Lithium ion battery auxiliary coating material and preparation method and application thereof

Abstract

The invention discloses a lithium ion battery auxiliary coating material as well as a preparation method and application thereof, and relates to the technical field of lithium ion batteries. The invention provides a porous composite oxide formed by silicon dioxide nanowires and titanium dioxide nanoparticles, the whole porous composite oxide is of a porous structure, and when the porous composite oxide is used as an auxiliary coating material of a lithium ion battery, the surface of a negative graphite pole piece can be coated with the porous composite oxide to form a porous coating. Both SiO2 and TiO2 have excellent electrolyte infiltration capacity, and the porous structure formed by nanoscale materials can greatly improve the infiltration performance of the electrolyte, so that lithium ions can be quickly diffused on the diaphragm side and the negative electrode surface side, the rate capability of the lithium ion battery is favorably exerted, and the service life of the lithium ion battery is prolonged. And meanwhile, uniform distribution of charging and discharging current obtained by the graphite cathode due to the fact that the infiltration electrolyte becomes strong is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery auxiliary coating material, a preparation method and an application thereof. Background Art

[0002] Lithium-ion batteries, with their high energy density, long cycle life, high voltage plateau, low self-discharge rate, and low cost, have found widespread application in consumer electronics, electric bicycles, electric vehicles, power tools, and energy storage. A lithium-ion battery generally consists of positive and negative electrodes, a separator, an electrolyte interposed between the electrodes and the separator, and a casing. Lithium-ion battery performance is directly related to the positive and negative electrode materials and formulations, the separator characteristics, and the electrolyte composition. Different performance requirements require tailored design.

[0003] The demand for high-rate performance in lithium-ion batteries is becoming increasingly urgent. For example, in electric vehicle applications, faster charging performance is required to reduce recharging time. In power tools, higher discharge rate performance is required to output higher power. High-rate performance is also highly demanded in the fields of model aircraft and mobile phones. In addition to targeted design of the battery and electrode structures, high-rate battery design generally requires matching the corresponding positive and negative electrode materials, electrolyte, and separator. Positive and negative electrode materials are generally selected with a smaller particle size to reduce the diffusion distance of lithium ions within the material. The electrolyte must have high lithium ion conductivity, and the separator must have a higher porosity. However, the negative electrode graphite material has a general ability to wet electrolyte, and polyolefin separators are less effective in wetting electrolyte. This affects the uniformity of the charge and discharge current distribution, causes an increase in internal resistance, limits the rate performance, and even poses a safety hazard. The industry generally uses ceramic or PVDF adhesive to coat separators to improve electrolyte wettability. However, ceramic coatings are generally micron-sized, which can clog the nanometer-sized separator pores, reducing lithium ion diffusion channels and affecting rate performance. PVDF adhesive-coated separators, with their nanometer-sized coating particles, are not porous and can also clog the separator pores.

[0004] Therefore, there is an urgent need to improve the electrolyte wetting performance of the graphite negative electrode without affecting the lithium ion diffusion rate and ensuring the battery's rate performance.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a lithium-ion battery auxiliary coating material and its preparation method and application, aiming to improve the electrolyte infiltration performance of the graphite negative electrode and improve the battery rate performance.

[0007] The present invention is achieved in that:

[0008] In a first aspect, the present invention provides a lithium-ion battery auxiliary coating material, comprising a porous composite oxide formed by silica nanowires and titanium dioxide nanoparticles, wherein the mass of the silica nanowires accounts for 50%-90% of the total amount of the porous composite oxide.

[0009] In an optional embodiment, the mass proportion of the silicon dioxide nanowires in the total amount of the porous composite oxide is 80%-85%;

[0010] and / or, the silica nanowires have a diameter of 100 nm to 900 nm and a length of 5 μm to 100 μm;

[0011] and / or, the particle size of the titanium dioxide nanoparticles is 50 nm to 500 nm;

[0012] And / or, the porosity of the porous composite oxide is 40%-80%.

