Titanium oxide modified nano silicon-graphite composite negative electrode material and preparation method thereof, lithium ion battery and electric equipment

Abstract

The invention provides a titanium oxide modified nano silicon-graphite composite negative electrode material and a preparation method thereof, a lithium ion battery and electric equipment, and relates to the field of lithium ion batteries. Carrying out first mixing on nano silicon and a solvent to obtain a nano silicon solution; performing second mixing on the nano silicon solution, a titanium source, a dispersing agent and a conductive agent to obtain first mixed slurry; performing third mixing on the first mixed slurry, resin and graphite to obtain second mixed slurry; performing spray drying on the second mixed slurry to obtain a composite negative electrode precursor; under a protective atmosphere, performing first high-temperature treatment on the composite negative electrode precursor to obtain a primary coated composite negative electrode material; and performing fourth mixing and second high-temperature treatment on the primary coated composite negative electrode material and a carbon source in a protective atmosphere to obtain the titanium oxide modified nano silicon-graphite composite negative electrode material. The process involved in the whole preparation process is simple, the operability is high, the production cost is low, and large-scale production is easier to realize.

Description

Technical Field

[0001] The present application relates to the field of lithium-ion batteries, and in particular to a titanium oxide-modified nano-silicon-graphite composite negative electrode material and a preparation method thereof, a lithium-ion battery, and electrical equipment. Background Art

[0002] With the rapid development of information technology and new energy vehicles, energy demand has become increasingly diversified, miniaturized and lightweight, and the application scenarios of lithium batteries have continued to expand and update. At present, the market demand for improving the energy density of lithium-ion batteries is becoming more and more close. People are constantly seeking and improving the specific capacity of the positive electrode while also constantly seeking and improving the specific capacity of the negative electrode to improve the energy density of lithium-ion batteries.

[0003] Traditional graphite-based negative electrode materials have a low lithium storage capacity (372mAh / g) and a low lithium insertion potential, which can no longer meet the high power and high capacity requirements of future automotive lithium-ion batteries.

[0004] Silicon-based negative electrode materials have attracted much attention due to their high theoretical capacity (4200mAh / g), but their volume expansion during charging and discharging leads to structural collapse and capacity attenuation. In the existing technology, the expansion is often alleviated by reducing the particle size of silicon materials to nanometers, carbon coating, and composite graphite materials to achieve the purpose of enhancing structural stability. However, the following problems still exist: Nano-silicon prepared by traditional sand milling method is very easy to oxidize and agglomerate, and the accumulation effect is formed again in the subsequent coating and granulation process, resulting in limited coating effect and insufficient coating layer performance. It is difficult for a single-layer carbon coating to take into account the requirements of buffering volume expansion and conductivity. The bonding force between nano-silicon and carbon layer is not strong, and it is very easy to gradually lose connection with the expansion changes during charging and discharging, resulting in coating.

[0005] However, the graphite composite process is complex, and the problems of uniform dispersion and interface bonding between nano-silicon and graphite have not been effectively solved. Summary of the Invention

[0006] The purpose of this application is to provide a titanium oxide modified nano-silicon-graphite composite negative electrode material and a preparation method thereof, a lithium ion battery and an electrical device to solve the above problems.

[0007] To achieve the above objectives, the present application provides a first aspect of a method for preparing a titanium oxide modified nano-silicon-graphite composite negative electrode material, comprising:

[0008] performing a first mixing of nano-silicon and a solvent to obtain a nano-silicon solution;

[0009] performing a second mixing of the nano-silicon solution, titanium source, dispersant, and conductive agent to obtain a first mixed slurry;

[0010] performing a third mixing of the first mixed slurry, resin and graphite to obtain a second mixed slurry;

[0011] spray drying the second mixed slurry to obtain a composite negative electrode precursor;

[0012] Under a protective atmosphere, subjecting the composite negative electrode precursor to a first high-temperature treatment to obtain a primary coated composite negative electrode material;

[0013] Under a protective atmosphere, the primary coated composite negative electrode material and a carbon source are subjected to a fourth mixing and a second high-temperature treatment to obtain a titanium oxide modified nano-silicon-graphite composite negative electrode material.

