Negative electrode material and preparation method therefor, and battery

Abstract

A negative electrode material and a preparation method therefor, and a battery. The negative electrode material comprises a secondary particle, wherein the secondary particle comprises a plurality of agglomerated primary particles, and the primary particles comprise active substances doped with an iron element and a nickel element; and the mass content of the iron element in the negative electrode material is A ppm, the mass content of the nickel element in the negative electrode material is B ppm, and 9.2≤A / B≤20. The negative electrode material provided by the present application enhances the hardness of the nano silicon, improves the stability of the nano silicon particles, and reduces the volume change of the negative electrode material, thereby further improving the cycling stability of the battery.

Description

Negative electrode material and preparation method thereof, and battery

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on September 28, 2023, with application number 202311294624.4 and application name “Negative electrode material and preparation method thereof, lithium-ion battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of negative electrode materials, and in particular to negative electrode materials and preparation methods thereof, and batteries. Background Art

[0003] With market development in recent years, the demand for high-energy-density anode materials has continued to grow. Lithium-ion batteries are used not only in mobile devices like smartphones and laptops, but also in electric vehicles. Surveys indicate that long driving range is a key concern for consumers, and the range of electric vehicles directly impacts the user experience. To address this, the development of power batteries with higher energy density is necessary. The positive and negative electrode materials are the core of the battery and determine its efficiency. Currently, the commercially available anode material is graphite, but its capacity is already near its theoretical upper limit, with limited potential for further improvement. Therefore, the development of a new generation of high-energy-density anode materials is urgently needed.

[0004] Silicon anodes are widely considered the next generation of battery negative electrode materials, offering advantages such as high capacity, abundant resources, and relative safety. However, silicon anodes experience dramatic volume expansion during cycling, leading to material pulverization and fragmentation, and rapid battery degradation.

[0005] Therefore, how to reduce the pulverization and breakage of silicon materials and improve the cycle stability of silicon negative electrode materials remains an urgent problem that needs to be solved.

[0006] Application Contents

[0007] The present application provides a negative electrode material and a preparation method thereof, and a battery, which can enhance the hardness of negative electrode material particles and improve the cycle stability of negative electrode material particles.

[0008] In a first aspect, the present application provides a negative electrode material, which includes secondary particles, the secondary particles include a plurality of agglomerated primary particles, and the primary particles include an active substance doped with iron and nickel elements; wherein the mass content of the iron element in the negative electrode material is Appm, the mass content of the nickel element in the negative electrode material is Bppm, and 9.2≤A / B≤20.

[0009] In a second aspect, the present application provides a method for preparing a negative electrode material, comprising the following steps:

[0010] A mixture of a silicon source precursor, an iron dopant, and a nickel dopant is heat-treated to obtain primary particles doped with iron and nickel; the primary particles are coated to obtain the negative electrode material, wherein the mass content of the iron element in the negative electrode material is Appm, the mass content of the nickel element in the negative electrode material is Bppm, and 9.2≤A / B≤20.

[0011] In a third aspect, the present application provides a battery, which includes the above-mentioned negative electrode material or the negative electrode material prepared according to the above-mentioned preparation method.

[0012] The technical solution of this application has at least the following beneficial effects:

[0013] In the negative electrode material provided in the present application, the negative electrode material includes secondary particles, the secondary particles include multiple agglomerated primary particles, and the primary particles include active substances doped with iron and nickel elements; the mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and 9.2≤A / B≤20. By adding iron and nickel elements to the negative electrode material, iron and nickel are co-doped. Since the atomic number of nickel is greater than that of iron, the greater the volume difference between nickel atoms and silicon atoms, the more obvious the solid solution strengthening effect, and iron-nickel co-doping can enhance the hardness of the negative electrode material; in addition, the content of iron doped into the negative electrode material is controlled to be higher than that of nickel. This is because the volume of iron atoms is less affected by heat, while the volume expansion effect of nickel atoms after heating is larger than that of iron atoms. Therefore, controlling the A / B ratio within the above range can strengthen the hardness of the negative electrode material on the basis of reducing the volume expansion effect of the doped metal elements, thereby effectively alleviating the volume expansion stress of the negative electrode material, enhancing the structural stability of the negative electrode material, and improving the cycle life of the battery prepared with the negative electrode material, so that the obtained negative electrode material has good electronic conductivity and electrochemical properties.

[0014] In the preparation method of the negative electrode material provided in the present application, a mixture of a silicon source precursor, an iron dopant and a nickel dopant is heat-treated to obtain primary particles doped with iron and nickel. The primary particles include active substances doped with iron and nickel. The primary particles are then coated to obtain negative electrode materials doped with iron and nickel. By adding iron and nickel elements to the primary particles, the hardness of the primary particles is enhanced, the volume expansion of the active substances can be effectively alleviated, the structural stability of the negative electrode materials can be enhanced, and the cycle life of the battery prepared with the negative electrode materials can be improved; and the entire preparation process is simple and easy to prepare industrially. The prepared negative electrode material has a stable structure and an improved first coulombic efficiency, which enhances the structural stability of the negative electrode material and improves the cycle stability of the negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG1 is a process flow chart of a method for preparing a negative electrode material provided in this application;

[0016] FIG2 is a scanning electron microscope (SEM) image of the negative electrode material prepared in Example 1 of the present application;

[0017] FIG3 is an XRD pattern of the negative electrode material prepared in Example 1 of the present application;

[0018] FIG4 is a schematic diagram of the first charge and discharge curve of the negative electrode material prepared in Example 1 of the present application;

[0019] FIG5 is a schematic diagram of the cycle performance curve of the negative electrode material prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0020] To better illustrate the present application and facilitate understanding of the technical solution of the present application, the present application is further described below. However, the following embodiments are merely simplified examples of the present application and do not represent or limit the scope of protection of the present application. The scope of protection of the present application shall be subject to the claims.

