CN115241461A - Method for preparing modified lithium titanate composite material and modified lithium titanate composite material - Google Patents

Abstract

The invention provides a method for preparing a modified lithium titanate composite material and the modified lithium titanate composite material, wherein the method comprises the following steps: mixing a titanium source, a lithium source and a first aluminum source by a wet method, and then calcining for the first time to obtain a mixture comprising lithium titanate and lithium aluminum oxide; and mixing at least one of a second aluminum source and a conductive agent with the mixture, and then optionally calcining for the second time to obtain the modified lithium titanate composite material. By adopting the technical scheme, the problem of low rate capability of the lithium titanate material in the prior art is effectively solved.

Description

Method for preparing modified lithium titanate composite material and modified lithium titanate composite material

technical field

The invention relates to the technical field of lithium titanate preparation, in particular to a method for preparing a modified lithium titanate composite material and a modified lithium titanate composite material.

Background technique

Lithium titanate has the characteristics of high lithium intercalation potential, no lithium dendrites, and high thermal stability in charge and discharge states, so it has excellent safety as a negative electrode material for lithium ion batteries. In addition, the volume of lithium titanate anode material does not change basically during the charging and discharging process, which is called "zero strain" material, and does not form an SEI film, and the cycle life can reach more than 10,000 times. However, when the lithium titanate negative electrode is charged and discharged, due to the catalytic reaction of the Ti-O bond to the electrolyte, the lithium titanate battery is prone to flatulence. Especially at high temperature, the flatulence phenomenon significantly affects the stability of the battery. In addition, although lithium titanate has excellent rate performance, the high rate application of lithium titanate is still limited by low electronic conductivity (10 ^-13 S/cm) and slow ion mobility (10 ^-9 ~ 10 ^-13 cm ² s ^-1 ). Therefore, lithium titanate batteries have defects such as poor high rate performance and instability in some working conditions.

For the problem of low rate capability of lithium titanate materials in the prior art, no effective solution has been proposed yet.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to provide a method for preparing a modified lithium titanate composite material and a modified lithium titanate composite material, so as to solve the problem of low rate capability of the lithium titanate material in the prior art.

In order to achieve the above purpose, according to one aspect of the present invention, there is provided a method for preparing a modified lithium titanate composite material, comprising: mixing a titanium source, a lithium source and a first aluminum source by a wet method and then performing a calcination to obtain a Including a mixture of lithium titanate and lithium alumina; after mixing at least one of a second aluminum source and a conductive agent with the mixture, optional secondary calcination is performed to obtain a modified lithium titanate composite material.

Further, the method includes: after wet mixing the titanium source, the lithium source and the first aluminum source, performing ball milling, spray drying and calcination in sequence to obtain a mixture; mixing the mixture with the second aluminum source and then performing a second ball milling in sequence , secondary spray drying, the product obtained after secondary spray drying is sequentially calcined and sieved for a second time, or, the product obtained after secondary spray drying is sequentially dried and sieved to obtain modified titanic acid. Lithium composites.

Further, the method comprises: after wet mixing the titanium source, the lithium source and the first aluminum source, ball milling, one spray drying, and one calcination are performed in sequence to obtain the mixture; Grinding and secondary spray drying, the products obtained after secondary spray drying are sequentially calcined and screened for a second time, or the products obtained after secondary spray drying are sequentially dried and screened to obtain modified titanium Lithium oxide composite.

Further, the titanium source is a liquid titanium source, and the method includes: wet-mixing the titanium source, the lithium source, and the first aluminum source, then spray-drying, and calcining the spray-dried product once to obtain the mixture.

Further, the method includes: after wet mixing the titanium source, the lithium source, and the first aluminum source, performing ball milling, spray drying, and calcination in sequence to obtain a mixture; mixing the mixture with the second aluminum source and then performing a second ball milling, The product obtained after the secondary ball milling is mixed with the conductive agent and then ground and spray-dried for the second time. The obtained product is sequentially dried and screened to obtain a modified lithium titanate composite material.

Further, the first aluminum source is one or more of aluminum chloride hexahydrate, aluminum nitrate of crystal water, aluminum sulfate, aluminum acetate, aluminum citrate, aluminum oxide, aluminum hydroxide, boehmite, and/ Or, the second aluminum source is one or more of aluminum chloride hexahydrate, aluminum nitrate of crystal water, aluminum sulfate, aluminum acetate, aluminum citrate, aluminum oxide, aluminum hydroxide, and boehmite.

Further, the titanium source is one or more of titanium dioxide, titanium tetrachloride, titanium hydroxide, metatitanic acid, tetrabutyl titanate, titanium oxide sulfate, tetraethyl titanate, and isopropyl titanate.

Further, the lithium source is one or more of lithium chloride, lithium oxalate, lithium nitrate, lithium carbonate, lithium acetate, lithium hydroxide monohydrate, and lithium fluoride.

Further, the conductive agent is conductive carbon black SP, conductive silver nanoparticles, conductive copper nanoparticles, conductive gold nanoparticles, silver nanowires, copper nanowires, carbon nanotubes, vapor grown carbon fibers, zinc oxide nanorods, silicon carbide nanometers. One or more of wire and graphene.

Further, in the mixing step of mixing at least one of the second aluminum source and the conductive agent with the mixture, the mass of the conductive agent is 0.5-10% of the mass of the mixture.