[0014] Optionally, the preparation method of the titanium oxide modified nano-silicon-graphite composite negative electrode material meets at least one of the following conditions:

[0015] A. The D50 of the nano-silicon in the nano-silicon solution is less than 100 nm, and the D90 is less than 400 nm;

[0016] B. the nano-silicon comprises pure nano-silicon and / or photovoltaic silicon waste;

[0017] C. The D50 of the graphite is 2 μm-6 μm.

[0018] Optionally, the preparation method of the titanium oxide modified nano-silicon-graphite composite negative electrode material meets at least one of the following conditions:

[0019] A. The titanium source comprises one or more of tetrabutyl titanate, isopropyl titanate and titanium tetrachloride;

[0020] B. the dispersant comprises PVP;

[0021] C. The conductive agent includes one or more of carbon black, acetylene black, carbon nanotubes and graphene;

[0022] D. the solvent includes an alcohol solvent;

[0023] E. the resin comprises one or more of phenolic resin, epoxy resin and urea-formaldehyde resin;

[0024] F. The graphite includes one or more of natural crystalline graphite, natural cryptocrystalline graphite, natural crystalline vein graphite, artificial graphite and conductive graphite.

[0025] Optionally, the preparation method of the titanium oxide modified nano-silicon-graphite composite negative electrode material meets at least one of the following conditions:

[0026] A. The mass ratio of the nano-silicon to the solvent is 5-20:100;

[0027] B. the solid content of the titanium source in the first mixed slurry is 2%-8%;

[0028] C. the solid content of the dispersant in the first mixed slurry is 20%-30%;

[0029] D. The solid content of the conductive agent in the first mixed slurry is 0.5%-3%;

[0030] E. The mass ratio of the nano-silicon, the resin and the graphite is 1:0.6-1.5:1-3;

[0031] F. The mass ratio of the primary coated composite negative electrode material to the carbon source is 100:5-12.

[0032] Optionally, the preparation method of the titanium oxide modified nano-silicon-graphite composite negative electrode material meets at least one of the following conditions:

[0033] A. The second mixing time is 2h-5h;

[0034] B. When performing the first mixing, the second mixing and the third mixing, each is also independently subjected to sand grinding, and the diameter of the zirconium beads used in the sand grinding is less than 0.5 mm.

[0035] Optionally, the first high temperature treatment includes a third high temperature treatment and a fourth high temperature treatment performed sequentially;

[0036] The third high temperature treatment has a heating rate of 15°C / min-25°C / min, a holding temperature of 300°C-600°C, and a holding time of 1h-3h;

[0037] The fourth high temperature treatment has a heating rate of 10°C / min-20°C / min, a holding temperature of 600°C-1000°C, and a holding time of 4h-12h.

[0038] Optionally, the second high temperature treatment includes a fifth high temperature treatment and a sixth high temperature treatment performed sequentially;

[0039] The fifth high temperature treatment is performed at a holding temperature of 250°C-350°C, a holding time of ≥3h, and a rotation speed of 50r / min-100r / min;

[0040] The sixth high-temperature treatment has a holding temperature of 900-1100° C., a holding time of ≥5 hours, and a rotation speed of 50 r / min-100 r / min.

[0041] The second aspect of the present application provides a titanium oxide modified nano-silicon-graphite composite negative electrode material, which is prepared by the preparation method of the titanium oxide modified nano-silicon-graphite composite negative electrode material.

[0042] The third aspect of the present application provides a lithium-ion battery, comprising the titanium oxide modified nano-silicon-graphite composite negative electrode material.

[0043] A fourth aspect of the present application provides an electrical device comprising the lithium-ion battery.

[0044] Compared with the prior art, the advantages of this application include:

[0045] The preparation method of the titanium oxide modified nano-silicon-graphite composite negative electrode material provided in the present application effectively avoids nano-silicon agglomeration and surface modification by sequentially adding a dispersant, a modifier, a conductive agent and a carbon source during the sand milling process; the titanium source added during the preparation process forms firm modification sites on the surface of the nano-silicon particles by utilizing the high binding energy of the Ti-O bond and the Si-O bond, greatly improving the expansion effect of the nano-silicon particles and enhancing the conductivity of the particle surface; small-particle graphite particles are continuously added during the sand milling process so that the nano-silicon particles modified with the titanium source are uniformly dispersed in the gaps and surfaces of the graphite particles, and then a carbon-coated composite negative electrode material is obtained by spray drying and a first high-temperature treatment, and a second high-temperature treatment is performed under the viscosity of the carbon source, thereby realizing the preparation of the titanium oxide modified nano-silicon-graphite composite negative electrode material; the entire preparation process involves simple processes, strong operability, low production costs, and is easier to achieve large-scale production.

