Li-ion Secondary Batteries Research Articles

Relaxation Analysis of Li-Co-O Cathode Material for Li Ion Secondary Batteries

Li-ion secondary batteries (LIBs) have received much attention as one of the next generation battery system due to its high energy density and operation power, and the research study to improve its performance have been proceeding actively with the recent drastic increase of demands for portable electronic devices and electric vehicle. The research on the crystal phase/ structure of electrode materials is essential to understand the electrode behavior at the lithium insertion/extraction process and to design the advanced high efficiency electrode. The relaxation analysis is important to make the transition of electrode material from kinetic state to equilibrium state clear. We have reported on the relaxation phenomenon of changing their crystal phase/structure after the lithium insertion/extraction process for various electrode materials such as γ-Fe2O3, 1‐3 LiMn2O4, 4‐6 LiFePO4 7 and LiNi1/3Co1/3Mn1/3O2, 8 by using powder X-ray diffraction (XRD) measurement and the Rietveld analysis method. In the previous study on relaxation analysis of γ-Fe2O3 electrode material, it was found that the iron occupancy of 8a sites decreased and that of 16c sites increased with lithium insertion, then the iron occupancy of 8a sites increased and that of 16c sites gradually decreased at the relaxation process after the lithium insertion. It is considered that the lithium preferentially favored the 8a site kinetically, whereas the 16c site is occupied thermodynamically. 1‐3 Recently, we investigated the relaxation phenomenon of LiMn2O4 with the coexistence state of two phases, the Li-rich phase and the Lilean phase, after the lithium insertion by using the Rietveld method, and found that the mole fraction of the Li-rich phase increased and that of the Li-lean phase decreased with the relaxation time. It is considered that, at the lithium insertion process, the Li-lean phase has more vacancies than the Li-rich phase due to lithium deficiency and that the structure of the Li-lean phase was maintained even containing excess lithium in order to promote lithium diffusion. It is considered that the Li-lean phase containing excess lithium formed during the lithium insertion process separated into the Li-lean phase without excess lithium and the Li-rich phase during the relaxation process. 4‐6 LiCoO2 with a layered rock-salt structure is the most widely used cathode material for LIBs due to its excellent reversibility and a high electrochemical potential at the lithium contents x from 1 to 0.5 in terms of LixCoO2. 9‐12 Reimers et al. reported that the phase of LixCoO2 changes as single hexagonal phase for x = 1.00‐0.93, two hexagonal phases for x = 0.93‐0.75, single hexagonal phase for x = 0.75 - near 0.5. 12 In this study, we prepared LixCoO2 samples (x = 0.90, 0.85 and 0.80) at the region of two hexagonal phases coexistence by charging/discharging the cell at the various C rate, then investigated the phase change of the two hexagonal phases with the elapsed time after the lithium extraction/insertion process by using XRD measurement and the Rietveld analysis method.

SiOx Nanoparticles Synthesized by an Evaporation and Condensation Process Using Induction Melting of Silicon and Gas Injection

SiO(x) nanoparticles were synthesized using a specially designed induction melting system equipped with a segmented graphite crucible. The graphite crucible with the segmented wall was the key to enhancing the evaporation rate due to the increase of the evaporation area and convection of the silicon melt. Injection of the gas mixture of oxygen (O2) and argon (Ar) on silicon (Si) melt caused the formation of SiO(x) nanoparticles. The evaporated SiO(x) nanoparticles were then cooled and condensed in a process chamber. The effects of the O2/Ar ratio in the injection gas on the microstructures of the SiO(x) nanoparticles were then investigated. Synthesized SiO(x) nanoparticles were proven to be of a homogeneous amorphous phase with average diameters of 30-35 nm. The microstructures were independent from the O2/Ar ratio of the injected gas. However, x increased from 1.36 to 1.84 as the O2/Ar ratio increased. The purity of the synthesized nanoparticles was about 99.9%. SiO(x) nanoparticles could be applied as the active anode material in a lithium (Li) ion secondary battery.