[0013] In a second aspect, the present invention provides a method for preparing a lithium-ion battery auxiliary coating material according to any one of the aforementioned embodiments, comprising: mixing and dispersing a silicon source and a titanium source to obtain a mixed slurry, and sequentially coating, drying, and calcining the mixed slurry.

[0014] In an optional embodiment, the preparation process of the mixed slurry includes: mixing the silicon source, the titanium source and the dispersant, and performing wet ball milling after pre-dispersion.

[0015] In an optional embodiment, the silicon source is silicon powder having an initial particle size of 2 μm to 5 μm;

[0016] and / or, the titanium source is selected from at least one of TiO2 and Ti(OH)4, and the initial particle size of the titanium source is 5 μm-20 μm;

[0017] and / or, the dispersant is selected from at least one of ethanol, acetone, N-methylpyrrolidone, N,N-dimethylformamide, isopropyl alcohol, ethyl acetate, propylene carbonate, butyrolactone, dimethyl sulfoxide, chloroform, toluene, xylene, tetrahydrofuran, and acetonitrile;

[0018] and / or, the mass ratio of the total amount of the silicon source and the titanium source to the dispersant is 1:(2-6);

[0019] And / or, during the pre-dispersion process, the stirring rate is controlled to be 10 Hz-60 Hz and the stirring time is 0.5 h-3 h;

[0020] And / or, during the wet ball milling process, the ball milling speed is controlled to be 800 rpm-2500 rpm, and the ball milling time is 8 hours-24 hours.

[0021] In an optional embodiment, the mixed slurry and the adhesive are mixed, and then coated and dried to obtain a dry powder, which is then calcined and crushed.

[0022] In an optional embodiment, during the coating and drying process, the drying temperature is controlled to be 80° C.-180° C.;

[0023] and / or, during the calcination process, controlling the calcination temperature to 500° C.-1000° C. and the calcination time to 2 h-6 h;

[0024] and / or, the adhesive is selected from at least one of carboxymethyl cellulose, polyvinylidene fluoride, sodium alginate, polyethylene glycol, polyvinyl pyrrolidone and polyvinyl butyral;

[0025] And / or, the mass ratio of the total amount of the silicon source and the titanium source to the adhesive is 100:(1-25).

[0026] In a third aspect, the present invention provides a modified graphite negative electrode, comprising a negative electrode current collector, a graphite negative electrode active coating loaded on at least one side of the negative electrode current collector, an auxiliary coating loaded on the graphite negative electrode active coating, the auxiliary coating containing any one of the lithium ion battery auxiliary coating materials in the aforementioned embodiments or a lithium ion battery auxiliary coating material prepared by the preparation method in any one of the aforementioned embodiments.

[0027] In an optional embodiment, the auxiliary coating further contains a binder, and the mass ratio of the lithium ion battery auxiliary coating material to the binder is 100:(5-15);

[0028] Preferably, the binder is selected from at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber emulsion, polyacrylic acid and sodium alginate.

[0029] In a fourth aspect, the present invention provides a lithium battery comprising the modified graphite negative electrode described in the aforementioned embodiment.

[0030] The present invention has the following beneficial effects: It provides a porous composite oxide formed from silicon dioxide nanowires and titanium dioxide nanoparticles, which exhibits an overall porous structure. When used as an auxiliary coating material for lithium-ion batteries, it can be applied to the surface of a negative graphite electrode to form a porous coating. Both SiO2 and TiO2 have excellent electrolyte wetting capabilities, and the porous structure of the nanoscale materials significantly enhances electrolyte wetting, allowing for rapid lithium ion diffusion on both the separator side and the negative electrode surface. This is beneficial for the rate performance of lithium-ion batteries and also contributes to the uniform distribution of charge and discharge currents achieved by the graphite negative electrode due to enhanced electrolyte wetting.