[0046] The titanium oxide modified nano-silicon-graphite composite negative electrode material provided in the present application includes a core and a first carbon coating layer and a second carbon coating layer stacked on the surface of the core; by optimizing the core structure of the composite negative electrode material, titanium oxide and small-particle graphite are introduced to participate in the construction of the core of the composite negative electrode material. The core of the composite negative electrode material enables silicon particles to be embedded in the gaps and surfaces of graphite particles, with loose distribution, effectively avoiding the aggregation effect of silicon particles, and greatly reducing the specific surface area of the resulting material. First of all, regarding the introduction of titanium oxide, on the one hand, due to the high binding energy of Ti-O bonds and Si-O bonds, the titanium oxide modification points are very strong. Even after undergoing huge volume changes, titanium oxide will not fall off from the surface of the nano-silicon particles, ensuring stability during the cycle. On the other hand, the reducing property of silicon converts titanium dioxide into oxygen-deficient titanium dioxide, which helps to enhance the conductivity of the titanium oxide modification layer on the surface of the nano-silicon, thereby enhancing the conductivity of the composite negative electrode material; and through the addition of conductive agents, a flexible conductive network is constructed inside the composite particles, which inhibits particle expansion while enhancing the conductive connection between the nano-silicon particles; finally, based on the above core structure, a double carbon layer coating is introduced, and the hard carbon structure (first carbon coating layer) formed by the resin base is used to improve the particle strength of the composite material. The second carbon coating layer effectively improves the specific surface area of the composite negative electrode material, reduces the interface reaction between the composite negative electrode material and the electrolyte, and ultimately improves the conductivity and cycle stability of the composite negative electrode material.

[0047] The lithium-ion battery and electrical equipment provided in this application have high capacity and long service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0049] Figure 1 Schematic diagram of the structure of titanium oxide modified nano-silicon-graphite composite negative electrode material;

[0050] Figure 2 This is an SEM image of the titanium oxide modified nano-silicon-graphite composite negative electrode material provided in Example 1. DETAILED DESCRIPTION

[0051] As used herein:

[0052] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0053] The conjunction "consisting of" excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim, rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0054] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0055] In these examples, parts and percentages are by mass unless otherwise indicated.

[0056] "Parts by mass" refers to the basic unit of measurement used to express the mass ratio of multiple components. One part can represent any unit of mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, this means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, we could say that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number representing a multiplication factor). It's important to note that, unlike parts by mass, the sum of the mass of all components is not limited to 100 parts.

[0057] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0058] The first aspect of the present application provides a method for preparing a titanium oxide modified nano-silicon-graphite composite negative electrode material, comprising:

[0059] performing a first mixing of nano-silicon and a solvent to obtain a nano-silicon solution;

[0060] performing a second mixing of the nano-silicon solution, titanium source, dispersant, and conductive agent to obtain a first mixed slurry;

[0061] performing a third mixing of the first mixed slurry, resin and graphite to obtain a second mixed slurry;

[0062] spray drying the second mixed slurry to obtain a composite negative electrode precursor;

[0063] Under a protective atmosphere, subjecting the composite negative electrode precursor to a first high-temperature treatment to obtain a primary coated composite negative electrode material;

[0064] Under a protective atmosphere, the primary coated composite negative electrode material and a carbon source are subjected to a fourth mixing and a second high-temperature treatment to obtain a titanium oxide modified nano-silicon-graphite composite negative electrode material.

[0065] In some embodiments, the carbon source comprises one or more of sucrose, glucose, asphalt, furfuryl alcohol, epoxy resin, and phenolic resin.

[0066] In some embodiments, the protective atmosphere includes one or more of nitrogen, argon, or helium.

[0067] It should be noted that the order of adding the raw materials should be reasonable to ensure the effective distribution of the modification sites on the surface of the silicon particles.

