WO2017197675A1 - Lithium titanate-modified material and manufacturing method thereof - Google Patents

Abstract

The present invention relates to the technical field of electrochemistry. Disclosed is a lithium titanate-modified material. The modified material consists of a micro- and nanoscale structure, and comprises a lithium titanate (LTO), a zinc titanate (ZTO), and nitrogen-doped carbon nanotubes (N-CNTs). The invention uses simple manufacturing techniques, requires only mild conditions and low costs, demonstrates great reproducibility, and can therefore be used in large-scale manufacturing. The synthesized composite material has fine and uniformly distributed grain sizes, and addresses an issue of low electrical conductivity and low energy density. Electrochemical testing of the material demonstrated higher initial discharge capacity and cyclic specific capacity, and excellent rate performance and cycling stability. The energy density of the material is increased by 20-40% relative to a commercialized LTO. The invention provides an ideal negative electrode material of a lithium-ion battery, and offers potential applications in portable electronic devices, electric vehicles, and aerospace industries.

Description

Lithium titanate modified material and preparation method thereof Technical field

The invention belongs to the technical field of electrochemistry, and particularly relates to a lithium titanate modified material and a preparation method thereof.

Background technique

Lithium-ion batteries are widely used due to their high energy density, high operating voltage, and no memory effect. With the demand for higher energy density and power density batteries, the development of new battery materials is imminent. At present, commercial graphite anode materials have good cycle performance, but their specific capacity is low, and it is easy to cause safety hazards under high current charge and discharge conditions, which limits its application in large-scale energy storage. Spinel-type lithium titanate (LTO) has almost no change in the framework structure during lithium ion intercalation and extraction. It is a "zero strain" material with excellent charge and discharge cycle stability. The lithium-insertion potential is high and does not cause precipitation of supported lithium. It is a highly safe lithium ion anode material. However, lithium titanate also has its shortcomings, such as low theoretical specific capacity (175 mAh / g), low battery voltage caused by high lithium insertion potential, resulting in low specific energy of the battery; at the same time the material itself is poor in conductivity (inherent conductivity 10 -9S/cm), it is easy to generate large polarization when charging and discharging large currents, which limits the promotion of its application. At present, the academic community mostly uses ion doping to reduce the electrode potential of lithium titanate (Electrochimica Acta 2008, 53:7079); through material nanocrystallization, preparation of special morphology of lithium titanate or carbon or carbon nanotubes (CNTs) coating and other methods to solve the problem of lithium titanate material material degradation due to low electronic conductivity (J. Am. Chem. Soc. 2012, 134: 7874; RSC Adv., 2012, 2: 10306) . Chinese Patent Publication No. CN201210163712.6, CN201010575269.4, CN 201310036005.5, CN201010149910.8 report a method for modifying carbon nanotubes and carbon modified lithium titanate, and such methods can improve the electronic conductivity of lithium titanate. However, there are some problems in the above methods: (1) ion doping causes the electrode potential of lithium titanate material to decrease in a limited range, and thus it is impossible to greatly increase the energy density of the material; (2) carbon coating is mostly based on expensive organic The high-temperature thermal decomposition of the carbon source is achieved, the energy consumption is too high, and the environment is not friendly; (3) the carbon nanotubes need to be surface acidified or esterified before use, the process is complicated and environmentally unfriendly; in order to achieve uniform dispersion of carbon nanotubes Add expensive dispersants.

The nanostructured zinc ferrite (ZnFe ₂ O ₄ ) is a superior binary spinel lithium ion anode material, exhibiting high capacity characteristics, and has a stable lithium insertion potential platform (about 0.9V), which does not cause lithium deposition. , greatly improving the safety of the battery, and the material has the advantages of non-toxic, non-polluting, high safety performance, wide source of raw materials, etc., which provides feasibility for enhancing the energy density of lithium titanate composite with lithium titanate composite. Reference, however, the pure phase ZnFe ₂ O ₄ material has poor conductivity; the material volume expansion effect is large, resulting in damage to the electrode matrix structure, thereby affecting the cycle stability of the battery.

