Ag/C包覆对Li[Li0.2Mn0.54Ni0.13Co0.13]O2电化学性能的影响

运用共沉淀和元素化学沉积相结合的方法,制备出了具有Ag/C 包覆层的层状富锂固溶体材料Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂. 通过X 射线衍射（XRD）、场发射扫描电子显微镜（SEM）、透射电子显微镜（TEM）、恒流充放电、循环伏安（CV）,电化学阻抗谱（EIS）和X 射线能量散射谱（EDS）方法,研究了Ag/C 包覆层对Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂电化学性能的影响. 结果表明,Ag/C 包覆层的厚度约为25 nm,Ag/C 包覆在保持了固溶体材料α-NaFeO₂ 六方层状晶体结构的前提下,显著地改善了Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ 的电化学性能. 在2.0-4.8 V（vs Li/Li⁺）的电压范围内,首次放电（0.05C）容量由242.6 mAh·g^-1提高到272.4 mAh·g^-1,库仑效率由67.6%升高到77.4%;在0.2C倍率下,30 次循环后,Ag/C 包覆的电极材料容量为222.6 mAh·g^-1,比未包覆电极材料的容量高出14.45%;包覆后的电极材料在1C下的容量仍为0.05C下的81.3%. 循环伏安及电化学交流阻抗谱研究表明,Ag/C包覆层抑制了材料在充放电过程中氧的损失,有效降低了Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂颗粒的界面膜电阻与电化学反应电阻.     

Impacts of fluorine on the electrochemical properties of Li[Ni0.5Mn0.5]O2 and Li[Li0.2Ni0.15Co0.1Mn0.55]O2

The impact of the fluorine substitution on the electrochemical properties of layered lithium nickel manganese positive electrode materials for lithium ion batteries is summarized. The addition of a controlled amount of fluorine to the oxygen lattice can effectively improve the capacity retention as well as reduce the impedance of the positive electrode materials. The fluorination of the nickel and manganese based layered oxide cathode material has also led to significant improvement in cycle life and power capability of the battery.     

High-pressure structure of Li2CO3

The high-pressure behavior of Li₂CO₃ is studied up to 25 GPa with synchrotron angle-dispersive powder X-ray diffraction in diamond anvil cells and synthesis using a multi-anvil apparatus. A new non-quenchable hexagonal polymorph (P6₃/mcm, Z=2) occurs above 10 GPa with carbonate groups in a staggered configuration along the c-axis—a=4.4568(2) Å and c=5.1254(6) Å at 10 GPa. Two columns of face-shared distorted octahedra around the Li atoms are linked through octahedral edges. The oxygen atoms are coordinated to one carbon atom and four lithium atoms to form a distorted square pyramid. Splittings of X-ray reflections for the new polymorph observed above about 22 GPa under non-hydrostatic conditions arise from orthorhombic or monoclinic distortions of the hexagonal lattice. The results of this study are discussed in relation to the structural features found in other Me₂CO₃ carbonates (Me: Na, K, Rb, Cs) at atmospheric conditions.     

Origin of the irreversible plateau (4.5 V) of Li[Li0.182Ni0.182Co0.091Mn0.545]O2 layered material

Layered LiNi_0.4Co_0.2Mn_0.4O₂, Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂, Li[Li_1/3Mn_2/3]O₂ powder materials were prepared by rheological phase method. XRD characterization shows that these samples all have analogous structure to LiCoO₂. Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ can be considered to be the solid solution of LiNi_0.4Co_0.2Mn_0.4O₂ and Li[Li_1/3Mn_2/3]O₂. Detailed information from XRD, ex situ XPS measurement and electrochemical analysis of these three materials reveals the origin of the irreversible plateau (4.5 V) of Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ electrode. The irreversible oxidation reaction occurred in the first charging above 4.5 V is ascribed to the contribution of Li[Li_1/3Mn_2/3]O₂ component, which maybe extract Li⁺ from the transition layer in Li[Li_1/3Mn_2/3]O₂ or Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ through oxygen release. This step also activates Mn⁴⁺ of Li[Li_1/3Mn_2/3]O₂ or Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂, it can be reversibly reduced/oxidized between Mn⁴⁺ and Mn³⁺ in the subsequent cycles.     