[0068] In some embodiments, the method for preparing the titanium oxide modified nano-silicon-graphite composite negative electrode material satisfies at least one of the following conditions:

[0069] A. The D50 of the nano-silicon in the nano-silicon solution is less than 100 nm, and the D90 is less than 400 nm;

[0070] Optionally, the D50 of the nano-silicon in the nano-silicon solution may be 1 nm, 10 nm, 50 nm, 90 nm, or any value <100 nm, and the D90 may be 1 nm, 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, or any value <400 nm;

[0071] B. the nano-silicon comprises pure nano-silicon and / or photovoltaic silicon waste;

[0072] In some embodiments, the nano-silicon comprises photovoltaic silicon waste. For example, the photovoltaic silicon powder is a silicon powder material obtained by purifying and removing impurities from common commercial photovoltaic silicon waste and screening the particle size to be less than 2 microns.

[0073] C. The D50 of the graphite is 2 μm-6 μm.

[0074] Optionally, the D50 of the graphite may be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, or any value between 2 μm and 6 μm.

[0075] In some embodiments, the method for preparing the titanium oxide modified nano-silicon-graphite composite negative electrode material satisfies at least one of the following conditions:

[0076] A. The titanium source comprises one or more of tetrabutyl titanate, isopropyl titanate and titanium tetrachloride;

[0077] B. the dispersant comprises PVP;

[0078] C. The conductive agent includes one or more of carbon black, acetylene black, carbon nanotubes and graphene;

[0079] Preferably, the conductive agent comprises single-walled carbon nanotubes;

[0080] D. the solvent includes an alcohol solvent;

[0081] It should be noted that the alcohol solvent includes one or more of methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerol, n-butanol, 1,3-butanediol, 1,4-butanediol, n-pentanol and 2-hexanol;

[0082] E. the resin comprises one or more of phenolic resin, epoxy resin and urea-formaldehyde resin;

[0083] F. The graphite includes one or more of natural crystalline graphite, natural cryptocrystalline graphite, natural crystalline vein graphite, artificial graphite and conductive graphite.

[0084] Preferably, the graphite comprises artificial graphite.

[0085] In some embodiments, the method for preparing the titanium oxide modified nano-silicon-graphite composite negative electrode material satisfies at least one of the following conditions:

[0086] A. The mass ratio of the nano-silicon to the solvent is 5-20:100;

[0087] Optionally, the mass ratio of nano-silicon to solvent can be 5:100, 10:100, 15:100, 20:100 or any value between 5-20:100;

[0088] B. the solid content of the titanium source in the first mixed slurry is 2%-8%;

[0089] Optionally, the solid content of the titanium source in the first mixed slurry may be 2%, 4%, 6%, 8%, or any value between 2% and 8%;

[0090] C. the solid content of the dispersant in the first mixed slurry is 20%-30%;

[0091] Optionally, the solid content of the dispersant in the first mixed slurry may be 20%, 25%, 30%, or any value between 20% and 30%;

[0092] D. The solid content of the conductive agent in the first mixed slurry is 0.5%-3%;

[0093] Optionally, the solid content of the conductive agent in the first mixed slurry may be 0.5%, 1%, 2%, 3%, or any value between 0.5% and 3%;

[0094] E. The mass ratio of the nano-silicon, the resin and the graphite is 1:0.6-1.5:1-3;

[0095] Optionally, the mass ratio of nano-silicon, resin and graphite can be 1:0.6:1, 1:1.5:1, 1:0.6:2, 1:0.6:3, 1:1.5:3 or any value between 1:0.6-1.5:1-3;

[0096] F. The mass ratio of the primary coated composite negative electrode material to the carbon source is 100:5-12.

[0097] Optionally, the mass ratio of the primary coating composite negative electrode material to the carbon source can be 100:5, 100:10, 100:12 or any value between 100:5 and 12.

[0098] In some embodiments, the method for preparing the titanium oxide modified nano-silicon-graphite composite negative electrode material satisfies at least one of the following conditions:

[0099] A. The second mixing time is 2h-5h;

[0100] Optionally, the second mixing time can be 2h, 3h, 4h, 5h or any value between 2h and 5h;

[0101] B. When performing the first mixing, the second mixing and the third mixing, each is also independently subjected to sand grinding, and the diameter of the zirconium beads used in the sand grinding is less than 0.5 mm.

