Long cycle lithium battery negative electrode material and preparation method and application thereof

Abstract

The present invention relates to a long-cycle lithium battery negative electrode material and a preparation method and application thereof. The long-cycle lithium battery negative electrode material comprises: a silicon-based powder material, a carbon layer material and a titanium dioxide coating material; the silicon-based powder material is a powder material containing electrochemical activity accounting for 90wt%-99.49wt% of the negative electrode material, including one or more of silicon dioxide, modified silicon dioxide, doped silicon dioxide and amorphous silicon alloy; the carbon layer material is a soft carbon material accounting for 0.5wt%-7wt% of the negative electrode material; the titanium dioxide coating material is titanium dioxide accounting for 0.01wt%-3wt% of the negative electrode material; the outer surface of the silicon-based powder material is coated with the carbon layer material, and the titanium dioxide coating material is coated on the surface of the carbon layer material to form the long-cycle lithium battery negative electrode material.

Description

Technical Field

[0001] The present invention relates to the field of material technology, and in particular to a long-cycle lithium battery negative electrode material and a preparation method and application thereof. Background Art

[0002] Silicon-based lithium-ion negative electrode materials are mainly divided into two categories: crystalline silicon and silicon oxide. Silicon negative electrode materials have extremely high theoretical specific capacity (4200mAh / g), while the theoretical capacity of the current mainstream graphite negative electrode is only 372mAh / g. The capacity of silicon negative electrode materials is more than ten times that of graphite negative electrode, so it has more development potential, but the disadvantages of silicon negative electrode are obvious. The volume expansion effect of up to 400% has restricted its practical application. In comparison, silicon oxide materials have smaller volume expansion and a certain high capacity. Therefore, silicon oxide lithium-ion battery negative electrode materials are more popular.

[0003] In patent CN201811523656.6, the applicant dispersed silicon dioxide particles in a surfactant, added an alcohol solution of a titanium dioxide precursor, mixed and dried, and heat-treated in an inert atmosphere at 400-550°C to obtain a first mixture containing TiO2@SiO; the first mixture was mixed with graphite, a conductive agent, and a CMC / PAA binder to obtain a slurry; the slurry was applied to the surface of the current collector, dried at 50-80°C, and then heat-treated at 80-150°C to obtain the titanium dioxide / silicon dioxide / graphite composite electrode. The TiO2@SiO obtained in this patent has a charging capacity of only 1280mAh / g and a first efficiency of only 71.5%, mainly because the surface of silicon dioxide is easily oxidized during spray drying, resulting in an irreversible increase in capacity.

[0004] In patent CN201911380610.8, the applicant calcined titanium source, lithium source and silicon source as raw materials to obtain silicon-based / lithium titanate composite materials. Since titanium dioxide is used as the titanium source, the surface bonding between titanium dioxide and silicon oxide is not strong enough, which affects the later cycle performance. Summary of the invention

[0005] The embodiments of the present invention provide a long-cycle lithium battery negative electrode material, a preparation method and an application thereof. By carbon-coating the surface of a silicon-based material and then in-situ growing titanium dioxide, the double coating structure of the titanium dioxide layer and the carbon film greatly reduces the volume expansion effect, while avoiding the oxidation of the silicon oxide surface during spray drying. In addition, titanium dioxide can improve the lithium ion diffusion coefficient and surface impedance, so that the electrochemical performance of the negative electrode material can be improved. Moreover, the lattice channels of titanium dioxide are more open, and lithium ions are more easily deintercalated, so the rate performance is also improved.

[0006] In a first aspect, an embodiment of the present invention provides a long-cycle lithium battery negative electrode material, a silicon-based powder material, a carbon layer material, and a titanium dioxide coating material;

[0007] The silicon-based powder material is a powder material containing electrochemical activity, accounting for 90wt%-99.49wt% of the negative electrode material, including one or more of silicon oxide, modified silicon oxide, doped silicon oxide, and amorphous silicon alloy;

[0008] The carbon layer material is a soft carbon material accounting for 0.5wt%-7wt% of the negative electrode material;

[0009] The titanium dioxide coating material is titanium dioxide accounting for 0.01wt%-3wt% of the negative electrode material;

[0010] The outer surface of the silicon-based powder material is coated with the carbon layer material, and the titanium dioxide coating material is coated on the surface of the carbon layer material to form the long-cycle lithium battery negative electrode material.

