Iron-silicon composite negative electrode material applied to lithium ion battery as well as preparation method and application of iron-silicon composite negative electrode material

Abstract

The invention provides an iron-silicon composite negative electrode material applied to a lithium ion battery and a preparation method and application of the iron-silicon composite negative electrode material, the iron-silicon composite negative electrode material is prepared from an iron source and a silicon source, the silicon source is mortar waste, and the molar ratio of the silicon element in the silicon source to the iron element in the iron source is (0.5-5): 1. Compared with the prior art, the method has the advantages that the low-cost mortar waste in the photovoltaic industry is used as a raw material and is converted into the iron-silicon composite negative electrode material by designing a synthetic route, so that the full utilization of the waste in the photovoltaic or semiconductor industry is realized, the resource utilization rate is increased, the economic benefit is great, and the production cost is reduced by regulating and controlling the feeding ratio of the silicon source to the iron source. The proportion of the components in the product can be regulated and controlled, and balance optimization of the conductivity, the volume stability and the capacity of the material is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy materials, and in particular to an iron-silicon composite negative electrode material for lithium-ion batteries, a preparation method thereof, and applications thereof. Background Art

[0002] With the increasingly serious energy crisis and environmental pollution problems, the development of clean energy and efficient energy storage technology has become the focus of today's society. Among various energy storage devices, lithium-ion batteries have been widely used in portable electronic devices, electric vehicles and large-scale energy storage systems due to their high energy density, long cycle life and environmental friendliness. Lithium-ion batteries are mainly composed of four core components: positive electrode, negative electrode, electrolyte and separator. Among them, the negative electrode material, which is the main body of lithium ion insertion / extraction, has a theoretical capacity and actual performance that directly determines the energy density and cycle life of the battery. The theoretical capacity of the graphite negative electrode, which currently dominates the market, is 372mAh g -1 The actual capacity in practical applications has also approached this theoretical limit, making it difficult to meet the future development needs of high energy density lithium-ion batteries. Therefore, the development of new negative electrode materials with high specific capacity and long cycle life has become an important direction in lithium-ion battery research.

[0003] Silicon-based anode materials have attracted widespread attention due to their unique advantages. First, the theoretical specific capacity of silicon is as high as 4200 mAh g -1 (Forming Li 22 Si5), which is more than 10 times that of traditional graphite negative electrode; secondly, the lithium deintercalation potential of silicon is low (about 0.4V vs.Li / Li + ), which helps maintain the battery's operating voltage. Silicon is also abundant, relatively low-cost, and environmentally friendly. However, silicon-based anode materials face significant challenges in practical applications: volume changes of over 300% during lithiation / delithiation can lead to pulverization of the active material and destruction of the electrode structure. Furthermore, the interface between silicon and the electrolyte is continuously exposed, forming a new solid electrolyte interphase (SEI) film, which consumes significant amounts of electrolyte and lithium ions, reducing the battery's coulombic efficiency and cycle life.

[0004] CN114864918A discloses a high performance Si-Fe x Si y The preparation method of the negative electrode material of lithium ion battery comprises weighing an iron source, a carbon source and a silicon source, mixing the iron source and carbon source dispersion with the silicon source dispersion according to the Fe:Si molar ratio of 1:3, and calcining the precipitate in one step to obtain Si-Fe x Si y Negative electrode material, but this Si-Fe x Si y The silicon source of the negative electrode material is nano-silicon powder, which is relatively expensive. Summary of the Invention

[0005] The purpose of the present invention is to solve the above problems and provide an iron-silicon composite negative electrode material for lithium-ion batteries, its preparation method and application. The present invention uses silicon cutting waste (mortar waste) from the photovoltaic industry as the silicon source, introduces iron elements into silicon-based materials, and constructs a multi-phase synergistic iron-silicon composite negative electrode material through a composite strategy, thereby solving the problems of poor conductivity, severe volume expansion, poor electrochemical cycle stability, and high cost of silicon-based negative electrode materials.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The first object of the present invention is to provide an iron-silicon composite negative electrode material for lithium-ion batteries, wherein the iron-silicon composite negative electrode material is prepared by an iron source and a silicon source, wherein the silicon source is mortar waste, and the molar ratio of the silicon element in the silicon source to the iron element in the iron source is (0.5-5):1.