[0021] In a first aspect, the present application provides a negative electrode material, comprising secondary particles, the secondary particles comprising a plurality of agglomerated primary particles, the primary particles comprising an active material doped with iron and nickel; wherein the mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and 9.2≤A / B≤20. In the present invention, the term "primary particle" refers to the primary structure of a single particle, and the term "secondary particle" refers to an aggregate of primary particles aggregated through physical or chemical bonding between the primary particles, i.e., a secondary structure, without intentionally performing a process of agglomerating or combining the primary particles that constitute the secondary particles.

[0022] In the negative electrode material provided by the present application, the negative electrode material includes secondary particles, the secondary particles include multiple agglomerated primary particles, and the primary particles include active substances doped with iron and nickel elements; the mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and 9.2≤A / B≤20. By adding iron and nickel elements to the negative electrode material, iron and nickel are co-doped. Since the atomic number of nickel is greater than that of iron, the greater the volume difference between nickel atoms and silicon atoms, the more obvious the solid solution strengthening effect. Iron-nickel co-doping can enhance the hardness of the negative electrode material. In addition, the content of iron doped into the negative electrode material is controlled to be higher than that of nickel. This is because the volume change of iron atoms when heated is small, while the volume expansion effect of nickel atoms after heating is larger than that of iron atoms. Therefore, by controlling the A / B ratio within the above range, the hardness of the negative electrode material can be enhanced on the basis of reducing the volume expansion effect of the doped metal elements, thereby effectively alleviating the volume expansion of the active substance, enhancing the structural stability of the negative electrode material, and improving the cycle life of the battery prepared with the negative electrode material, so that the obtained negative electrode material has good electronic conductivity and electrochemical properties.

[0023] Specifically, the mass content of iron in the negative electrode material Appm is to the mass content of nickel in the negative electrode material Bppm, that is, A / B can be 9.2, 10, 12, 14, 16, 18, 20, etc., and is not limited here. Controlling the ratio of the mass content of iron to the mass content of nickel, and doping the negative electrode material with nickel and iron elements can improve the hardness of the negative electrode material. During the rolling of the electrode sheet or the reciprocating charge and discharge process, it can resist the stress caused by the expansion of the active material, inhibit particle pulverization and breakage, and improve the cycle stability of the battery prepared with the negative electrode material.

[0024] In some embodiments, the active material refers to a material that can react with lithium to insert and remove lithium.

[0025] The active material includes at least one of a single metal, a metal oxide, and a metal alloy. Furthermore, the metal includes at least one of Li, Na, K, Sn, Ge, Si, Fe, Mg, Ti, Zn, Al, P, and Cu. A single metal refers to a single metal, a metal oxide refers to an oxide of the above metal, and a metal alloy refers to an alloy containing at least one of the above metals.

[0026] In some embodiments, the active material includes a silicon-based material, which includes at least one of crystalline silicon, amorphous silicon, silicon oxide, a silicon alloy, and a composite of crystalline silicon and amorphous silicon. Specifically, the silicon alloy may be a silicon-lithium alloy, a silicon-magnesium alloy, or the like. Of course, it should be noted that in some cases, the silicon alloy includes elemental particles and alloys.

[0027] In some embodiments, the total mass content of iron and nickel in the negative electrode material is less than 1%, specifically 0.99%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2% or 0.1%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable. After many experiments, it was found that the addition of iron and nickel elements is controlled within the above ranges, which significantly improves the material performance; when the total mass content of iron and nickel elements in the negative electrode material is greater than the above range, the magnetism of iron and nickel will have a greater impact on the negative electrode material, which is not conducive to the cycle stability of the battery prepared with the negative electrode material. It can be seen that controlling the mass content of iron and nickel elements in the negative electrode material can control the magnetic substances in the negative electrode material from exceeding the standard, reduce the fatigue and aging of the negative electrode material affected by the magnetic field, and improve the hardness of the negative electrode material without affecting the electrochemical performance of the negative electrode material to resist the stress caused by expansion, inhibit particle pulverization and breakage, and improve the cycle stability of the battery prepared with the negative electrode material.

[0028] In some embodiments, the mass content of iron in the negative electrode material is Appm, 0.1≤A≤1000, more specifically, it can be 0.1ppm, 20ppm, 100ppm, 300ppm, 500ppm, 700ppm, 900ppm or 1000ppm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] In some embodiments, the mass content of nickel element in the negative electrode material is Bppm, 0.1≤B≤500, more specifically, it can be 0.1ppm, 20ppm, 100ppm, 200ppm, 300ppm, 400ppm or 500ppm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] In some embodiments, the average particle size D of the primary particles is 50 It is 1nm to 500nm, specifically 1nm, 50nm, 100nm, 200nm, 300nm, 400nm or 500nm, etc., but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable. Through multiple experiments, it was found that nano-scale primary particles have high surface energy and strong particle structure, which can inhibit the volume expansion of silicon. However, since the smaller the particle size of the nano-scale primary particles, the greater their surface energy, they are prone to agglomeration during the charge and discharge process, and the particle size is too small, the production process cost is high. Preferably, the average particle size D of the primary particles is 200nm. 50 The average particle size D of the primary particles is preferably 1 nm to 200 nm. 50 It is 5nm~100nm.

