CN115842122A - Lithium titanate-coated graphite composite material, preparation method thereof, secondary battery, battery module, battery pack and electric device comprising lithium titanate-coated graphite composite material - Google Patents
Lithium titanate-coated graphite composite material, preparation method thereof, secondary battery, battery module, battery pack and electric device comprising lithium titanate-coated graphite composite material Download PDFInfo
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- CN115842122A CN115842122A CN202210269069.9A CN202210269069A CN115842122A CN 115842122 A CN115842122 A CN 115842122A CN 202210269069 A CN202210269069 A CN 202210269069A CN 115842122 A CN115842122 A CN 115842122A
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- Prior art keywords
- lithium
- composite material
- lithium titanate
- coated graphite
- graphite composite
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 135
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 135
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 title claims abstract description 112
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 106
- 229910002804 graphite Inorganic materials 0.000 title claims abstract description 93
- 239000010439 graphite Substances 0.000 title claims abstract description 93
- 239000002131 composite material Substances 0.000 title claims abstract description 79
- 238000002360 preparation method Methods 0.000 title abstract description 21
- 150000001875 compounds Chemical class 0.000 claims abstract description 43
- 239000010936 titanium Substances 0.000 claims abstract description 24
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- 239000002738 chelating agent Substances 0.000 claims abstract description 15
- 238000001035 drying Methods 0.000 claims abstract description 15
- 238000006243 chemical reaction Methods 0.000 claims abstract description 14
- 238000010438 heat treatment Methods 0.000 claims abstract description 14
- 238000001354 calcination Methods 0.000 claims abstract description 10
- 238000000034 method Methods 0.000 claims description 57
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- 230000008569 process Effects 0.000 claims description 12
- XIXADJRWDQXREU-UHFFFAOYSA-M lithium acetate Chemical compound [Li+].CC([O-])=O XIXADJRWDQXREU-UHFFFAOYSA-M 0.000 claims description 10
- 238000001694 spray drying Methods 0.000 claims description 10
- ATRRKUHOCOJYRX-UHFFFAOYSA-N Ammonium bicarbonate Chemical compound [NH4+].OC([O-])=O ATRRKUHOCOJYRX-UHFFFAOYSA-N 0.000 claims description 9
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 9
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- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 9
- VXUYXOFXAQZZMF-UHFFFAOYSA-N titanium(IV) isopropoxide Chemical compound CC(C)O[Ti](OC(C)C)(OC(C)C)OC(C)C VXUYXOFXAQZZMF-UHFFFAOYSA-N 0.000 claims description 9
- 229910000013 Ammonium bicarbonate Inorganic materials 0.000 claims description 6
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 6
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- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Chemical compound [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 claims description 6
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- VZTDIZULWFCMLS-UHFFFAOYSA-N ammonium formate Chemical compound [NH4+].[O-]C=O VZTDIZULWFCMLS-UHFFFAOYSA-N 0.000 claims description 3
- VBIXEXWLHSRNKB-UHFFFAOYSA-N ammonium oxalate Chemical compound [NH4+].[NH4+].[O-]C(=O)C([O-])=O VBIXEXWLHSRNKB-UHFFFAOYSA-N 0.000 claims description 3
- YHWCPXVTRSHPNY-UHFFFAOYSA-N butan-1-olate;titanium(4+) Chemical compound [Ti+4].CCCC[O-].CCCC[O-].CCCC[O-].CCCC[O-] YHWCPXVTRSHPNY-UHFFFAOYSA-N 0.000 claims description 3
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention provides a lithium titanate-coated graphite composite material, a preparation method thereof, a secondary battery, a battery module, a battery pack and an electric device comprising the lithium titanate-coated graphite composite material. The preparation method comprises the steps of carrying out heating reaction on a titanium source compound, a lithium source compound, graphite, a chelating agent and a solvent at the temperature of 40-220 ℃ to obtain slurry C; and drying and calcining the slurry C to obtain the lithium titanate-coated graphite composite material. The preparation method is beneficial to forming a compact and uniform lithium titanate coating layer, and has the advantages of environmental protection and the like; and the lithium titanate coated graphite composite material is applied to the secondary battery, so that the storage performance of the battery is improved.
Description
Technical Field
The application relates to the technical field of lithium batteries, in particular to a lithium titanate-coated graphite composite material, a preparation method thereof, a secondary battery, a battery module, a battery pack and an electric device comprising the lithium titanate-coated graphite composite material.
Background
In recent years, with the application range of lithium ion batteries becoming wider, lithium ion batteries are widely used in energy storage power systems such as hydraulic power, thermal power, wind power and solar power stations, and in a plurality of fields such as electric tools, electric bicycles, electric motorcycles, electric automobiles, military equipment and aerospace. However, when the lithium ion battery is in a low state of charge SOC for a long period of time, active lithium in the graphite-based carbon negative electrode material reacts with the electrolyte, resulting in an increase in the anode potential. When the anode potential rises to reach the decomposition potential (1.8V) of the SEI film, the SEI film is decomposed, the problem of sudden rise of gas generation is caused, serious potential safety hazard is caused, and the performance of the battery is reduced.
For solving the problems, the graphite material mainly comprises lithium titanate by means of doping and cladding at present, wherein the lithium titanate-clad graphite composite material is a relatively effective means. However, the method for preparing the composite material has the defects of difficult industrialization, immature process technology, environment-friendliness and the like, and the formed lithium titanate coating layer has low compactness.