[0011] Preferably, the titanium dioxide is obtained by calcining a titanium dioxide precursor material, and the titanium dioxide precursor material includes one or more of tetrabutyl titanate, n-butyl titanate, tetraethyl titanate, isopropyl titanate, titanium isooctylate or titanium acetylacetonate.

[0012] Preferably, in the long cycle negative electrode material, the reaction temperature of the coating process of coating the soft carbon material on the outer surface of the silicon-based powder material is not higher than 1000°C.

[0013] In a second aspect, an embodiment of the present invention provides a method for preparing the negative electrode material for a long-cycle lithium battery according to the first aspect, the preparation method comprising:

[0014] The silicon-based powder material is placed in a high-temperature rotary furnace, heated to 800° C.-1000° C. under a protective atmosphere, an organic gas source is introduced for chemical vapor deposition, and the temperature is kept for 2-4 hours. After the organic gas source is turned off and the temperature is lowered, a soft carbon-coated silicon-based negative electrode material is obtained;

[0015] The soft carbon-coated silicon-based negative electrode material and the titanium dioxide precursor are dispersed in a first solvent in a first ratio and water is added in a second ratio for a hydrolysis reaction for 6-24 hours, and the dispersion after the hydrolysis reaction is spray-dried to obtain a primary product; the first solution includes any one or more of methanol, ethanol, ethylene glycol, isopropanol, acetone, and tetrahydrofuran;

[0016] The primary product is kept at 800-1000° C. in a protective atmosphere for 6-24 hours to obtain the long-cycle lithium battery negative electrode material.

[0017] Preferably, the organic gas source includes: one or more of methane, acetylene, propylene or propane;

[0018] The protective atmosphere includes: a nitrogen atmosphere or an inert gas atmosphere.

[0019] Preferably, the first ratio is: the mass ratio of the soft carbon-coated silicon-based negative electrode material to the titanium dioxide precursor is 1:0.06-1:0.001;

[0020] The mass of the first solvent is 1-10 times the total mass of the soft carbon-coated silicon-based negative electrode material and the titanium dioxide precursor;

[0021] The second ratio is: the mass ratio of water to titanium dioxide precursor is 10: 1-100: 1. In a third aspect, an embodiment of the present invention provides a negative electrode sheet of a lithium battery, comprising the long-cycle lithium battery negative electrode material described in the first aspect.

[0022] In a fourth aspect, an embodiment of the present invention provides a lithium battery, comprising the negative electrode plate described in the third aspect above.

[0023] Preferably, the lithium battery includes any one of a lithium-ion battery, a lithium-ion supercapacitor, a lithium-sulfur battery, and an all-solid-state lithium battery.

[0024] Preferably, the lithium battery is used as a vehicle power battery.

[0025] An embodiment of the present invention provides a long-cycle lithium battery negative electrode material. A layer of high-quality and uniform soft carbon is coated on the surface of a silicon-based powder material by vapor deposition technology, and then spray-dried and calcined to obtain a silicon-based material with a double coating of titanium dioxide and soft carbon. The double coating structure formed by carbon-coating the surface of the silicon-based material and then in-situ growing titanium dioxide greatly reduces the volume expansion effect. At the same time, titanium dioxide can improve the lithium ion diffusion coefficient and surface impedance, so that the electrochemical performance of the negative electrode material can be improved. Not only that, the surface of the silicon-based powder material after carbon coating has more active sites, which will be beneficial to the loading of the titanium source on the surface, thereby forming a dense titanium dioxide structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The technical solution of the embodiment of the present invention is further described in detail below through the drawings and examples.

[0027] Figure 1 A flow chart of a method for preparing a negative electrode material for a long-cycle lithium battery provided by an embodiment of the present invention;

[0028] Figure 2 A scanning electron microscope (SEM) image of the negative electrode material for a long-cycle lithium battery provided in Example 1 of the present invention;

[0029] Figure 3A scanning electron microscope (SEM) image of the silicon-based lithium-ion battery negative electrode material provided in Comparative Example 1 of the present invention;

[0030] Figure 4 This is a scanning electron microscope (SEM) image of the silicon-based lithium-ion battery negative electrode material provided in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0031] The present invention is further described below through the accompanying drawings and specific embodiments, but it should be understood that these embodiments are only used for more detailed description and should not be understood as limiting the present invention in any form, that is, they are not intended to limit the protection scope of the present invention.