[0031] In addition, TiO2 is coated on the surface of the graphite negative electrode, and its conductivity becomes stronger after charging, which can promote the electronic conductivity of the graphite negative electrode surface and promote the improvement of rate performance in terms of electronic conductivity. + Contact tends to form Li2SiO3 and Li4Ti5O 12 mixture, that is, the surface has the function of adsorbing lithium ions, which will enrich the negative electrode surface with Li + , thereby promoting the diffusion of lithium ions during the charging and discharging process, which is beneficial to the rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 Process flow chart for preparing auxiliary coating materials for lithium-ion batteries;

[0034] Figure 2 This is the SEM image of the material prepared in Example 1 (1000 times magnification);

[0035] Figure 3 This is the SEM image of the material prepared in Example 1 (10,000 times magnification);

[0036] Figure 4 This is the XRD pattern of the auxiliary coating material prepared in Example 1. DETAILED DESCRIPTION

[0037] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0038] In the prior art, the application of auxiliary coatings to separators can lead to problems such as reduced rate performance, and the poor electrolyte wetting performance of graphite negative electrodes can lead to slow and uneven lithium ion diffusion. To address the above problems existing in the prior art, embodiments of the present invention provide a lithium-ion battery auxiliary coating material, which is applied to the surface of the graphite negative electrode to form a porous coating, thereby solving the problem of reduced rate performance caused by the application of auxiliary coatings to separators, and simultaneously solving the problem of slow and uneven lithium ion diffusion caused by poor electrolyte wetting of the graphite negative electrode.

[0039] An embodiment of the present invention provides a lithium-ion battery auxiliary coating material, including a porous composite oxide formed by silicon dioxide nanowires and titanium dioxide nanoparticles. The lithium-ion battery auxiliary coating material provided by the embodiment of the present invention is a mixed composite oxide of SiO2 nanowires and TiO2 nanoparticles, which has a porous structure as a whole. It is coated on the surface of the negative electrode graphite pole piece to form a porous coating. Both SiO2 and TiO2 have excellent electrolyte wetting capabilities, and the porous structure characteristics composed of nano-scale materials can greatly improve the electrolyte wetting performance, so that lithium ions can be quickly diffused on both the diaphragm side and the negative electrode surface side, solving the problem of reduced rate performance of the diaphragm due to the application of the auxiliary coating, and at the same time solving the problem of slow and uneven lithium ion diffusion caused by poor electrolyte wetting of the graphite negative electrode.

[0040] In the total amount of the porous composite oxide, the mass proportion of the silica nanowires is 50%-90%, preferably 80%-85%, and specifically can be 50%, 60%, 70%, 80%, 83%, 85%, 90%, etc. By adjusting the mass proportion of the silica nanowires, the rate performance of the battery can be further improved. If the mass proportion of the silica nanowires exceeds the above range, the battery rate performance will decrease. Specifically, if the mass proportion of the silica nanowires is too small, the formation of the porous structure will be reduced. If the mass proportion of the silica nanowires is too large, the impedance will increase. Therefore, if the mass proportion of the silica nanowires is too large or too small, it is not conducive to improving the rate performance of the battery.

[0041] In some embodiments, the diameter of the silica nanowires is 100 nm to 900 nm, such as 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, etc. The length of the silica nanowires is 5 μm to 100 μm, such as 5 μm, 8 μm, 10 μm, 30 μm, 50 μm, 80 μm, 100 μm, etc. The particle size of the titanium dioxide nanoparticles is 50 nm to 500 nm, such as 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, etc. The size of the silica nanowires and titanium dioxide nanoparticles is preferably within the above range to control the porosity of the porous composite oxide to 40%-80% (such as 40%, 50%, 60%, 70%, 80%, etc.), which is beneficial to improving the wetting performance of the electrolyte and allowing lithium ions to diffuse rapidly on both the diaphragm side and the negative electrode surface side.

