Differential Capacity Plots Research Articles

Materials Safety Study of Practical Nano-Silicon + Graphite Anodes for Lithium-Ion Batteries

Silicon has long been sought as a replacement to graphite anodes in next generation lithium-ion batteries due largely to it’s extremely high theoretical capacity of ~3500 mAh g-1 (for the formation of Li15Si4). This full value has yet to be realized in a practical electrode system due to both mechanical degradation caused by volume change during lithiation / delithiation and electrode surface instability that combine to cause rapid loss of capacity. However, advances in binder materials, materials synthesis of nano-silicon, and electrolyte additives have enabled the development of graphite and nano-silicon (Graphite + nSi) composite anodes that possess greater specific capacity that typical graphite electrodes and can be practically incorporated into improved lithium-ion cells. Sandia National Labs is conducting both materials scale and battery scale safety tests to determine the effects of nano-silicon incorporation on the safety performance of lithium-ion batteries. This study will focus on the effects of varying the silicon content in Graphite + nSi electrodes, using different binder materials, and using different electrolytes or additives on the failure mechanisms and characteristics of lithium-ion battery materials. Performance of Graphite + 15 % nSi Electrodes Electrodes of both graphite and Graphite + 15 % nSi composite were prepared using an aqueous LiPAA binder and 1.2 M LiPF6 in EC:EMC (3:7) electrolyte1. The electrodes possessed areal capacities of approximately 1.6 mAh cm-2 and were cycled in both half-cell configuration vs. lithium foil and in full cell configuration vs. an NCM 523 cathode. The voltage vs. capacity curve for the two electrodes, see Figure 1a, show several plateaus below 0.2 V arising from graphite activity with lithium while the 15 % nSi electrode also has significant capacity at higher voltages arising from lithiation of silicon which gives Graphite + 15 % nSi a specific capacity of 610 mAh g-1 compared to 319 mAh g-1 for graphite only. The differential capacity plot in Figure 1b shows more clearly the capacity contribution from the silicon peaks which occur at roughly 0.45 V and 0.25 V during charge and discharge. Figure 1d shows the cathode capacity retention and coulombic efficiency for the composite anode tested in full cell configuration, demonstrating the continued need for performance improvement for greater capacity retention. Figure 2 shows post cycling DSC analysis carried out on Graphite + 15 % nSi electrodes extracted from cycled full cells. After several formation cycles the cells were discharged to a prescribed voltage corresponding to a given state-of-charge (SOC). As expected the higher SOC electrodes generated more heat during testing. The various voltages were also selected for the given lithiation state of the anode: at 3.1 V the anode is fully delithiated, showing minimal thermal response; at 3.4 V the graphite is delithiated and the silicon is lithiated, making it the primary reactant and contributor to the thermal response at this state; at 4.1 V both graphite and silicon are lithiated so the resulting DSC will be a combined response of the two lithiated materials. As such, by looking at the 3.4 V DSC curve it can be seen that silicon has two strong exothermic peaks at ~ 200 °C and 260 °C, while the 4.1 V curve shows additional exothermic peaks at both 150 °C and 300 °C corresponding to lithiated graphite. So far this data agrees with previous results comparing graphite to silicon electrodes. References Klett M., Gilbert J. A., Trask S. E., Polzin B. J., Jansen A. N., Dees D. W., Abraham D. P., J. Electrochem. Soc., 163, A875 (2016). Acknowledgment: Sandia Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation for the U. S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL 85000. Figure 1

4-(Trimethylsiloxy)-3-Pentene-2-One As a Novel Film-Forming Agent for High-Voltage LiNi0.5Mn1.5O4 Positive Electrode

As an effort to improve energy density of lithium-ion batteries (LIBs), the nickel-doped manganese spinel (LiNi0.5Mn1.5O4, LNMO) has been projected as a high-voltage positive electrode. The high working voltage (> 4.6 V vs. Li/Li+) and outstanding structural stability are advantageous with respect to energy density and cycle life. This advantage is, however, offset by the oxidative instability of electrolytes (> 4.3 V), which is even more serious at elevated temperatures.1 The commonly used electrolytes decompose and surface films deposit on the positive electrodes to lead to capacity fading.2, 3 In order to prevent electrolyte oxidation and film growth, the LNMO electrode should be passivated. To this end, the film-forming agents are added into electrolytes, which electrochemically decompose prior to the carbonate-based electrolytes to form passivation layer on the positive electrode. In this study, 4-(trimethylsiloxy)-3-pentene-2-one (TMSPO) was tested as a film-forming agent for LNMO electrode. TMSPO is oxidatively decomposed at 3.6 V (vs. Li/Li+) prior to the oxidation reaction of the carbonate-based electrolyte (1.3 M LiPF6 in EC : EMC : DEC = 3 : 2 : 5 (v/v/v)). The surface film derived from TMSPO shows good passivation ability to improve both Coulombic efficiency and cycle life of Li/LNMO cell (Fig. 1b). Electrolyte depletion and film growth are not serious in TMSPO-added cell. In contrast, the film derived from the carbonate-based electrolyte is poorly passivating. Cell polarization resulting from electrolyte decomposition/film deposition continues to cause capacity fading. References 1 .J. B. Goodenough and Y. Kim, J. Power Sources, 196, 6688-6694 (2011). 2. T. Yoon, S. Park, J. Mun, J. H. Ryu, W. Choi, Y.-S. Kang, J.-H. Park, and S. M. Oh, J. Power Sources, 215, 312-316 (2012). 3. D. Aurbach, B. Markovsky, Y. Talyossef, G. Salitra, H.-J. Kim, and S. Choi, J. Power Sources, 162, 780-789 (2006). Figure 1. (a); Differential capacity plot in the 1stcharging at 25℃, and (b) Coulombic efficiency and cycle performance at 60℃ Figure 1

