CN110838574A - High-capacity composite negative electrode material for lithium ion battery, preparation method thereof, and lithium ion battery comprising the composite material - Google Patents

Abstract

The invention discloses a high-capacity composite negative electrode material for lithium ion batteries, a preparation method thereof, and a lithium ion battery comprising the composite material. The composite negative electrode material comprises mesocarbon microspheres, dispersed in the mesocarbon microspheres The inner modified nano-silicon alloy, and the outer carbon material coating layer of the mesophase carbon microspheres. The method includes: 1) dispersing the modified nano-silicon alloy in the raw material of mesocarbon microspheres, carrying out a polymerization reaction, and separating to obtain a precursor; 2) carrying out coating modification and sintering on the obtained precursor to obtain a composite negative electrode material. The process of the invention is simple, and the large-scale production is easy. The prepared composite negative electrode material has excellent electrochemical performance, and when the composite negative electrode material is applied to a lithium ion battery, it exhibits high specific capacity, high efficiency and excellent cycle life.

Description

High-capacity composite negative electrode material for lithium ion battery, preparation method thereof, and composite negative electrode material comprising the same composite lithium-ion battery

technical field

The invention belongs to the application field of negative electrode materials for lithium ion batteries, relates to a composite negative electrode material, a preparation method thereof, and a lithium ion battery comprising the composite negative electrode material, and in particular relates to a high-capacity composite negative electrode material for lithium ion batteries, a preparation method thereof, and a lithium ion battery. Lithium-ion batteries containing the composite material.

Background technique

Lithium-ion batteries have the advantages of high energy density, high cycle life, and good safety. They are now widely used in portable electronic devices, and their applications in electric vehicles and other fields are growing rapidly. Mesocarbon microspheres are used as anode materials for lithium-ion batteries due to their advantages of high bulk density, small specific surface, good rate performance, and good safety performance, but their specific capacity is not high, only 340mAh/g, which cannot meet the There is an increasing demand for high energy density lithium-ion batteries in today's market. The theoretical specific capacity of silicon material as a negative electrode material is high (4200mA h/g). However, the silicon negative electrode is accompanied by a large volume expansion (up to 300%) during the process of lithium extraction/intercalation, resulting in the fragmentation and pulverization of silicon particles. The material is deactivated, resulting in a serious degradation of the cycle performance; in addition, the conductivity of silicon itself is not high, and the rate performance is poor.

CN107768671A discloses a preparation method of silicon mesocarbon microspheres for lithium ion batteries, comprising the following steps: adding elemental silicon or silicon-containing oxides to raw materials, after mixing uniformly, conducting thermal polycondensation reaction, and then separating to obtain silicon The mesophase carbon microspheres as the core are green spheres, and then the mesophase carbon microspheres with silicon as the core for lithium ion batteries are obtained by carbonization. Although this method improves the capacity of mesocarbon microspheres, the dispersion effect of silicon and silicon-containing oxides in mesocarbon microspheres is not good, and the electrical conductivity and expansion of silicon and silicon-containing oxides are poor, resulting in material The capacity cannot be further improved, and the material expands greatly.

SUMMARY OF THE INVENTION

In view of the above-mentioned problems in the prior art, the purpose of the present invention is to provide a composite negative electrode material, a preparation method thereof and a lithium ion battery comprising the composite negative electrode material, especially to provide a high-capacity composite negative electrode material for lithium ion batteries , a preparation method thereof and a lithium ion battery comprising the composite material.

The "high capacity" in the "high capacity composite negative electrode material" in the present invention refers to the first reversible capacity at 0.1C of 800-1100mAh/g.

For achieving the above object, the present invention adopts the following technical solutions:

In a first aspect, the present invention provides a composite negative electrode material (see FIG. 1 for a schematic diagram of its structure), the composite negative electrode material includes mesocarbon microspheres and modified nano-silicon alloys dispersed in the interior of the mesocarbon microspheres , and a carbon material coating layer covering the outside of the mesocarbon microspheres.

Compared with pure silicon, the invention adopts nano-silicon alloy material as active material, which has better conductivity and lower expansion, and further reduces the expansion of silicon alloy after nano-scale, and improves cycle performance. The carbon coating modification of nano-silicon alloy can effectively improve its lipophilicity, thereby improving the dispersion effect and bonding of nano-silicon alloy in mesocarbon microspheres, and avoiding the deterioration of material properties caused by local agglomeration of nano-silicon alloy materials. Dispersing the modified nano-silicon alloys inside the mesocarbon microspheres can effectively increase the capacity of the mesocarbon microspheres and further reduce the expansion of the nano-silicon alloys. Finally, carbon coating is carried out on the surface of the mesophase carbon microsphere particles to further reduce the material expansion performance and material specific surface area, and improve the material performance.

In the present invention, "comprising" can also be replaced by closed "is" or "consisting of". When the composite negative electrode material is composed of mesocarbon microspheres, modified nano-silicon alloys dispersed inside the mesocarbon microspheres, and a carbon material coating layer coated on the outside of the mesocarbon microspheres When constructed, the composite anode material exhibits better electrochemical performance, including high specific capacity, high efficiency, and excellent cycle life.

As a preferred technical solution of the composite negative electrode material of the present invention, in the process of preparing the mesocarbon microspheres, the dispersion of the modified nano-alloy inside the mesocarbon microspheres is realized.

Preferably, the modified nano-silicon alloy is a carbon-coated modified nano-silicon alloy. Carbon coating modification can better improve the lipophilicity of nano-silicon alloys, and increase its binding and dispersibility within mesophase carbon microspheres.

Preferably, the modified nano-silicon alloy is composed of a nano-silicon alloy and a carbon-coated modified layer coated on the surface of the nano-silicon alloy.