According to another aspect of the present invention, a modified lithium titanate composite material is provided, which is prepared by the above-mentioned preparation method; preferably, in the modified lithium titanate composite material, the quality of lithium alumina is that of lithium titanate. 0.5-15% of the mass, and the mass of alumina is 0-15% of the mass of the mixture.

By applying the technical scheme of the present invention, after the titanium source, the lithium source and the first aluminum source are mixed by a wet method, the crystallization process of the lithium titanate is regulated in the subsequent calcination process, the crystal particle size of the lithium titanate is reduced, and at the same time It will generate fast lithium ion conductor lithium alumina, improve the migration rate of lithium ions on the surface of lithium titanate, and then play the effect of improving the rate performance of lithium titanate negative material. After the mixture is mixed, an optional secondary calcination can be performed, so that at least one of the second aluminum source and the conductive agent can modify the surface of the lithium titanate material, and the second aluminum source is converted into alumina, which can affect the trace water and the electrolyte in the electrolyte. The acid has a removal effect, improves the surface stability of the lithium titanate material, and helps to solve the flatulence problem of the lithium titanate material. The addition of the conductive agent can improve the conductivity of the lithium titanate material and solve the problem of low conductivity of the lithium titanate material. The technical solution of the present application effectively solves the problem of low rate capability of the lithium titanate material in the prior art.

Description of drawings

The accompanying drawings forming a part of the present application are used to provide further understanding of the present invention, and the exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the attached image:

FIG. 1 shows a schematic flowchart of an embodiment of a method for preparing a modified lithium titanate composite material according to the present invention.

Detailed ways

It should be noted that the embodiments in the present application and the features of the embodiments may be combined with each other in the case of no conflict. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, devices, components and/or combinations thereof.

It should be noted that the terms "first", "second", etc. in the description and claims of the present application and the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific sequence or sequence. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein can, for example, be practiced in sequences other than those illustrated or described herein. Furthermore, the terms "comprising" and "having" and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those expressly listed Rather, those steps or units may include other steps or units not expressly listed or inherent to these processes, methods, products or devices.

Now, exemplary embodiments according to the present application will be described in more detail with reference to the accompanying drawings. These exemplary embodiments may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It should be understood that these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of these exemplary embodiments to those of ordinary skill in the art, and in the accompanying drawings, which may be exaggerated for the sake of clarity The thicknesses of layers and regions are described, and the same reference numerals are used to denote the same devices, and thus their descriptions will be omitted.

The potential of lithium titanate is higher than that of pure metal lithium, it is not easy to generate lithium dendrites, and the discharge voltage is stable, thus improving the safety performance of lithium batteries. Lithium titanate batteries have been tested and found that under severe tests such as acupuncture, extrusion, and short circuit, there is no smoke, no fire, and no explosion, and the safety is much higher than other lithium batteries. Compared with carbon anode materials, lithium titanate batteries have a higher lithium ion diffusion coefficient and can be charged and discharged at high rates. While greatly shortening the charging time, the impact on the cycle life is small, and the thermal stability is also strong. The battery made of lithium titanate as the negative electrode material also has the advantages of long cycle life and good resistance to wide temperature. The above advantages make lithium titanate materials have better performance and greater market potential than traditional battery anode materials. However, the lithium titanate material is used as the negative electrode material in the battery. Due to its own characteristics, the material and the electrolyte are prone to interaction and gas evolution occurs during the charge-discharge cycle reaction. Therefore, ordinary lithium titanate batteries are easy to Flatulence occurs, resulting in bulging of the battery cells, and the electrical performance will also be greatly reduced, which greatly reduces the theoretical cycle life of the lithium titanate battery. At the same time, lithium titanate materials have electronic conductivity and slow ion mobility, resulting in low rate performance of lithium titanate materials. The above-mentioned defects seriously restrict the large-scale market application of lithium titanate batteries. Therefore, how to improve the stability and rate performance of lithium titanate materials has become a technical problem that needs to be solved urgently in the industry.

In terms of bulk structure, ion doping, recombination, and nanoscale are effective modification strategies to improve their electronic/ionic conductivity and reaction kinetics. In terms of surface structure, in order to improve the surface stability and fast charging performance of lithium titanate materials, various coating and modification methods have been proposed.

Optionally, by coating aluminum oxide on the surface of lithium titanate, the water absorption of lithium titanate is reduced, the decomposition effect of Ti-O bond on the electrolyte is reduced, and the flatulence problem of lithium titanate is improved. With this technical solution, the coating of alumina will affect the migration of lithium ions into the lithium titanate material, thereby reducing the conductivity of the lithium titanate negative electrode material.

Alternatively, Mg- and Al-doped lithium titanate materials with carbon coating are fabricated by carbon coating, which can significantly improve the electrical conductivity, exhibit high specific discharge capacity and excellent cycling stability at high rates. . Carbon coating can improve the conductivity of the material, but at high rates, it will hinder the migration of lithium ions and affect the rate performance of lithium titanate anode materials.

With reference to FIG. 1 , according to a specific embodiment of the present application, a method for preparing a modified lithium titanate composite material is provided. to obtain a mixture comprising lithium titanate and lithium alumina; after mixing at least one of the second aluminum source and the conductive agent with the mixture, optional secondary calcination is performed to obtain a modified lithium titanate composite material.