Therefore, the existing preparation method of graphite composite material containing lithium titanate still needs to be improved.
Disclosure of Invention
The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a lithium titanate-coated graphite composite material having a dense and uniform lithium titanate coating layer, which is advantageous in suppressing an increase in the anode potential and improving the storage performance of a battery when the composite material is used as a secondary battery.
In order to achieve the above objects, the present application provides a method of preparing a lithium titanate-coated graphite composite material.
A first aspect of the present application provides a method for preparing a lithium titanate-coated graphite composite material, the method comprising a step of subjecting a titanium source compound, a lithium source compound, graphite, a chelating agent, and a solvent to a heating reaction at 40-220 ℃ to obtain slurry C; and drying and calcining the slurry C to obtain the lithium titanate-coated graphite composite material.
In an alternative embodiment, a method of preparing a lithium titanate-coated graphite composite material includes the steps of:
s1: mixing a titanium source compound, a lithium source compound, graphite, a chelating agent and a solvent to obtain a suspension B;
s2: heating the suspension B at 40-220 ℃ for reaction to obtain slurry C;
s3: and drying and calcining the slurry C to obtain the lithium titanate-coated graphite composite material.
When the prepared lithium titanate-coated graphite composite material is used as an anode material of a secondary battery, the consumption of active lithium in graphite is reduced, the increase of the anode potential is inhibited, and the problem of sudden increase of gas production is avoided.
In an alternative embodiment, in step S1, the titanium source compound is selected from at least one of isopropyl titanate, tetrabutyl titanate, titanium dioxide; the lithium source compound is at least one selected from lithium acetate, lithium hydroxide, lithium nitrate and lithium carbonate.
The lithium titanate prepared from the above titanium source compound and lithium source compound has a lithium deintercalation potential of about 1.55V. In addition, when the graphite coated with lithium titanate is used as an anode, the increase of the anode potential is relatively gentle, so that the increase of the anode potential to the decomposition potential of the SEI film of 1.8V is inhibited, and the storage performance of the secondary battery is improved.
In an alternative embodiment, in step S1, the chelating agent is selected from at least one of ammonium carbonate, ammonium bicarbonate, oxalic acid, urea, citric acid, ammonium formate, ammonium oxalate. The chelating agent is capable of reacting with the lithium source compound and the titanium source compound to form corresponding chelates.
In an alternative embodiment, in step S2, the suspension B is heated to 50-90 ℃ for 2-14h, optionally 8-12h. This facilitates the formation of a dense and uniform coating.
In an alternative embodiment, in step S3, the drying is performed by spray drying, with a feed inlet temperature of 120-250 ℃, optionally 150-200 ℃, and a feed pump speed of 3-40L/min, optionally 3-10L/min. By spray drying, solid-liquid separation can be directly performed, thereby avoiding the filtration operation and the accompanying loss of a large amount of eluent (e.g., water or organic solvent). Is beneficial to improving the production efficiency, saving the production cost and reducing the environmental pollution.
A second aspect of the present application provides a lithium titanate-coated graphite composite material obtained by the method for preparing a lithium titanate-coated graphite composite material provided by the first aspect of the present application.
In an alternative embodiment, the lithium titanate in the lithium titanate-coated graphite composite material is in an amount of 0.1 to 10 wt%, optionally 1 to 3wt%, based on the weight of the graphite.
The weight of graphite is the weight of graphite added during the preparation process. Due to the existence of lithium titanate, the composite material has higher plateau voltage (about 1.55V), so that the rising of the anode potential of the lithium ion battery can be effectively inhibited, the SEI film is prevented from being decomposed (the decomposition voltage is 1.8V), and the gas production is reduced.
In an alternative embodiment, the lithium titanate-coated graphite composite material has a specific surface area SSA of 1.1 to 2.1m 2 G, optionally 1.22-1.99m 2 (iv) g. This is advantageous in reducing exposure of active lithium in graphite to an electrolyte, and improving cycle performance and storage performance of a secondary battery.
A third aspect of the present application provides a secondary battery comprising the lithium titanate-coated graphite composite material produced by the production method according to the first aspect of the present application, or the lithium titanate-coated graphite composite material according to the second aspect of the present application.
A fourth aspect of the present application provides a battery module including the secondary battery described in the third aspect of the present application.
A fifth aspect of the present application provides a battery pack including the battery module according to the fourth aspect of the present application.
A sixth aspect of the present application provides an electric device including at least one of the secondary battery according to the third aspect of the present application, the battery module according to the fourth aspect of the present application, or the battery pack according to the fifth aspect of the present application.
The lithium titanate coated graphite composite material secondary battery provided by the application has the advantages that the storage performance is improved, the secondary battery can be placed for a long time under low SOC, and the gas production is low. Accordingly, the battery pack, the battery module and the electric device have good storage capacity.
Drawings
Fig. 1 is an electron microscope image of the lithium titanate-coated graphite composite material of example 1;
fig. 2 is a schematic view of a secondary battery according to an embodiment of the present application.
Fig. 3 is an exploded view of the secondary battery according to the embodiment of the present application shown in fig. 2.
Fig. 4 is a schematic view of a battery module according to an embodiment of the present application.
Fig. 5 is a schematic view of a battery pack according to an embodiment of the present application.
Fig. 6 is an exploded view of the battery pack according to the embodiment of the present application shown in fig. 5.
