【作者】 穆磊；

【导师】 石秋芝； 杨长春；

【作者基本信息】 郑州大学 ， 物理化学， 2007， 硕士

【摘要】 继层状结构的LiCoO₂被广泛应用于小容量、低倍率锂离子电池之后，新型锂离子电池正极材料不断被提出，其中价格较低、资源丰富、比容量较高、具有层状结构的LiNiO₂系列化合物，被认为是有希望的正极材料。但是，它的纯相态晶体较难合成，循环过程中结构不稳定又导致容量衰减，这阻碍了它的实际应用。采用金属元素掺杂形成多元固溶体，以改善该材料的结构稳定性，提高其电化学活性，是该材料领域一个普遍使用的方法。本论文采用两段式高温固相反应方法，由不同含镍化合物，通过引入二价、三价、四价的掺杂金属元素，制备出锂离子电池正极材料用层状锂镍钴基氧化物LiNi_0.7Co_0.3O₂的掺杂化合物LiNi_0.7Co_0.3-xM_xO₂(M=Ga³⁺，Mg²⁺，Al³⁺，Ti⁴⁺，Sr³⁺)。论文应用粉末X射线衍射（XRD）、热重（TG）、扫描电镜（SEM）、循环伏安（CV）和实验电池性能测试等技术手段，对比研究了不同含镍化合物、前驱体制备工艺、前后两段烧结温度、烧结时间、烧结气氛等工艺参数，对所制材料的晶体结构、热稳定性、晶体颗粒形貌、电化学活性等性能的影响。结论如下：1、锂镍钴基氧化物LiNi_0.7Co_0.3O₂的研究：在氧气气氛下，用不同的含镍化合物制备LiNi_0.7Co_0.3O₂，系统考察了烧结温度和烧结时间对所制产物晶体结构的影响。1．1．在氧气气氛中，用γ-NiOOH、β-NiOOH、Ni（OH）₂、Ni₂O₃等为镍源，经600℃-650℃和700℃-800℃两段烧结的高温固相反应，均能得到六方层状结构的LiNi_0.7Co_0.3O₂。以γ-NiOOH为镍源，所制得的LiNi_0.7Co_0.3O₂没有电化学活性。由β-NiOOH，Ni₂O₃，Ni（OH）₂制备LiNi_0.7Co_0.3O₂，最佳的第二阶段烧结条件分别为700℃20小时、700℃30小时、750℃20～25小时。由β-NiOOH和Ni（OH）₂所制LiNi_0.7Co_0.3O₂的晶体结构更适宜于作为正极材料。1．2．由Ni（OH）₂制备LiNi_0.7Co_0.3O₂时，随着第二段烧结温度的升高，产物的结晶度提高，精细峰分裂明显，第二段烧结温度维持在800℃时容易引起锂离子的缺失，引起杂质相的生成，材料的电化学性能下降。在相同的烧结温度下，延长烧结时间具有同样的效果。2、掺杂化合物LiNi_0.7Co_0.3-xM_xO₂(M=Ga³⁺，Mg²⁺，Al³⁺，Ti⁴⁺，Sr³⁺)的研究：用高温固相法合成LiNi_0.7Co_0.3-xM_xO₂(M=Ga³⁺，Mg²⁺，Al³⁺，Ti⁴⁺，Sr³⁺)化合物，用X-射线衍射、热重分析，模拟电池的充放电以及为微电极循环伏安法对所得样品的结构、热稳定性和电化学性能进行了测试，结果表明：2．1．在氧气气氛中，用高温固相法所制LiNi_0.7Co_0.3-xGa_xO₂（x=0.01，0.03，0.05）的晶体结晶度受前驱体制备条件的影响，原料经压片后进行第一阶段烧结，较原料不经压片直接进行第一阶段烧结，所制LiNi_0.7Co_0.3-xGa_xO₂（x=0.01，0.03，0.05）的晶体结晶度高。2．2．镓掺杂对LiNi_0.7Co_0.3-xGa_xO₂（x=0.01，0.03，0.05）结构和热稳定性的影响。随着镓掺杂量的增加LiNi_0.7Co_0.3-xGa_xO₂（x=0.01，0.03，0.05）的结晶度提高。热重分析显示，第二段烧结温度在800℃以下时，镓的掺入有利于提高正极材料LiNi_0.7Co_0.3O₂的热稳定性。2．3．实验电池充放电结果和循环伏安测试结果显示，镓的引入有利于提高所制LiNi_0.7Co_0.3-xGa_xO₂（x=0.01，0.03，0.05）的质量比容量及其在充放电循环中的结构稳定性。结构稳定表明循环过程中LiNi_0.7Co_0.3-xGa_xO₂（x=0.01，0.03，0.05）没有发生相变，镓的掺入对其层状结构起到“钉扎”作用，抑制了它在充电过程中的相变。2．4．对LiNi_0.7Co_0.2M_0.1O₂(M=Mg²⁺、Al³⁺、Ti⁴⁺、Sr³⁺)的初步研究结果显示，Al³⁺和少量的Ti⁴⁺或Sr³⁺共同掺杂，使LiNi_0.7Co_0.2M_0.1O₂的晶胞体积变小，I_（003）／I_（104）值增大说明层间结合力增强；加入镁后a值没有变化，c值略有增加，是因为Mg²⁺的半径与Li⁺的半径较为接近，比其它阳离子大(Mg²⁺：0.072nm；Li⁺：0.076nm；：0.051nm；Co³⁺：0.053nm；Ni³⁺：0.056nm)。更多还原

【Abstract】 Following the extensive usage of LiCoO₂ with layer structure, served as cathode material in lithium ion battery, which have small capacity and used with low multiple ratio discharge current, several new cathode materials have being proposed. The layer structure LiNiO₂, was one kind of compounds among them, which have the feature of plenty raw material source, relatively low price and higher specific capacity. It was believed to be a hopeful cathode material for lithium ion batter}’. However, in practice it is difficulty to synthesis pure phase layer structure LiNiO₂, and the instability of its layer structure during cycling lead to the decline of its specific capacity, all these shortcomings hinder it from practical applying. In order to modify the crystal structure stability of LiNiO₂ and improve its electrochemical property, one useful method commonly used in the field of researching LiNiO₂ based cathode