[0031] In some embodiments, the particle size of the primary particles satisfies the following relationship: (D 100 -D 10 ) / D 50 ≥1.5, specifically 1.5nm, 2nm, 5nm, 10nm, 50nm, 100nm, 200nm, etc., but not limited to the listed values. Other values ​​not listed in this range are also applicable. It should be noted that the particle size of the primary particles is small, and the average particle size D can be obtained by performing particle size analysis on the SEM using Nano Measure software. 50 、D 10 and maximum particle size D 100The specific test method is as follows: Set the SEM photo to 50K magnification, use Nano Measure software to measure the size of 200 particles in the SEM photo, calculate the average particle size of the 200 particles as D1, and the maximum value among the 200 particles is the maximum value of the primary particle D2. Then repeat the measurement of the results in at least 10 SEM photos, and then calculate the mean of the average values. The maximum value of the primary particle is the maximum value D of the particles in at least 10 SEM statistics. 100 The average particle size of the primary particles is (D1 + D2 + ... + D10) / 10 of the 10th statistical average particle size. D10 represents the particle size corresponding to the 10% cumulative particle size distribution percentage of the powder.

[0032] In some embodiments, the negative electrode material further comprises a carbon material located on at least a portion of the surface of the secondary particles and / or the primary particles, with the carbon material forming a carbon layer. Specifically, the carbon layer comprises amorphous carbon, which has good compatibility with the electrolyte and ensures the stability of the electrical performance of the negative electrode material during charge and discharge. Exemplarily, the amorphous carbon in the carbon layer can be derived from at least one of petroleum asphalt, coal tar pitch, modified asphalt, and mesophase asphalt, which has been carbonized.

[0033] In some embodiments, the active material includes a silicon-based material, which is also doped with oxygen. The mass content of oxygen in the negative electrode material is 0.1% to 18%, specifically 0.1%, 1%, 3%, 6%, 9%, 12%, 15%, 18%, etc., but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable. Adding oxygen in the above range can reduce the volume expansion of the silicon-based material and improve the cycle performance of the battery prepared with the negative electrode material including the silicon-based material. When the oxygen content in the silicon-based material is too high, the capacity and first coulombic efficiency of the negative electrode material including the silicon-based material will be reduced.

[0034] In some embodiments, the specific surface area of ​​the negative electrode material is 0.1 m 2 / g~5m 2 / g; specifically 0.1m 2 / g, 0.3m 2 / g, 0.5m 2 / g, 1.0m 2 / g, 1.8m 2 / g, 2.6m 2 / g, 3.5m 2 / g, 5.0m 2 / g, of course, it can also be other numbers within the above range, which is not limited here. Controlling the specific surface area of ​​the negative electrode material within the above range is beneficial to improving the cycle performance of the lithium battery made of the negative electrode material.

[0035] In some embodiments, the median particle size of the negative electrode material is 0.5 μm to 30 μm; specifically, it can be 0.5 μm, 1 μm, 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, 25 μm, or 30 μm, etc., and of course, other values ​​within the above range are also possible and are not limited here. It can be understood that controlling the median particle size of the negative electrode material within the above range is beneficial to improving the cycle performance of the negative electrode material.

[0036] In a second aspect, the present application provides a method for preparing a negative electrode material, as shown in FIG1 , comprising the following steps:

[0037] S10, heat-treating a mixture containing an active material precursor, an iron dopant, and a nickel dopant to obtain primary particles doped with iron and nickel;

[0038] S20, coating the primary particles to obtain a negative electrode material, wherein the mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and 9.2≤A / B≤20.

[0039] In the preparation method of the negative electrode material provided in the present application, a mixture containing an active material precursor, an iron dopant and a nickel dopant is subjected to heat treatment to obtain primary particles doped with iron and nickel, and the primary particles doped with iron and nickel are then subjected to coating treatment to obtain the negative electrode material doped with iron and nickel. By adding iron and nickel elements to the primary particles, the hardness of the primary particles is strengthened, which can effectively alleviate the volume expansion of the negative electrode material during the lithium insertion and extraction process, enhance the structural stability of the negative electrode material, and improve the cycle life of the battery prepared by the negative electrode material; and the entire preparation process is simple and easy to prepare industrially. The prepared negative electrode material has a stable structure and an improved first coulombic efficiency, which enhances the structural stability of the negative electrode material and improves the cycle stability of the battery prepared by the negative electrode material.

[0040] The following is a detailed introduction to the preparation method provided in this scheme:

[0041] S10, heat-treating a mixture containing an active material precursor, an iron dopant, and a nickel dopant to obtain primary particles doped with iron and nickel.

[0042] In some embodiments, the iron dopant includes iron powder, ferric nitrate, nickel nitrate, ferrous lactate (C6H 10 At least one of FeO6·3H2O), ferric citrate (FeC6H5O7), hematite (K4[Fe(CN)6]·3H2O), ferric glycinate (Fe[C2H4O2N]2) and ferrocene (Fe(C5H5)2).

[0043] In some embodiments, the nickel dopant includes at least one of nickel oleate, nickel propionate, nickel butyrate, nickel octoate, nickel lactate, nickel benzoate, nickel bis(acetylacetonate), nickel salicylate, and nickel alkylphenyl salicylate.

[0044] In some embodiments, the step of heat-treating a mixture containing an active material precursor, an iron dopant, and a nickel dopant includes forming primary particles from a vapor-phase active material, such as a silicon source precursor, using a vapor deposition method, and doping the primary particles with metal vapor generated by the iron dopant and the nickel dopant. It will be appreciated that the iron dopant and the nickel dopant are compounds that readily decompose at low temperatures. Upon heating, these compounds decompose to produce vapor containing the metal element.