[0032] The present invention relates to a long-cycle lithium battery negative electrode material, comprising: a silicon-based powder material, a carbon layer material and a titanium dioxide coating material; wherein the outer surface of the silicon-based powder material is coated with the carbon layer material, and the titanium dioxide coating material is coated on the surface of the carbon layer material to form the long-cycle lithium battery negative electrode material.

[0033] The silicon-based powder material is an electrochemically active powder material accounting for 90wt%-99.49wt% of the negative electrode material, including one or more of silicon oxide, modified silicon oxide, doped silicon oxide, and amorphous silicon alloy;

[0034] The carbon layer material is a soft carbon material accounting for 0.5wt%-7wt% of the negative electrode material; the reaction temperature of the coating process of coating the soft carbon material on the outer surface of the silicon-based powder material is not higher than 1000°C.

[0035] The titanium dioxide coating material is titanium dioxide accounting for 0.01wt%-3wt% of the negative electrode material; the titanium dioxide is obtained by calcining the titanium dioxide precursor material. The titanium dioxide precursor material includes: one or more of tetrabutyl titanate, n-butyl titanate, tetraethyl titanate, isopropyl titanate, titanium isooctylate or titanium acetylacetonate.

[0036] Preferably, in the long cycle negative electrode material, the silicon-based powder material accounts for 92wt%-98wt%, the titanium dioxide accounts for 0.01wt%-2wt%, and the soft carbon material accounts for 1wt%-6wt%.

[0037] The present invention coats a layer of high-quality and uniform soft carbon on the surface of a silicon-based powder material through vapor deposition technology, and then spray-dries and calcines it to obtain a silicon-based material with a double coating of titanium dioxide and soft carbon. The double coating structure formed by carbon-coating the surface of the silicon-based material and then in-situ growing titanium dioxide greatly reduces the volume expansion effect. At the same time, titanium dioxide can improve the lithium ion diffusion coefficient and surface impedance, so that the electrochemical performance of the negative electrode material can be improved. In addition, the surface of the silicon-based powder material after carbon coating has more active sites, which is conducive to the loading of the titanium source on the surface, thereby forming a dense titanium dioxide structure.

[0038] The long-cycle negative electrode material proposed in the present invention can be used to prepare negative electrode plates for lithium batteries. The negative electrode plates can be used in lithium batteries such as lithium-ion batteries, lithium-ion supercapacitors, lithium-sulfur batteries, and all-solid-state lithium batteries, and are particularly suitable for long-range large-scale automotive power batteries.

[0039] The long cycle negative electrode material of the present invention can be prepared according to the following method, the main steps are as follows: Figure 1 As shown, including:

[0040] Step 110, placing the silicon-based powder material in a high-temperature rotary furnace, heating it to 800°C-1000°C under a protective atmosphere, introducing an organic gas source for chemical vapor deposition, keeping the temperature for 2-4 hours, and closing the organic gas source to cool down to obtain a soft carbon-coated silicon-based negative electrode material;

[0041] Specifically, the silicon-based powder material is a powder material containing electrochemical activity, including one or more of silicon oxide, modified silicon oxide, doped silicon oxide, and amorphous silicon alloy;

[0042] The organic gas source includes: one or more of methane, acetylene, propylene or propane;

[0043] The protective atmosphere includes: nitrogen atmosphere or inert gas atmosphere.

[0044] Preferably, the heating rate is 2°C / min.

[0045] Step 120, dispersing the soft carbon-coated silicon-based negative electrode material and the titanium dioxide precursor in a first solvent at a first ratio and adding water at a second ratio to perform a hydrolysis reaction for 6-24 hours, and spray drying the dispersion after the hydrolysis reaction to obtain a primary product;

[0046] The titanium dioxide precursor material includes one or more of tetrabutyl titanate, n-butyl titanate, tetraethyl titanate, isopropyl titanate, titanium isooctylate or titanium acetylacetonate.

[0047] The first solution includes any one or more of methanol, ethanol, ethylene glycol, isopropanol, acetone, and tetrahydrofuran.