One-Step Fabrication of Sulfur Composite Electrode for All-Solid-State Lithium-Sulfur Battery Using High-Temperature Mechanical Milling Method

Since higher energy and power density than those of lithium ion batteries are required for next generation battery system, lithium-sulfur battery attracts attention because of its large theoretical capacity of sulfur: 1672 mAh g–1. All-solid-state battery system incorporating solid electrolyte can solve serious issue of dissolution of lithium polysulfide during battery reaction and contribute higher power and energy density [1]. However, ionic/electronic-insulating properties of sulfur prevents practical use of sulfur as electrode. Therefore, composite electrodes incorporating sulfur, conductive carbons and solid electrolytes are fabricated for use in solid-state battery system. In this study, sulfur, acetylene black and Li2S-GeS2-P2S5based solid electrolyte were mixed to obtain the composite electrode using a planetary ball milling apparatus, which has temperature control system. Structures and electrochemical properties of the composites and their milling-temperature dependences were investigated. Solid electrolyte of Li4–x Ge1–x P x S4 (x = 0.75) was prepared by a solid-state reaction method [2]. Ionic conductivity of the solid electrolyte was evaluated by ac-impedance method at room temperature. Sulfur, acetylene black and solid electrolyte were milled with a weight ratio of 25:25:50 (wt.%). Various mixing time (10–600 min) and temperature during mixing (298–443 K) were examined; their structure and electrochemical properties in all-solid-state battery were evaluated using scanning electron microscopy (SEM), XRD measurement, Raman spectroscopy and galvanostatic charge-discharge test. All-solid-state batteries were constructed in an Ar-filled glove box for charge-discharge measurements [3]. Electrochemical properties of the cells were evaluated by galvanostatic charge-discharge measurements using multi-channel galvanostat. A constant current of 83.75 mA g–1(1/20 C) was applied for charging and discharging at room temperature. Since the composite electrode prepared by 300 min-milling at room temperature showed highest initial discharge capacity about 1200 mAh g-1, milling time was determined at 300 min for high temperature milling process. Composite electrodes were prepared by high temperature milling at 403, 423 and 443 K; in this temperature region, the sulfur exists as liquid phase. Increase in milling temperature contributed to larger capacity and better capacity retention during charge-discharge reactions for 20 cycles. Raman spectroscopy indicated that novel structure unit including Ge-S-Ge bonding was generated in the composite via milling process. The novel unit could be due to the reaction between sulfur and solid electrolyte. Differential capacity plots of the charge-discharge curves and ex situRaman spectroscopy revealed that the novel structure units might contribute to the charge-discharge reaction and phase transition reaction during charge-discharge process occurred reversibly for the composite electrode with high temperature milling. On the other hand, the composited prepared at room temperature showed capacity fading during cycling due to irreversible phase transition of the electrode. Liquid phase sulfur during milling process could contribute to construct the electronic and ionic conduction pathways in the composite matrix because the liquid phase is suitable for nano/atomic scale distribution and better contact to the each component. One-step high-temperature milling process can be a promising candidate for sulfur composite electrode fabrication. Acknowledgements This work was supported by a Grant-in-Aid from the Advanced Low Carbon Technology Research and Development Program, Specially Promoted Research for Innovative Next Generation Batteries (ALCA- SPRING) of the Japan Science and Technology Agency (JST).