[0045] In some embodiments, the temperature of vapor deposition is 300°C to 1000°C, more specifically, it can be 300°C, 350°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C or 1000°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] In some embodiments, the gas-phase silicon source precursor includes at least one of silane, disilane, trisilane, tetrasilane, and monosilane.

[0047] In some embodiments, the flow rate of the gas-phase silicon source precursor is 5 scc to 1000 scc, more specifically, it can be 5 scc, 30 scc, 60 scc, 200 scc, 300 scc, 600 scc, 800 scc or 1000 scc, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0048] In some embodiments, the mass ratio of the iron dopant to the nickel dopant is 0.1 to 30, specifically 0.1, 0.5, 1, 2, 5, 8, 10, 15, 20, 25, or 30, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] In some embodiments, the step of heat-treating the mixture containing the silicon source precursor, the iron dopant, and the nickel dopant may be performed by liquid phase mixing. Specifically, the step includes adding a metal reducing agent to the liquid mixture containing the silicon source precursor, the iron dopant, and the nickel dopant, and heat-treating the mixture obtained by solid-liquid separation to obtain primary particles doped with nickel and iron.

[0050] In some embodiments, the liquid silicon source precursor includes at least one of trichlorosilane, silicon tetrachloride, methylchlorosilane, polysilane, and triethylchlorosilane.

[0051] In some embodiments, the mass ratio of the liquid silicon source precursor, the iron dopant, the nickel dopant, and the metal reducing agent is (40-100):(0.01-1):(0.05-1):(0.01-5). Specifically, the mass ratios may be 40:0.01:0.05:0.01, 40:0.05:0.1:0.1, 40:0.05:0.1:0.5, 100:1:0.5:0.1, or 100:1:1:5, but are not limited to the values ​​listed above. Other values ​​not listed within this numerical range are also applicable.

[0052] In some embodiments, the metal reducing agent includes at least one of magnesium powder, zinc powder, aluminum powder, lithium powder, sodium powder, and potassium powder.

[0053] In some embodiments, the mass ratio of the metal reducing agent to the liquid silicon source precursor is (0.01-5):100.

[0054] In some embodiments, the heat treatment temperature is 400-1200°C, and the heat treatment time is 1h-15h; the heat treatment temperature can be specifically 400°C, 500°C, 600°C, 700°C, 800°C, 950°C, 1500°C, 1200°C, etc., and the heat treatment time can be specifically 1h, 2h, 4h, 6h, 9h, 11h, 12h, 14h, 15h, etc., which are not limited here.

[0055] In some embodiments, a coating agent is further added to the mixture, and the mixture is heat-treated under the protection of an inert gas, and then acid-treated to obtain primary particles doped with nickel and iron.

[0056] In some embodiments, the coating agent comprises at least one of a liquid carbon source or a solid carbon source. Exemplarily, the solid carbon source comprises at least one of sugars, esters, hydrocarbons, organic acids, and polymers.

[0057] In some embodiments, the inert gas includes at least one of helium, neon, argon, krypton, and xenon.

[0058] In some embodiments, the heat treatment temperature is 500°C to 1000°C, more specifically 500°C, 600°C, 700°C, 800°C, 900°C, or 1000°C, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable. The heat treatment time is 11 hours to 115 hours, specifically 11 hours, 20 hours, 30 hours, 50 hours, 70 hours, 80 hours, 90 hours, 100 hours, 115 hours, etc., which are not limited here.

[0059] In some embodiments, the acid used in the acid treatment includes at least one of hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and acetic acid.

[0060] S20, coating the primary particles to obtain a negative electrode material, wherein the mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and 9.2≤A / B≤20.

[0061] In some embodiments, the coating process includes at least one of a solid phase carbon coating process, a liquid phase carbon coating process, and a vapor phase carbon coating process.

[0062] In some embodiments, the coating treatment is a solid-phase carbon coating treatment, which specifically includes: carbonizing a mixture obtained by mixing primary particles with a solid-phase carbon source to obtain a negative electrode material.

[0063] In some embodiments, the temperature of the carbonization treatment is 500°C to 1000°C. Specifically, it can be 500°C, 600°C, 650°C, 800°C, 950°C, 1000°C, etc., but it is not limited to the values ​​listed, and other values ​​not listed in the numerical range are also applicable. The holding time of the carbonization treatment is 30 minutes to 24 hours, specifically, it can be 30 minutes, 2 hours, 5 hours, 8 hours, 11 hours, 13 hours, 16 hours, 17 hours, 18 hours, 20 hours, 24 hours, etc., but it is not limited to the values ​​listed, and other values ​​not listed in the numerical range are also applicable.

[0064] It can be understood that controlling the carbonization treatment temperature within an appropriate range can reduce the occurrence of thermal decomposition of primary particles due to excessively high temperatures, and reduce the occurrence of insufficient carbonization of primary particles due to excessively low temperatures. The sufficient carbonization of the primary particle coating can make the primary particles more fully mixed with the solid carbon source, thereby reducing product impedance.

[0065] In some embodiments, the solid carbon source includes at least one of sugars, esters, hydrocarbons, organic acids, and high molecular weight polymers.

[0066] In some embodiments, the solid carbon source includes at least one of polyvinyl chloride, polyvinyl butyral, polyacrylonitrile, polyacrylic acid, polyethylene glycol, polypyrrole, polyaniline, sucrose, glucose, maltose, citric acid, asphalt, furfural resin, epoxy resin and phenolic resin.

