Fundamental scientific aspects of lithium ion batteries(ⅩⅣ)—Calculation methods

基础理论的创新与计算机性能的大幅度提升为高精度与多尺度的计算模拟提供了可能,这些方法也在锂离子电池的研究中得到了广泛的应用。本文介绍了第一性原理、密度泛函理论、分子动力学、蒙特卡罗、相场模拟、分子力场、有限元等不同时间与空间尺度上的模拟方法的基本原理,并探讨了这些方法在锂离子电池基础研究中的应用,如计算电池电压、电极材料的电子结构、能带结构、迁移路径、缺陷生成能、离子在材料体相及不同微观结构中的输运、材料中温度场分布、应力场分布等。     

Preparation of Sn–Co alloy electrode for lithium ion batteries by pulse electrodeposition

Sn–Co alloy films for Li-ion batteries were prepared by pulse electrodeposition on the copper foils as current collectors. Nanocrystalline Sn–Co alloy electrodes produced by using a solution containing cobalt chloride and tin chloride at constant electrodeposition conditions (pulse on-time t_on at 5 ms and pulse off-time t_off at 5 ms) with varying peak current densities, Jp have been investigated. The structures of the electroplated Sn–Co alloy thin films were studied to reveal film morphology current density relationships and the effect of the current density parameters on the electrochemical properties. X-Ray Diffractometer (XRD), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area analyzer and Energy-Dispersive X-ray Spectroscopy (EDS) facilities were used for determination the relationships between structure and experimental parameters. Cyclic voltammetry (CV) tests were carried out to reveal reversible reactions between cobalt–tin and lithium. Galvanostatic charge/discharge (GC) measurements were performed in the cells formed by using anode composite materials produced by pulse electro co-deposition. The discharge capacities of these cells were cyclically tested by a battery tester at a constant current in the different voltage ranges between 0.02 V–1.5 V. The results have shown that Sn–Co alloy yielded promising reversible discharge capacities with a satisfactory cycle life for an alternative anode material to apply for the Li-ion batteries.     

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.     

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.     

Core–shell tin-multi walled carbon nanotube composite anodes for lithium ion batteries

Carbon nanotube papers were produced from Multi wall carbon nanotubes (MWCNTs). Tin deposition was conducted via RF magnetron sputtering technique on the MWCNT papers to produce tin-MWCNT composite anodes. The effect of different sputtering power on the electrochemical performance of anodes was investigated. Galvanostatic charge/discharge technique was employed to determine the cyclic performance of the anode electrodes. Results showed that improvement on cyclic performance of tin anodes was achieved with novel composite tin-MWCNT composite anode structures.     

Microstructure and electrochemical performance of thin film anodes for lithium ion batteries in immiscible Al–Sn system

The immiscible Al–Sn alloy thin films prepared by electron-beam deposition were first investigated as possible negative electrodes for lithium ion batteries. In the complex structure of the Al–Sn thin films, tiny Sn particles dispersed homogeneously in the Al active matrix. Their electrochemical characteristics were tested in comparison with the pure Al and Sn films. Cyclic voltammetry results indicated that the Li⁺-transport rates in these Al–Sn alloy films were significantly enhanced. Charge–discharge tests showed that the Al–Sn alloy film anodes had good cycle performance. The electrode with high Al content (Al–33 wt%Sn) delivered a high initial discharge capacity of 752 mAh g⁻¹ while the electrode with high Sn content (Al–64 wt%Sn) had better cycleability with a stable specific capacity of about 300 mAh g⁻¹ under 0.8 C rate. The good performance of these immiscible Al–Sn alloy film anodes was attributed to their unique microstructure. The mechanism of lithiation and delithiation reaction had been proposed based on cyclic voltammograms and impedance response of the Al–Sn alloy thin film electrodes. Our preliminary results demonstrate that the Al–Sn immiscible alloy is a potential candidate negative material for Li-ion battery.     

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.     

