A study on the charge-discharge mechanism of Co3O4 as an anode for the Li ion secondary battery

Co₃O₄ has shown acceptable electrochemical properties as the anode material of Li secondary batteries. In detail, its capacity reached about 700 mAh/g, twice as high as graphite, and 93.4% of initial capacity was retained after 100 cycles. EIS (electrochemical impedance spectroscopy) analyses revealed that after the 1st cycle, the insertion or extraction of Li ions in Co₃O₄ can occur homogeneously and reversibly (randless-like behavior, homogeneous mixture: Co + Li₂O (in the state of Li insertion), Co₃O₄ (in the state of Li extraction)). In fact, the coulombic efficiency of Co₃O₄ was almost 100% except for the 1st cycle. According to P. Poizot's research on several kinds of transition metal oxides, such as Co₃O₄, CoO, NiO, etc., a small Li₂O particle size and catalytic activity of the transition metal are expected to decrease the binding energy of Li₂O tremendously. As a result, Li₂O should be easy to decompose, and transition metal oxides should be able to charge or discharge reversibly by formation or decomposition of Li₂O. However, this assumption has never been confirmed by experimental results. In our results, the CV (cyclic voltammogram) of a Li₂O-Co mixture shows much larger oxidation and reduction peaks than that of Li₂O. Based on XRD analyses, oxidation and reduction in the CV of Li₂O correspond, respectively, to the decomposition and formation of Li₂O. So, it can be asserted that Co addition to Li₂O facilitates decomposition and formation processes in Li₂O and that the catalytic effect of the transition metal must be one of the main causes that make Li₂O form or decompose repeatedly.     

Fabrication of all-solid-state battery using Li5La3Ta2O12 ceramic electrolyte

The chemical and electrochemical properties of Li₅La₃Ta₂O₁₂ (LLTa) solid electrolyte were extensively investigated to determine its compatibility with an all-solid-state battery. A well-sintered LLTa pellet with a garnet-like structure was obtained after sintering at 1200 °C for 24 h. Li ion conductivity of the LLTa pellet was estimated to be 1.3×10⁻⁴ S cm⁻¹. The LLTa pellet was stable when in contact with lithium metal. This indicates that Li metal anode, which is the best anode material, can be applied with the LLTa system. A full cell composed of LiCoO₂/LLTa/Li configuration was constructed, and its electrochemical properties were tested. In the resulting cyclic voltammogram, a clear redox couple of LiCoO₂ was observed, implying that the all-solid-state battery with the Li metal anode was successfully operated at room temperature. The redox peaks of the battery were still observed even after one year of storage in an Ar-filled glove-box. It can be concluded that the LLTa electrolyte is a promising candidate for the all-solid-state battery because of its relatively high Li ion conductivity and good stability when in contact with Li metal anode and LiCoO₂ cathode.     

The effect of Co-Co3O4 coating on the electrochemical properties of Si as an anode material for Li ion battery

In order to improve the electrochemical performance of Si as an anode material for Li ion secondary batteries, a biphasic layer composed of Co and Co₃O₄ was coated on Si particles by sol-gel method. Compared to Si, Co-Co₃O₄ coated Si showed the drastic improvement in several electrochemical properties, such as initial coulombic efficiency (55% → 88%), cyclic efficiency and cycle life. The comparison between Co-Co₃O₄ coated Si and heat-treated Si without the coating let us know that the improvement of electrochemical properties only results from Co-Co₃O₄ coating layer. Little changed cyclic properties (cyclic efficiency and cycle life) of Co-Co₃O₄ coated Si even at a higher charge-discharge rate insinuated that Co-Co₃O₄ coating layer plays a crucial role in maintaining the electronic contacts between particles and conducting parts. When trying to measure a thickness variation of the electrodes each containing Si and Co-Co₃O₄ coated Si as active materials, it was notified that Co-Co₃O₄ coating layer can accommodate the volume expansion of Si during Li⁺ insertion, which has its original thickness almost recovered after Li⁺ extraction.     