[0008] Further preferably, the molar ratio of the silicon element in the silicon source to the iron element in the iron source is (0.5-2):1.

[0009] Furthermore, the mortar waste is the mortar waste left after cutting single crystal silicon wafers in the photovoltaic industry.

[0010] Furthermore, the iron source is ferric chloride hexahydrate.

[0011] Furthermore, the iron source is iron oleate.

[0012] Further preferably, the mortar waste is a micron-sized flake material with a thickness of 5-50 nm and a silicon content of more than 90 wt%.

[0013] Furthermore, by controlling the feeding ratio of the iron source and the silicon source, a high-capacity or high-rate iron-silicon composite negative electrode material can be obtained.

[0014] Furthermore, when the molar ratio of the silicon element in the silicon source to the iron element in the iron source is 1:2, a high-capacity iron-silicon composite negative electrode material is obtained.

[0015] Furthermore, at a rate of 0.1C, the capacity of the high-capacity iron-silicon composite negative electrode material stabilized at 774 mAh g after 10 cycles. -1 .

[0016] Furthermore, when the molar ratio of the silicon element in the silicon source to the iron element in the iron source is 2:1, a high-rate iron-silicon composite negative electrode material is obtained.

[0017] Furthermore, the high-rate iron-silicon composite negative electrode material maintains 366 mAh g at a current of 1.6 C. -1capacity, and after recovering 0.1C, the capacity remained above 94% of the original.

[0018] A second object of the present invention is to provide a method for preparing an iron-silicon composite negative electrode material for lithium-ion batteries, the method comprising the following steps:

[0019] (1) dissolving ferric chloride hexahydrate in a first solvent to obtain a ferric chloride solution;

[0020] (2) dissolving sodium oleate in a second solvent to obtain a sodium oleate solution;

[0021] (3) adding the sodium oleate solution obtained in step (2) to the mortar waste and continuously stirring the dispersion;

[0022] (4) During the continuous stirring process of step (3), the ferric chloride solution obtained in step (1) is added to the dispersion in step (3). After all the ferric chloride solution is added, stirring is continued to obtain a dispersion after the reaction;

[0023] (5) evaporating and removing the solvent in the dispersion obtained after the reaction in step (4) to obtain a solid-phase precursor;

[0024] (6) calcining the solid-phase precursor obtained in step (5), cooling naturally to room temperature after calcination, washing and drying the obtained solid to obtain the iron-silicon composite negative electrode material.

[0025] Furthermore, in step (1), the first solvent is methanol;

[0026] In step (1), the concentration of the ferric chloride solution is 0.1-2 mol L -1 .

[0027] Furthermore, the molar ratio of sodium oleate in step (2) to ferric chloride hexahydrate in step (1) is (1-5):1;

[0028] In step (2), the second solvent is a mixed solvent of methanol and n-hexane, and the volume ratio of methanol to n-hexanol in the mixed solvent is 5:1-1:5;

[0029] In step (2), the concentration of the sodium oleate solution is 0.08 to 0.42 mol L -1 .

[0030] Furthermore, the molar ratio of silicon in the mortar waste in step (3) to iron in the ferric chloride hexahydrate in step (1) is (0.5-5):1;

[0031] In step (3), the conditions for continuous stirring are: stirring temperature of 40-60°C, and rotation speed of 200-600 rpm, that is, stirring at 40-60°C and a rotation speed of 200-600 rpm.

[0032] Furthermore, in step (4), the ferric chloride solution obtained in step (1) is added dropwise to the dispersion in step (3);

[0033] In step (4), the stirring time of the continued stirring is 20-60 minutes, and the temperature and speed of the continued stirring are the same as those of the continuous stirring in step (3).

[0034] Furthermore, in step (5), the system temperature during evaporation is 60-90°C.