[0067] In some embodiments, the mass ratio of the solid carbon source to the primary particles is 5:(5-95), specifically, it can be 5:5, 5:15, 5:35, 5:50, 5:60, 5:75, 5:95, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0068] In a third aspect, the present application provides a battery, which comprises the negative electrode material of the first aspect or the negative electrode material prepared by the preparation method of the second aspect.

[0069] In some other embodiments, the negative electrode material can be applied to lithium-ion batteries, or other electrochemical devices such as sodium-ion batteries.

[0070] Those skilled in the art will understand that the above-described method for preparing a lithium-ion battery is merely an example, and other methods commonly used in the art may be employed without departing from the disclosure of this application.

[0071] The following further illustrates the embodiments of the present invention in multiple embodiments. The embodiments of the present invention are not limited to the following specific embodiments. Within the scope of protection, appropriate changes can be made to the implementation.

[0072] Example 1

[0073] The method for preparing the negative electrode material of this embodiment includes the following steps:

[0074] (1) Place 5 g of iron nitrate powder Fe(NO3)3 and 0.8 g of nickel nitrate powder Ni(NO3)2 on the substrate of the vapor phase chemical deposition equipment, then introduce silane, control the silane flow rate to 50 scc, raise the temperature to 600°C, and after vapor deposition reaction for 1 hour, obtain primary particles.

[0075] (2) The primary particles were mixed with phenolic resin in a mass ratio of 40:43, and the mixture was placed in a high-temperature box furnace, nitrogen was introduced, and carbonized at 950°C for 2 hours. The carbonized product was crushed, sieved, and then graded to obtain a negative electrode material.

[0076] The negative electrode material prepared in this embodiment includes secondary particles, which include multiple agglomerated primary particles, and the primary particles include silicon particles doped with iron and nickel elements. The mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and the A / B ratio is 9.2.

[0077] FIG2 is a scanning electron microscope image of the negative electrode material prepared in Example 1.

[0078] FIG3 is an XRD pattern of the negative electrode material prepared in Example 1. It can be observed from the figure that characteristic peaks of silicon exist in the negative electrode material.

[0079] FIG4 is the first charge and discharge curve of the negative electrode material prepared in Example 1. As can be seen from FIG4 , the first charge and discharge capacity of the negative electrode material is relatively high, reaching 1855 mAh / g, and the first coulombic efficiency is also relatively high.

[0080] FIG5 is a cycle performance curve of the negative electrode material prepared in Example 1. As can be seen from FIG5 , the capacity retention rate of the negative electrode material after 100 cycles is 94.2%, and the negative electrode material has excellent cycle performance.

[0081] Example 2

[0082] The method for preparing the negative electrode material of this embodiment includes the following steps:

[0083] (1) Silicon tetrachloride, ferric chloride solution, and nickel chloride solution were added to a reaction kettle and mixed. Then, magnesium powder was added. The mass ratio of silicon tetrachloride: magnesium: ferric chloride: nickel chloride was 100: 28.5: 0.5: 0.03. The reaction kettle was heated to 300°C in a sealed state and subjected to a reduction reaction for 15 hours to obtain primary particles. Primary particles with an A / B ratio of 14.4 were obtained.

[0084] (2) The primary particles were mixed with sucrose in a mass ratio of 55:69, and the mixture was placed in a high-temperature box furnace, nitrogen was introduced, and carbonized at 920°C for 4 hours. The carbonized product was crushed, sieved, and then graded to obtain a negative electrode material.

[0085] The negative electrode material prepared in this embodiment includes secondary particles, which include multiple agglomerated primary particles, and the primary particles include silicon particles doped with iron and nickel elements. The mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and the A / B ratio is 14.4.

[0086] Example 3

[0087] (1) Silica nanoparticles, metallic aluminum powder, and mixed asphalt were added to a reactor, wherein the mass ratio of silica nanoparticles: metallic aluminum: mixed asphalt was 180:25:110. 0.6 g of ferric chloride and 0.1 g of nickel chloride were then added. The mixture was heated to 950°C under an argon atmosphere and reacted for 12 hours. After cooling, the product was immersed in an acid solution for washing and dried to obtain primary particles. The primary particles contained an A / B ratio of 9.6.

[0088] (2) The primary particles were mixed with phenolic resin in a mass ratio of 50:65, and the mixture was placed in a high-temperature box furnace, nitrogen was introduced, and carbonized at 980°C for 5 hours. The carbonized product was crushed, sieved, and then graded to obtain a negative electrode material.

[0089] The negative electrode material prepared in this embodiment includes secondary particles, which include multiple agglomerated primary particles, and the primary particles include silicon particles doped with iron and nickel elements. The mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and the A / B ratio is 9.6.

[0090] Example 4

[0091] (1) Place 9 g of iron nitrate powder Fe(NO3)3 and 1.8 g of nickel nitrate powder Ni(NO3)2 on the substrate of the vapor phase chemical deposition equipment, then introduce silane and acetylene gas, control the volume ratio of silane and acetylene to be 25:1, and the flow rate of silane and acetylene to be 60 scc. Heat to 700 ° C, and vapor deposition reaction for 3 hours to obtain primary particles.

[0092] (2) The primary particles were mixed with phenolic resin in a mass ratio of 30:45, and the mixture was placed in a high-temperature box furnace, nitrogen was introduced, and carbonized at 820°C for 4 hours. The carbonized product was crushed, sieved, and then graded to obtain a negative electrode material.

