WO2024000814A1 - 一种正极活性材料的制备方法及其应用 - Google Patents

一种正极活性材料的制备方法及其应用 Download PDF

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WO2024000814A1
WO2024000814A1 PCT/CN2022/118008 CN2022118008W WO2024000814A1 WO 2024000814 A1 WO2024000814 A1 WO 2024000814A1 CN 2022118008 W CN2022118008 W CN 2022118008W WO 2024000814 A1 WO2024000814 A1 WO 2024000814A1
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preparation
precursor
active material
present
accelerator
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王雀乐
李长东
阮丁山
刘伟健
缪建麟
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广东邦普循环科技有限公司
湖南邦普循环科技有限公司
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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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    • H01M4/625—Carbon or graphite
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    • Y02E60/10—Energy storage using batteries

Definitions

  • the invention belongs to the technical field of lithium-ion battery materials, and specifically relates to a preparation method of a positive active material and its application.
  • Li 5 FeO 4 has the advantages of low charging voltage platform and high theoretical capacity. It is an excellent electrochemical active material, but traditional synthesis There are still some problems with the Li 5 FeO 4 method.
  • the common preparation method uses a hydrothermal method to prepare an iron source, and then uses a high-temperature solid-state sintering method to synthesize Li 5 FeO 4 , or directly uses micron-sized iron oxide and lithium hydroxide to directly solidify it at high temperature. Phase sintering synthesis.
  • the main disadvantages of these two methods are that they require high energy consumption, low production capacity, or the primary particles of the synthetic materials are large, resulting in long lithium ion migration paths, relatively low capacity, and poor stability. Resulting in higher production costs.
  • Li 5 FeO 4 materials generally have the problem of poor conductivity.
  • the present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a preparation method of positive active materials and its application. The process is simple, relatively energy-saving, and the produced product has the advantages of good conductivity and high capacity.
  • a preparation method of cathode active material including the following steps:
  • the reactions involved in the above process mainly include:
  • Step S3 sintering process (taking lithium hydroxide monohydrate as an example): 1Fe 3 O 4 ⁇ 3FeO+0.5O 2 ; 22FeO+0.5O 2 ⁇ Fe 2 O 3 ; 3Fe 2 O 3 +10LiOH ⁇ H 2 O ⁇ 2Li 5 FeO 4 +15H 2 O.
  • iron ferric oxide has poor stability in the presence of moisture (the precursor contains a small amount of water, and the lithium hydroxide has a high amount of lithium, contains bound water, and the hydroxyl group will dehydrate at high temperatures). It is easy to decompose into ferrous oxide and oxygen. Ferrous oxide is also very unstable. When it encounters oxygen, it will be immediately oxidized into ferric oxide.
  • the temperature of the self-propagating reaction in step S2 is approximately 200-300°C, and the carbon source will not be oxidized at this temperature.
  • step S1 the pH of the mixed solution is 1-5.
  • the dispersant is at least one of polyethylene glycol, polyvinyl alcohol or polyethylene oxide.
  • step S1 the added amount of the dispersant is 1-20% of the mass of the conductive carbon source.
  • the conductive carbon source is at least one of carbon nanotubes, graphite powder, glucose or conductive carbon black.
  • the particle size Dv50 of the conductive carbon source is 80 nm-200 nm.
  • step S1 the amount of the conductive carbon source added is 2-10% by weight of the final theoretical output of Li 5 FeO 4 .
  • the amount of the conductive carbon source added is 4-8% by weight of the final theoretical output of Li 5 FeO 4 .
  • the accelerator is at least one of acetaldehyde, ethyl acetate, formic acid or ethylene glycol.
  • step S1 the molar ratio of the accelerator to nitrate ions in the mixed solution is 1.1-1.3.
  • step S1 the specific preparation process of the mixed solution is: adding the dispersant and conductive carbon source to the acidic ferric nitrate solution to obtain a dispersion, and mixing the accelerator with water to obtain an accelerator. solution, and then mix the dispersion liquid and the accelerator solution to obtain the mixed liquid.
  • step S1 the concentration of the acidic ferric nitrate solution is 0.1-5 mol/L.
  • step S1 the pH of the acidic ferric nitrate solution is ⁇ 5.0.