[0035] Furthermore, in step (6), the calcination is carried out under atmosphere protection, and the atmosphere is any one or more of argon, nitrogen, and 5% H2 / Ar mixed gas;

[0036] In step (6), the heating rate of the calcination is 2-10°C min -1 , calcination temperature is 550-950℃, holding time is 1-5 hours;

[0037] In step (6), the washing is performed with water;

[0038] In step (6), the drying temperature is 50-80°C.

[0039] The third object of the present invention is to provide a lithium-ion battery negative electrode, wherein the battery negative electrode is prepared using the iron-silicon composite negative electrode material, or the battery negative electrode contains the iron-silicon composite negative electrode material.

[0040] Furthermore, the lithium-ion battery includes a positive electrode material, a negative electrode material, an electrolyte and a separator; the negative electrode material includes the iron-silicon composite negative electrode material.

[0041] A fourth object of the present invention is to provide an application of an iron-silicon composite negative electrode material for lithium-ion batteries, wherein the iron-silicon composite negative electrode material is used in lithium-ion batteries.

[0042] Furthermore, high-capacity iron-silicon composite negative electrode materials are used in application scenarios with high energy density requirements, such as electric vehicles, aerospace and other application scenarios.

[0043] Furthermore, high-rate iron-silicon composite negative electrode materials are used in fast-charging devices.

[0044] The technical concept of the present invention is as follows:

[0045] To address the problems of poor conductivity, severe volume expansion, poor electrochemical cycle stability, and high cost of existing silicon-based negative electrode materials, the present invention introduces iron into the silicon-based negative electrode material to enhance the material's conductivity and improve the composite material's carrier transport and diffusion capabilities. Simultaneously, through a chemical reaction process, pores are created within the material to accommodate the enormous volume expansion during lithium insertion and extraction. Furthermore, the introduction of iron enhances interfacial bonding through metallic bonds, inhibits silicon particle pulverization, and catalyzes the formation of a graphite-like structure in the carbon element during the reaction, ultimately achieving the goal of optimizing material performance and increasing electrochemical lithium storage capacity. Using low-cost photovoltaic industry mortar waste as a high-purity silicon source can significantly reduce costs and lower the actual application price of negative electrode materials.

[0046] The present invention uses silicon cutting waste from the photovoltaic industry as a silicon source, introduces iron elements into silicon-based materials, and constructs a multi-phase synergistic iron-silicon composite negative electrode material through a composite strategy. Photovoltaic silicon waste has a nano-scale lamellar structure and high purity characteristics. Its two-dimensional skeleton can provide a fast channel for lithium ion transmission, while reducing the cost of silicon source. The introduction of iron elements optimizes material properties through multiple mechanisms: first, the silicate network of ferrous silicate can inhibit the expansion of silicon particles through strong Si-O bonds, and its intracrystalline cavity structure can effectively accommodate the volume change caused by lithium embedding; second, iron carbide acts as a conductive skeleton to enhance the electronic conductivity of the composite material and shorten the lithium ion diffusion path; third, the formation of iron-silicon alloys can enhance the interfacial bonding force through metallic bonds and inhibit the pulverization of silicon particles. In addition, the synergistic effect of silicon crystals and iron-based phases can induce a uniform distribution of lithium ions, reduce local stress concentration, and the iron element can catalyze the carbon element in the reaction to form a graphite-like structure, thereby improving the stability of the material.

[0047] Compared with the prior art, the present invention has the following characteristics:

[0048] 1) The iron-silicon composite negative electrode material for lithium-ion batteries provided by the present invention, as well as its preparation method and application, uses low-cost photovoltaic industry mortar waste as raw material. By designing a synthesis route, it is converted into an iron-silicon composite negative electrode material, thereby fully utilizing waste from the photovoltaic or semiconductor industry, improving resource utilization, and having great economic benefits.

[0049] 2) The iron-silicon composite negative electrode material for lithium-ion batteries provided by the present invention, as well as its preparation method and application, can adjust the proportion of components in the product by regulating the feed ratio of silicon source and iron source, thereby achieving balanced optimization of the material's conductivity, volume stability and capacity.