By applying the technical scheme of the present invention, after the titanium source, the lithium source and the first aluminum source are mixed by a wet method, the crystallization process of the lithium titanate is regulated in the subsequent calcination process, the crystal particle size of the lithium titanate is reduced, and at the same time It will generate fast lithium ion conductor lithium alumina, improve the migration rate of lithium ions on the surface of lithium titanate, and then play the effect of improving the rate performance of lithium titanate negative material. After the mixture is mixed, an optional secondary calcination can be performed, so that at least one of the second aluminum source and the conductive agent can modify the surface of the lithium titanate material, and the second aluminum source is converted into alumina, which can affect the trace water and the electrolyte in the electrolyte. The acid has a removal effect, improves the surface stability of the lithium titanate material, and helps to solve the flatulence problem of the lithium titanate material. The addition of the conductive agent can improve the conductivity of the lithium titanate material and solve the problem of low conductivity of the lithium titanate material. The technical solution of the present application effectively solves the problem of low rate capability of the lithium titanate material in the prior art.

Specifically, the first aluminum source acts as a fast lithium ion conductor source, and reacts with the lithium source to generate a fast lithium ion conductor, and the fast ion conductor can significantly improve the conductivity of the lithium titanate material. After the titanium source, the lithium source, and the first aluminum source are wet-mixed and then calcined once, a mixture including lithium titanate and lithium alumina as a fast lithium ion conductor is obtained.

In fact, when the size of the material is reduced to the nanoscale, the diffusion process of lithium ions inside the material will not be the main step of controlling the charge and discharge rate, but the diffusion of lithium ions to the surface of the material and the migration to the inside of the material. The surface structure of the material become particularly important. Using the technical solution of this embodiment, at least one of the second aluminum source and the conductive agent is used to modify the surface of the lithium titanate material, and the aluminum source is converted into alumina, which has the effect of removing trace water and acid in the electrolyte, improving the The stability of the lithium titanate surface, and the addition of a conductive agent can improve the conductivity of the lithium titanate material, and generally improve the rate performance and high temperature stability of the lithium titanate negative electrode material.

In an optional embodiment, during the mixing process of the raw materials used for preparing lithium titanate, an additive that suppresses excessive crystallization of lithium titanate during subsequent calcination can be added, and a first aluminum source can be added at the same time, which can reduce the concentration of lithium titanate. The crystal particle size increases the migration rate of lithium ions on the surface of lithium titanate.

Optionally, an additive for inhibiting the growth of lithium titanate crystals and a fast lithium ion conductor precursor are firstly added in the liquid phase mixing stage, and after one calcination, a product in which small lithium titanate crystals and fast lithium ion conductor lithium alumina are mixed is formed. Secondly, the surface modification of alumina and/or conductive agent is performed by ball milling and/or grinding, so as to improve the lithium ion migration rate, electronic conductivity and surface stability of the lithium titanate material.

The method comprises: wet mixing titanium source, lithium source and first aluminum source, and then performing ball milling, spray drying and calcination in sequence to obtain a mixture; mixing the mixture with the second aluminum source and then performing secondary ball milling and secondary calcination in sequence. spray drying, the product obtained after the secondary spray drying is sequentially subjected to secondary calcination and sieving, or, the product obtained after the secondary spray drying is sequentially dried and sieved to obtain the modified lithium titanate composite material . As shown in Figure 1, first, in the wet mixing process 1, the titanium source, the lithium source and the first aluminum source are added, and after the ball milling process 2 (the titanium source is a solid titanium source, the ball milling process 2 is the primary ball milling), Or without the ball milling process 2 (the titanium source is a liquid titanium source), the spray drying process 3 (the spray drying process 3 is the primary spray drying), the calcination process 4 (the calcination process 4 is the primary calcination), and the sieving process 42. , to obtain a modified lithium titanate composite (lithium titanate and lithium alumina mixture A). Or, after the primary calcination, the ball milling step 5 (the ball milling step 5 is the secondary ball milling) is carried out, the second aluminum source is added at the same time, and the secondary spraying step 6 (secondary spraying step 6) and the secondary calcining step 7 (two The secondary calcination step 7 is the secondary calcination), and finally the sieving step 8 is used to obtain the modified lithium titanate composite material (the first composite B10 of lithium titanate, lithium alumina and alumina mixed type lithium titanate). For example, the product obtained after the secondary spraying step 6 is directly subjected to the drying step 72, and after sieving, a modified lithium titanate composite material (a second composite of lithium titanate, lithium alumina and alumina mixed lithium titanate) is obtained. material B20).

Further, the method comprises: after wet mixing the titanium source, the lithium source and the first aluminum source, ball milling, one spray drying, and one calcination are performed in sequence to obtain the mixture; Grinding and secondary spray drying, the products obtained after secondary spray drying are sequentially calcined and screened for a second time, or the products obtained after secondary spray drying are sequentially dried and screened to obtain modified titanium Lithium oxide composite. As shown in FIG. 1 , after the calcination step 4, the conductive agent and the second aluminum source are added, and the grinding and dispersing step 43 (the grinding and dispersing step 43 is grinding) and the secondary spraying step 44 (the secondary spraying step 44 is the secondary spraying) are carried out. After drying), secondary calcination process 45 (secondary calcination process 45 is secondary calcination) and sieving process 46, the modified lithium titanate composite material (the surface of lithium titanate and lithium alumina mixture is coated with conductive agent and oxidized) is obtained. The first composite product C10 of aluminum), or, the product obtained after the secondary spraying process 44 is directly subjected to the drying process 452, and after sieving, another modified lithium titanate composite material (lithium titanate and The lithium alumina mixture is coated with a second composite product of the conductive agent and alumina (C20).