material was partially substituting the Ni atom in LiNiO₂ by variety metal elements to form solid solution of multi-components.In this thesis, several additive compounds of LiNi_0.7Co_0.3-xM_xO₂(M= Ga³⁺, Mg²⁺, Al³⁺, Ti⁴⁺, Sr³⁺) belong to the family of LiNi_0.7Co_0.3O₂ were synthesized for lithium ion battery cathode material The method used here was tow steps sintering process which contains high temperature solid reactions in two different temperature ranges. The raw material used here were several nickel containing compounds. The additive metal elements were that with the valance of two, three and four. The effects of technology parameters upon the feature of yields, have been studied comparatively, using the technologies of powder X-ray diffraction （XRD）, thermo-gravimetric analysis （TG）, scanning electric microscope （SEM）, cyclic voltammegram（CV）, and charge-discharge feature probe by simulated cell, from the views of crystal structure, thermal stability, particle morphology and electrochemical property. The technology parameters been taken into account are, the raw materials of nickel containing compounds, the technology for producing precursors, the temperature used in former and later sintering stage, the sustaining time and the atmosphere for sintering. The results are showed as follow. 1. Research on the material based on LiNi_0.7Co_0.3O₂In oxygen atmosphere, LiNi_0.7Co_0.3O₂ was produced using different nickel contained compounds, the effects of sintering temperature and continuing sintering time upon the crystal structure of target products have been studied systematically.1.1 In the oxygen atmosphere, all the products (LiNi_0.7Co_0.3O₂) with well-ordered hexagonal layer structure are synthesized by the two-step calcinations process, with the 1st step sintering temperature range from 600℃to 650℃, and the 2nd step sintering temperature range from 700℃to 800℃, when using different nickel contain compounds as raw material, such asγ-NiOOH、β-NiOOH、Ni（OH）₂、Ni₂O₃ and so on . But the product fromγ-NiOOH does not have electrochemical activity. The optimum sintering temperature and sustaining sintering time in second calcinations process for synthesizing LiNi_0.7Co_0.3O₂ fromβ-NiOOH, Ni₂O₃, Ni（OH）₂ raw materials, are sintering at 700℃for 20 hours, sintering at 700℃for 30 hours and sintering at 750℃for 20～25 hours respectively. The products of LiNi_0.7Co_0.3O₂ made from Ni（OH）₂ andβ-NiOOH are much more suitable to be used as cathode material for lithium ion battery than other products made from other nickel containing compounds.1.2 When Ni（OH）₂ were used to produce LiNi_0.7Co_0.3O₂, with increasing the temperature of second calcinations process, the crystal structural （degree of crystal） of the product was enhanced and the splitting of fine peak in XRD spectra was obviously. When the temperature of second calcinations process was maintained at 800℃, the electrochemical performance of the