Summary of the invention

In order to make up for the deficiencies of the prior art, the present invention provides a lithium titanate modified material and a preparation method thereof. It is a new lithium ion battery anode material with high cycle specific capacity, high first charge and discharge efficiency, good rate performance and cycle stability.

The invention is achieved by the following technical solutions:

A lithium titanate modified material is special in that the modified material is composed of a micro/nano structure, including lithium titanate LTO, zinc titanate ZFO, and nitrogen-doped carbon nanotube NCNTs. The advantages of lithium titanate as a negative electrode material are high safety performance, good cycle stability, high first charge and discharge efficiency, but low specific capacity of materials, low electronic conductivity, and high cost; the present invention adopts low cost for this problem. And the high specific capacity of zinc ferrite to make up, but for the zinc ferrite, its electronic conductivity is also very low, the first charge and discharge efficiency is low, while the material in the charge and discharge process, the volume expansion is too large, resulting in stability degradation; In response to this problem, the present invention employs nitrogen-doped carbon nanotubes to buffer the volume change of the zinc ferrite during charge and discharge to stabilize the material, reduce the thermal conductivity, increase the mechanical strength and electronic conductivity of the material, and the micro-nano structure also contributes to lithium ions. Embedding and transfer.

Further, the lithium titanate modified material of the present invention has a chemical composition of xZFO·yNCNTs·zLTO, and x, y, and z represent the contents of ZFO, NCNTs, and LTO, respectively, wherein 0.01≤x≤0.50, 0.01≤y≤0.10, 0.4≤z≤0.98, x+y+z=1; the N atom content in the NCNTs is 0.01-6 at%, and the average particle size of the LTO is 5-100 μm.

The lithium titanate modified material of the present invention can be obtained by post-treatment mixing of LTO, ZFO and NCNTs, or can be obtained by in-situ synthesis.

The preparation method of the lithium titanate modified material of the present invention comprises the following steps when the sample is obtained by post-treatment mixing:

(1) ultrasonically dispersing NCNTs in a lower alcohol;

(2) Add LTO and ZFO to the ultrasonically dispersed NCNTs, stir them evenly, and then place them in an oven for drying;

(3) ball-mixing the dried mixture;

(4) The ball-milled sample is annealed and heat-treated under an inert atmosphere.

among them,

The lower alcohol in the step (1) is a mixture of one or more of methanol, ethanol, and propanol.

The inert atmosphere in the step (4) is He, N ₂ or Ar, and the heat treatment temperature is 200-700 ° C for 0.1-10 h.

The preparation method of the lithium titanate modified material of the present invention comprises the following steps when the sample is obtained by in situ synthesis:

(1) ultrasonically dispersing NCNTs in a lower alcohol;

(2) dissolving iron salt and zinc salt into a solution;

(3) mixing the NCNTs dispersed in the step (1) with the iron salt and the zinc salt solution of the step (2), and sufficiently stirring, and then performing ultrasonic treatment;

(4) adding LTO in portions to the solution of step (3), stirring and drying;

(5) The sample after drying is heated in an inert atmosphere, calcined, and cooled.

among them,

The iron salt in the step (2) is at least two of ferric chloride, ferric nitrate, ferric citrate and iron acetate, and the zinc salt is one or more of anhydrous zinc sulfate, zinc chloride and zinc sulfate; zinc The molar ratio of zinc to iron in the salt and iron salt is 1:1.8-2.2.

The method of mixing the NCNTs with the iron salt and the zinc salt solution in the step (3) is to add the dispersed NCNTs to the solution of the step (2) in stages or to add the solution of the step (2) to the dispersed NCNTs. , the process of mixing is kept stirring.

The stirring time in the step (4) is 0-20 h.

The inert atmosphere in the step (5) is He, N ₂ or Ar, the gas flow rate is 20-1000 sccm, the calcination temperature is 500-1000 ° C, and the treatment time is 0.1-10 h.