Electron spin resonance of diluted solid solutions of Gd2O3 in CeO2

Electron spin resonance spectra of Gd³⁺ in diluted solid solutions of Gd₂O₃ in CeO₂ have been studied at room temperature for Gd concentrations between 0.01 and 1.00 mol%. While in the case of Mn²⁺:CeO₂ samples, both the linewidth and the line intensity go through a maximum between 0.2 and 0.4% Mn and then start to decrease, in the case of Gd³⁺:CeO₂ samples the linewidth and the line intensity increase monotonically with the dopant concentration. This as taken as evidence that in Gd₂O₃-CeO₂ diluted solid solutions there are no clustering effects similar to the ones observed in Mn:CeO₂ solid solutions. It is not clear why clustering effects are present in Mn:CeO₂ solid solutions and not in Gd:CeO₂ solid solutions; however, it seems reasonable to assume that this is due to the fact that the ionic radius of Mn²⁺ (81 pm) is about 25% smaller that that of Gd³⁺ (107.8 pm). In any case, the fact that Gd:CeO₂ solid solutions do not exhibit clustering effects means that ESR linewidth data can be used to estimate the concentration of Gd in CeO₂ samples, as it is possible to do in several solid solutions of paramagnetic ions in ceramic materials. The results also suggest that the range of the exchange interaction between Gd³⁺ ions in CeO₂ is about 0.89 nm.     

Formation of LiAlyNi1−yO2 solid solutions under high and atmospheric pressure

Three methods were used for the synthesis of LiAl_yNi_1−yO₂ solid solutions with layered crystal structure: citrate and hydroxide precursor methods at atmospheric pressure and high-pressure synthesis in oxygen-rich atmosphere (3 GPa). Structural characterization of the oxides was performed by powder XRD analysis and electron paramagnetic resonance (EPR) spectroscopy. Irrespective of the different preparation techniques used, it was found that LiAl_yNi_1−yO₂ solid solutions can be formed in the limited concentration range of 0?y?0.5 and 0.75?y?1.0. The unit cell parameter a decreases linearly with the Al content whereas the unit cell parameter c increases sharper as compared to the linear interpolation of the c parameter calculated for the two end compositions LiNiO₂ and LiAlO₂. In these compositions, aluminum substitutes for Ni in the NiO₂-layer, the mean Al_yNi_1−y-O bond length decreasing. The extent of the trigonal distortion of Al_yNi_1−yO₆ and LiO₆-octahedra varies with the aluminum content and depends on the synthesis procedure used. The LiO₆-octahedra are more flexible to tolerate the increased trigonal distortion as compared to the Al_yNi_1−yO₆-octahedra. High-pressure synthesis favors the formation of oxides with a higher extent of trigonal distortion of both Al_yNi_1−yO₆ and LiO₆-octahedra. From EPR measurements, it was shown that local cationic distribution in LiAl_yNi_1−yO₂ depends on the synthesis temperature. At atmospheric pressure, higher synthesis temperatures promote the reaction of cation mixing between the layers.     

Electrochemical kinetics and cycling performance of nano Li[Li0.23Co0.3Mn0.47]O2 cathode material for lithium ion batteries

Li[Li_0.23Co_0.3Mn_0.47]O₂ cathode material was prepared by a sol–gel method. The material had a primary particle size of about 100 nm, covered by a 30 Å of Li₂CO₃ layer. The material showed promising electrochemical performance when cycled up to 3C rate. The electrochemical kinetics of the first charge was much slower than that of the second charge, due to the complex electrochemical process which involved not only Li⁺ diffusion but also release of oxygen. By taking account of this, the material was pre-charged very slowly (C/50) in the first cycle. This led to excellent electrochemical performance in the following cycles. For instance, the 1C-rate capacity increased to 168 mA h g⁻¹ after 50 cycles, comparing with the 145 mA h g⁻¹ obtained without pre-charging.     

锂离子电池正极材料Li[Li0.2Ni0.2Mn0.6]O2的酸浸改性研究

为提高锂离子电池正极材料Li[Li0.2Ni0.2Mn0.6]O2的首次充放电效率,对固相法合成的该材料进行了酸浸的改性研究。通过X射线衍射(XRD)、扫描电子显微镜(SEM)对所得样品的结构、形貌进行了表征。结果表明,Li[Li0.2Ni0.2Mn0.6]O2经过酸处理后,首次放电效率得到了较大的提高,但是放电中值电压明显下降。其中,0.5 mol.L-1的硝酸浸泡5 h的效果最佳,首次放电效率达到了86.7%,同时放电容量达到最大值的循环次数大大减少。酸浸改性的原因被归结于材料表面出现了富锂尖晶石结构Li4Mn5O12相。     