products declined, because of the escape of lithium lead deficiency and impurity phase may be produced during calcinations at relatively high temperature. The same result was occurred, when the sustaining sintering time is lengthened under the same calcinations temperature.2. Research of doped compound LiNi_0.7Co_0.3-xM_xO₂ (M= Ga³⁺, Mg³⁺, Al³⁺, Ti⁴⁺, Sr³⁺)LiNi_0.7Co_0.3-xM_xO₂ (M= Ga³⁺, Mg²⁺, Al³⁺, Ti⁴⁺,Sr³⁺) was synthesized by the high temperature solid state reaction . The performance feature of the target products were compared, from the views of crystal structure, thermal stability and electrochemical property, by means of X-ray diffraction （XRD）, thermal gravimetric analysis （TGA）, charge-discharge of simulated cell and cyclic voltammogram （CV）. The results are showed as followed:2.1 In the oxygen atmosphere , the structural performance of LiNi_0.7Co_0.3-xGa_xO₂ （x=0.01,0.03,0.05） synthesized by the high temperature solid state reaction waseffected by the preparation condition of the precursor . The precursor was prepared by two different processes: （i） the raw material were compressed to be pellet before the first calcinations step, （ii） the raw material were mixed only without compress before the first calcinations step. The structural performance of LiNi_0.7Co_0.3-xGa_xO₂ （x=0.01,0.03,0.05） from the first processes was better .2.2 The influence of doped Gallium to the crystal structure and the thermal stability of LiNi_0.7Co_0.3-xGa_xO₂ （x=0.01,0.03,0.05） . With increase the quantity of doped Gallium in LiNi_0.7Co_0.3-xGa_xO₂, its crystal performance （degree of crystal） was enhanced. The results of thermo-gravimetric analysis （TG） shown that, if the temperature of second calcinations process was lower than 800℃, the additive of Gallium was conducive to increase the thermal stability of LiNi_0.7Co_0.3O₂ cathode material.2.3. The tests of charge-discharge of simulated cell and cyclic voltammogram （CV） revealed that when Ga doped, the capacity of LiNi_0.7Co_0.3-xGa_xO₂ （x=0.01,0.03,0.05） increased and structural stability of the cathode was improved during the charge-discharge. The gallium doping stabilized the crystal structure of the LiNi_0.7Co_0.3-xGa_xO₂ （x-0.01,0.03,0.05） during charging, suppression of the phase transitions.2.4 The results of preliminary study about LiNi_0.7Co_0.2M_0.1O₂ (M= Mg²⁺, Al³⁺, Ti⁴⁺, Sr³⁺) shown that: when simultaneously multiple additive Al³⁺ and a few Ti⁴⁺ or Sr³⁺ to LiNi_0.7Co_0.2M_0.1O₂, the unit cell volume of LiNi_0.7Co_0.2M_0.1O₂ was decreased, and the ratio value of I_（003） /I_（104） was increased, these revealed that the inter layer binding force were enhanced. If Mg²⁺ was doped, the value of a does not change ,the value of c increase slightly, the reason for that were the radius of Mg²⁺is approaches to the radius of Li+, and it is bigger than the radius of other positive ions （Mg2+ :0.072nm; Li+:0.076nm;: 0.051nm; Co3+:0.053nm; Ni3+:0.056nm）.更多还原