WO2019205356A1 - 一种氮掺杂钛酸锂复合材料及其制备方法与锂离子电池 - Google Patents

一种氮掺杂钛酸锂复合材料及其制备方法与锂离子电池 Download PDF

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WO2019205356A1
WO2019205356A1 PCT/CN2018/100815 CN2018100815W WO2019205356A1 WO 2019205356 A1 WO2019205356 A1 WO 2019205356A1 CN 2018100815 W CN2018100815 W CN 2018100815W WO 2019205356 A1 WO2019205356 A1 WO 2019205356A1
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nitrogen
composite material
lithium titanate
nano
titanate composite
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PCT/CN2018/100815
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French (fr)
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李瑛�
苏陈良
俞兆喆
田冰冰
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深圳大学
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the invention relates to the technical field of battery materials, in particular to a nitrogen-doped lithium titanate composite material, a preparation method thereof and a lithium ion battery.
  • a conventional negative electrode material is a carbon negative electrode material.
  • the carbon negative electrode has been successfully commercialized, its battery safety problem, especially the safety problem at a large rate, has forced people to search for a safe and reliable new negative electrode material that is lithium-inserted at a potential higher than the lithium-ion potential of the carbon negative electrode.
  • low-potential transition metal oxides and composite oxides have attracted extensive attention as anode materials for lithium-ion batteries, especially the zero-strain material Li 4 Ti 5 O 12 with its 1.5V (vs. Li/Li + ) voltage.
  • the charging/discharging efficiency close to 1 and the superior cycle performance have attracted much attention, and it is an electrode material which has great potential as a negative electrode material for a power type lithium ion battery.
  • lithium titanate has poor electronic conductivity, which limits its high rate performance. Therefore, it is necessary to improve its conductivity by modifying it, thereby improving the large-rate performance of lithium titanate while maintaining its high reversible electrochemical capacity and good cycle performance.
  • the methods capable of improving the lithium titanate rate performance mainly include: preparing nanometer-sized lithium titanate, bulk doping of lithium titanate and introducing a conductive phase.
  • the present invention aims to provide a nitrogen-doped lithium titanate composite material, a preparation method thereof and a lithium ion battery, aiming at solving the carbon coating and conductivity of the lithium titanate by the prior method.
  • the problem is limited and the contrast capacity is not improved.
  • a method for preparing a nitrogen-doped lithium titanate composite material comprising the steps of:
  • the precursor is heated to 700 to 1000 ° C under an inert atmosphere, and then calcined in a reducing atmosphere for 5 to 20 hours, and finally cooled and ground to obtain a nitrogen-doped lithium titanate composite material.
  • the nanoparticles are selected from the group consisting of nano titanium, nano aluminum, nano vanadium, nano zirconium, nano cerium, nano magnesium, nano calcium, One or more of nano boron, nano manganese, nano tungsten, nano carbon nitride and nano titanium nitride.
  • the dispersing agent is selected from the group consisting of polyethylene glycol, sodium lauryl sulfate, triethylhexyl phosphate, and methyl pentane
  • the dispersing agent is selected from the group consisting of polyethylene glycol, sodium lauryl sulfate, triethylhexyl phosphate, and methyl pentane
  • the dispersing agent is selected from the group consisting of polyethylene glycol, sodium lauryl sulfate, triethylhexyl phosphate, and methyl pentane
  • an alcohol a cellulose derivative, a polyacrylamide, a guar gum, a fatty acid polyethylene glycol ester, and a silane coupling agent.
  • the lithium source is one or more selected from the group consisting of lithium hydroxide, lithium acetate, and lithium nitrate.
  • the titanium source is selected from the group consisting of butyl titanate, titanium tetrachloride, metatitanic acid, n-propyl titanate, titanium One or more of isopropyl acid acrylate and acetylacetone titanium oxide titanate coupling agent.
  • the ratio of the amount of the lithium source, the titanium source and the nanoparticle is 0.75-0.90:1:0.01-0.1.
  • the inert atmosphere is selected from one of argon gas, nitrogen gas and helium gas.
  • the reducing atmosphere is one selected from the group consisting of ammonia gas and nitrogen-hydrogen mixture gas.
  • a nitrogen-doped lithium titanate composite material prepared by the method for preparing a nitrogen-doped lithium titanate composite material according to the present invention.
  • a lithium ion battery comprising a negative electrode, wherein the material of the negative electrode is a nitrogen-doped lithium titanate composite material according to the invention.
  • the nitrogen-doped lithium titanate composite prepared by the invention has good electronic conductivity, high lithium ion diffusion speed and stable structure; the introduction of the auxiliary nitrogen-doped nanoparticles not only effectively inhibits the activity of the tetravalent titanium ions, but also The problem that the electrolyte is catalyzed by tetravalent titanium ions to generate gas is alleviated to a large extent, and the crystal structure of lithium titanate is stabilized, and the lattice stability of the lithium titanate material in the process of deintercalating lithium is prolonged. The service life of lithium titanate batteries.