[0093] The negative electrode material prepared in this embodiment includes secondary particles, which include multiple agglomerated primary particles. The negative electrode material also includes carbon material located on at least part of the surface of the secondary particles and the primary particles; the primary particles include silicon particles doped with iron and nickel elements, wherein the mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and the A / B ratio is 10.6.

[0094] Example 5

[0095] (1) Add trichlorosilane solution to a reactor, then add fructose solution and metallic zinc powder in equal volume ratios, wherein the mass ratio of trichlorosilane: metallic zinc powder: fructose is 100:29.5:11.4, then add 1.6 g of ferric chloride and 0.3 g of nickel chloride, heat to 350 ° C in a sealed state, react for 15 h, and obtain primary particles after centrifugal drying.

[0096] (2) The primary particles were mixed with sucrose in a mass ratio of 20:45, and the mixture was placed in a high-temperature box furnace, nitrogen was introduced, and carbonized at 950°C for 2 hours. The carbonized product was crushed, sieved, and then graded to obtain a negative electrode material.

[0097] The negative electrode material prepared in this embodiment includes secondary particles, which include multiple agglomerated primary particles. The negative electrode material also includes carbon material located on at least part of the surface of the secondary particles and the primary particles; the primary particles include silicon particles doped with iron and nickel elements, wherein the mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and the A / B ratio is 19.

[0098] Example 6

[0099] (1) 400 g of commercial SiO particles were used as raw materials, and then 1 g of iron nitrate Fe(NO3)3 and 0.1 g of nickel nitrate powder Ni(NO3)2 were added. The mixture was ground under a nitrogen atmosphere at a speed of 400 rpm for 6 h to obtain primary particles.

[0100] (2) The primary particles were mixed with phenolic resin in a mass ratio of 40:33, and the mixture was placed in a high-temperature box furnace, nitrogen was introduced, and carbonized at 950°C for 2 hours. The carbonized product was crushed, sieved, and then graded to obtain a negative electrode material.

[0101] The negative electrode material prepared in this embodiment includes secondary particles, which include multiple agglomerated primary particles, and the primary particles include silicon particles doped with iron and nickel elements. The mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and the A / B ratio is 9.9.

[0102] Example 7

[0103] (1) 600 g of commercial LiSi particles were used as raw materials, and then 1 g of iron nitrate Fe(NO3)3 and 0.09 g of nickel nitrate powder Ni(NO3)2 were added. The mixture was ground under an argon atmosphere at a speed of 450 rpm for 5 h to obtain primary particles.

[0104] (2) The primary particles were mixed with polyvinyl alcohol in a mass ratio of 50:56, and the mixture was placed in a high-temperature box furnace, nitrogen was introduced, and carbonized at 850°C for 6 hours. The carbonized product was crushed, sieved, and then graded to obtain a negative electrode material.

[0105] The negative electrode material prepared in this embodiment includes secondary particles, which include multiple agglomerated primary particles, and the primary particles include silicon particles doped with iron and nickel elements. The mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and the A / B ratio is 9.3.

[0106] Comparative Example 1

[0107] The difference from Example 1 is that the negative electrode material is obtained without the coating treatment in step (2).

[0108] The negative electrode material prepared in this comparative example includes primary particles, and the primary particles include active materials doped with iron and nickel elements.

[0109] Comparative Example 2

[0110] The difference from Example 1 is that:

[0111] (1) Place 0.5 g of iron nitrate powder and 0.32 g of nickel nitrate powder on a substrate of a vapor phase chemical deposition device, then introduce silane at a flow rate of 50 scc, raise the temperature to 600°C, and react for 1 hour to obtain primary particles.

[0112] The negative electrode material prepared in this embodiment includes primary particles, which include silicon particles doped with iron and nickel. The mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and the A / B ratio is 9.0.

[0113] Comparative Example 3

[0114] The difference from Example 1 is that:

[0115] (1) Place 12 g of iron nitrate powder and 1 g of nickel nitrate powder on a CVD device substrate, then introduce silane at a flow rate of 50 scc, raise the temperature to 600°C, and react for 1 hour to obtain primary particles.

[0116] The negative electrode material prepared in this embodiment includes primary particles, which include silicon particles doped with iron and nickel. The mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and the A / B ratio is 21.2.

[0117] Comparative Example 4

[0118] The difference from Example 1 is that the doping of Fe and Ni in step (1) is not performed to obtain the negative electrode material.

[0119] The negative electrode material prepared in this embodiment includes secondary particles, wherein the secondary particles include a plurality of agglomerated primary particles, and the primary particles include silicon particles.

[0120] Comparative Example 5

[0121] The difference from Example 1 is: 17.2g of iron nitrate powder Fe(NO3)3 is placed on the substrate of the vapor chemical deposition equipment, and then silane is introduced, the silane flow rate is controlled to 50scc, the temperature is raised to 600℃, and after the vapor deposition reaction for 1h, primary particles are obtained.

[0122] The negative electrode material prepared in this embodiment includes secondary particles, which include multiple agglomerated primary particles, and the primary particles include silicon particles. The mass content of iron in the negative electrode material is Appm, the mass content of nickel in the negative electrode material is Bppm, and the A / B ratio is 82.

[0123] Comparative Example 6

[0124] The difference from Example 1 is that: 0.8g of nickel nitrate powder Ni(NO3)2 is placed on the substrate of the vapor chemical deposition equipment, and then silane is introduced, the silane flow rate is controlled to 50scc, the temperature is raised to 600℃, and after the vapor deposition reaction for 1h, primary particles are obtained.