[0050] 3) The iron-silicon composite negative electrode material for lithium-ion batteries provided by the present invention, and its preparation method and application, prepared with a high-capacity guided ratio (Fe / Si=2): at a rate of 0.1C, after 10 cycles, it stabilized at 774 mAh g -1The capacity is suitable for applications with high energy density requirements. Its advantage comes from the Fe 2+ The uniform distribution of sites brings about reversible lithiation reaction activity, and the outer layer graphite-like structure brings about stability.

[0051] 4) The iron-silicon composite negative electrode material for lithium-ion batteries provided by the present invention, its preparation method and application, the prepared high-rate guide ratio (Fe / Si=0.5): it can still maintain 366mAh g at a high current of 1.6C. -1 The capacity can be maintained at more than 94% of the original capacity after recovering to 0.1C, meeting the needs of fast charging equipment. This is attributed to the promotion of lithium ion migration by the three-dimensional conductive network constructed by the iron-rich phase.

[0052] 5) The iron-silicon composite negative electrode material for lithium-ion batteries provided by the present invention, as well as its preparation method and application, does not require a long-term high-temperature reaction and avoids the use of dangerous gases such as acetylene, and is relatively energy-saving and safe. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 These are characterization diagrams of mortar waste from the photovoltaic industry, (ab) are scanning electron microscope images of mortar waste from the photovoltaic industry; (c) is the XRD spectrum of mortar waste from the photovoltaic industry.

[0054] Figure 2 This is the XRD pattern of the iron-silicon composite negative electrode material obtained under different feed ratios.

[0055] Figure 3 1 is a scanning electron microscope image of the iron-silicon composite negative electrode material prepared in Example 1 at different magnifications.

[0056] Figure 4 The iron-silicon composite negative electrode material prepared in Example 1 is 0.4Ag -1 Cycling performance diagram at different current densities.

[0057] Figure 5 1 is a scanning electron microscope image of the iron-silicon composite negative electrode material prepared in Example 2 at different magnifications.

[0058] Figure 6 This is a rate performance diagram of the iron-silicon composite negative electrode material prepared in Example 2 at different current densities. DETAILED DESCRIPTION

[0059] The present invention is described in detail below with reference to specific embodiments, but is by no means intended to limit the present invention. Any features, such as preparation methods, materials, structures, or composition ratios, that are not explicitly described in this technical solution are considered to be common technical features disclosed in the prior art.

[0060] The present invention provides a method for preparing an iron-silicon composite negative electrode material based on the above-mentioned silicon-based negative electrode material, comprising the following steps:

[0061] (1) Weigh a certain amount of ferric chloride hexahydrate and dissolve it in 5 mL of methanol solvent, stirring to fully dissolve it to obtain a ferric chloride solution;

[0062] (2) Sodium oleate was weighed at a molar ratio of ferric chloride to sodium oleate of 1:(1-5) and dissolved in 60 mL of a mixed solvent of methanol and n-hexane to obtain a sodium oleate solution;

[0063] (3) The molar ratio of silicon to iron is (0.5-5):1. Weigh the corresponding amount of mortar waste, add the sodium oleate solution obtained in step (2), and stir at 40-60°C and 200-600 rpm to uniformly disperse the mortar powder in the solution;

[0064] (4) While continuing to stir, the ferric chloride solution obtained in step (1) is added dropwise to the dispersion obtained in step (3). After all the ferric chloride solution is added, stirring is continued for 20-60 minutes while maintaining the temperature and speed to allow the reaction to proceed fully;

[0065] (5) After the reaction is completed, the system temperature is raised to 60-90°C, and all the solvent is evaporated to obtain a solid-phase precursor;

[0066] (6) Transfer the precursor to a porcelain ark and heat it at 2-10℃min under atmosphere protection. -1 The temperature is raised to 550-950°C at a heating rate and kept at this temperature for 1-5 hours. After that, the mixture is naturally cooled to room temperature. The obtained solid is washed with deionized water to remove impurities and dried in a vacuum oven at 50-80°C to finally obtain an iron-silicon composite negative electrode material.

