Method for preparing carbon-coated lithium titanate negative electrode material by one-step solid phase method

Abstract

The invention discloses a method for preparing a carbon-coated lithium titanate negative electrode material by a one-step solid phase method, and belongs to the technical field of lithium ion battery materials. The method comprises the following steps: uniformly mixing and dispersing carbon-containing lithium salt, titanium salt and metal hydride to obtain a solid mixture; and roasting the obtained solid mixture in a protective atmosphere to obtain the carbon-coated lithium titanate negative electrode material. According to the preparation method, a certain amount of metal hydride is added into the reaction raw materials, a high-temperature solid-phase method is used, and carbon in the carbon-containing lithium source is reduced by the metal hydride to serve as a carbon source, so that the carbon-coated lithium titanate negative electrode material can be directly synthesized in one step, additional carbon sources and technological processes are not needed, and the preparation technology is greatly simplified.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a one-step solid-state method for preparing carbon-coated lithium titanate anode material. Background Technology

[0002] Since its commercialization, lithium-ion batteries have developed rapidly over the past two decades, and research on them has continued uninterrupted. The key factor determining the performance of lithium-ion batteries is their electrode materials, and research focuses mainly on the preparation process, doping, coating and other modification methods that have a major impact on the electrochemical performance of positive and negative electrode materials.

[0003] Carbon materials were the first commercially available anode materials for lithium-ion batteries. They are widely available, inexpensive, and can be mass-produced. However, due to the higher demands placed on the power performance and long-term cycle capability of lithium-ion batteries by electric vehicles and large energy storage devices, traditional graphite anode materials still suffer from drawbacks such as the tendency to form a non-active layer in the electrolyte of lithium-ion battery systems, leading to significant irreversible capacity loss during the first charge-discharge cycle, thus sacrificing the precious lithium-ion resources of the positive electrode; rapid capacity decay under high-current charge-discharge; poor safety; high-temperature runaway; and poor low-temperature performance, which limit the development of lithium-ion batteries.

[0004] Another anode material on the market is lithium titanate (Li4Ti5O4). 12 LTO (Li+) material has advantages that other anode materials do not have: (1) it has a high coulombic efficiency, and its specific capacity is close to the theoretical capacity when charged and discharged at low rates; (2) the voltage plateau during charging and discharging is around 1.55V (vs. Li+ / Li), which is higher than that of Li+. + The reduction potential greatly increases the battery safety performance; (3) The structure is stable and there is no change in the structure during charging and discharging, which is called "zero strain". It has a good long cycle life and high stability performance. Compared with carbon materials, lithium ions have better diffusion in LTO. However, LTO is a very poor electronic conductor, which makes LTO capacity decay quickly during high current charging and discharging and has poor rate performance, which restricts its application as a high rate negative electrode material in lithium-ion power batteries.

[0005] To improve the electronic conductivity of LTO anode materials, current modification research mainly focuses on two aspects: surface modification and ion doping. This allows for improvements in fast charge / discharge performance and high-rate performance of the battery, even at the expense of a small amount of reversible specific capacity, thus meeting the high-power requirements of power batteries. Surface modification primarily enhances the electronic conductivity of the particle surface by applying a layer of highly conductive material.

[0006] Conventional surface modification methods primarily involve carbon coating. Existing technologies typically use sucrose, citric acid, or stearic acid as carbon sources, employing high-temperature solid-state methods or sol-gel methods to prepare carbon-coated LTO materials. The resulting carbon-coated LTO materials exhibit good rate performance and cycle stability. However, the carbon coating method requires a two-step process: first, synthesizing LTO; and second, adding a carbon source for coating. This significantly increases the process length, and the addition of an extra carbon source raises production costs, undoubtedly further limiting its commercial application.