The effect of quaternary ammonium on discharge characteristic of a non-aqueous electrolyte Li/O2 battery

The effect of quaternary ammonium on discharge characteristic of Li/O₂ cells was studied by using Super-P carbon as air cathode, a 0.2 mol kg⁻¹ LiSO₃CF₃ 1:3 (wt.) PC/DME solution as baseline electrolyte, and tetrabutylammonium triflate (NBu₄SO₃CF₃) as an electrolyte additive or a co-salt. Results show that Li/O₂ cells can run normally in an electrolyte with NBu₄SO₃CF₃ as the sole conductive salt. However, such cells suffer lower voltage and capacity as compared with those using the lithium ionic baseline electrolyte. This is due to the larger molar volume of quaternary ammonium cation, which results in less deposition of oxygen reduction products on the surface of carbon. When used as an electrolyte additive or a co-salt, the ammonium is shown to increase capacity of Li/O₂ cells. The plot of differential capacity versus cell voltage shows that the Li/O₂ cell with ammonium added has broad and scatted differential capacity peaks between the voltages of two reactions of “2Li + O₂ → Li₂O₂” and “2Li + Li₂O₂ → 2Li₂O”. This phenomenon can be attributed to the phase transfer catalysis (PTC) property of quaternary ammonium on the second reaction. Due to inverse effects of the cation geometric volume and the PTC property of ammonium ions on the discharge capacity, there is an optimum range for the concentration of ammonium. It is shown that the addition of NBu₄SO₃CF₃ increases discharge capacity of Li/O₂ cell only when its concentration is in a range from 5 mol% to 50 mol% vs. the total of Li/ammonium mixed salt, and that the optimum concentration is about 5 mol%. In this work we show that the addition of 5 mol% NBu₄SO₃CF₃ into the baseline electrolyte can increase discharge capacity of a Li/O₂ cell from 732 mAh g⁻¹ to 1068 mAh g⁻¹ (in reference to the weight of Super-P carbon) when the cell is discharged at 0.2 mA cm⁻².     

Measurement of concentration profiles over ZnO–Cr2O3/CeO2–ZrO2 monolithic catalyst in oxidative steam reforming of methanol

Oxidative steam reforming of methanol (OSRM) reaction was investigated over a novel monolithic ZnO–Cr₂O₃/CeO₂–ZrO₂ catalyst developed in our laboratory. A novel flat-bed reactor was designed to measure the concentration profiles of the monolithic catalyst beds under different operation conditions: water-to-methanol mole ratio (W/M) between 1 and 1.5; oxygen-to-methanol mole ratio (O/M) in the range of 0.1–0.3; space velocity ranging from 1840 to 2890 h^− 1; and reaction temperature in the scale of 400–440 °C. On the basis of these results, reaction pathways for the OSRM were discussed. It is indicated that only three independent reactions dominate in our reaction system, namely, the partial oxidation of methanol, the steam reforming of methanol and the methanol decomposition reaction, whereas the water–gas shift and the reverse water–gas shift reactions should be ignored. In addition, the steam reforming of methanol proceeds along all the catalyst bed, whereas methanol decomposition and oxidation reactions occur mainly at the entrance of the catalyst bed.     

离子液体BMIMBF4对全钒液流电池正极电解液的影响

为提高全钒液流电池的能量密度和正极电解液稳定性,采用循环伏安、交流阻抗等方法,研究了1-丁基-3-甲基咪唑四氟硼酸盐（BMIMBF₄）作为正极电解液添加剂对溶液稳定性和电化学反应活性的影响,并对其机理进行了初步探讨。实验结果表明,添加BMIMBF₄后,正极电解液中五价钒离子的稳定性显著提高,电解液的电化学反应活性也有所提升。当添加量为1%时,电池的单位体积电容量比有所增加,并且能量效率有所提升。     