Further, the method includes: after wet mixing the titanium source, the lithium source, and the first aluminum source, performing ball milling, spray drying, and calcination in sequence to obtain a mixture; mixing the mixture with the second aluminum source and then performing a second ball milling, The product obtained after the secondary ball milling is mixed with the conductive agent and then ground and spray-dried for the second time. The obtained product is sequentially dried and screened to obtain a modified lithium titanate composite material. As shown in FIG. 1, after adding the second aluminum source to carry out the ball milling step 5 (the ball milling step 5 is the secondary ball milling), the conductive agent is added, and the grinding and dispersing step 43 and the secondary spraying step 44 are performed (the secondary spraying step 44 is the second ball milling step 44). secondary spray drying), secondary calcination step 45 and sieving step 46 to obtain a modified lithium titanate composite material (a third composite C30 of alumina and conductive agent mixed with lithium titanate-lithium alumina).

In another optional embodiment, by changing the mixing and calcining sequence of the conductive agent and the second aluminum source, at least one other modified lithium titanate composite material can be obtained. That is, after the first ball milling), the conductive agent is added, and the grinding and dispersing step 23, the spray drying step 24 (the spray drying step 24 is the first spray drying), the calcination step 25 (the calcination step 25 is the first calcination), and the sieving step 262 After the A modified lithium titanate composite (lithium titanate, lithium alumina and conductive agent mixture D). Alternatively, the product obtained after the calcination process 25 is subjected to the secondary grinding process 26, and the second aluminum source is added, and then the secondary spray process 27, the secondary calcination process 28, and the sieving process 29 are performed to obtain a modified titanic acid. Lithium composite material (a first composite E10 coated with alumina and comprising lithium titanate, lithium alumina and a conductive agent). Alternatively, the product obtained after the secondary spraying process 27 is directly subjected to the drying process 282 and the sieving process 29 to obtain another modified lithium titanate composite material (a A second complex of aluminum lithium and conductive agent E20). It should be noted that the lithium titanate and lithium alumina mixture A shown in FIG. 1 was obtained by calcining 4 (primary calcination) and then sieving. The mixed lithium titanate compound B includes B10 and B20. The coated lithium titanate composite C includes C10, C20, and C30. Lithium titanate, lithium alumina and conductive agent mixture D were obtained by sifting after calcination 25 (one calcination). The composite E coated with alumina, mixed with lithium titanate, lithium alumina and conductive agent includes E10 and E20.

Optionally, the titanium source is a liquid titanium source, and the method includes: wet-mixing the titanium source, the lithium source, and the first aluminum source, then spray-drying, and calcining the spray-dried product once to obtain a mixture.

It should be noted that the modified lithium titanate composite material includes at least one of alumina and a conductive agent, lithium titanate, and lithium alumina.

It should be noted that, in the wet mixing process involved in the above embodiment, the stirring speed is 10-60 Hz, and the stirring time is 1-10 h. In the ball milling process involved, the linear speed of the ball milling is 5-20m/s, the time is 4-48h, and the particle size of the zirconium ball is 0.05-0.6mm. The spray drying involved has an inlet temperature of 200-1000°C and an outlet temperature of 80-200°C. In the calcination process involved, the calcination temperature is 500-1500°C, the calcination time is 2-20h, and the atmosphere is an air atmosphere or a nitrogen atmosphere. In the grinding and dispersing process involved, the rotating speed is 2000-10000r/min, the time is 1-8h, and the gap is 0.2-0.8mm. In the sieving process involved, the sieving mesh number is 100-500 mesh.

Further, the first aluminum source is one or more of aluminum chloride hexahydrate, aluminum nitrate of crystal water, aluminum sulfate, aluminum acetate, aluminum citrate, aluminum oxide, aluminum hydroxide, and boehmite. The second aluminum source is one or more of aluminum chloride hexahydrate, aluminum nitrate of crystal water, aluminum sulfate, aluminum acetate, aluminum citrate, aluminum oxide, aluminum hydroxide, and boehmite. That is, the first aluminum source is AlCl ₃ .6H ₂ O, Al(NO ₃ ) ₃ .9H ₂ O, Al ₂ (SO ₄ ) ₃ , (CH ₃ COO) ₃ Al, C ₆ H ₅ AlO ₇ , at least one of Al ₂ O ₃ , Al(OH) ₃ and AlOOH.

Further, the titanium source is one or more of titanium dioxide, titanium tetrachloride, titanium hydroxide, metatitanic acid, tetrabutyl titanate, titanium oxide sulfate, tetraethyl titanate, and isopropyl titanate. That is, the titanium source is TiO ₂ , TiCl ₄ , Ti(OH) ₄ , TiO(OH) ₂ , Ti(OC ₄ H ₉ ) ₄ , TiOSO ₄ , Ti(OC ₂ H ₅ ) ₄ , isotitanate at least one of propyl esters.

Further, the lithium source is one or more of lithium chloride, lithium oxalate, lithium nitrate, lithium carbonate, lithium acetate, lithium hydroxide monohydrate, and lithium fluoride. That is, the lithium source is at least one of LiCl, Li ₂ C ₂ O ₄ , LiNO ₃ , Li ₂ CO ₃ , CH ₃ COOLi, LiOH.H ₂ O, and LiF.