Evaluation of the Electrochemical Properties of Crystalline Copper Antimonide Thin Film Anodes for Lithium Ion Batteries Produced by Single Step Electrodeposition

Electrodeposited crystalline Cu2Sb thin films are studied to evaluate the use of these electrodes as model systems for studying Cu2Sb as a lithium ion battery anode material. The films have been characterized with an emphasis on determining the film quality and relating the structure, composition, and morphology to the resulting electrochemical and morphological transformations that occur during electrochemical lithiation and delithiation. It is shown that electrodeposition can produce high quality films that are devoid of major defects and can be used to provide mechanistic insight on the electrochemistry of reversible lithium alloying. The CuxSb films show that the fundamental reaction mechanism remains largely unchanged for copper concentrations of 1>x>3. For the first time we show that the copper concentration greatly affects critical criteria for anode materials such as the initial coulombic efficiency and reversible capacity of the electrode material. Voltage limit experiments show that an overpotential is required to remove trapped lithium states. Additional ex-situ experiments reveal that internal strain created during the lithiation process is relieved by buckling, greatly altering the film surface area and geometry, and resulting in the formation of cracks upon delithiation. This process is only semi-reversible, and strained areas remain visible even when discharged outside the voltage window of Cu2Sb determined by differential capacity plots. The results presented here indicate that these electroplated thin films are useful as analytical tools for showing pathways to improving the performance and fundamental understanding of alloy based lithium-ion battery anodes.

The Effect of Binders on the Performance of Silicon Oxide

The higher specific capacity and richness in natural resources makes SiOx-based become a research focus by international scholar in recent years. A lot volume changes of material in the process of cycling which affects the batteries’ cycling performance, thereby limiting its development and usage. While choosing suitable binder is critical to effectively enhance the performance of the silicon oxide (SiOx) that has high specific capacity and easy pulverization. Researched the lithium insertion/extraction properties of SiOx composite electrode which prepared with polyvinylidene fluoride (PVDF), LA132 (which major copolymerization chain is polyacrylonitrile-polyacrylic acid (PAN-PAA)), polyacrylic acid (PAA). Electrochemical cycling tests with a current density of 160mA/g shows that SiOx electrode with conventional binder PVDF results in rapid capacity loss, while aqueous binder LA132 and PAA could dramatically improve cycle performance of SiOx. SiOx with PAA electrode exhibits reversible capacity still up to 1090mAh/g after 50 cycles. The analysis and characterization methods of SEM, EIS, XRD and differential capacity plots, it is prove that amorphous or little crystalline binder have physical or chemical reaction with –OH of SiOx and formed class network constitute. The expansion pulverization of SiOx power limited in original domain and maintained electronic and ionic conductivity effectively, improved cycle performance of materials. Acknowledgements The project was supported by the Shanghai Science and Technology Development Fund (15DZ2282000).

Mn(II) Scavenging Electrolyte Additive and Functional Binder

Introduction Mn(II) dissolution from lithium manganese oxide (LiMn2O4) positive electrode and Mn plating on graphite negative electrode are the well-known failure mode in lithium-ion chemistry [1]. The Mn plating degrades the electrochemical performances of graphite electrodes in two ways. One is the self-discharge of graphite, which is accompanied by Mn plating. The other is the degradation of solid electrolyte interphase (SEI), which leads to forthcoming electrolyte decomposition and film deposition. As a result, cell polarization becomes severe due to an increment in film resistance, which eventually leads to a cell failure [2]. To overcome the issues raised by Mn plating on graphite electrodes, several countermeasures have been made. For examples, the scavengers for hydrofluoric acid (HF), which attacks the positive electrodes to leach out Mn ions, have been used as the electrolyte additive. Also Mn(II) scavengers have been developed [3,4]. In this study, 1,4,8,11-tetraazacyclotetradenate (cyclam) and 1,4,7,10-tetraazacyclododecane (cyclen) is tested as a Mn(II) scavenger. Those tetradentate azamacrocyclic compounds are applied as an electrolyte additve or attached on the chains of polyvinylalcohol (PVA) binder. The Mn plating on graphite electrodes seems to be suppressed due to a strong compex formation with Mn(II) ions. Namely, the Mn plating is thermodynamically unfavored due to the complex formation since the reduction potential of Mn(II) moves to the more negative direction than that for the solvent-solvated Mn(II) ions. Moreover, the Mn plating is kinetically hindered due to higher overpotential that is caused by a strong chelate complex formation. Experimental A beaker-type three-electrode cells were fabricated with a graphite electrode (DAG 87 : Super P : PVdF binder = 85:5:10 in wt. ratio), a Li counter electrode and a Li reference electrode. 10 mM of Mn(ClO4)2 was dissolved into an electrolyte solution (1.0 M LiPF6 in EC/DEC, 1/1 = v/v) to simulate the Mn(II)-dissolved electrolyte. To examine the additive effect, 1.0 wt. % of cyclam was added into the Mn(II)-containing electrolyte solution. The cyclen-attached PVA was synthesized by mixing 8 wt. % PVA/water solution and 50 mg of cyclen that carries a carboxylic acid functional group. After casting the mixed solution on Cu foil, esterification was performed at 150 0C for 12 h under vaccum. To examine the Mn(II) scavenging action, the cyclen-attached PVA/Cu foil was immersed in the Mn(II)-containing electrolyte solution for 48 h. Finally, the Mn(II) ions entrapped in the cyclen-attached PVA were leached out by using the mixture of nitric, hydrofluoric and hydrochloric acid. Mn(II) concentration was analyzed by using inductively-coupled plasma atomic emission spectroscopy (ICP-AES). Results and discussion The differential capacity (dQ/dV) plots obtained in the first lithiation period show that the reduction current responsible for Mn plating, which appears in the wide potential range (0.0 ~ 0.8 V vs. Li/Li+) in the Mn(II)-containing electrolyte, disappears when cyclam is added (Fig. 1a). Clearly, cyclam plays the Mn(II) scavenging role. The Mn(II) concentration entrapped in the cyclen-attached PVA is compared with that entrapped in the pure PVA. The comparison shown Fig. 1b ascertains the strong compex formation betweeen Mn(II) ions and cyclen being attached in PVA. The cyclen-attached PVA can be used as a binder for graphite electrode fabrication, which has Mn(II) scavanging function.

