LiNi0.4Co0.2Mn0.4O2与LiMn2O4共混正极材料电化学性能

为开发具有优良循环性能和安全性能的大型锂离子电池的正极材料,将不同比例的LiNi_(0.4)Co_(0.2)Mn_(0.4)O_2和Li Mn2O4材料进行共混,研究了LiNi_(0.4)Co_(0.2)Mn_(0.4)O_2和Li Mn2O4共混以及共混比例(10∶0、8∶2、7∶3、6∶4、5∶5、0∶10)对锂离子电池的首次放电性能、循环性能和倍率性能以及交流阻抗和循环伏安曲线的影响,并采用扫描电镜对电极材料进行了表征.研究结果表明,共混比例会影响材料的电化学性能,8∶2,7∶3和6∶4配比的混合材料的体积比容量、循环性能和倍率性能要好于纯LiNi_(0.4)Co_(0.2)Mn_(0.4)O_2和Li Mn2O4材料.其中,8∶2配比的材料性能最好.     

离子掺杂和碳修饰对Li_2FeSiO_4结构和性能的影响

采用高温固相反应方法合成锂离子电池正极Li_2Fe_(1-x-y)Mn_xNi_ySiO_4/C复合材料,并采用X-ray线衍射、扫描电子显微镜和电化学分析方法,研究了Ni和Mn离子共掺杂及碳修饰复合改性对复合材料结构和性能的影响。结果表明,复合改性没有对材料的晶体结构造成改变,镍锰离子共掺杂和表面碳包覆能有效提高材料的比容量和循环性能;以C/32倍率充放电,复合掺杂得到的Li_2Fe_(0.6)Mn_(0.2)Ni_(0.2)SiO_4/C材料样品的电化学性能最优,根据实测结果,该复合材料的首次放电比容量达到149 m Ah·g~(-1),充放电循环10次以后容量保持率仍有95.3%。     

Al_2O_3包覆对富锂锰基正极材料Li_(1.2)Mn_(0.54)Co_(0.13)Ni_(0.13)O_2的电化学性能影响

采用水热法合成富锂三元正极材料,探究了最佳包覆比例下Al_2O_3包覆对材料的电化学性能影响.采用扫描电镜(SEM)和X射线衍射仪(XRD)表征了富锂三元正极材料的表面形貌和结构,通过循环伏安(CV)、交流阻抗(EIS)技术分析了材料电化学性的影响因素.结果表明,通过异丙醇铝水解制得了氧化铝包覆层,提高了材料的比容量,稳定了材料的结构.     

纳米砂磨辅助固相合成LiNi_(0.8)Co_(0.15)Al_(0.05)O_2及Li_2CO_3加入方式对其结构性能的影响

以Li_2CO_3为锂源,采用纳米砂磨辅助固相合成了纯相LiNi_(0.8)Co_(0.15)Al_(0.05)O_2正极材料,研究了Li_2CO_3加入方式对所得样品结构、形貌以及电化学性能的影响.结果表明,加锂方式基本不影响材料的形貌和尺寸,但对材料的微结构和性能有明显的影响.纳米砂磨一步混合所有原料烧结所得LiNi_(0.8)Co_(0.15)Al_(0.05)O_2样品的阳离子混排程度比后研磨加碳酸锂烧结所得LiNi_(0.8)Co_(0.15)Al_(0.05)O_2样品的要低,更利于锂离子的扩散,对应的样品具有更高的放电比容量和库伦效率,但循环性能没有太大的差别.纳米砂磨一步混合所有原料在800℃烧结得到的LiNi_(0.8)Co_(0.15)Al_(0.05)O_2样品,1C循环首次放电比容量可达170.9 m Ah/g,50次循环后容量保持率为92.6%.     