Fig. 7 is a schematic diagram of an electric device in which a secondary battery according to an embodiment of the present application is used as a power source.
Description of reference numerals:
1, a battery pack; 2, putting the box body on the box body; 3, discharging the box body; 4 a battery module; 5 a secondary battery; 51 a housing; 52 an electrode assembly; 53 a cap assembly.
Detailed Description
Hereinafter, embodiments of the negative electrode sheet and the method for manufacturing the same, the positive electrode sheet, the secondary battery, the battery module, the battery pack, and the electrical device according to the present application are specifically disclosed in detail with reference to the drawings as appropriate. But a detailed description thereof will be omitted. For example, detailed descriptions of already known matters and repetitive descriptions of actually the same configurations may be omitted. This is to avoid unnecessarily obscuring the following description, and to facilitate understanding by those skilled in the art. The drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.
The "ranges" disclosed herein are defined in terms of lower limits and upper limits, with a given range being defined by a selection of one lower limit and one upper limit that define the boundaries of the particular range. Ranges defined in this manner may or may not include the stated limits and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3,4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-6. In this application, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is only a shorthand representation of the combination of these numbers. In addition, when a parameter is an integer of 2 or more, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, or the like.
All embodiments and alternative embodiments of the present application may be combined with each other to form new solutions, if not specifically stated.
All technical and optional features of the present application may be combined with each other to form new solutions, if not specifically mentioned.
All steps of the present application may be performed sequentially or randomly, preferably sequentially, if not specifically stated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially. For example, the method may further comprise step (c), meaning that step (c) may be added to the method in any order, for example, the method may comprise steps (a), (b) and (c), may also comprise steps (a), (c) and (b), may also comprise steps (c), (a) and (b), etc.
The terms "comprises" and "comprising" as used herein mean either open or closed unless otherwise specified. For example, "comprising" and "comprises" may mean that other components not listed may also be included or included, or that only listed components may be included or included.
In this application, the term "or" is inclusive, if not otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or not present); a is false (or not present) and B is true (or present); or both a and B are true (or present).
At present, graphite carbon cathode materials are mainly adopted as cathode materials of lithium ion batteries, and a Solid Electrolyte Interface (SEI) film is formed on the surface of the cathode materials in the battery formation process to hinder the reaction of active lithium and electrolyte and reduce the gas production. However, since the graphite is in a non-plateau region during the storage of the lithium ion battery in a low state of charge SOC (including 0% SOC), the active lithium in the graphite is continuously subjected to a reduction reaction with the electrolyte, resulting in a decrease in the active lithium and a rapid increase in the anode potential. When the anode potential rises to 1.8V, the SEI film decomposes to generate a large amount of gas, causing problems of swelling of the battery and deterioration of the battery performance.
To solve such problems, graphite materials comprising Lithium Titanate (LTO) are currently mainly doped, coated or coated. The method for preparing the composite material mainly comprises the following steps: 1. the sol-gel method requires the addition of inorganic film-forming additives and organic solvents, and the formed coating layer is not compact, has a complex process and pollutes the environment; 2. the atomic layer deposition method has immature process and is difficult to be used for large-scale production; 3. a coprecipitation method including stirring a dispersion containing a lithium source compound, a titanium source compound, graphite, and a chelating agent at room temperature, then filtering the slurry, washing a filter cake with a large amount of a solvent, drying, and crushing; the cladding layer of the composite material formed by the method has low compactness, long time consumption and high cost.
The inventor finds that in the deposition method, the compactness of the lithium titanate coating layer can be improved by carrying out heating reaction on the dispersion liquid and carrying out spray drying on the slurry, and the solid-liquid separation is directly carried out by using the spray drying, so that the waste of a large amount of solvent caused by the filtering operation is avoided, and the time cost, the economic cost and the environmental cost are reduced.
Therefore, the application provides a lithium titanate-coated graphite material and a preparation method thereof, and aims to solve the technical problems of improving the compactness of a lithium titanate coating layer, saving the cost, improving the storage performance of a battery and the like.
A first aspect of the application provides a method for preparing a lithium titanate-coated graphite composite material, which comprises the steps of carrying out heating reaction on a titanium source compound, a lithium source compound, graphite, a chelating agent and a solvent at 40-220 ℃ to obtain slurry C; and drying and calcining the slurry C to obtain the lithium titanate-coated graphite composite material.
In some embodiments, a method of preparing a lithium titanate-coated graphite composite material includes the steps of:
s1: mixing a titanium source compound, a lithium source compound, graphite, a chelating agent and a solvent to obtain a suspension B;
s2: heating the suspension B at 40-220 ℃ for reaction to obtain slurry C;
s3: and drying and calcining the slurry C to obtain the lithium titanate-coated graphite composite material.
By the above preparation method, a dense and uniform lithium titanate coating layer can be formed on the surface of the anode graphite, see the SEM picture of example 1 shown in FIG. 1 (Sigma-02-33 scanning electron microscope of ZEISS, germany, in which magnification is 5K, voltage is 10KV, and scale is 1 μm,). The method is beneficial to reducing the active area of the secondary battery in direct contact with the electrolyte during storage, inhibiting the consumption of active lithium in the anode, preventing the increase of the anode potential during storage, keeping the anode potential below the decomposition potential (1.8V) of the SEI film and avoiding the problem of sudden increase of gas production.
Wherein, step S1 includes the following specific steps:
s100: adding a titanium source compound and a lithium source compound into a solvent to obtain a mixed solution A;
s101: and adding graphite and a chelating agent into the mixed solution A prepared in the step S101 to obtain a suspension B.