  • the preparation process of the invention is simple, the process parameters are easy to control, the production cost is low, and the invention is suitable for industrial large-scale production.
  • Example 1 is an XRD pattern of a nitrogen-doped lithium titanate composite material prepared in Example 1, Example 2, and Example 3;
  • Example 2 is a comparison diagram of EIS of a nitrogen-doped lithium titanate composite material prepared in Example 1 and a conventional lithium non-titanium nitride material;
  • Example 3 is a graph showing the first charge and discharge curves of the nitrogen-doped lithium titanate composite material 0.2C obtained in Example 1;
  • Example 4 is a graph showing the first charge and discharge curves of the nitrogen-doped lithium titanate composite material 5C obtained in Example 2;
  • Fig. 5 is a graph showing the cycle performance of the nitrogen-doped lithium titanate composite material 5C prepared and discharged in Example 2.
  • the present invention provides a nitrogen-doped lithium titanate composite material, a method for preparing the same, and a lithium ion battery.
  • the present invention will be further described in detail below in order to clarify and clarify the objects, technical solutions and effects of the present invention. It is understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
  • the invention provides a preparation method of a nitrogen-doped lithium titanate composite material, which comprises the following steps:
  • the precursor is heated to 700 to 1000 ° C under an inert atmosphere, and then calcined in a reducing atmosphere for 5 to 20 hours, and finally cooled and ground to obtain a nitrogen-doped lithium titanate composite material.
  • the step (1) specifically comprises: first adding a dispersing agent to a solvent (such as anhydrous ethanol), and then ultrasonically dispersing the nanoparticles in a solvent containing a dispersing agent, and the ultrasonic dispersion time is 1.5-2.5 h (eg, 2 h). .
  • a solvent such as anhydrous ethanol
  • the nanoparticles are selected from the group consisting of nano titanium, nano aluminum, nano vanadium, nano zirconium, nano cerium, nano magnesium, nano calcium, nano boron, nano manganese, nano tungsten, nano carbon nitride and nano titanium nitride. One or more.
  • the dispersing agent is selected from the group consisting of polyethylene glycol, sodium lauryl sulfate, triethylhexylphosphoric acid, methylpentanol, cellulose derivatives, polyacrylamide, guar gum, fatty acid polyethylene glycol One or more of an ester, a silane coupling agent, and the like.
  • the step (2) specifically includes dividing the solvent in which the nanoparticles are dispersed into two parts, adding a lithium source to a part of the solution, adding a titanium source to the other part of the solution, and mixing the two parts of the solution to obtain a sol. If a lithium source and a titanium source are directly added to a solvent in which nanoparticles are dispersed, the lithium source and the titanium source react rapidly, affecting the particle size, morphology, and properties of the target product. In the present invention, a lithium source and a titanium source are separately added to the two portions of the solution, and then the two portions of the solution are mixed, so that the separation can be better to form the sol.
  • the lithium source is selected from one or more of lithium hydroxide, lithium acetate, lithium nitrate, and the like.
  • the titanium source is selected from the group consisting of butyl titanate, titanium tetrachloride, metatitanic acid, n-propyl titanate, isopropyl titanate, and acetylacetonate titanate coupling agent. kind or more.
  • the ratio of the amounts of the lithium source, the titanium source and the nanoparticles is from 0.75 to 0.90:1:0.01-0.1. Maintaining an excess of about 3% of lithium ions can supplement the lithium loss during sintering and contribute to the integrity of the grains.
  • the step (5) specifically includes: heating the precursor to a temperature of 700 to 1000 ° C at 4-6 ° C / min in an inert atmosphere, switching the inert atmosphere to a reducing atmosphere, and calcining at a constant temperature for 5 to 20 hours, and then reducing atmosphere Switching to an inert atmosphere, naturally cooling to room temperature, grinding, and sieving, to obtain nitrogen-doped nano-titanium titanate powder.
  • the above-mentioned high-temperature conditions use a reducing atmosphere to assist nitrogen doping, and an inert atmosphere is used in the heating and cooling processes to ensure the structural stability of the target product.
  • the inert atmosphere is selected from one of argon, nitrogen, helium and the like.
  • the reducing atmosphere is selected from one of ammonia gas, nitrogen-hydrogen gas mixture and the like.
  • the nitrogen-doped nanoparticles of the present invention release nitrogen ions themselves to help nitrite lithium titanate, or react with nitrogen to produce nitrides with high electron conductivity, or capture oxygen molecules in lithium titanate to form oxides while helping titanium Lithium acid is converted to lithium titanate.