Sn~(4+)掺杂对正极材料Li_(1/3)Ni_(1/3)Co_(1/3)Mn_(1/3)O_2性能的影响

采用共沉淀法合成掺杂的Li_(1/3)Ni_(1/3)Co_(1/3)Mn_(1/3-x)Sn_xO_2的正极材料,通过X射线光谱、扫描电镜、充放电测试等技术对Li_(1/3)Ni_(1/3)Co_(1/3)Mn_(1/3-x)SnxO_2材料的结构、形貌、电化学性能进行表征。结果表明,采用共沉淀法Sn4+能有效掺杂进正极材料Li_(1/3)Ni_(1/3)Co_(1/3)Mn_(1/3)O_2的体相结构。掺杂量x=0.04时,在2.8~4.2V、0.2C倍率下掺杂的正极材料首次充放电比容量为138.5mA·h/g,30次循环后的容量保持率为96.96%。掺杂Sn4+对Li_(1/3)Ni_(1/3)Co_(1/3) Mn_(1/3)O_2正极材料改性后,材料仍保持典型的α-NaFeO_2层状结构,且晶型良好,表明Sn4+掺杂能够有效改善材料的电化学性能。     

石墨烯包覆富锂层状正极材料的电化学性能

采用固相配位法制得石墨烯包覆的Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2富锂层状正极材料。用X射线衍射、场发射扫描电镜、循环伏安、恒流充放电和电化学阻抗谱等分析技术对其相组成、微结构和电化学性能进行表征。结果表明:石墨烯包覆Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2材料的电化学性能显著提高,该材料在电流密度为20 mA/g(0.1C)和1 000 mA/g(5C)时的放电比容量分别为240,132 mAh/g;在电流密度为200 mA/g(1C)时,充放电循环100次后,其比容量保持率为84%。     

醋酸对Li_(1.42)Ni_(0.08)Mn_(0.70)Co_(0.08)O_(2.00)固溶体正极材料电化学性能的影响

以Li_2CO_3、NiCO_3·2Ni(0H)_2·4H_20、MnC0_3、Co(CH_3COO)_2·4H_20、醋酸溶液和聚乙烯醇为原料,制备出具有α-NaFeO_2层状结构的Li_(1.42)Ni(0.08)Mn_(0.7)Co_(0.08)O_(2.00)富锂固溶体正极材料.通过红外光谱、X射线衍射、恒电流充放电测试、交流阻抗和循环伏安法等方法研究了制备样品的结构及电化学性能.研究表明:按0.707 5 mol碳酸锂比例加入2.5 g醋酸时制备得到的正极材料充放电性能最好,在1C条件下,首次放电容量93.2 mAh/g,30次循环后容量达到177.2 mAh/g.     

高镍三元正极材料LiNi0.8Co0.1Mn0.1O2的合成与改性

LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2是一种具有高能量密度的锂离子电池正极材料,但实际应用中的循环性能不佳、热稳定性差等缺陷亟待改善。本研究通过高温固相反应法制备了LiNi_(0.8)-Co_(0.1)Mn_(0.1)O_2材料,并采用H_3BO_3对其进行包覆改性。扫描电镜(SEM)显示包覆热处理后正极材料表面形成了一层不均匀絮状包覆物,X射线光电子能谱(XPS)测试显示该包覆物为LiBO_2和Li_2B_4O_7的混合物。电化学测试表明包覆物有效减缓了循环过程中的阻抗增加,显著提升了正极材料的容量与循环性能,其中0.5%包覆的正极材料0.2 C首次放电容量达到195.9 mAh·g~(-1),1 C循环100周后容量保持率达到88.7%。     

共沉淀法制备Li[Li0.2Ni0.2Mn0.6]O2及其性能研究

采用共沉淀法在不同pH条件下制备得到球形的前驱体,通过固相法与锂源合成正极材料Li[Li_0.2Ni_0.2Mn_0.6]O₂,对样品进行了XRD、SEM以及电化学性能分析。结果表明:制得的前驱体呈球状颗粒,其中pH=8.0时制得的前驱体的结晶度和球形形貌最理想;合成的正极材料具有层状结构,在950℃下合成的材料电化学性能和循环稳定性最佳,在2.0⁴.8 V、0.2 C条件下,首次放电比容量为220.4 m Ah/g,循环20次后保持率高达97%。此外,该材料的倍率性能也最好,在1 C下充放电,其放电比容量仍保持200.9 m Ah/g。 更多还原     