[0102] It is important to note that sanding can reduce the particle size of the material and prevent silicon agglomeration.

[0103] Optionally, the diameter of the zirconium beads can be any value between 0.01 mm, 0.1 mm, 0.4 mm or less than 0.5 mm.

[0104] In some embodiments, the first high temperature treatment includes a third high temperature treatment and a fourth high temperature treatment performed sequentially;

[0105] The third high temperature treatment has a heating rate of 15°C / min-25°C / min, a holding temperature of 300°C-600°C, and a holding time of 1h-3h;

[0106] Optionally, the heating rate of the third high temperature treatment may be 15°C / min, 20°C / min, 25°C / min, or any value between 15°C / min and 25°C / min; the holding temperature may be 300°C, 400°C, 500°C, 600°C, or any value between 300°C and 600°C; and the holding time may be 1 hour, 2 hours, 3 hours, or any value between 1 hour and 3 hours.

[0107] The fourth high temperature treatment has a heating rate of 10°C / min-20°C / min, a holding temperature of 600°C-1000°C, and a holding time of 4h-12h.

[0108] Optionally, the heating rate of the fourth high temperature treatment can be 10℃ / min, 15℃ / min, 20℃ / min or any value between 10℃ / min-20℃ / min, the holding temperature can be 600℃, 700℃, 800℃, 900℃, 1000℃ or any value between 600℃-1000℃, and the holding time can be 4h, 8h, 12h or any value between 4h-12h.

[0109] In some embodiments, the second high temperature treatment includes a fifth high temperature treatment and a sixth high temperature treatment performed sequentially;

[0110] The fifth high temperature treatment is performed at a holding temperature of 250°C-350°C, a holding time of ≥3h, and a rotation speed of 50r / min-100r / min;

[0111] Optionally, the holding temperature of the fifth high temperature treatment may be 250° C., 300° C., 350° C., or any value between 250° C. and 350° C.; the holding time may be 3 h, 4 h, 5 h, 10 h, or any value ≥ 3 h; and the rotation speed may be 50 r / min, 75 r / min, 100 r / min, or any value between 50 r / min and 100 r / min.

[0112] The sixth high-temperature treatment has a holding temperature of 900-1100° C., a holding time of ≥5 hours, and a rotation speed of 50 r / min-100 r / min.

[0113] Optionally, the holding temperature of the sixth high temperature treatment can be 900℃, 1000℃, 1100℃ or any value between 900-1100℃, the holding time can be 5h, 8h, 10h, 15h or any value ≥5h, and the rotation speed can be 50r / min, 75r / min, 100r / min or any value between 50r / min-100r / min.

[0114] It should be noted that the setting of gradient temperature increase during carbonization is conducive to controlling the decomposition rate, allowing unstable substances (such as moisture and low molecular weight organic matter) to fully decompose and escape, which helps to reduce the impact of residual impurities on the integrity of the carbon skeleton and form a dense carbonized layer.

[0115] The second aspect of the present application provides a titanium oxide modified nano-silicon-graphite composite negative electrode material, which is prepared by the preparation method of the titanium oxide modified nano-silicon-graphite composite negative electrode material.

[0116] In some embodiments, the titanium oxide modified nano silicon-graphite composite negative electrode material prepared by the preparation method of the titanium oxide modified nano silicon-graphite composite negative electrode material of the present application comprises a core and a first carbon coating layer and a second carbon coating layer stacked on the surface of the core, and the specific structure is as follows: Figure 1 As shown, the core includes small-size graphite particles, nano-silicon particles and conductive agents arranged on the surface and gaps of the graphite particles, wherein a titanium oxide coating layer is provided on the surface of the nano-silicon particles; and the first carbon coating layer is provided between the core and the second coating layer.

[0117] It should be noted that titanium oxide modification and multilayer carbon coating reduce the direct contact between silicon particles and the electrolyte.

[0118] It should also be noted that the structural design of the titanium oxide-modified nano-silicon-graphite composite negative electrode material contains both flexible connections (long chain structures formed by carbonization of conductive agents or dispersants) and rigid connections (such as hard carbon formed by titanium oxide and resin), which inhibit expansion on the one hand and improve conductivity on the other.

[0119] The third aspect of the present application provides a lithium-ion battery, comprising the titanium oxide modified nano-silicon-graphite composite negative electrode material.