[0048] The first ratio is: the mass ratio of the soft carbon-coated silicon-based negative electrode material to the titanium dioxide precursor is 1:0.06-1:0.001;

[0049] The mass of the first solvent is 1-10 times the total mass of the soft carbon-coated silicon-based negative electrode material and the titanium dioxide precursor;

[0050] The second ratio is: the mass ratio of water to titanium dioxide precursor is 10:1-100:1.

[0051] Step 130, heat the primary product at 800-1000° C. in a protective atmosphere for 6-24 hours to obtain a negative electrode material for a long-cycle lithium battery.

[0052] The mixing ratio of each material shall be based on the component ratio in the final long-cycle negative electrode material.

[0053] The embodiment of the present invention provides a method for preparing a long-cycle negative electrode material, which isolates side reactions and improves electronic conductivity by coating the surface of a silicon-based material with carbon, and at the same time, the excellent carbon layer can alleviate the volume change of the silicon-based material when lithium is extracted and inserted. On this basis, the complex morphology of the carbon layer surface is used to in-situ coat a titanium dioxide precursor, and a long-cycle lithium battery negative electrode material double-coated with a carbon layer and a titanium dioxide layer is obtained by high-temperature calcination.

[0054] In order to better understand the technical solution provided by the present invention, the following uses multiple specific examples to illustrate the specific process of preparing long-cycle negative electrode materials using the method provided by the above embodiment of the present invention, as well as the method of applying it to secondary batteries and the battery characteristics.

[0055] Example 1

[0056] This embodiment 1 provides a long cycle negative electrode material.

[0057] The long cycle negative electrode material of this embodiment is recorded as sample 1#, and is composed of 95 wt% silicon dioxide, 2 wt% titanium dioxide and 3 wt% soft carbon.

[0058] The specific preparation process is as follows: silicon dioxide is placed in a high-temperature rotary furnace under an argon atmosphere and heated to 1000°C, argon and propylene in an amount equal to that of argon are introduced in a volume ratio of 1:1 for chemical vapor deposition, and the temperature is kept for 2 hours, and the gas source is turned off to cool down to obtain a carbon-coated silicon-based material. 1 kg of carbon-coated silicon-based negative electrode material and 45 g of isooctyl titanium are dispersed in 5.23 kg of ethanol solvent and 900 g of water are added for hydrolysis reaction for 12 hours, and the dispersion is spray-dried to obtain the primary product; the primary product is kept at 900°C in an inert gas atmosphere for 12 hours to obtain a long-cycle lithium battery negative electrode material (sample 1#).

[0059] Figure 2This is a scanning electron microscope (SEM) image of the long cycle lithium battery negative electrode material provided in Example 1 of the present invention.

[0060] The obtained negative electrode material, conductive additive carbon black, and adhesive (1:1 sodium cellulose and styrene-butadiene rubber) are weighed in a ratio of 95:2:3. The slurry is prepared in a pulper at room temperature. The prepared slurry is evenly coated on the copper foil. After drying in a blast drying oven at 50°C for 2 hours, it is cut into 8×8mm pole pieces and vacuum dried in a vacuum drying oven at 100°C for 10 hours. The dried pole pieces are then transferred to the glove box for standby use for battery assembly.

[0061] The simulated battery was assembled in a glove box containing a high-purity Ar atmosphere, using metallic lithium as the counter electrode and 1 mol of LiPF 6 The battery was assembled using a solution in ethylene carbonate (EC) / dimethyl carbonate (DMC) (v:v=1:1) as the electrolyte. The constant current charge and discharge mode test was performed using a charge and discharge instrument, with a discharge cut-off voltage of 0.005V and a charge cut-off voltage of 1.5V. The first week of charge and discharge tests were performed at a current density of C / 10, and the second week of discharge tests were performed at a current density of C / 10.

[0062] Example 2

[0063] This embodiment 2 provides a long cycle negative electrode material.

[0064] The long cycle negative electrode material of this embodiment is recorded as sample 2#, and is composed of 97 wt% of modified silicon oxide, 1 wt% of titanium dioxide and 2 wt% of soft carbon.