  • step S1 the concentration of the accelerator solution is 0.2-10 mol/L.
  • step S2 heating to above 50°C can induce the self-propagating reaction.
  • the particle size Dv50 of the precursor is 100-500 nm.
  • step S2 the water content of the precursor is 0.3-0.8wt%.
  • the micro-oxygen atmosphere is composed of inert gas and oxygen, wherein the oxygen content is 0.3-1.3%.
  • the oxygen content in the micro-oxygen atmosphere is 0.3-1.3%.
  • the purpose of using inert gas protection is to prevent the carbon source from being oxidized due to excessive oxygen content.
  • the lithium source is at least one of lithium hydroxide monohydrate, lithium oxide or anhydrous lithium hydroxide.
  • the lithium source is lithium hydroxide monohydrate.
  • step S3 the molar ratio of Li in the lithium source to Fe in the precursor is 5.0-5.8.
  • the sintering temperature is 480-700°C.
  • step S3 the sintering time is 6-20 h.
  • the hydrocarbon gas is selected from at least one of methane, acetylene or ethylene.
  • step S4 the particle size Dv50 of the cathode active material Li 5 FeO 4 is 3-6 ⁇ m.
  • step S4 the vacuum vapor deposition coating is performed at 250-700°C. Further, the processing time of the vacuum vapor deposition coating is 2-8 hours.
  • step S4 the pressure of the vacuum vapor deposition coating is -20 ⁇ 5kpa.
  • the invention also provides the application of the preparation method in preparing lithium ion batteries.
  • the present invention synthesizes nanoscale precursors through a self-propagating reaction between oxidizing substances and reducing substances, and introduces a higher content of carbon source substances in the precursor synthesis stage, which can effectively suppress the growth of material particles when synthesizing materials. It is large and improves the conductivity of the material at the same time; through this synthesis process, the cathode active material Li 5 FeO 4 with fine and uniform particles and high capacity can be synthesized.
  • the present invention uses specific raw materials to induce a violent self-propagating reaction under certain heating conditions, releasing a large amount of heat, the solvent evaporates into gas, and the materials are evaporated to dryness while reacting, thereby obtaining a precursor with fine and uniform particles.
  • This synthesis method is suitable for The equipment requirements are low, the synthesis process is simple, relatively energy-saving, the processing cost is low, the efficiency is high, and it is easy to realize industrialization.
  • Figure 1 is a schematic diagram of the synthesis process of the present invention
  • Figure 2 is an SEM image of the precursor synthesized in Example 1 of the present invention.
  • Figure 3 is an SEM image of Li 5 FeO 4 synthesized in Example 1 of the present invention.
  • Figure 4 is the charge and discharge curve of Li 5 FeO 4 synthesized in Example 1 of the present invention.
  • Figure 5 is an SEM image of Li 5 FeO 4 synthesized in Example 2 of the present invention.
  • Figure 6 is the charge and discharge curve of Li 5 FeO 4 synthesized in Example 2 of the present invention.
  • Figure 7 is an SEM image of Li 5 FeO 4 synthesized in Comparative Example 1;
  • Figure 8 is the charge and discharge curve of Li 5 FeO 4 synthesized in Comparative Example 1.
  • a lithium ion battery cathode active material Li 5 FeO 4 is prepared. Refer to Figure 1. The specific process is:
  • step (3) Add the accelerator solution prepared in step (2) to the acidic ferric nitrate solution prepared in step (1), stir thoroughly to obtain a mixed solution with a pH of 3.5, and heat it to make the temperature in the solution system higher than 50 °C, at this time, a self-propagating reaction can be initiated, a large amount of heat is released, the solvent is evaporated, and a precursor Fe 3 O 4 with a particle size Dv50 of 200 nm and a water content of 0.5wt% is obtained, see Figure 2;
  • the obtained Fe 3 O 4 is mixed with lithium hydroxide monohydrate, where the molar ratio of Li/Fe is 5.3.
  • the mixing equipment used is a high-speed mixer with a mixing speed of 600 rpm.
  • the mixed materials are mixed in a nitrogen atmosphere (oxygen Content is 0.7%), the sintering temperature is 700°C, the sintering time is 18h, and Li 5 FeO 4 block material can be obtained;
  • Li 5 FeO 4 block material Pulverize the obtained Li 5 FeO 4 block material under a nitrogen atmosphere, control its Dv50 at 4-6 ⁇ m, and perform vacuum vapor deposition coating on the crushed material.