Further, the conductive agent is conductive carbon black SP, conductive silver nanoparticles, conductive copper nanoparticles, conductive gold nanoparticles, silver nanowires, copper nanowires, carbon nanotubes (CNT), vapor grown carbon fibers (VGCF), zinc oxide One or more of (ZnO) nanorods, silicon carbide (SiC) nanowires, and graphene.

Further, in the mixing step of mixing at least one of the second aluminum source and the conductive agent with the mixture, the mass of the conductive agent is 0.5-10% of the mass of the mixture.

In an optional embodiment, the amount of lithium alumina added is 0.5-15% of the mass of lithium titanate. After the added aluminum source is converted into alumina, its mass is 0-15% of the lithium titanate and lithium alumina powder theoretically formed in the previous process. The amount of the conductive agent added is 0.5-10% of the lithium titanate and lithium alumina powders theoretically formed in the previous process.

According to another aspect of the present invention, a modified lithium titanate composite material is provided, which is prepared by the above-mentioned preparation method; preferably, in the modified lithium titanate composite material, the quality of lithium alumina is that of lithium titanate. 0.5-15% of the mass, and the mass of alumina is 0-15% of the mass of the mixture. It should be noted that, according to the content of the components in the target composite material, the amount of raw materials in the preparation process can be adjusted accordingly.

As an exemplary embodiment, with reference to Figure 1, the method for preparing the modified lithium titanate composite material is as follows:

First, the first wet mixing step 1 is to mix and stir the titanium source, the lithium source and the first aluminum source. In the mixing tank, add 11.7kg of deionized water, then add 18.9kg of lithium source lithium nitrate _LiNO3 crystal, 1.06kg of aluminum source Al(OH) ₃ powder, and 3.2kg of titanium source metatitanate TiO(OH) ₂ powder, mix Stir for 2 hours at a stirring speed of 30 Hz, then transfer the slurry to a ball mill transfer tank, and perform ball milling process 2. The ball milling linear speed is 10 m/s, and the time is 8 hours, so that the titanium source and the first aluminum source are fully mixed, and the particles of the material are diameter reduced to less than 50 nm. Next, spray drying process 3 is carried out, the inlet temperature is 300 ° C, and the outlet temperature is 120 ° C, to obtain an Al(OH) ₃ - TiO(OH) ₂ mixture with LiNO ₃ evenly distributed. The mixture obtained by spray drying operation 3 is carried out calcination operation 4, calcination temperature 800 DEG C, calcination time 8h, atmosphere is air atmosphere, after cooling, obtain lithium aluminate-lithium titanate mixture 29.5kg, wherein the mass of lithium aluminate accounts for 29.5kg. 3% of the mass of lithium titanate. Take 5kg of it and pass it through a 300-mesh sieve to obtain a modified lithium titanate composite material (one of lithium titanate and lithium alumina mixture A, labelled as A1) with a mass of 4.6kg.

Second, in the ball milling step 5, add 53.2kg of deionized water, 15kg of calcined powder, and 0.88kg of boehmite into the ball mill transfer tank, and after mixing evenly, carry out ball milling with a rotational speed of 15m/s and a time of 24h. The ball-milled product obtained is carried out to secondary spray drying operation 6, and the inlet and outlet temperatures are respectively 300° C. and 120° C. to obtain spray powder 15.3kg. Then get spray powder 5.3kg and carry out drying operation 72, 200 ℃ of temperature, time 4h, cross 300 mesh sieves again, obtain a kind of modified lithium titanate composite material (the lithium titanate of mixed alumina-lithium aluminate The first mixture B1) has a mass of 4.9 kg, in which the proportion of alumina is 5%. Get the remaining powder 10kg of spray-drying operation 6 gained, pass secondary calcination, temperature is 750 DEG C, time 6h, after crossing 300 mesh sieves, obtain a kind of modified lithium titanate composite material (titanium mixed with alumina) Lithium oxide-lithium alumina second mixture B2), with a mass of 9.2 kg, in which alumina accounts for 5%.

Third, in the calcination step 4, take the remaining powder 9.5kg, and carry out the grinding and dispersing step 43. First, add 28.5kg of deionized water to the grinding transfer tank, and then add 0.95kg of conductive agent CNT slurry (containing CNT 5%) (0.5%), nano-alumina 0.19kg (2%), particle size 30nm, conductive agent SP 95g (1%) and calcined powder 9.5kg, solid content 25%, and then ground For dispersion, the rotating speed is 5000r/min, the time is 2h, and the gap is 0.4mm. The obtained slurry is carried out spray drying operation 44, inlet temperature 500 DEG C, outlet temperature 130 DEG C, obtains 9.3kg of spray powder. Get spray powder 4.3kg and dry at 200 DEG C, cross 200 mesh sieves, obtain a kind of modified lithium titanate composite material (surface is coated with the first lithium titanate-lithium aluminate of aluminum oxide and conductive agent). Complex C1) with a mass of 4.1 kg. Get remaining spray powder 5kg, carry out secondary calcination operation 45, calcination temperature is 700 DEG C, and the time is 4h, and atmosphere is nitrogen atmosphere, and the powder obtained crosses 200 mesh sieves, and obtains another kind of modified lithium titanate The composite material (the second composite C2 of lithium titanate-lithium alumina coated with aluminum oxide and conductive agent), with a mass of 4.6 kg.