Importance of Reduction and Oxidation Stability of High Voltage Electrolytes and Additives

The electrolyte is a critical component for rechargeable Li-ion batteries, especially batteries containing high voltage cathodes. A series of electrolyte salts, solvents and additives was investigated via cyclic voltammetry (CV) on glassy carbon (GC) electrodes. Quantum chemistry (QC) calculations were used for prediction of oxidation and reduction stability of electrolyte components such as ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), tris(trimethylsilyl) phosphate (TMSP), 1,3-propane sultone (PS), tris(hexafluoroisopropyl) phosphate (HFiPP) and lithium salts such as LiPF6, LiBF4, lithium difluoro(oxalato)borate (LiDFOB), lithium 4,5-dicyano-2-trifluoromethyl-imidazolide (LiTDI), and lithium bis(trifluoromethanesulfonimide) (LiTFSI). QC calculations predicted that defluorination of LiPF6 and LiTFSI aggregates coupled with electron transfer significantly increased their reduction potential, while H-transfer upon oxidation lowered oxidation potential for many solvents. The composition of the Li+ cation solvation shell was estimated from the binding energies for the Li+–solvent complexes using cluster-continuum calculations and was used to provide insight into the experimental data on electrolyte reduction. Full coin cell data was acquired using LiNi0.5Mn1.5O4 (LNMO) cathodes with graphite anodes at 25°C and 55°C. Differential capacity plots (dQ/dE vs. E) and electrochemical impedance spectroscopy (EIS) results. The electrolyte with the most desirable performance was 1M LiPF6 in 3:7 EC:EMC (wt%) with 1wt% TMSP. Oxidative CV experiments show that the TMSP containing electrolyte has a slightly lower oxidation stability compared to the baseline, which is consistent with the order of oxidation stability of electrolyte components from QC calculations. The EIS measurements showed that the TMSP containing electrolyte had the lowest impedance after cycling and the dQ/dE plots show that the redox reactions retained their peak shape and area more so than an electrolyte without TMSP, indicating a greater capacity retention. Density functional theory calculations of TMSP oxidation on the LNMO surface were performed in order to provide insight into the additive role in improving cell performance.

Electrochemical lithium quasi-intercalation with arsenic

To investigate the electrochemical reaction mechanism of As, which shows poor electrochemical reversibility with Li, an As/C nanocomposite was prepared using a straightforward high-energy mechanical milling technique. The electrochemical reaction mechanism of the As/C nanocomposite electrode with Li was elucidated by ex situ XRD and HRTEM analyses in combination with differential capacity plot analysis. Electrochemical tests showed that the As/C nanocomposite exhibited good reversibility between the LiAs (0.85 V) and As (2 V) phases showing quasi-intercalation reaction.

Exploring Cycling Behavior of Lifsi-Bearing Electrolytes in Li1.03(Ni0.5Mn0.3Co0.2)0.97O2//Graphite cells