[0120] A fourth aspect of the present application provides an electrical device comprising the lithium-ion battery.

[0121] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be understood by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0122] Example 1

[0123] This embodiment provides a method for preparing a titanium oxide modified nano-silicon-graphite composite negative electrode material, the specific steps of which include:

[0124] S1: The first step is to prepare nano-silicon slurry. Take 250g of photovoltaic silicon powder, stir and disperse it in 1500g of anhydrous ethanol, and then put the dispersed slurry into a sand mill for 10 hours. The process controls the sand milling speed to 1000r / min. Test the silicon particle size and if it meets the requirements (D50 <100nm, D90 <400nm), proceed to the next step.

[0125] S2: 20 g of butyl titanate was slowly dripped into the nano-silicon slurry, and after sand milling for 2 h, 100 g of PVP (average molecular weight: 58,000) was added and treated for 1 h. Then, 5 g of single-walled carbon nanotube powder was added and sand milling was continued for another 1 h.

[0126] S3: adding 250 g of phenolic resin powder and 750 g of artificial graphite particles to the sand-milled slurry, continuing the sand-milling process for 2 h, and spray-drying the obtained precursor slurry to obtain a composite negative electrode precursor;

[0127] S4: Add the above composite negative electrode precursor into a box furnace, raise the temperature to 450°C at a heating rate of 20°C / min under N2 protective atmosphere and keep it warm for 2 hours, then raise the temperature to 900°C at a heating rate of 15°C / min and keep it warm for 5 hours, and obtain a primary coated composite negative electrode material after high-temperature carbonization treatment;

[0128] S5: The primary coated composite negative electrode material was mixed with 25g glucose and 45g high temperature asphalt and added to a rolling fusion coating machine for secondary high temperature coating. First, the mixture was rotated at a speed of 800r / min for 30min; then the temperature was raised to 280℃ under nitrogen protection and the coating was rotated for 3h (coating speed was 80r / min), and then the temperature was raised to 1000℃ and the carbonization was started for 5h (carbonization speed was 50r / min). After the carbonization was completed, the material was cooled to room temperature with the furnace, sieved and demagnetized to obtain a titanium oxide modified nano-silicon-graphite composite negative electrode material. The SEM of the titanium oxide modified nano-silicon-graphite composite negative electrode material is as follows: Figure 2 shown.

[0129] Example 2

[0130] The difference from Example 1 is that the amount of butyl titanate is 30 g.

[0131] Example 3

[0132] The difference from Example 1 is that the amount of butyl titanate is 30 g and the amount of phenolic resin powder is 300 g.

[0133] Example 4

[0134] The difference from Example 1 is that the phenolic resin powder is 300 g, the artificial graphite particles are 1000 g, the glucose is 30.4 g, and the high-temperature asphalt is 59.6 g.

[0135] Example 5

[0136] The difference from Example 1 is that no glucose is added, and only 45 g of high-temperature asphalt is added.

[0137] Comparative Example 1

[0138] Take 250g of photovoltaic silicon powder, 750g of artificial graphite powder, 25g of glucose and 45g of high-temperature asphalt and add them into a rolling fusion coating machine for high-temperature coating. First, at a speed of 800r / min, the mixing time is 30min; then, under nitrogen protection, the temperature is raised to 280℃ and the coating is rotated for 3h (the coating speed is 80r / min), and then the temperature is raised to 1000℃ and the carbonization is started for 5h (the carbonization speed is 50r / min). After the carbonization is completed, it is cooled to room temperature with the furnace, sieved and demagnetized to obtain the micron silicon / graphite composite negative electrode material.

[0139] Comparative Example 2

[0140] S1: The first step is to prepare nano-silicon slurry. Take 250g of photovoltaic silicon powder, stir and disperse it in 1500g of anhydrous ethanol, and then put the dispersed slurry into a sand mill for 10 hours. The sand milling speed is controlled at 1000r / min. The silicon particle size meets the requirements (D50 <100nm, D90 <400nm) and proceed to the next step.