In the present invention, the "mixed solution" includes a liquid in which each component contained therein is completely soluble in a solvent, and also includes a liquid in which some components are not completely or partially soluble in a solvent, such as a suspension, an emulsion, a dispersion, a suspension, and the like.
Wherein the lithium source compound: a titanium source compound: chelating agent: the weight ratio of the graphite is 1: (1.35-31.8): (4-22): (16-575), optionally 1: (5-20): (5-30): (40-250).
Wherein, in some embodiments, in step S100, the titanium source compound is selected from at least one of isopropyl titanate, tetrabutyl titanate, titanium dioxide; the lithium source compound is at least one selected from lithium acetate, lithium hydroxide, lithium nitrate and lithium carbonate; the titanium source compound and the lithium source compound are added in an amount such that the molar ratio of the titanium element to the lithium element is (1.25-2.25) to 1, optionally (1.5-2.0): 1.
a lithium titanate obtained by using a titanium source compound and a lithium source compound as raw materials, the potential for lithium deintercalation of which is about 1.55V; furthermore, when the graphite coated by lithium titanate is used as an anode, the anode potential rises more smoothly, so that the anode potential is inhibited from rising to the decomposition potential of the SEI film by 1.8V, the sudden rise of gas generation is avoided, and the storage performance of the secondary battery is improved.
Optionally, in step S100, a surfactant is further added, wherein the surfactant is at least one selected from cetyl trimethyl ammonium bromide, hydroxyethyl cellulose, poloxamer, sodium hexadecyl benzene sulfonate, polyvinylpyrrolidone, sodium dodecyl sulfate, polyvinyl alcohol, and sodium oleate, and the surfactant is used in an amount of 1 to 5 wt%, optionally 2 to 3wt%, based on the weight of the titanium source compound. Thereby, the titanium source compound and the lithium source compound are dispersed in the solvent sufficiently to facilitate their complete dissolution in the solvent.
In step S100, the solvent may be deionized water, an organic solvent, or a mixed solution of deionized water and an organic solvent; the organic solvent is selected from at least one of methanol, ethanol, isopropanol, polyethylene glycol, ethylene glycol, glycerol, propylene glycol, benzyl alcohol, phenethyl alcohol, dimethylformamide, acetonitrile, dimethyl sulfoxide, oleic acid and oleylamine. Alternatively, the present invention uses only deionized water as a solvent, excluding any other organic solvent. Thus, the method of the present invention is environmentally friendly, can avoid environmental pollution caused by organic solvents, and its corresponding post-treatment steps or processes.
In step S101, graphite is selected from natural graphite or artificial graphite.
In some embodiments, in a specific step S101 comprised by step S1, the chelating agent is selected from at least one of ammonium carbonate, ammonium bicarbonate, oxalic acid, urea, citric acid, ammonium formate, ammonium oxalate; the chelating agent is used for reacting with the lithium source compound and the titanium source compound to generate corresponding chelate.
In step S101, the stirring time is 0.5 to 2.5 hours, optionally 1 to 2 hours.
In some embodiments, in step S2, suspension B is reacted at 50-90 deg.C for 2-14h, optionally 8-12h. The method is beneficial to regulating the morphology of the lithium titanate coating layer, better plays the coating role of lithium titanate on graphite and forms a compact and uniform coating layer.
In some embodiments, in step S3, the drying is performed by spray drying, with a feed inlet temperature of 120-250 deg.C, optionally 150-200 deg.C, and a feed pump speed of 3-40L/min, optionally 3-10L/min.
The slurry C is dried and granulated through spray drying to obtain precursor powder of the lithium titanate-coated graphite composite material, so that solid-liquid separation can be directly performed, waste of water resources is reduced (compared with the prior art, the loss of a large amount of water caused by filtering operation is generally used), and the compactness of a coating layer can be improved. Therefore, the method is a green preparation process.
In step S3, the precursor powder of the lithium titanate-coated graphite composite material obtained by drying is calcined in an inert atmosphere, wherein the inert atmosphere can be argon Ar or nitrogen N 2 Or other mixed gas, the calcining temperature is 600-900 ℃, and the calcining time is 4-12h, thus obtaining the lithium titanate coated graphite composite material.
A second aspect of the present application provides a lithium titanate-coated graphite composite material obtained by the above preparation method. Due to the existence of the compact and uniform lithium titanate coating layer and the high plateau voltage (about 1.55V) of the lithium titanate, the composite material can effectively reduce the consumption of active lithium in graphite, inhibit the rising of the anode potential of the lithium ion battery, avoid the decomposition of an SEI film (1.8V) and reduce the gas production.
In some embodiments, the lithium titanate-coated graphite composite has a content of lithium titanate in the range of 0.1 to 10 weight percent, optionally 1 to 3 weight percent, based on the weight of graphite, calculated as the ratio of the weight of lithium titanate to the weight of graphite added. When the content of lithium titanate is too low and is less than the lower limit value of 0.1 wt%, the graphite coating is not compact enough, and the increase of the anode potential cannot be effectively inhibited; when the content of lithium titanate is too high and exceeds the upper limit of 10 wt%, it is not preferable to delithiate the anode active material.