  • the gas used is a mixture of methane and acetylene with a molar ratio of 4:1. Mixed gas, in which the coating temperature is 400°C, the time is 8h, and the pressure is -20kpa. After the coating is completed, the cathode active material Li 5 FeO 4 with good performance can be obtained.
  • a lithium ion battery cathode active material Li 5 FeO 4 is prepared.
  • the specific process is:
  • step (3) Add the accelerator solution prepared in step (2) to the acidic ferric nitrate solution prepared in step (1), stir thoroughly to obtain a mixed solution with a pH of 4.0, and heat it to make the temperature in the solution system higher than 50 °C, at this time, a self-propagating reaction can be triggered, a large amount of heat is released, the solvent is evaporated, and a precursor Fe 3 O 4 with a Dv50 of 250nm and a water content of 0.6wt% is obtained;
  • the obtained Fe 3 O 4 is mixed with lithium hydroxide monohydrate, where the molar ratio of Li/Fe is 5.2.
  • the mixing equipment used is a high-speed mixer with a mixing speed of 600 rpm.
  • the mixed materials are mixed in a nitrogen atmosphere (oxygen Content is 1.0%), the sintering temperature is 670°C, the sintering time is 18h, and Li 5 FeO 4 block material can be obtained;
  • Li 5 FeO 4 block material Pulverize the obtained Li 5 FeO 4 block material under a nitrogen atmosphere, control its Dv50 at 4-6 ⁇ m, and perform vacuum vapor deposition coating on the crushed material.
  • the gas used is a molar ratio of methane and acetylene of 4:1.
  • Mixed gas in which the coating temperature is 400°C, the time is 8h, and the pressure is -20kpa. After the coating is completed, the cathode active material Li 5 FeO 4 with good performance can be obtained.
  • a lithium-ion battery cathode active material Li 5 FeO 4 was prepared using a traditional high-temperature solid-state method, using conventional existing iron oxide (Dv50 is 3 ⁇ m, BET is 25 m 2 /g) as the iron source, and carbon nanotubes are Carbon source, the specific process is:
  • the Li 5 FeO 4 synthesized in Examples 1, 2 and Comparative Example 1 are respectively made into button batteries, which require steps such as slurry preparation, coating, drying, tableting, assembly, and cabinet testing: 1 Prepare the slurry , weigh 10g of material and mix it with conductive agent and binder. The mass ratio of material: conductive agent: binder is 8:1:1. The binder used is PVDF, and the solvent used is N-methylpyrrolidone.
  • the agent is conductive carbon; 2 Coating, use a scraper to coat on the aluminum foil; the coating thickness is controlled to 200 ⁇ m ⁇ 30 ⁇ m, 3 Drying, dry the coated pole piece in a vacuum drying oven, the drying temperature is 120 °C, drying time is 2 hours; 4 Pressing, use a roller machine to press the dried pole pieces into tablets; 5 Assemble the positive electrode piece, negative electrode piece, separator, electrolyte and other battery parts into a button battery. The specific capacity was tested under the conditions of charging voltage 4.25V and charging rate 0.1C.
  • Figure 4 is the charge and discharge curve of Li 5 FeO 4 synthesized in Example 1. It can be seen from the figure that its capacity can reach 625mAh/g.
  • Figure 6 is the charge and discharge curve of Li 5 FeO 4 synthesized in Example 2. It can be seen from the figure that its capacity can reach 648mAh/g.
  • Figure 8 shows the charge and discharge curve of Li 5 FeO 4 synthesized in Comparative Example 1. It can be seen from the figure that its capacity can reach 512mAh/g.