Theoretical and technological aspects of flow batteries：Measurement of state of charge

电池实际可放出的瓦时容量与实际可放出的最大瓦时容量的比值定义为荷电状态,准确测定荷电状态对储能应用十分重要。本文从理论和应用角度,讨论全钒液流电池荷电状态的理论概念、工程定义和主要影响因素;提出2种确定最大瓦时容量的方法,其中实测法准确度更高,包含钒离子跨膜迁移、水分子扩散、负极电解液析氢和被氧化的信息,用于表征储能系统的荷电状态具有实际价值;阐述最大瓦时容量、电化学瓦时容量和理论瓦时容量的区别与联系。所提出的荷电状态确定方法,能够用于全钒液流电池SOC的估计。     

Preparation and characterization of a new nanosized silicon–nickel–graphite composite as anode material for lithium ion batteries

A new type of nanosized silicon–nickel–graphite (Si–Ni–G) composite was prepared by high energy mechanical milling (HEMM) and pyrolysis using SiO as the precursor of Si for the first time. X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM) and scanning electron microscopy (SEM) were used to determine the phases obtained and to observe the microstructure and distribution of the composite. The composite powders consisted of Si, Ni, SiO₂, NiO and a series of Si–Ni alloys. The formation of the inactive SiO₂ and Si–Ni alloy phases could accommodate the large volume changes of the active particles during cycling. In addition, cyclic voltammetry (CV) and galvanostatic discharge/charge tests were carried out to characterize the electrochemical properties of the composite. The composite electrodes exhibited an initial discharge and charge capacity of 1450.3 and 956.4 mAh g⁻¹, respectively, maintaining a reversible capacity of above 900 mAh g⁻¹ for nearly 60 cycles.     

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.     

Preparation and performances of porous polyacrylonitrile–methyl methacrylate membrane for lithium-ion batteries

A copolymer, polyacrylonitrile–methyl methacrylate P(AN–MMA), was synthesized by suspension polymerization with acrylonitrile (AN) and methyl methacrylate (MMA) as monomers. With this copolymer, polymer membrane was prepared by phase inversion. The performances of the polymer were characterized by FTIR, SEM, DSC/TG, EIS and LSV. The copolymer contains CH₂, CN and CO bonds, and shows its thermal stability up to 300 °C. The polymer membrane has a porous structure with an average pore diameter of 0.5 μm. The conductivity of the polymer electrolyte is 1.25 mS cm⁻¹ at room temperature, and it is electrochemically stable up to 5 V (vs. Li). Using the polymer electrolyte as the gel polymer electrolyte (GPE), the cell Li/GPE/LiCoO₂ shows its cyclic stability as good as the cell with liquid electrolyte.     

Fundamental aspects of the Ti–H system: theoretical and experimental behaviour

We study the interaction of hydrogen with titanium in order to characterize some important microscopic and macroscopic properties of this system. It is technologically important because, among other applications, the Ti–H system is used as structural material in many applications due to the combination of two important mechanical properties, which are resistance to the corrosion and hardness. Using a calculus program based on the jellium model for the material, we obtain values of properties that are important in the determination of the macroscopic behaviour of the Ti–H system, such as the variation of the electronic density and of the induced density of states due to the presence of the hydrogen in the matrix of Ti. From an experimental point of view, we hydride a titanium matrix in order to determine the effects of the process on the properties of the material structure.The general features of these theoretical and experimental methods are discussed and the corresponding results are compared with experimental data.     

Electrochemical properties of melt-spun Al–Si–Mn alloy anodes for lithium-ion batteries

Al_60−XSi₄₀Mn_X (X = 0, 1, 3, 5, 7 and 10 at.%) ribbons were prepared by melt spinning. A supersaturated solid solution of Si and Mn in fcc α-Al with very fine microstructures have been obtained in the ribbons. The electrochemical measurements have revealed that the Al–Si–Mn alloys with some compositions can exhibit a high Li inserting specific capacity and stable cycle performance. A specific capacity of more than 500 mAh g⁻¹ and the cycle efficiency of 90% have been achieved in melt-spun Al₅₅Si₄₀Mn₅ and Al₅₃Si₄₀Mn₇ alloys after 10 cycles. An ordered phase, δ′ (Al₃Li), seems to be formed in the alloys after Li inserting, whereas no other compounds with Li have been detected. It is evident that the supersaturated solid solution plays the main role in improving the specific capacity and cycle performance. Refinement of grains could facilitate the diffusion of Li atoms. The coexistence of multi-phases has limited the alloy volume expansion during Li inserting. As a result, a high-specific capacity and a stable cycle performance have been achieved.     