[0141] S2: 100 g of PVP (average molecular weight: 58,000) was added to the sand-grinding slurry and treated for 1 h;

[0142] S3: adding 750 g of artificial graphite particles, continuing the sand milling process for 2 h, and spray drying the obtained precursor slurry to obtain a composite negative electrode precursor;

[0143] S4: Add the above composite negative electrode precursor into a box furnace, raise the temperature to 450°C at a heating rate of 15-25°C / min under N2 protective atmosphere and keep it warm for 2 hours, then raise the temperature to 900°C at a heating rate of 10-20°C / min and keep it warm for 3 hours, and obtain a primary coated composite negative electrode material after high-temperature carbonization treatment;

[0144] S5: The composite negative electrode material coated once was mixed with 25g of glucose and 45g of high-temperature asphalt and added into a rolling fusion coating machine for secondary high-temperature coating. First, the mixing time was 30min at a speed of 800r / min; then, the temperature was raised to 280℃ under nitrogen protection and the coating was carried out for 3h (the coating speed was 80r / min), and then the temperature was raised to 1000℃ and the carbonization was started for 5h (the carbonization speed was 50r / min). After the carbonization was completed, the material was cooled to room temperature with the furnace, sieved, and demagnetized to obtain a nano-silicon-graphite composite negative electrode material.

[0145] Comparative Example 3

[0146] The difference from Example 1 is that step S5 is not performed, and a primary coated composite negative electrode material is obtained.

[0147] Comparative Example 4

[0148] The difference from Example 1 is that no butyl titanate is added.

[0149] Comparative Example 5

[0150] The difference from Example 1 is that butyl titanate, PVP, single-walled carbon nanotube powder, phenolic resin powder and artificial graphite particles are added to the nano-silicon slurry and mixed simultaneously without stepwise addition.

[0151] The negative electrode materials prepared in the above examples and comparative examples were subjected to material powder tests, and lithium-ion batteries were prepared using the negative electrode materials prepared in the examples and comparative examples, and their electrochemical properties were tested. The test results are shown in Table 1.

[0152] The preparation method of the lithium-ion battery specifically includes: compounding the negative electrode materials provided in the embodiments and comparative examples with graphite, mixing and dissolving the compounded negative electrode material, conductive agent and binder in a solvent in a mass ratio of 95:2:3, controlling the solid content to 48%, coating on a copper foil current collector, and vacuum drying to obtain a negative electrode sheet. The obtained negative electrode sheet is combined with a ternary 5 series positive electrode sheet, and the process is followed by winding, packaging, baking, liquid injection, formation, and capacity division to obtain a lithium-ion battery (battery model is 18650 cylindrical battery with a nominal capacity of 3000mAh).

[0153] The 18650 cylindrical lithium-ion battery was tested using the battery testing system of Shenzhen Xinwei Co., Ltd. The test conditions were: room temperature, 0.5C constant current charge and discharge, and charge and discharge cut-off voltage of 2.5V-4.2V.

[0154] Table 1 Performance test

[0155]

[0156] analyze:

[0157] Table 1 shows the physical, chemical, and performance indicators of titanium oxide-modified nano-silicon-graphite composite anode materials prepared in the Examples and Comparative Examples of this application. The composite structure constructed in this application increased the cycle life of the composite anode material to over 680 cycles, and reduced the electrode expansion rate to 35% (calculated by disassembly after 50 cycles of full charge).

[0158] Comparing Example 1 with Comparative Example 4, it can be seen that the addition of titanium oxide modification significantly improves the material's cycling performance. Furthermore, Comparative Example 5 shows that this improvement is no longer significant after changing the order of raw material addition during the sanding process. It is inferred that the mixed addition hinders the deposition process of the titanium source and the silicon particle surface, resulting in the ineffective generation of modified sites. Comparing Example 1 with Comparative Examples 2 and 3, the design of the carbon coating significantly improves the overall performance of the material, with the first carbon coating layer having a more pronounced effect on cycling.

[0159] In summary, the titanium oxide modified nano-silicon-graphite composite structure proposed in this application shows good capacity retention during the charge and discharge cycle, and has a high first coulombic efficiency and cycle life, and has broad application prospects.