动态水热法一步合成尖晶石锰酸锂及性能研究

尖晶石锰酸锂(LiMn 2O 4)是低成本锂离子电池的理想正极材料。采用动态水热法成功地一步合成了一系列粒径较小(<50 nm)且分布较窄的LiMn 2O 4材料,并运用XRD,SEM,CV,EIS和充放电测试等多种方法表征其晶相、形貌和电化学性能。研究结果表明水热温度对产物成分和电化学性能有很大影响。在180℃和200℃条件下制得的LiMn 2O 4材料为纯相尖晶石晶型。180℃合成的材料具有更好的电化学性能,在1 C倍率循环时,LiMn 2O 4材料的首次放电比容量为102.4 mAh/g,循环50周后容量保持率为95.5%。600℃热处理对材料结构和性能具有明显的改善作用,1 C倍率循环时,首次放电比容量达到112.7 mAh/g,循环50周后容量保持率为94.2%。研究成果为低成本锰酸锂正极材料的制备提供了一条理想的工艺路线。     

Synthesis and properties of Li<Subscript>2</Subscript>MnSiO<Subscript>4</Subscript>/C cathode materials for Li-ion batteries

Carbon was coated on the surface of Li₂MnSiO₄ to improve the electrochemical performance as cathode materials, which were synthesized by the solution method followed by heat treatment at 700 °C and the solid-state method followed by heat treatment at 950 °C. It is shown that the cycling performance is greatly enhanced by carbon coating, compared with the pristine Li₂MnSiO₄ cathode obtained by the solution method. The initial discharge capacity of Li₂MnSiO₄/C nanocomposite is 280.9 mAh/g at 0.05 C with the carbon content of 33.3 wt%. The reasons for the improved electrochemical performance are smaller grain size and higher electronic conductivity due to the carbon coating. The Li₂MnSiO₄/C cathode material obtained by the solid-state method exhibits poor cycling performance, the initial discharge capacity is less than 25 mAh/g.     

Synthesis and characterization of Mg3(PO4)2-coated Li1.05Ni1/3Mn1/3Co1/3O2 cathode material for Li-ion battery

Mg₃(PO₄)₂-coated Li_1.05Ni_1/3Mn_1/3Co_1/3O₂ cathode materials were synthesized via co-precipitation method. The morphology, structure, electrochemical performance and thermal stability were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS), charge/discharge cycling and differential scanning calorimeter (DSC). SEM analysis shows that Mg₃(PO₄)₂-coating changes the morphologies of their particles and increases the grains size. XRD and CV results show that Mg₃(PO₄)₂-coating powder is homogeneous and has better layered structure than the bare one. Mg₃(PO₄)₂-coating improved high rate discharge capacity and cycle-life performance. The reason why the cycling performance of Mg₃(PO₄)₂-coated sample at 55 °C was better than that of room temperature was the increasing of lithium-ion diffusion rate and charge transfer rate with temperature rising. Mg₃(PO₄)₂-coating improved the cathode thermal stability, and the result was consistent with thermal abuse tests using Li-ion cells: the Mg₃(PO₄)₂ coated Li_1.05Ni_1/3Mn_1/3Co_1/3O₂ cathode did not exhibit thermal runaway with smoke and explosion, in contrast to the cells containing the bare Li_1.05Ni_1/3Mn_1/3Co_1/3O₂. Funded by the National Natural Science Foundation of China (No. 20273047)     

Modification of LiCo1/3Ni1/3Mn1/3O2 cathode material by CeO2-coating

LiCo_1/3Ni_1/3Mn_1/3O₂ was coated by a layer of 1.0 wt% CeO₂ via sol-gel method. The bared and coated LiMn_1/3Co_1/3Ni_1/3O₂ was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammogram (CV) and galvanotactic charge-discharge test. The results show that the coating layer has no effect on the crystal structure, only coating on the surface; the 1.0 wt% CeO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ exhibits better discharge capacity and cycling performance than the bared LiCo_1/3Ni_1/3Mn_1/3O₂. The discharge capacity of 1.0 wt% CeO₂-coated cathode is 182.5 mAh·g⁻¹ at a current density of 20 mA·g⁻¹, in contrast to 165.8 mAh·g⁻¹of the bared sample. The discharge capacity retention of 1.0 wt% CeO₂-coated sample after 12 cycles reaches 93.2%, in comparison with 86.6% of the bared sample. CV results show that the CeO₂ coating could suppress phase transitions and prevent the surface of cathode material from direct contact with the electrolyte, thus enhance the electrochemical performance of the coated material.     