Preferably, the nano-silicon alloy is any one or a combination of at least two of silicon-iron alloy, silicon-nickel alloy, silicon-titanium alloy, silicon-tin alloy, silicon-copper alloy or silicon-aluminum alloy, and the combination is typical but not limited Typical examples are: the combination of ferrosilicon and silicon-nickel alloy, the combination of silicon-iron alloy and silicon-titanium alloy, the combination of silicon-nickel alloy and silicon-tin alloy, the combination of silicon-titanium alloy and silicon-aluminum alloy, the combination of silicon-iron alloy, silicon-nickel alloy and silicon The combination of copper alloy, the combination of silicon-nickel alloy, silicon-titanium alloy and silicon-aluminum alloy, the combination of silicon-nickel alloy, silicon-titanium alloy, silicon-tin alloy and silicon-aluminum alloy, etc.

As a preferred technical solution of the composite negative electrode material of the present invention, based on the total mass of the composite negative electrode material being 100 wt %, the mass percentage of the nano-silicon alloy is 10 wt % to 60 wt %, and the carbon coating modified layer The mass percentage of the carbon material is 1wt% to 8wt%, the mass percentage of the mesocarbon microspheres is 30wt% to 80wt%, and the mass percentage of the carbon material coating layer is 3wt% to 20wt%.

In this preferred technical solution, the mass percentage of the nano-silicon alloy is, for example, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt% or 60wt%, etc.; The mass percentage content of the carbon coating modified layer is, for example, 1wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 5wt%, 5.5wt%, 6wt%, 7wt% or 8wt%, etc.; The mass percentage content of mesocarbon microspheres is, for example, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 60wt%, 65wt%, 70wt% or 80wt%, etc.; the mass percentage content of the carbon material coating layer For example, it is 3wt%, 5wt%, 7wt%, 10wt%, 12wt%, 15wt%, 16wt%, 18wt% or 20wt% and the like.

More preferably, preferably, based on the total mass of the composite negative electrode material being 100 wt %, the mass percentage of the nano-silicon alloy is 20 wt % to 50 wt %, and the mass percentage of the carbon coating modified layer is 2 wt % to 6 wt %, the mass percentage of the mesocarbon microspheres is 40 wt % to 70 wt %, and the mass percentage of the carbon material coating layer is 5 wt % to 15 wt %.

Preferably, the median particle size of the composite negative electrode material is 1 μm to 45 μm, such as 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 17.5 μm, 20 μm, 22 μm or 25 μm, etc., preferably 5 μm to 25 μm.

Preferably, the median particle size of the nano-silicon alloy is 50 nm to 800 nm, such as 50 nm, 60 nm, 80 nm, 100 nm, 150 nm, 200 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 600 nm, 650 nm, 700 nm or 800 nm, etc., It is preferably 100 nm to 500 nm.

In a second aspect, the present invention provides a method for preparing a composite negative electrode material as described in the first aspect, the method comprising the following steps:

(1) dispersing the modified nano-silicon alloy in the raw material of mesocarbon microspheres, and carrying out a polymerization reaction to obtain a first precursor;

(2) separating the first precursor to obtain the second precursor;

(3) coating and modifying the second precursor to obtain the third precursor;

(4) Sintering the third precursor to obtain a composite negative electrode material.

In the method of the present invention, the separation described in step (2) is a necessary step, because: in step (1), the raw materials of mesocarbon microspheres (such as pitch, coal tar and synthetic resin, etc.) are converted into molten state through polymerization reaction, and the obtained In the first precursor, the mesocarbon microspheres containing the nano-silicon alloy are dispersed in the mother liquor, and the mesocarbon microspheres containing the nano-silicon alloy need to be separated through the separation of step (2) for subsequent coating. step.

In the method of the invention, the modified nano-silicon alloy is introduced in the process of preparing the mesophase carbon microspheres by high-temperature polymerization, so that a structure in which the modified nano-silicon alloy is dispersed inside the mesophase carbon microspheres can be formed, and the modified nano-silicon alloy can improve the Due to the lipophilicity of nano-silicon, it can be well dispersed inside the mesocarbon microspheres and has high binding. This unique internal dispersion structure (this structure is equivalent to the modified nano-silicon alloy embedded in the mesocarbon microspheres) middle) can well relieve the expansion of the silicon alloy, and at the same time effectively suppress the side reaction between the material and the electrolyte, and further coat the carbon material coating layer on the outside of the mesocarbon microspheres to obtain a composite negative electrode material, and the composite negative electrode When the material is applied to lithium-ion batteries, it exhibits high specific capacity, high efficiency and excellent cycle life.

As a preferred technical solution of the method of the present invention, the modified nano-silicon alloy in step (1) is a carbon-coated modified nano-silicon alloy.

Preferably, the preparation method of the carbon-coated modified nano-silicon alloy is a gas-phase coating method, comprising: placing the nano-silicon alloy in a reaction furnace, using an organic carbon source gas as a coating source, and having a protective Under the condition of gas, the surface of nano-silicon alloy was modified by carbon coating.

As a preferred technical solution for the preparation method of the carbon-coated modified nano-silicon alloy, the method includes: placing the nano-silicon alloy in a rotary kiln, adjusting the rotational speed of the rotary kiln to be 0.1 r/min to 5 r/min, A protective gas is introduced, the temperature is raised to 500 DEG C to 1200 DEG C, an organic carbon source gas is introduced, and the temperature is maintained to obtain a carbon-coated modified nano-silicon alloy.

In this preferred technical solution, the rotating speed of the rotary furnace is 0.1r/min～5r/min, such as 0.1r/min, 0.5r/min, 1r/min, 2r/min, 3r/min, 4r/min or 5r/min etc.; raise the temperature to 500°C to 1200°C, such as 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C, etc.