Core–shell Ni0.5TiOPO4/C composites as anode materials in Li ion batteries

Pristine Ni_0.5TiOPO₄ was prepared via a traditional solid-state reaction, and then Ni_0.5TiOPO₄/C composites with core–shell nanostructures were synthesized by hydrothermally treating Ni_0.5TiOPO₄ in glucose solution. X-ray diffraction patterns indicate that Ni_0.5TiOPO₄/C crystallizes in monoclinic P2₁/c space group. Scanning electron microscopy and transmission electron microscopy show that the small particles with different sizes are coated with uniform carbon film of ∼3 nm in thickness. Raman spectroscopy also confirms the presence of carbon in the composites. Ni_0.5TiOPO₄/C composites presented a capacity of 276 mAh g⁻¹ after 30 cycles at the current density of 42.7 mA g⁻¹, much higher than that of pristine Ni_0.5TiOPO₄ (155 mAh g⁻¹). The improved electrochemical performances can be attributed to the existence of carbon shell.     

Cathodic performance of VOPO4 with various crystal phases for Li ion rechargeable battery

Cathodic performance of six different VOPO₄ phases for Li ion rechargeable battery was investigated. It was found that VOPO₄ exhibits a high flat discharge potential of 3.7 V for Li ion electrochemical intercalation and de-intercalation excepting for β- and ε-types. On the other hand, slightly higher flat discharge potential of 3.9 and 3.8 V was observed for β- and ε-types. Capacity for Li intercalation is strongly related with the crystal structure of VOPO₄. In particular, δ-phase exhibits the largest reversible capacity of ca. 130 mAh/g among the examined VOPO₄. High capacity for Li intercalation in δ-phase VOPO₄ hardly decreased over 30 times of charge and discharge cycles. Although the reversible capacity decreased with increasing the current density for charge and discharge, large capacity of 80 mAh/g was still sustained at 0.4 mA/cm² for δ-type VOPO₄.     

Suppression of crystallization in a plastic crystal electrolyte (SN/LiClO4) by a polymeric additive (polyethylene oxide) for battery applications

A basic problem with many promising solid electrolyte materials for battery applications is that crystallization in these materials at room temperature makes ionic mobilities plummet, thus compromising battery function. In the present work, we consider the use of a polymer additive (polyethylene oxide, PEO) to inhibit the crystallization of a promising battery electrolyte material, the organic crystal forming molecule succinonitrile (SN) mixed with a salt (LiClO₄). While SN spherulite formation still occurs at low PEO concentrations, the SN spherulites become progressively irregular and smaller with an increasing PEO concentration until a ‘critical’ PEO concentration (20% molar fraction PEO) is reached where SN crystallization is no longer observable by optical microscopy at room temperature. Increasing the PEO concentration further to 70% (molar fraction PEO) leads to a high PEO concentration regime where PEO spherulites become readily apparent by optical microscopy. Additional diffraction and thermodynamic measurements establish the predominantly amorphous nature of our electrolyte-polymer mixtures at intermediate PEO concentrations (20-60% molar fraction PEO) and electrical conductivity measurements confirm that these complex mixtures exhibit the phenomenology of glass-forming liquids. Importantly, the intermediate PEO concentration electrolyte-polymer mixtures retain a relatively high conductivity at room temperature in comparison to the semicrystalline materials that are obtained at low and high PEO concentrations. We have thus demonstrated an effective strategy for creating highly conductive and stable conductive polymer-electrolyte materials at room temperature that are promising for battery applications.     

Inactivation of Escherichia coli in Na2SO4 electrolyte using boron-doped diamond anode