  • the formation mechanism of the nitrogen-doped lithium titanate composite material of the present invention is further explained below: in the formation of lithium titanate, due to the presence of a reducing atmosphere, such as a nitrogen atmosphere, a part of the oxygen position during the crystallization of the product particles will occur. Occupied by active nitrogen to achieve nitrogen doping. In addition, the incorporated nano-ion itself releases nitrogen to occupy a portion of the oxygen, or captures an oxygen atom in the lithium titanate to form an oxide, and the oxygen position in the lithium titanate is occupied by the nitrogen atom, further assisting the nitrogen Doping.
  • a reducing atmosphere such as a nitrogen atmosphere
  • the invention adopts a method of introducing auxiliary nitrogen-doped nanoparticles to prepare a nitrogen-doped lithium titanate composite material with good electron conductivity and high lithium ion diffusion speed, and solves the application of the existing lithium titanate material.
  • the problem that the electrolyte is catalytically cracked by tetravalent titanium ions to generate gas also stabilizes the crystal structure of lithium titanate, increases the lattice stability of the lithium titanate material in the process of deintercalating lithium, and prolongs the lithium titanate battery. Service life.
  • the preparation method of the method is simple, and is suitable for the modified production of the existing lithium titanate material, and the production cost is low, and is suitable for industrial large-scale production.
  • the invention also provides a nitrogen-doped lithium titanate composite material, which is prepared by the preparation method of the nitrogen-doped lithium titanate composite material of the invention.
  • the invention also provides a lithium ion battery, comprising a negative electrode, wherein the material of the negative electrode is the nitrogen-doped lithium titanate composite material according to the invention.
  • polyethylene glycol was added to absolute ethanol, and then the nano titanium powder was ultrasonically dispersed in anhydrous ethanol containing polyethylene glycol, and ultrasonically dispersed for 2 hours.
  • the sol was heated to 60 ° C and stirred at constant temperature for 4 h to form a gel.
  • the gel was dried at 120 ° C to obtain a precursor.
  • the precursor was heated to 700 ° C at 5 ° C / min in an argon atmosphere, and the argon atmosphere was switched to an ammonia atmosphere at a constant temperature for 5 h. Then, the ammonia gas atmosphere was switched to an argon atmosphere, and the mixture was naturally cooled to room temperature and then ground. After passing through a 150 mesh sieve, a nitrogen-doped nano-titanium titanate powder was obtained. The powder color is white. After the X-ray powder diffraction (XRD) test, it is a single spinel structure of lithium titanate, as shown in a of FIG.
  • XRD X-ray powder diffraction
  • the electrochemical test was carried out under the following conditions: the prepared nitrogen-doped lithium titanate composite material was used as the active material, Super P (super carbon) was used as the conductive agent, PVDF (polyvinylidene fluoride) was used as the binder, and NMP (N- Methyl-2-pyrrolidone) is a solvent-adjusted slurry applied to a copper foil to form an electrode sheet.
  • a lithium sheet was used as a counter electrode, the electrolyte concentration was 1 mol/L, and the polypropylene microporous membrane was a separator of the battery, and assembled into a test battery.
  • a button cell was assembled in an argon-filled glove box for electrochemical testing.
  • the charge and discharge voltage ranges from 1.0 to 2.5V.
  • the product was assembled into a battery according to the above method.
  • the initial discharge capacity was greater than 190 mAh/g at 0.2 C, and the charging capacity was close to 180 mAh/g, as shown in FIG.
  • the resistance of lithium titanate (LTON) is significantly reduced after nitrogen doping, and its electrochemical impedance is compared with that of lithium non-titanium titanate (LTO) as shown in Fig. 2.
  • polyethylene glycol was added to absolute ethanol, and then the nano metal titanium powder was ultrasonically dispersed in absolute ethanol containing polyethylene glycol, and ultrasonically dispersed for 2 hours.
  • the sol was heated to 60 ° C and stirred at constant temperature for 4 h to form a gel.
  • the gel was dried at 120 ° C to obtain a precursor.
  • the precursor was heated to 800 ° C at 5 ° C / min in an argon atmosphere, the argon atmosphere was switched to an ammonia atmosphere, and the temperature was kept at 5 °, then the ammonia atmosphere was switched to an argon atmosphere, and finally cooled to room temperature, and then ground. After passing through a 150 mesh sieve, a nitrogen-doped lithium titanate powder was obtained.
  • the nitrogen-doped lithium titanate powder is light gray in color.
  • XRD X-ray powder diffraction
  • the prepared nitrogen-doped lithium titanate powder was assembled into a battery according to the method of Example 1.
  • the first discharge capacity was about 160 mAh/g at 5 C, and the charge capacity was about 155 mAh/g, as shown in FIG. After 12,000 cycles, the capacity retention rate is greater than 80%, as shown in Figure 5.
  • polyethylene glycol was added to absolute ethanol, and then the nano metal titanium powder was ultrasonically dispersed in absolute ethanol containing polyethylene glycol, and ultrasonically dispersed for 2 hours.
