Initial Charge-discharge Cycle Research Articles

Improving Zinc-Ion Batteries’ Performance: The Role of Nitrogen Doping in V2O3/C Cathodes

This study presents the synthesis and electrochemical evaluation of nitrogen-doped vanadium oxide (N−V2O3/C) as a cathode material for aqueous zinc-ion batteries (AZIBs), using a hydrothermal method. Compared to undoped V2O3/C, N−V2O3/C exhibits enhanced electrical conductivity, capacity, and electrochemical kinetics, attributed to the incorporation of pyridinic and pyrrolic nitrogen. The initial charge–discharge cycles indicate phase transitions to amorphous vanadium oxides, enhancing conductivity. N−V2O3/C shows a high specific capacity of 168.4 mAh g−1 at 10 A g−1 and remarkable reversibility, highlighted by the transient existence of intermediate species during cycling. Optimal electrochemical performance is achieved with a vanadium-to-nitrogen molar ratio of 2:3, indicating the significant impact of the nitrogen doping concentration on the material’s efficiency. This work underscores the potential of N−V2O3/C as a superior cathode material for AZIBs.

P-doped hard carbon material for anode of sodium ion battery was prepared by using polyphosphoric acid modified petroleum asphalt as precursor

The practical value of hard carbon anode in sodium ion batteries has garnered significant attention. Asphalt-derived hard carbon offers lower cost and scale advantages compared to expensive resin and bio-based hard carbon materials. However, the synthesis of asphalt-derived hard carbon with significantly enhanced reversible capacity remains challenging. This study focuses on synthesizing P-doped hard carbon material using polyphosphoric acid-modified petroleum asphalt as a precursor and the pre-oxidation method. Doping P elements in hard carbon induces deformation of the molecular layer structure within the pseudo-graphite domains, expanding graphite layer spacing and increasing the number of internal closed micropores, thereby enhancing the sodium storage capacity of the matrix. The reversible capacity of P-doped hard carbon (PHC-1300) increased from 240.3 mA h g−1 to 359.9 mA h g−1 during the initial charge-discharge cycle at a rate of 0.05 C compared to undoped hard carbon (HC-1300). Moreover, phosphate exhibits higher reduction ability than adjacent carbon atoms, generating electron holes that partially compensate for limited electron conduction capability in hard carbon material. The electronic conductivity of the material increases from 26.1114 S cm−1 to 36.6418 S cm−1, demonstrating a significant enhancement compared to high graphitized soft carbon (SC-1300).Therefore, the practical significance of employing this straightforward precursor modification method to prepare P-doped hard carbon warrants attention.

Uncorrelated Sparse Autoencoder With Long Short-Term Memory for State-of-Charge Estimations in Lithium-Ion Battery Cells

For the safe and reliable operation of battery-driven machines, accurate state-of-charge (SOC) estimations are necessary. Unfortunately, existing methods often fail to identify patterns relevant to long-term SOC estimation due to complex battery cell characteristics such as aging. In this paper, we propose the Uncorrelated Sparse Autoencoder with Long Short-Term Memory (USAL). USAL is a novel neural network that addresses the challenging task of long-term SOC estimation given a limited initial history of a cell’s charge-discharge behavior. USAL uses a multi-task learning strategy to harness the advantages of sparse autoencoders and Long Short-term Memory (LSTM) networks by enforcing correlation penalties. The USAL simultaneously learns to (i) generate a latent space of informative SOC encodings from commonly measured cell characteristics, (ii) penalize for high multicollinearity between encodings, and (iii) identify non-trivial long and short temporal correlations between the encodings using LSTM cells. USAL outperforms benchmarked models in our experiments when trained on five initial charge-discharge cycles across multiple battery cells using three publicly available accelerated aging datasets. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This paper proposes USAL, a custom-built deep neural network to address the challenging task of long-term SOC estimations in battery cells. Long-term SOC estimation involves estimating SOC for cycles near End-Of-Life (EOL) given some initial charge-discharge cycles. Three fundamental steps involved in long-term SOC estimations using USAL are (i) exploiting a multi-task learning strategy to learn efficient encodings given limited training data, (ii) penalizing these encodings for high correlations to efficiently transform measured inputs into a space of informative features, and (iii) mapping of aging-related trends to support long-term SOC estimations. USAL is designed to be a data-driven SOC estimation method that is (i) capable of alerting the user to a faulty cell when integrated into a real-life Battery Management System (BMS) and (ii) identifying the relative quality of a battery cell from only a few initial charge-discharge cycles.

