Study on lithium/air secondary batteries—Stability of NASICON-type lithium ion conducting glass–ceramics with water

The water stability of the fast lithium ion conducting glass–ceramic electrolyte, Li_1+x+yAl_xTi_2−xSi_yP_3−yO₁₂ (LATP), has been examined in distilled water, and aqueous solutions of LiNO₃, LiCl, LiOH, and HCl. This glass–ceramics are stable in aqueous LiNO₃ and aqueous LiCl, and unstable in aqueous 0.1 M HCl and 1 M LiOH. In distilled water, the electrical conductivity slightly increases as a function of immersion time in water. The Li–Al/Li_3−xPO_4−yN_y/LATP/aqueous 1 M LiCl/Pt cell, where lithium phosphors oxynitrides Li_3−xPO_4−yN_y (LiPON) are used to protect the direct reaction of Li and LATP, shows a stable open circuit voltage (OCV) of 3.64 V at 25 °C, and no cell resistance change for 1 week. Lithium phosphors oxynitride is effectively used as a protective layer to suppress the reaction between the LATP and Li metal. The water-stable Li/LiPON/LATP system can be used in Li/air secondary batteries with the air electrode containing water.     

CNTs@γ-Fe2O3@C composite electrode for high capacity lithium ion storage

Electrode materials with high specific capacity and cycle stability are the key factors that determine the overall performance of lithium ion batteries (LIBs) for new smart electronic device, and such materials with high performance are still challenging. Here, we report a composite material Carbon nanotube @ Iron oxide @ Carbon (γ-CNTs@γ-Fe₂O₃@C) with coaxial cable structure in hydrothermal method with the assistance of glucose. The as-prepared composite materials show superior electrochemical properties with good rate capability and excellent cycling performance, which show the great potential of CNTs@γ-Fe₂O₃@C for practical production and application in energy devices.     

Terminology of lithium battery（Draft）

结合国内外历史尚和当前的用词习惯,本文对锂电池在研究和开发中常见的定义、术语、名词进行了归纳、整理,部份容易引起歧义的进行了解读。相关文件已提交中华人民共和国工业和信息化部电子行业信息标准中全国碱性蓄电池标准化技术委员会。本文为草案,非正式发布文本,标注部分将不会出现在正式发布的文件中,请以正式发布文本为准,本文仅供参考。     

Synthesis and characterization of spinel LiMn2−xNixO4 for lithium/polymer battery applications

Spinel LiMn₂O₄ and LiMn_1.95Ni_0.05O₄ powders with sub-micron, narrow-size-distribution, and phase-pure particles are synthesized by a sol–gel method. The effects of heat treatment on the physicochemical properties of the spinel LiMn₂O₄ powder are examined with X-ray diffractometry, the Brunauer–Emmett–Teller method and scanning electron microscopy. For lithium/polymer battery applications, the LiMn₂O₄ and LiMn_1.95Ni_0.05O₄ electrodes are characterized electrochemically by charge–discharge experiments and a.c.-impedance spectroscopy. Although the Ni-doped electrode has a smaller initial capacity of 126 mA h g⁻¹, it exhibits better cycling performance than the conventional electrode which delivers a higher initial capacity of 145 mA h g⁻¹. The improvement in cycling performance of the former electrode is attributed to stabilization of the spinel structure by the presence of nickel ion. The cycling performance of a Li/polymer electrolyte/LiMn_1.95Ni_0.05O₄ cell at various temperatures is discussed in terms of interfacial resistance and lithium-ion diffusion determined by a.c.-impedance spectroscopy.     

Synthesis and characterization of lithium aluminum-doped spinel (LiAlxMn2−xO4) for lithium secondary battery

LiAl_xMn_2−xO₄ has been synthesized using various aluminum starting materials, such as Al(NO₃)₃, Al(OH)₃, AlF₃ and Al₂O₃ at 600–800°C for 20 h in air or oxygen atmosphere. A melt-impregnation method was used to synthesize Al-doped spinel with good battery performance in this research. The Al-doped content and the intensity ratio of (3 1 1)/(4 0 0) peaks can be important parameters in synthesizing Al-doped spinel which satisfies the requirements of high discharge capacity and good cycleability at the same time. The decrease in Mn³⁺ ion by Al substitution induces a high average oxidation state of Mn ion in the LiAl_xMn_2−xO₄ material. The electrochemical behavior of all samples was studied in Li/LiPF₆-EC/DMC (1:2 by volume)/LiAl_xMn_2−xO₄ cells. Especially, the initial and last discharge capacity of LiAl_0.09Mn_1.97O₄ using LiOH, Mn₃O₄ and Al(OH)₃ complex were 128.7 and 115.5 mAh/g after 100 cycles. The Al substitution in LiMn₂O₄ was an excellent method of enhancing the cycleability of stoichiometric spinel during electrochemical cycling.     