Introduction There is increasing interest in finding alternatives to the LiPF6 electrolyte salt currently used in lithium-ion cells. Among the various candidates, LiFSI (Lithium bis(fluorosulfonyl)imide) has attracted much recent attention because it is reported to have higher ionic conductivity, better high temperature stability, and improved stability towards hydrolysis than LiPF6.1-4 In addition LiFSI is reported to be compatible with graphite and silicon based negative electrodes creating stable solid electrode interphase layers that enhance cell life. In this work we compare the cycling behavior of cells with Li1.03(Ni0.5Mn0.3Co0.2)0.97O2–based and graphite-based electrodes, and full cells with these electrodes, in LiFSI- and LiPF6-bearing electrolytes. Results from such studies are expected to determine the suitability and limits of LiFSI-bearing electrolytes in lithium-ion cells for transportation applications. Materials and Cells All electrochemical tests were conducted in 2032-type coin cells (1.6 cm2 area electrodes). Al clad parts were used for the positive electrode half cells and for full cell tests; non Al-clad parts were used for the negative electrode half cell tests. Positive and negative electrodes were obtained from the Cell Analysis, Modeling and Prototyping (CAMP) Facility at Argonne. The positive electrodes contained 90 wt% Li1.03(Ni0.5Mn0.3Co0.2)0.97O2 (Toda NCM523), 5 wt% C45 carbon (Timcal), and 5 wt% PVdF (Solvay 5130). The negative electrodes contained ~92 wt% graphite (Superior Graphite SLC1520P), 6 wt% PVdF (Kureha KF 9300) and 2 wt% SuperP (Timcal). The LiFSI salt was purchased from Sarchem Laboratories, EC and EMC solvents from BASF, and FEC from Solvay. Various Celgard separators (2325, 2400, 3501) were examined to determine their compatibility with LiFSI. Results Fig. 1 shows that the first two cycles of full cells with EC:EMC (3:7, w/w) + 1.2M LiPF6 (aka LiPF6) or 1.2M LiFSI (aka LiFSI) electrolytes are very similar. This similarity is also seen in the differential capacity plots (Fig. 2). However, Fig. 2 inset, which is an expanded view of the 1.5-3.5 V first charge shows differences between the SEI formation characteristics of LiPF6and LiFSI electrolytes; i.e., the LiFSI salt alters interaction of the solvent with the graphite electrode. Other observations from our experiments include the following: The Celgard separator type did not affect the data; similar data were obtained for all cells.Initial impedance behavior is similar for cells with the LiPF6 and LiFSI electrolytes.Significant self-discharge is observed for LiFSI-bearing full cells cycled at >4.2V; the upper cutoff voltage (UCV) for these cells should be ≤4.1 V. In contrast, LiPF6-bearing full cells can be cycled at voltages ≤4.5V. More information on cell performance and performance degradation, including data from self-discharge, capacity retention, and impedance measurements at 30° and 55°C will be discussed during our presentation. Strategies to overcome the current limitations of LiFSI-bearing electrolytes will also be highlighted. Acknowledgements We acknowledge support from the U.S. Department of Energy’s Office of Vehicle Technologies. We are grateful to S. Trask, B. Polzin, and A. Jansen, from the CAMP Facility (Argonne) for the electrodes, and to M. Kras from the Materials Engineering Research Facility (MERF) for assembling the coin cells, used in this work. These facilities are fully supported within the core funding of the Applied Battery Research (ABR) for Transportation Program. References (1) http://www.boulderionics.com(2) Han et al.; J. Power Sources, 2011, 196, 3623. (3) Phillipe et al.; J. Am. Chem. Soc, 2013, 135, 9829. (4) Shkrob et al.; J.Phys. Chem. C, 2014, 118, 19661. Figure 1

Role of 1, 3-Propane Sultone and Vinylene Carbonate in Solid Electrolyte Interface (SEI) Formation and Gas Generation

The cycling performance, ex-situ surface analysis, and in-situ gas analysis of lithium ion batteries containing the widely used electrolyte additives VC and PS has been investigated. All of the electrolytes have good cycling performance at 25°C. However, the electrolytes containing additives have better discharge capacity retention and coulombic efficiency upon cycling at 55°C. Analysis of the differential capacity plots suggest that both VC and PS are reduced prior to the carbonates and alter the structure of the anode SEI. Ex-situ surface analysis confirms structural differences of the anode SEI. Electrodes cycled in the presence of PS contain lithium alkyl sulphonate (RSO3Li) on the surface of the anodes. The presence of the lithium alkyl sulfonate leads to higher lithium ion conductivity of the anode SEI. Electrodes cycled with added VC contain poly(VC) in the anode SEI. The presence of the poly(VC) leads to improved stability of the SEI. Anodes cycled with both VC and PS contain lithium alkyl sulphonate and poly(VC) which leads to an SEI with both high conductivity and high thermal stability. In-situ gas analysis shows that both additives, VC and PS, are able to reduce the ethylene evolution during SEI formation by nearly 70 %. The formation of poly(VC) for electrodes cycled in VC is accompanied by CO2 evolution. The presence of the lithium sulfonate for PS leads to a lower onset potential of ethylene evolution. For VC, the only gaseous byproduct during reduction is CO2, while PS shows no gaseous reduction products. The combination of both additives leads to a superposition of the described phenomena. The reduction of gas evolution during SEI formation would allow a faster and easier industrial formation procedure for Li-ion batteries.