As an exemplary embodiment, with reference to Figure 1, the method for preparing the modified lithium titanate composite material is as follows:

First, in the wet mixing step 1, add 72.1kg of deionized water, 9.6kg of lithium oxalate Li ₂ C ₂ O ₄ powder, and hydrated aluminum nitrate (Al(NO ₃ ) ₃ .9H ₂ O) crystals into the stirring tank 5.68kg, titanium hydroxide Ti(OH) ₄ powder 2.52kg, then stirred at 40Hz stirring speed for 3h, the obtained slurry was transferred to the ball mill transfer tank, then 20.6kg of deionized water was added, and the ball milling process 2 was carried out, ball milling line The speed is 8m/s, the ball milling time is 20h, and the particle size of the zirconium ball is 0.2mm. The obtained slurry was transferred to the grinding and dispersing transfer tank, adding conductive agent SP 0.21 kg, 5% CNT 2.1 kg, VGCF 0.21 kg, adding 13 kg of water, and carrying out grinding and dispersing step 23, the rotating speed was 5000 r/min, and the time was 5h, the gap is 0.3mm. The slurry after dispersion is completed, carries out spray drying operation 24, and inlet temperature is 350 DEG C, and outlet temperature is 110 DEG C, and obtains spray powder 35.3kg. Then carry out calcination operation 25, calcination temperature 850 ℃, calcination time 6h, atmosphere is nitrogen atmosphere, make lithium source react with titanium source and the first aluminum source and change into lithium titanate and lithium alumina, obtain the conductive agent doped A mixture of lithium titanate-lithium alumina, with a mass of 20.6kg. Take 5.6kg and pass it through a 400-mesh sieve to obtain a modified lithium titanate composite material (a mixture of lithium titanate, lithium alumina and conductive agent without alumina coating D1), with a mass of 5.1kg, of which lithium alumina accounts for The proportion of lithium titanate is 5%, SP is 1% of lithium titanate-lithium alumina, CNT is 0.5%, and VGCF is 1%.

Second, the remaining 15kg of calcined powder, carry out the secondary grinding process 26, at first add 46.4kg of deionized water in the grinding transfer tank, then add 15kg of calcined powder, add 3% of the calcined powder nano-alumina (particle size) 30nm), that is, 0.45kg. After the feeding is completed, grinding and dispersing are carried out. The dispersing speed is 4000r/min, the time is 6h, and the gap is 0.35mm. The obtained slurry is carried out secondary spraying process 27, with an inlet temperature of 280°C and an outlet temperature of 105°C to obtain 14.5kg of spray powder. Get 6.5kg and carry out drying operation 282, 200 ℃ of temperature, time 5h, then cross 200 mesh sieves, obtain a kind of modified lithium titanate composite material (with aluminum oxide coating, lithium titanate-lithium aluminum oxide-conductive The first mixed product E1), the mass is 5.6kg.

In addition, remaining 8kg powder in the spray powder, carry out 28 operations of secondary calcination, temperature is 700 DEG C, time 3h, atmosphere is nitrogen atmosphere, the powder after the calcination that obtains, crosses 200 mesh sieves, obtains a kind of modified Lithium titanate composite material (alumina-coated, lithium titanate-lithium alumina-conducting agent second mixed product E2), with a mass of 6.8kg.

As an exemplary embodiment, with reference to Figure 1, the method for preparing the modified lithium titanate composite material is as follows:

In wet mixing process 1, in the stirring tank, add 28.2kg of deionized water, add 2.82kg of lithium source LiOH.H ₂ O crystal, after stirring and dissolving, add and dissolve 2.39kg of aluminum source hydrated aluminum nitrate Al ( NO ₃ ) ₃ .9H ₂ O aqueous solution, the water required for dissolution is 3.98 kg, and Al(OH) ₃ is precipitated during the addition. Then, in the stirring process, an ethanol solution in which 25.87 kg of tetrabutyl titanate was dissolved was added, and the ethanol required for dissolution was 51.7 kg. During the addition, the tetrabutyl titanate was converted into titanium oxyhydroxide TiO(OH) ₂ . After the addition of all the materials, the mixture was stirred for 6 hours at a stirring speed of 30 Hz. After stirring, the slurry obtained is transferred into the spray drying feeding tank, and carries out spray drying operation 3, 250 ℃ of inlet temperature, 85 ℃ of outlet temperature, obtains spray powder 9.5kg. The calcination process 4 is carried out to the powder, the calcination temperature is 800 ° C, the calcination time is 5h, and the atmosphere is an air atmosphere to obtain 6.55kg of the calcined powder, and the designed lithium alumina ratio is 6%. The obtained calcined powder was subjected to ball milling step 5, 20.6 kg of deionized water was added to the ball milling transfer tank, and 0.31 kg of aluminum source boehmite was added at the same time, the ball milling linear speed was 10 m/s, the ball milling time was 30 h, and the particle size of the ball-milled zirconium ball was 0.2 mm. Make the particle size less than 100 nm. The slurry obtained is transferred to the grinding and dispersing transfer tank, and the grinding and dispersing operation 43 is carried out, while adding conductive agent SP 0.13kg, the graphene 1.31kg of content 5%, and adding water 3.2kg, and the add-on of the design SP is that of calcining the gained powder. 2%, graphene is 1%, and solid content is 22%. The grinding speed is 6000r/min, the grinding time is 8h, and the grinding gap is 0.4mm. The obtained slurry carries out spray drying operation 44, 280 ℃ of inlet temperatures, 105 ℃ of outlet temperatures, and spray powder 6.54kg. Then carry out calcination operation 45, calcination temperature 750 ℃, calcination time 5h, atmosphere is nitrogen atmosphere, obtain calcined powder 6.12kg. Finally, pass through a 250-mesh sieve to obtain a modified lithium titanate composite material (a lithium titanate-lithium alumina composite product C3 mixed with a conductive agent and alumina) with a mass of 5.53 kg.