Electrochemical disinfection in chloride-free electrolyte has attracted more and more attention due to advantages of no production of disinfection byproducts (DBPs), and boron-doped diamond (BDD) anode with several unique properties has shown great potential in this field. In this study, inactivation of Escherichia coli (E. coli) was investigated in Na₂SO₄ electrolyte using BDD anode. Firstly, disinfection tests were carried on at different current density. The inactivation rate of E. coli and also the concentration of hydroxyl radical (OH) increased with the current density, which indicated the major role of OH in the disinfection process. At 20 mA cm⁻² the energy consumption was the lowest to reach an equal inactivation. Moreover, it was found that inactivation rate of E. coli rose with the increasing Na₂SO₄ concentration and they were inactivated more faster in Na₂SO₄ than in NaH₂PO₄ or NaNO₃ electrolyte even in the presence of OH scavenger, which could be attributed to the oxidants produced in the electrolysis of SO₄²⁻, such as peroxodisulfate (S₂O₈²⁻). And the role of S₂O₈²⁻ was proved in the disinfection experiments. These results demonstrated that, besides hydroxyl radical and its consecutive products, oxidants produced in SO₄²⁻ electrolysis at BDD anode played a role in electrochemical disinfection in Na₂SO₄ electrolyte.     

Characterisation and modelling of the transport properties in lithium battery gel electrolytes: Part I. The binary electrolyte PC/LiClO4

A recent development trend for rechargeable lithium batteries is the use of ternary gel electrolytes. The main advantage of the gels is the mechanical rigidity, which improves as the polymer content is increased. However, the transport properties deteriorate with increasing polymer amount. This dualistic optimisation problem has caused an increased interest in understanding the transport processes in gels, however no full characterisation or modelling study could be found in the literature. In this paper, which is the first part of a study of the transport in the ternary gel system PMMA/PC/LiClO₄, the liquid electrolyte PC/LiClO₄ is characterised and modelled for concentrations between 0.1 and 2 M according to a previously employed methodology, based on electrochemical measurements. A model using concentration dependent interaction parameters proved to describe the results in the whole concentration region well. The cationic transport number and salt diffusivity were determined to be approximately 0.3 and 1e−10 m²/s, respectively. The mean ionic activity factor variations prove to be substantial. Furthermore, it was demonstrated that the inter-ionic friction was important to consider at concentrations above 1 M. The fundamental friction parameters determined in this part will be used in the following part of the study to describe the friction between ions and solvent.     

Electrochemical formation of Yb-Ni alloy films by Li codeposition method in a molten LiCl-KCl-YbCl3 system

Electrochemical formation of Yb-Ni alloy films at a Ni cathode was investigated in a molten LiCl-KCl-YbCl₃ (0.5 mol%) at 723 K. A very thin YbNi₂ film (∼100 nm) was formed by potentiostatic electrolysis at 0.10 V (vs. Li⁺/Li) for 24 h. A much thicker YbNi₂ alloy film (∼7 μm) was formed by Li codeposition method (cathodic galvanostatic electrolysis at 50 mA cm⁻²) for 1 h. The formed YbNi₂ films were changed to Yb₂Ni₁₇ and α-Ni phases by anodic potentiostatic electrolysis depending on the applied potentials. The formation potentials of Yb₂Ni₁₇ and YbNi₂ were found to be 0.75 and 0.25 V, respectively.     

Electrochemical properties of TiP2O7 and LiTi2(PO4)3 as anode material for lithium ion battery with aqueous solution electrolyte

Some polyanionic compounds, e.g. TiP₂O₇ and LiTi₂(PO₄)₃ with 3D framework structure were proposed to be used as anodes of lithium ion battery with aqueous electrolyte. The cyclic voltammetry properties TiP₂O₇ and LiTi₂(PO₄)₃ suggested that Li-ion de/intercalation reaction can occur without serious hydrogen evolution in 5 M LiNO₃ aqueous solution. The TiP₂O₇ and LiTi₂(PO₄)₃ give capacities of about 80 mAh/g between potentials of −0.50 V and 0 V (versus SHE) and 90 mAh/g between −0.65 V and −0.10 V (versus SHE), respectively. A test cell consisting of TiP₂O₇/5 M LiNO₃/LiMn₂O₄ delivers approximately 42 mAh/g (weight of cathode and anode) at average voltage of 1.40 V, and LiTi₂(PO₄)₃/5 M LiNO₃/LiMn₂O₄ delivers approximately 45 mAh/g at average voltage of 1.50 V. Both as-assembled cells suffered from short cycle life. The capacity fading may be related to deterioration of anode material.     