[0160] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

[0161] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and to form distinct embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of this application and should not be construed as an admission or any implication that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing a titanium oxide modified nano-silicon-graphite composite negative electrode material, characterized in that: include: performing a first mixing of nano-silicon and a solvent to obtain a nano-silicon solution; performing a second mixing of the nano-silicon solution, titanium source, dispersant, and conductive agent to obtain a first mixed slurry; performing a third mixing of the first mixed slurry, resin and graphite to obtain a second mixed slurry; spray drying the second mixed slurry to obtain a composite negative electrode precursor; Under a protective atmosphere, subjecting the composite negative electrode precursor to a first high-temperature treatment to obtain a primary coated composite negative electrode material; Under a protective atmosphere, the primary coated composite negative electrode material and a carbon source are subjected to a fourth mixing and a second high-temperature treatment to obtain a titanium oxide modified nano-silicon-graphite composite negative electrode material.

2. The method for preparing the titanium oxide modified nano-silicon-graphite composite negative electrode material according to claim 1, wherein: At least one of the following conditions is met: A. The D50 of the nano-silicon in the nano-silicon solution is less than 100 nm, and the D90 is less than 400 nm; B. the nano-silicon comprises pure nano-silicon and / or photovoltaic silicon waste; C. The D50 of the graphite is 2 μm-6 μm.

3. The method for preparing the titanium oxide modified nano-silicon-graphite composite negative electrode material according to claim 1, wherein: At least one of the following conditions is met: A. The titanium source comprises one or more of tetrabutyl titanate, isopropyl titanate and titanium tetrachloride; B. the dispersant comprises PVP; C. The conductive agent includes one or more of carbon black, acetylene black, carbon nanotubes and graphene; D. the solvent includes an alcohol solvent; E. the resin comprises one or more of phenolic resin, epoxy resin and urea-formaldehyde resin; F. The graphite includes one or more of natural crystalline graphite, natural cryptocrystalline graphite, natural crystalline vein graphite, artificial graphite and conductive graphite.

4. The method for preparing the titanium oxide modified nano-silicon-graphite composite negative electrode material according to claim 3, characterized in that: At least one of the following conditions is met: A. The mass ratio of the nano-silicon to the solvent is 5-20:100; B. the solid content of the titanium source in the first mixed slurry is 2%-8%; C. the solid content of the dispersant in the first mixed slurry is 20%-30%; D. The solid content of the conductive agent in the first mixed slurry is 0.5%-3%; E. The mass ratio of the nano-silicon, the resin and the graphite is 1:0.6-1.5:1-3; F. The mass ratio of the primary coated composite negative electrode material to the carbon source is 100:5-12.

5. The method for preparing the titanium oxide modified nano-silicon-graphite composite negative electrode material according to claim 1, wherein: At least one of the following conditions is met: A. The second mixing time is 2h-5h; B. When performing the first mixing, the second mixing and the third mixing, each is also independently subjected to sand grinding, and the diameter of the zirconium beads used in the sand grinding is less than 0.5 mm.

6. The method for preparing the titanium oxide modified nano-silicon-graphite composite negative electrode material according to claim 1, characterized in that: The first high temperature treatment includes a third high temperature treatment and a fourth high temperature treatment performed sequentially; The third high temperature treatment has a heating rate of 15°C / min-25°C / min, a holding temperature of 300°C-600°C, and a holding time of 1h-3h; The fourth high temperature treatment has a heating rate of 10°C / min-20°C / min, a holding temperature of 600°C-1000°C, and a holding time of 4h-12h.

7. The method for preparing the titanium oxide modified nano-silicon-graphite composite negative electrode material according to any one of claims 1 to 6, characterized in that: The second high temperature treatment includes a fifth high temperature treatment and a sixth high temperature treatment performed sequentially; The fifth high temperature treatment is performed at a holding temperature of 250°C-350°C, a holding time of ≥3h, and a rotation speed of 50r / min-100r / min; The sixth high-temperature treatment has a holding temperature of 900-1100° C., a holding time of ≥5 hours, and a rotation speed of 50 r / min-100 r / min.

8. A titanium oxide modified nano-silicon-graphite composite negative electrode material, characterized in that: The titanium oxide modified nano-silicon-graphite composite negative electrode material is prepared by the preparation method of any one of claims 1 to 7.

9. A lithium-ion battery, characterized in that: The invention comprises the titanium oxide modified nano-silicon-graphite composite negative electrode material according to claim 8.

10. An electrical device, characterized in that: Including the lithium ion battery according to claim 9.

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