表面化学侵蚀改性富锂层状正极材料Li[Li0.2Mn0.54Ni0.13Co0.13]O2

采用3种不同pH值的去离子水,NH₄NO₃和H₂C₂O₄溶液对富锂层状正极材料Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂进行表面化学侵蚀改性,旨在改善其整体电化学性能。ICP结果表明pH值对材料中Li的析出具有显著影响。X射线衍射（XRD）表明表面化学侵蚀对材料的结构有影响。拉曼光谱（Raman spectroscopy）表明材料表面结构发生了变化。H₂C₂O₄溶液侵蚀过的样品的首次效率有了极大提高,但同时中值电压和循环性能显著恶化。NH₄NO₃溶液侵蚀过的样品的首次效率从63%提高到了85%,1C倍率下的放电比容量从149 mAh·g^-1提高到194 mAh·g^-1,同时保持了温和的中值电压变化曲线。通过高分辨透射电镜（HRTEM）,X射线光电子能谱（XPS）和电化学阻抗谱（EIS）对改性机理进行了研究。     

表面化学侵蚀改性富锂层状正极材料Li[Li0.2Mn0.54Ni0.13Co0.13]O2

采用3种不同pH值的去离子水,NH₄NO₃和H₂C₂O₄溶液对富锂层状正极材料Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂进行表面化学侵蚀改性,旨在改善其整体电化学性能。ICP结果表明pH值对材料中Li的析出具有显著影响。X射线衍射（XRD）表明表面化学侵蚀对材料的结构有影响。拉曼光谱（Raman spectroscopy）表明材料表面结构发生了变化。H₂C₂O₄溶液侵蚀过的样品的首次效率有了极大提高,但同时中值电压和循环性能显著恶化。NH₄NO₃溶液侵蚀过的样品的首次效率从63%提高到了85%,1C倍率下的放电比容量从149 mAh·g^-1提高到194 mAh·g^-1,同时保持了温和的中值电压变化曲线。通过高分辨透射电镜（HRTEM）,X射线光电子能谱（XPS）和电化学阻抗谱（EIS）对改性机理进行了研究。     

溶胶凝胶法合成富锂正极材料Li[Li0.2Ni0.2Mn0.6]O2及性能表征

以LiOH.H2O、Mn(CH3COO)2.4H2O和Ni(CH3COO)2.4H2O为原料,分别用柠檬酸(CA)与乙二胺四乙酸(EDTA)为配位剂,采用溶胶凝胶法结合固相烧结法制备富锂固溶体正极材料Li[Li0.2Ni0.2Mn0.6]O2。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、激光粒度仪对所得样品的结构、形貌、粒径分布进行了表征,并测试了材料的电化学性能。采用CA配位制备的材料的电化学性能优于用EDTA配位制备的材料的电化学性能,室温下以18 mA.g-1的电流密度,在2.0~4.8 V电压范围内充放电,用CA制备的材料首次充电比容量高达324 mAh.g-1,首次库伦效率达82%;在180 mA.g-1的电流下,其可逆比容量保持在120 mAh.g-1。     

Identification of Superoxide O2- during Thermal Decomposition of Molten KNO3-NaNO2-NaNO3 Salt by Electron Paramagnetic Resonance and UV-Vis Absorption Spectroscopy

On account of excellent thermal physical properties, molten nitrates/nitrites salt has been widely employed in heat transfer and thermal storage industry, especially in concentrated solar power system. The thermal stability study of molten nitrate/nitrite salt is of great importance for this system, and the decomposition mechanism is the most complicated part of it. The oxide species O₂^2- and O₂^- were considered as intermediates in molten KNO₃-NaNO₃ while hard to been detected in high temperature molten salt due to their trace concentration and low stability. In this work, the homemade in situ high temperature UVVis instrument and a commercial electron paramagnetic resonance were utilized to supply evidence for the formation of superoxide during a slow decomposition process of heat transfer salt (HTS, 53 wt% KNO₃/40 wt% NaNO₂/7 wt% NaNO₃). It is found that the superoxide is more easily generated from molten NaNO₂ compared to NaNO₃, and it has an absorption band at 420-440 nm in HTS which red shifts as temperature increases. The band is assigned to charge-transfer transition in NaO₂ or KO₂, responsible for the yellow color of the molten nitrate/nitrite salt. Furthermore, the UV absorption bands of molten NaNO₂ and NaNO₃ are also obtained and compared with that of HTS.     