锂离子电池硅酸锰锂电极材料的研究进展

具有斜方晶系结构的硅酸锰锂（LizMnSi04）是近年来备受关注的锂离子电池正极材料,作者详细叙述了近年来国内外对Li2MnSiO4研究状况,着重介绍了各种制备方法和改性方法,其中溶胶凝胶法是目前应用最多的制备方法,而掺杂改性的方法是目前比较有效的改性方法。同时还介绍了这些方法所存在的问题。     

Electrochemical formation of Sm-Co alloy films by Li codeposition method in a molten LiCl-KCl-SmCl3 system

Electrochemical formation of Sm-Co alloy films at a Co cathode was studied in a molten LiCl-KCl-SmCl₃ (0.5 mol.%) at 723 K. Very thin film (∼100 nm) of SmCo₂ alloy was obtained by potentiostatic electrolysis at 0.20 V (vs. Li⁺/Li) for 24 h. Much thicker alloy film (∼5 μm) was formed by Li codeposition method (cathodic galvanostatic electrolysis at 50 mA cm⁻²) for 1 h. The formed alloy phase was suggested as Li_xSm₄Co₆ (x∼3). The formed alloy film was changed to various Sm-Co alloy phases by anodic potentiostatic electrolysis depending on the applied potentials. The formation potentials of Sm₂Co₁₇, SmCo₃, SmCo₂ and Li_xSm₄Co₆ were found to be 1.40, 0.80, 0.30 and 0.05 V, respectively.     

High rate capability and long-term cyclability of Li4Ti4.9V0.1O12 as anode material in lithium ion battery

Li₄Ti_4.9V_0.1O₁₂ nanometric powders were synthesized via a facile solid-state reaction method under inert atmosphere. XRD analyses demonstrated that the V-ions successfully entered the structure of cubic spinel-type Li₄Ti₅O₁₂ (LTO), reduced the lattice parameter and no impurities appeared. Compared with the pristine LTO, the electronic conductivity of Li₄Ti_4.9V_0.1O₁₂ powders is as high as 2.9 × 10⁻¹ S cm⁻¹, which should be attributed to the transformation of some Ti³⁺ from Ti⁴⁺ induced by the efficient V-ions doping and the deficient oxygen condition. Meanwhile, the results of XPS and EDS further proved the coexistence of V⁵⁺ and Ti³⁺ ions. This mixed Ti⁴⁺/Ti³⁺ ions can remarkably improve its cycle stability at high discharge–charge rates because of the enhancement of the electronic conductivity. The images of SEM showed that Li₄Ti_4.9V_0.1O₁₂ powders have smaller particles and narrower particle size distribution under 330 nm. And EIS indicates that Li₄Ti_4.9V_0.1O₁₂ has a faster lithium-ion diffusivity than LTO. Between 1.0 and 2.5 V, the electrochemical performance, especially at high rates, is excellent. The discharge capacities are as high as 166 mAh g⁻¹ at 0.5C and 117.3 mAh g⁻¹ at 5C. At the rate of 2C, it exhibits a long-term cyclability, retaining over 97.9% of its initial discharge capacity beyond 1713 cycles. These outstanding electrochemical performances should be ascribed to its nanometric particle size and high conductivity (both electron and lithium ion). Therefore, the as-prepared material is promising for such extensive applications as plug-in hybrid electric vehicles and electric vehicles.     

Understanding the voltage profile of Li insertion into LiNi0.5−yFeyMn1.5O4 in Li cells

LiNi_0.5−yM_yMn_1.5O₄ compounds have proven to be of great interest as active cathode material for high-voltage lithium-ion cells. The electrochemical behavior of LiNi_0.5−yFe_yMn_1.5O₄ compounds as cathode material in lithium cells is studied here. The charge-discharge curves are characterized by three main plateaus, ascribable to the removal (during charge) or filling (during discharge) of d electrons corresponding to the different redox pairs present: Fe^IV/Fe^III, Ni^IV/Ni^II and Mn^IV/Mn^III. Taking into account the entropy associated to the lithium extraction/insertion and the filling of the different electronic levels, the modelization gives a good reproducibility of the experimental electrochemical curves. The standard potential μ⁰ of the redox pairs were estimated to be ca. −4.90, −4.80 and −4.23 eV, respectively.     