Electrochemical properties and lithium ion solvation behavior of sulfone–ester mixed electrolytes for high-voltage rechargeable lithium cells

Sulfone–ester mixed solvent electrolytes were examined for 5 V-class high-voltage rechargeable lithium cells. As the base-electrolyte, sulfolane (SL)–ethyl acetate (EA) (1:1 mixing volume ratio) containing 1 M LiBF₄ solute was investigated. Electrolyte conductivity, electrochemical stability, Li⁺ ion solvation behavior and cycleability of lithium electrode were evaluated. ¹³C NMR measurement results suggest that Li⁺ ions are solvated with both SL and EA. Charge–discharge cycling efficiency of lithium anode in SL–EA electrolytes was poor, being due to its poor tolerance for reduction. To improve lithium charge–discharge cycling efficiency in SL–EA electrolytes, following three trials were carried out: (i) improvement of the cathodic stability of electrolyte solutions by change in polarization through modification of solvent structure; isopropyl methyl sulfone and methyl isobutyrate were investigated as alternative SL and EA, respectively, (ii) suppression of the reaction between lithium and electrolyte solutions by addition of low reactivity surfactants of cycloalkanes (decalin and adamantane) or triethylene glycol derivatives (triglyme, 1,8-bis(tert-butyldimethylsilyloxy)-3,6-dioxaoctane and triethylene glycol di(methanesulfonate)) into SL–EA electrolytes, and (iii) change in surface film by addition of surface film formation agent of vinylene carbonate (VC) into SL–EA electrolytes. These trials made lithium cycling behavior better. Lithium cycling efficiency tended to increase with a decrease in overpotential. VC addition was most effective for improvement of lithium cycling efficiency among these additives. Stable surface film is formed on lithium anode by adding VC and the resistance between anode/electrolyte interfaces showed a constant value with an increase in cycle number. When the electrolyte solutions without VC, the interfacial resistance increased with an increase in cycle number. VC addition to SL–EA was effective not only for Li/LiCoO₂ cell with charge cut-off voltage of 4.5 V but also for Li/LiNi_0.5Mn_1.5O₄ cells even with high charge cut-off voltage of 5 V in Li/LiNi_0.5Mn_1.5O₄ cells.     

Mechanochemical synthesis of α-Fe2O3 nanoparticles and their application to all-solid-state lithium batteries

α-Fe₂O₃ fine particles have been prepared by a mechanochemical process and a solution process. α-Fe₂O₃ nanoparticles with aggregates composed of the several tens nm primary particles were produced by the mechanochemical process. The nanoparticles were applied to the electrode as an active material for all-solid-state lithium batteries and the electrochemical properties of the cell were investigated. Typical charge–discharge curves, as seen in the liquid type cell using the α-Fe₂O₃ nanoparticles as an electrode were observed in the all-solid-state cell. The first discharge capacity of the cell of about 780 mAh g⁻¹ was, however, smaller than the capacity of a cell using α-Fe₂O₃ particles prepared by the solution process, which were monodispersed particles of 250 nm without aggregates. In order to develop electrochemical performance of all-solid-state batteries, it is important to use the electrode particles without aggregation which lead to the formation of good solid–solid interface between active material and solid electrolyte particles.C     

Ion-implantation modification of lithium–phosphorus oxynitride thin-films

Among various solid electrolytes, the lithium–phosphorus oxynitride (Lipon) electrolyte synthesized by sputtering of Li₃PO₄ in pure N₂ has a good ionic conductivity of 2(±1)×10⁻⁶ S cm⁻¹ at 25° C. As the nitrogen concentration increases in the Lipon electrolyte, the ionic conductivity is reported to increase as a result of a higher degree of cross-links. When Lipon films are deposited by sputtering, however, it is reported that the maximum nitrogen concentration saturates approximately at 6 at.%. By non-equilibrium processes, such as ion-implantation, nitrogen concentration can be controlled over 6 at.%. This study investigates the effect of nitrogen concentration on the ionic conductivity in Lipon films by using ion-implantation. Impedance measurements at 25° C show that the nitrogen-implanted Lipon films enhance or retard the ionic conductivity over a wide range after nitrogen-implantation, when compared with as-deposited thin-films.     