  • the sol was heated to 60 ° C and stirred at constant temperature for 4 h to form a gel.
  • the gel was dried at 120 ° C to obtain a precursor.
  • the precursor was heated to 900 ° C at 5 ° C / min in an argon atmosphere, and the argon atmosphere was switched to an ammonia atmosphere at a constant temperature for 5 h, then the ammonia gas atmosphere was switched to an argon atmosphere, and naturally cooled to room temperature, and then ground. After passing through a 150 mesh sieve, a nitrogen-doped lithium titanate powder was obtained. The powder color is dark gray. After the X-ray powder diffraction (XRD) test, it is a single spinel structure of lithium titanate, as shown by c in FIG.
  • XRD X-ray powder diffraction
  • Example 1 Other conditions are the same as in the first embodiment except that the nano metal titanium powder is replaced by the nano metal aluminum powder, and the same is performed in an ammonia gas atmosphere at a temperature of 700 ° C and a constant temperature of 5 h to obtain a nitrogen-doped lithium titanate powder. body.
  • the obtained product was assembled into a battery in the same manner as in Example 1.
  • the first charge and discharge capacity at 5 C was about 150 mAh/g, and the capacity after about 100 cycles was about 110 mAh/g.
  • Example 1 Other conditions are the same as in the first embodiment except that the nano metal titanium powder is replaced by the nano metal vanadium powder, and the same is performed in an ammonia gas atmosphere at a temperature of 700 ° C and a constant temperature of 5 h to obtain a nitrogen-doped lithium titanate powder. body.
  • the obtained product was assembled into a battery in the same manner as in Example 1.
  • the first charge and discharge capacity at 5 C was about 152 mAh/g, and the capacity after about 100 cycles was about 115 mAh/g.
  • the present invention provides a nitrogen-doped lithium titanate composite material, a preparation method thereof, and a lithium ion battery.