[0067] According to the above preparation method, preferably, in step (1), the concentration of the ferric chloride solution is 0.1-2 mol L -1 .

[0068] According to the above preparation method, preferably, in step (2), the molar ratio of sodium oleate to ferric chloride is (1-5):1.

[0069] According to the above preparation method, preferably, in step (2), the volume ratio of methanol to n-hexanol in the mixed solvent is 5:1-1:5.

[0070] According to the above preparation method, preferably, in step (3), the molar ratio of the added amount of the mortar to the iron oleate is (0.5-5):1.

[0071] According to the above preparation method, preferably, in step (3), the stirring temperature is 40-60° C. and the rotation speed is 200-600 rpm.

[0072] According to the above preparation method, preferably, in step (4), the stirring time is 20-60 minutes.

[0073] According to the above preparation method, preferably, in step (5), the system temperature during evaporation of the solvent is 60-90°C.

[0074] According to the above preparation method, preferably, in step (6), the atmosphere is any one of argon, nitrogen, and 5% H2 / Ar mixed gas.

[0075] According to the above preparation method, preferably, in step (6), the calcination heating rate is 2-10°C min -1 The calcination temperature is 550-950℃ and the holding time is 1-5 hours.

[0076] According to the above preparation method, preferably, in step (6), the drying temperature is 50-80°C.

[0077] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0078] The field emission electron microscopy (SEM) measurements in the examples were performed using a JSM-7401F (JEOL, Japan) field emission scanning electron microscope (SEM). The X-ray diffraction (XRD) characterizations were performed using a Bruker D8 ADVANCE X-ray powder diffractometer operating at Cu Kα, 40 kV, and 30 mA.

[0079] Lithium-ion batteries were assembled and tested using the following method.

[0080] Battery Assembly: The electrochemical lithium storage performance of the material was tested using CR2016 button cells. 70% iron-silicon composite anode material, 15% acetylene black, and 15% polyacrylic acid binder (commercially available) were weighed and mixed in a small beaker for 8 hours to obtain a uniformly mixed anode slurry. The anode slurry was evenly coated onto copper foil and dried in a 60°C oven. After drying, the anode sheets were pressed and punched to produce 12 mm diameter anode sheets. The dried and weighed anode sheets were immediately transferred to an argon-filled glove box (oxygen <5 ppm, water <1 ppm) for assembly. A CR2016 button cell was constructed using a lithium metal sheet as the counter electrode, a 1M LiPF4 electrolyte in a 1:1 ratio of EC:DEC (with 10% by weight of FEC), a Whatman GF / A separator, and a nickel foam sheet as the filler.

[0081] Charge and discharge test: The charge and discharge test was performed on the Xinwei battery test system, which was set to constant current-constant voltage charge and discharge. The current density was set as the set value, and the charge and discharge voltage range was set to 0.01-1.5V.

[0082] Example 1

[0083] This embodiment provides a method for preparing an iron-silicon composite negative electrode material, comprising the following steps:

[0084] (1) Weigh 5 mmol of ferric chloride hexahydrate and dissolve it in 5 mL of methanol solvent, stirring until it is fully dissolved to obtain a ferric chloride solution;

[0085] (2) Weigh 15 mmol of sodium oleate and dissolve it in a mixed solvent consisting of 30 mL of methanol and 30 mL of n-hexane to obtain a sodium oleate solution;

[0086] (3) Weigh 2.5 mmol (in terms of silicon element) of mortar waste, add the sodium oleate solution obtained in step (2), and continue stirring at 400 rpm at 50° C. to uniformly disperse the mortar powder in the solution;

[0087] (4) During the continuous stirring process of step (3), the ferric chloride solution obtained in step (1) is added dropwise to the dispersion obtained in step (3). After all the ferric chloride solution is added, the temperature and speed are maintained and stirring is continued for 30 minutes to allow the reaction to proceed fully;

[0088] (5) After the reaction is completed, the system temperature is raised to 70°C, and all the solvent is evaporated to obtain a solid-phase precursor;

[0089] (6) The precursor obtained in step (5) was transferred to a porcelain ark and heated at 5°C min under nitrogen atmosphere. -1The temperature was raised to 750°C at a heating rate and kept at this temperature for 2 hours. After that, the mixture was naturally cooled to room temperature. The obtained solid was washed with deionized water to remove impurities and dried in a vacuum oven at 60°C to finally obtain an iron-silicon composite negative electrode material.