(Invited) SiO and LiNi0.5Mn1.5O4 Composite Electrodes with Functional Polymer Binders

This study focuses on the optimization of polymer binders in lithium-ion batteries (LIBs) to facilitate the development of high-energy-density storage devices. Despite 30 years of commercialization, the demand for high energy density storage devices has continued to increase, making LIBs a topic of significant research interest. One major avenue of research has focused on high-voltage positive electrode materials such as LiNi0.5Mn1.5O4 (LNMO) and high-capacity negative electrode materials like SiO. However, the practical use of these materials is hindered by issues associated with electrolyte decomposition and large volume changes during the charge-discharge process.To address these challenges, we explored the chemistry of polymer binders blended in composite electrodes to maintain the structure of the electrode and form a passivation/protective layer on the active material surface to suppress side reactions.(1, 2) In particular, we investigated the use of "functional binders" to improve the performance of high-voltage LNMO composite electrodes. We synthesized sulfated alginate binders, which are significantly cheaper and stiffer than commonly used poly(vinylidene fluoride) (PVdF) and uniformly cover the surface of LNMO.(3)The high polarity of the sulfate group also increased the binder's affinity for the electrolyte. During the initial charge-discharge cycle, the electrolyte decomposition products generated on the alginate-covered active materials participated in the formation of a protective passivation layer that suppressed further decomposition during subsequent cycles, resulting in enhanced cycling and rate performances.We also explored the use of partially-neutralized crosslinked sodium polyacrylate (CLPA) binders with flexible monomers to mitigate the effects of volume changes in SiO electrodes.(4)Additionally, we investigated the “maturation” effects on battery performances by storing the composite electrodes with CLPA-based binders in a humid atmosphere for a few days before drying. Our results show that the binder with 20% flexible monomer (CLPA-20) exhibited the highest peel strength and long-term cyclability, and the maturation treatment further improved these properties. Cross-sectional SEM images revealed that the binder and conductive carbon were uniformly dispersed in the composite layer in the matured electrodes, indicating the migration of active materials and binders during the maturation process. Furthermore, surface analysis of the cycled electrode showed that the superior mechanical properties of the electrode endowed by the maturation treatment helped in maintaining the passivation layer on the active material surface, resulting in improved cycling performance.Overall, our findings suggest that optimizing polymer binders can enhance the performance of LIBs by controlling the electrode reaction via binder chemistry. The strategies developed in this study could facilitate the future development of high-energy-density LIBs, making them more accessible and commercially viable for various applications.References (1) R. Tatara, S. Komaba et al., ChemElectroChem, 8, 4345 (2021).(2) H. Isozumi, R. Tatara, S. Komaba et al., ACS Appl. Energy Mater., 3, 7978 (2020).(3) A. Oishi, R. Tatara, S. Komaba et al., ACS Appl. Mater. Interfaces, 14, 51808 (2022).(4) S. Yamazaki, R. Tatara, S. Komaba et al., Mater. Adv., 4, 1637 (2023).

Localised degradation within sulfide-based all-solid-state electrodes visualised by Raman mapping.

The distribution of degradation products, before and after cycling, within common sulfide-based solid electrolytes (β-Li3PS4, Li6PS5Cl and Li10GeP2S12) was mapped using Raman microscopy. All composite electrodes displayed the appearance of side reaction products after the initial charge-discharge cycle, located at the site of a LiNi0.6Mn0.2Co0.2O2 particle.

Sulfated Alginate as an Effective Polymer Binder for High-Voltage LiNi0.5Mn1.5O4 Electrodes in Lithium-Ion Batteries.

