15wt% lithium hexafluorophosphate (LiPF 6 ), and stir thoroughly until it is completely dissolved to prepare an electrolyte.

[0148] 4) Isolation film

[0149] A polyethylene (PE) film coated with nano-aluminum oxide was used as the isolation film.

[0150] 5) Preparation of batteries

[0151] The positive electrode sheet, the isolation film, and the negative electrode sheet are stacked and wound in order to obtain a wound electrode assembly; the electrode assembly is added to an outer square aluminum shell, and the electrolyte is injected after drying. After packaging, standing, formation, aging, secondary packaging, capacity and other processes, the secondary battery of Example 1 is obtained.

[0152] During the preparation of the secondary batteries in Examples 2 to 31 and Comparative Examples 1 to 5, the preparation method of the tin phosphide compound or the thickness and compaction density of the negative electrode sheet were adjusted. The specific product parameters are shown in Table 1.

[0153] Among them, in Comparative Example 3, the tin phosphide compound was prepared by ball milling and high temperature as follows:

[0154] Ball milling: Metallic tin and red phosphorus were weighed according to a mass ratio of 5.6:1, sealed in a stainless steel ball milling jar under an argon atmosphere, and taken out after 30 h by high-energy balls rotating at 350 r / min (the ball milling medium was stainless steel grinding balls with a diameter of 0.5 cm) to obtain Sn 3 P 2 electrode material;

[0155] High temperature: 30 g of concentrated ammonia water was weighed, then 50 g of tin tetrachloride pentahydrate was added and the hydrothermal reaction was continued at 130 °C for 6 h, and then dried to obtain tin oxide material; the tin oxide was mixed with sodium hypophosphite, ground, and then sintered at 500 °C for 6 h; the product was washed with 0.1 mol / L hydrochloric acid, then washed with deionized water until neutral, washed with alcohol and dried to obtain Sn 4 P 3 material.

[0156] Using the obtained Sn 4 P 3 material, the negative electrode sheet was prepared in the same manner as in Example 1.

[0157] In Comparative Example 5, commercially available Sn 4 P 3 (CAS: 12286-33-8; Aladdin reagent) was used as the negative electrode active material, and the negative electrode sheet was prepared in the same manner as in Example 1 except for this.

[0158] II. Performance Test

[0159] 1. Tin Phosphide Compound

[0160] 1). Porosity Test

[0161] The pore testing method described above is the mercury intrusion method. The mercury intrusion instrument used in the experiment can be selected as PoreMaster 60 (Quantachrome Instruments, USA). The pressure applied in the low-pressure station (LP) is about 0.6 to 50 PSI (corresponding to pore diameters ranging from 355 - 4 microns), and the pressure applied in the high-pressure station (HP) is 20 to 60000 PSI (corresponding to pore diameters ranging from 10 - 0.004 microns). By adjusting the pressure, the pore structure within an appropriate range (corresponding to pores > 50 nm in this patent) can be measured. The specific operation method is as follows: Cut the treated carbon fiber into small pieces and place them in a sample container. Use a penetrometer made of glass as the sample container, apply pressure to the sample, and conduct the measurement.

[0162] 2) Measurement of specific surface area

[0163] In this solution, the specific surface area has the meaning well-known in the art. Usually, the specific surface area is expressed in the unit of m 2 / g and can be measured using methods and instruments known in the art. For example, referring to GB / T 19587 - 2017, the specific surface area can be measured by the inert gas (such as nitrogen) adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method. Among them, the nitrogen adsorption specific surface area analysis test can be carried out using the Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics Company, USA.

[0164] 3) Measurement of Dv50

[0165] Referring to the laser diffraction method for particle size distribution in GB / T19077 - 2016, weigh 0.1 g - 0.13 g of the stannous phosphide compound sample to be measured in a 50 mL beaker, add 5 g of anhydrous ethanol, place a stirring bar of about 2.5 mm, and seal it with plastic wrap. After ultrasonic treatment of the sample for 5 min, transfer it to a magnetic stirrer and stir at 500 revolutions per minute for more than 20 min. Two samples are taken from each batch of products for testing. The test is carried out using the Mastersizer2000E laser particle size analyzer of Malvern Instruments Limited, UK.