[0007] For example, Chinese patent application No. 201110451727.8 discloses a method for preparing a nano-carbon-coated spinel lithium titanate battery anode material, including the following steps: placing titanium dioxide and a lithium source into a dispersant, mixing them uniformly, and then drying; pre-calcining the dried mixture at a temperature of 400-800℃ for 2-36 hours under a first atmosphere, and then naturally cooling to room temperature to obtain an intermediate product; placing the obtained intermediate product and a carbon source into a dispersant, mixing them uniformly, and then drying; and second-calcining the mixture of the dried intermediate product, carbon source, and dispersant at a temperature of 700-950℃ for 2-36 hours under a second atmosphere, and then naturally cooling to room temperature to obtain nano-carbon-coated spinel lithium titanate. This application still requires a two-step synthesis process, namely, first synthesizing lithium titanate, and then carbonizing it to prepare the carbon-coated lithium titanate material, so its preparation process is relatively complex. Summary of the Invention

[0008] This invention provides a one-step solid-state method for preparing carbon-coated lithium titanate anode materials, thereby solving the technical problem that the preparation of carbon-coated LTO materials usually requires two steps, which is relatively complex and requires the addition of an additional carbon source.

[0009] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a one-step solid-state method for preparing carbon-coated lithium titanate anode materials, comprising: Carbon-containing lithium salts, titanium salts, and metal hydrides are mixed and dispersed uniformly to obtain a solid mixture; and The resulting solid mixture was calcined under a protective atmosphere to obtain a lithium titanate anode material with carbon coating.

[0010] To address the technical problem that existing carbon-coated lithium titanate anode materials typically require a two-step synthesis process, which is relatively complex, this application creatively introduces a novel approach. By adding a certain amount of metal hydride to the reaction raw materials and using a high-temperature solid-state method, the hydrogen gas released by the metal hydride at high temperatures is utilized to reduce the carbon in the carbon-containing lithium source to elemental carbon, thus enabling the direct one-step synthesis of carbon-coated lithium titanate anode materials without the need for additional carbon sources and processes. This significantly simplifies the preparation process while effectively ensuring the performance of the resulting carbon-coated lithium titanate anode material, meeting the application requirements for ionic conductivity, high-rate charge-discharge capacity, and cycle stability.

[0011] Furthermore, the reaction conditions of this application are relatively mild, requiring only a calcination reaction under a protective atmosphere, which is more conducive to industrial-scale application. In addition, this application reduces carbon in the carbon-containing lithium source by adding metal hydrides, and the reduction temperature is basically consistent with the temperature window of lithium titanate solid-state synthesis, so it will not affect the original lithium titanate solid-state synthesis process.

[0012] According to any preparation method of the present invention, the metal hydride is at least one selected from titanium hydride, zirconium hydride, magnesium hydride, lithium hydride, scandium hydride, and vanadium hydride, but is not limited to these hydrides. Other elemental elements in the periodic table that can form hydrides with hydrogen can also be used as synthetic materials. The metal hydride is further preferably titanium hydride, zirconium hydride, and lithium hydride. When lithium hydride is used, it can also replace part of the carbon-containing lithium salt as a lithium source.

[0013] According to any preparation method of the present invention, the ratio of the number of moles of metal elements in the metal hydride to the sum of the number of moles of metal elements in the titanium salt and the metal hydride is 0.01 to 0.4; the ratio of the number of moles of lithium elements in the carbon-containing lithium salt to the sum of the number of moles of metal elements in the titanium salt and the metal hydride is 0.8 to 0.89.

[0014] The "sum of the number of moles of metal elements in titanium salts and metal hydrides" mentioned here refers to the sum of the number of moles of titanium in titanium salts and the corresponding metal elements in metal hydrides. For example, when titanium hydride is used as the metal hydride, it refers to the sum of the number of moles of titanium in titanium salts and titanium hydride. When zirconium hydride is used as the metal hydride, it refers to the sum of the number of moles of titanium in titanium salts and zirconium in zirconium hydride.

[0015] According to any preparation method of the present invention, the obtained solid mixture is calcined under a protective atmosphere, and the calcination conditions include: a calcination temperature of 500℃ to 850℃ and a calcination time of 5 to 32 hours. It should be noted that the calcination temperature here can be a fixed temperature for a certain time, or it can be a segmented calcination at different temperatures.

[0016] A further preferred method is to first calcine at a low temperature of 500℃~750℃ for 5~10 hours to minimize the volatilization of lithium carbonate; and then calcine at a high temperature of 800℃~850℃ for 8~20 hours to accelerate element diffusion and make the composition uniform.

[0017] According to any preparation method of the present invention, the carbon-containing lithium salt includes at least one of lithium carbonate, lithium acetate, lithium formate, lithium lactate, lithium isopropoxide, lithium organic carboxylic acid, and long-chain or short-chain alkyl lithium. The titanium salt includes at least one of titanium oxide, orthotitanic acid, and metatitanic acid.