Spinel electrodes for lithium batteries — A review

This paper briefly reviews recent electrochemical data of several transition-metal oxide and sulphide spinel compounds of general formula A[B₂]X₄ that have been employed as cathode materials in both room-temperature and high-temperature (400 °C) lithium cells. Particular attention is given to the performance of the oxide spinels M₃O₄ (M  Fe, Co, Mn) that have like A- and B-type cations, the lithium spinels Li[M₂]O₄ (M  Ti, V, Mn) and LiFe₅O₈, and the thiospinels CuCo₂S₄ and CuTi₂S₄. Reaction processes and the structural characteristics of the reaction products are highlighted.     

Synthesis and performance of lithium vanadium phosphate as cathode materials for lithium ion batteries by a sol–gel method

Monoclinic lithium vanadium phosphate, Li₃V₂(PO₄)₃, was synthesized by a sol–gel method under Ar/H₂ (8% H₂) atmosphere. The influence of sintering temperatures on the synthesis of Li₃V₂(PO₄)₃ has been investigated using X-ray diffraction (XRD), SEM and electrochemical methods. XRD patterns show that the Li₃V₂(PO₄)₃ crystallinity with monoclinic structure increases with the sintering temperature from 700 to 800 °C and then decreases from 800 to 900 °C. SEM results indicate that the particle size of as-prepared samples increases with the sintering temperature increase and there is minor carbon particles on the surface of the sample particles, which are very useful to enhance the conductivity of Li₃V₂(PO₄)₃. Charge–discharge tests show the 800 °C-sample exhibits the highest initial discharge capacity of 131.2 mAh g⁻¹ at 10 mA g⁻¹ in the voltage range of 3.0–4.2 V with good capacity retention. CV experiment exhibits that there are three anodic peaks at 3.61, 3.70 and 4.11 V on lithium extraction as well as three cathodic peaks at 3.53, 3.61 and 4.00 V on lithium reinsertion at 0.02 mV s⁻¹ between 3.0 and 4.3 V. It is suggested that the optimal sintering temperature is 800 °C in order to obtain pure monoclinic Li₃V₂(PO₄)₃ with good electrochemical performance by the sol–gel method, and the monoclinic Li₃V₂(PO₄)₃ can be used as candidate cathode materials for lithium ion batteries.     

All-solid-state lithium secondary batteries with oxide-coated LiCoO2 electrode and Li2S–P2S5 electrolyte

All-solid-state lithium secondary batteries using LiCoO₂ active materials coated with Li₂SiO₃ and SiO₂ oxide films and Li₂S–P₂S₅ solid electrolytes were fabricated and their electrochemical performance was investigated. The electrochemical performace of the all-solid-state cells at a high voltage region was highly improved by using oxide-coated LiCoO₂. The oxide coatings are effective in suppressing the formation of an interfacial resistance between LiCoO₂ and the solid electrolyte at a high cutoff voltage of 4.6 V (vs. Li). As a result, charge–discharge capacities and cycle performance at the cutoff voltage were improved. The cell with Li₂SiO₃-coated LiCoO₂ showed a large initial discharge capacity of 130 mAh g⁻¹ and a good capacity retention of 110 mAh g⁻¹ after 50th cycles at the cutoff voltage of 4.6 V (vs. Li).     

Pseudo catalytic ammonia synthesis by lithium–tin alloy

In this work, nitrogenation, ammonia generation, regeneration reactions of lithium-tin alloy is investigated as pseudo catalytic process of ammonia synthesis. Li₁₇Sn₄ synthesized by thermochemical method at 500 °C can react with 0.1 MPa of N₂ below 400 °C. Nano or amorphous lithium nitride would be formed by the nitrogenation. By reaction of the nitrogenated samples and H₂, ammonia is generated at 300 °C under 0.1 MPa. The initial alloy phase Li₁₇Sn₄ is regenerated below 350 °C from the products after the ammonia generation process. Based on the above three step process, ammonia can be pseudo-catalytically synthesized from N₂ and H₂ below 400 °C under ambient pressure. Furthermore, the reactivity for the ammonia synthesis using Li–Sn alloy is preserved during the NH₃ synthesis cycles due to the characteristic reaction process based on the Li extraction and insertion.     