[0166] 2. Negative electrode plate

[0167] 1) Measurement of the thickness of the negative electrode film layer

[0168] Use a micrometer (number of acquisition points > 14) to measure the thickness A of the copper foil and the thickness B of the negative electrode plate. Since both sides of the copper foil are coated with active materials, the thickness of the negative electrode film layer on one side is: (B - A) / 2.

[0169] 2) Measurement of the compaction density of the negative electrode film layer

[0170] The compaction density CD of the negative electrode film layer is determined by measuring the mass of the negative electrode film layer on one side per unit area (g / cm 2 ) and the thickness of the negative electrode film layer on one side (cm) (the number of sampling points > 14). Specifically, the compaction density PD of the negative electrode film layer = the mass of the negative electrode film layer on one side per unit area (g / cm 2 ) / the thickness of the negative electrode film layer (cm).

[0171] 3. Battery

[0172] 1). Gravimetric capacity

[0173] After the prepared battery is left standing for 12 h, at 25 °C, it is discharged at a constant current of 0.1C to 0.005V, and the discharge capacity is recorded; then it is charged at a constant current of 0.1C to 2.5V, and the charge capacity is recorded. The ratio of the charge capacity to the mass of the negative electrode active material is the initial Coulombic efficiency of the negative electrode active material.

[0174] 2). Cycling performance

[0175] At 25 °C, the prepared secondary battery is charged at a constant current of 0.33C to 3.65V, then charged at a constant voltage of 0.05C, then left standing for 10 minutes, and then discharged at a constant current of 0.33C to 2.5V. The recorded discharge capacity is C0. According to the above charge-discharge process, 100 and 1000 cycles are carried out, and the discharge capacities are recorded as C1 and C2 respectively. The 1000-cycle capacity retention rate of the battery at 0.33C = C2 / C0 × 100%.

[0176] 3). Fast charging performance

[0177] At 25 °C, the prepared secondary battery is charged at a constant current of 2C to 3.65V, then charged at a constant voltage of 0.05C, then left standing for 10 minutes, and then discharged at a constant current of 2C to 2.5V. The recorded discharge capacity is C3. According to the above charge-discharge process, 100 and 1000 cycles are carried out, and the discharge capacities are recorded as C4 and C5 respectively. The 1000-cycle capacity retention rate of the battery at 2C = C5 / C3 × 100%.

[0178] 4). DC impedance

[0179] At 25 °C, the state of charge of the battery is adjusted to 50% SOC, left standing for 30 min, and the battery voltage at this time is recorded as U1 (V). It is discharged at 0.36C for 10 s, and the battery voltage at this time is recorded as U2 (V). The corresponding discharge current I (mA) of the battery is 0.36 × the battery design capacity (mAh). The DC impedance DCR (mΩ) = (U1 - U2) / I.

[0180] III. Analysis of test results of each example and comparative example

[0181] Prepare the batteries of each example and comparative example respectively according to the above method, and measure various performance parameters. The results are shown in Table 1 below.

[0182] Table 1

[0183]

[0184] It can be seen from Table 1 that in Examples 1-23 of the present application, by using a stannous phosphide compound satisfying the general formula of the present application as the negative electrode material and controlling its porosity within the range of the present application, the obtained secondary battery has a high specific capacity, excellent fast charging performance, a high cycle capacity retention rate, and a low impedance of the negative electrode film, and the improvement of the battery performance brought by the negative electrode material is significant.

[0185] In addition, it can also be seen from Table 1 that in Comparative Examples 1-5 of the present application, since the porosity of the stannous phosphide compound used as the negative electrode material is not within the specific range of the present application, the evaluation indexes such as the specific capacity, fast charging performance, cycle capacity retention rate, and impedance of the negative electrode film of the obtained secondary battery all decrease. Especially in Comparative Examples 1-2, the above various performance indexes decrease significantly compared with the examples of the present application.