[0018] However, it should be noted that the selection of the carbon-containing lithium salt and titanium salt is not limited to the specific substances mentioned above.

[0019] According to any preparation method of the present invention, the step of uniformly mixing and dispersing the carbon-containing lithium salt, titanium salt, and metal hydride to obtain a solid mixture specifically includes: A liquid dispersant is used to mix and disperse carbon-containing lithium salts, titanium salts and metal hydrides evenly to obtain a mixed slurry; The resulting mixed slurry was dried to obtain a solid mixture.

[0020] According to any preparation method of the present invention, the liquid dispersant is at least one of water, alcohol, ketone, aldehyde, ether, organic acid, alkane, organic amine, and amide, and the mass ratio of the sum of the masses of the lithium salt, titanium salt, and metal hydride to the mass of the liquid dispersant is 0.125 to 0.625.

[0021] According to any of the preparation methods of the present invention, the carbon-containing lithium salt, titanium salt and metal hydride are mixed and dispersed uniformly using a liquid dispersant. The mixing process can be carried out by ball milling, ultrasonication or stirring, or other methods, as long as the mixing effect of each raw material can be guaranteed.

[0022] According to any preparation method of the present invention, the obtained mixed slurry is dried, and the specific drying method includes, but is not limited to, spray drying, oven drying and vacuum drying.

[0023] According to any of the preparation methods of the present invention, the thickness of the carbon coating layer in the obtained lithium titanate anode material with carbon coating is 5~20 nm.

[0024] In summary, compared with the prior art, the present invention can achieve the following beneficial effects: (1) This invention uses a high-temperature solid-state method to reduce carbon in a carbon-containing lithium source with metal hydride as a carbon source, thereby directly synthesizing carbon-coated lithium titanate anode material in one step without adding an additional carbon source, which greatly simplifies the preparation process, and the carbon-coated lithium titanate anode material prepared can meet its application performance requirements.

[0025] (2) The preparation process of the present invention has relatively mild reaction conditions, and only requires calcination under inert gas protection, which is conducive to industrial promotion and application. Attached Figure Description

[0026] Figure 1 The XRD patterns of the carbon-coated lithium titanate anode materials prepared in some embodiments of the present invention are shown below. Figure 2 This is a TEM image of the carbon-coated lithium titanate anode material prepared in Example 1 of the present invention; Figure 3 The image shows the Raman spectrum of the carbon-coated lithium titanate anode material prepared in Example 1 of this invention. Figure 4 XPS spectrum of the carbon-coated lithium titanate anode material prepared in Example 1 of this invention; Figure 5 This is a TEM image of the carbon-coated lithium titanate anode material prepared in Example 2 of the present invention; Figure 6 The image shows the XRD pattern of the carbon-coated lithium titanate anode material prepared in Example 3 of this invention. Figure 7 This is a TEM image of the carbon-coated lithium titanate anode material prepared in Example 3 of the present invention; Figure 8 The energy dispersive spectrum of the carbon-coated lithium titanate anode material prepared in Example 3 of this invention is shown. Detailed Implementation

[0027] The present invention will be further illustrated below with reference to specific embodiments. However, due to space limitations, only some embodiments are listed below for illustration, and these embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field. The essential features and significant effects of the present invention can be seen from the following embodiments. The described embodiments are some embodiments of the present invention, but not all embodiments. Therefore, they do not limit the present invention in any way. Any non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are within the protection scope of the present invention.

[0028] Meanwhile, the terms "comprising" and "including" in this application indicate the presence of the features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0029] It should also be understood that, for clarity, certain features of this disclosure may be described herein in the context of individual embodiments, but may also be provided in combination with each other in individual embodiments. That is, unless obviously incompatible or specifically excluded, each individual embodiment is considered to be combinable with any other embodiment, and such combination is considered to represent another different embodiment. Conversely, for brevity, various features of this disclosure described in the context of individual embodiments may also be provided individually or in any sub-combination. Finally, while a particular embodiment may be described as part of a series of steps or part of a more general structure, each step or substructure may also be considered an independent embodiment in itself.