[0042] The embodiment of the present invention provides a method for preparing a lithium-ion battery auxiliary coating material, comprising mixing and dispersing a silicon source and a titanium source to obtain a mixed slurry, and then coating, drying, and calcining the mixed slurry in sequence to obtain a lithium-ion battery auxiliary coating material. Figure 1, the specific steps are as follows:

[0043] S1. Pre-dispersion

[0044] The silicon source, titanium source and dispersant are mixed and pre-dispersed to make the raw materials uniformly mixed.

[0045] In some embodiments, the silicon source may be silicon powder, but is not limited thereto. The initial particle size of the silicon powder may be 2 μm to 5 μm, such as 2 μm, 3 μm, 4 μm, 5 μm, etc. The titanium source is selected from at least one of TiO2 and Ti(OH)4, and the titanium source may be any one or more of the above. The initial particle size of the titanium source may be 5 μm to 20 μm, such as 5 μm, 10 μm, 15 μm, 20 μm, etc. The initial particle size of the silicon powder and the titanium source within the above range can regulate the size of the resulting silica nanowires and titanium dioxide nanoparticles to meet the requirements.

[0046] In some embodiments, the dispersant is selected from at least one of ethanol, acetone, N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), isopropyl alcohol, ethyl acetate, propylene carbonate, butyrolactone, dimethyl sulfoxide, chloroform, toluene, xylene, tetrahydrofuran, and acetonitrile. The dispersant can be any one or more of the above, and all of the above dispersants can effectively disperse the silicon source and titanium source. The mass ratio of the total amount of silicon source and titanium source to the dispersant is 1:(2-6), such as 1:2, 1:3, 1:4, 1:5, 1:6, etc. The dispersant can be added in two batches: one portion before pre-dispersion and another portion after pre-dispersion to wash the material remaining in the container during the transfer process, so that the pre-dispersed material enters the ball milling stage.

[0047] Furthermore, during the pre-dispersion process, the stirring rate is controlled to be 10 Hz-60 Hz, such as 10 Hz, 20 Hz, 30 Hz, 40 Hz, 50 Hz, 60 Hz, etc.; the stirring time is 0.5 h-3 h, such as 0.5 h, 1.0 h, 2.0 h, 3.0 h, etc.

[0048] S2, ball milling

[0049] The pre-dispersed materials are wet ball-milled to fully mix the silicon source and the titanium source.

[0050] In some embodiments, during the wet ball milling process, the ball milling speed is controlled to be 800r / min-2500r / min, such as 800r / min, 1000r / min, 1500r / min, 2000r / min, 2500r / min, etc.; the ball milling time is 8h-24h, such as 8h, 10h, 15h, 20h, 24h, etc.

[0051] S3, stirring

[0052] The mixed slurry and the adhesive are mixed and stirred. By introducing the adhesive, the binding force between the silicon source and the titanium source is increased, which facilitates the subsequent coating and drying to prepare a dry powder.

[0053] In some embodiments, the binder is selected from at least one of carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), sodium alginate, polyethylene glycol, polyvinyl pyrrolidone (PVP), and polyvinyl butyral (PVB), and the binder can be any one or more of the above. The mass ratio of the total amount of the silicon source and the titanium source to the binder is 100:(1-25), such as 100:1, 100:2, 100:5, 100:20, 100:23, 100:25, etc.

[0054] In some embodiments, the stirring rate may be 30 Hz-60 Hz, and the stirring time may be 3 h-10 h, so that the adhesive, silicon source, and titanium source are evenly mixed to form a uniform slurry.

[0055] S4, coating and drying

[0056] The slurry obtained in step S3 is coated and dried, and then the powder is peeled off to obtain dry powder.

[0057] Specifically, the slurry obtained in step S3 can be coated on a substrate, and the powder can be peeled off after drying. The substrate used can be copper foil, copper-nickel alloy foil, stainless steel foil, aluminum alloy foil, etc. After drying, the powder can be peeled off by heating, scraping, or vibration.

[0058] In some embodiments, during the coating and drying process, the drying temperature is controlled to be 80°C-180°C, such as 80°C, 100°C, 150°C, 180°C, etc., and the dispersant is removed after drying.