碳酸盐共沉淀法制备Li[Li0.2Co0.13Ni0.13Mn0.54]O2中加料方式对产物性能的影响

采用碳酸钠和碳酸氢铵作为沉淀剂和络合剂,在水溶液中共沉淀Mn2+、Ni2+和Co2+以获得混合过渡金属元素的碳酸盐沉淀前驱体Mn0.675Ni0.1625Co0.1625CO3。并进一步合成高容量锂离子电池正极材料Li[Li0.2Co0.13Ni0.13Mn0.54]O2。考察了3种不同加料方式对共沉淀前驱体的结构、形貌和元素比例的影响,以及对最终产物的结构、形貌和电化学性能的影响。     

High-pressure synthesis and structural behavior of sodium orthonitrate Na3NO4

Sodium orthonitrate (Na₃NO₄) is an unusual phase containing the first example of isolated tetrahedrally bonded NO₄³⁻ groups. This compound was obtained originally by heating together mixtures of Na₂O and NaNO₃ for periods extending up to >14 days in evacuated chambers. Considering the negative volume change between reactants and products, it was inferred that a high-pressure synthesis route might favor the formation of the Na₃NO₄ compound. We found that the recovered sample is likely to be a high-pressure polymorph, containing NO₄³⁻ groups as evidenced by Raman spectroscopy. The high-pressure behavior of Na₃NO₄ was studied using Raman spectroscopy and synchrotron X-ray diffraction in a diamond anvil cell above 60 GPa. We found no evidence for major structural transformations, even following laser heating experiments carried out at high pressure, although broadening of the Raman peaks could indicate the onset of disordering at higher pressure.     

EPR spectroscopic studies in (30 − x) Li2O-xK2O-10CdO-59B2O3-1MnO2 multi-component glass system

EPR studies were carried out in (30 - x) Li₂O-xK₂O-10CdO-59B₂O₃-1MnO₂ multi-component glass system to understand the effect of the variation in the alkali ratios on the EPR parameters. The observed EPR spectra of Mn²⁺ ion exhibits resonances at g = 2.0, 3.3 and 4.3. The resonance at g = 2.0 is due to Mn²⁺ ions in an environment close to the octahedral symmetry, where as the resonances at g = 3.3 & 4.3 are due to the rhombic surroundings of Mn²⁺ ions. Hyperfine splitting constant values at g = 2.0 and number of paramagnetic centers & paramagnetic susceptibility at different observed resonances were evaluated. These parameters show non linear variation with progressive substitution of Li⁺ ion with K⁺ ions may be due to the changes in cation field strengths and local structural variation due to the variation in mixed alkali ion ratios.     

Stabilization of over-stoichiometric Mn in layered Na2/3MnO2

Sodium manganates with nominal composition Na_2/3MnO₂ were prepared by solid state reaction between Na₂CO₃ and MnCO₃ at 1000 °C. The composition and structure of Na_xMnO₂ were controlled by the rate of cooling from the temperature of preparation. This is a consequence of the capability of Na_2/3MnO₂ to accommodate over‐stoichiometric Mn⁴⁺ ions up to 12.5%. Structural characterization was carried out by XRD powder diffractions, TEM analysis and Raman spectroscopy. The composition and oxidation state of manganese were determined by chemical analysis and magnetic susceptibility measurements. The manganese distribution in the layers was analysed using electron paramagnetic resonance (EPR) spectroscopy. By quenching from 1000 °C, the orthorhombic distorted modification is stabilized. A phase separation into orthorhombic and hexagonal modifications takes place when Na_2/3MnO₂ is slow cooled. The structure changes are concomitant with an increase in the oxidation state of Mn. The over‐stoichiometric Mn⁴⁺ ions are accommodated in the hexagonal modification by creation of vacancies in the MnO₂‐layers.     

Structure and properties of ordered Li2IrO3 and Li2PtO3

The structures of Li₂MO₃ (M=Ir, Pt) can be derived from the well-known Li-ion battery cathode material, LiCoO₂, through ordering of Li⁺ and M⁴⁺ ions in the layers that are exclusively occupied by cobalt in LiCoO₂. The additional cation ordering lowers the symmetry from rhombohedral (R-3m) to monoclinic (C2/m). Unlike Li₂RuO₃ no evidence is found for a further distortion of the structure driven by formation of metal-metal bonds. Thermal analysis studies coupled with both ex-situ and in-situ X-ray diffraction measurements show that these compounds are stable up to temperatures approaching 1375 K in O₂, N₂, and air, but decompose at much lower temperatures in forming gas (5% H₂:95% N₂) due to reduction of the transition metal to its elemental form. Li₂IrO₃ undergoes a slightly more complicated decomposition in reducing atmospheres, which appears to involve loss of oxygen prior to collapse of the layered Li₂IrO₃ structure. Electrical measurements, UV-visible reflectance spectroscopy and electronic band structure calculations show that Li₂IrO₃ is metallic, while Li₂PtO₃ is a semiconductor, with a band gap of 2.3 eV.     