Although the increasing demand for high-energy-density lithium-ion batteries (LIBs) has inspired extensive research on high-voltage cathode materials, such as LiNi0.5Mn1.5O4 (LNMO), their commercialization is hindered by problems associated with the decomposition of common carbonate solvent-based electrolytes at elevated voltages. To address these problems, we prepared high-voltage LNMO composite electrodes using five polymer binders (two sulfated and two nonsulfated alginate binders and a poly(vinylidene fluoride) conventional binder) and compared their electrochemical performances at ∼5 V vs Li/Li+. The effects of binder type on electrode performance were probed by analyzing cycled electrodes using soft/hard X-ray photoelectron spectroscopy and scanning transmission electron microscopy. The best-performing sulfated binder, sulfated alginate, uniformly covers the surface of LNMO and increased its affinity for the electrolyte. The electrolyte decomposition products generated in the initial charge-discharge cycle on the alginate-covered electrode participated in the formation of a protective passivation layer that suppressed further decomposition during subsequent cycles, resulting in enhanced cycling and rate performances. The results of this study provide a basis for the cost-effective and technically undemanding fabrication of high-energy-density LIBs.

Incorporation of Poly(Ionic Liquid) with PVDF-HFP-Based Polymer Electrolyte for All-Solid-State Lithium-Ion Batteries

A solid-state polymer electrolyte membrane is formed by blending poly(vinylidene fluoride-co-hexafluoropropylene) with the synthesized copolymer of poly(methyl methacrylate-co-1-vinyl-3-butyl-imidazolium bis(trifluoromethanesulfonyl)imide, in which lithium bis(trifluoromethane)sulfonimide molecules are applied as the source of lithium ions. The accordingly formed membrane that contains 14 wt.% of P(MMA-co-VBIm-TFSI), 56 wt.% of PVDF-HFP, and 30 wt.% of LiTFSI manifests the best electrochemical properties, achieving an ionic conductivity of 1.11 × 10−4 S·cm−1 at 30 °C and 4.26 × 10−4 S·cm−1 at 80 °C, a Li-ion transference number of 0.36, and a wide electrochemical stability window of 4.7 V (vs. Li/Li+). The thus-assembled all-solid-state lithium-ion battery of LiFePO4/SPE/Li delivers a discharge specific capacity of 148 mAh·g−1 in the initial charge–discharge cycle at 0.1 C under 60 °C. The capacity retention of the cell is 95.2% after 50 cycles at 0.1 C and the Coulombic efficiency remains close to 100% during the cycling process.

Synthesis, characterisation and electrochemical evaluation of lithium titanate anode for lithium ion cells

Lithium titanate, Li4Ti5O12 (LTO), a promising anode material for high power lithium ion (Li-ion) cells, was synthesised by sol-gel method using hydrated titania and lithium carbonate as precursors. The synthesised material was characterised by Fourier-transform infrared spectroscopy and X-ray diffraction methods. The morphology of the material was studied by scanning electron microscopy. The electrochemical evaluation of LTO electrode in Li-ion cells was carried out by assembling LTO electrode versus Li metal as counter electrode in half cell. The cell was subjected to initial charge-discharge cycles at C/10 rate and then tested at different rates viz. C/5, C/2, 1C, 2C, 5C, 10C and 20C. The specific capacity at these rates was 170, 167, 165, 164, 161, 160, 160 and 155 mAh/g, respectively. The columbic efficiency of the cell was close to 100% at these rates. Herein, we demonstrate that a pristine LTO formed by simple sol-gel method can retain more than 90% of the capacity at high current rate of 20C.

Exothermal behavior and microstructure of a LiNi1/3Mn1/3Co1/3O2 electrode layer using a Li4SnS4 solid electrolyte

A positive electrode containing Li3PS4 (LPS) glasses and LiNi1/3Mn1/3Co1/3O2 (NMC) is a promising candidate for sulfide-based all-solid-state lithium batteries owing to its excellent charge–discharge cycle characteristics. However, sulfide-based solid electrolytes exhibit low chemical stability in air. This disadvantage affects process cost and thermal stability of all-solid-state cells. To resolve these issues, in this study, we focus on solid electrolytes, Li4SnS4 (LSS), that do not generate H2S gas in air. The thermal behavior and microstructure of LSS–NMC positive electrode composites before and after the initial charge–discharge cycle are investigated. The initially charged LSS–NMC composites exhibit several exothermal reactions above 250 °C. However, pristine and initially discharged samples do not show any considerable exothermal reactions. For LPS–NMC composites, by contrast, exothermal reactions are detected regardless of the charging and discharging state. To clarify the exothermic factors of initially charged LSS–NMC composites, we performed ex situ transmission electron microscopy observation and X-ray diffraction measurements. It is determined that SnS2, transition metal sulfides, and metal oxides are formed above 300 °C, which is attributable to LSS and NMC decomposition reactions. On the basis of the relation between thermal behavior and corresponding structural changes, exothermic factors and thermal stability of LSS–NMC composites are discussed in comparison with LPS–NMC composites.