In the present invention, lithium titanate (chemical formula is Li) 4 Ti 5 O 12 Molecular weight of 460) is calculated based on the molar amount of lithium contained in the lithium source compound. For example, when 1mol of lithium acetate is used as the lithium source compound, the molar amount of lithium titanate obtained is 0.25mol, and the weight is 0.25 × 460=115g.
In some embodiments, the lithium titanate-coated graphite composite has a specific surface area SSA of 1.1 to 2.1m 2 G, optionally 1.22-1.99m 2 (ii) in terms of/g. This is favorable for the composite material to have better stability on the surface when being used as an anode active material, and can effectively reduce the exposure of active lithium in graphite to electrolyte, thereby effectively reducing the exposure of the active lithium in the graphite to the electrolyteAnd cycle performance and storage performance of the secondary battery are improved. It should be understood that the lithium titanate-coated graphite composite material of the present application can be used not only for lithium batteries, but also for any other batteries, battery modules, battery packs or electrical devices requiring reduction of gas production and improvement of storage.
The lithium titanate coated graphite composite material has the particle size of 5-45 mu m and the volume median particle size Dv50 of 13-20 mu m.
The secondary battery, the battery module, the battery pack, and the electric device according to the present application will be described below.
Secondary battery
In one embodiment, a secondary battery is provided that includes the lithium titanate-coated graphite composite material of the present application.
In general, a secondary battery includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. In the process of charging and discharging the battery, active ions are embedded and separated back and forth between the positive pole piece and the negative pole piece. The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The isolating membrane is arranged between the positive pole piece and the negative pole piece, mainly plays a role in preventing the short circuit of the positive pole and the negative pole, and can enable ions to pass through.
[ Positive electrode sheet ]
The positive pole piece includes the anodal mass flow body and sets up the anodal rete on anodal mass flow body at least one surface, and anodal rete includes the anodal active material of this application first aspect.
As an example, the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two surfaces opposite to the positive electrode current collector.
In some embodiments, the positive electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
In some embodiments, the positive active material may employ a positive active material for a battery, which is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: olivine structured lithium-containing phosphates, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material of a battery may be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide (e.g., liCoO) 2 ) Lithium nickel oxide (e.g., liNiO) 2 ) Lithium manganese oxide (e.g., liMnO) 2 、LiMn 2 O 4 ) Lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi) 1/3 Co 1/3 Mn 1/3 O 2 (may also be abbreviated as NCM) 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O 2 (may also be abbreviated as NCM) 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O 2 (may also be abbreviated as NCM) 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O 2 (may also be abbreviated as NCM) 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (may also be abbreviated as NCM) 811 ) Lithium nickel cobalt aluminum oxides (e.g., liNi) 0.85 Co 0.15 Al 0.05 O 2 ) And modified compounds thereof, and the like. Examples of olivine structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (e.g., liFePO) 4 (also referred to as LFP for short)), a composite material of lithium iron phosphate and carbon, and lithium manganese phosphate (e.g., liMnPO) 4 ) At least one of a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.
In some embodiments, the positive electrode film layer further optionally includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluoroacrylate resin.
In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
In some embodiments, the positive electrode sheet may be prepared by: dispersing the above components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and coating the positive electrode slurry on a positive electrode current collector, and drying, cold pressing and the like to obtain the positive electrode piece.
[ negative electrode sheet ]
The negative pole piece includes the negative pole mass flow body and sets up the negative pole rete on the negative pole mass flow body at least one surface, and the negative pole rete includes negative pole active material.
As an example, the negative electrode current collector has two surfaces opposite in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two surfaces opposite to the negative electrode current collector.
In some embodiments, the negative electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
In some embodiments, the negative active material is a lithium titanate-coated graphite composite obtained by the preparation method of the present invention.
In some embodiments, the anode film layer further optionally includes a binder. The binder may be at least one selected from Styrene Butadiene Rubber (SBR), polyacrylic acid (PAA), sodium Polyacrylate (PAAs), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium Alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).
In some embodiments, the negative electrode film layer further optionally includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
In some embodiments, the negative electrode film layer may also optionally include other adjuvants, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.
In some embodiments, the negative electrode sheet can be prepared by: dispersing the components for preparing the negative electrode plate, such as a negative electrode active material, a conductive agent, a binder and any other components, in a solvent (such as deionized water) to form negative electrode slurry; and coating the negative electrode slurry on a negative electrode current collector, and drying, cold pressing and the like to obtain the negative electrode pole piece.
[ electrolyte ]
The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The kind of the electrolyte is not particularly limited and may be selected as desired. For example, the electrolyte may be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolytic solution).
In some embodiments, the electrolyte is an electrolytic solution. The electrolyte includes an electrolyte salt and a solvent.
In some embodiments, the electrolyte salt may be selected from lithium hexafluorophosphate (LiPF) 6 ) Lithium tetrafluoroborate (LiBF) 4 ) Lithium perchlorate (LiClO) 4 ) Lithium hexafluoroarsenate (LiAsF) 6 ) Lithium bis (fluorosulfonylimide) (LiFSI), lithium bis (trifluoromethanesulfonylimide) (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalato borate (LiDFOB), lithium dioxaoxalato borate (L)iBOB), lithium difluorophosphate (LiPO) 2 F 2 ) One or more of lithium difluorooxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP).