[0090] Figure 2 The XRD pattern of the iron-silicon composite negative electrode material prepared according to the method of Example 1 is Fe:Si=2:1, in which the main corresponding substances are ferrous silicate, iron-silicon alloy and iron carbide. The peaks of ferrous silicate and iron carbide are dominant.

[0091] Figure 3 These are scanning electron microscope images of the iron-silicon composite negative electrode material prepared according to the method of Example 1 at different magnifications. It can be seen from the images that the particles are evenly distributed, there is less agglomeration, the particle surface is flat, and the pore structure is moderate.

[0092] Figure 4 The iron-silicon composite negative electrode material prepared according to the method of Example 1 was assembled into a button-type lithium-ion battery. -1 The cycle performance test under the current density of 10 ... -1 , with good cycle stability.

[0093] After the iron-silicon composite negative electrode material prepared according to the method of Example 1 was assembled into a button-type lithium-ion battery, the current density was 0.4, 0.8, 1.6, 3.2, and 6.4Ag, respectively. -1 When the discharge capacity is 277, 193, 145, 106 and 67 mAh g -1 It is worth noting that when the current density returns to the initial 0.4Ag -1 When the cycle test is continued, the discharge capacity can reach 213mAh g -1 , recovered to 76% of the discharge capacity at the same current density in the first cycle.

[0094] Example 2:

[0095] This embodiment provides a method for preparing an iron-silicon composite negative electrode material, which is based on the method of Example 1, except that the amount of mortar waste (calculated as silicon element) added in step (3) is 10 mmol.

[0096] Figure 2 Fe:Si=1:2 is the XRD spectrum of the iron-silicon composite negative electrode material prepared according to the method of Example 2, wherein the main corresponding substances are ferrous silicate, iron-silicon alloy and iron carbide, and the peak of ferrous silicate is dominant.

[0097] Figure 5These are scanning electron microscope images of the iron-silicon composite negative electrode material prepared according to the method of Example 2 at different magnifications. It can be found that at a scale of 40 μm, larger agglomerates coexist with dispersed small particles. The agglomerate structure is loose, with small particles distributed among them. The particle surface is rough, presenting an irregular porous structure.

[0098] Figure 6 The iron-silicon composite negative electrode material prepared according to the method of Example 2 was assembled into a button-type lithium-ion battery. When the current density was 0.4, 0.8, 1.6, 3.2, 6.4Ag, the -1 When the discharge capacity is 840, 757, 662, 544 and 366 mAh g -1 It is worth noting that when the current density returns to the initial 0.4Ag -1 When the cycle test is continued, the discharge capacity can reach 790mAh g -1 , recovered to 94% of the discharge capacity at the same current density in the first cycle, showing excellent rate performance, and maintaining stable capacity output and good reversibility at different charge and discharge rates.

[0099] The iron-silicon composite negative electrode material prepared according to the method of Example 2 was assembled into a button-type lithium-ion battery. -1 The cycle performance test under the current density of 10 ... -1 .

[0100] Example 3

[0101] This embodiment provides a method for preparing an iron-silicon composite negative electrode material, which is based on the method of Example 1, except that the amount of mortar waste (calculated as silicon element) added in step (3) is 5 mmol.

[0102] Figure 2 Fe:Si=1:1 is the XRD spectrum of the iron-silicon composite negative electrode material prepared according to the method of Example 3, wherein the main corresponding substances are ferrous silicate, iron-silicon alloy and iron carbide, and the peak of ferrous silicate is dominant.

[0103] The iron-silicon composite negative electrode material prepared according to the method of Example 3 was assembled into a button-type lithium-ion battery. -1 The cycle performance test under the current density of 10 ... -1 .