The lithium titanate modified material prepared by the invention is subjected to electrochemical performance test, and the test is carried out under the following conditions: the weight ratio of the obtained active material to polyvinylidene fluoride (PVDF) and the conductive agent is 8:1:1. The mixture was mixed with N-methylpyrrolidone (NMP) as a solvent, stirred for 6 hours, uniformly coated on a copper foil, and dried under vacuum at 110 ° C to obtain a working electrode sheet. The electrolyte was 1 mol/L of LiPF6/ethylene carbonate (EC)-dimethyl carbonate (DMC) (1:1 by volume); the separator was a polypropylene/polyethylene microporous membrane (Celgard 2500). All batteries (2032 button cells) were assembled in a water-free, oxygen-free glove box with a lithium sheet as the counter electrode. The battery was measured after activation for 12 hours after assembly to allow the electrolyte to sufficiently wet the electrode. The charge and discharge test was performed on the battery performance test system with a voltage range of 0.5-3.0V.

The beneficial effects of the invention are:

(1) The negative electrode material prepared by the invention is a novel ternary composite negative electrode material;

(2) Composite anode material The particle powder is fine and evenly distributed, and has good electrical conductivity;

(3) Lithium titanate as the main material can ensure high safety performance, excellent cycle stability and high first charge and discharge efficiency; adding zinc ferrite can reduce the cost of materials and increase the energy density of materials; The hybrid carbon nanotubes can effectively inhibit the volume change of the material during charging and discharging, resulting in rapid capacity decay and poor cycle performance, increasing the mechanical strength and electronic conductivity of the material, and the micro-nano structure also contributes to the insertion of lithium ions. And transmission;

(4) The energy density of the material of the present invention can be increased by 20-40% compared to lithium titanate which has been commercially applied;

(5) The preparation process of the invention is simple, the cost is low, the environment is friendly, the safety is high, and the experiment repeatability is good.

DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an SEM image of a sample of Example 12 of the present invention.

Figure 2 is a graph showing the cycle stability of different samples of the present invention at 1C rate.

Figure 3 is a graph showing the cycle stability test of the sample of Example 13 of the present invention.

detailed description

The present invention will be further described in detail below with reference to the drawings and specific embodiments, but not limited to the scope of the invention.

Example 1

In this embodiment, a lithium titanate modified material 0.02ZFO·0.02NCNTs·0.96LTO is prepared by a post-treatment mixing method.

Ultrasonic dispersion of 0.2 g of NCNTs into methanol, then adding 0.2 g of ZFO and stirring for 30 min, continuing to ultrasonic for 1 h, then adding 9.6 g of LTO, repeating the stirring and sonication steps, drying in an oven, and passing the mixture through a ball mill. after stirring the second mixture, samples were dried in an atmosphere of N ₂ 200 ℃ heat treatment time 1h.

According to the deduction test, the first discharge specific capacity at 0.25 mA is 193 mAh·g ^-1 , the first charge and discharge efficiency is 85%, and the discharge specific capacity at ^{1 C} is 190 mAh·g ^-1 .

Example 2

In this embodiment, a lithium titanate modified material 0.05ZFO·0.02NCNTs·0.93LTO is prepared by a post-treatment mixing method.

Ultrasonic dispersion of 0.2g of NCNTs into alcohol, followed by adding 0.5g of ZFO for 30min, continuing to ultrasonic for 1h, then adding 9.3g of LTO, repeating stirring and sonication, drying in an oven, passing the mixture through a ball mill The mixture was stirred for two times, and after the sample was dried, the heat treatment time was 0.5 h at 500 ° C under a N ₂ atmosphere.

According to the deduction test, the first discharge specific capacity at 0.2C was 228 mAh·g ^-1 , the first charge and discharge efficiency was 82%, and the discharge specific capacity at ^{1 C} was 195 mAh·g ^-1 .

Example 3

In this embodiment, a lithium titanate modified material of 0.1ZFO·0.05NCNTs·0.88LTO is prepared by a post-treatment mixing method.

Ultrasonic dispersion of 0.2 g of NCNTs into propanol, followed by addition of 1.0 g of ZFO for 30 min, followed by ultrasonication for 1 h, then 8.8 g of LTO, repeated stirring and sonication, drying in an oven, and passing the mixture through a ball mill The mixture was stirred for two times, and after the sample was dried, it was heat-treated at 300 ° C for 1 h under a N ₂ atmosphere.

