合成条件对半固相碳热还原法制备LiFePO_4/C性能的影响

以硝酸铁、磷酸锂为原料,聚乙烯醇(PVA)为碳源和还原剂,采用半固相碳热还原法一步合成LiFePO4/C,研究了煅烧时间、煅烧温度以及碳含量对材料性能的影响,利用XRD、SEM和恒流充放电等手段研究各个样品的晶型结构、粒度形貌及其电化学性能的影响,结果表明:聚乙烯醇过量5%,在烧结温度700℃下维持7h可以得到性能最佳样品,0.1C倍率时放电首次比容量达到152.9mAh.g-1,0.5C倍率放电容量可达138.6mAh.g-1,循环40次后容量维持率97%,具有良好的循环稳定性。     

新型锡/碳复合材料的制备及其用于锂离子电池负极材料的研究

以煤焦油和SnCl2为原料,采用液相分散和碳热还原的方法制备了一种新型的锡/碳(Sn/C)复合材料.采用XRD、SEM及TEM手段对复合材料进行了结构表征,并对材料的电化学性能进行了检测.结果表明,金属锡以200nm大小的颗粒分散在碳材料中,复合材料的首次放电容量在371mAh·g-1,循环50次后比容量维持在305mAh·g-1以上,具有优异的循环性能.     

锂电池正极材料LiNi0.8Co0.1Mn0.1O2的制备与性能

运用"溶胶-喷雾干燥-煅烧"新技术合成了正极材料LiNi0.8Co0.1Mn0.1O2,采用XRD、SEM、电化学阻抗谱(EIS)及充放电测试研究了煅烧温度对所制材料结构和电性能的影响。结果表明,在750~850℃都可制备得到纯相LiNi0.8Co0.1Mn0.1O2。其中,800℃所合成样品具有适宜的晶粒大小、最佳的晶化程度和阳离子有序度,最小的电荷传递阻抗,最大的锂离子扩散系数和最佳的电化学表现。该样品0.2C首次放电容量达到189.1mAh·g-1,以5C循环的放电比容量仍可达到136mAh·g-1,第30周0.2C放电容量达初始容量的97.5%,显示出高容量、良好的倍率与循环性能。     

苯胺用量对固相法合成LiFePO_4/C电化学性能的影响

通过聚苯胺包覆法制备LiFePO4/C,研究了苯胺用量对LiFePO4/C电化学性能的影响。采用X射线衍射(XRD)测试材料结构并用扫描电镜(SEM)和透射电镜(TEM),观察材料形貌及碳层包覆情况。结果表明:该方法制得的LiFePO4结晶度高并且具有规整的球状结构,粒径在50~80nm之间,碳层厚度约为2.5nm。经电化学性能测试发现:在相同合成工艺下,苯胺用量对合成的LiFePO4/C的电化学性能有很大影响.当苯胺加入量为0.5mL时所得LiFePO4/C(6mmol)的电化学性能最佳,0.2C下首次放电比容量可达161.6mAh·g-1,5C下放电比容量可达112.2mAh·g-1,且在5C下循环300次无明显衰减。     

高温固相还原法合成LiFePO4/C正极材料及其电化学性能

以Fe2O3为铁源，用环氧树脂对反应前驱体进行包覆，通过固相还原法制备了LiFePO4／C复合正极材料．采用XRD、SEM、循环伏安以及充放电测试等方法对其晶体结构、表观形貌和电化学性能进行了研究．研究结果表明，煅烧温度对材料的电化学性能有较大影响，在700℃煅烧所得产物为单一的橄榄石型晶体结构，粒径分布较均匀，且具有良好的电化学性能．以0．1C倍率进行充放电，其首次放电容量为150．3mAh／g，充放电循环20周后，容量保持率达99．2％；以1．0、2．0C倍率进行充放电，其首次放电容量分别为131．4和122．1mAh／g．其在过充条件下的电性能也佳，过充后还能继续放电，但在过放电条件下，其电性能迅速劣化．     