[0065] The specific preparation process is as follows: the modified silicon oxide is placed in a high-temperature rotary furnace in an argon atmosphere and heated to 850°C, argon and acetylene are introduced in a volume ratio of 2:1 for chemical vapor deposition, and the temperature is kept for 3 hours, and the gas source is turned off to cool down to obtain a carbon-coated silicon-based material. 1 kg of carbon-coated silicon-based negative electrode material and 42.5 g of tetrabutyl titanate are dispersed in 5.21 kg of ethanol solvent and 850 g of water are added for hydrolysis reaction for 12 hours. The dispersion is spray-dried to obtain the initial product; the initial product is kept at 900°C in an inert gas atmosphere for 12 hours to obtain a long-cycle lithium battery negative electrode material (sample 2#).

[0066] Example 3

[0067] This embodiment 3 provides a long cycle negative electrode material.

[0068] The long cycle negative electrode material of this embodiment is recorded as sample 3#, and is composed of 93.5wt% amorphous silicon alloy, 1.5wt% titanium dioxide and 5wt% soft carbon.

[0069] The specific preparation process is as follows: Place the amorphous silicon alloy in a high-temperature rotary furnace in an argon atmosphere and heat it to 950°C, introduce argon and mixed gas at a volume ratio of 1:2 for chemical vapor deposition, wherein the mixed gas is composed of natural gas and acetylene at a volume ratio of 1:1, keep warm for 2 hours, turn off the gas source to cool down to obtain a carbon-coated silicon-based material. Disperse 1kg of carbon-coated silicon-based negative electrode material and 49.1g of titanium acetylacetonate in 5.25kg of ethanol solvent and add 982g of water for hydrolysis reaction for 12 hours, and the dispersion is spray-dried to obtain the initial product; the initial product is kept warm at 900°C in an inert gas atmosphere for 12 hours to obtain a long-cycle lithium battery negative electrode material (sample 3#).

[0070] Example 4

[0071] This embodiment 4 provides a long cycle negative electrode material.

[0072] The long cycle negative electrode material of this embodiment is recorded as sample 4#, and is composed of 95.7 wt% doped silicon dioxide, 0.8 wt% titanium dioxide and 3.5 wt% soft carbon.

[0073] The specific preparation process is as follows: doped silicon oxide is placed in a high-temperature rotary furnace in an argon atmosphere and heated to 1000°C, argon and methane are introduced in a volume ratio of 1:2 for chemical vapor deposition, and the temperature is kept for 2 hours, and the gas source is turned off to cool down to obtain a carbon-coated silicon-based material. 1kg of carbon-coated silicon-based negative electrode material and 26.2g of titanium acetylacetonate are dispersed in 5.13kg of ethanol solvent and 524g of water are added for hydrolysis reaction for 12 hours. The dispersion is spray-dried to obtain the initial product; the initial product is kept at 900°C in an inert gas atmosphere for 12 hours to obtain the long-cycle lithium battery negative electrode material (sample 4#).

[0074] Example 5

[0075] This embodiment 5 provides a long cycle negative electrode material.

[0076] The long cycle negative electrode material of this embodiment is recorded as sample 5#, and is composed of 96.0 wt% silicon dioxide, 1.4 wt% titanium dioxide and 2.6 wt% soft carbon.

[0077] The specific preparation process is as follows: silicon dioxide is placed in a high-temperature rotary furnace under an argon atmosphere and heated to 900°C, argon and propane are introduced at a volume ratio of 1:2.5 for chemical vapor deposition, and the temperature is kept for 1.5 hours. The gas source is turned off to cool down to obtain a carbon-coated silicon-based material. 1 kg of carbon-coated silicon-based negative electrode material and 38 g of isooctyl titanium are dispersed in 5.19 kg of ethanol solvent and 760 g of water are added for hydrolysis reaction for 12 hours. The dispersion is spray-dried to obtain a primary product; the primary product is kept at 900°C in an inert gas atmosphere for 12 hours to obtain the long-cycle lithium battery negative electrode material (sample 5#).

[0078] Example 6

[0079] This embodiment 6 provides a long cycle negative electrode material.

[0080] The long cycle negative electrode material of this embodiment is recorded as sample 6#, and is composed of 97.0 wt% of modified silicon dioxide, 0.5 wt% of titanium dioxide and 2.5 wt% of soft carbon.