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Abstract

本发明公开了一种正极活性材料的制备方法及其应用，将分散剂、导电碳源、硝酸铁、促进剂和水混合配制成酸性的混合液，将混合液加热至诱发其发生自蔓延反应，反应结束后得到前驱体，将前驱体与锂源混合，在微氧气氛下进行烧结，将烧结料进行粉碎，所得粉碎料用烃类气体进行真空气相沉积包覆，即得正极活性材料。本发明通过氧化性物质与还原性物质发生自蔓延反应合成纳米级的前驱体，并在前驱体合成阶段就引入较高含量的碳源物质，这在合成材料时可有效抑制材料颗粒长大，同时改善材料的导电性；通过该合成工艺，能合成颗粒细小均匀，容量较高的正极活性材料。

Description

一种正极活性材料的制备方法及其应用 技术领域
本发明属于锂离子电池材料技术领域，具体涉及一种正极活性材料的制备方法及其应用。
背景技术
目前，新能源汽车市场需求发展迅猛，产能不断扩张，锂电池销量也随之不断扩张。目前，市场对于锂电池的关键指标循环容量密度要求也越来越高，锂离子电池在首次充放电时，由于SEI膜的形成以及充放电效率低，会造成部分锂离子损失，进而导致锂离子电池循环容量偏低，为解决此问题，通常在正极材料中加入活性材料进行改善，而Li 5FeO 4具有充电电压平台低，理论容量高的优点，是优良的电化学活性物质，但传统合成Li 5FeO 4方法仍存在一些问题，常见的制备方法利用水热法制备铁源，再利用高温固相烧结法进行合成Li 5FeO 4，或者直接利用微米级氧化铁与氢氧化锂直接高温固相烧结合成，这两种方法的缺点主要是所需要能耗较高，产能较低，或者合成材料的一次颗粒大，造成锂离子迁移路径长，容量相对较低，稳定性也较差，进而造成生产成本较高。此外，Li 5FeO 4材料还普遍存在导电性差的问题。
发明内容
本发明旨在至少解决上述现有技术中存在的技术问题之一。为此，本发明提出一种正极活性材料的制备方法及其应用，该工艺简单，相对节能，制得的产品具有导电性好，容量高的优点。
根据本发明的一个方面，提出了一种正极活性材料的制备方法，包括以下步骤：
S1：将分散剂、导电碳源、硝酸铁、促进剂和水混合配制成酸性的混合液，其中所述促进剂为还原性有机物；
S2：将所述混合液加热至诱发其发生自蔓延反应，反应结束后得到前驱体；
S3：将所述前驱体与锂源混合，在微氧气氛下进行烧结，得到烧结料；
S4：将所述烧结料进行粉碎，所得粉碎料用烃类气体进行真空气相沉积包覆，即得正极 活性材料Li 5FeO 4。
以上过程涉及的反应主要有：
(1)步骤S2前驱体的生成：2Fe 3++Fe 2++4O 2-→Fe 3O 4，其中的亚铁离子来源于过量的促进剂还原。
(2)步骤S3烧结过程(以单水氢氧化锂为例)：①Fe 3O 4→3FeO+0.5O 2；②2FeO+0.5O 2→Fe 2O 3；③Fe 2O 3+10LiOH·H 2O→2Li 5FeO 4+15H 2O。烧结过程中，四氧化三铁在有水分情况下(前驱体含有少量水，以及氢氧化锂配锂量高，含结合水，以及羟基在高温下均会脱水)，稳定性较差，在高温下容易分解为氧化亚铁和氧气，氧化亚铁也很不稳定，遇到氧气会立刻被氧化成三氧化二铁。
需要说明的是，步骤S2中所述自蔓延反应的温度大概在200-300℃，此温度下不会造成碳源的氧化。
在本发明的一些实施方式中，步骤S1中，所述混合液的pH为1-5。
在本发明的一些实施方式中，步骤S1中，所述分散剂为聚乙二醇、聚乙烯醇或聚氧化乙烯中的至少一种。
在本发明的一些实施方式中，步骤S1中，所述分散剂的添加量为所述导电碳源质量的1-20％。
在本发明的一些实施方式中，步骤S1中，所述导电碳源为碳纳米管、石墨粉、葡萄糖或导电炭黑中的至少一种。优选的，所述导电碳源的粒径Dv50为80nm-200nm。