According to the deduction test, the first discharge specific capacity at 0.2C was 258 mAh·g ^-1 , the first charge and discharge efficiency was 77%, and the discharge specific capacity at ^{1 C} was 210 mAh·g ^-1 .

Example 4

In this embodiment, a lithium titanate modified material 0.5ZFO·0.05NCNTs·0.4LTO is prepared by a post-treatment mixing method.

Ultrasonic dispersion of 0.5g of NCNTs into methanol, then adding 5.0g of ZFO for 30min, continuing to ultrasonic for 1h, then adding 4.5g of LTO, repeating the stirring and sonication steps, drying in an oven, and passing the mixture through a ball mill. The mixture was stirred for two times, and after the sample was dried, it was heat-treated at 500 ° C for 1 h under a N ₂ atmosphere.

According to the deduction test, the first discharge specific capacity at 0.25 mA is 538 mAh·g ^-1 , the first charge and discharge efficiency is 65%, and the discharge specific capacity at ^{1 C} is 350 mAh·g ^-1 .

Example 5

In this embodiment, a lithium titanate modified material 0.5ZFO·0.1NCNTs·0.4LTO is prepared by a post-treatment mixing method.

Ultrasonic dispersion of 1.0 g of NCNTs into alcohol, followed by addition of 5.0 g of ZFO for 30 min, followed by ultrasonic for 1 h, then 4.0 g of LTO, repeated stirring and sonication, drying in an oven, and passing the mixture through a ball mill The mixture was stirred for two times, and after the sample was dried, it was heat-treated at 700 ° C for 10 hours in an N 2 atmosphere.

According to the deduction test results, the first discharge specific capacity at 0.2C was 658mAh·g-1, the first charge and discharge efficiency was 70%, and the discharge specific capacity at 1C was 558mAh·g-1.

Example 6

In this example, lithium iron nitrate was used as the iron source, and the lithium titanate modified material 0.02ZFO·0.02NCNTs·0.96LTO was prepared by in-situ synthesis method (the stoichiometric ratio of zinc and iron was 1:2).

Weigh 0.25g of zinc nitrate and 0.67g of ferric nitrate dissolved in ethanol solution, ultrasonically disperse 0.2g of NCNTs into methanol, and then add ultrasonically dispersed NCNTs to the above solution, stir for 10h and sonicate for 10h. Then, 9.6 g of LTO was added and stirred well, and then oven-dried, under a gas flow rate of 100 sccm N _{2 under} an inert gas flow, a heat treatment time of 700 ° C for 10 h, and then cooled to obtain the material.

According to the deduction test, the first discharge specific capacity at 0.2C was 198 mAh·g ^-1 , the first charge and discharge efficiency was 89%, and the discharge specific capacity at ^{1 C} was 193 mAh·g ^-1 .

Example 7

In this embodiment, lithium iron nitrate is used as an iron source, and a lithium titanate modified material 0.02ZFO·0.02NCNTs·0.96LTO (stoichiometric ratio of zinc and iron is 1:1.8) is prepared by in-situ synthesis.

Weigh 0.25g of zinc nitrate and 0.60g of ferric nitrate dissolved in ethanol solution, ultrasonically disperse 0.2g of NCNTs into methanol, and then add ultrasonically dispersed NCNTs to the above solution, stir for 10h and sonicate for 10h. Then, 9.6 g of LTO was added and stirred well, and then oven-dried, under a gas flow rate of 500 sccm N _{2 under} an inert gas flow, a heat treatment time of 700 ° C for 10 h, and then cooled to obtain the material.

According to the deduction test, the first discharge specific capacity at 0.2C is 195mAh·g ^-1 , the first charge and discharge efficiency is 90%, and the discharge specific capacity at 1C is 190mAh·g ^-1 .

Example 8

In this example, lithium iron nitrate was used as the iron source, and the lithium titanate modified material 0.02ZFO·0.02NCNTs·0.96LTO (the stoichiometric ratio of zinc and iron was 1:2.2) was prepared by in-situ synthesis.