Comparison of the Structure and Phase Changes of Carbon-Coated SiO and Li-Doped Carbon-Coated SiO During Repeated Charge–Discharge Cycling

Carbon-coated SiO (SiO–C), which is a high-capacity anode material, experiences a significant capacity drop in the initial charge–discharge cycles. In contrast, Li-doped SiO–C (Li–SiO–C), which has been recently developed, exhibits a significantly smaller capacity drop. To explain this difference, we performed a detailed investigation of the structures and phase changes associated with the charge–discharge cycling of these materials by comparing their Si structures and electronic states obtained from solid-state magic-angle spinning nuclear magnetic resonance and Si K-edge X-ray absorption fine structure measurements. The results show that, in the case of SiO–C, the Li4SiO4 generated during charge is partially decomposed during discharge in the initial charge–discharge cycles. These generation and decomposition behaviors are most intense during the first 20 cycles. We believe that this phenomenon is the cause of the increased irreversible capacity observed in the initial cycles of SiO–C. In addition, we confirmed that Li2SiO3, a component of Li–SiO–C, is relatively stable electrochemically, although some of it gradually converts into Li4SiO4 during charge–discharge cycling. The presence of Li2SiO3 at the outset implies that less Li4SiO4 is generated during charging compared to SiO–C, which we believe explains the lack of a significant capacity drop in the initial cycles of Li–SiO–C.

Microscopic Elucidation of Solid-Electrolyte Interphase (SEI) Film Formation via Atomistic Reaction Simulations: Importance of Functional Groups of Electrolyte and Intact Additive Molecules.

Secondary batteries such as Li-ion battery are expected to be utilized as not only ubiquitous electric power sources such as mobile phones but also large-scale electricity storage devices. Therefore, it is urgent to develop the higher performance secondary batteries. Their lifetime and stability are found to be strongly dependent on the nature of passivation film called solid electrolyte interphase (SEI) film formed on the anode surface in the initial charge-discharge cycle. However, since it is difficult to directly observe the film formation processes in experiment, its microscopic mechanism is still not found. On the other hand, although the theoretical methods are useful complement to the experiment, some new methodologies are necessary to understand the long-term processes of SEI film, which is produced as a result of that a lot of chemical reactions proceed simultaneously. Under the circumstances, we have developed Red Moon method that can simulate such complex chemical reaction systems, and were able to analyze for the first time the SEI film formation processes on the anode surface at the atomistic level. Then, we clarified theoretically the microscopic mechanism of the additive effect which is essential to improve the Na-ion battery performance so as to enhance the SEI film formation. This new microscopic insight must provide an important guiding principle for use in designing the most suitable electrolytes for developing high-performance secondary batteries.

Effect of Prelithiation Process for Hard Carbon Negative Electrode on the Rate and Cycling Behaviors of Lithium-Ion Batteries

Two prelithiation processes (shallow Li-ion insertion, and thrice-repeated deep Li-ion insertion and extraction) were applied to the hard carbon (HC) negative electrode (NE) used in lithium-ion batteries (LIBs). LIB full-cells were assembled using Li(Ni0.5Co0.2Mn0.3)O2 positive electrodes (PEs) and the prelithiated HC NEs. The assembled full-cells were charged and discharged under a low current density, increasing current densities in a stepwise manner, and then constant under a high current density. The prelithiation process of shallow Li-ion insertion resulted in the high Coulombic efficiency (CE) of the full-cell at the initial charge-discharge cycles as well as in a superior rate capability. The prelithiation process of thrice-repeated Li-ion insertion and extraction attained an even higher CE and a high charge-discharge specific capacity under a low current density. However, both prelithiation processes decreased the capacity retention during charge-discharge cycling under a high current density, ascertaining a trade-off relationship between the increased CE and the cycling performance. Further elimination of the irreversible capacity of the HC NE was responsible for the higher utilization of both the PE and NE, attaining higher initial performances, but allowing the larger capacity to fade throughout charge-discharge cycling.