在本发明的一些实施方式中，步骤S1中，所述导电碳源的添加量为最终理论产出Li 5FeO 4重量的2-10％。优选的，所述导电碳源的添加量为最终理论产出Li 5FeO 4重量的4-8％。
在本发明的一些实施方式中，步骤S1中，所述促进剂为乙醛、乙酸乙酯、甲酸或乙二醇中的至少一种。
在本发明的一些实施方式中，步骤S1中，所述混合液中，所述促进剂与硝酸根离子的摩尔比为1.1-1.3。
在本发明的一些实施方式中，步骤S1中，所述混合液的具体配制过程为：将分散剂和导电碳源加入到酸性硝酸铁溶液中得到分散液，将促进剂与水混合得到促进剂溶液，再将所述 分散液和所述促进剂溶液混合，得到所述混合液。
在本发明的一些实施方式中，步骤S1中，所述酸性硝酸铁溶液的浓度为0.1-5mol/L。
在本发明的一些实施方式中，步骤S1中，所述酸性硝酸铁溶液的pH＜5.0。
在本发明的一些实施方式中，步骤S1中，所述促进剂溶液的浓度为0.2-10mol/L。
在本发明的一些实施方式中，步骤S2中，加热至50℃以上可诱发所述自蔓延反应。
在本发明的一些实施方式中，步骤S2中，所述前驱体的粒径Dv50为100-500nm。
在本发明的一些实施方式中，步骤S2中，所述前驱体的水含量为0.3-0.8wt％。
在本发明的一些实施方式中，步骤S3中，所述微氧气氛由惰性气与氧气组成，其中氧气含量为0.3-1.3％。优选的，所述微氧气氛中氧气含量为0.3-1.3％。采用惰性气保护的目的是防止氧气含量过高导致碳源被氧化。
在本发明的一些实施方式中，步骤S3中，所述锂源为单水氢氧化锂、氧化锂或无水氢氧化锂中的至少一种。优选的，所述锂源为单水氢氧化锂。
在本发明的一些实施方式中，步骤S3中，所述锂源中的Li与所述前驱体中的Fe的摩尔比为5.0-5.8。
在本发明的一些实施方式中，步骤S3中，所述烧结的温度为480-700℃。
在本发明的一些实施方式中，步骤S3中，所述烧结的时间为6-20h。
在本发明的一些实施方式中，步骤S4中，所述烃类气体选自甲烷、乙炔或乙烯中的至少一种。
在本发明的一些实施方式中，步骤S4中，所述正极活性材料Li 5FeO 4的粒径Dv50为3-6μm。
在本发明的一些实施方式中，步骤S4中，所述真空气相沉积包覆在250-700℃下进行。进一步地，所述真空气相沉积包覆的处理时间为2-8h。
在本发明的一些实施方式中，步骤S4中，所述真空气相沉积包覆的压力为-20～5kpa。
本发明还提供所述的制备方法在制备锂离子电池中的应用。
根据本发明的一种优选的实施方式，至少具有以下有益效果：
1、本发明通过氧化性物质与还原性物质发生自蔓延反应合成纳米级的前驱体，并在前驱 体合成阶段就引入较高含量的碳源物质，这在合成材料时可有效抑制材料颗粒长大，同时改善材料的导电性；通过该合成工艺，能合成颗粒细小均匀，容量较高的正极活性材料Li 5FeO 4。
2、本发明采用特定的原料在一定加热条件下诱发产生剧烈的自蔓延反应，放出大量热量，溶剂蒸发成气体，物料边反应边蒸干，即得到颗粒细小均匀的前驱体，该合成方法对设备要求较低，合成工艺简单，相对节能，加工成本低，效率高，易于实现产业化。
附图说明
下面结合附图和实施例对本发明做进一步的说明，其中：
图1为本发明的合成工艺示意图；
图2为本发明实施例1合成的前驱体SEM图；
图3为本发明实施例1合成的Li 5FeO 4的SEM图；
图4为本发明实施例1合成的Li 5FeO 4的充放电曲线；
图5为本发明实施例2合成的Li 5FeO 4的SEM图；
图6为本发明实施例2合成的Li 5FeO 4的充放电曲线；
图7为对比例1合成的Li 5FeO 4的SEM图；
图8为对比例1合成的Li 5FeO 4的充放电曲线。
具体实施方式