[0081] The specific preparation process is as follows: the modified silicon oxide is placed in a high-temperature rotary furnace under an argon atmosphere and heated to 800°C, argon and acetylene are introduced in a volume ratio of 2:4 for chemical vapor deposition, and the temperature is kept for 2 hours, and the gas source is turned off to cool down to obtain a carbon-coated silicon-based material. 1 kg of carbon-coated silicon-based negative electrode material and 21.4 g of n-butyl titanate are dispersed in 5.11 kg of ethanol solvent and 428 g of water are added for hydrolysis reaction for 12 hours. The dispersion is spray-dried to obtain the initial product; the initial product is kept at 900°C in an inert gas atmosphere for 12 hours to obtain the long-cycle lithium battery negative electrode material (sample 6#).

[0082] Example 7

[0083] This embodiment 7 provides a long cycle negative electrode material.

[0084] The long cycle negative electrode material of this embodiment is recorded as sample 7#, and is composed of 96.9 wt% doped silicon dioxide, 1.1 wt% titanium dioxide and 3.0 wt% soft carbon.

[0085] The specific preparation process is as follows: Place doped silicon oxide in a high-temperature rotary furnace in an argon atmosphere and heat it to 950°C, introduce argon and mixed gas at a volume ratio of 1:3 for chemical vapor deposition, wherein the mixed gas is composed of acetylene and propane at a volume ratio of 1:2, keep warm for 1.5 hours, turn off the gas source to cool down to obtain a carbon-coated silicon-based material. Disperse 1kg of carbon-coated silicon-based negative electrode material and 38.8g of isopropyl titanate in 5.2kg of ethanol solvent and add 776g of water for hydrolysis reaction for 12 hours, and the dispersion is spray-dried to obtain the initial product; the initial product is kept warm at 900°C in an inert gas atmosphere for 12 hours to obtain the long-cycle lithium battery negative electrode material (sample 7#).

[0086] Example 8

[0087] This Example 8 provides a long cycle negative electrode material.

[0088] The long cycle negative electrode material of this embodiment is recorded as sample 8#, and is composed of 94.0 wt% silicon dioxide, 1.8 wt% titanium dioxide and 4.2 wt% soft carbon.

[0089] The specific preparation process is as follows: silicon dioxide is placed in a high-temperature rotary furnace under an argon atmosphere and heated to 1000°C, and argon and mixed gas are introduced at a volume ratio of 1:2 for chemical vapor deposition, wherein the mixed gas is composed of propylene and propane at a volume ratio of 1:1, and the temperature is kept for 1.2 hours, and the gas source is turned off to cool down to obtain a carbon-coated silicon-based material. 1kg of carbon-coated silicon-based negative electrode material and 51.4g of tetraethyl titanate are dispersed in 5.26kg of ethanol solvent and 1028g of water is added for hydrolysis reaction for 12 hours, and the dispersion is spray-dried to obtain the initial product; the initial product is kept at 900°C in an inert gas atmosphere for 12 hours to obtain the long-cycle lithium battery negative electrode material (sample 8#).

[0090] For better comparison, we prepared comparison samples as follows.

[0091] Comparative Example 1

[0092] This comparative example provides a lithium-ion battery negative electrode material for comparison with Example 1, recorded as sample #9, which is composed of 97 wt% silicon dioxide and 3 wt% soft carbon.

[0093] The specific preparation process is as follows: silicon 2 oxide is placed in a high-temperature rotary furnace in an argon atmosphere and heated to 1000°C, argon and propylene in an amount equal to that of argon are introduced in a volume ratio of 1:1 for chemical vapor deposition, the temperature is kept for 2 hours, the gas source is turned off and the temperature is lowered to obtain sample 9#.

[0094] Figure 3 This is a scanning electron microscope (SEM) image of the silicon-based lithium-ion battery negative electrode material provided in Comparative Example 1 of the present invention.

[0095] Comparative Example 2

[0096] This comparative example provides a lithium ion battery negative electrode material for comparison with Example 1, recorded as sample 10#, which is composed of 95wt% silicon dioxide, 2wt% titanium dioxide and 3wt% soft carbon coated in the outermost layer.