[0059] S5. Calcination

[0060] The dried powder obtained in step S4 is calcined. After calcination, the structure of the material is stabilized and a porous structure is formed, thereby increasing the porosity of the material. During the calcination process, silicon reacts with oxygen in the air to produce SiO2, and the titanium source, such as Ti(OH)4, is converted into TiO2.

[0061] In some embodiments, during the calcination process, the calcination temperature is controlled to be 500℃-1000℃, such as 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, etc.; the calcination time is 2h-6h, such as 2h, 3h, 4h, 5h, 6h, etc.

[0062] S6, crush

[0063] The calcined material is crushed to break up the agglomerated material during the calcination process to obtain the final product.

[0064] The embodiment of the present invention prepares a composite oxide auxiliary material of SiO2 nanowires and TiO2 nanoparticles through a simple and easy method of ball milling, introducing a glue solution, coating, drying, and calcining, with an overall porous structure. After the composite oxide auxiliary material is applied to the graphite negative electrode, the electrolyte infiltration performance can be significantly improved, allowing lithium ions to diffuse rapidly on both the diaphragm side and the negative electrode surface side, thereby promoting the battery's rate performance. The preparation method provided by the embodiment of the present invention is easy to scale up and provides a technical solution for improving the performance of lithium-ion batteries.

[0065] The embodiment of the present invention also provides a modified graphite negative electrode, including a negative electrode current collector, a graphite negative electrode active coating loaded on at least one side of the negative electrode current collector, an auxiliary coating loaded on the graphite negative electrode active coating, and the auxiliary coating containing the lithium ion battery auxiliary coating material provided by the embodiment of the present invention. TiO2 is coated on the surface of the graphite negative electrode, and its conductivity becomes stronger after charging, which can promote the electronic conductivity of the surface of the graphite negative electrode, solving the problem that the conductivity of the general insulating ceramic coating deteriorates after coating and affects the rate performance. SiO2 and TiO2 and Li + Contact tends to form Li2SiO3 and Li4Ti5O 12 mixture, that is, the surface has the function of adsorbing lithium ions, which will enrich the negative electrode surface with Li + , thereby promoting the diffusion of lithium ions during the charging and discharging process, and solving the problem of hindering the diffusion of lithium ions after coating ceramic materials.

[0066] Specifically, the negative electrode current collector is not limited to any type and can be a commonly used negative electrode current collector, such as copper foil. The composition of the graphite negative electrode active coating is not limited, and any commonly used graphite negative electrode active coating composition is suitable. After forming the graphite negative electrode active coating, a lithium-ion battery auxiliary coating material and a binder are mixed, then applied and dried to form a coating.

[0067] In some embodiments, the auxiliary coating further comprises a binder, and the mass ratio of the lithium-ion battery auxiliary coating material to the binder is 100:(5-15), such as 100:5, 100:8, 100:10, 100:12, 100:15, etc. The binder is selected from at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber latex, polyacrylic acid, and sodium alginate, and the binder can be any one or more of the above.

[0068] Embodiments of the present invention also provide a lithium battery comprising the modified graphite anode provided by the embodiments of the present invention, and further comprising a positive electrode, a separator, an electrolyte, and the like to form a complete battery structure. Replacing the conventional graphite anode with the modified graphite anode significantly enhances the electrolyte wetting performance, allowing rapid lithium ion diffusion on both the separator side and the anode surface, thereby enhancing the rate performance of the lithium-ion battery and promoting uniform distribution of charge and discharge currents due to enhanced electrolyte wetting of the graphite anode.

[0069] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0070] Example 1

[0071] This embodiment provides a method for preparing a lithium ion battery auxiliary coating material. Figure 1 , the specific steps are as follows:

[0072] (1) 373 g of silicon powder with an initial particle size D50 of 3 μm, 290 g of titanium source Ti(OH)4 with an initial particle size D50 of 7 μm, and 1500 g of dispersant NMP were added to a stirring tank to perform pre-dispersion step 1. The stirring rate was controlled at 30 Hz and the stirring time was 1 h. After discharging, 1000 g of NMP was added to clean the equipment, and the cleaning liquid was incorporated into the slurry.