Determination of the safety level of an advanced lithium ion battery having a nanostructured Sn-C anode, a high voltage LiNi0.5Mn1.5O4 cathode, and a polyvinylidene fluoride-based gel electrolyte

In this work we evaluate the safety characteristics of an advanced Sn-C/EC:PC 1:1, LiPF₆ PVdF gel electrolyte (GPE)/LiNi_0.5Mn_1.5O₄ lithium ion polymer battery. The tests are performed by using a complex analysis that combines Differential Scanning Calorimetry (DSC) Thermal Gravimetric Analysis (TGA), and Mass Spectrometry (MS). This is a very convenient tool since it detects eventual thermal decomposition processes and provides information on the nature of their products. The results of the DSC-TGA-MS analysis are here reported and discussed. They demonstrate that both the anode and the cathode sides of the battery may stand temperatures up to ca. 200 °C without undergoing thermal decomposition. This is a convincing evidence that the Sn-C/LiNi_0.5Mn_1.5O₄ lithium ion polymer battery is safe.     

Hydrothermal synthesis of nanostructured Co3O4 materials under pulsed magnetic field and with an aging technique, and their electrochemical performance as anode for lithium-ion battery

Co₃O₄ nanoparticle samples were prepared as anode materials for lithium-ion batteries by the hydrothermal synthesis method without magnetic field (Co₃O₄-0T), under pulsed magnetic field (Co₃O₄-4T), and by using an aging technique (Co₃O₄-Aging), respectively. The morphology and structural properties of the Co₃O₄ nanoparticles were investigated by field-emission scanning electron microscopy (FE-SEM), and X-ray diffraction (XRD). FE-SEM measurements demonstrated that the Co₃O₄ sample formed under a 4 T magnetic field consisted of large agglomerated spheres composed of numerous quasi-spherical nanoparticles with a typical diameter of ∼25 nm and had more compact and smoother surfaces compared to a reference sample prepared without magnetic field. After the aging process, large Co₃O₄ hollow spheres composed of numerous spherical nanoparticles with a typical diameter of ∼20 nm were formed. Electrochemical measurements showed that Co₃O₄ materials prepared by the aging technique (Co₃O₄-Aging) yielded the best electrochemical performance compared with the other samples. Capacities were maintained at 274, 348, and 407 mAh g⁻¹ up to 100 cycles for the Co₃O₄-0T, Co₃O₄-4T, and Co₃O₄-Aging materials, which are about 26, 27, and 30% of initial discharge capacities, respectively. The capacity loss is in the order of Co₃O₄-Aging < Co₃O₄-4T < Co₃O₄-0T. Thus, the morphology affects not only the discharge capacity, but also the cycling stability of Li-ion batteries.     

Corrosion resistance of oxide layers formed on AZ91 Mg alloy in KMnO4 electrolyte by plasma electrolytic oxidation

The plasma electrolytic oxidation (PEO) process in AZ91 Mg alloy is studied using a solution containing KOH + KF + Na₂SiO₃ both with and without potassium permanganate (KMnO₄). The addition of potassium permanganate to the electrolyte influences coating thickness, surface morphology and the microstructure of oxide layers obtained by the PEO process. Oxide layers formed on AZ91 Mg alloy by the electrolyte containing KMnO₄ consists of MgO, MgF₂, Mg₂SiO₄ and Mn₂O₃. The corrosion resistance of the sample processed in bath containing KMnO₄ was superior to that of the sample processed in the bath without KMnO₄. It is suggested that enhancement of the corrosion resistance of AZ91 Mg alloy depends strongly on the presence of manganese oxide in the oxide layer.