  • the invention adopts a method of introducing auxiliary nitrogen-doped nanoparticles to prepare a nitrogen-doped lithium titanate composite material with good electron conductivity and high lithium ion diffusion speed, and solves the problem that the existing lithium titanate material is applied in high-rate charge and discharge process.
  • the problem of low electron conductivity and large grain boundary resistance is encountered.
  • the introduction of auxiliary nitrogen-doped nanoparticles not only effectively inhibits the activity of tetravalent titanium ions, but also relieves the electrolyte by tetravalent titanium ions to a large extent.
  • the problem of catalytic cracking to generate gas also stabilizes the crystal structure of lithium titanate, increases the lattice stability of lithium titanate material in the process of deintercalating lithium, and prolongs the service life of lithium titanate battery.
  • the preparation process of the method is simple, and the lithium titanate used can be synthesized by any method without affecting the performance of the composite material, and is suitable for the modified production of the existing lithium titanate material, and the production cost is low, and is suitable for industrial large-scale production. produce.

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Abstract

本发明公开一种氮掺杂钛酸锂复合材料及其制备方法与锂离子电池，制备方法包括步骤：将纳米粒子分散于含有分散剂的溶剂中；将上述分散有纳米粒子的溶剂分成两部分，往一部分溶液中加入锂源，另一部分溶液中加入钛源，再混合两部分溶液制得溶胶；将溶胶加热至40～100℃，恒温搅拌4～10h，形成凝胶；将凝胶在100～200℃下去除溶剂得到前驱体；将前驱体在惰性气氛下加热到700～1000℃，然后在还原性气氛下煅烧5～20h，最后经冷却、研磨，得到氮掺杂钛酸锂复合材料。本发明制备的氮掺杂钛酸锂复合材料电子导电性良好，锂离子扩散速度快，结构稳定；本发明锂离子电池使用寿命长。

Description

一种氮掺杂钛酸锂复合材料及其制备方法与锂离子电池 技术领域
本发明涉及电池材料技术领域，尤其涉及一种氮掺杂钛酸锂复合材料及其制备方法与锂离子电池。
背景技术
目前，锂离子电池用负极材料的研究重点正朝着高比容量，大倍率，高循环性能和高安全性能的动力型电池材料方向发展。传统的负极材料是碳负极材料。虽然碳负极已经成功地商业化，但是其存在的电池安全问题特别是大倍率下的安全问题，迫使人们寻找比碳负极嵌锂电位稍高的电位下嵌锂的安全可靠的新型负极材料。其中低电位过渡金属氧化物及复合氧化物作为锂离子电池的负极材料引起了人们的广泛注意，尤其是零应变材料Li 4Ti 5O 12，以其1.5V(vs.Li/Li +)电压、接近1的充放电效率和优越的循环性能广受关注，是一种很有潜力作为动力型锂离子电池负极材料的电极材料。
但是钛酸锂具有较差的电子导电性，这就限制了其高倍率性能。因此需要通过对其改性来改善其导电性，从而提高钛酸锂的大倍率性能，同时要保持其高可逆电化学容量和良好的循环性能。目前能够改善钛酸锂倍率性能的方法主要有：制备纳米粒径的钛酸锂，钛酸锂本体掺杂和引入导电相。目前有公开通过不同方法对钛酸锂进行碳包覆，虽然对其性能有一定改善，但是对其导电能力提高有限并且对比容量没有提高。
因此，现有技术还有待于改进和发展。
发明内容