Li[Ni1/3Mn1/3Co1/3]O2掺杂Mo研究

采用高温固相合成法制备了Li[Ni_(1－x)/3Mn_(1－x)/3Co_(1－x)/3Mo_x]O₂ (x＝0, 0.005, 0.01, 0.02). 对它们进行了XRD, SEM, 循环伏安及充放电容量测试, 结果发现, 掺杂x＝0.01 Mo的样品具有较高的嵌锂容量和良好的循环稳定性, 在20 mA/g放电电流密度和2.3～4.6 V的电压范围内具有211.6 mAh/g的首次放电比容量, 循环50周后放电比容量仍能达到185.9 mAh/g, 容量损失为12.1%.     

Mn environment in layered Li[Mg0.5−xNixMn0.5]O2 oxides monitored by EPR spectroscopy

X-band and high-frequency EPR spectroscopy were used for studying the manganese environment in layered Li[Mg_xNi_0.5−xMn_0.5]O₂, 0?x?0.5. Both layered LiMg_0.5Mn_0.5O₂ and monoclinic Li[Li_1/3Mn_2/3]O₂ oxides (containing Mn⁴⁺ ions only) were used as EPR standards. The EPR study was extended to the Ni-substituted analogues, where both Ni²⁺ and Mn⁴⁺ are paramagnetic. For LiMg_0.5−xNi_xMn_0.5O₂ and Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂, an EPR response from Mn⁴⁺ ions only was detected, while the Ni²⁺ ions remained EPR silent in the frequency range of 9.23-285 GHz. For the diamagnetically diluted oxides, LiMg_0.25Ni_0.25Mn_0.5O₂ and Li[Li_0.10Ni_0.35Mn_0.55]O₂, two types of Mn⁴⁺ ions located in a mixed (Mn-Ni-Li)-environment and in a Ni-Mn environment, respectively, were registered by high-field experiments. In the X-band, comparative analysis of the EPR line width of Mn⁴⁺ ions permits to extract the composition of the first coordination sphere of Mn in layered LiMg_0.5−xNi_xMn_0.5O₂ (0?x?0.5) and Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂ (x>0.2). It was shown that a fraction of Mn⁴⁺ are in an environment resembling the ordered “α,β”-type arrangement in Li_1−δ1Ni_δ1[Li_{(1−2x)/3+δ1}Ni_2x/3−δ1)_α(Mn_(2−x)/3Ni_x/3)_β]O₂ (where and δ₁=0.06 were calculated), while the rest of Mn⁴⁺ are in the Ni,Mn-environment corresponding to the Li_1−δ2Ni_δ2[Ni_1−yMn_y]O₂ () composition with a statistical Ni,Mn distribution. For Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂ with x?0.2, IR spectroscopy indicated that the ordered α,β-type arrangement is retained upon Ni introduction into monoclinic Li[Li_1/3Mn_2/3]O₂.     

Ag3Ni2O4—A new stage-2 intercalation compound of 2H-AgNiO2 and physical properties of 2H-AgNiO2 above ambient temperature

Ag₃Ni₂O₄ was obtained as single crystals from a mixture of 2H-AgNiO₂ and Ag₂O in oxygen high-pressure autoclaves (P6₃/mmc (no. 194), a=2.9331(6), c=28.313(9) Å, Z=2). It may be regarded as a stage-2 intercalation compound of the host 2H-AgNiO₂ and is the first staging compound constituted of alternating subvalent and Ag⁺ sheets, inserted between NiO₂⁻ slabs. From a structural point of view, Ag₃Ni₂O₄ represents an intermediate between AgNiO₂ and the recently reported Ag₂NiO₂. The electronic structures of 2H-AgNiO₂ and Ag₃Ni₂O₄ have been investigated based on DFT band structure calculations. The high-temperature characteristics of the starting material 2H-AgNiO₂ were investigated. The inverse magnetic susceptibility, electrical resistivity and differential scanning calorimetry (DSC) show a phase transition in the temperature range of .