Multistage Mechanism of Lithium Intercalation into Graphite Anodes in the Presence of the Solid Electrolyte Interface.

A so-called solid electrolyte interface (SEI) in a lithium-ion battery largely determines the performance of the whole system. However, it is one of the least understood objects in these types of batteries. SEIs are formed during the initial charge-discharge cycles, prevent the organic electrolytes from further decomposition, and at the same time govern lithium intercalation into the graphite anodes. In this work, we use electrochemical impedance spectroscopy and atomic force microscopy to investigate the properties of a SEI film and an electrified "graphite/SEI/electrolyte interface". We reveal a multistage mechanism of lithium intercalation and de-intercalation in the case of graphite anodes covered by SEI. On the basis of this mechanism, we propose a relatively simple model, which perfectly explains the impedance response of the "graphite/SEI/electrolyte" interface at different temperatures and states of charge. From the whole data obtained in this work, it is suggested that not only Li+ but also negatively charged species, such as anions from the electrolyte or functional groups of the SEI, likely interact with the surface of the graphite anode.

Irreversible capacity and rate-capability properties of lithium-ion negative electrode based on natural graphite

In this paper, the results of experimental work with doped natural graphite are presented and described. The graphite material plays major role within negative electrode materials used in lithium-ion batteries. Behavior of graphite used as an active material for negative electrodes in lithium-ion cell was widely investigated and published. The one key characteristic property of graphite is its irreversible capacity loss. The irreversible capacity represents losses which occur in the graphite negative electrode within initial charge-discharge cycles (process called cell formatting). This phenomenon is associated connected with lower negative electrode potential vs. lithium (Li/Li+) and the growth of the Solid Electrolyte Interphase (SEI) layer. The SEI layer is important and necessary for proper operation of the lithium-ion cell; on the other hand growth of the SEI layer limits and lowers the theoretical capacity of lithium-ion cell by up to 40%. A possible way how to offset these losses is to dope the graphite material by lithium atoms before its use in the lithium-ion cell. The lithiation process has been studied as a possible way how to dope the (pre-lithiated) natural graphite prior to its use as an active electrode material. Suppression of irreversible capacity losses at initial charge-discharge cycles is the main focus of our investigation.

Effect of Using Fluorinated Ether and Sulfone as Electrolyte Solvents for Lithium Ion Batteries with Lithium-Rich Layered Cathodes and Silicon Oxide Anodes

We examined fluorinated ether and sulfone as electrolyte solvents for Lithium (Li) ion batteries with Li-rich layered cathodes and Silicon oxide anodes. We evaluated the mixture of cyclic carbonate, sulfone compound, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropopyl ether (FE1). The gas volume after the initial charge-discharge process increased with the amount of ethylene carbonate (EC) or 4-fluoro 1,3-dioxolane 2-one (FEC). These results show that the reaction between EC or FEC and cathode-active material can be considered to be the cause of gas evolution in the initial charge-discharge cycle. We evaluated sulfone compounds and low-viscosity solvents. By using electrolyte solution with ethyl isopropyl sulfone, FE1, and FEC as electrolyte solvents, the retention capacity after 500 cycles increased to around 67%, which was larger than that of conventional electrolyte solutions such as 1 M LiPF6 EC/diethyl carbonate (30/70 v/v).

Effect of Using Fluorinated Ether and Sulfone As Electrolyte Solvents for Lithium Ion Batteries with Lithium Rich Layered Cathode and Silicon Oxide Anode