Preferably, in the preparation process of the carbon-coated modified nano-silicon alloy, the protective gas includes any one or a combination of at least two of nitrogen, helium, neon, argon, krypton or xenon;

Preferably, in the preparation process of the carbon-coated modified nano-silicon alloy, the heating rate to 500°C to 1200°C is 0.5°C/min to 20°C/min, such as 0.5°C/min, 1°C/min , 3°C/min, 5°C/min, 8°C/min, 10°C/min, 12.5°C/min, 15°C/min or 20°C/min, etc.

Preferably, in the preparation process of the carbon-coated modified nano-silicon alloy, the organic carbon source gas is any one or at least two of hydrocarbons and/or aromatic hydrocarbon derivatives with 1 to 3 benzene rings The combination is preferably any one or a combination of at least two of methane, ethylene, acetylene, benzene, toluene, xylene, acetone, styrene or phenol.

Preferably, in the preparation process of the carbon-coated modified nano-silicon alloy, the flow rate of the organic carbon source gas is 0.1L/min～20L/min, such as 0.1L/min, 0.5L/min, 1L/min min, 5L/min, 7L/min, 10L/min, 12L/min, 14L/min, 16L/min, 18L/min or 20L/min, etc., preferably 2L/min～10L/min.

Preferably, in the preparation process of the carbon-coated modified nano-silicon alloy, the heat preservation time is 0.1h to 10h, such as 0.1h, 0.5h, 1h, 3h, 5h, 6h, 8h or 10h, etc., preferably 1h ~ 5h.

In the method of the present invention, the carbon coating modification is preferably carried out on the nano-silicon alloy by the gas-phase coating method, and parameters such as the rotating speed of the rotary furnace, the reaction temperature, the flow rate of the organic carbon source gas and the holding time are controlled to make the nano-silicon alloy A carbon-coated modified layer with suitable thickness and uniform coating is formed on the surface, which is beneficial to improve the lipophilicity of the nano-silicon alloy surface, improve its dispersibility and bonding within the mesocarbon microspheres, and further improve the composite negative electrode material. electrochemical performance.

As a preferred technical solution of the method of the present invention, the raw material of the mesocarbon microspheres in step (1) is any one of coal tar, coal tar, petroleum tar, petroleum residue, synthetic asphalt, synthetic resin or heavy oil or a combination of at least two, typical but non-limiting examples of the combination are: a combination of coal tar and coal tar, a combination of coal tar and petroleum tar, a combination of coal tar and petroleum residue, a combination of coal tar and heavy oil, Combination of coal tar, coal tar and petroleum asphalt, combination of coal tar, petroleum residue and synthetic asphalt, combination of petroleum asphalt, petroleum residue and synthetic resin, combination of coal tar, coal tar, petroleum residue and heavy oil, etc.

Preferably, step (1) includes:

(A) Place the raw materials of the modified nano-silicon alloy and mesocarbon microspheres in a reaction kettle, introduce a protective gas, heat the temperature to 200°C to 350°C, and stir to make the modified nano-silicon alloy in the mesocarbon microspheres. uniformly dispersed in the raw materials;

(B) then the temperature is raised to 400°C to 550°C, the pressure is controlled to be 0.1 MPa to 12 MPa, and the temperature is maintained, and the raw material of the mesocarbon microspheres undergoes thermal polycondensation reaction to obtain the first precursor.

In this preferred technical solution, the reaction kettle described in step (A) is a high temperature and high pressure reaction kettle.

In this preferred technical solution, the temperature in step (A) is raised to 200°C to 350°C, such as 200°C, 220°C, 245°C, 265°C, 285°C, 300°C, 320°C or 350°C, etc.

In this preferred technical solution, the temperature in step (B) is raised to 400°C to 550°C, such as 400°C, 420°C, 430°C, 440°C, 460°C, 480°C, 500°C, 525°C or 550°C, etc.

In this preferred technical solution, the control pressure in step (B) is 0.1 MPa to 12 MPa, such as 0.1 MPa, 0.5 MPa, 1 MPa, 3 MPa, 5 MPa, 7 MPa, 10 MPa, 11 MPa or 12 MPa.

Preferably, the rate of temperature increase in step (A) is 0.5°C/min～15°C/min, such as 0.5°C/min, 1°C/min, 2°C/min, 3°C/min, 5°C/min, 7°C/min °C/min, 8 °C/min, 10 °C/min, 12 °C/min, 14 °C/min or 15 °C/min, etc.

Preferably, the stirring speed of step (A) is 500rpm～2500rpm, such as 500rpm, 650rpm, 800rpm, 900rpm, 1000rpm, 1100rpm, 1250rpm, 1500rpm, 1700rpm, 2000rpm, 2200rpm or 2500rpm, etc.; the stirring time is preferably 1h ~2h, eg 1h, 1.2h, 1.5h, 1.7h or 2h, etc.

Preferably, in step (A), based on the total mass of the raw materials of the modified nano-silicon alloy and mesocarbon microspheres being 100%, the mass percentage of the modified nano-silicon alloy is 20% to 55%, For example, 20%, 22.5%, 25%, 30%, 33%, 36%, 40%, 45%, 47%, 50%, 52%, 54% or 55%, etc., preferably 30% to 50%.

Preferably, the heating rate of step (B) is 0.5°C/min～15°C/min, such as 0.5°C/min, 1.5°C/min, 3°C/min, 5°C/min, 8°C/min, 10°C/min °C/min, 12 °C/min, 13 °C/min or 15 °C/min, etc.

Preferably, the control pressure in step (B) is 1MPa～8Mpa, such as 1Mpa, 2Mpa, 3Mpa, 4Mpa, 5Mpa, 6Mpa, 7Mpa or 8Mpa, etc.

Preferably, the incubation time in step (B) is 1 h to 15 h, such as 1 h, 3 h, 5 h, 7 h, 8 h, 10 h, 12 h, 13 h, 14 h or 15 h, and the like.