Understanding the Effect of Lithium Bis(oxalato) Borate (LiBOB) on the Structural and Electrochemical Aging of Li and Mn Rich High Capacity Li1.2Ni0.16Mn0.56Co0.08O2 Cathodes

Li1.2Mn0.56Ni0.16Co0.08O2 synthesized by self-combustion reaction (SCR) was studied as a cathode material for advanced Li ion batteries in standard electrolyte solutions with and without Lithium Bis(oxalate) borate (LiBOB) at 30 and 45°C. When these cathodes were tested with LiBOB as an additive in solution, a capacity retention of 98% could be demonstrated during 50 cycles due to a unique stabilizing effect of this additive against 86% in standard electrolyte. Its presence in solutions suppresses the irreversible charge required to activate this cathode material. When cycled at 45°C, the capacity retention of Li1.2Mn0.56Ni0.16Co0.08O2 cathodes in LiBOB containing solutions may reach 97% during 50 cycles as compared to 78% in standard electrolyte solutions. The effect of LiBOB was examined by electrochemical (differential capacity plot and impedance) and structural analysis (Raman and TEM study). The presence of LiBOB in solutions leads to relatively low impedance of these cathodes. HRTEM and Raman spectral studies show that presence of LiBOB in solutions has bulk effect on this cathode material. While the initially present Li2MnO3 phase completely disappears upon cycling in standard solutions when the upper potential limit is above 4.5V, it does not fully disappear in solutions containing LiBOB.

A Fundamental Understanding of Li Insertion/Extraction Behaviors in SnO and SnO2

The electrochemical reaction mechanisms of the tin oxides, SnO and SnO2, were investigated to obtain a fundamental understanding of their Li insertion/extraction behaviors using ex situ X-ray diffraction, X-ray absorption near edge structure, X-ray absorption fine structure, and high-resolution transmission electron microscopy analyses along with differential capacity plots. The results of the analyses thoroughly demonstrated partial recombination reactions of SnO and SnO2.

Effects of structural patterns and degree of crystallinity on the performance of nanostructured ZnO as anode material for lithium-ion batteries

The effects of structural patterns and degree of crystallinity on the electrochemical performance of ZnO were systematically studied using a controllable synthesis. The microspheres assembled with distorted nanosheets, hexagonal nanorods and radial assembly of nanorods of ZnO were successfully prepared by the hydrothermal reaction of zinc nitrate, hexamethylenetetramine and different amount of trisodium citrate. ZnO microspheres were calcinated at different temperatures (300, 600 and 900°C) to increase their degree of crystallization. Constant current charge and discharge measurements show that the capacity retention of the microspheres and radial assembled nanorods are higher than that of hexagonal nanorods. This may be due to their inner spacing of specific structure patterns that can accommodate and restrain the volume changes during cycling. Additionally, the capacity of ZnO microspheres can be improved by short-time calcinations at 600 or 900°C for their crystallization. The studies of differential capacity versus potential plots indicate that the enhanced degree of crystallization facilitates the alloying and dealloying of the reduction products of ZnO. Therefore, both large specific capacity and good capacity retention can be expected with highly crystallized specific nanostructures of ZnO with the sufficient inner spacing. The ZnO microspheres calcinated at 600°C show the best performance with a specific capacity of 1328.2mAhg−1 for the first cycle and 662.8mAhg−1 for the 50th cycle at 0.1C with an operating potential of 0.05–3.00V.

Effect of electrolyte on cycle performances of the electrodeposited Sn–O–C composite anode of lithium secondary batteries

The electrodeposited Sn–O–C composite anode cycling with LiClO4 delivered stable cycle performances showing discharge capacity of 473 mA h g of Sn−1 with 95% of coulombic efficiency at 100th cycle. However, the anode showed poor cycle performances with LiPF6 delivering discharge capacity of 69 mA h g of Sn−1 at 100th cycle with 70% of coulombic efficiency. Electrochemical investigation performed by cyclic voltammetry and differential capacity plots revealed that the Sn–O–C composite cycling with LiPF6 suffered from retarded phase transition reaction between Li and Sn during charge/discharge process. X-ray photoelectron spectroscopy declared the existence of fluorinated-Sn and LiF. Moreover, energy dispersive X-ray spectroscopy found increase in their amount with repeated cycles. The morphologies of the Sn–O–C composite cycled with LiPF6 showed aggregated particles containing the chemical state of fluorinated-Sn and LiF on its surface. Furthermore, the significant pulverization and aggregation of the active material were observed from the Sn–O–C composite cycled by LiPF6 rather than that of LiClO4, which was probably promoted by the generated HF strongly corroding metallic component.