Weigh 0.25 g of zinc nitrate and 0.74 g of ferric nitrate in an ethanol solution, ultrasonically disperse 0.2 g of NCNTs into the alcohol, and then add the ultrasonically dispersed NCNTs to the above solution, stirring for 10 h and sonicating. After 10 h, 9.6 g of LTO was added and stirred well, and then placed in an oven for drying at a gas flow rate of 100 sccm N _{2 under} an inert gas flow at 800 ° C for 10 h, followed by cooling to obtain the material.

According to the deduction test, the first discharge specific capacity at 0.2C is 190mAh·g ^-1 , the first charge and discharge efficiency is 85%, and the discharge specific capacity at 1C is 185mAh·g ^-1 .

Example 9

In this embodiment, lithium ferric chloride modified material 0.02ZFO·0.02NCNTs·0.96LTO was prepared by in-situ synthesis using ferric chloride as the iron source.

Weigh 0.25 g of zinc nitrate and 0.44 g of ferric chloride dissolved in ethanol solution, ultrasonically disperse 0.2 g of NCNTs into methanol, and then add ultrasonically dispersed NCNTs to the above solution, stirring for 10 h and ultrasonication. After treatment for 10 h, 9.6 g of LTO was added and stirred thoroughly, and then oven-dried, under a gas flow rate of 50 sccm N _{2 under} an inert gas flow, at 700 ° C for a heat treatment time of 10 h, and then cooled to obtain the material.

According to the deduction test, the first discharge specific capacity was 0.2 mAh·g ^{-1 at} 0.2 C, the first charge and discharge efficiency was 80%, and the discharge specific capacity at ^{1 C} was 173 mAh·g ^-1 .

Example 10

In this embodiment, lithium titanate modified material 0.02ZFO·0.02NCNTs·0.96LTO was prepared by in-situ synthesis using iron acetate as iron source.

Weigh 0.25 g of zinc nitrate and 0.70 g of iron acetate in a propanol solution, ultrasonically disperse 0.2 g of NCNTs into methanol, and then add the ultrasonically dispersed NCNTs to the above solution, stirring for 10 h and sonicating. After 10 h, 9.6 g of LTO was added and stirred well, and then placed in an oven for drying at a gas flow rate of 100 sccm N2 under an inert gas flow at 600 ° C for 10 h, followed by cooling to obtain the material.

According to the deduction test, the first discharge specific capacity at 0.25 mA is 175 mAh·g-1, the first charge and discharge efficiency is 89%, and the discharge specific capacity at 1 C is 165 mAh·g-1.

Example 11

In this embodiment, zinc chloride is used as a zinc source, and a lithium titanate modified material 0.02ZFO·0.02NCNTs·0.96LTO is prepared by in-situ synthesis.

0.20 g of zinc chloride and 0.44 g of ferric chloride were weighed and dissolved in an ethanol solution, 0.2 g of NCNTs were ultrasonically dispersed into methanol, and then ultrasonically dispersed NCNTs were added to the above solution, and stirring was continued for 10 hours. After ultrasonic treatment for 10 h, then 9.6 g of LTO was added and stirred well, and then oven-dried, under a gas flow rate of 1000 sccm N _{2 under} an inert gas flow, a heat treatment time of 700 ° C for 10 h, and then cooled to obtain the material.

According to the deduction test, the first discharge specific capacity at 0.2C was 178mAh·g ^-1 , the first charge and discharge efficiency was 88%, and the discharge specific capacity at 1C was 174mAh·g ^-1 .

Example 12

In this embodiment, lithium iron nitrate is used as an iron source, and a lithium titanate modified material of 0.1ZFO·0.02NCNTs·0.88LTO is prepared by in-situ synthesis.

Weigh 1.23 g of zinc nitrate and 3.35 g of ferric nitrate dissolved in ethanol solution, ultrasonically disperse 0.2 g of NCNTs into methanol, and then add ultrasonically dispersed NCNTs to the above solution, stirring for 10 h and sonicating for 10 h. Then, 8.8 g of LTO was added and stirred well, and then oven-dried, under a gas flow rate of 100 sccm N _{2 under} an inert gas flow, a heat treatment time of 700 ° C for 10 h, and then cooled to obtain the material.