As a preferred technical solution of the method of the present invention, the separation method in step (2) includes any one of precipitation separation method, centrifugal separation method or solvent separation method.

Preferably, the method of coating modification in step (3) is any one of a liquid phase coating method or a solid phase coating method.

Preferably, the process steps of the liquid phase coating method include: dispersing the second precursor and the organic matter in an organic solvent system, and drying to obtain the third precursor.

Preferably, in the process of liquid phase coating, the organic solvent is any one or a combination of at least two of ether, alcohol or ketone.

Preferably, the process steps of the solid-phase coating method include: placing the second precursor and the organic substance in a VC high-efficiency mixer, and mixing for at least 0.5 hours to obtain the third precursor.

Preferably, in the process of solid-phase coating, the rotational speed of the VC high-efficiency mixer is adjusted to be 500r/min～3000r/min, such as 500r/min, 650r/min, 800r/min, 1000r/min, 1200r/min, 1500r/min, 2000r/min, 2200r/min, 2600r/min or 3000r/min, etc.

Preferably, in the liquid phase coating method and the solid phase coating method, the organic substance is independently any one or a combination of at least two of polyesters, sugars, organic acids or asphalt.

Preferably, in the liquid-phase coating method and the solid-phase coating method, the organic matter is in powder form, and the median particle size is independently 0.1 μm to 25 μm, such as 0.1 μm, 1 μm, 3 μm, 6 μm, 10 μm, 15 μm, 18 μm , 20 μm, 22 μm or 25 μm, etc., preferably 0.5 μm to 8 μm.

As a preferred technical solution of the method of the present invention, the sintering in step (4) includes: placing the third precursor in a reactor, introducing a protective gas, heating the temperature to 500°C to 1200°C, and maintaining the temperature to obtain a composite negative electrode Material.

In this preferred technical solution, the temperature is raised to 500°C to 1200°C, such as 500°C, 600°C, 700°C, 750°C, 800°C, 900°C, 950°C, 1000°C, 1100°C or 1200°C, etc.

Preferably, during the sintering process in step (4), the reactor includes any one of a vacuum furnace, a box furnace, a rotary furnace, a roller kiln, a push-plate kiln or a tube furnace.

Preferably, during the sintering process in step (4), the protective gas includes any one or a combination of at least two of nitrogen, helium, neon, argon or xenon.

Preferably, in the sintering process of step (4), the heating rate is 0.5°C/min～20°C/min, such as 0.5°C/min, 1°C/min, 3°C/min, 5°C/min, 7°C/min °C/min, 10 °C/min, 12 °C/min, 13 °C/min or 15 °C/min, etc.

Preferably, in the sintering process of step (4), the holding time is 0.5h to 10h, for example, 0.5h, 1h, 3h, 5h, 6h, 8h or 10h.

As a further preferred technical solution of the method of the present invention, the method comprises the following steps:

(1) Place the nano-silicon alloy with a median particle size of 100nm to 500nm in a rotary furnace, adjust the speed of the rotary furnace to 0.1r/min to 5r/min, and introduce protective gas at a temperature of 0.5°C/min to 20 The rate of ℃/min is heated to 500℃～1200℃, and the organic carbon source gas is introduced, and the flow rate of the organic carbon source gas is 2 L/min～10L/min, the temperature is kept for 1h～5h, and the carbon coating is obtained by natural cooling. Modified nano-silicon alloy;

The carbon-coated modified nano-silicon alloy and the raw materials of mesophase carbon microspheres are placed in a high temperature and high pressure reaction kettle, a protective gas is introduced, and the temperature is raised to 200 ℃ ~ 350 ℃ at a rate of 0.5 ℃ / min ~ 15 ℃ / min. ℃, stir at a speed of 500rpm to 2500rpm for 1h to 2h, so that the modified nano-silicon alloy is uniformly dispersed in the raw material of mesocarbon microspheres; ℃, the control pressure is 2MPa～5MPa, and the temperature is kept for 1h～15h, the raw material of the mesocarbon microspheres undergoes thermal polycondensation reaction, and the first precursor is obtained;

(2) separating the first precursor to obtain the second precursor;

(3) adopting the liquid phase coating method or the solid phase coating method, and using organic matter as the carbon source to carry out carbon source coating on the second precursor to obtain the third precursor;

(4) The third precursor is placed in the reactor, heated to 500°C to 1200°C at a rate of 0.5°C/min to 20.0°C/min, kept for 0.5h to 10h, and naturally cooled to obtain a median particle size of medium A composite negative electrode material with a particle size of 1 μm to 45 μm;

Wherein, based on the total mass of the raw materials of the modified nano-silicon alloy and mesocarbon microspheres being 100%, the mass percentage of the modified nano-silicon alloy is 20% to 55%;

Taking the total mass of the second precursor and the organic matter as 100%, the mass percentage of the second precursor is 75% to 95%, such as 75%, 80%, 82%, 85%, 87.5% , 90%, 915%, 93% or 95%, etc.;

The nano-silicon alloy is any one or a combination of at least two of silicon-iron alloy, silicon-nickel alloy, silicon-titanium alloy, silicon-tin alloy, silicon-copper alloy or silicon-aluminum alloy;

The raw material of the mesocarbon microspheres is any one or a combination of at least two of coal pitch, coal tar, petroleum pitch, petroleum residue, synthetic pitch, synthetic resin or heavy oil;

The organic substance is any one or a combination of at least two of polyesters, sugars, organic acids or asphalt.

In this preferred technical solution, by controlling the parameters of the gas phase coating process in step (1), a carbon coating layer with suitable thickness and uniform coating is formed on the surface of the nano-silicon alloy, and the modified nano-silicon alloy and Parameters such as the amount of raw materials of mesocarbon microspheres and the amount of organic matter in step (3) can form good dispersion and effective coating, which can greatly improve the first reversible capacity, first Coulomb efficiency and cycle performance of the material.