In some embodiments, the solvent may be selected from one or more of Ethylene Carbonate (EC), propylene Carbonate (PC), ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl Propyl Carbonate (MPC), ethyl Propyl Carbonate (EPC), butylene Carbonate (BC), fluoro Ethylene Carbonate (FEC), methyl Formate (MF), methyl Acetate (MA), ethyl Acetate (EA), propyl Acetate (PA), methyl Propionate (MP), ethyl Propionate (EP), propyl Propionate (PP), methyl Butyrate (MB), ethyl Butyrate (EB), 1, 4-butyrolactone (GBL), sulfolane (SF), dimethylsulfone (MSM), methylethylsulfone (EMS), and diethylsulfone (ESE).
In some embodiments, the electrolyte may optionally further comprise an additive. For example, the additive can comprise a negative electrode film forming additive, can also comprise a positive electrode film forming additive, and can also comprise an additive capable of improving certain performances of the battery, such as an additive capable of improving the overcharge performance of the battery, an additive capable of improving the high-temperature performance of the battery, an additive capable of improving the low-temperature performance of the battery, and the like.
[ isolation film ]
In some embodiments, a separator is further included in the secondary battery. The isolating film is arranged between the positive pole piece and the negative pole piece to play an isolating role. The type of the separator is not particularly limited, and any known separator having a porous structure and good chemical and mechanical stability may be used.
In some embodiments, the material of the isolation film may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.
[ outer Package ]
In some embodiments, the secondary battery may include an overwrap for encapsulating the positive electrode tab, the negative electrode tab, and the electrolyte. As one example, the positive electrode sheet, the negative electrode sheet, and the separator may be laminated or wound to form a laminated structure cell or a wound structure cell, the cell being enclosed within an outer package; the electrolyte can adopt electrolyte, and the electrolyte is soaked in the battery core. The number of the battery cells in the secondary battery can be one or more, and can be adjusted according to requirements.
In one embodiment, the present application provides an electrode assembly. In some embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process. The exterior package may be used to enclose the electrode assembly and the electrolyte.
In some embodiments, the outer package of the secondary battery may be a pouch, for example, a pouch-type pouch. The soft bag can be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS) and the like. In some embodiments, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like.
Method for manufacturing secondary battery
In one embodiment, the present application provides a method for preparing a secondary battery, wherein the negative electrode sheet described herein or the negative electrode sheet prepared according to the method described herein is used.
The preparation of the secondary battery may further include a step of assembling the negative electrode sheet, the positive electrode sheet and the electrolyte of the present application to form a secondary battery. In some embodiments, the positive electrode plate, the separator, and the negative electrode plate may be sequentially wound or laminated, so that the separator is located between the positive electrode plate and the negative electrode plate to perform an isolation function, thereby obtaining the battery cell. And (4) placing the battery core in an outer package, injecting electrolyte and sealing to obtain the secondary battery. The battery group margin of the secondary battery is 90-95%.
In some embodiments, the preparation of the secondary battery may further include a step of preparing a positive electrode tab. As an example, a positive electrode active material, a conductive agent, and a binder may be dispersed in a solvent (e.g., N-methylpyrrolidone, NMP for short) to form a uniform positive electrode slurry; and coating the positive electrode slurry on a positive electrode current collector, and drying, cold pressing and the like to obtain the positive electrode piece.
In some embodiments, the preparation of the secondary battery comprises the step of preparing a negative electrode sheet according to the methods described herein.
The shape of the secondary battery is not particularly limited, and may be a cylindrical shape, a square shape, or any other arbitrary shape. For example, fig. 2 is a secondary battery 5 of a square structure as an example.
In some embodiments, referring to fig. 3, the outer package may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodating chamber, and a cover plate 53 can be provided to cover the opening to close the accommodating chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is enclosed within the receiving cavity. The electrolyte is impregnated into the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 may be one or more, and those skilled in the art can select them according to the actual needs.
Electric device, battery module, or battery pack
In one embodiment, the present application provides an electric device, a battery module, or a battery pack, wherein the electric device, battery module, or battery comprises a secondary battery as described herein or a secondary battery prepared according to the methods described herein.
In some embodiments, the secondary batteries may be assembled into a battery module, and the number of the secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.
Fig. 4 is a battery module 4 as an example. Referring to fig. 4, in the battery module 4, a plurality of secondary batteries 5 may be arranged in series along the longitudinal direction of the battery module 4. Of course, the arrangement may be in any other manner. The plurality of secondary batteries 5 may be further fixed by a fastener.
Alternatively, the battery module 4 may further include a case having an accommodation space in which the plurality of secondary batteries 5 are accommodated.
In some embodiments, the battery modules may be assembled into a battery pack, and the number of the battery modules contained in the battery pack may be one or more, and the specific number may be selected by one skilled in the art according to the application and the capacity of the battery pack.
Fig. 5 and 6 are a battery pack 1 as an example. Referring to fig. 5 and 6, a battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery box comprises an upper box body 2 and a lower box body 3, wherein the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4. A plurality of battery modules 4 may be arranged in any manner in the battery box.
In addition, the present application also provides an electric device, which comprises at least one of the secondary battery, the battery module or the battery pack provided by the present application. The secondary battery, the battery module, or the battery pack may be used as a power source of an electric device, and may also be used as an energy storage unit of the electric device. The powered device may include a mobile device (e.g., a mobile phone, a laptop computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, and a satellite, an energy storage system, etc., but is not limited thereto.
As the electricity-using device, a secondary battery, a battery module, or a battery pack may be selected according to its use requirement.
Fig. 7 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle or a plug-in hybrid electric vehicle and the like. In order to meet the demand of the electric device for high power and high energy density of the secondary battery, a battery pack or a battery module may be used.