Introduction Li rich layered cathode is one of the candidates for next generation cathode active material of Lithium ion batteries, because of large capacity more than 250 mAh/g. On the other hand, because of the higher potential than conventional cathode active materials, Li rich layered cathode has the problem of the capacity fading and gas emission. We have studied fluorinated electrolyte solvents for high voltage operation batteries with LiNi0.5Mn1.5O4 cathode1) 2), and we have reported that fluorinated ether and fluorinated phosphate were effective to reduce gas emission in high voltage operation cells at elevated temperature. In this report, we examined fluorinated ether and sulfone as electrolyte solvents for Lithium ion batteries with Li rich layered cathode and SiO anode. Experimental Li(LixNiyMn1-x-y)O2 was used as a cathode active material, and SiO was used as an active anode material. The discharge capacity as a function of cycle number was tested using stack type laminated cells with these active materials. Ethylene carbonate (EC), diethyl carbonate (DEC), DES (Diethyl sulfone) and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (FE) were used as electrolyte solvents. EC/DEC (30/70 v/v) and EC/DES/FE (x/(30-x)/70 v/v/v (x=0,5,10)) were used as electrolyte solutions. The volume of the cells was measured by the Archimedes method before and after initial 3 charge discharge cycles between 4.5 V and 1.5 V. After that, cycle tests were performed between 4.5 V and 1.5 V at 45 ºC. Results Figure 1 shows discharge capacity retention as a function of cycle number for Li(LixNiyMn1-x-y)O2/SiO cells with electrolyte solutions of EC/DEC (30/70 v/v) and EC/DES/FE (5/25/70 v/v/v). Capacity retention of EC/DES/FE after 200 cycles was larger than that of EC/DEC. DES and FE seem to have higher oxidation resistance than DEC and to have the effect of cycle life improvement. Figure 2 shows the volumes increase of cells after initial 3 charge-discharge cycles at 45 °C. The cause of volume increase is gas emission. The volume increase of the cell with EC/DEC (30/70 v/v) was larger than that with EC/DES/FE (x/(30-x)/50 v/v/v). Gas volume increased with amount of EC in electrolyte of EC/DES/FE. This result shows that the cause of gas emission at initial charge-discharge process seems to be due to the reaction between electrolyte solvents and cathode. EC is considered to be the cause of gas emission in initial charge discharge cycles. References T.Noguchi, M.Uehara, Y.Katoh, K.Utsugi, PRiMe 2012 , No.824 (2012) T.Noguchi, Y.Katoh, K.Utsugi, 228th ECS Meeting , No.358(2015) Figure 1

Estimating the thickness of diffusive solid electrolyte interface

The solid electrolyte interface (SEI) is a hierarchical structure formed in the transition zone between the electrode and the electrolyte. The properties of lithium-ion (Li-ion) battery, such as cycle life, irreversible capacity loss, self-discharge rate, electrode corrosion and safety are usually ascribed to the quality of the SEI, which are highly dependent on the thickness. Thus, understanding the formation mechanism and the SEI thickness is of prime interest. First, we apply dimensional analysis to obtain an explicit relation between the thickness and the number density in this study. Then the SEI thickness in the initial charge-discharge cycle is analyzed and estimated for the first time using the Cahn-Hilliard phase-field model. In addition, the SEI thickness by molecular dynamics simulation validates the theoretical results. It has been shown that the established model and the simulation in this paper estimate the SEI thickness concisely within order-of-magnitude of nanometers. Our results may help in evaluating the performance of SEI and assist the future design of Li-ion battery.

EIS and Structual Analysis of LiCoO2 Cathode Degradation Behavior in Libs at Initial Stage of Charge-Discharge Cycles