[0030] Example 1 1.458 g of lithium carbonate, 3.466 g of titanium dioxide, and 0.114 g of titanium hydride were added to a ball mill jar, along with 20 ml of anhydrous ethanol. The mixture was ball-milled for 3 hours at 300 rpm. The resulting slurry was then placed in a drying oven and dried at 85°C for 12 hours to obtain a solid mixture. This solid mixture was then ground into powder using a mortar and pestle. The powder was placed in a muffle furnace and calcined at 800°C for 16 hours under an Ar protective atmosphere to obtain carbon-coated lithium titanate anode material.

[0031] The X-ray diffraction (XRD) pattern, transmission electron microscope (TEM) image, X-ray photoelectron spectroscopy (XPS) image, and Raman spectrum of the carbon-coated lithium titanate anode material obtained in this embodiment are shown below. Figures 1-4 As shown.

[0032] Figure 1 The spectrum corresponding to 0.05 (red spectrum) shows the lithium titanate synthesized in this embodiment. It can be seen that the synthesized substance has a typical lithium titanate structure, which is in good agreement with the PDF. Combined with XPS results ( Figure 3 The presence of carbon peaks indicates that carbon was reduced during the synthesis of lithium titanate in this embodiment. Most of the titanium in lithium titanate is in the form of Ti. 4+ In the presence of titanium hydride, the protective atmosphere of Ar is reducing, so a small amount of titanium remains as Ti. 3+ It exists. According to... Figure 2 It can be seen that the lithium titanate particles are surrounded by a layer of carbon. According to Raman spectroscopy (… Figure 4 The results show that I D \I GThe ratio is less than 1, indicating that the coated carbon is in the form of graphitized carbon.

[0033] Example 2 1.566g of lithium carbonate, 2.743g of titanium dioxide, and 0.734g of titanium hydride were added to a ball mill jar, along with 20ml of anhydrous ethanol. The mixture was ball-milled for 3 hours at 300 rpm. The resulting slurry was then placed in a drying oven and dried at 85°C for 12 hours to obtain a solid mixture. This solid mixture was then ground into powder using a mortar and pestle. The powder was placed in a muffle furnace and calcined at 800°C for 16 hours under an Ar protective atmosphere to obtain carbon-coated lithium titanate anode material.

[0034] The XRD and TEM images of the carbon-coated lithium titanate anode material obtained in this embodiment are shown below. Figure 1 , Figure 5 As shown. Figure 1 The spectrum corresponding to 0.3 in the figure shows the lithium titanate synthesized in this embodiment. It can be seen that the synthesized substance has a typical lithium titanate structure, which is in good agreement with the PDF. According to Figure 5 It can also be seen that the lithium titanate particles are surrounded by a layer of carbon, and the amount of carbon coated in Example 1 increases with the increase of titanium hydride addition.

[0035] Example 3 1.469 g of lithium carbonate, 3.308 g of titanium dioxide, and 0.256 g of zirconium hydride were added to a ball mill jar, along with 20 ml of anhydrous ethanol. The mixture was ball-milled for 3 hours at 300 r / min. The resulting slurry was placed in a drying oven and dried at 85°C for 12 hours to obtain a solid mixture. The solid mixture was then ground into powder using a mortar and pestle. The powder was placed in a muffle furnace and calcined at 750°C for 5 hours under an Ar protective atmosphere at a heating rate of 8°C / min. The temperature was then increased to 850°C and calcined for 16 hours to obtain carbon-coated lithium titanate anode material.

[0036] The XRD pattern, TEM pattern, and energy dispersive spectroscopy pattern of the carbon-coated lithium titanate anode material obtained in this embodiment are as follows: Figure 6 , Figure 7 , Figure 8 As shown. According to Figure 8 It can be seen that the LTO synthesized in this embodiment contains zirconium.

[0037] Example 4 2.160 g of lithium acetate, 2.723 g of titanium dioxide, and 0.189 g of titanium hydride were added to a ball mill jar, along with 20 ml of anhydrous ethanol. The mixture was ball-milled for 3 hours at 300 r / min. The resulting slurry was placed in a drying oven and dried at 85 °C for 12 hours to obtain a solid mixture. The solid mixture was then ground into powder using a mortar and pestle. The powder was placed in a muffle furnace and calcined at 500 °C for 6 hours under an Ar protective atmosphere at a heating rate of 8 °C / min. The temperature was then increased to 800 °C and calcined for 20 hours to obtain carbon-coated lithium titanate anode material.