Li0.97+δTi0.03Fe0.97Mn0.03 PO4/C复合材料的制备及其电化学性能研究

用共沉淀法合成Fe0.97Mn0.03PO4前驱体,再通过碳热还原法合成多元掺杂的Li0.97 δTi0.03Fe0.97Mn0.03PO4/C复合材料,利用X射线衍射(XRD),扫描电镜(SEM)、傅立叶红外光谱(FTIR)等测试手段对样品的晶体结构、表观形貌、谱学性质等进行了分析研究,对其倍率放电性能及循环性能等进行了测试,并与不掺杂的LiFePO4/C复合材料进行了比较.研究表明,掺杂过程中,掺杂的Mn4 、Ti4 离子能与LiFePO4形成单一的橄榄石型晶体结构,晶型完整,产物形貌规则,平均粒径在1um左右.用Li0.97 δTi0.03Fe0.97Mn0.03PO4/C为正极材料制作的电池分别以0.2,1,5、10C倍率放电,首次放电容量为134.0、133.4,130.1和127.2mAh·g-1,并表现出良好的循环性能.     

球形LiFePO4材料碳包覆的研究

主要研究了采用不同碳源和掺碳量包覆对液相共沉淀-碳热还原法制备的球形LiFePO4材料性能的影响.结果表明,采用过量5%葡萄糖作碳源制备的材料在0.1C下,首次放电比容量达到了154.6mAh/g,并且循环性能良好.     

磷铁制备复合材料LiFePO4/C的新方法研究

以磷铁为原料,采用两步烧结的碳热还原法成功合成了LiFePO4材料并研究了不同时间对烧结产物的影响,该方法可以实现原料的循环利用,对环境零排放。采用XRD,恒电流充放电法,交流阻抗对样品晶型和电化学性能进行表征和研究。烧结15h的样品具有最接近标准卡片的晶型,在0.05C时的放电容量也最大可以达到162.3mAh/g。在0.5C循环15次后放电容量仍有124.6mAh/g,衰减仅为2.02%,具有良好的循环性。对比4个样品,15h烧结的样品也就有最小的反应阻抗仅为56Ω。     

富氮中空炭微球的制备及其用作锂硫电池的电化学性能

分别以多巴胺和正硅酸乙酯为碳源和硅源,先采用一步法合成出球形C@SiO_2复合材料,然后通过化学刻蚀制得一种表面积达875 m2·g-1、表面富含N原子的中空炭微球(N-HCS)。N-HCS独特的纳米结构可以有效地抑制硫在充放电过程中的体积膨胀和聚硫化物的穿梭效应,同时表面掺杂的氮能够提高活性物质的导电性,进而提高正极材料的循环稳定性和大倍率性能。结果表明,该碳/硫复合材料的在0.2 C电流密度下的首次放电容量达1 179 mAh·g~(-1);经100次反复充放电后,其放电容量仍可保持在540 mAh·g~(-1);具有较好的大电流倍率性能,在电流密度为1 C和2 C时,其可逆放电容量可分别稳定在343 mAh·g~(-1)和247 mAh·g~(-1)。     

用碳热还原法制备LiFePO4/C复合正极材料

以Fe2O3为铁源,以葡萄糖为碳添加剂,利用碳热还原法成功地制备了LiFePO4/C复合材料.研究了不同焙烧温度对样品性能的影响.利用X射线衍射仪、扫描电镜和碳硫(质量分数)分析方法对所得样品的晶体结构、表面形貌、含碳量进行分析研究.研究结果表明,样品中碳含量(质量分数)为10%的LiFePO4/C复合材料为单一的橄榄石型晶体结构, 碳的加入使LiFePO4 颗粒粒径减小.碳分散于晶体颗粒之间,增强了颗粒之间的导电性.电化学性能测试结果表明,LiFePO4/C充放电性能和循环性能都得到显著改善.其中,碳含量为10%在700℃下焙烧8h合成出的样品电化学性能最佳,在0.1、0.5和1C倍率下放电,LiFePO4/C首次放电比容量达159.3、137.0、130.6mAh/g,充放电循环30次,容量只衰减了2.2%、5.3%、7.6%.其表现出良好的循环性能.     

