基于动态参数响应模型的动力锂离子电池循环容量衰减研究

结合锂离子电池容量衰减主要机制,建立了基于动态参数响应的电化学热耦合模型,研究磷酸铁锂电池循环寿命及电池内部的电化学行为.模型采用恒流恒压充放电制度对电池进行循环充放电仿真计算.结果显示:800次循环后,电池容量衰减率约为6.35%,电池内部固体电解质界面膜阻抗增大了15.6 m?·m~(-2).分别探讨了充放电倍率、负极活性物质颗粒粒径、负极固相体积分数对电池循环寿命的影响.研究表明:400次循环后,相较于1C(C表示充放电倍率)倍率下的容量衰减率3.31%,2C,3C,4C容量衰减率分别达到3.93%,4.69%和5.04%;负极活性颗粒粒径为2和10μm时对应容量衰减率分别为2.89%,3.87%,差值接近1%;固相体积分数在[0.5,0.6]区间内能保持最好的电池循环稳定性和寿命发挥.     

Sn3InSb4合金嵌Li性能的第一性原理研究

采用第一性原理超软赝势平面波方法计算了Sn₃InSb₄的嵌Li性能,得到各种嵌Li相的嵌Li形成能、理论质量比容量、体积膨胀率、能带结构、态密度和差分电荷密度等.从能量角度分析,Li在嵌入时,优先占据晶胞的四面体间隙位置,然后逐步挤出处于节点位置的Sn原子和In原子.在嵌Li过程中,材料表现出较大的体积膨胀率(11.74%-43.40%),这是导致Sn₃InSb₄作为Li离子电极材料循环性能差的重要原因.态密度计算表明,体系的导电性能首先随嵌Li量的增加而增加,当所有的间隙位置被Li填满,发生Sn的替换反应时,富Li态合金相的导电性反而下降.     

LiFePO4在不同pH值水溶液中电化学性能表现及其衰减机理

LiFePO₄在含Li⁺水溶液中的电化学性能稳定性与水溶液的pH值密切相关,当溶液的pH值达到11后LiFePO₄在充放电循环过程中的容量衰减十分明显. 通过循环伏安测试、交流阻抗测试、电极充放电性能测试、非原位X射线衍射测试以及化学分析的方式对其容量衰减机理进行了研究. 结果表明LiFePO₄在pH=7的LiNO₃水溶液中具有相对最高的电化学稳定性,但是LiFePO₄材料在水溶液中较之其在有机电解液中依然会有较差的电化学性能表现. 认为LiFePO₄在水介质中的容量衰减现象归因于其在持续充放电过程中的Li、Fe、P溶解,同时电极表面也会附着一层沉淀物. 这些最终导致了材料晶体结构的破坏、电极极化的增大以及电极容量的衰减.     

新型特效Na离子吸附剂Li1+xAlxTi2-x(PO4)3的光谱研究

采用高温固相法合成了新型特效Na离子吸附剂Li1 xAlxTi2-x(PO4)3.用XRD,FTIR,Raman等手段研究了其结构形态;对材料的激光拉曼光谱和红外光谱进行了研究和指认;并对其吸附性能进行了研究.结果表明少量Al的加入未影响到LiTi2(PO4)3的晶体结构,但使Li1 xAlxTi2-x(PO4)3对Na离子产生了特效吸附作用,可用于高纯锂盐制备过程中微量杂质钠离子的分离.其最佳吸附条件为:当x=0.4时,在pH值为10.0～11.0条件下,Li1 xAlxTi2-x(PO4)3的吸附容量达到11.76 mg·g-1.     

新型稀磁半导体Fe掺杂LiZnP的光电性质

采用基于密度泛函理论的第一性原理计算法研究了新型稀磁半导体Li_(1±)_y(Zn_(1-)_xFe_x)P (x=0, 0.0625;y=0, 0.0625)的电子结构、磁性及光学性质.结果表明,Fe的掺入使体系产生自旋极化杂质带,Fe的3d态与Li2s态,Zn4s态以及P3p态的态密度峰在费米能级处出现重叠,产生sp-d轨道杂化,此时体系净磁矩最大,材料表现出金属性,导电性增强.当Li空位时,导电性减弱,但杂质带宽度最大,居里温度最高.而Li填隙时,体系形成能最低,材料变为半金属性,表现为100%自旋注入,表明掺杂体系的磁性和电性可以分别通过Fe的掺入和Li的含量进行调控.对比光学性质发现,Li空位时,在介电函数虚部和复折射率函数的低能区出现新峰,扩大了对低频电磁波的吸收范围.能量损失函数表明掺杂体系具有明显的蓝移效应,且Li填隙时有更强的等离子共振频率.     