According to the deduction test, the first discharge specific capacity at 250C is 250 mAh·g ^-1 , the first charge and discharge efficiency is 84%, and the discharge specific capacity at ^{1 C} is 200 mAh·g ^-1 .

Example 13

In this embodiment, lithium iron nitrate is used as an iron source, and a lithium titanate modified material of 0.1ZFO·0.02NCNTs·0.88LTO is prepared by in-situ synthesis.

Weigh 1.23g of zinc nitrate and 3.68g of ferric nitrate dissolved in ethanol solution, ultrasonically disperse 0.2g of NCNTs into methanol, and then add ultrasonically dispersed NCNTs to the above solution, stir for 5h and sonicate for 10h. Then, 8.8 g of LTO was added and stirred well, and then oven-dried, under a gas flow rate of 80 sccm N _{2 under} an inert gas flow, a heat treatment time of 600 ° C for 5 h, and then cooled to obtain the material.

According to the deduction test, the first discharge specific capacity at 230C was 230 mAh·g ^-1 , the first charge and discharge efficiency was 87%, and the discharge specific capacity at ^{1 C} was 195 mAh·g ^-1 .

Example 14

In this embodiment, lithium iron nitrate is used as an iron source, and a lithium titanate modified material 0.1ZFO·0.1NCNTs·0.8LTO is prepared by in-situ synthesis.

1.23 g of zinc nitrate and 3.68 g of ferric nitrate were weighed and dissolved in an ethanol solution, 1.0 g of NCNTs were ultrasonically dispersed into methanol, and then ultrasonically dispersed NCNTs were added to the above solution, stirring was continued for 5 hours and sonicated for 10 hours. , then after the addition of 8.0g LTO stirred sufficiently dried in an oven, under an inert gas flow rate 100sccm N ₂ gas flow, the heat treatment time 800 10H deg.] C, then cooled, to obtain the material.

According to the deduction test, the first discharge specific capacity at 230C was 230 mAh·g ^-1 , the first charge and discharge efficiency was 82%, and the discharge specific capacity at ^{1 C} was 205 mAh·g ^-1 .

Example 15

In this embodiment, lithium iron nitrate is used as an iron source, and a lithium titanate modified material 0.5ZFO·0.02NCNTs·0.48LTO is prepared by in-situ synthesis.

Weigh 6.17g of zinc nitrate and 16.76g of ferric nitrate dissolved in ethanol solution, ultrasonically disperse 0.2g of NCNTs into methanol, and then add ultrasonically dispersed NCNTs to the above solution, stir for 5h and sonicate for 10h. Then, 4.8 g of LTO was added and stirred well, and then placed in an oven to be dried at a gas flow rate of 100 sccm N _{2 under} an inert gas flow at 1000 ° C for 10 h, and then cooled to obtain the material.

Buckle electrical test result, the initial discharge capacity of 0.2C 650mAh · g ^-1, the first charge and discharge efficiency of 65% at 1C discharge capacity was 589mAh · g ^-1.

Example 16

In this embodiment, lithium iron nitrate is used as an iron source, and a lithium titanate modified material 0.5ZFO·0.1NCNTs·0.4LTO is prepared by in-situ synthesis.

Weigh 6.17g of zinc nitrate and 16.76g of ferric nitrate dissolved in ethanol solution, ultrasonically disperse 1.0g of NCNTs into methanol, and then add ultrasonically dispersed NCNTs to the above solution, stir for 5h and sonicate for 10h. Then, 4.0 g of LTO was added to the mixture and thoroughly dried, and then oven-dried, under a gas flow rate of 100 sccm N _{2 under} an inert gas flow, at 700 ° C for a heat treatment time of 10 h, and then cooled to obtain the material.

According to the deduction test, the first discharge specific capacity at 0.25 mA is 670 mAh·g ^-1 , the first charge and discharge efficiency is 75%, and the discharge specific capacity at ^{1 C} is 600 mAh·g ^-1 .

Example 17

In this embodiment, lithium ferric chloride modified material 0.5ZFO·0.1NCNTs·0.4LTO was prepared by in-situ synthesis using ferric chloride as the iron source.