[0125] The negative electrode material prepared in this embodiment includes secondary particles, which include multiple agglomerated primary particles, and the primary particles include silicon particles. The mass content of iron element in the negative electrode material is Appm, the mass content of nickel element in the negative electrode material is Bppm, and the A / B ratio is 0.06.

[0126] Test method:

[0127] (1) Test of the mass content of iron and nickel in the negative electrode material:

[0128] The ICP method is used to test the Fe and Ni content in the particles, and the standard is GB / T38823-2020.

[0129] (2) Particle size of primary particles:

[0130] Set the SEM image to 50K magnification and use Nano Measure software to measure the size of 200 particles in the SEM image. Calculate the average particle size of these 200 particles as D1, and the maximum value among the 200 particles as the maximum primary particle size, D2. Repeat the measurement for at least 10 SEM images and calculate the mean of the averages. The maximum primary particle size is the maximum value of the particles in the 10 SEM images. The average primary particle size is (D1 + D2 + ... + D10) / 10 of the 10 statistical average particle sizes.

[0131] (3) Specific surface area of ​​negative electrode material:

[0132] The dynamic specific surface area rapid tester JW-DX of Beijing Jingwei Gaobo Science and Technology Co., Ltd. was used for testing. The unit is m 2 / g.

[0133] (4) Median particle size of negative electrode material:

[0134] The particle size distribution range of the negative electrode material was tested by Malvern laser particle size analyzer.

[0135] (5) Test of the mass content of oxygen in the negative electrode material:

[0136] The oxygen content of the negative electrode material was tested using an oxygen content tester in accordance with ISO 17053:2005.

[0137] (6) Compressive hardness test of negative electrode materials:

[0138] The compressive hardness was tested by a nanoindenter using a load of 0.6N and an indentation depth of 0.5μm.

[0139] (7) Electrochemical performance test

[0140] The negative electrode materials prepared in the examples and comparative examples were dissolved in N-methylpyrrolidone at a mass ratio of 94:1:5, carboxymethyl cellulose, and styrene-butadiene rubber, respectively, to a solid content of 50%. The materials were then coated onto a copper foil current collector and vacuum-dried to produce negative electrode plates. A metal lithium plate was used as the counter electrode, and a 1 mol / L LiPF6 / (ethylene carbonate + dimethyl carbonate + ethyl methyl carbonate) (v / v = 1:1:1) electrolyte, Celgard 2400 separator, and housing were assembled using conventional production processes into 18650 cylindrical single cells to form cylindrical batteries. The charge and discharge tests of the cylindrical batteries were conducted on the LAND battery testing system of Wuhan Jinnuo Electronics Co., Ltd. at room temperature, with a constant current of 0.2C and a charge and discharge voltage limit of 2.75 to 4.2V. The initial thickness of the lithium-ion battery plate was measured as H0 using a micrometer. The battery was cycled to obtain the first reversible specific capacity, first cycle charge capacity, and first cycle discharge capacity. First coulombic efficiency = first cycle discharge capacity / first cycle charge capacity.

[0141] The results of the above performance tests are as follows:

[0142] Table 1. Performance parameters of negative electrode materials and batteries prepared in various examples and comparative examples

[0143] As can be seen from Table 1, the test data of Examples 1 to 7 show that by adding an appropriate amount of iron and nickel elements to nano-silicon, the hardness of nano-silicon is strengthened, the volume expansion of the negative electrode material including nano-silicon can be effectively alleviated, the structural stability of the negative electrode material can be enhanced, and the cycle life of the battery prepared by the negative electrode material can be improved, so that the obtained negative electrode material has good electronic conductivity and electrochemical properties.

[0144] The active material in Example 6 is silicon oxide SiO, which has a relatively low theoretical capacity. Therefore, the first reversible capacity and first coulombic efficiency of the prepared negative electrode material are relatively reduced. However, due to the addition of appropriate amounts of iron and nickel elements, the hardness of the negative electrode material is enhanced, which can effectively alleviate the volume expansion of the negative electrode material during the lithium insertion and deintercalation process, enhance the structural stability of the negative electrode material, and improve the cycle life of the battery prepared with the negative electrode material.

[0145] Comparative Example 1 Compared with Example 1, in the process of preparing the graphite negative electrode material, the primary particles were not coated, the performance of the product was difficult to improve, and the first coulombic efficiency and cycle performance of the battery were reduced. It can be seen from this that the coated carbon material can, on the one hand, reduce the electrolyte from entering the internal side reactions that lead to a decrease in the first coulombic efficiency, and on the other hand, it can alleviate the volume expansion of silicon by synergistically doping the primary particles with iron and nickel elements, reduce the volume expansion of the entire composite negative electrode material, reduce the swelling of the electrode sheet, and thus improve the cycle stability of the battery prepared by the negative electrode material.

[0146] Compared with Example 1, the ratio of the doped iron and nickel contents (i.e., A / B) in Comparative Examples 2 and 3 is outside the scope of this application, and the cycle performance of the batteries prepared with the negative electrode materials is reduced. In addition, too little doping with iron and nickel has a weak effect on the volume expansion of the primary particles and cannot effectively alleviate the volume expansion of the negative electrode material caused by silicon during lithium insertion and extraction. Excessive doping with iron and nickel, due to their inherent magnetic properties, will have an adverse effect on the negative electrode material and will not alleviate the volume expansion of the negative electrode material.

[0147] Compared with Example 1, in Comparative Example 4, the compressive hardness of the primary particles of the negative electrode material is greatly reduced without doping with iron and nickel elements. During the charge and discharge cycle, the volume expansion stress of the negative electrode material particles during the lithium insertion and deintercalation process easily causes the particles to break, and the cycle stability of the battery prepared with the negative electrode material is reduced.