[0073] (2) The slurry obtained in step (1) was transferred to a ball mill transfer tank and subjected to ball milling step 2 at a ball milling speed of 2000 r / min for 18 h to obtain a ball milled slurry.

[0074] (3) The slurry obtained in step (2) was transferred to a stirring tank, 163 g of PVDF was added, and then stirring step 3 was carried out at a speed of 50 Hz for 4 hours.

[0075] (4) The slurry obtained in step (3) was transferred to an oven coating feeding tank and subjected to coating and drying step 4. The foil material was copper foil and the drying temperature was 150°C. The coating was then scraped off to obtain 760g of dry powder.

[0076] (5) The powder was calcined in air at step 5 at a temperature of 650°C for 4 hours to obtain 920 g of calcined powder. During the calcination process, silicon reacted with oxygen in the air to produce SiO2, and the titanium source Ti(OH)4 was converted into TiO2.

[0077] (6) Finally, the calcined powder was pulverized and passed through a 400-mesh sieve to obtain 833 g of powder.

[0078] The SEM image of the auxiliary coating material prepared in Example 1 is as follows: Figure 2 and Figure 3As shown, it is primarily composed of interwoven nanowires and nanoparticles distributed on them, exhibiting a porous structure. The nanowires have diameters ranging from 200 to 600 nm and can extend to over 50 μm in length. The nanoparticles have diameters ranging from 300 to 800 nm.

[0079] To verify the composition, XRD analysis was performed, and the XRD patterns are shown in Figure 4 In the figure, ■ corresponds to the peak of SiO2, and ● corresponds to the peak of TiO2. The strong, broad peak between 15-30° is the characteristic peak of amorphous SiO2, indicating the production of SiO2. The peak corresponding to the dot is the characteristic peak of TiO2, indicating that the material contains TiO2 and has a crystalline structure. A high proportion of silicon was added during the material preparation process, and the SEM image shows a large amount of nanowires, indicating that the nanowires are SiO2. Amorphous structures can form curved nanowires, while crystalline structures generally have straight features. Therefore, the nanowires can be attributed to SiO2.

[0080] In the product obtained in this example, the mass ratio of SiO2 nanowires to TiO2 nanoparticles is 80:20.

[0081] Example 2

[0082] This embodiment provides a method for preparing a lithium ion battery auxiliary coating material. Figure 1 , the specific steps are as follows:

[0083] (1) 397 g of silicon powder with an initial particle size D50 of 2 μm, 150 g of titanium source TiO2 with an initial particle size D50 of 10 μm, and 1300 g of dispersant isopropanol were added to a stirring tank and pre-dispersion step 1 was carried out at a stirring rate of 40 Hz and a stirring time of 2 h. After discharging, 1000 g of isopropanol was added to clean the equipment, and the cleaning liquid was incorporated into the slurry.

[0084] (2) The slurry obtained in step (1) was transferred to a ball mill transfer tank and subjected to ball milling step 2 at a ball milling speed of 1500 r / min for 24 h to obtain a ball milled slurry.

[0085] (3) The slurry obtained in step (2) was transferred to a stirring tank, 109 g of PVP was added, and then stirring step 3 was carried out at a speed of 40 Hz for 3 h.

[0086] (4) The slurry obtained in step (3) was transferred to an oven coating feeding tank and subjected to coating and drying step 4. The foil material was copper foil and the drying temperature was 100°C. The coating was then scraped off to obtain 603g of dry powder.

[0087] (5) The dried powder obtained in step (4) was subjected to calcination in air at step 5 at a temperature of 750° C. for 3 hours to obtain 910 g of calcined powder. During the calcination process, silicon reacts with oxygen in air to produce SiO2, while the structure of the titanium source TiO2 remains unchanged.