[0104] After the iron-silicon composite negative electrode material prepared according to the method of Example 3 was assembled into a button-type lithium-ion battery, the current density was 0.4, 0.8, 1.6, 3.2, and 6.4Ag, respectively.-1 When the discharge capacity is 238, 200, 174, 145 and 111 mAh g -1 It is worth noting that when the current density returns to the initial 0.4Ag -1 When the cycle test is continued, the discharge capacity can reach 224mAh g -1 , recovered to 94% of the discharge capacity at the same current density in the first cycle.

[0105] Example 4

[0106] This embodiment provides a method for preparing an iron-silicon composite negative electrode material, which is based on the method of Example 1, except that the amount of mortar waste (calculated as silicon element) added in step (3) is 1.25 mmol.

[0107] Figure 2 Fe:Si=4:1 is the XRD spectrum of the iron-silicon composite negative electrode material prepared according to the method of Example 4, wherein the main corresponding substances are ferrous silicate, iron-silicon alloy and iron carbide, and the peak corresponding to ferrosilicon alloy is dominant.

[0108] After the iron-silicon composite negative electrode material prepared according to the method of Example 4 was assembled into a button-type lithium-ion battery, the -1 The cycle performance test under the current density of 10 ... -1 .

[0109] After the iron-silicon composite negative electrode material prepared according to the method of Example 4 was assembled into a button-type lithium-ion battery, the current density was 0.4, 0.8, 1.6, 3.2, and 6.4Ag, respectively. -1 When the discharge capacity is 236, 193, 158, 121 and 75 mAh g -1 .

[0110] Comparative Example

[0111] This comparative example provides a method for preparing an iron-silicon composite negative electrode material, which is based on the method of Example 1, except that the amount of mortar waste (calculated as silicon element) added in step (3) is 20 mmol.

[0112] Figure 2 Fe:Si=1:4 is the XRD spectrum of the iron-silicon composite negative electrode material prepared according to the comparative example method, in which the main corresponding substances are ferrous silicate, iron-silicon alloy and iron carbide, and the peaks corresponding to ferrous silicate and ferrosilicon alloy are dominant.

[0113] After the iron-silicon composite negative electrode material prepared according to the comparative example was assembled into a button-type lithium-ion battery, the -1The cycle performance test under the current density of 10 ... -1 .

[0114] After the iron-silicon composite negative electrode material prepared according to the comparative example was assembled into a button-type lithium-ion battery, the current density was 0.4, 0.8, 1.6, 3.2, and 6.4Ag, respectively. -1 When the discharge capacity is 1376, 696, 253, 68 and 19 mAh g -1 .

[0115] In summary, with a high capacity-oriented ratio of Fe / Si = 2: at a rate of 0.1C, it stabilized at 774 mAh g after 10 cycles. -1 The capacity is suitable for applications with high energy density requirements. Its advantage comes from the Fe 2+ The reversible lithiation activity brought by the uniform distribution of sites and the stability brought by the graphite-like structure of the outer layer; with a high rate-guided ratio of Fe / Si = 0.5: it still maintains 366mAh g at a high current of 1.6C -1 The capacity can be maintained at more than 94% of the original capacity after recovering to 0.1C, which meets the needs of fast charging equipment. This is attributed to the promotion of lithium ion migration by the three-dimensional conductive network constructed by the iron-rich phase. By using different ratios, iron-silicon composite negative electrode materials suitable for lithium-ion batteries in different application scenarios can be prepared.

[0116] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. An iron-silicon composite negative electrode material for lithium-ion batteries, characterized in that: The iron-silicon composite negative electrode material is prepared from an iron source and a silicon source, the silicon source is mortar waste, and the molar ratio of the silicon element in the silicon source to the iron element in the iron source is (0.5-5):

1.

2. The iron-silicon composite negative electrode material for lithium-ion batteries according to claim 1, characterized in that: By controlling the feeding ratio of iron source and silicon source, a high-capacity or high-rate iron-silicon composite negative electrode material can be obtained.