In a third aspect, the present invention provides a lithium ion battery, the lithium ion battery comprising the composite negative electrode material described in the first aspect.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The composite negative electrode material of the present invention has a novel structure, and the modified nano-silicon alloy improves the lipophilicity of nano-silicon, and increases its binding and dispersibility within the mesocarbon microspheres. This unique structure can The expansion of the silicon alloy is well relieved, and the side reaction between the material and the electrolyte is effectively suppressed, and the carbon material coating layer is further coated on the outside of the mesocarbon microspheres to obtain a composite negative electrode material, which is applied to the composite negative electrode material. When used as lithium-ion batteries, it exhibits high specific capacity, high efficiency and excellent cycle life.

(2) The method of the present invention can form a structure in which the modified nano-silicon alloy is dispersed inside the mesocarbon microspheres by introducing the modified nano-silicon alloy in the process of preparing the meso-carbon microspheres by the polymerization reaction. The modified nano-silicon The alloy improves the lipophilicity of nano-silicon, which can be well dispersed inside the mesocarbon microspheres and has high bonding. This unique structure can well relieve the expansion of the silicon alloy, and at the same time effectively inhibit the interaction between the material and the electrolyte. side reactions.

The present invention preferably adopts the gas-phase coating method to carry out carbon coating modification on the nano-silicon alloy, and controls parameters such as the rotational speed of the rotary kiln, the reaction temperature, the flow rate of the organic carbon source gas and the holding time, so that the surface of the nano-silicon alloy forms a suitable thickness And coated with a uniform carbon coating modified layer, which is conducive to improving the lipophilicity of the surface of the nano-silicon alloy, improving its dispersion and binding within the mesocarbon microspheres, and then improving the electrochemical performance of the composite negative electrode material. .

(3) The process of the present invention is simple, and it is easy to produce on a large scale.

Description of drawings

1 is a schematic structural diagram of a composite negative electrode material provided by the present invention, wherein 1- mesophase carbon microspheres, 2-modified silicon nano-alloy, 3-carbon material coating layer;

FIG. 2 is a cycle curve obtained by using the negative electrode material of Example 1 to make a battery and test it.

Detailed ways

The technical solutions of the present invention are further described below with reference to the accompanying drawings and through specific embodiments.

Adopt the following method to test the negative electrode material of each embodiment and comparative example:

①Use the following methods to test the first charge and discharge performance:

The negative electrode materials, conductive agents and binders of each embodiment and comparative example are dispersed in a solvent according to a mass percentage of 90:5:5 and mixed, and the obtained mixed slurry is coated on the copper foil current collector, dried in a vacuum, and prepared. Then, 1 mol/L LiPF ₆ /EC+DMC+EMC (v/v=1:1:1) electrolyte, SK (12μm) separator, and outer shell were assembled by conventional technology to assemble CR2016 button battery. Chemical performance test The current density of 0.1C is equal to 800-1100mA h/g. The test results are shown in Table 1.

②Use the following methods to test the cycle performance:

Disperse and mix the negative electrode material, conductive agent and binder in a solvent according to the mass percentage of 95:2:3, coat it on the copper foil current collector, vacuum dry to obtain the negative electrode piece; then the traditional mature technology The prepared ternary positive electrode, 1mol/L LiPF ₆ /EC+DMC+EMC (v/v=1:1:1) electrolyte, SK (12μm) separator, and shell were assembled with 18650 cylindrical monomer by conventional production process Battery. The charge-discharge test of the cylindrical battery was carried out on the LAND battery test system of Wuhan Jinnuo Electronics Co., Ltd., under normal temperature conditions, constant current charge and discharge at a rate of 1C, and the charge-discharge voltage was limited to 2.75-4.2V. The test results are shown in Table 1.

Example 1

(1) Place the ferrosilicon alloy with a particle size of 150nm in a rotary furnace, adjust the rotation speed to 1.5r/min, feed nitrogen, heat up to 850°C at a heating rate of 5.0°C/min, feed acetylene gas, and the flow rate is 2.0 L/min, hold for 1 h, and cool to room temperature naturally to obtain modified nano-ferrosilicon alloy;

(2) place the modified nano-ferrosilicon alloy and coal pitch in a high-temperature and high-pressure reaction kettle at a mass ratio of 50:50, feed nitrogen, and heat up to 250°C at a heating rate of 5.0°C/min, and in the reaction kettle at a stirring speed of 2200rpm Stir for 1 h, then heat up to 500 °C at a heating rate of 3.0 °C/min, control the pressure to 2 MPa, and keep the temperature for 5 h to obtain the first precursor; the second precursor is obtained by solvent separation;

(3) Place the second precursor and asphalt in a VC high-efficiency mixer at a ratio of 90:10, adjust the rotational speed to 2000.0 r/min, and mix for 0.5 h to obtain a third precursor; place the third precursor in a box furnace , nitrogen gas was introduced, the temperature was raised to 900°C at a heating rate of 5.0°C/min, maintained for 1.0 h, and cooled to room temperature naturally to obtain a high-capacity composite negative electrode material.

Figure 2 shows the cycle curve obtained by using the negative electrode material of this embodiment to make a battery and test it. It can be seen that it has very excellent cycle performance, and the capacity retention rate is still as high as 89.3% after 500 cycles of 1C/1C.