As another example, the device may be a cell phone, a tablet, a laptop, etc. The device is generally required to be thin and light, and a secondary battery may be used as a power source.
Examples
Hereinafter, examples of the present application will be described. The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the present disclosure. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
1. Preparation examples
Example 1
(1) 1.42g of isopropyl titanate (0.005 mol), 0.198g of lithium acetate (0.003 mol) were dissolved in 100ml of deionized water, and the molar ratio of the Ti element (based on isopropyl titanate) and the Li element (based on lithium acetate) was 5:3, then 0.0345g of surfactant cetyl trimethyl ammonium bromide is added to prepare a mixed solution A;
(2) Adding 1.19g of ammonium bicarbonate (0.015 mol) into the mixed solution A, adding 34.5g of artificial graphite, and stirring for 1 hour to react to form a suspension B;
(3) Then transferring the mixed solution B into a stainless steel reaction kettle with a polytetrafluoroethylene lining in a hydrothermal box, and carrying out heating reaction for 12 hours at the temperature of 60 ℃ to prepare slurry C;
(4) And (4) carrying out spray drying on the slurry C to obtain precursor powder of the lithium titanate coated graphite, wherein the temperature of a feed port of the spray drying is 180 ℃, and the pump speed of the feed port is 5L/min.
(5) And (5) calcining the powder prepared in the step (4) in a nitrogen inert atmosphere at the temperature of 600 ℃ for 8 hours to obtain the lithium titanate coated graphite composite material.
The content of lithium titanate in the prepared lithium titanate-coated graphite composite material was 1% by weight, expressed as G.R. @1wt% LTO. The SEM is shown in figure 1 (scanning electron microscope Sigma-02-33, ZEISS, germany, at a magnification of 5K, 10KV, and 1 μm).
The specific surface area SSA of the lithium titanate coated graphite composite material is 1.99m 2 G, dv10 of 10.5. Mu.m, dv50 of 17.6. Mu.m, dv90 of 29.1. Mu.m, dv99 was 38.5. Mu.m.
Example 2
The procedure of example 1 was repeated except that steps 1 and 2:
(1) 2.84g of isopropyl titanate (0.01 mol) and 0.396g of lithium acetate (0.006 mol) were dissolved in 100ml of deionized water, and the molar ratio of the Ti element (based on the isopropyl titanate) and the Li element (based on the lithium acetate) was 5:3, then 0.069g of surfactant cetyl trimethyl ammonium bromide is added to prepare a mixed solution A;
(2) Adding 2.38g of ammonium bicarbonate into the mixed solution A, adding 34.5g of artificial graphite, and stirring for 1 hour to react to form a suspension B;
the content of lithium titanate in the lithium titanate-coated graphite composite material prepared was 2% by weight, expressed as g.r. @2wt% lto.
The specific surface area SSA of the lithium titanate-coated graphite composite material is 1.20m 2 G, dv10 of 7.3. Mu.m, dv50 of 15.6. Mu.m, dv90 of 29.6. Mu.m and Dv99 of 40.9. Mu.m.
Example 3
The procedure of example 1 was repeated except that steps 1 and 2:
(1) 4.26g of isopropyl titanate (0.015 mol), 0.594g of lithium acetate (0.009 mol) are dissolved in 100ml of deionized water, the molar ratio of the Ti element (based on isopropyl titanate) and the Li element (based on lithium acetate) being 5:3, then adding 0.11g of surfactant cetyl trimethyl ammonium bromide to prepare a mixed solution A;
(2) Adding 3.57g of ammonium bicarbonate into the mixed solution A, adding 34.5g of artificial graphite, and stirring for 1 hour to react to form a suspension B;
the content of lithium titanate in the lithium titanate-coated graphite composite material prepared was 3% by weight, expressed as g.r. @3wt% lto.
The specific surface area SSA of the lithium titanate-coated graphite composite material is 1.22m 2 In terms of a specific ratio of Dv10 of 8.5. Mu.m, dv50 of 16.2. Mu.m, dv90 of 28.9. Mu.m, and Dv99 of 40.3. Mu.m.
Examples 4 to 8
The procedure of example 1 was repeated except that the heating reaction temperature in step (3) was 40, 50, 90, 200, 220 ℃.
Example 9
The procedure of example 1 was repeated except that the heating reaction time in step (3) was 8 hours, respectively.
Examples 10 to 13
The procedure of example 1 was repeated except that the feed port temperatures for the spray drying in step (4) were 100, 150, 200, and 250 ℃.
The various parameters are summarized in table 1.
2. Preparation of comparative example
Comparative example 1
The procedure of example 1 was repeated except that the heating reaction of step 3 was not carried out.
Comparative example 2
The procedure of example 1 was repeated except that the heating reaction of step 3 was not performed, and the slurry C was filtered and then dried in a vacuum oven at 60 ℃ for 12 hours in step 4.