Study of the Consumption of Vinylene Carbonate in LiNi0.3Mn0.3Co0.3O2/Graphite Cells By Gas Chromatography Coupled with Mass Spectrometry (GC-MS)

Introduction The fate of VC during the first charge of LiNi0.33Mn0.33Co0.33O2/graphite cells was investigated using GC-MS measurements made on the electrolyte following a procedure described by Petibon et al.1. Experiments were also made to determine at which electrode VC reacts subsequent to the formation cycle. Experimental In order to measure the composition of the electrolyte at selected states of charge, the cells were first discharged to an open circuit potential near 0 V, and opened outside the glove box. The jelly roll was then put in a vial containing 10 mL of dichloromethane and shaken for 15 min. The supernatant was then filtered using a syringe filter. A few drops of the filtrate were added to a vial containing 10.0 mL of dichloromethane and 0.5 mL of distilled water, shaken for 5 min and set aside for another 5 min. The organic layer was then injected in the GC-MS for analysis. This procedure is described in detail in reference [1]. Results and discussion Figure 1 shows the amount of VC left in cells initially containing 2% VC charged to different voltage cut-off during the first charge (formation cycle), alongside the potential versus capacity curve. Figure 1 shows that while an important portion of the initial VC present in the cell reacts early on during the first charge (before a cell potential of 3.0 V), there is still a substantial amount of VC that reacts later on. This means that looking at the reduction peaks in the differential capacity versus voltage plots of the first few mAh of the first charge does not give a complete picture about the reactivity of additives.Figure 2 shows the amount of VC consumed in cells initially containing 2.2% VC or 4.6% VC and held at either 3.9 V or 4.2 V for 200 h at 40°C. At cell potentials of 3.9 V and 4.2 V, the graphite electrode is at the same potential (~80 mV vs Li/Li+). This means that any difference in the amount of VC consumed between cells held at 3.9 V or 4.2 V is due to the positive electrode. Figure 2 shows that there is no real statistical difference between the amount of VC consumed whether cells are held at 3.9 V or 4.2 V. This indicates that there is no detectable amount of VC that is consumed (oxidized) at the positive electrode and that the negative electrode is responsible for the consumption of VC. This does not mean that VC cannot affect the positive electrode, however. Conclusion The fate of VC during cycling has been measured by GC-MS. The consumption of VC at different states of charge during the formation cycle showed that while a great amount reacts at the negative electrode early on (cell potential smaller than 3.0 V), there is still a substantial portion that is consumed afterward. In addition, measurements of the amount of VC consumed in cells held at different potentials suggested that there was no measurable amount of VC consumed at the positive electrode. Reference 1. R. Petibon, et al., “Study of major electrolyte components in Li ion cells using liquid-liquid extraction and gas chromatography coupled with mass spectrometry”, submitted to J. Electrochem. Soc., Feb. 2014 *

Germanium Nanowire Based Lithium-Ion Anode Exhibiting a Stable and High Capacity Over 1000 Cycles

Ge nanowire (NW) based materials have emerged as viable candidates for next generation rechargeable lithium-ion battery anodes with energy and power densities that are multiples of current graphitic based electrodes.1-3 The key advance is the capability of NWs to overcome the well-known pulverization problem that is detrimental to the cycle life and hence viability of their bulk counterparts. NWs also provide good electrical conductivity along their length, have a high interfacial area in contact with the electrolyte, have an optimal short diffusion distance for Li-ion transport and can be grown directly from current collectors, eliminating the need for binders and conductive additives 4,5 Here we demonstrate stable cycling over 1100 cycles of Sn seeded Ge NWs grown directly from a current collector via a solvent vapour growth system. We show by ex-situ high-resolution transmission electron microscopy and high-resolution scanning electron microscopy studies that the NW array transforms into a robust, porous network structure within the first 100 cycles.6 Once this network is formed it is highly stable, maintaining a capacity of ̴ 900 mAh/g over the following 1000 cycles. The electrolyte additive, vinylene carbonate (VC), was found to play an important role, facilitating the formation of this stable network morphology. The electrode material described here has several advantages as it is formed in a low energy, wet-chemical process with Ge NWs nucleating and growing from an evaporated Sn layer on stainless steel. Sn also has a high maximum theoretical capacity and we show both physically (HRTEM) and electrochemically (differential capacity plots) that the Sn seeds at the end of the NWs reversibly alloy with lithium and contribute to the electrodes overall specific capacity. The NW electrode architecture performed exceptionally well in rate capability tests achieving a discharge capacity of 435 mAh/g after 80 cycles at a discharge rate of 100C. Considering the low cost and low energy required, especially when compared with CVD systems, we believe our synthetic protocol to be an attractive and scalable synthesis approach for high-performance group IV nanowire based electrodes.Chan, C. K.; Zhang, X. F.; Cui, Y. Nano Lett. 2008, 8, 307-309.Chockla, A. M.; Klavetter, K.; Mullins, C. B.; Korgel, B. A. ACS Appl. Mater. & Interfaces 2012, 4, 4658-4664.Yuan, F.-W.; Yang, H.-J.; Tuan, H.-Y. ACS Nano 2012 , 6, 9932-9942.Choi, N. S.; Yao, Y.; Cui, Y.; Cho, J. J. Mater. Chem. 2011, 21, 9825-9840.Wu, H.; Cui, Y. Nano Today 2012, 7, 414-429.Kennedy, T.; Mullane, E.; Geaney, H.; Osiak, M.; O’Dwyer, C.; Ryan, K.M. Nano Lett. 2013, DOI:10.1021/nl403979s