Example 2

(1) Place a silicon-titanium alloy with a particle size of 200 nm in a rotary furnace, adjust the rotation speed to 3 r/min, feed argon gas, heat up to 950 °C at a heating rate of 3.0 °C/min, feed methane gas, and the flow rate is 5.0L/min, heat preservation for 3h, and natural cooling to room temperature to obtain modified nano-silicon-titanium alloy;

(2) Put the nano-silicon-titanium alloy and coal tar in a high temperature and high pressure reaction kettle in a mass ratio of 30:70, pass argon gas, heat up to 200 °C at a heating rate of 3.0 °C/min, and stir at 1500 rpm in the reaction kettle Stir at a speed for 2h, then heat up to 450°C at a heating rate of 5.0°C/min, control the pressure to 5MPa, and keep the temperature for 7h to obtain the first precursor; the second precursor is obtained by centrifugal separation;

(3) Disperse the second precursor and glucose in ethanol at a ratio of 85:15, and dry to obtain the third precursor; place the third precursor in a rotary kiln, introduce nitrogen gas, and heat up at a rate of 3.0°C/min The temperature was raised to 700° C., the temperature was maintained for 2.0 h, and then cooled to room temperature naturally to obtain a high-capacity composite negative electrode material.

Example 3

(1) Place the silicon-copper alloy with a particle size of 300nm in a rotary furnace, adjust the rotation speed to 5r/min, feed nitrogen, heat up to 700°C at a heating rate of 2.0°C/min, feed ethylene gas, and the flow rate is 7.0 L/min, heat preservation for 5h, and natural cooling to room temperature to obtain modified nano-silicon copper alloy;

(2) Place the modified nano-silicon copper alloy and petroleum pitch in a high-temperature and high-pressure reaction kettle in a mass ratio of 40:60, feed nitrogen, heat up to 300°C at a heating rate of 10.0°C/min, and stir at 800rpm in the reaction kettle. Stir at a speed for 2h, then heat up to 480°C at a heating rate of 6.0°C/min, control the pressure to 10MPa, and keep the temperature for 10h to obtain the first precursor; the second precursor is obtained by precipitation and separation;

(3) Place the second precursor and glucose in a VC high-efficiency mixer at a ratio of 82:18, adjust the rotational speed to 3000.0 r/min, and mix for 0.5 h to obtain a third precursor; place the third precursor in a box furnace In the process, nitrogen gas was introduced, the temperature was raised to 1100°C at a heating rate of 10.0°C/min, the temperature was maintained for 3.0 h, and then cooled to room temperature naturally to obtain a high-capacity composite negative electrode material.

Example 4

(1) Place the silicon-nickel alloy with a particle size of 500nm in a rotary furnace, adjust the rotation speed to 2.5r/min, feed argon gas, heat up to 1100°C at a heating rate of 15.0°C/min, feed styrene gas, The flow rate was 15.0 L/min, the temperature was kept for 0.5 h, and then cooled to room temperature naturally to obtain the modified nano-silicon-nickel alloy;

(2) Place the nano-silicon-nickel alloy and synthetic pitch in a high-temperature and high-pressure reaction kettle in a mass ratio of 45:55, feed argon gas, heat up to 350°C at a heating rate of 7.0°C/min, and stir at 1000rpm in the reaction kettle Stir at a speed of 1.8h, then heat up to 550°C at a heating rate of 10.0°C/min, control the pressure to 8MPa, and keep the temperature for 12h to obtain the first precursor; the second precursor is obtained by centrifugal separation;

(3) Disperse the second precursor and citric acid in acetone at a ratio of 78:22, and dry to obtain the third precursor; place the third precursor in a rotary kiln, feed nitrogen gas, and heat up at 1.0°C/min The rate of heating was increased to 600 °C, the temperature was kept for 10.0 h, and then cooled to room temperature naturally to obtain a high-capacity composite negative electrode material.

Example 5

(1) Place the silicon-aluminum alloy with a particle size of 750nm in a rotary furnace, adjust the rotation speed to 4r/min, feed nitrogen, heat up to 600°C at a heating rate of 6.0°C/min, feed benzene gas, and the flow rate is 3.5 L/min, heat preservation for 7.5h, and natural cooling to room temperature to obtain modified nano-silicon-aluminum alloy;

(2) place the modified nano-silicon aluminum alloy and petroleum residue in a high-temperature and high-pressure reaction kettle at a mass ratio of 42:58, feed nitrogen, and heat up to 275°C at a heating rate of 5.0°C/min, in the reaction kettle at 2250rpm Stir at a stirring speed for 1.5h, then heat up to 400°C at a heating rate of 8.0°C/min, control the pressure to 12MPa, and keep the temperature for 3h to obtain the first precursor; the second precursor is obtained by solvent separation;

(3) Place the second precursor and asphalt in a VC high-efficiency mixer at a ratio of 95:5, adjust the rotational speed to 1500.0 r/min, and mix for 4 hours to obtain a third precursor; place the third precursor in a box furnace , nitrogen gas was introduced, the temperature was raised to 600°C at a heating rate of 5.0°C/min, maintained for 10.0 h, and cooled to room temperature naturally to obtain a high-capacity composite negative electrode material.

Example 6

(1) Place the silicon-tin alloy with a particle size of 80nm in a rotary furnace, adjust the rotation speed to 2r/min, feed argon gas, heat up to 1000°C at a heating rate of 10.0°C/min, feed acetone gas, and the flow rate is 1.0L/min, heat preservation for 8h, and natural cooling to room temperature to obtain modified nano-silicon-tin alloy;

(2) Put the nano-silicon-tin alloy and heavy oil in a high temperature and high pressure reaction kettle at a mass ratio of 35:65, feed argon gas, heat up to 200°C at a heating rate of 4.0°C/min, and stir at a speed of 2000rpm in the reaction kettle. Stir for 2h, then raise the temperature to 500°C at a heating rate of 8.0°C/min, control the pressure to 6.5MPa, and keep the temperature for 3h to obtain the first precursor; the second precursor is obtained by centrifugal separation;

(3) Disperse the second precursor and glucose in methyl ether at a ratio of 80:20, and dry to obtain the third precursor; place the third precursor in a rotary kiln, feed helium gas, and heat at 8.0°C/min The heating rate was increased to 800° C., the temperature was maintained for 7.0 h, and then cooled to room temperature naturally to obtain a high-capacity composite negative electrode material.