[0097] The specific preparation process is as follows: 1 kg of silicon dioxide and 45 g of titanium isooctoxide are dispersed in 5.23 kg of ethanol solvent and 900 g of water is added for hydrolysis reaction for 12 hours. The dispersion is spray dried to obtain the primary product; the primary product is kept at 900°C in an inert gas atmosphere for 12 hours to obtain a silicon-based lithium ion negative electrode material coated with titanium dioxide. The silicon dioxide coated with titanium dioxide is placed in a high-temperature rotary furnace under an argon atmosphere and heated to 1000°C. Argon and propylene in an amount equal to that of argon are introduced in a volume ratio of 1:1 for chemical vapor deposition. The temperature is kept for 2 hours, and the gas source is turned off to cool down to obtain sample 10#.

[0098] Comparative Example 3

[0099] The comparative example provides a lithium ion battery negative electrode material for comparison with Example 1, which is recorded as sample 11# and is composed of 92wt% silicon dioxide, 6wt% titanium dioxide and 2wt% soft carbon.

[0100] The specific preparation process is as follows: silicon dioxide is placed in a high-temperature rotary furnace under an argon atmosphere and heated to 1000°C, argon and propylene in an amount equal to that of argon are introduced in a volume ratio of 1:1 for chemical vapor deposition, and the temperature is kept for 2 hours, and the gas source is turned off to cool down to obtain a carbon-coated silicon-based material. 1 kg of carbon-coated silicon-based negative electrode material and 135 g of isooctyl titanium are dispersed in 5.68 kg of ethanol solvent and 2700 g of water are added for hydrolysis reaction for 12 hours, and the dispersion is spray-dried to obtain the primary product; the primary product is kept at 900°C in an inert gas atmosphere for 12 hours to obtain sample 11#.

[0101] Figure 4 This is a scanning electron microscope (SEM) image of the silicon-based lithium-ion battery negative electrode material provided in Comparative Example 3 of the present invention.

[0102] pass Figure 2 , Figure 3 , Figure 4 The comparison shows that: by properly adjusting the ratio of titanium dioxide precursor, Figure 2 A dense titanium dioxide coating is formed on the surface, and the uniform protrusions suggest the structure of titanium dioxide particles. Figure 3 This is the SEM morphology of the product without adding titanium dioxide precursor. It can be clearly seen from the picture that the particle surface is smooth and no titanium dioxide is formed. Figure 4 This is the morphology of the embodiment with excessive addition of titanium dioxide precursor. Due to the excessive amount of precursor added, the hydrolysis is not sufficient, the surface particle size is inconsistent and irregular, and the surface titanium dioxide coating is too large, which affects the battery's gram capacity and initial efficiency.

[0103] The negative electrode materials in Examples 1-8 and Comparative Examples 1-3 were tested for initial efficiency, 0.1C reversible capacity, full battery cycle retention rate (used with graphite at 450 mAh / g), and other indicators, and the results are listed in Table 1.

[0104] Test items Initial efficiency 0.1C reversible capacity (mAh / g) 500-week cycle retention rate Example 1 1# 78.3 1799 95％ Example 2 2# 79.7 1812 94％ Example 3 3# 78.9 1768 96％ Example 4 4# 79.1 1742 93％ Example 5 5# 78.2 1745 94％ Example 6 6# 79.5 1766 96％ Example 7 7# 78.8 1738 95％ Example 8 8# 79.3 1805 96％ Comparative Example 1 9# 78.4 1688 78％ Comparative Example 2 10# 72.4 1386 72％ Comparative Example 3 11# 73.6 1465 92％

[0105] Table 1

[0106] It can be seen from the data in Table 1 that, under the same conditions, Examples 1-8 all adopt carbon coating first and then titanium dioxide coating, and the initial efficiency and full battery cycle retention rate are very high. Comparative Examples 1-3 use different coating methods for comparison, and none of them achieves the desired effect. From the perspective of Comparative Example 1, when only simple carbon coating is performed, the mechanical properties of the carbon layer are not sufficient to maintain the volume expansion of the silicon-based material. After 500 cycles, the carbon layer ruptures, and the material pulverization problem caused by stress causes the battery's cycle performance to decline. From Comparative Example 2, when the silicon oxide material is first coated with titanium dioxide, due to the lack of protection of the carbon layer, the silicon oxide material is exposed to an environment with sufficient oxygen content, and the first efficiency and charge specific capacity of silicon oxide are significantly reduced, which is not conducive to the later cycle improvement and capacity release. From comparative example 3, when the content of titanium dioxide is increased, part of the titanium dioxide precursor is not fully hydrolyzed, and dense large titanium dioxide particles are formed on the surface. Although the cycle performance of the material can be improved, excessive titanium dioxide coating hinders the diffusion of lithium ions and increases the irreversible capacity. Therefore, reasonable regulation of the carbon layer and titanium dioxide content is conducive to the improvement of cycle performance.