Adsorption and Diffusion of Lithium on Layered Silicon for Li-Ion Storage

The energy density of Li-ion batteries depends critically on the specific charge capacity of the constituent electrodes. Silicene, the silicon analogue to graphene, being of atomic thickness could serve as high-capacity host of Li in Li-ion secondary batteries. In this work, we employ first-principles calculations to investigate the interaction of Li with Si in model electrodes of free-standing single-layer and double-layer silicene. More specifically, we identify strong binding sites for Li, calculate the energy barriers accompanying Li diffusion, and present our findings in the context of previous theoretical work related to Li-ion storage in other structural forms of silicon: the bulk and nanowires. The binding energy of Li is ~2.2 eV per Li atom and shows small variation with respect to Li content and silicene thickness (one or two layers) while the barriers for Li diffusion are relatively low, typically less than 0.6 eV. We use our theoretical findings to assess the suitability of two-dimensional silicon in the form of silicene layers for Li-ion storage.

Preparation and characteristics of Li4Ti5O12 with various dopants as anode electrode for hybrid supercapacitor

Spinel-Li4Ti5O12 is successfully synthesized by a solid phase synthesis. The Li4Ti5O12 powders with various dopants (Al3+, Cr3+, Mg2+) synthesized at 800 °C are in accordance with the Li4Ti5O12 cubic spinel phase structure. The dopants are inserted into the lattice structure of Li4Ti5O12 without causing any changes in structural characteristics. In order to study the effect on various dopants, the hybrid supercapacitor is prepared by using un-doped Li4Ti5O12 and doped Li4Ti5O12 in this work. The electrochemical performance of the hybrid supercapacitor is characterized by impedance spectroscopy and cycle performance. The results show Cr3+ and Mg2+ dopants enhance the conductivity of Li4Ti5O12. Also, Al3+ substitution improves the reversible capacity and cycling stability of Li4Ti5O12. It is found that effect of dopant on the electrochemical performance of Li4Ti5O12 as electrode material for hybrid supercapacitor where the EDLC and the Li ion secondary battery coexist in one cell system.

Safety of High Capacity All Solid State Li-Ion Secondary Battery

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機能補完材としての炭素ナノ繊維のエネルギー・環境分野への応用

Carbon nanofibers (CNFs) have unique structural characteristics, such as a nanometer diameter, a fibrous structure, and high crystallinity, and thus, are expected to be promising important materials for energy and environment applications. However, difficulties in handling and the high production costs of CNFs often hamper the industrialization of products from CNF alone. On the other hand, hybridization of CNF with other materials can improve their weaknesses, increase performance, and/or give them new abilities. In this paper, we introduce the effectiveness of CNFs as complementary functional materials especially for applications in the energy and environment fields, such as Li-ion secondary batteries, fuel cells, electric double-layer capacitors, and air purification.

Microstructure and phase analyses of melt-spun Si-Ni base anode materials for Li-ion battery

Si-based anode composite materials have been studied to improve the performance and the durability of Li-ion secondary batteries in this study. Si-Ni-Al, Si-Ni-Cu and Si-Ni-Cu-Al base alloys were designed and rapidly solidified at the cooling rate of about 106 °C/sec by optimizing the melt spinning. The ribbons were characterized using FE-SEM equipped with EDS, X-ray diffractometer and HR-TEM. The thin ribbons of Si-Ni-Al alloy consisted of nano-sized Si particles and amorphous matrix, which was regarded as an ideal microstructure for the anode material. At the wheel side of the ribbon, 20–30 nm of Si particles were formed (Zone A); whereas at the air side relatively large Si particles were distributed (Zone B). The Si-Ni-Cu alloy showed coarser Si particles than the Si-Ni-Al alloy, and its matrix consisted of NiSi2, Cu3Si and amorphous structures. Finally, the microstructure of the Si-Ni-Cu-Al alloy strips was composed of coarse Si particles, CuNi, Al4Cu9, NiSi2, and unknown phases, and the size of those Si particles were too large to be used for the anode materials.

