Synthesis and characterization of Li2MnSiO4/C nanocomposite cathode material for lithium ion batteries

A high capacity Li₂MnSiO₄/C nanocomposite cathode material with good rate performance for lithium ion batteries through a solution route has been successfully prepared. The material is able to deliver a reversible capacity of 209 mAh g⁻¹ in the first cycle, i.e. more than one electron exchange can be reversible cycled in the materials. The highly dispersion of nanocrystalline Li₂MnSiO₄ which was surround by a thin film of carbon was attributed to the cause of excellent performance of the materials. Ex situ XRD and IR results show that poor cycling behavior of Li₂MnSiO₄ might be due to an amorphization process of the materials.     

Lithium intercalation and alloying effects on electronic structures of spinel lithium manganese oxides

Employing the DV-Xα molecular orbital method, lithium intercalation effect and alloying effect have been investigated on the electronic structures of spinel M_xMn_2−xO₄ and LiM_xMn_2−xO₄ (M=Ti, V, Cr, Mn, Fe, Co, Ni and Cu). It is found that the lithium intercalation induces the electron transfer from Li to the surrounding O ions, and enlarges the Mn-3d/O-2p band gap greatly. Such a modification of the oxygen electronic state is probably related to the electrochemical cell voltage. This lithium intercalation effect still holds even in the alloyed systems. However, the amount of transferred charges from M to O ions changes depending on the alloying element, M. So the alloying addition modifies the oxygen electronic state and influences the lithium intercalation process indirectly.     

Lithium metal hydrides (Li2CaH4 and Li2SrH4) for hydrogen storage; mechanical,electronic and optical properties

Hydrogen storage is a critical step for commercialisation of hydrogen consumed energy production. Among other storage methods, solid state storage of hydrogen attracts much attention and requires extensive research. This study rationally and systematically designs novel solid state hydrides; Li₂CaH₄ (GHD is obtained as −6.95 wt %) and Li₂SrH₄ (GHD is obtained as −3.83 wt %) using computational method. As a first step, we suggest and predict crystal structures of solid state Li₂CaH₄ and Li₂SrH₄ hydrides and look for synthesizability. Then, the mechanical stabilities of hydrides are identified using elastic constants. Both hydrides fulfil the well-known Born stability criteria, indicating that both Li₂CaH₄ and Li₂SrH₄ are mechanically stable materials. Several critical parameters, bulk modulus, shear modulus, Cauchy pressures, anisotropy factors of hydrides and bonding characteristics are obtained and evaluated. Furthermore, electronic and optical band structures of hydrides are computed. Both Li₂CaH₄ and Li₂SrH₄ have indirect bands gaps as 0.96 eV (Г-U) and 1.10 eV (Г-R). Thus, both materials are electronically semiconducting. Also, Bader charge analysis of hydrides have been carried out. Charge density distribution suggests an ionic-like (or polarized covalent) bonding interaction between the atoms.     

热风炉烟气余热资源测定与利用研究

韶关冶炼厂热风炉烟气的余热尚未回收利用,经测定其余热资源总量为1878kW,温度平均280℃,为二类余热资源。如果应用溴化锂吸收式制冷技术,可利用热风炉烟气余热资源制取冷冻水,用于工艺冷却,如鼓风炉空气脱湿。经测算仅降低焦比和增加喷煤量两方面,韶关冶炼厂鼓风炉空气脱湿产生的经济效益每年就可达1500万元左右。     

Cellulose as a binding material in graphitic anodes for Li ion batteries: a performance and degradation study

Four types of cellulose, in particular carboxy methyl cellulose (CMC), are tested as potential binding materials in graphitic anodes for lithium ion batteries. It is shown that a minimum content of a cellulose which gives acceptable anode properties (reversible capacity>300 mA h g⁻¹ during the first 10 cycles, irreversible loss<20%) is about 2 wt.%, which is less than in the case of conventional polymeric binders (5-10 wt.%). Kinetics of insertion-deinsertion and passivation processes seem not to be affected by the presence of cellulose. Explanation for the electrode failure at cellulose contents lower than 1 wt.% is given based on X-ray diffraction and microscopy investigations. Finally, the structure (distribution) of cellulose in the composite anode material is discussed and (indirectly) checked with a series of experiments. Most results are compared with the corresponding results obtained either with gelatin or conventional polymeric binders or both.     