Effects of carbon sources on electrochemical performance of Li4Ti5O12/C composite anode materials

Li₄Ti₅O₁₂/C composite materials were synthesized by two-step solid state reaction method with glucose, sucrose, and starch as carbon sources, respectively. The effects of carbon sources on the structure, morphology, and electrochemical performance of Li₄Ti₅O₁₂/C composite materials were investigated by SEM, XRD and electrochemical tests. The results indicate that carbon sources have almost no effect on the structure of Li₄Ti₅O₁₂/C composite materials. The initial discharge capacities of the Li₄Ti₅O₁₂/C composite materials are slightly lower than those of as-synthesized Li₄Ti₅O₁₂. However, Li₄Ti₅O₁₂/C composite materials show better electrochemical rate performance than the as-synthesized Li₄Ti₅O₁₂. The capacity retention (79%) of the Li₄Ti₅O₁₂/C composite materials with starch as carbon source, is higher than that of Li₄Ti₅O₁₂/C composite materials with glucose and sucrose as carbon source at current rate of 2.0C.     

Characteristics of LiCoO2, LiMn2O4 and LiNi0.45Co0.1Mn0.45O2 as cathodes of lithium ion batteries

LiNi_0.45Co_0.10Mn_0.45O₂ was synthesized from Li₂CO₃ and a triple oxide of nickel, cobalt and manganese at 950 °C in air. The structures and characteristics of LiNi_0.45Co_0.10Mn_0.45O₂, LiCoO₂ and LiMn₂O₄ were investigated by XRD, SEM and electrochemical measurements. The results show that LiNi_0.45Co_0.10Mn_0.45O₂ has a layered structure with hexagonal lattice. The commercial LiCoO₂ has sphere-like appearance and smooth surfaces, while the LiMn₂O₄ and LiNi_0.45Co_0.10Mn_0.45O₂ consist of cornered and uneven particles. LiNi_0.45Co_0.10Mn_0.45O₂ has a large discharge capacity of 140.9 mA · h/g in practical lithium ion battery, which is 33.4% and 2.8% above that of LiMn₂O₄ and LiCoO₂, respectively. LiCoO₂ and LiMn₂O₄ have higher discharge voltage and better rate-capability than LiNi_0.45Co_0.10Mn_0.45O₂. All the three cathodes have excellent cycling performance with capacity retention of above 89.3% at the 250th cycle. Batteries with LiMn₂O₄ or LiNi_0.45Co_0.10Mn_0.45O₂ cathodes show better safety performance under abusive conditions than those with LiCoO₂ cathodes. Foundation item: Project(50302016) supported by the National Natural Science Foundation of China; Project(2005037698) supported by the Postdoctoral Science Foundation of China     

Preparation of LiFePO4 for lithium ion battery using Fe2P2O7 as precursor

In order to obtain a new precursor for LiFePO4, Fe2P2O7 with high purity was prepared through solid phase reaction at 650 ℃ using starting materials of FeC2O4 and NH4H2PO4 in an argon atmosphere. Using the as-prepared Fe2P2O7, Li2CO3 and glucose as raw materials, pure LiFePO4 and LiFePO4/C composite materials were respectively synthesized by solid state reaction at 700 ℃ in an argon atmosphere. X-ray diffractometry and scanning electron microscopy（SEM） were employed to characterize the as-prepared Fe2P2O7, LiFePO4 and LiFePO4/C. The as-prepared Fe2P2O7 crystallizes in the Cl space group and belongs to β-Fe2P2O7 for crystal phase. The particle size distribution of Fe2P2O7 observed by SEM is 0.4-3.0 μm. During the Li^＋ ion chemical intercalation, radical P2O7^4- is disrupted into two PO4^3- ions in the presence of O^2-, thus providing a feasible technique to dispose this poor dissolvable pyrophosphate. LiFePO4/C composite exhibits initial charge and discharge capacities of 154 and 132 mA·h/g, respectively.     