First principles study on Mn-doped LiFePO4 as cathode material for rechargeable lithium batteries

The electronic structure and diffusion energy barriers of Li ions in pure and Mn-doped LiFePO4 have been studied using density functional theory(DFT).The results demonstrate clearly that Fe-O covalent bond is weaker than P-O covalent bond.Pure LiFePO4 has band gap of 0.56 eV and diffusion energy barrier of 2.57 eV for Li ions,while the dopant has small band gap of 0.25 eV and low diffusion energy barrier of 2.31 eV,which indicates that the electronic and ionic conductivity of LiFePO4 have been improved owing to doping.     

碱金属改性的纳米氧化锌基荧光材料

研究了Zn （NO3）2·6H2O、CO （NH2）2、R-C6H4-SO3Na、Eu2O3和LiNO3为原料,通过均匀沉淀法制备了Eu3＋、Li＋共掺杂的纳米ZnO材料,并通过改变Li＋的掺杂比例来研究纳米氧化锌基材料的发光性能,用XRD、紫外和荧光等分析手段对样品进行表征.结果表明：制得的纳米粉体粒径在50nm左右,引入Li＋后增强了纳米ZnO∶Eu3＋材料的紫外可见光吸收和红色发光性能,且与Li＋的掺杂浓度有关,当Li＋∶Eu3＋的摩尔比为0.6时,其在601nm处的特征峰最强.     

纳米铜掺杂Li(Ni_(0.6)Co_(0.2)Mn_(0.2))O_2正极材料的制备和性能研究

通过Cu纳米颗粒掺杂制备了Li[(Ni_(0.6)Co_(0.2)Mn_(0.2))_(1-x)Cu_x]O_2三元正极材料,并通过调节Cu的掺杂量,讨论了Cu的掺入对Li[(Ni_(0.6)Co_(0.2)Mn_(0.2))_(1-x)Cu_x]O_2三元正极材料晶体结构、表面形貌、电化学性能和循环性能等一系列性能的影响,铜掺杂量为x=0.01时,在0.2C倍率下的首次放电比容量达到了219.1 mAh/g,经过50次充放电循环之后,剩余比容量为115.4 mAh/g。最终结果为Li[(Ni_(0.6)Co_(0.2)Mn_(0.2))_(1-x)Cu_x]O_2中Cu的掺入量为x=0.01时,所得正极材料的电化学性能和循环性能最为优异。     

溶剂热制备锂电池负极材料CNT-ZnFe2O4及其电化学性能

为了改善锂离子电池负极材料ZnFe₂O₄导电性差和循环寿命低的缺点,利用溶剂热反应方法制备了ZnFe₂O₄,并通过复合碳纳米管对ZnFe₂O₄进行改性。充放电测试结果表明：经过50次充放电后,碳纳米管复合改性后的ZnFe₂O₄容量保持在860 mA·h·g^-1,具有较好的循环稳定性。碳纳米管具有良好的导电性与导热性,改善了ZnFe₂O₄导电性差的缺点。     

基于镍泡沫支撑的Co_3O_4纳米多孔结构的高性能超级电容器电极

在众多能量存储和转化器件中,超级电容器由于具有功率密度高、充放电迅速和优异的循环性能的优点而被广泛研究.然而,较低的比容量和能量密度,限制了超级电容作为大尺度能量存储和转化器件的广泛应用.为了提高超级电容器的比容量,需要增大电极材料和电解质的接触面积,进而促进电极材料俘获/释放电解质中的粒子(例如电子、离子或者小分子).在此,我们通过简单的水热法联合高温退火实验方案能够大规模制备出镍泡沫支撑的Co_3O_4多孔纳米结构.无需借助导电胶和粘合剂,在集流器镍泡沫上"生长"Co_3O_4多孔纳米结构直接作为超级电容的电极材料.这种多孔纳米结构和一体化设计思路不仅能够有效提高电极的导电性,而且能够有效缩短离子和电子的迁移路径.由于多孔的结构特征和优异的导电性能,Co_3O_4电极表现出超高比容量(在电流密度为2.5 m A·cm~(-2)和5.5 m A·cm~(-2)时,比容量分别为1.87 F·cm(-2)(936 F·g-1)和1.80 F·cm~(-2)(907 F·g-1))、较好的倍率性能(电流密度从2.5 m A·cm~(-2)增大到100 m A·cm~(-2)时,保留其48.37%的初始电容)和超高的循环稳定性(经历4000次电流密度为10 m A·cm~(-2)的循环充放电过程,保留其92.3%的比容量).这种多孔纳米结构和一体化设计思路对设计其他高性能储能器件具有重要的指导意义.     