以下将结合实施例对本发明的构思及产生的技术效果进行清楚、完整地描述，以充分地理解本发明的目的、特征和效果。显然，所描述的实施例只是本发明的一部分实施例，而不是全部实施例，基于本发明的实施例，本领域的技术人员在不付出创造性劳动的前提下所获得的其他实施例，均属于本发明保护的范围。
实施例1
本实施例制备了一种锂离子电池正极活性材料Li 5FeO 4，参照图1，具体过程为：
(1)配制10L浓度为1mol/L的酸性硝酸铁溶液，并缓慢加入浓度为95％的浓硝酸，利用pH计调节溶液pH为2.5，并在溶液中加入一定比例的分散剂和导电碳源，该实施例分散剂选用聚乙二醇，其添加量为导电碳源重量的15％，导电碳源选用Dv50为80nm的碳纳米管， 其添加量为最终合成Li 5FeO 4材料理论重量的5％；
(2)配置浓度为2mol/L的促进剂溶液，其活性物质为乙醛，乙醛的用量为酸性硝酸铁溶液中硝酸根离子摩尔量的1.15倍；
(3)把步骤(2)所配促进剂溶液加入到步骤(1)所配酸性硝酸铁溶液中，充分搅拌得到pH为3.5的混合液，并对其加热，使溶液体系内温度高于50℃，此时可引发自蔓延反应，放出大量热量，把溶剂蒸发，得到粒径Dv50为200nm、水含量为0.5wt％的前驱体Fe 3O 4，参见图2；
(4)所得Fe 3O 4与单水氢氧化锂进行混合，其中Li/Fe的摩尔比为5.3，所用混合设备为高速混合机，混合转速为600rpm，其中，混合后物料在氮气氛围(氧含量为0.7％)下进行烧结，烧结温度为700℃，烧结时间为18h，可得Li 5FeO 4块状物料；
(5)把所得Li 5FeO 4块状物料在氮气气氛下进行粉碎，控制其Dv50在4-6μm，对粉碎物料进行真空气相沉积包覆，所用气体为摩尔比4：1的甲烷与乙炔的混合气体，其中包覆温度为400℃，时间8h，压力为-20kpa，包覆结束后，可得性能良好的正极活性材料Li 5FeO 4。
表征测试：经过该合成方法制备的Li 5FeO 4，参见图3，所形成的颗粒比较小，利用碳硫仪测得其碳含量为4.7％，其粒径Dv50为5.2μm。
实施例2
本实施例制备了一种锂离子电池正极活性材料Li 5FeO 4，具体过程为：
(1)配制10L浓度为2mol/L的酸性硝酸铁溶液，并缓慢加入浓度为95％的浓硝酸，利用pH计调节溶液pH为3，并在溶液中加入一定比例的分散剂和导电碳源，该实施例分散剂选用聚乙烯醇，其添加量为导电碳源重量的15％，导电碳源选用Dv50为120nm的石墨粉，其添加量为最终合成Li 5FeO 4材料理论重量的5％；
(2)配置浓度为15mol/L的甲酸溶液作为促进剂溶液，甲酸的用量为酸性硝酸铁溶液中硝酸根离子摩尔量的1.15倍；
(3)把步骤(2)所配促进剂溶液加入到步骤(1)所配酸性硝酸铁溶液中，充分搅拌得到pH为4.0的混合液，并对其加热，使溶液体系内温度高于50℃，此时可引发自蔓延反应，放出大量热量，把溶剂蒸发，得到Dv50为250nm、水含量为0.6wt％的前驱体Fe 3O 4；
(4)所得Fe 3O 4与单水氢氧化锂进行混合，其中Li/Fe的摩尔比为5.2，所用混合设备为高速混合机，混合转速为600rpm，其中，混合后物料在氮气氛围(氧含量为1.0％)下进行烧结，烧结温度为670℃，烧结时间为18h，可得Li 5FeO 4块状物料；
(5)把所得Li 5FeO 4块状物料在氮气气氛下进行粉碎，控制其Dv50在4-6μm，对粉碎物料进行真空气相沉积包覆，所用气体为摩尔比4：1的甲烷与乙炔的混合气体，其中包覆温度为400℃，时间8h，压力为-20kpa，包覆结束后，可得性能良好的正极活性材料Li 5FeO 4。
表征测试：经过该合成方法制备的Li 5FeO 4，参见图5，所形成的材料整体均匀性良好，利用碳硫仪测得其碳含量为4.1％，其粒径Dv50为5.8μm。
对比例1