[0088] (6) Finally, the calcined powder was pulverized and passed through a 400-mesh sieve to obtain 812 g of powder.

[0089] In the product prepared in this example, the mass ratio of SiO2 nanowires to TiO2 nanoparticles is 85:15.

[0090] Example 3

[0091] The only difference from Example 1 is that the feeding amounts of silicon powder and titanium source are changed to 233 g and 725 g, respectively. The mass ratio of SiO2 nanowires and TiO2 nanoparticles finally obtained is 50:50.

[0092] Example 4

[0093] The only difference from Example 1 is that the feeding amounts of silicon powder and titanium source are changed to 420 g and 145 g, respectively. The mass ratio of SiO2 nanowires and TiO2 nanoparticles finally obtained is 90:10.

[0094] Example 5

[0095] The only difference from Example 1 is that the calcination temperature in step (5) is 550° C. and the calcination time is 5 h.

[0096] Example 6

[0097] The only difference from Example 1 is that the calcination temperature in step (5) is 900° C. and the calcination time is 2.2 h.

[0098] Comparative Example 1

[0099] The only difference from Example 1 was that the silicon powder and titanium source were added in 140 g and 653 g, respectively. All other ingredients and processes remained unchanged. The resulting composite powder had a mass ratio of SiO nanowires to TiO nanoparticles of 40:60.

[0100] Comparative Example 2

[0101] The only difference from Example 1 was that the silicon powder and titanium source were added in 327 g and 54 g, respectively. All other ingredients and processes remained unchanged. The resulting composite powder had a mass ratio of SiO nanowires to TiO nanoparticles of 95:5.

[0102] Comparative Example 3

[0103] In Example 1, no titanium source was added to the feed, and SiO2 nanowires were finally obtained.

[0104] Comparative Example 4

[0105] In Example 1, no silicon source was added to the feed, but only a titanium source was added, and TiO2 nanoparticles were finally obtained.

[0106] Comparative Example 5

[0107] Micron-sized boehmite on the market with a D50 of 1.3 μm was directly used for rate performance comparison.

[0108] Test Example 1

[0109] The use effects of the lithium ion battery auxiliary coating materials prepared in the examples and comparative examples were tested, and the results are shown in Table 1.

[0110] Test method: The auxiliary materials obtained or purchased above were used to make a buckle half-cell, with a lithium metal sheet as the counter electrode. The graphite slurry formula is graphite: conductive carbon black: CMC: SBR = 85:10:2:3. The auxiliary coating slurry formula is auxiliary materials: CMC: SBR = 90:5:5. First apply the graphite coating, dry it, and then apply the auxiliary coating. After rolling, punching, baking, and assembly (using a conventional PE wet-process diaphragm), the charge and discharge test was finally carried out. The charge and discharge voltage was 0.005V~2.0V, the charge and discharge current was 0.33C (1C=350mAh / g), and the rate test rate was 3C. Only the rate discharge was measured. The ratio of the 3C rate discharge capacity to the 0.33C rate discharge capacity is the 3C rate discharge rate. The test results are shown in Table 1.

[0111] Table 1. Summary of 3C rate discharge in different examples and comparative examples

[0112]

[0113]

[0114] As can be seen from Table 1, the embodiment has a coating of both SiO2 nanowires and TiO2 nanoparticles, and the buckling rate performance shows higher specific capacitance and rate performance, mainly because the porous structure composed of SiO2 nanowires promotes electrolyte infiltration and TiO2 promotes electronic conductivity after lithium insertion. Too many TiO2 nanoparticles (Comparative Example 1) and too many SiO2 nanowires (Comparative Example 2) will affect the rate performance, mainly because the former will reduce the formation of the porous structure, while the latter will increase the impedance. The auxiliary coating with only SiO2 nanowires (Comparative Example 3) and only TiO2 nanoparticles (Comparative Example 4) will further reduce the buckling rate performance.