[0186] It should be noted that the present application is not limited to the described embodiments. The described embodiments are only examples, and embodiments having the same structure and the same effect as the technical idea within the technical solution scope of the present application are included in the technical scope of the present application. In addition, within the scope of not departing from the gist of the present application, various modifications that can be thought of by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode material, characterized in that, it contains stannic phosphide compounds, and the stannic phosphide compounds include compounds with the general formula shown in Formula I, Sn a P b Formula I wherein, 0 < a ≤ 4, 0 < b ≤ 3; the porosity of the stannic phosphide compounds is 11% - 20%, and can be optionally 5% - 15%.

2. The negative electrode material according to claim 1, characterized in that, The stannous phosphide compound includes Sn 3 P 2 , Sn 4 P 3 , SnP 3 , SnP, SnP 0.94 and at least one of the following, optionally including Sn 3 P 2 , Sn 4 P 3 and at least one of the following.

3. The negative electrode material according to claim 1 or 2, characterized in that, The specific surface area of the stannous phosphide compound is 60 m 2 / g to 100 m 2 / g, and can be optionally 75 m 2 / g to 95 m 2 / g.

4. The negative electrode material according to any one of claims 1 to 3, characterized in that, the Dv50 of the stannic phosphide compounds is 10 μm - 25 μm, and can be optionally 12 μm - 18 μm.

5. A method for preparing a negative electrode material, characterized in that, the negative electrode material contains stannic phosphide compounds, and the preparation method includes: adding raw materials including a tin source and a phosphorus source to an amine solvent for reaction to obtain the stannic phosphide compounds.

6. The preparation method according to claim 5, characterized in that, the tin source includes at least one of metallic tin and organotin compounds, and optionally includes metallic tin; the organotin compounds include at least one of monobutyltin, dibutyltin, tributyltin, tributyltin oxide, trimethyltin, triphenyltin, dioctyltin.

7. The preparation method according to claim 5 or 6, characterized in that, the phosphorus source includes at least one of red phosphorus and organophosphorus compounds, the phosphorus-containing compounds include at least one of phosphorous acid, hydrocarbon phosphonous acid, hydrocarbon hypophosphorous acid, phosphite, ethyl hypophosphite, hydrocarbon phosphite.

8. The preparation method according to any one of claims 5 to 7, characterized in that, the amine solvent includes at least one of ethylenediamine, aniline, cyclohexylamine, monoethanolamine, diethanolamine, diisopropanolamine, N-methyldiethanolamine, N,N-dimethylformamide, and can be optionally ethylenediamine.

9. The preparation method according to any one of claims 5 to 8, characterized in that, the temperature of the reaction is 150°C - 250°C, and can be optionally 180°C - 220°C, and the time of the reaction is 12 h - 30 h, and can be optionally 18 h - 24 h.

10. The preparation method according to any one of claims 5 to 9, characterized in that, the molar ratio of the tin source to the phosphorus source is 0.8:1 - 8:1, and can be optionally 1.3:1 - 5.6:

1.

11. A negative electrode plate, characterized in that, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, and the negative electrode film layer includes the negative electrode material according to any one of claims 1 to 4 or the negative electrode material prepared by the preparation method according to any one of claims 5 to 10.

12. The negative electrode plate according to claim 11, characterized in that, the negative electrode plate satisfies: the porosity of the negative electrode material is 5% - 15%, and can be optionally 8% - 12%; the weight content of the stannic phosphide compounds in the negative electrode film layer is 93% - 98%, and can be optionally 95% - 97%; the thickness of the negative electrode film layer is 50 μm - 100 μm, and can be optionally 60 μm - 80 μm.

13. The negative electrode sheet according to claim 11 or 12, characterized in that based on the total weight of the negative electrode film layer, the weight content W of the negative electrode material is 93%-98%, optionally 95%-97%.

14. The negative electrode sheet according to claim 12 or 13, characterized in that the thickness of the negative electrode film layer is 50-100 μm, optionally 60-80 μm.

15. The negative electrode sheet according to any one of claims 12 to 14, characterized in that The compaction density of the negative electrode film layer is 1.5 - 2.8 g / cm 3 , and it can be optionally 1.8 - 2.5 g / cm 3 .

16. A secondary battery, characterized in that the secondary battery includes the negative electrode sheet according to any one of claims 11 to 15.

17. An electrical device, characterized in that it includes the secondary battery according to claim 16.

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