Novel electrospun poly(vinylidene fluoride-co-hexafluoropropylene)–in situ SiO2 composite membrane-based polymer electrolyte for lithium batteries

Composite membranes of poly(vinylidene fluoride-co-hexafluoropropylene) {P(VdF-HFP)} and different composition of silica have been prepared by electrospinning polymer solution containing in situ generated silica. These membranes are made up of fibers of 1–2 μm diameters. These fibers are stacked in layers to produce fully interconnected pores that results in high porosity. Polymer electrolytes were prepared by immobilizing 1 M LiPF₆ in ethylene carbonate (EC)/dimethyl carbonate (DMC) in the membranes. The composite membranes exhibit a high electrolyte uptake of 550–600%. The optimum electrochemical properties have been observed for the polymer electrolyte containing 6% in situ silica to show ionic conductivity of 8.06 mS cm⁻¹ at 20 °C, electrolyte retention ratio of 0.85, anodic stability up to 4.6 V versus Li/Li⁺, and a good compatibility with lithium metal resulting in low interfacial resistance. A first cycle specific capacity of 170 mAh g⁻¹ was obtained when the polymer electrolyte was evaluated in a Li/lithium iron phosphate (LiFePO₄) cell at 0.1 C-rate at 25 °C, corresponding to 100% utilization of the cathode material. The properties of composite membrane prepared with in situ silica were observed to be comparatively better than the one prepared by direct addition of silica.     

Preparation and electrochemical properties of lithium–sulfur polymer batteries

The lithium/sulfur (Li–S) batteries consist of a composite cathode, a polymer electrolyte, and a lithium anode. The composite cathode is made from elemental sulfur (or lithium sulfide), carbon black, PEO, LiClO₄, and acetonitrile. The polymer electrolyte is made of gel-type linear poly(ethylene oxide) (PEO) with tetra ethylene glycol dimethyl ether. Cells based on Li₂S or sulfur have open-circuit voltages of about 2.2 and 2.5 V, respectively. The former cell shows two reduction peaks and one oxidation peak. It is suggested that the first reduction peak is caused by the change from polysulfide to short lithium polysulfide, and the second reduction peak by the change from short lithium polysulfide to lithium sulfide (Li₂S, Li₂S₂). The cell based on sulfur has the same reduction mechanism as that of Li₂S, which is caused by the multi process (first and second reduction) of lithium polysulfide. On charge–discharge cycling, the first discharge has a higher capacity than subsequent discharges and the flat discharge voltage is about 2.0 V. As the current load is increased, the discharge capacity decreases. One reason for this fading capacity and low sulfur utilization is the aggregation of sulfur (or polysulfide) with cycling.     

A novel bifunctional catalyst of Ba0.9Co0.5Fe0.4Nb0.1O3−δ perovskite for lithium–air battery

Ba_0.9Co_0.5Fe_0.4Nb_0.1O₃ (BCFN) perovskite has been synthesized by a solid-state reaction method, and characterized by XRD, SEM, BET. This oxide has a porous structure and a specific surface area of 10.24 m² g⁻¹ after ball-milled 24 h. The catalytic activity of the oxide for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in 0.1 M KOH solution has been studied by using a rotating ring-disk electrode (RRDE) technique. RRDE results show that the ORR mainly favors a direct four electron pathway, and a maximum cathodic current density of −5.70 mA cm⁻² at 2500 rpm was obtained, which is close to that of Pt/C (20 wt.% Pt on carbon) electrocatalyst in the same testing conditions. Compared with behaviors of pure C and Pt/C electrode, a lower onset potential of BCFN for OER is observed, and a bigger anodic current at the same applied potential is obtained. Considering small surface area of the BCFN catalyst, a big overpotential is given in the discharge–charge curves. However, the outputs of 2032 coin Li–air batteries in a dry gas mixture composed of 80 vol.% pure N₂ and 20 vol.% pure O₂ demonstrated that BCFN could be a potential bifunctional catalyst for the Li–air battery.     

Study of cobalt-doped lithium–nickel oxides as cathodes for MCFC

Cobalt substituted lithium–nickel oxides were synthesized by a solid-state reaction procedure using lithium nitrate, nickel hydroxide and cobalt oxalate precursor and were characterized as cathodes for molten carbonate fuel cell (MCFC). LiNi_0.8Co_0.2O₂ cathodes were prepared using non-aqueous tape casting technique followed by sintering in air. The X-ray diffraction (XRD) analysis of sintered LiNi_1−xCo_xO₂ indicated that lithium evaporation occurs during heating. The lithium loss decreases with an increase of the cobalt content in the mixed oxides. The stability studies showed that dissolution of nickel into the molten carbonate melt is smaller in the case of LiNi_1−xCo_xO₂ cathodes compared to the dissolution values reported in the literature for state-of-the-art NiO. Pore volume analysis of the sintered electrode indicated a mean pore size of 3 μm and a porosity of 40%. A current density of 160 mA/cm² was observed when LiNi_0.8Co_0.2O₂ cathodes were polarized at 140 mV. The electrochemical impedance spectroscopy (EIS) studies done on LiNi_0.8Co_0.2O₂ cathodes under different gas conditions indicated that the rate of the cathodic discharge reaction depends on the O₂ and CO₂ partial pressures.     