Synthesis and electrochemical properties of Cr-doped Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> cathode materials for lithium-ion batteries

Cr-doped Li₃V₂(PO₄)₃ cathode materials Li₃V_2−x Cr _x (PO₄)₃ were prepared by a carbothermal reduction(CTR) process. The properties of the Cr-doped Li₃V₂(PO₄)₃ were investigated by X-ray diffraction (XRD), scanning electron microscopic (SEM), and electrochemical measurements. Results show that the Cr-doped Li₃V₂(PO₄)₃ has the same monoclinic structure as the undoped Li₃V₂(PO₄)₃, and the particle size of Cr-doped Li₃V₂(PO₄)₃ is smaller than that of the undoped Li₃V₂(PO₄)₃ and the smallest particle size is only about 1 μm. The Cr-doped Li₃V₂(PO₄)₃ samples were investigated on the Li extraction/insertion performances through charge/discharge, cyclic voltammogram (CV), and electrochemical impedance spectra(EIS). The optimal doping content of Cr was that x=0.04 in the Li₃V_2−x Cr _x (PO₄)₃ samples to achieve high discharge capacity and good cyclic stability. The electrode reaction reversibility was enhanced, and the charge transfer resistance was decreased through the Cr-doping. The improved electrochemical performances of the Cr-doped Li₃V₂(PO₄)₃ cathode materials are attributed to the addition of Cr³⁺ ion by stabilizing the monoclinic structure. Funded by the Guangxi Natural Science Foundation(No. 0832259) and the National Basic Research Program of China (No. 2007CB613607)     

Influence on performance and structure of spinel LiMn2O4 for lithium-ion batteries by doping rare-earth Sm

The spinel LiMn₂O₄ used as cathode materials for lithium-ion batteries was synthesized by mechano-chemistry fluid activation process, and modified by doping rare-earth Sm. Thesting of X-ray diffraction, cyclic voltammograms, charge-discharge and SEM was carried out for LiMn₂O₄ cathode materials and the modified materials. The results show that the cathode materials doped rare earth Li _x Mn_2−y Sm _z O₄ (0.95⩽x⩽1.2, 0⩽y⩽0.3, 0⩽z⩽0.2) exhibit standard spinel structure, high reversibility of electrochemistry and excellent properties of charge-discharge. In EC: DMC(1 : 1)+1 mol/L LiPF₆ electrolyte with discharge capacity more than 130 mA · h/g, and its capacity is deteriorated less than 15% after 300 cycles at room temperature and less than 20% after 200 cycles at 55°C. At the same time, Crystal Field Theory was applied to explain the function and mechanism of doped rare earth element. Foundation item: Project (02JJY2081) supported by the Natural Science Foundation of Hunan Province     

Effect of baking processes on properties of TiB2/C composite cathode material

Pitch and TiB₂/C green composite cathode material were respectively analyzed with simultaneous DSC-TGA, and effects of three baking processes of TiB₂/C composite cathode material, i.e. K25, K5 and M5, on properties of TiB₂/C composite cathode material were investigated. The results show that thermogravimetric behavior of pitch and TiB₂/C green composite cathode is similar, and appears the largest mass loss rate in the temperature range from 200 to 600°C. The bulk density variation of sample K5 before and after baking is the largest (11.9%), that of sample K25 is the second, and that of sample M5 is the smallest (6.7%). The crushing strength of sample M5 is the biggest (51.2 MPa), that of sample K25 is the next, and that of sample K5 is the smallest (32.8 MPa). But, the orders of the electrical resistivity and electrolysis expansion of samples are just opposite with the order of crushing strength. The heating rate has a great impact on the microstructure of sample. The faster the heating rate is, the bigger the pore size and porosity of sample are. Compared with the heating rate between 200 and 600° of samples K25 and K5, that of sample M5 is slower and suitable for baking process of TiB₂/C composite cathode material. Foundation item: Project (2005CB623703) supported by the Major State Basic Research and Development Program of China; Project (2008AA030502) supported by the National High-Tech Research and Development Program of China