[0148] Compared with Example 1, in Comparative Example 5, only ferric nitrate was added, resulting in an excessively large A / B ratio in the final negative electrode material. That is, too much iron was added, and the magnetism of iron would have a greater impact on the negative electrode material, which is not conducive to the cycle stability of the negative electrode material.

[0149] Compared with Example 1, in Comparative Example 6, only nickel nitrate was added. The volume expansion effect of the nickel element was obvious in the heated state, which led to the aggravated volume expansion of the active material. Compared with the synergistic effect of the nickel element and the iron element, the expansion inhibition effect brought by the single nickel element was poor, which was not conducive to the cycle stability of the negative electrode material.

[0150] The applicant declares that while the above-mentioned embodiments are used to illustrate the detailed process equipment and process flow of the present application, the present application is not limited to the above-mentioned detailed process equipment and process flow, which does not mean that the present application must rely on the above-mentioned detailed process equipment and process flow in order to be implemented. Those skilled in the art should understand that any improvements to the present application, equivalent replacements for the raw materials of the present application's products, addition of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present application.

Claims

1. A negative electrode material, characterized in that: The negative electrode material includes secondary particles, the secondary particles include a plurality of agglomerated primary particles, and the primary particles include active substances doped with iron and nickel elements; wherein the mass content of the iron element in the negative electrode material is A ppm, the mass content of the nickel element in the negative electrode material is B ppm, and 9.2≤A / B≤20.

2. The negative electrode material according to claim 1, characterized in that The total mass content of the iron element and the nickel element in the negative electrode material is less than 1%.

3. The negative electrode material according to claim 2, characterized in that The negative electrode material satisfies at least one of the following characteristics: (1) The mass content of the iron element in the negative electrode material is A ppm, 0.1≤A≤1000; (2) The mass content of the nickel element in the negative electrode material is B ppm, 0.1≤B≤500.

4. The negative electrode material according to claim 1, characterized in that The compressive hardness of the negative electrode material is ≥100Mpa.

5. The negative electrode material according to claim 1, characterized in that The negative electrode material satisfies at least one of the following characteristics: (1) The active material comprises a silicon-based material; (2) The active material includes a silicon-based material, and the silicon-based material includes at least one of crystalline silicon, amorphous silicon, silicon oxide, silicon alloy, and a composite of crystalline silicon and amorphous silicon.

6. The negative electrode material according to claim 1, characterized in that The negative electrode material satisfies at least one of the following characteristics: (1) The average particle size D of the primary particles 50 1nm~500nm; (2) The particle size of the primary particles satisfies the following relationship: (D 100 -D 10 ) / D 50 ≥1.

5.

7. The negative electrode material according to any one of claims 1 to 6, characterized in that The active material comprises a silicon-based material, the silicon-based material is further doped with oxygen, and the mass content of the oxygen element in the negative electrode material is 0.1% to 18%.

8. The negative electrode material according to any one of claims 1 to 6, characterized in that: The negative electrode material further includes a carbon material located on at least a portion of the surface of the secondary particles and / or the primary particles.

9. The negative electrode material according to any one of claims 1 to 6, characterized in that: The specific surface area of ​​the negative electrode material is 0.1 m 2 / g~5m 2 / g.

10. The negative electrode material according to any one of claims 1 to 6, characterized in that: The median particle size of the negative electrode material is 0.5 μm to 30 μm.

11. A method for preparing a negative electrode material, characterized in that: The following steps are involved: A mixture containing a silicon source precursor, an iron dopant and a nickel dopant is heat-treated to obtain primary particles doped with iron and nickel; the primary particles are coated to obtain the negative electrode material, wherein the mass content of the iron element in the negative electrode material is A ppm, the mass content of the nickel element in the negative electrode material is B ppm, and 9.2≤A / B≤20.

12. The preparation method according to claim 11, characterized in that: The iron dopant comprises at least one of iron powder, ferric nitrate, nickel nitrate, ferrous lactate, ferric citrate, ferrous hematemesis, ferric glycinate and ferrocene; and / or, The nickel dopant includes at least one of nickel oleate, nickel propionate, nickel butyrate, nickel octanoate, nickel lactate, nickel benzoate, bis(acetylacetonate)nickel, nickel salicylate and alkylphenylsalicylate nickel.

13. The preparation method according to claim 11, characterized in that: The step of heat treating a mixture containing a silicon source precursor, an iron dopant and a nickel dopant comprises: forming primary particles from a gas phase silicon source precursor by a vapor deposition method, and doping metal vapor generated by the iron dopant and the nickel dopant into the primary particles; wherein the mass ratio of the iron dopant to the nickel dopant is 0.1 to 30.

14. The preparation method according to claim 11, characterized in that: The step of heat treating a mixture containing a silicon source precursor, an iron dopant and a nickel dopant comprises: adding a metal reducing agent to a mixed liquid containing a liquid silicon source precursor, an iron dopant and a nickel dopant, and heat treating the mixture obtained by solid-liquid separation to obtain primary particles doped with nickel and iron; wherein the mass ratio of the liquid silicon source precursor, the iron dopant, the nickel dopant and the metal reducing agent is (40-100):(0.01-1):(0.05-1):(0.01-5).

15. A battery, characterized in that: The battery comprises the negative electrode material according to any one of claims 1 to 11 or the negative electrode material prepared by the method for preparing the negative electrode material according to any one of claims 12 to 14.

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