鉴于上述现有技术的不足，本发明的目的在于提供一种氮掺杂钛酸锂复合材料及其制备方法与锂离子电池，旨在解决现有方法对钛酸锂进行碳包覆，导电能力提高有限并且对比容量没有提高的问题。
本发明的技术方案如下：
一种氮掺杂钛酸锂复合材料的制备方法，其中，包括以下步骤：
(1)将纳米粒子分散于含有分散剂的溶剂中；
(2)将上述分散有纳米粒子的溶剂分成两部分，往一部分溶液中加入锂源，另一部分溶液中加入钛源，再混合两部分溶液制得溶胶；
(3)将溶胶加热至40～100℃，恒温搅拌4～10h，形成凝胶；
(4)将凝胶在100～200℃下去除溶剂得到前驱体；
(5)将前驱体在惰性气氛下加热到700～1000℃，然后在还原性气氛下煅烧5～20h，最后经冷却、研磨，得到氮掺杂钛酸锂复合材料。
所述的氮掺杂钛酸锂复合材料的制备方法，其中，步骤(1)中，所述纳米粒子选自纳米钛、纳米铝、纳米钒、纳米锆、纳米钽、纳米镁、纳米钙、纳米硼、纳米锰、纳米钨、纳米氮化碳和纳米氮化钛中一种或多种。
所述的氮掺杂钛酸锂复合材料的制备方法，其中，步骤(1)中，所述分散剂选自聚乙二醇、十二烷基硫酸钠、三乙基己基磷酸、甲基戊醇、纤维素衍生物、聚丙烯酰胺、古尔胶、脂肪酸聚乙二醇酯和硅烷偶联剂中的一种或多种。
所述的氮掺杂钛酸锂复合材料的制备方法，其中，步骤(2)中，所述锂源选自氢氧化锂、醋酸锂和硝酸锂中的一种或多种。
所述的氮掺杂钛酸锂复合材料的制备方法，其中，步骤(2)中，所述钛源选自钛酸丁酯、四氯化钛、偏钛酸、钛酸正丙酯、钛酸异丙酯和乙酰丙酮氧化钛合钛酸酯偶联剂中的一种或多种。
所述的氮掺杂钛酸锂复合材料的制备方法，其中，步骤(2)中，所述锂源、钛源和纳米粒子的物质的量之比为0.75-0.90:1:0.01-0.1。
所述的氮掺杂钛酸锂复合材料的制备方法，其中，步骤(5)中，所述惰性气氛选自氩气、氮气和氦气中的一种。
所述的氮掺杂钛酸锂复合材料的制备方法，其中，步骤(5)中，所述还原性气氛选自氨气和氮氢混合气中的一种。
一种氮掺杂钛酸锂复合材料，其中，采用本发明所述的氮掺杂钛酸锂复合材料的制备方法制备得到。
一种锂离子电池，包括负极，其中，所述负极的材料为本发明所述的氮掺杂钛酸锂复合材料。
有益效果：本发明制备的氮掺杂钛酸锂复合材料电子导电性良好，锂离子扩散速度快，结构稳定；辅助氮掺杂纳米粒子的引入不但有效抑制了四价钛离子的活跃性，较大程度上缓解了电解液被四价钛离子催化裂解而产生气体的问题，还稳定了钛酸锂的晶体结构，增加了钛酸锂材料在脱嵌锂过程中的晶格稳定性，延 长了钛酸锂电池的使用寿命。另外，本发明制备工艺简单，过程参数易控，生产成本较低，适用于工业化大规模生产。
附图说明
图1为实施例1，实施例2和实施例3制得的氮掺杂钛酸锂复合材料的XRD图；
图2为实施例1制得的氮掺杂钛酸锂复合材料与常规未氮化钛酸锂材料的EIS对比图；
图3为实施例1制得的氮掺杂钛酸锂复合材料0.2C的首次充放电曲线图；
图4为实施例2制得的氮掺杂钛酸锂复合材料5C的首次充放电曲线图；
图5为实施例2制得的氮掺杂钛酸锂复合材料5C充放的循环性能图。
具体实施方式
本发明提供一种氮掺杂钛酸锂复合材料及其制备方法与锂离子电池，为使本发明的目的、技术方案及效果更加清楚、明确，以下对本发明进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。
本发明提供一种氮掺杂钛酸锂复合材料的制备方法，其中，包括以下步骤：
(1)将纳米粒子分散于含有分散剂的溶剂中；
(2)将上述分散有纳米粒子的溶剂分成两部分，往一部分溶液中加入锂源，另一部分溶液中加入钛源，再混合两部分溶液制得溶胶；
(3)将溶胶加热至40～100℃，恒温搅拌4～10h，形成凝胶；
(4)将凝胶在100～200℃下去除溶剂得到前驱体；
(5)将前驱体在惰性气氛下加热到700～1000℃，然后在还原性气氛下煅烧5～20h，最后经冷却、研磨，得到氮掺杂钛酸锂复合材料。
所述步骤(1)具体包括：首先将分散剂加入溶剂(如无水乙醇)当中，然后将纳米粒子超声分散于含有分散剂的溶剂当中，超声分散的时间为1.5-2.5h(如2h)。
优选地，所述纳米粒子选自纳米钛、纳米铝、纳米钒、纳米锆、纳米钽、纳米镁、纳米钙、纳米硼、纳米锰、纳米钨、纳米氮化碳和纳米氮化钛等中一种或多种。
优选地，所述分散剂选自聚乙二醇、十二烷基硫酸钠、三乙基己基磷酸、甲 基戊醇、纤维素衍生物、聚丙烯酰胺、古尔胶、脂肪酸聚乙二醇酯和硅烷偶联剂等中的一种或多种。
所述步骤(2)具体包括：将上述分散有纳米粒子的溶剂分成两部分，往一部分溶液中加入锂源，另一部分溶液中加入钛源，再混合两部分溶液制得溶胶。若往分散有纳米粒子的溶剂中直接加入锂源和钛源，锂源和钛源会快速反应掉，影响目标产物的粒径、形貌和性能。本发明采用往两部分溶液中分别加入锂源和钛源，然后再混合两部分溶液，这样分开加入能更好的形成溶胶。
优选地，所述锂源选自氢氧化锂、醋酸锂和硝酸锂等中的一种或多种。
优选地，所述钛源选自钛酸丁酯、四氯化钛、偏钛酸、钛酸正丙酯、钛酸异丙酯和乙酰丙酮氧化钛合钛酸酯偶联剂等中的一种或多种。