Vacancy-driven anisotropic defect distribution in the battery-cathode material LiFePO4

Li-ion mobility in LiFePO(4), a key property for energy applications, is impeded by Fe antisite defects (Fe(Li)) that form in select b-axis channels. Here we combine first-principles calculations, statistical mechanics, and scanning transmission electron microscopy to identify the origin of the effect: Li vacancies (V(Li)) are confined in one-dimensional b-axis channels, shuttling between neighboring Fe(Li). Segregation in select channels results in shorter Fe(Li)-Fe(Li) spans, whereby the energy is lowered by the V(Li)'s spending more time bound to end-point Fe(Li)'s. V(Li)-Fe(Li)-V(Li) complexes also form, accounting for observed electron energy loss spectroscopy features.     

LiFePO4 晶格动力学性质的第一性原理研究

基于考虑了Fe-3d电子间的库仑作用U和交换作用J的GGA+U方案,应用第一性原理计算系统研究了LiFePO₄的晶格动力学性质.我们计算并分析了玻恩有效电荷张量、布里渊区中心的声子频率和声子色散曲线.玻恩有效电荷张量显示各向异性,佐证了LiFePO₄中锂离子沿一维通道[010]方向迁移的机理.布里渊区中心点声子频率的计算值和相应的实验结果符合得比较好. 关键词： 4')" href="#">LiFePO₄ 晶格动力学 第一性原理计算     

Modeling of LiFePO_4 battery open circuit voltage hysteresis based on recursive discrete Preisach model

This paper focuses on the modeling of LiFePO4 battery open circuit voltage(OCV) hysteresis. There exists obvious hysteresis in LiFePO4 battery OCV, which makes it complicated to model the LiFePO4 battery. In this paper, the recursive discrete Preisach model(RDPM) is applied to the modeling of LiFePO4 battery OCV hysteresis. The theory of RDPM is illustrated in detail and the RDPM on LiFePO4 battery OCV hysteresis modeling is verified in experiment. The robust of RDPM under different working conditions are also demonstrated in simulation and experiment. The simulation and experimental results show that the proposed method can significantly improve the accuracy of LiFePO4 battery OCV hysteresis modeling when the battery OCV characteristic changes, which conduces to the online state estimation of LiFePO4 battery.     

Atomic-scale visualization of antisite defects in LiFePO4

We visualize the antisite exchange defects in LiFePO4 crystals with an ordered olivine structure by using annular dark-field scanning transmission electron microscopy (STEM). A recognizable bright contrast is observed in some of the Li columns of STEM images in a sample annealed at a lower temperature, which directly demonstrates the disordered occupations by Fe atoms. Furthermore, such exchange defects appear to be locally aggregated rather than homogeneously dispersed in the lattice, although their overall concentration is fairly low. The present study emphasizes the significance of atomic-level observations for the defect distribution that cannot be predicted by macroscopic analytical methods.     