锂交换法制备六氟磷酸锂及表征

六氟磷酸和吡啶反应生成吡啶六氟磷酸,吡啶六氟磷酸和氢氧化锂通过锂交换反应生成吡啶六氟磷酸锂,在四氢呋喃溶剂中,吡啶六氟磷酸锂与浓硫酸反应生成六氟磷酸锂。实验研究了溶剂、反应温度、反应时间、配料比等对锂交换反应的影响,得到适宜的工艺条件:65℃反应4 h,原料配比n(C5H5NHPF6)∶n(LiOH)=1.0∶1.0,此条件下吡啶六氟磷酸锂收率94.5%;经核磁共振、红外光谱检测,吡啶六氟磷酸锂和LiPF6是目的产物。     

锂离子电池炭负极材料研究现状与发展

综述了近年来各种炭材料作为锂离子电池负极材料的新进展,着重分析了石墨、焦炭和难石墨化炭在放电容量、不可逆容量损失、充放电电位和充放电速率等主要性能上的差异以及与其结构之间的联系;指出以PAS为代表的热解炭(低于800℃)和纳米炭材料将是锂离子电池负极材料的发展方向。     

Glyme-based nonaqueous electrolytes for rechargeable lithium cells

Poly(ethylene glycol)dimethyl ethers [(CH₃O(CH₂CH₂O)_nCH₃, n = 1, 2, 3, and 4)] are generally known as “glymes”. This study examines the conductivity, lithium ion solvation state and charge-discharge cycling efficiency of lithium metal anodes in glyme-based electrolytes for rechargeable lithium cells. 1 M (M: mol l⁻¹) LiPF₆ was used as the solute. The properties of the glymes were investigated by using a ternary mixed solvent consisting of n-glyme, ethylene carbonate (EC) and methylethylcarbonate (MEC). This was because the solubility of LiPF₆ is far less than 1 M in an n-glyme single solvent. The glyme solutions exhibited higher conductivity and higher lithium cycling efficiency than EC/MEC. The conductivity tended to increase with decreases in ethylene oxide chain number (n) and solution viscosity. The decrease in the solution viscosity resulted from the change in the lithium ion solvation structure that occurred when a glyme was added to EC/MEC. The selective solvation of the glyme with respect to lithium ions was clearly demonstrated by -NMR measurements. The lithium cycling efficiency value depended on the charge-discharge current (I_ps). When n increased there was an increase in lithium cycling efficiency at a low I_ps and a decrease in the reduction potential of the glymes. When the conductivities including those at low temperature (below 0 °C), and charge-discharge cycling at a high current are taken into account, di- or tri-glyme is superior to the other glymes tested here.     

Synthetic optimization of Li[Ni1/3Co1/3Mn1/3]O2 via co-precipitation

Li[Ni_1/3Co_1/3Mn_1/3]O₂ powders were synthesized from co-precipitated spherical metal hydroxide, (Ni_1/3Co_1/3Mn_1/3)(OH)₂. The preparation of metal hydroxide was significantly dependent on synthetic conditions, such as pH, amount of chelating agent, stirring speed, etc. The optimized condition resulted in (Ni_1/3Co_1/3Mn_1/3)(OH)₂, of which the particle size distribution was uniform and the particle shape was spherical, as observed by scanning electron microscopy. Calcination of the uniform metal hydroxide with LiOH at higher temperature led to a well-ordered layer-structured Li[Ni_1/3Co_1/3Mn_1/3]O₂, as confirmed by Rietveld refinement of X-ray diffraction pattern. Due to the homogeneity of the metal hydroxide, (Ni_1/3Co_1/3Mn_1/3)(OH)₂, the final product, Li[Ni_1/3Co_1/3Mn_1/3]O₂, was also significantly uniform, i.e., the average particle size was of about 10 μm in diameter and the distribution was relatively narrow. As a result, the corresponding tap-density was also high approximately 2.39 g cm−3, of which the value is comparable to that of commercialized LiCoO₂. In the voltage range of 2.8-4.3, 2.8-4.4, and 2.8-4.5 V, the discharge capacities of Li[Ni_1/3Co_1/3Mn_1/3]O₂ electrode were 159, 168, and 177 mAh g⁻¹, respectively. For elevated temperature operation (55 °C), the resulted capacity was of about 168 mAh g⁻¹ with an excellent cyclability.