优选地，所述锂源、钛源和纳米粒子的物质的量之比为0.75-0.90:1:0.01-0.1。保持锂离子3％左右的过剩，可以补充烧结过程中的锂损失，有利于晶粒的完整性。
所述步骤(5)具体包括：将前驱体在惰性气氛中以4-6℃/min升温至700～1000℃，将惰性气氛切换为还原性气氛，恒温煅烧5～20h，然后将还原性气氛切换为惰性气氛，自然冷却至室温后，研磨，过筛，得到氮掺杂纳米钛酸锂粉体。上述高温条件下使用还原性气氛是为了辅助氮参杂，升温和降温过程采用惰性气氛是为了保证目标产物的结构稳定性。
优选地，所述惰性气氛选自氩气、氮气和氦气等中的一种。
优选地，所述还原性气氛选自氨气和氮氢混合气等中的一种。
本发明辅助氮掺杂的纳米粒子本身释放氮元素帮助钛酸锂氮化，或者与氮元素反应产生具有高电子导电性的氮化物，或者夺取钛酸锂中的氧分子形成氧化物同时帮助钛酸锂转变为氮化钛酸锂。
下面对本发明氮掺杂钛酸锂复合材料的形成机理作进一步地说明：在钛酸锂的形成过程中，由于还原性气氛的存在，例如氮气氛，产物颗粒晶化的过程中部分氧位置会被活泼的氮占据，实现氮掺杂。另外，掺入的纳米离子本身释放氮元素来占据部分氧的位置，或者夺取了钛酸锂中的氧原子形成了氧化物，而钛酸锂中的氧位置被氮原子所占据，进一步辅助氮掺杂。
本发明与现有技术相比，采用引入辅助氮掺杂纳米粒子的方法来制备电子导 电性良好，锂离子扩散速度快的氮掺杂钛酸锂复合材料，解决了现有钛酸锂材料应用于高倍率充放电过程中遇到的电子导电率较低和晶界电阻较大的问题；辅助氮掺杂纳米粒子的引入不但有效抑制了四价钛离子的活跃性，较大程度上缓解了电解液被四价钛离子催化裂解而产生气体的问题，还稳定了钛酸锂的晶体结构，增加了钛酸锂材料在脱嵌锂过程中的晶格稳定性，延长了钛酸锂电池的使用寿命。另外，本方法制备工序简单，适用于对现有钛酸锂材料的改性生产，生产成本较低，适用于工业化大规模生产。
本发明还提供一种氮掺杂钛酸锂复合材料，其中，采用本发明所述的氮掺杂钛酸锂复合材料的制备方法制备得到。
本发明还提供一种锂离子电池，包括负极，其中，所述负极的材料为本发明所述的氮掺杂钛酸锂复合材料。
下面通过实施例对本发明进一步说明。
实施例1
本实施例氮掺杂钛酸锂复合材料的制备方法，包括以下步骤：
称取醋酸锂4.25g，钛酸丁酯17.36g，纳米金属钛粉0.48g，聚乙二醇1g，无水乙醇25g。
首先将聚乙二醇加入无水乙醇当中，然后将纳米钛粉超声分散于含有聚乙二醇的无水乙醇当中，超声分散2h。
取分散有纳米钛粉的无水乙醇15g，将钛酸丁酯加入其中，将醋酸锂加入其余分散有纳米钛粉的无水乙醇当中，搅拌条件下混合两种溶液制得溶胶。
将溶胶加热至60℃，恒温搅拌4h，形成凝胶。
将凝胶在120℃条件下烘干得到前驱体。
将前驱体在氩气气氛中以5℃/min升温至700℃，将氩气气氛切换为氨气气氛，恒温5h，然后将氨气气氛切换为氩气气氛，自然冷却至室温后，研磨，过150目筛，得到氮掺杂纳米钛酸锂粉体。粉体颜色为白色。经X-射线粉末衍射(XRD)测试后为单一尖晶石结构的钛酸锂，如图1中a所示。
电化学测试是在以下条件进行：以制备的氮掺杂钛酸锂复合材料为活性物质，Super P(超级炭)为导电剂，PVDF(聚偏氟乙烯)为粘结剂，NMP(N-甲基-2-吡咯烷酮)为溶剂调成料浆涂于铜箔上作成电极片。以锂片作为对电极，电解液浓 度为1mol/L，聚丙烯微孔膜为电池的隔膜，组装成测试电池。在充满氩气的手套箱中组装成扣式电池，进行电化学测试。充放电电压范围为1.0～2.5V。将产品按上述方法组装成电池，0.2C时首次放电容量大于190mAh/g，充电容量接近180mAh/g，如图3所示。氮掺杂后钛酸锂(LTON)电阻明显降低，其电化学阻抗与未氮化钛酸锂(LTO)比较如图2所示。
实施例2
本实施例氮掺杂钛酸锂复合材料的制备方法，包括以下步骤：
称取醋酸锂4.25g，钛酸丁酯17.36g，纳米金属钛粉0.48g，聚乙二醇1g，无水乙醇25g。
首先将聚乙二醇加入无水乙醇当中，然后将纳米金属钛粉超声分散于含有聚乙二醇的无水乙醇当中，超声分散2h。
取分散有纳米金属钛粉的无水乙醇15g，将钛酸丁酯加入其中，将醋酸锂加入其余分散有纳米金属钛粉的无水乙醇当中，搅拌条件下混合两种溶液制得溶胶。
将溶胶加热至60℃，恒温搅拌4h，形成凝胶。
将凝胶在120℃条件下烘干得到前驱体。
将前驱体在氩气气氛中以5℃/min升温至800℃，将氩气气氛切换为氨气气氛，恒温5h，然后将氨气气氛切换为氩气气氛，最后自然冷却至室温后，研磨，过150目筛，得到氮掺杂钛酸锂粉体。氮掺杂钛酸锂粉体颜色为浅灰色。经X-射线粉末衍射(XRD)测试后为单一尖晶石结构的钛酸锂，如图1中b所示。
制得的氮掺杂钛酸锂粉体按实施例1的方法组装成电池，5C时首次放电容量为160mAh/g左右，充电容量为155mAh/g左右，如图4所示。经过12000次循环以后容量保持率大于80％，如图5所示。
实施例3