Electrochemical properties of Li–Mg alloy electrodes for lithium batteries

Li–Mg alloy electrodes are prepared by two methods: (1) direct-alloying through the melting of mole percent specific mixtures of Li and Mg metal under vacuum and (2) the kinetically-controlled vapor formation and deposition (KCVD) of a Li–Mg alloy on a substrate. It is found that processing conditions greatly influence the microstructures and surface morphologies, and hence, the electrochemical properties of the Li–Mg alloy electrodes. When applying the KCVD technique, the composition of each prepared alloy is determined by independently varying the temperature of the molten lithium, the temperature of magnesium with which the lithium interacts, and the temperature of the substrate on which the intimately mixed Li–Mg mixture is deposited. Here, the required temperature for lithium induced Mg vaporization is more than 200°C below the magnesium melting point. The effect of these variable temperatures on the microstructure, morphology, and electrochemical properties of the vapor-deposited alloys has been studied. The diffusion coefficients for lithium in the Li–Mg alloy electrodes prepared by the KCVD method are in the range 1.2×10⁻⁷ to 5.2×10⁻⁷ cm² s⁻¹ at room temperature, two to three orders of magnitude larger than those in other lithium alloy systems (e.g. 6.0×10⁻¹⁰ cm² s⁻¹ in LiAl). These observations suggest that Li–Mg alloys prepared by the KCVD method might be used effectively to prevent dendrite formation, improving the cycleability of lithium electrodes and the rechargeability of lithium batteries as a result of the high diffusion coefficient of lithium atoms in the Li–Mg alloy. Li–Mg alloy electrodes also appear to show not only the potential for higher rate capabilities (power densities) but also for larger capacities (energy densities) which might considerably exceed those of lithiated carbon or Sn-based electrodes for lithium batteries.     

New insight on the lithium hydride–water vapor reaction system

The reaction of lithium hydride (LiH) powder with pure water vapor (H₂O and D₂O) was studied by thermogravimetry and in situ infrared spectroscopy at 298 K over a large pressure range. The mean particle size of LiH is around 27 μm. At very low pressure, the hydrolysis starts with the formation of lithium oxide (Li₂O). Then, both Li₂O and lithium hydroxide (LiOH) are formed on increasing pressure, thus, creating a Li₂O/LiOH bilayer. The reaction takes place through the consumption of LiH and the formation of Li₂O at the LiH/Li₂O interface and through the consumption of Li₂O and the formation of LiOH at the Li₂O/LiOH interface. Above 10 hPa, only the monohydrate LiOH·H₂O is formed. This hydration reaction of LiOH into LiOH·H₂O occurs at a lower pressure (8 hPa) after the first hydration-dehydration cycle. The hydrolysis mechanism proposed in this paper suggests that the diffusion of ionic species across the intermediate Li₂O layer is the rate limiting step of the reaction.     

Characteristics of δ-AgyV2O5 as a lithium insertion host

δ-Ag_yV₂O₅ has been characterized as the active material for secondary lithium batteries by using electrochemical measurements and X-ray diffraction. Lithium insertion proceeds in three steps that include deposition of metallic silver and phase transformation to ε-Li_xV₂O₅. Metallic silver does not return to the original matrix during recharging. During the charge process, additional lithium is accommodated in the first and second steps.     

Aligned nickel–cobalt oxide nanosheet arrays for lithium ion battery applications

Aligned nickel–cobalt nanosheet arrays are deposited on nickel foam substrates by means of chemical bath deposition technique. The nanosheet arrays are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The electrochemical performances as anode materials of lithium ion batteries are investigated by galvanostatic charge–discharge cycle and cyclic voltammetry (CV) tests. The results show that the nickel–cobalt oxide film prepared from the solution in which Ni/Co = 3/1 has the best performance. Its initial charge capacity at 0.1 A g⁻¹ is 798 mAh g⁻¹. When cycled at higher current densities of 0.5 and 1.0 A g⁻¹, the initial charge capacities are 570 and 500 mAh g⁻¹, and 84% and 86% can be retained after 50 cycles, respectively. It is believed that the interconnected nanosheet-array structure and the nickel–cobalt binary composition play important roles in their electrochemical performances.