Fe doped Li1.2Mn0.6-x/2Ni0.2-x/2FexO2 (x≤0.1) as cathode materials for lithium-ion batteries

A series of Li1.2Mn0.6-x/2Ni0.2-x/2FexO2 (x=0, 0.03, 0.06, 0.10) cathode materials has been prepared by a modified Pechini process. The structure and morphology of the obtained materials have been examined by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. The electrochemical properties of Li1.2Mn0.6-x/2Ni0.2-x/2FexO2 have been characterized systematically and Li1.2Mn0.585Ni0.185Fe0.03O2 exhibits the best cyclic stability and high-rate capability. The Li1.2Mn0.585Ni0.185Fe0.03O2 electrode delivers a large reversible discharge capacity of 261.6 mAh g−1 at 0.1C-rate with a high capacity retention rate of 90.9% after 80 cycles. Meanwhile it displays obviously improved rate capability with the capacity of 187.3 mAh g−1 at the 1C-rate and stable cycling performance of 165 mAh g−1 after 150 cycles. The effects of a small amount of Fe doping are explored through ex-situ XRD, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscope (HRTEM), differential capacity vs. voltage (dQ/dV) plots and electrochemical impedance spectroscopy (EIS). The results show stable layered structure and well-crystallized particle surface for Li1.2Mn0.585Ni0.185Fe0.03O2 electrode in contrast with spinel nanodonmains distribution and amorphous surface region for Li1.2Mn0.6Ni0.2O2 electrode upon cycling, which account for the outstanding electrochemical performance of Fe doped Li1.2Mn0.6Ni0.2O2 cathode material.

Electrochemical performance of tin-based nano-composite electrodes using a vinylene carbonate-containing electrolyte for Li-ion cells

Tin represents a promising material to increase the specific capacity compared to the state of the art graphite anodes in lithium ion cells. The aim of this work is to explain the electrochemical behavior of tin-based hydrocarbon nanoparticulate composite electrodes, synthesized by means of a microwave plasma technique without any binder or slurry process. A comprehensive electrochemical characterization shows that adding vinylene carbonate (VC) to the electrolyte improves the electrochemical performance. Electrochemical impedance spectroscopy (EIS) and post mortem investigations of the cycled electrode material by X-ray photoelectron spectroscopy (XPS) reveal the formation of a polymeric SEI during the first cycles, being responsible for the improvement. The differential capacity plots of the discharging process show that the lithium richest phase (Li22Sn5) is formed during electrochemical loading. A comprehensive characterization with specially designed electrochemical tests finally demonstrates the decrease of capacity with increasing temperature. This is due to intensified mechanical stresses and a fresh SEI formation. Due to destruction of the electrode material degradation is also observed with increasing current density. The SEI layer on the surface of the electrodes is confirmed by scanning electron microscopy (SEM) investigations and energy dispersive X-ray spectroscopy (EDS) elemental mapping.

Characterization of Aluminum Doped Lithium-Manganese Rich Composites for Higher Rate Lithium-Ion Cathodes

The effect of synthesis method and aluminum doping on layered lithium-manganese rich, mixed metal oxides is presented. Co-precipitation and sol-gel synthesized lithium-manganese rich composite materials revealed differences in capacity and cycle life, which appears from X-ray photoelectron spectra to be strongly related to the particles’ surface reactivity. Small amounts of aluminum doping to the sol-gel material were shown to improve the rate capability and cyclability, in addition to decreasing voltage fade, as shown by differential capacity plots. The electrochemistry of an aluminum doped material was revealed to be highly dependent on the degree of aluminum doping – with the behavior of 1% doped material giving a maximum capacity of 201 mAh g−1 at 150 mAg−1 and a capacity retention of 88% after 200 cycles.

Effect of Fe substitution on electrochemical properties of Sn3.95Fe0.05P3 alloy anode for lithium ion batteries

Sn3.95Fe0.05P3 alloy was synthesized via a solvothermal method, using tin metal, iron metal and amorphous red phosphorous. The XRD and TEM results showed that Fe ion was successfully substituted on original the Sn4P3 layered structure without any structure changes. The Sn3.95Fe0.05P3 alloy anode showed a higher initial charge capacity and coloumbic efficiency of 1304mAhg−1 and 73% compared with the Sn4P3 alloy anode, respectively. Additionally, a relatively large capacity of about 420mAhg−1 after 100th cycles was achieved in the Sn3.95Fe0.05P3 anode, whereas the capacity of the Sn4P3 anode remained at only about 100mAhg−1 after 100cycles. Fe atoms as an inactive matrix could be dispersed between the tin atoms, resulting in the suppression of tin agglomeration in Sn3.95Fe0.05P3 during cycling. It is confirmed from the voltage profile and differential capacity plots that the Fe ion in the Sn3.95Fe0.05P3 structure could stabilize the structure and improve the electrochemical properties during cycling.