A Bayesian framework for on-line degradation assessment and residual life prediction of secondary batteries inspacecraft

The paper presents a Bayesian framework consisting of off-line population degradation modeling and on-line degradation assessment and residual life prediction for secondary batteries in the field. We use a Wiener process with random drift, diffusion coefficient and measurement error to characterize the off-line population degradation of secondary battery capacity, thereby capturing several sources of uncertainty including unit-to-unit variation, time uncertainty and stochastic correlation. Via maximum likelihood, and using observed capacity data with unknown measurement error, we estimate the parameters in this off-line population model. To achieve the requirements for on-line degradation assessment and residual life prediction, we exploit a particle filter-based state and static parameter joint estimation method, by which the posterior degradation model is updated iteratively and the degradation state of an individual battery is estimated at the sametime.A case study of some Li-ion type secondary batteries not only shows the effectiveness of our method, but also provides some useful insights regarding the necessity of on-line updating and the apparent differences between the population and individual unit degradation modeling and assessment problems.

Imidazolium Based Ionic Liquid Electrolytes for Li-Ion Secondary Batteries Based on Graphite and LiFePO4

This manuscript reports the development of a safe and green lithium-ion battery using lithium iron phosphate (LiFePO4) as a positive electrode, graphite (Cgr) as a negative electrode, and an Ionic Liquid (IL) electrolyte solution based on 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)-imide (C1C6ImNTf2). Vinylene carbonate (VC) was tested as an electrolyte additive. The electrochemical stability of (C1C6ImNTf2) and their binary mixture referred as (Li)(C1C6ImNTf2) were investigated. In addition the electrochemical behavior of the graphite electrode was studied through cyclic voltammetry experiments in the presence and absence of VC co- additive. Complementary cycling tests demonstrated the benefic effect of VC on the charge-discharge performances for the full Lithium ion configuration based on Cgr/LiFePO4.

Fading mechanisms of carbon-coated and disproportionated Si/SiOx negative electrode (Si/SiOx/C) in Li-ion secondary batteries: Dynamics and component analysis by TEM

This article addresses the fading mechanisms observed in carbon-coated and disproportionated Si/SiOx/C negative electrode for Li-ion secondary batteries. A combined characterization revealed that Si/SiOx consisted of multiple nano-sized domains of amorphous Si and SiOx, with some crystalline Si. The initial discharge capacity of Si/SiOx/C was 1380mAhg−1, however, it decreased to 578mAhg−1 at the 90th cycle. The electrode exhibited two different fading modes: local fading and global fading. Through intensive TEM analysis, it was concluded that both fading modes were closely related to the structural change in Si/SiOx/C during alloying/de-alloying. Local fading was induced by the contact loss between active material and conducting carbon, and the limited buffering effect of lithium silicates. Global fading was attributed to the crumbling of Si/SiOx, which limited further alloying, leading to ever decreasing discharge capacity. Both fading modes were thoroughly investigated and monitored by qualitative and quantitative STEM-EDX analysis.

Improving the Electrochemical Performance of Li-Ion Secondary Batteries by Optimizing the Sn/C Composite Anode Materials