Combining the above examples, nine types of modified lithium titanate composite materials including A1, B1, B2, C1, C2, D1, E1, E2, and C3 were prepared. In order to investigate the influence of lithium aluminate on the rate of lithium titanate, the preparation of lithium titanate without lithium aluminate was carried out. In the process, the first aluminum source was not added, and the amount of lithium salt lithium oxalate was reduced to 8.85kg, and finally a composite E3 coated with alumina and mixed with lithium titanate-conducting agent was obtained, with a mass of 16.2kg.

In order to investigate the capacity and first effect of various modified lithium titanates, half-cells were fabricated. The negative electrode was metal lithium, and the positive electrode was modified lithium titanate: conductive carbon black: PVDF (vinylidene fluoride) = 85: 10:5. The charging and discharging voltage is 1V-3V, and the charging and discharging current is 0.5C (1C=160mAh/g). The test results are shown in Table 2 below:

Table 1:

Lithium Titanate Type 0.5C reversible gram specific capacity (mAh/g) First effect (%) A1 166 98.4 B1 163 97.8 B2 165 98.5 C1 166 98.1 C2 168 98.8 D1 168 98.3 E1 163 97.5 E2 165 98.5 C3 167 98.3 Comparative Example E3 165 98.4

In order to investigate the performance of various modified lithium titanates prepared, and to compare the rate performance, a lithium titanate material without lithium alumina modification was purchased from the market. As a comparative example, a laminated small soft pack battery 358595 was produced. The positive electrode is made of NCM523 ternary material, the negative electrode is the modified lithium titanate composite material prepared in the above embodiment, the diaphragm is made of 18-micron ceramic diaphragm, and the electrolyte is a conventional electrolyte purchased from the market. The positive electrode slurry formula is 96% NCM523, 1.2% polyvinylidene fluoride PVDF, 2% conductive agent SP, 0.8% carbon nanotube CNT, and the negative electrode formula is 94% modified lithium titanate, 2% PVDF, 1% polyacrylic acid, 2% SP, 1% CNT. Both the positive and negative electrodes use N-methylpyrrolidone (NMP) dispersant. After stirring, coating, rolling, cutting, lamination, tab welding, packaging, baking, liquid injection, formation and volume separation, 358595 small soft pack laminated battery was prepared with a rated capacity of 2Ah. Investigate the battery’s high temperature storage at 60°C for 7 days, 5C charging rate, 5C discharging rate, the charging and discharging range is 1.5-2.8V, the charging is constant current and constant voltage charging, the cut-off current is 0.5C, and the charging rate only calculates the constant current charging part . The test results are shown in Table 2 below:

Table 2:

Capacity retention rate/% for 7 days at 60°C Is it flatulence after high temperature storage 5C charging rate/% 5C discharge rate/% A1 \ Yes 96.3 94.5 B1 96.8 no 96.6 95.3 B2 97.3 no 95.6 94.5 C1 97.5 no 97.4 96.5 C2 98.6 no 97.6 95.8 D1 \ Yes 97.3 95.7 E1 98.0 no 96.6 95.0 E2 98.5 no 97.1 95.2 C3 98.4 no 97.5 95.5 E3 98.2 no 90.4 89.3

It can be seen from the above table that, in terms of high temperature storage, lithium titanate without alumina modification has flatulence after high temperature storage, and the other has no flatulence problem, indicating that adding alumina can improve the high temperature stability of lithium titanate. In terms of rate performance, there are conductive agents and lithium titanate modified with lithium alumina, and the rate performance is the best. The rate performance of various lithium titanate modified with lithium aluminum oxide is significantly higher than that of the comparative example E3 without lithium aluminum oxide modification, indicating that adding lithium aluminum oxide can improve the rate performance of lithium titanate. The formation of lithium aluminate is synchronized with the on-site process of lithium titanate, which can suppress the increase of lithium titanate crystals, reduce the size of lithium titanate crystals, and also promote rate performance. In addition, on the basis of lithium alumina modification, adding a conductive agent can further improve the rate capability. For example, the rate capability of the D1 material with the addition of the conductive agent is higher than that of the A1 material without the addition of the conductive agent.

From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve the following technical effects: by adding lithium titanate and fast lithium ion conductor precursors, in the subsequent calcination process, lithium titanate and lithium alumina simultaneously The formation of lithium alumina can inhibit the crystal size of lithium titanate from becoming larger, reduce the migration distance of lithium ions inside lithium titanate, and improve the rate performance of lithium titanate. And lithium alumina is a fast lithium ion conductor, which can promote the migration of lithium ions and improve the rate capability of lithium titanate. The addition of the conductive agent can promote the electronic conductivity and further improve the rateability. On the other hand, in the process of preparing lithium titanate, alumina that can be neutralized with a trace amount of water and acid is introduced to improve the high temperature stability of lithium titanate. The preparation process of the modified lithium titanate is simple, no waste liquid and waste residue are generated, and it is easy to be produced on a large scale.