Weigh 6.17 g of zinc nitrate and 11.2 g of ferric chloride dissolved in propanol solution, ultrasonically disperse 1.0 g of NCNTs into methanol, and then add ultrasonically dispersed NCNTs to the above solution, stirring for 10 h and stirring. After ultrasonic treatment for 10 h, then 4.0 g of LTO was added and stirred well, and then oven-dried, under a gas flow rate of 100 sccm N _{2 under} an inert gas flow, a heat treatment time of 1000 ° C for 10 h, and then cooled to obtain the material.

According to the deduction test, the first discharge specific capacity at 0.2C was 560 mAh·g ^-1 , the first charge and discharge efficiency was 79%, and the discharge specific capacity at ^{1 C} was 520 mAh·g ^-1 .

Comparative example

In this embodiment, electrochemical tests were carried out using LTO and ZFO as electrode materials, respectively.

The specific capacities measured for the samples of the different examples described above at different magnifications are shown in the following table:

Claims (10)

1. A lithium titanate modified material, characterized in that the modified material is composed of a micro/nano structure, including lithium titanate LTO, zinc titanate ZFO and nitrogen-doped carbon nanotube NCNTs.
2. The lithium titanate modified material according to claim 1, wherein the chemical composition of the modified material is xZFO·yNCNTs·zLTO, and x, y and z represent the contents of ZFO, NCNTs and LTO, respectively. Wherein, 0.01 ≤ x ≤ 0.50, 0.01 ≤ y ≤ 0.10, 0.4 ≤ z ≤ 0.98, and x + y + z = 1.
3. A lithium titanate-modified material according to claim 1 or 2, wherein the NCNTs have a N atom content of 0.01 to 6 at%, and the LTO has an average particle size of 5 to 100 μm.
4. The method for preparing a lithium titanate modified material according to claim 1, wherein the sample is obtained by post-treatment mixing, comprising the following steps:

   (1) ultrasonically dispersing NCNTs in a lower alcohol;

   (2) Add LTO and ZFO to the ultrasonically dispersed NCNTs, stir them evenly, and then place them in an oven for drying;

   (3) ball-mixing the dried mixture;

   (4) The ball-milled sample is annealed and heat-treated under an inert atmosphere.
5. The method for preparing a lithium titanate modified material according to claim 4, wherein the lower alcohol in the step (1) is a mixture of one or more of methanol, ethanol and propanol.
6. The method for preparing a lithium titanate modified material according to claim 4, wherein the inert atmosphere in the step (4) is He, N ₂ or Ar, the heat treatment temperature is 200-700 ° C, and the time is 0.1- 10h.
7. The method for preparing a lithium titanate modified material according to claim 1, wherein the sample is obtained by in situ synthesis, comprising the following steps:

   (1) ultrasonically dispersing NCNTs in a lower alcohol;

   (2) dissolving iron salt and zinc salt into a solution;

   (3) mixing the NCNTs dispersed in the step (1) with the iron salt and the zinc salt solution of the step (2), and sufficiently stirring, and then performing ultrasonic treatment;

   (4) adding LTO in portions to the solution of step (3), stirring and drying;

   (5) The sample after drying is heated in an inert atmosphere, calcined, and cooled.
8. The method for preparing a lithium titanate modified material according to claim 7, wherein the iron salt in the step (2) is at least two of ferric chloride, ferric nitrate, ferric citrate and iron acetate. The zinc salt is one or more of anhydrous zinc sulfate, zinc chloride and zinc sulfate; the molar ratio of zinc to iron in the zinc salt and the iron salt is 1:1.8-2.2.
9. The method for preparing a lithium titanate modified material according to claim 7, wherein the mixing method of the NCNTs and the iron salt and the zinc salt solution in the step (3) is to add the dispersed NCNTs to the step. (2) in solution Or the solution of the step (2) is added to the dispersed NCNTs in portions, and the stirring process is continued.
10. The production method of claim 7 modified lithium titanate material as claimed in claim, wherein: step (4) stirring time is 0-20h; in step (5) in an inert atmosphere of He, N ₂ or Ar, The gas flow rate is 20-1000 sccm, the calcination temperature is 500-1000 ° C, and the treatment time is 0.1-10 h.

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