[0038] Example 5 1.944 g of lithium formate, 3.004 g of metatitanic acid, and 0.170 g of titanium hydride were added to a ball mill jar, along with 10 ml of anhydrous ethanol. The mixture was ball-milled for 3.5 h at a speed of 350 r / min. The resulting slurry was placed in a drying oven and dried at 88 °C for 11 h to obtain a solid mixture. The solid mixture was then ground into powder using a mortar and pestle. The powder was placed in a muffle furnace and calcined at 520 °C for 9 h under an Ar protective atmosphere at a heating rate of 8.5 °C / min. The temperature was then increased to 830 °C and calcined for 15 h to obtain carbon-coated lithium titanate anode material.

Claims

1. A method for preparing carbon-coated lithium titanate anode material in a one-step solid-state process, characterized in that, include: Carbon-containing lithium salts, titanium salts, and metal hydrides are mixed and dispersed uniformly to obtain a solid mixture; and The resulting solid mixture was calcined under a protective atmosphere to obtain a lithium titanate anode material with carbon coating.

2. The method for preparing carbon-coated lithium titanate anode material by one-step solid-state method according to claim 1, characterized in that, The metal hydride is at least one of titanium hydride, zirconium hydride, magnesium hydride, lithium hydride, scandium hydride, and vanadium hydride.

3. The method for preparing carbon-coated lithium titanate anode material by one-step solid-state method according to claim 2, characterized in that, The ratio of the number of moles of metal elements in the metal hydride to the sum of the number of moles of metal elements in the titanium salt and the metal hydride is 0.01 to 0.4; the ratio of the number of moles of lithium elements in the carbon-containing lithium salt to the sum of the number of moles of metal elements in the titanium salt and the metal hydride is 0.8 to 0.

89.

4. The method for preparing carbon-coated lithium titanate anode material in one step using solid-state method according to claim 2, characterized in that, The resulting solid mixture is calcined under a protective atmosphere. The calcination conditions include a calcination temperature of 500℃ to 850℃ and a calcination time of 5 to 32 hours.

5. The method for preparing carbon-coated lithium titanate anode material by one-step solid-state method according to claim 4, characterized in that, The resulting solid mixture is calcined under a protective atmosphere. The calcination conditions include: first calcining at 500℃~750℃ for 5~10 hours, and then calcining at 800℃~850℃ for 8~20 hours.

6. The method for preparing carbon-coated lithium titanate anode material by one-step solid-state method according to any one of claims 1-5, characterized in that, The carbon-containing lithium salt includes at least one of lithium carbonate, lithium acetate, lithium formate, lithium lactate, lithium isopropoxide, lithium organic carboxylic acids, and long-chain or short-chain alkyl lithium. The titanium salt includes at least one of titanium oxide, orthotitanic acid, and metatitanic acid.

7. The method for preparing carbon-coated lithium titanate anode material by one-step solid-state method according to any one of claims 1-5, characterized in that, The process of uniformly mixing and dispersing carbon-containing lithium salts, titanium salts, and metal hydrides to obtain a solid mixture specifically includes: A liquid dispersant is used to mix and disperse carbon-containing lithium salts, titanium salts and metal hydrides evenly to obtain a mixed slurry; The resulting mixed slurry was dried to obtain a solid mixture.

8. The method for preparing carbon-coated lithium titanate anode material by one-step solid-state method according to claim 7, characterized in that, The liquid dispersant is at least one of water, alcohol, ketone, aldehyde, ether, organic acid, alkane, organic amine, and amide, and the mass ratio of the sum of the masses of the lithium salt, titanium salt, and metal hydride to the mass of the liquid dispersant is 0.125 to 0.

625.

9. The method for preparing carbon-coated lithium titanate anode material by one-step solid-state method according to claim 7, characterized in that, The method of using a liquid dispersant to uniformly mix and disperse carbon-containing lithium salts, titanium salts and metal hydrides involves ball milling, ultrasonication or stirring. The resulting mixed slurry is then dried, specifically by spray drying, oven drying, or vacuum drying.

10. The method for preparing carbon-coated lithium titanate anode material by one-step solid-state method according to any one of claims 1-5, characterized in that, In the obtained lithium titanate anode material with carbon coating, the thickness of the carbon coating layer is 5~20nm.

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