3. Application examples
1. Preparation of secondary battery
(1) Preparing a negative pole piece: the lithium titanate coated graphite composite materials prepared in the examples 1 and 4-13 and the comparative examples 1-2 are mixed with Styrene Butadiene Rubber (SBR), conductive agent Super P carbon black and sodium methyl cellulose (CMC) according to the weight ratio of 96.5%:1.8%:0.5%:1.2% to prepare slurry, the prepared slurry is coated on a copper foil current collector, and the copper foil current collector is dried in an oven and then is cold-pressed for standby, and the compacting range is as follows: 1.5g/cm 3 ；
(2) Positive pole piece: a metal lithium sheet is taken as a counter electrode;
(3) Preparing an electrolyte: ethylene Carbonate (EC), ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC) were mixed in a volume ratio of 1 6 Uniformly dissolving in the above solution to obtain an electrolyte solution, wherein LiPF 6 The concentration of (A) is 1mol/L;
a diaphragm: a Polyethylene (PE) film was used as a separator film and had a thickness of 12 μm.
(4) Preparing a secondary battery: manually winding the above parts in an argon-protected glove box to prepare a secondary battery, wherein the outer package is a plastic shell with the thickness of 1.5mm and the height of 48mm (width) × 204mm (length) × 86mm (height); the battery pack margin was 93%.
2. Preparation of three-electrode cell
Similar to the secondary battery preparation operation except that in step (4), at the time of manual winding, copper wire was implanted in the anode side and was in contact with the anode, and a lithium plating operation was performed before measurement.
4. Measurement method
1. Method for measuring specific surface area
The lithium titanate-coated graphite composite materials prepared in examples 1 to 3 were measured by analyzing the specific surface area by a gas adsorption method and measuring the specific surface area of solid matter according to GB/T19587-2004< determination of specific surface area of gas adsorption method >.
2.D V 50、D V 10、D V Test methods for 90 and Dv99
The lithium titanate-coated graphite composite materials prepared in examples 1 to 3 were measured using a laser particle Size analyzer (Malven Master Size 3000) according to the standard GB/T19077.1-2016.
3. The full-cell voltage testing method comprises the following steps:
the prepared secondary battery was discharged to 2.5V at 25 c and then placed in a high-low temperature chamber at 70 c to monitor the change in the voltage of the full battery with a novacon tester.
4. The anode potential testing method comprises the following steps:
the prepared three-electrode cell was discharged to 2.5V at 25 ℃, and then placed in a 70 ℃ high-low temperature chamber to monitor the change in the anode potential with a newcastle tester.
The results of the full cell voltage and the anode potential measured at day 25 are summarized in table 1.
Table 1: relevant Process parameters and Performance data for examples 1 and 4-13 and comparative examples 1-2
According to the above results, the voltage of the battery is still maintained at a higher voltage level when the battery is stored for 25 days in a low SOC state according to the embodiment of the present invention; the anode potentials of the battery cells are lower and are far less than the decomposition potential (1.8V) of the SEI film. In contrast, in comparative examples 1 to 2, both the full cell voltage and the anode potential were not effectively improved.
The present application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exhibiting the same operation and effect within the technical scope of the present application are all included in the technical scope of the present application. In addition, various modifications that can be conceived by those skilled in the art are applied to the embodiments and other embodiments are also included in the scope of the present application, in which some of the constituent elements in the embodiments are combined and constructed, without departing from the scope of the present application.
Claims (12)
1. A method for preparing a lithium titanate-coated graphite composite material is characterized by comprising the following steps: heating and reacting a titanium source compound, a lithium source compound, graphite, a chelating agent and a solvent at 40-220 ℃ to obtain slurry C; and then drying and calcining the slurry C to obtain the lithium titanate coated graphite composite material.
2. The method according to claim 1, characterized by comprising the steps of:
s1: mixing a titanium source compound, a lithium source compound, graphite, a chelating agent and a solvent to obtain a suspension B;
s2: heating the suspension B at 40-220 ℃ for reaction to obtain slurry C;
s3: drying and calcining the slurry C to obtain the lithium titanate coated graphite composite material; wherein, in step S1, the titanium source compound is at least one selected from isopropyl titanate, tetrabutyl titanate, and titanium dioxide; the lithium source compound is at least one selected from lithium acetate, lithium hydroxide, lithium nitrate and lithium carbonate.
3. The method according to claim 1 or 2, wherein in step S1 the chelating agent is selected from at least one of ammonium carbonate, ammonium bicarbonate, oxalic acid, urea, citric acid, ammonium formate, ammonium oxalate.
4. The method according to any one of claims 1 to 3, wherein in step S2, the suspension B is subjected to a heating reaction at 50-90 ℃ for 2-14h, optionally 8-12h.
5. The method according to any one of claims 1-4, wherein in step S3 the drying is performed by spray drying, the feed inlet temperature being 120-250 ℃, optionally 150-200 ℃.
6. A lithium titanate-coated graphite composite material prepared by the process of any one of claims 1-5.
7. The lithium titanate-coated graphite composite material of claim 6, wherein the lithium titanate in the lithium titanate-coated graphite composite material is in an amount of 0.1 to 10 wt%, optionally 1 to 3wt%, based on the weight of graphite.
8. The lithium titanate-coated graphite composite material according to claim 6 or 7, wherein the lithium titanate-coated graphite composite material has a specific surface area SSA of 1.1-2.1m 2 G, optionally 1.22-1.99m 2 /g。
9. A secondary battery comprising the lithium titanate-coated graphite composite material prepared by the method of any one of claims 1 to 5, and the lithium titanate-coated graphite composite material of any one of claims 6 to 8.
10. A battery module characterized by comprising the secondary battery according to claim 9.
11. A battery pack comprising the battery module according to claim 10.
12. An electric device comprising at least one selected from the secondary battery according to claim 9, the battery module according to claim 10, and the battery pack according to claim 11.
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