[0115] Comparative Example 5 uses micron-sized boehmite on the market as an auxiliary coating, which shows the worst rate performance. This is mainly because it has no porous structure and will block the lithium ion diffusion channel; it is an insulating material, does not promote conductivity, and has no lithium ion adsorption characteristics, which will increase the battery impedance and ultimately show low rate characteristics.

[0116] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A lithium ion battery auxiliary coating material, characterized in that: The porous composite oxide is formed by silicon dioxide nanowires and titanium dioxide nanoparticles, wherein the mass of the silicon dioxide nanowires accounts for 50% to 90% of the total amount of the porous composite oxide.

2. The lithium-ion battery auxiliary coating material according to claim 1, characterized in that: In the total amount of the porous composite oxide, the mass proportion of the silicon dioxide nanowires is 80%-85%; and / or, the silica nanowires have a diameter of 100 nm to 900 nm and a length of 5 μm to 100 μm; And / or, the particle size of the titanium dioxide nanoparticles is 50nm-500nm; And / or, the porosity of the porous composite oxide is 40%-80%.

3. A method for preparing the auxiliary coating material for lithium-ion batteries according to any one of claims 1 to 2, characterized in that: include: A silicon source and a titanium source are mixed and dispersed to obtain a mixed slurry, which is then coated, dried, and calcined in sequence.

4. The preparation method according to claim 3, characterized in that The preparation process of the mixed slurry includes: mixing the silicon source, the titanium source and the dispersant, and then wet ball milling after pre-dispersion.

5. The preparation method according to claim 4, characterized in that The silicon source is silicon powder with an initial particle size of 2 μm-5 μm; And / or, the titanium source is selected from at least one of TiO2 and Ti(OH)4, and the initial particle size of the titanium source is 5 μm-20 μm; and / or, the dispersant is selected from at least one of ethanol, acetone, N-methylpyrrolidone, N,N-dimethylformamide, isopropyl alcohol, ethyl acetate, propylene carbonate, butyrolactone, dimethyl sulfoxide, chloroform, toluene, xylene, tetrahydrofuran and acetonitrile; and / or, the mass ratio of the total amount of the silicon source and the titanium source to the dispersant is 1:(2-6); And / or, during the pre-dispersion process, the stirring rate is controlled to be 10 Hz-60 Hz, and the stirring time is 0.5 h-3 h; And / or, during the wet ball milling process, the ball milling speed is controlled to be 800 rpm-2500 rpm, and the ball milling time is 8 hours-24 hours.

6. The preparation method according to claim 3, characterized in that The mixed slurry and the adhesive are mixed, and then coated and dried to obtain dry powder, and the dry powder is calcined and crushed.

7. The preparation method according to claim 6, characterized in that During the coating and drying process, the drying temperature is controlled at 80℃-180℃; and / or, during the calcination process, controlling the calcination temperature to 500° C.-1000° C. and the calcination time to 2 h-6 h; and / or, the adhesive is selected from at least one of carboxymethyl cellulose, polyvinylidene fluoride, sodium alginate, polyethylene glycol, polyvinyl pyrrolidone and polyvinyl butyral; And / or, the mass ratio of the total amount of the silicon source and the titanium source to the adhesive is 100:(1-25).

8. A modified graphite negative electrode, characterized in that The invention comprises a negative electrode current collector, wherein at least one side of the negative electrode current collector is loaded with a graphite negative electrode active coating, and an auxiliary coating is loaded on the graphite negative electrode active coating, wherein the auxiliary coating contains the lithium ion battery auxiliary coating material according to any one of claims 1 to 2 or the lithium ion battery auxiliary coating material prepared by the preparation method according to any one of claims 3 to 7.

9. The modified graphite negative electrode according to claim 8, characterized in that The auxiliary coating further contains a binder, and the mass ratio of the lithium ion battery auxiliary coating material to the binder is 100:(5-15); Preferably, the binder is selected from at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber emulsion, polyacrylic acid and sodium alginate.

10. A lithium battery, characterized in that: Comprising the modified graphite negative electrode according to claim 8.

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