Structural and optical properties of AlxOy/Pt/AlxOy multilayer absorber

We report on the microstructure and optical properties of Al_xO_y–Pt–Al_xO_y interference-type multilayer films, deposited by electron beam (e-beam) deposition onto corning 1737 glass, silicon (1 1 1) and copper substrates. The structural properties were investigated by Rutherford backscattering spectrometry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The optical properties were extracted from specular reflection/transmission, diffuse reflectance and emissometer measurements. The stratification of the coatings consists of a semi-transparent middle Pt layer sandwiched between two layers of Al_xO_y. The top and bottom Al_xO_y layers were non-stoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of Al_xO_y. The surface roughness of the stack was found to be comparable to the inter-particle distance. The optical calculations confirm a high solar absorptance of ∼0.94 and a low thermal emittance of ∼0.06 for the multilayer stack, which is attributed not only to the optimized nature of the multilayer interference stacks, but also to the specific surface morphology and texture of the coatings. These optical characteristics validate the spectral selectivity of the Al_xO_y–Pt–Al_xO_y interference-type multilayer stack for use in high temperature solar-thermal applications.     

Synthesis of a new perovskite Pb(Li14Nb34)O3

A high-pressure technique was adopted to obtain perovskite-type $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$. A new perovskite $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$ was characterized to have a cubic symmetry with $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 4.069}\text{A}\text{?}$; Li and Nb ions in the B-site of perovskite lattice may be in a random arrangement.     

Bulk crystalline BaPb34Bi14O3: A ceramic superconductor

The preparation conditions of the high T_C ceramic superconductor Ba(Pb,Bi)O₃ is correlated with the superconducting transition. Transition onsets of all materials are similar, but transition widths and transition completeness is strongly dependent on firing temperature. Only materials prepared over a narrow temperature range, resulting in a nearly ideal weight loss, have a complete and narrow transition.     

Optimization of AlxOy/Pt/AlxOy multilayer spectrally selective coatings for solar-thermal applications

Spectrally selective Al_xO_y/Pt/Al_xO_y multilayer absorber coatings were deposited onto corning 1737 glass, Si (111) and copper substrates using electron beam (e-beam) vacuum evaporator at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit multilayer solar absorber coatings. The optical constants (n and k) measured using spectroscopic ellipsometry, showed that both Al_xO_y layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance α ∼ 0.94 ± 0.01 and low thermal emittance ? ∼ 0.06 ± 0.01 at 82 °C. The Rutherford backscattering spectroscopy (RBS) data of Al_xO_y/Pt/Al_xO_y multilayer absorber indicated the Al_xO_y layers present in the coating were nearly stoichiometry. The scanning electron microscope analysis (SEM) result indicated that the average diameter and inter-particles distance of Pt grains were statistically about 146 ± 0.17 nm and 6-10 ± 0.2 nm respectively.     

Electrostriction in Pb (Zn13Nb23)O3

The electrostriction in $\text{Pb (Zn}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)}\text{O}{}_3$ crystals has been investigated using a strain gauge method. In the ferroelectric phase below 140 C, the strain vs the electric field shows a hysteresis, which is ascribed to the effect of ferroelectric domains. A quadratic relation holds between the strain x and the electric polarization P as x = QP² above about 170 C in the paraelectric phase. Values of the electrostrictive Q coefficients are determined from the measurements near 190 C, as Q₁₁ = 1.6·10^?2m⁴/C², Q₁₂ = ?0.86·10^?2m⁴/C², and Q₄₄ = 0.85·10^?2m⁴/C².     