Comparative Example 1

The high-capacity composite negative electrode material was prepared in the same manner as in Example 1, except that the modified nano-ferrosilicon alloy was replaced with nano-silicon, no modification treatment was performed, and the third precursor was not subjected to coating treatment; 1 Make the battery in the same way.

Table 1

The negative electrode materials of the embodiments of the present invention have high specific capacity, high efficiency and excellent cycle life. In Comparative Example 1, nano-silicon with poor expansion and electrical conductivity was used as the active material, and no modification treatment was performed, resulting in poor dispersion of silicon in the mesocarbon microspheres, and particle agglomeration caused the material to expand greatly and cycle performance. Not good; in Comparative Example 1, the surface of the mesocarbon microspheres was not coated with carbon. Due to the poor dispersion of nano-silicon in the raw material of mesocarbon microspheres, some nano-silicon may be exposed on the surface of the mesocarbon microspheres. As a result, the specific surface area is increased, the side reactions of the electrolyte are increased, the coulombic efficiency of the material is low, the expansion of silicon cannot be well suppressed, and the cycle performance is further deteriorated.

The applicant declares that the present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims (10)

1. a composite negative electrode material, is characterized in that, described composite negative electrode material comprises mesophase carbon microspheres, the modified nano-silicon alloy dispersed in the interior of described mesophase carbon microspheres, and is coated on described mesophase carbon microspheres Carbon material coating on the outside of the carbon microspheres. 2. The composite negative electrode material according to claim 1, wherein in the process of preparing the mesocarbon microspheres, the dispersion of the modified nano-alloy in the mesocarbon microspheres is realized; Preferably, the modified nano-silicon alloy is a carbon-coated modified nano-silicon alloy; Preferably, the modified nano-silicon alloy is composed of a nano-silicon alloy and a carbon-coated modified layer coated on the surface of the nano-silicon alloy; Preferably, the nano-silicon alloy is any one or a combination of at least two of silicon-iron alloy, silicon-nickel alloy, silicon-titanium alloy, silicon-tin alloy, silicon-copper alloy or silicon-aluminum alloy. 3. The composite negative electrode material according to claim 1 or 2, characterized in that, based on the total mass of the composite negative electrode material being 100 wt%, the mass percentage of the nano-silicon alloy is 10 wt% to 60 wt%, The mass percentage of the carbon coating modified layer is 1wt% to 8wt%, the mass percentage of the mesocarbon microspheres is 30wt% to 80wt%, and the mass percentage of the carbon material coating layer is 3wt% to 20wt% %; Preferably, based on the total mass of the composite negative electrode material being 100 wt %, the mass percentage of the nano-silicon alloy is 20 wt % to 50 wt %, and the mass percentage of the carbon coating modified layer is 2 wt % to 6 wt %. %, the mass percentage of the mesocarbon microspheres is 40wt% to 70wt%, and the mass percentage of the carbon material coating layer is 5wt% to 15wt%; Preferably, the median particle size of the composite negative electrode material is 1 μm˜45 μm, preferably 5 μm˜25 μm; Preferably, the median particle size of the nano-silicon alloy is 50 nm to 800 nm, preferably 100 nm to 500 nm. 4. The preparation method of the composite negative electrode material according to any one of claims 1-3, wherein the method comprises the following steps: (1) dispersing the modified nano-silicon alloy in the raw material of mesocarbon microspheres, and carrying out a polymerization reaction to obtain a first precursor; (2) separating the first precursor to obtain the second precursor; (3) coating and modifying the second precursor to obtain the third precursor; (4) Sintering the third precursor to obtain a composite negative electrode material. 5. The method according to claim 4, wherein the modified nano-silicon alloy in step (1) is a carbon-coated modified nano-silicon alloy; Preferably, the preparation method of the carbon-coated modified nano-silicon alloy is a gas-phase coating method, comprising: placing the nano-silicon alloy in a reaction furnace, using an organic carbon source gas as a coating source, and having a protective Under the condition of gas, carbon coating modification is carried out on the surface of nano-silicon alloy; Preferably, the preparation process of the carbon-coated modified nano-silicon alloy includes: placing the nano-silicon alloy in a rotary kiln, adjusting the rotational speed of the rotary kiln to be 0.1 r/min to 5 r/min, introducing protective gas, The temperature is raised to 500 ℃ ~ 1200 ℃, and organic carbon source gas is introduced, and the temperature is kept warm to obtain a carbon-coated modified nano-silicon alloy; Preferably, in the preparation process of the carbon-coated modified nano-silicon alloy, the protective gas includes any one or a combination of at least two of nitrogen, helium, neon, argon, krypton or xenon; Preferably, in the preparation process of the carbon-coated modified nano-silicon alloy, the heating rate to 500°C to 1200°C is 0.5°C/min to 20°C/min; Preferably, in the preparation process of the carbon-coated modified nano-silicon alloy, the organic carbon source gas is any one or at least two of hydrocarbons and/or aromatic hydrocarbon derivatives with 1 to 3 benzene rings combination, preferably any one or a combination of at least two of methane, ethylene, acetylene, benzene, toluene, xylene, acetone, styrene or phenol; Preferably, in the preparation process of the carbon-coated modified nano-silicon alloy, the flow rate of the organic carbon source gas is 0.1L/min～20L/min, preferably 2L/min～10L/min; Preferably, in the preparation process of the carbon-coated modified nano-silicon alloy, the heat preservation time is 0.1 h to 10 h, preferably 1 h to 5 h. 6. method according to claim 4 or 5 is characterized in that, the raw material of the described mesocarbon microspheres of step (1) is coal pitch, coal tar, petroleum pitch, petroleum residue, synthetic pitch, synthetic