LiFePO4纳米管的制备与表征

采用溶胶凝胶法在氧化铝模板中成功的制备了LiFePO4一维纳米管阵列．扫描电子显微镜和透射电子显微镜表征结果表明所制备的LiFePO4纳米管具有单分散性,互相平行,高度有序。综合选区电子衍射、X射线衍射以及X光线能谱表征结果,所制备的LiFePO4纳米管为单一的橄榄石型结构．这种在室温和温和条件下合成的一维LiFePO4纳米管,可以做为新型的锂离子电池正极材料．     

花状磷酸铁锂的聚乙二醇辅助水热合成及其电化学性能

通过聚乙二醇辅助水热法制备了厚度为200 nm的片状磷酸铁锂晶体,并由此自组装为花状磷酸铁锂颗粒．聚乙二醇在水热体系中作为共溶剂使用,它能有效地降低磷酸铁锂片的厚度,并且作为软模板,使磷酸铁锂片自组装成花状结构．这样的花状磷酸铁锂虽然没经过碳包覆改性,在锂离子电池中仍具有高达140 mAh/g的放电容量,并且表现出优异的循环性能,在循环50次后,容量未出现衰减．这种未经碳包覆的磷酸铁锂材料表现出良好的电化学性能．     

Neutron-induced defects in the lithium tetraborate single crystals

The X-band ( x ; 9.4 v GHz) electron spin resonance (ESR) spectra of the un-doped isotopically enriched lithium tetraborate (LTB) Li 2 B 4 O 7 single crystals, irradiated by thermal neutrons (fluences | n =2.74 ‐ 10 15 1 1.79 v ‐ 10 18 v cm m 2 ) were investigated at 300 and 77 v K. The LTB crystals of high chemical purity and optical quality with different isotope compositions ( 6 Li 2 10 B 4 O 7 , 6 Li 2 11 B 4 O 7 , 7 Li 2 10 B 4 O 7 and 7 Li 2 11 B 4 O 7 ) were grown by Czochralski technique. The thermal neutrons (the total quantity >90%) with fluence near 10 18 v cm m 2 induce at least 4 different types of stable paramagnetic centers in the Li and B isotopically enriched LTB crystals. The ESR spectra, electron structure and efficiency of generation for centers, induced by thermal neutrons, essentially depend on neutron fluence and isotope composition of the LTB crystals. The local symmetry and the spin Hamiltonian parameters of the observed paramagnetic centers were determined and their electron structure were established. The possible models and formation mechanism of the radiation defects, induced by thermal neutrons in the LTB lattice, are proposed.     

Concentrated dual-salt electrolytes for improving the cycling stability of lithium metal anodes

Lithium(Li) metal is an ideal anode material for rechargeable Li batteries, due to its high theoretical specific capacity(3860 mAh/g), low density(0.534 g/cm~3), and low negative electrochemical potential(-3.040 V vs. standard hydrogen electrode). In this work, the concentrated electrolytes with dual salts, composed of Li[N(SO_2F)_2](Li FSI) and Li[N(SO_2CF_3)_2](Li TFSI) were studied. In this dual-salt system, the capacity retention can even be maintained at 95.7%after 100 cycles in Li|Li FePO_4 cells. A Li|Li cell can be cycled at 0.5 mA/cm~2 for more than 600 h, and a Li|Cu cell can be cycled at 0.5 m A/cm~2 for more than 200 cycles with a high average Coulombi efficiency of 99%. These results show that the concentrated dual-salt electrolytes exhibit superior electrochemical performance and would be a promising candidate for application in rechargeable Li batteries.     

A strategy to improve the electrochemical performance of Ni-rich positive electrodes: Na/F-co-doped LiNi_(0.6)Mn_(0.2)Co_(0.2)O_2

Ni-rich layered lithium transition metal oxides LiNi_xMn_yCo_zO_2(1-y-z ≥ 0.6) are promising candidates for cathode materials, but their practical applications are hindered by high-voltage instability and fast capacity fading. Using density functional theory calculations, we demonstrate that Na-, F-doping, and Na/F-co-doping can stabilize the structure and result into a higher open circuit voltage than pristine LiNi_(0.6)Mn_(0.2)Co_(0.2)O_2(NMC622) during the charging process, which may attain greater discharge capacity. F doping may inhibit the diffusion of Li ions at the beginning and end of charging; Na doping may improve Li ion diffusion due to the increase in Li layer spacing, consistent with prior experiments. Na/F-codoping into NMC622 promotes rate performance and reduces irreversible phase transitions for two reasons:(i) a synergistic effect between Na and F can effectively restrain the Ni/Li mixing and then enhances the mobility of Li ions and(ii) Ni/Li mixing hinders the Ni ions to migrate into Li layers and thus, stabilizes the structure. This study proposes that a layer cathode material with high electrochemical performance can be achieved via rational dopant modification, which is a promising strategy for designing efficient Li ion batteries.