Lithium ion batteries (LIBs) are widely applied not only in portable electronic devices but also electric vehicles and stationary energy storages. Electric vehicles and stationary energy storages require more safeness and higher durability of LIBs. Therefore, a dynamic and static degradation mechanism of LIBs required to be understood. Electrochemical impedance spectroscopy (EIS) is powerful for understanding of LIBs degradation mechanism. Impedance response of LIBs are complicated because various elemental steps, such as electron migration with inductive response, ion migration in bulk and electrode, and charge transfer of chemical reaction of cathode and anode, are included. In addition, some elemental steps overlap in close frequency region. Therefore, the impedance responses of cathode and anode have to be measured separately for detailed analysis. We have demonstrated impedance separation approaches for LIBs by using temperature control1, separable cell2,3 and micro reference electrode4. Among them, we reported a static degradation of LiCoO2 cathode observing impedance increase of LiCoO2 cathode under storage in the presence of HF.3 In present paper, we focused a dynamic degradation of LiCoO2 cathode caused by initial charge-discharge cycles. Impedance increase of LiCoO2 cathode in 20 charge-discharge cycles and the characteristics change of the active material are discussed. We evaluated a lab-made pouch-type LIB which was composed of a cathode whose active material was commercially available LiCoO2, an anode whose active material was commercially available graphite, and a reference electrode of Al wire (φ 25 μm, 4 mm) which was inserted between the cathode and anode with separation provided by a commercially available polyethylene separator. The electrolyte was 1 M LiPF6/ ethylene carbonate (EC)- diethyl carbonate (DEC) (50:50 vol.%). The EIS was carried out at the open circuit voltage of a state of charge in the frequency range of 100 kHz - 10 mHz and an AC amplitude of 10 mV0-p, while applying the defined voltages via a multi-channel potentiostat and a frequency response analyzer system. The charge-discharge test for degradation was carried out with a constant current of 35.0 mAh (ca. 0.5 C against design capacity) and a cut-off voltage of 4.2 V and 3.0 V via the charge-discharge system. Figure 1 shows impedance responses of LiCoO2 cathode separated from that of LIB by LiAl micro reference electrode after 0, 10, and 20 charge-discharge cycles at the SOC of ca. 60%. The Nyquist plot and Bode plots clearly show two semicircles whose top frequencies are ca. several kHz and several mHz. The latter semicircle is attributed to the charge transfer resistance. The former semicircle would be attributed to a kind of film on the cathode active material like solid electrolyte interphase on anode active material. The radius of those semicircles increased with charge-discharge cycles. Especially, the radius of the semicircle at several kHz increased. To reveal the reason, the crystal structures of the surface of the LiCoO2 particle were evaluated by transmission electron microscopy. The results imply the change of crystal structure with charge-discharge cycles. On the other hand, LiF formation was not confirmed. The surfaces of the LiCoO2 cathode were analyzed by Raman spectroscopy. As the result, the formation of CoO after charge-discharge cycles was confirmed. Therefore, those results suggest that the increase of impedance at several kHz attributed to the surface crystal structure rather than film formation on the active material. We will present the characteristics change with charge-discharge cycles in detail. Acknowledgement This work was supported by “Research & Development Initiative for Scientific Innovation of New Generation Batteries (RISING)” from New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Core-Shell Sn-Ni-Cu-Alloy@Carbon Nanorods to Array as Three-Dimensional Anode by Nanoelectrodeposition for High-Performance Lithium Ion Batteries.

We report the synthesis of a novel three-dimensional anode based on the core-shell Sn-Ni-Cu-alloy@carbon nanorods which was fabricated by pulse nanoelectrodeposition. Li ion batteries equipped with the three-dimensional anode demonstrated almost 100% capacity retention over 400 cycles at 450 mA g(-1) and excellent rate performance even up to 9000 mA g(-1) for advanced Li-ion battery. Insight of the high performance can be attributed to three key factors, Li-Sn alloys for Li-ion storage, Ni-Cu matrix for the electronic conductive and nanorods structure, and the carbon shell for the electronic/Li-ion conductive and holding stable solid electrolyte interphase (SEI), because these shells always kept stable volumes after extension of initial charge-discharge cycles.

Sputtering Deposition of Sn–Mo-Based Composite Anode for Thin-Film Li-Ion Batteries

The role of electrochemically inactive molybdenum in alleviating the anomalous volume expansion of tin anode upon charge–discharge cycling has been investigated. Tin–molybdenum thin-film composite anodes for Li-ion batteries were prepared using a direct-current sputtering method from a tin metal target incorporating molybdenum element. Results of structural and compositional analyses confirmed the presence of tin and molybdenum. The elemental ratio obtained from energy-dispersive x-ray spectroscopy confirmed the feasibility of tailoring the thin-film composition by varying the ratio of metallic elements present in the sputtering target. Scanning electron micrographs of the samples revealed the occurrence of flower-like open morphology with Mo inclusion in a Sn matrix. The gravimetric discharge capacity for pure Sn, Sn-rich, and Mo-rich samples was 733 mAh g−1, 572 mAh g−1, and 439 mAh g−1, respectively, with capacity retention after 50 cycles of 22%, 61%, and 74%, respectively. Mo inclusion reduced the surface resistivity of the Sn anode after the initial charge–discharge cycle. The charge-transfer resistance after the first cycle for pure Sn, Sn-rich, and Mo-rich samples was 17.395 Ω, 5.345 Ω, and 2.865 Ω, respectively. The lithium-ion diffusion coefficient also increased from 8.68 × 10−8 cm2S−1 for the pure Sn sample to 2.98 × 10−5 cm2S−1 for the Mo-rich sample.