Magnetic,electrical and thermal studies on the V1−xMox02

The monoclinic-to-tetragonal structure transition of oxides V_1?xMo_x0₂ with $\text{0≤}\text{x}\text{≤0.20}$ has been studied by means of DTA, X-ray diffraction, magnetic susceptibility (powder samples) and electrical conductivity (single crystals) measurements within the temperature region 80 K to 400 K. A linear decrease of the transition temperature of 11 K per atom % Mo was observed. The magnetic susceptibility of the low temperature phase was found to be temperature independent paramagnetic for all preparations. Electrical conductivity measurements on the same phase showed crystals with $\text{x}\text{? 0.04}$ to be semiconducting, while a metallic behavior was observed in the region $\text{0.10 ?}\text{x}\text{? 0.14}$.     

n-PbTep+−Pb1−xSnxTe heterojunctions prepared by a modified hot wall technique

$\text{n-PbTe}\text{p}{}^{\mathrm{+}}\text{?}\text{Pb}{}_{\mathrm{1?x}}\text{Sn}{}_{\mathrm{x}}\text{Te}$ heterojunctions with a long wavelength spectral cutoff (λ_c ≈ 6 μm) were prepared using the double-channel hot wall technique. The electrical and photoelectrical properties of the heterojunctions at 77, 197 and 300 K were investigated. Detectors with R_oA equal to 170 Ω cm² and a quantum efficiency of 25–40% were obtained. Reasons for the shift of the long wavelength spectral cutoff of the heterojunctions towards shorter wavelengths are given.     

Core-current-enhanced domain-wall pinning in nanocrystalline Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 15.5/B/sub 7/ ribbon

We have studied the influence of surface fields H/sub p/ (generated by either direct or alternating core current) on soft magnetic properties of amorphous and nanocrystalline Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 15.5/B/sub 7/ ribbon. While in an amorphous ribbon the coercive field H/sub c/ decreases with H/sub p/, in the same optimally annealed ribbon (H/sub c/=1.3 A/m, M/sub m//spl ap/M/sub s/) H/sub c/ increases with H/sub p/ for all the explored types of H/sub p/ (static and dynamic with different phases with respect to that of the magnetizing field H). The unexpected increase of H/sub c/ in nanocrystalline ribbon is associated with the influence of H/sub p/ on the surface and main (inner) domain structure. Here, we develop a model that takes into account this influence and explains the experimental results.     

Interfacial microstructure of NiSix/HfO2/SiOx/Si gate stacks

Integration of NiSi_x based fully silicided metal gates with HfO₂ high-k gate dielectrics offers promise for further scaling of complementary metal-oxide- semiconductor devices. A combination of high resolution transmission electron microscopy and small probe electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis has been applied to study interfacial reactions in the undoped gate stack. NiSi was found to be polycrystalline with the grain size decreasing from top to bottom of NiSi_x film. Ni content varies near the NiSi/HfO_x interface whereby both Ni-rich and monosilicide phases were observed. Spatially non-uniform distribution of oxygen along NiSi_x/HfO₂ interface was observed by dark field Scanning Transmission Electron Microscopy and EELS. Interfacial roughness of NiSi_x/HfO_x was found higher than that of poly-Si/HfO₂, likely due to compositional non-uniformity of NiSi_x. No intermixing between Hf, Ni and Si beyond interfacial roughness was observed.     

Reactive plasma deposited SixCyHz films

Si_xC_yH_z films have been prepared at 200°C by reactive plasma deposition from SiH₄ and CH₄ diluted in helium in a tubular reactor. These films have a ratio s (equal to $\text{Si}\text{(}\text{Si+C}\text{))}$ ranging from 0.2 to 0.8, a refractive index ranging from 1.96 to 2.6 and an optical energy band gap in the range 2.7-2.2 eV. The total quantity of hydrogen in the film is 40% when s=0.5. Infrared analysis shows that these films have large fractions of homonuclear bonds and that this material is best described as a polymer. Mass spectrometric measurements of the gaseous products formed in the SiH₄-CH₄-He plasma have been performed and the results are related to the composition of the deposited layers.