From the history of commercial anode materials, Sn/C-based material is the focus to enhance the cycling performance. A chemical solution method is used to synthesize the Sn compounds / graphite composite anodes. At the first part of this study, the cycle life was enhanced by adjusting various pH values. The multi-phase Sn compound containing Sn6O4(OH)4, SnO2, Sn3(PO4)2were deposited on slices of graphite of sample pH6. They were expected to provide a higher spectator to Sn ratio for improved cycleability. These phases could be reduced to metallic Sn, resulting in buffer matrix during 1stcycle. Therefore, the sample pH6 exhibited the best of electrochemical performance. For the cell cycled between 0.001V and 1.5V, the 1stcharge capacity was 758 mAhg-1. Even after 50 cycles, the capacity remained higher than 460 mAhg-1. Synthesizing Sn compounds / graphite composite anodes at pH6 with different initial Sn concentrations improved the cycling performance in the second part of this study. When the Sn concentration reached 0.12M, multi-phases of Sn compounds were deposited on the slices of graphite and the amount of Sn was the maximum. The agglomeration of Sn clusters was suppressed by buffering agent generated by the multi-phase of Sn compounds containing Sn6O4(OH)4, SnO2, Sn3(PO4)2. Therefore, the sample Sn0.12 M exhibitedthe best cycling behavior among all. During cycling between 0.001 V and 1.5 V, the 1stcharge capacity was around 734 mAhg-1. The capacity remained as high as 440 mAhg-1 even after 50 cycles.

Relaxation Behavior of Li4/3Ti5/3O4 Electrode for Li-ion Secondary Battery

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Large-scale first-principles molecular dynamics for electrochemical systems with O(N) methods

A method for large-scale first-principles molecular dynamics (MD) simulations on electrochemical systems has been developed by combining the effective screening medium (ESM) method with O(N) density functional theory (DFT). This implementation has been significantly simplified by the introduction of neutral atom potentials, which minimizes the modifications to existing DFT code. In order to demonstrate ability of this implementation, it has been applied to an electrochemical system consisting of a H-Si(111) electrode, which is a candidate anode for high-capacity Li-ion secondary batteries, and a propylene carbonate (PC) solvent to simulate how PC molecules in the vicinity of the electrode surface respond to an imposed electric field. The large-scale MD simulation clearly demonstrates that the combination of the ESM and O(N) DFT methods provides a useful tool for first-principles investigation of complicated electrochemical systems such as high-capacity batteries.

Preparation and Characteristics of Li4Ti5O12Anode Material for Hybrid Supercapacitor

Spinel-Li₄Ti?O₁₂ was successfully synthesized by a solid-phase method at 800, 850, and 900℃ according to the Li₄Ti?O₁₂ cubic spinel phase structure. To achieve higher EDLC energy density with the Li₄Ti?O₁₂, the negative electrode of the hybrid supercapacitor was studied in this work. The electrochemical performances of the hybrid supercapacitor and EDLC were characterized by constant current discharge curves, c-rate, and cycle performance testing. The capacitance (1st cycle) of the hybrid supercapacitor and EDLC was 209 and 109 F, respectively, which is higher than EDLC. The capacitance of the hybrid supercapacitor decreases from 209 F to 101 F after 20 cycles when discharged at several specific current densities ranging from 1 to 10 A. In contrast, capacitance of the EDLC hardly decreases after 20 cycles. Results show that hybrid supercapacitor benefits from the high rate capability of supercapacitor and high capacity of the battery. Findings also prove that the hybrid supercapacitor is an energy storage device where the supercapacitor and the Li ion secondary battery coexist in one cell system.

Microstructural and electrochemical properties of rf-sputtered LiMn2O4 thin film cathodes

Lithium transition metal oxides have received considerable attention in recent years as high voltage positive electrode materials in the fabrication of all solid state microbatteries. Among various lithium-based cathode materials, LiMn2O4 is one of the most promising cathode materials as it offers high energy density, high cell voltage, low cost, and low toxicity over the other electrode materials. Thin films of LiMn2O4 were prepared by radio frequency magnetron sputtering on gold-coated silicon substrates under various substrate temperatures ranging from 373 to 673 K in a partial pressure of 3 × 10−3 mbar with rf power 100 Watts. In the present investigation, the influence of substrate temperature on the growth and microstructural properties was studied. The films deposited at a substrate temperature less than 473 K was found to be X-ray amorphous. The initial crystallization has been observed at a substrate temperature of 523 K. The X-ray diffraction patterns of the films deposited in the substrate temperature range 523–673 K exhibited predominant (111) orientation representing cubic spinel structure with Fd3m symmetry. The grain size was found to be increased with the increase of substrate temperature as evidenced from SEM studies. However, additional impurity phases like Mn3O4 were observed for the films deposited at higher substrate temperatures (>673 K) because of re-evaporation of Li+ ions in the films. The electrochemical (EC) studies were carried for the films deposited at Ts = 673 K in aqueous media in the potential window of 0.0–1.2 V exhibited better electrochemical performance suggesting that the films are well suited as binder free thin film cathode material for commercially viable Li-ion secondary batteries.