3. The iron-silicon composite negative electrode material for lithium-ion batteries according to claim 2, characterized in that: When the molar ratio of silicon in the silicon source to iron in the iron source is 1:2, a high-capacity iron-silicon composite negative electrode material is obtained; At a rate of 0.1C, the capacity of the high-capacity iron-silicon composite negative electrode material stabilized at 774 mAh g after 10 cycles. -1 .

4. The iron-silicon composite negative electrode material for lithium-ion batteries according to claim 2, characterized in that: When the molar ratio of silicon in the silicon source to iron in the iron source is 2:1, a high-rate iron-silicon composite negative electrode material is obtained; The high-rate iron-silicon composite anode material maintains 366 mAh g at a current of 1.6C. -1 capacity, and after recovering 0.1C, the capacity remained above 94% of the original.

5. A method for preparing an iron-silicon composite negative electrode material for lithium-ion batteries according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: (1) dissolving ferric chloride hexahydrate in a first solvent to obtain a ferric chloride solution; (2) dissolving sodium oleate in a second solvent to obtain a sodium oleate solution; (3) adding the sodium oleate solution obtained in step (2) to the mortar waste and continuously stirring the dispersion; (4) During the continuous stirring process of step (3), the ferric chloride solution obtained in step (1) is added to the dispersion in step (3). After all the ferric chloride solution is added, stirring is continued to obtain a dispersion after the reaction; (5) evaporating and removing the solvent in the dispersion obtained after the reaction in step (4) to obtain a solid-phase precursor; (6) calcining the solid-phase precursor obtained in step (5), cooling naturally to room temperature after calcination, washing and drying the obtained solid to obtain the iron-silicon composite negative electrode material.

6. The method for preparing an iron-silicon composite negative electrode material for lithium-ion batteries according to claim 5, characterized in that: In step (1), the first solvent is methanol; In step (1), the concentration of the ferric chloride solution is 0.1-2 mol L -1 ; The molar ratio of sodium oleate in step (2) to ferric chloride hexahydrate in step (1) is (1-5):1; In step (2), the second solvent is a mixed solvent of methanol and n-hexane, and the volume ratio of methanol to n-hexanol in the mixed solvent is 5:1-1:5; In step (2), the concentration of the sodium oleate solution is 0.08 to 0.42 mol L -1 ; The molar ratio of silicon in the mortar waste in step (3) to iron in the ferric chloride hexahydrate in step (1) is (0.5-5):1; In step (3), the conditions for continuous stirring are: stirring temperature of 40-60°C and rotation speed of 200-600 rpm; In step (4), the ferric chloride solution obtained in step (1) is added dropwise to the dispersion in step (3); In step (4), the stirring time of the continued stirring is 20-60 minutes, and the temperature and speed of the continued stirring are the same as those of the continuous stirring in step (3); In step (5), the system temperature during evaporation is 60-90°C.

7. The method for preparing an iron-silicon composite negative electrode material for lithium-ion batteries according to claim 5, characterized in that: In step (6), the calcination is carried out under atmosphere protection, and the atmosphere is any one or more of argon, nitrogen, and 5% H2 / Ar mixed gas; In step (6), the heating rate of the calcination is 2-10°C min -1 , the calcination temperature is 550-950℃, and the holding time is 1-5 hours; In step (6), the washing is performed with water; In step (6), the drying temperature is 50-80°C.

8. A lithium ion battery negative electrode, characterized in that The battery negative electrode is prepared using the iron-silicon composite negative electrode material according to any one of claims 1 to 4, or the battery negative electrode contains the iron-silicon composite negative electrode material according to any one of claims 1 to 4.

9. The lithium-ion battery negative electrode according to claim 8, characterized in that The lithium-ion battery comprises a positive electrode material, a negative electrode material, an electrolyte and a separator; The negative electrode material includes the iron-silicon composite negative electrode material.

10. Use of the iron-silicon composite negative electrode material for lithium-ion batteries according to any one of claims 1 to 4, characterized in that: The iron-silicon composite negative electrode material is used in lithium-ion batteries.

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