resin or Any one or a combination of at least two heavy oils; Preferably, step (1) includes: (A) Place the raw materials of the modified nano-silicon alloy and mesocarbon microspheres in a reaction kettle, introduce a protective gas, heat the temperature to 200°C to 350°C, and stir to make the modified nano-silicon alloy in the mesocarbon microspheres. uniformly dispersed in the raw materials; (B) then heat up to 400 ℃～550 ℃, control the pressure to be 0.1MPa～12MPa, keep warm, the raw material of mesocarbon microspheres undergoes thermal polycondensation reaction to obtain the first precursor; Preferably, the heating rate of step (A) is 0.5°C/min～15°C/min; Preferably, the stirring speed of step (A) is 500rpm～2500rpm, and the stirring time is preferably 1h～2h; Preferably, in step (A), based on the total mass of the raw materials of the modified nano-silicon alloy and mesocarbon microspheres being 100%, the mass percentage of the modified nano-silicon alloy is 20% to 55%, Preferably, it is 30% to 50%; Preferably, the heating rate of step (B) is 0.5°C/min～15°C/min; Preferably, the control pressure in step (B) is 1MPa～8MPa; Preferably, the incubation time in step (B) is 1 h to 15 h. 7. The method according to any one of claims 4-6, wherein the method for separation in step (2) comprises: any one of precipitation separation method, centrifugal separation method or solvent separation method; Preferably, the method for coating modification in step (3) is: either a liquid-phase coating method or a solid-phase coating method; Preferably, the process steps of the liquid phase coating method include: dispersing the second precursor and the organic matter in an organic solvent system, and drying to obtain the third precursor; Preferably, in the process of liquid phase coating, the organic solvent is any one or a combination of at least two of ether, alcohol or ketone; Preferably, the process steps of the solid-phase coating method include: placing the second precursor and the organic substance in a VC high-efficiency mixer, and mixing for at least 0.5 h to obtain the third precursor; Preferably, in the process of solid phase coating, the rotational speed of the VC high-efficiency mixer is adjusted to be 500r/min～3000r/min; Preferably, in the liquid-phase coating method and the solid-phase coating method, the organic substance is independently any one or a combination of at least two of polyesters, sugars, organic acids or asphalt; Preferably, in the liquid phase coating method and the solid phase coating method, the organic matter is in the form of powder, and the median particle size is independently 0.1 μm to 25 μm, preferably 0.5 μm to 8 μm. 8. The method according to any one of claims 4-7, wherein the sintering in step (4) comprises: placing the third precursor in a reactor, feeding a protective gas, and raising the temperature to 500°C ~1200 ℃, heat preservation, to obtain composite negative electrode material; Preferably, during the sintering process in step (4), the reactor includes any one of a vacuum furnace, a box furnace, a rotary furnace, a roller kiln, a push-plate kiln or a tube furnace; Preferably, during the sintering process of step (4), the protective gas includes any one or a combination of at least two of nitrogen, helium, neon, argon or xenon; Preferably, during the sintering process in step (4), the heating rate is 0.5°C/min to 20°C/min; Preferably, in the sintering process of step (4), the time of heat preservation is 0.5 h to 10 h. 9. The method according to any one of claims 4-8, wherein the method comprises the steps of: (1) Place the nano-silicon alloy with a median particle size of 100nm to 500nm in a rotary furnace, adjust the speed of the rotary furnace to 0.1r/min to 5r/min, and introduce protective gas at a temperature of 0.5°C/min to 20 The rate of ℃/min is heated to 500 ℃～1200 ℃, and the organic carbon source gas is introduced, and the flow rate of the organic carbon source gas is 2L/min～10L/min, the temperature is kept for 1h～5h, and natural cooling is obtained to obtain the carbon coating modification. Properties of nano-silicon alloys; The carbon-coated modified nano-silicon alloy and the raw materials of mesophase carbon microspheres are placed in a high temperature and high pressure reaction kettle, a protective gas is introduced, and the temperature is raised to 200 ℃ ~ 350 ℃ at a rate of 0.5 ℃ / min ~ 15 ℃ / min. ℃, stir at a speed of 500rpm to 2500rpm for 1h to 2h, so that the modified nano-silicon alloy is uniformly dispersed in the raw material of mesocarbon microspheres; ℃, the control pressure is 2MPa～5MPa, and the temperature is kept for 1h～15h, the raw material of the mesocarbon microspheres undergoes thermal polycondensation reaction, and the first precursor is obtained; (2) separating the first precursor to obtain the second precursor; (3) adopting the liquid phase coating method or the solid phase coating method, and using organic matter as the carbon source to carry out carbon source coating on the second precursor to obtain the third precursor; (4) The third precursor is placed in the reactor, heated to 500°C to 1200°C at a rate of 0.5°C/min to 20.0°C/min, kept for 0.5h to 10h, and naturally cooled to obtain a median particle size of medium A composite negative electrode material with a particle size of 1 μm to 45 μm; Wherein, based on the total mass of the raw materials of the modified nano-silicon alloy and mesocarbon microspheres being 100%, the mass percentage of the modified nano-silicon alloy is 20% to 55%; Taking the total mass of the second precursor and organic matter as 100%, the mass percentage of the second precursor is 75% to 95%; The nano-silicon alloy is any one or a combination of at least two of silicon-iron alloy, silicon-nickel alloy, silicon-titanium alloy, silicon-tin alloy, silicon-copper alloy or silicon-aluminum alloy; The raw material of the mesocarbon microspheres is any one or a combination of at least two of coal pitch, coal tar, petroleum pitch, petroleum residue, synthetic pitch, synthetic resin or heavy oil; The organic substance is any one or a combination of at least two of polyesters, sugars, organic acids or asphalt. 10 . A lithium ion battery, characterized in that, the lithium ion battery comprises the composite negative electrode material according to any one of claims 1 to 3 .

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