本实施例氮掺杂钛酸锂复合材料的制备方法，包括以下步骤：
称取醋酸锂4.25g，钛酸丁酯17.36g，纳米金属钛粉0.48g，聚乙二醇1g，无水乙醇25g。
首先将聚乙二醇加入无水乙醇当中，然后将纳米金属钛粉超声分散于含有聚乙二醇的无水乙醇当中，超声分散2h。
取分散有纳米金属钛粉的无水乙醇15g，将钛酸丁酯加入其中，将醋酸锂加 入其余分散有纳米金属钛粉的无水乙醇当中，搅拌条件下混合两种溶液制得溶胶。
将溶胶加热至60℃，恒温搅拌4h，形成凝胶。
将凝胶在120℃条件下烘干得到前驱体。
将前驱体在氩气气氛中以5℃/min升温至900℃，将氩气气氛切换为氨气气氛，恒温5h，然后将氨气气氛切换为氩气气氛，自然冷却至室温后，研磨，过150目筛，得到氮掺杂钛酸锂粉体。粉体颜色为深灰色。经X-射线粉末衍射(XRD)测试后为单一尖晶石结构的钛酸锂，如图1中c所示。
实施例4
其他条件与实施例1相同，不同的是将纳米金属钛粉替换为纳米金属铝粉，同样在氨气气氛中进行煅烧，温度为700℃，恒温时间为5h，得到氮掺杂钛酸锂粉体。得到的产品按实施例1的方法组装成电池，5C时首次充放电容量约为150mAh/g，100次循环后容量约为110mAh/g。
实施例5
其他条件与实施例1相同，不同的是将纳米金属钛粉替换为纳米金属钒粉，同样在氨气气氛中进行煅烧，温度为700℃，恒温时间为5h，得到氮掺杂钛酸锂粉体。得到的产品按实施例1的方法组装成电池，5C时首次充放电容量约为152mAh/g，100次循环后容量约为115mAh/g。
综上所述，本发明提供的一种氮掺杂钛酸锂复合材料及其制备方法与锂离子电池。本发明采用引入辅助氮掺杂纳米粒子的方法来制备电子导电性良好，锂离子扩散速度快的氮掺杂钛酸锂复合材料，解决了现有钛酸锂材料应用于高倍率充放电过程中遇到的电子导电率较低和晶界电阻较大的问题；辅助氮掺杂纳米粒子的引入不但有效抑制了四价钛离子的活跃性，较大程度上缓解了电解液被四价钛离子催化裂解而产生气体的问题，还稳定了钛酸锂的晶体结构，增加了钛酸锂材料在脱嵌锂过程中的晶格稳定性，延长了钛酸锂电池的使用寿命。另外，本方法制备工序简单，所用钛酸锂可以是通过任何方法合成而不会影响复合材料性能，适用于对现有钛酸锂材料的改性生产，生产成本较低，适用于工业化大规模生产。
应当理解的是，本发明的应用不限于上述的举例，对本领域普通技术人员来说，可以根据上述说明加以改进或变换，所有这些改进和变换都应属于本发明所附权利要求的保护范围。

Claims (10)

  1. 一种氮掺杂钛酸锂复合材料的制备方法，其特征在于，包括以下步骤：
    (1)将纳米粒子分散于含有分散剂的溶剂中；
    (2)将上述分散有纳米粒子的溶剂分成两部分，往一部分溶液中加入锂源，另一部分溶液中加入钛源，再混合两部分溶液制得溶胶；
    (3)将溶胶加热至40～100℃，恒温搅拌4～10h，形成凝胶；
    (4)将凝胶在100～200℃下去除溶剂得到前驱体；
    (5)将前驱体在惰性气氛下加热到700～1000℃，然后在还原性气氛下煅烧5～20h，最后经冷却、研磨，得到氮掺杂钛酸锂复合材料。
  2. 根据权利要求1所述的氮掺杂钛酸锂复合材料的制备方法，其特征在于，步骤(1)中，所述纳米粒子选自纳米钛、纳米铝、纳米钒、纳米锆、纳米钽、纳米镁、纳米钙、纳米硼、纳米锰、纳米钨、纳米氮化碳和纳米氮化钛中一种或多种。
  3. 根据权利要求1所述的氮掺杂钛酸锂复合材料的制备方法，其特征在于，步骤(1)中，所述分散剂选自聚乙二醇、十二烷基硫酸钠、三乙基己基磷酸、甲基戊醇、纤维素衍生物、聚丙烯酰胺、古尔胶、脂肪酸聚乙二醇酯和硅烷偶联剂中的一种或多种。
  4. 根据权利要求1所述的氮掺杂钛酸锂复合材料的制备方法，其特征在于，步骤(2)中，所述锂源选自氢氧化锂、醋酸锂和硝酸锂中的一种或多种。
  5. 根据权利要求1所述的氮掺杂钛酸锂复合材料的制备方法，其特征在于，步骤(2)中，所述钛源选自钛酸丁酯、四氯化钛、偏钛酸、钛酸正丙酯、钛酸异丙酯和乙酰丙酮氧化钛合钛酸酯偶联剂中的一种或多种。
  6. 根据权利要求1所述的氮掺杂钛酸锂复合材料的制备方法，其特征在于，步骤(2)中，所述锂源、钛源和纳米粒子的物质的量之比为0.75-0.90:1:0.01-0.1。
  7. 根据权利要求1所述的氮掺杂钛酸锂复合材料的制备方法，其特征在于，步骤(5)中，所述惰性气氛选自氩气、氮气和氦气中的一种。
  8. 根据权利要求1所述的氮掺杂钛酸锂复合材料的制备方法，其特征在于，步骤(5)中，所述还原性气氛选自氨气和氮氢混合气中的一种。
  9. 一种氮掺杂钛酸锂复合材料，其特征在于，采用权利要求1-8任一项所述的氮掺杂钛酸锂复合材料的制备方法制备得到。
  10. 一种锂离子电池，包括负极，其特征在于，所述负极的材料为权利要求9所述的氮掺杂钛酸锂复合材料。
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