Relaxation Crystal Analysis of LiFePO4 Cathode for Li-Ion Secondary Battery

Lithium iron phosphate has been attracting much attention as the next generation cathode material in secondary Li-ion batteries. We inserted lithium into LiXFePO4 (x ≈ 0) electrochemically and investigated the relaxation process of two-phase after termination of lithium insertion process by means of X-ray Rietveld analysis. It was found that the amount of LiFePO4 decreased and that of FePO4 increased after the termination of lithium insertion. It is considered that LiFePO4 including lithium defects preferable for Li diffusion formed during lithium insertion and that the defective LiFePO4 separated to LiFePO4 without defects and FePO4 at the relaxation process.

A dicranopteris-like Fe–Sn–Sb–P alloy as a promising anode for lithium ion batteries

A novel dicranopteris-like Fe-Sn-Sb-P composite was prepared, for the first time, by electrodeposition. The quaternary Fe-Sn-Sb-P alloy of multiphase displayed an excellent cycling performance as an anode of Li ion secondary batteries.

Core/shell structure analysis for Li ion secondary battery electrode LiFePO<sub>4</sub>/C by small Angle X-ray scattering method.

Core/shell structure analysis for Li ion secondary battery electrode LiFePO<sub>4</sub>/C by small Angle X-ray scattering method.

Relationship between Electrochemical Pre-Treatment and Cycle Performance of a Li-Rich Solid-Solution Layered Li1^|^minus;^|^alpha;[Ni0.18Li0.20+^|^alpha;Co0.03Mn0.58]O2 Cathode for Li-Ion Secondary Batteries

In our previous paper (J. Power Sources, 183, 344 (2008)), we proposed the application of a pre-cycling treatment to a Li-rich solid-solution layered cathode (xLi2MnO3·yLi[Ni0.5Mn0.5]O2·zLi[Co1/3Ni1/3Mn1/3]O2 where (x + y + z = 1)) before the charge/discharge cycling process to obtain enhanced capacities stable above 250 mAh g−1. The aim of the present work is to reduce the duration of this pre-cycling process. The cycling performance dependence of Li1−α[Ni0.18Li0.20+αCo0.03Mn0.58]O2 on the pre-cycling processing parameters, such as the number of cycles, voltage limits, and current density was explored. The processing conditions were then optimized, which ultimately reduced the pre-cycling treatment time from one week to 6.5 h.

Synthesis of open tunnel-structured TiO 2(B) by nanosheets processes and its electrode properties for Li-ion secondary batteries

Open tunnel-structured TiO 2(B) was synthesized by using nanosheets processes. TiO 2(B) was obtained only when multi-lamellar tetratitanate nanosheets were used as the reassembly component. The electrochemical properties of the nanosheet-derived TiO 2(B) were influenced by guest ions of the self-reassembled nanosheets. When K + ions were used as guest ions for the self-reassembly of nanosheets, the pure TiO 2(B) phase was obtained and it exhibited a large discharge capacity of 253 mAh(g-TiO 2(B)) −1 ( x = 0.76, Li x TiO 2(B)) at a current density of 100 mA(g-TiO 2(B)) −1. This value was a larger than 170 mA(g-TiO 2(B)) −1 of TiO 2(B) prepared by a conventional method without the nanosheets process. The large capacity is attributed to an increased specific surface area achieved by the nanosheets process.