Synthesis and electrochemical characteristics of Li(Ni · M)O2 (M = Co,Mn) cathode for rechargeable lithium batteries

The synthesis and electrochemical characteristics of LiNiO₂ and Li(Ni · M)O₂ (M = Co or Mn) as the cathode materials for rechargeable lithium batteries were investigated. It was clarified from these investigations that LiNiO₂ has been produced from crystalline NiO, which was derived from Ni(OH)₂ and LiOH, and that the property of NiO had some influence on the LiNiO₂ preparation. It was assumed that the formation of the layered structure has been inhibited by the existence of the Ni vacancy and Ni³⁺ ion in NiO. The synthesis of a solid solution of Li(Ni · Co)O₂ suggested that a part of the Ni replacement by Co might inhibit the formation of the Ni vacancy of NiO and promote the formation of the layered structure. The capacity fading with increase in cycle number was suppressed by the replacement of a part of Ni with Co. We considered that the capacity fading was suppressed by the development of the layered structure wherein formation of Ni vacancy was suppressed by replacement with Co. LiNi_0.8Co_0.2O₂ prepared under the stream of oxygen gas showed a small irreversible capacity at first cycle and higher cycling capacity of ∼ 180 mA h g⁻¹.     

Zn4Sb3(C7) powders as a potential anode material for lithium-ion batteries

The electrochemical properties of β-Zn₄Sb₃ and Zn₄Sb₃C₇ as new lithium-ion anode materials were investigated. The reversible capacities of the pure Zn₄Sb₃ alloy electrode and 100 h milled Zn₄Sb₃ in the first cycle reached 503 and 566 mA h/g, respectively, but the cycle stability of Zn₄Sb₃ whether milled or not were obviously bad. It was demonstrated that cycle stability of Zn₄Sb₃ could be largely improved by milling after mixing with graphite. It was shown that Zn₄Sb₃C₇ composite has a lithium-ion extraction capacity of 581 mA h/g at the first cycle and 402 mA h/g at 10th cycle.     

Nusselt's Fundamental Law of Heat Transfer—Revisited

Almost a hundred years ago, in 1915, Wilhelm Nusselt published a paper entitled “Das Grundgesetz des Wärmeüberganges” (The Fundamental Law of Heat Transfer), which is often quoted in modern textbooks in this field of engineering science. Most of these modern textbooks, however, still use the notion of three mechanisms, modes, or kinds of heat transfer. Nusselt demonstrated, in this mentioned paper, that convection is nothing but conduction to a moving fluid. Nusselt's paper, however, usually is not quoted for this logical conclusion from facts already known in the late 19th and early 20th centuries, but for the principle of similarity or dimensional analysis, leading to the well-known dimensionless numbers widely used in fluid mechanics and heat transfer. The reasons for the reluctance of most (but fortunately not all) present-day experts to follow Nusselt in his logical argumentation have a number of mainly historical roots. This paper tries to explain why teaching our students that there are two mechanisms of heat transfer has a number of advantages over the “classical” method that is again and again repeated in our heat transfer literature.     

Hydrothermal synthesis of mixed crystal phases TiO2–reduced graphene oxide nanocomposites with small particle size for lithium ion batteries

A rutile and anatase mixed crystal phase of nano-rod TiO₂ and TiO₂–reduced graphene oxide (TiO₂–RGO) nanocomposites with small particle size were prepared via a facile hydrothermal approach with titanium tetrabutoxide and graphene oxide as the precursor. Hydrolysis of titanium tetrabutoxide and mild reduction of graphene oxide were simultaneously carried out. Compared with traditional multistep methods, a novel green synthetic route to produce TiO₂–RGO without toxic solvents or reducing agents was employed. TiO₂–RGO as anode of lithium ion batteries was characterized by extensive measurements. The nanocomposites exhibited notable improvement in lithium ion insertion/extraction behavior compared with TiO₂, indicating an initial irreversible capacity and a reversible capacity of 295.4 and 112.3 mA h g⁻¹ for TiO₂–RGO after 100 cycles at a high charge rate of 10 C. The enhanced electrochemical performance is attributed to increased conductivity in presence of reduced graphene oxide in TiO₂–RGO, a rutile and anatase mixed crystal phase of nano-rod TiO₂/GNS composites, small size of TiO₂ particles in nanocomposites, and enlarged electrode–electrolyte contact area, leading to more electroactive sites in TiO₂–RGO.     

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.