本对比例采用传统高温固相法制备了一种锂离子电池正极活性材料Li 5FeO 4，采用常规现有氧化铁(Dv50为3μm，BET为25m 2/g)为铁源，碳纳米管为碳源，具体过程为：
把氢氧化锂与氧化铁按照Li/Fe摩尔比5.3进行高速混合，其中碳纳米管的添加量为氧化铁质量的8％，所用设备为犁刀式混合机，混料转速为650rpm，混料时间为30min，把混合后物料在烧结温度为200℃保温烧结5h，然后在740℃下烧结16h，经粉碎后得到Li 5FeO 4。
表征测试：经过该合成方法得到的Li 5FeO 4，利用碳硫仪测得其碳含量为4.2％，其粒径Dv50为18μm。参见图7，所形成的颗粒非常大，主要是其使用铁源颗粒较大导致。
试验例
将实施例1、2，对比例1合成的Li 5FeO 4分别制成扣式电池，需要经过浆料的制备，涂布，干燥，压片，组装，上柜测试等步骤：①制备浆料，称取10g材料与导电剂，粘结剂混合，其中材料：导电剂：粘结剂的质量比为8:1:1，所用粘结剂为PVDF，所用溶剂为N-甲基吡咯烷酮，导电剂为导电炭；②涂布，使用刮刀在铝箔上进行涂布；其涂布厚度控制为200μm±30μm，③干燥，将涂布好的极片在真空干燥箱中进行干燥，干燥温度为120℃，干燥时间为2h；④压片，将干燥后极片使用对辊机进行压片；⑤将正极极片，负极极片，隔膜，电解液等电池零件组装成扣式电池。在充电电压4.25V，充电倍率0.1C的条件下测试比容量。
图4为实施例1合成的Li 5FeO 4的充放电曲线，从图中可见其容量能达到625mAh/g。
图6为实施例2合成的Li 5FeO 4的充放电曲线，从图中可见其容量能达到648mAh/g。
图8为对比例1合成的Li 5FeO 4的充放电曲线，从图中可见其容量能达到512mAh/g。
上面结合附图对本发明实施例作了详细说明，但是本发明不限于上述实施例，在所属技术领域普通技术人员所具备的知识范围内，还可以在不脱离本发明宗旨的前提下作出各种变化。此外，在不冲突的情况下，本发明的实施例及实施例中的特征可以相互组合。

Claims (10)

  1. 一种正极活性材料的制备方法，其特征在于，包括以下步骤：
    S1：将分散剂、导电碳源、硝酸铁、促进剂和水混合配制成酸性的混合液，其中所述促进剂为还原性有机物；
    S2：将所述混合液加热至诱发其发生自蔓延反应，反应结束后得到前驱体；
    S3：将所述前驱体与锂源混合，在微氧气氛下进行烧结，得到烧结料；
    S4：将所述烧结料进行粉碎，所得粉碎料用烃类气体进行真空气相沉积包覆，即得正极活性材料Li 5FeO 4。
  2. 根据权利要求1所述的制备方法，其特征在于，步骤S1中，所述混合液的pH为1-5。
  3. 根据权利要求1所述的制备方法，其特征在于，步骤S1中，所述分散剂为聚乙二醇、聚乙烯醇或聚氧化乙烯中的至少一种。
  4. 根据权利要求1所述的制备方法，其特征在于，步骤S1中，所述导电碳源为碳纳米管、石墨粉、葡萄糖或导电炭黑中的至少一种。
  5. 根据权利要求1所述的制备方法，其特征在于，步骤S1中，所述促进剂为乙醛、乙酸乙酯、甲酸或乙二醇中的至少一种。
  6. 根据权利要求1所述的制备方法，其特征在于，步骤S1中，所述混合液中，所述促进剂与硝酸根离子的摩尔比为1.1-1.3。
  7. 根据权利要求1所述的制备方法，其特征在于，步骤S2中，加热至50℃以上可诱发所述自蔓延反应。
  8. 根据权利要求1所述的制备方法，其特征在于，步骤S2中，所述前驱体的粒径Dv50为100-500nm。
  9. 根据权利要求1所述的制备方法，其特征在于，步骤S3中，所述烧结的温度为480-700℃。
  10. 如权利要求1-9任一项所述的制备方法在制备锂离子电池中的应用。
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