For ease of description, spatially relative terms, such as "on", "over", "on the surface", "above", etc., may be used herein to describe what is shown in the figures. The spatial positional relationship of one device or feature shown to other devices or features. It should be understood that spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "above" or "over" other devices or features would then be oriented "below" or "over" the other devices or features under other devices or constructions". Thus, the exemplary term "above" can encompass both an orientation of "above" and "below." The device may also be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptions used herein interpreted accordingly.

In addition to the above, it should be noted that "one embodiment", "another embodiment", "embodiment", etc. mentioned in this specification refer to the specific features, structures or Features are included in at least one embodiment generally described in this application. The appearances of the same expression in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure or characteristic is described in conjunction with any one embodiment, it is claimed that implementation of that feature, structure or characteristic in conjunction with other embodiments is also within the scope of the present invention.

In the above-mentioned embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference may be made to the relevant descriptions of other embodiments.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (12)

1. A method for preparing a modified lithium titanate composite material is characterized by comprising the following steps:

mixing a titanium source, a lithium source and a first aluminum source by a wet method, and then calcining for the first time to obtain a mixture comprising lithium titanate and lithium aluminum oxide;

and mixing at least one of a second aluminum source and a conductive agent with the mixture, and then optionally carrying out secondary calcination to obtain the modified lithium titanate composite material.

2. The process for preparing a modified lithium titanate composite of claim 1, characterized in that the process comprises:

wet mixing the titanium source, the lithium source and the first aluminum source, and then sequentially carrying out primary ball milling, primary spray drying and primary calcining to obtain a mixture;

and mixing the mixture with the second aluminum source, then sequentially carrying out secondary ball milling and secondary spray drying, and sequentially carrying out secondary calcination and sieving on the product obtained after the secondary spray drying, or sequentially drying and sieving the product obtained after the secondary spray drying to obtain the modified lithium titanate composite material.

3. The process for preparing a modified lithium titanate composite material according to claim 1, characterized in that the process comprises:

wet mixing the titanium source, the lithium source and the first aluminum source, and then sequentially performing ball milling, primary spray drying and primary calcining to obtain a mixture;

and simultaneously mixing the mixture with the second aluminum source and the conductive agent, sequentially grinding and secondarily spray-drying, sequentially calcining and sieving the product obtained after the secondary spray-drying, or sequentially drying and sieving the product obtained after the secondary spray-drying to obtain the modified lithium titanate composite material.

4. The process for preparing a modified lithium titanate composite material according to claim 1, wherein the titanium source is a liquid titanium source, the process comprising:

and carrying out wet mixing on the titanium source, the lithium source and the first aluminum source, then carrying out spray drying, and carrying out primary calcination on a product obtained after the spray drying to obtain the mixture.

5. The process for preparing a modified lithium titanate composite material according to claim 1, characterized in that the process comprises:

wet mixing the titanium source, the lithium source and the first aluminum source, and then sequentially carrying out primary ball milling, primary spray drying and primary calcining to obtain a mixture;

and mixing the mixture with the second aluminum source, then carrying out secondary ball milling, mixing a product obtained after the secondary ball milling with the conductive agent, then sequentially carrying out grinding and secondary spray drying, and sequentially carrying out secondary calcining and sieving on the product obtained after the secondary spray drying, or sequentially drying and sieving the product obtained after the secondary spray drying to obtain the modified lithium titanate composite material.

6. The method of preparing a modified lithium titanate composite material according to any one of claims 1 to 5, wherein the first aluminum source is one or more of aluminum chloride hexahydrate, aluminum nitrate of crystal water, aluminum sulfate, aluminum acetate, aluminum citrate, aluminum oxide, aluminum hydroxide, boehmite, and/or the second aluminum source is one or more of aluminum chloride hexahydrate, aluminum nitrate of crystal water, aluminum sulfate, aluminum acetate, aluminum citrate, aluminum oxide, aluminum hydroxide, boehmite.

7. The method of preparing a modified lithium titanate composite of any one of claims 1-5, wherein the titanium source is one or more of titanium dioxide, titanium tetrachloride, titanium hydroxide, metatitanic acid, tetrabutyl titanate, titanium oxysulfate, tetraethyl titanate, isopropyl titanate.

8. The process for preparing a modified lithium titanate composite material according to any one of claims 1-5, wherein the lithium source is one or more of lithium chloride, lithium oxalate, lithium nitrate, lithium carbonate, lithium acetate, lithium hydroxide monohydrate, lithium fluoride.

9. The method of preparing a modified lithium titanate composite material of any one of claims 1-5, wherein the conductive agent is one or more of conductive carbon black SP, conductive silver nanoparticles, conductive copper nanoparticles, conductive gold nanoparticles, silver nanowires, copper nanowires, carbon nanotubes, vapor grown carbon fibers, zinc oxide nanorods, silicon carbide nanowires, graphene.

10. The method for preparing a modified lithium titanate composite material according to any one of claims 1 to 5, wherein in the mixing step of mixing at least one of the second aluminum source and the conductive agent with the mixture, the mass of the conductive agent is 0.5 to 10% of the mass of the mixture.

11. A modified lithium titanate composite material characterized by being produced by the production method according to any one of claims 1 to 10.

12. The modified lithium titanate composite material according to claim 11, wherein the mass of the lithium alumina is 0.5 to 15% of the mass of the lithium titanate and the mass of the aluminum oxide is 0 to 15% of the mass of the mixture in the modified lithium titanate composite material.

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