[0107] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A long cycle lithium battery negative electrode material, characterized in that: The long-cycle lithium battery negative electrode material comprises: silicon-based powder material, carbon layer material and titanium dioxide coating material; The silicon-based powder material is a powder material containing electrochemical activity, accounting for 90wt%-99.49wt% of the negative electrode material, including one or more of silicon oxide, modified silicon oxide, and amorphous silicon alloy; The carbon layer material is a soft carbon material accounting for 0.5wt%-7wt% of the negative electrode material; The titanium dioxide coating material is titanium dioxide accounting for 0.01wt%-3wt% of the negative electrode material; The outer surface of the silicon-based powder material is coated with the carbon layer material, and the titanium dioxide coating material is coated on the surface of the carbon layer material to form the long-cycle lithium battery negative electrode material; The titanium dioxide is obtained by calcining a titanium dioxide precursor material, and the titanium dioxide precursor material includes one or more of tetrabutyl titanate, n-butyl titanate, tetraethyl titanate, isopropyl titanate, titanium isooctylate or titanium acetylacetonate.

2. The long cycle lithium battery negative electrode material according to claim 1, characterized in that: The silicon-based powder material includes doped silicon monoxide.

3. The long cycle lithium battery negative electrode material according to claim 1, characterized in that: In the long-cycle lithium battery negative electrode material, the reaction temperature of the coating process of coating the soft carbon material on the outer surface of the silicon-based powder material is not higher than 1000°C.

4. A method for preparing a negative electrode material for a long-cycle lithium battery according to any one of claims 1 to 3, characterized in that: The preparation method comprises: The silicon-based powder material is placed in a high-temperature rotary furnace, heated to 800° C.-1000° C. under a protective atmosphere, an organic gas source is introduced for chemical vapor deposition, and the temperature is kept for 2-4 hours. After the organic gas source is turned off and the temperature is lowered, a soft carbon-coated silicon-based negative electrode material is obtained; The soft carbon-coated silicon-based negative electrode material and the titanium dioxide precursor are dispersed in a first solvent in a first ratio and water is added in a second ratio to perform a hydrolysis reaction for 6-24 hours, and the dispersion after the hydrolysis reaction is spray-dried to obtain a primary product; the first solvent includes any one or more of methanol, ethanol, ethylene glycol, isopropanol, acetone, and tetrahydrofuran; The primary product is kept at 800-1000° C. in a protective atmosphere for 6-24 hours to obtain the long-cycle lithium battery negative electrode material.

5. The preparation method according to claim 4, characterized in that: The organic gas source includes: one or more of methane, acetylene, propylene or propane; The protective atmosphere includes an inert gas atmosphere.

6. The preparation method according to claim 5, characterized in that: The protective atmosphere includes a nitrogen atmosphere.

7. The preparation method according to claim 4, characterized in that: The first ratio is: the mass ratio of the soft carbon-coated silicon-based negative electrode material to the titanium dioxide precursor is 1:0.06-1:0.001; The mass of the first solvent is 1-10 times the total mass of the soft carbon-coated silicon-based negative electrode material and the titanium dioxide precursor; The second ratio is: the mass ratio of water to titanium dioxide precursor is 10:1-100:

1.

8. A negative electrode plate of a lithium battery, characterized in that: The negative electrode plate of the lithium battery comprises the long-cycle lithium battery negative electrode material according to any one of claims 1-3.

9. A lithium battery, characterized in that: The lithium battery comprises the negative electrode plate of the lithium battery according to claim 8.

10. The lithium battery according to claim 9, characterized in that: The lithium battery includes any one of a lithium ion battery, a lithium ion supercapacitor, a lithium sulfur battery, and an all-solid-state lithium battery.

11. The lithium battery according to claim 9, characterized in that: The lithium battery is used as a vehicle power battery.

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