Electrochemical lithium insertion into amorphous MoO3·2H2O

Following the route of synthesis of β-MoO₃ through soft chemistry methods a new amorphous material with composition MoO₃·2H₂O has been detected. The hydrated molybdenum oxide showed the capacity for electrochemical lithium insertion. The maximum amount of lithium incorporated in this material (∼3.3 Li/Mo) leads to a specific capacity of 490 Ah kg⁻¹. The charge–discharge curve showed a good reversibility in the potential range from 3.2 to 1.1 V versus Li⁺/Li⁰ where the cell voltage decreased monotonously as a function of the degree of lithium inserted. The electrochemical features of amorphous MoO₃·2H₂O suggest that it can be considered as a possible cathode candidate in rechargeable lithium batteries.     

Electrochemistry and safety of Li4Ti5O12 and graphite anodes paired with LiMn2O4 for hybrid electric vehicle Li-ion battery applications

A promising anode material for hybrid electric vehicles (HEVs) is Li₄Ti₅O₁₂ (LTO). LTO intercalates lithium at a voltage of ∼1.5 V relative to lithium metal, and thus this material has a lower energy compared to a graphite anode for a given cathode material. However, LTO has promising safety and cycle life characteristics relative to graphite anodes. Herein, we describe electrochemical and safety characterizations of LTO and graphite anodes paired with LiMn₂O₄ cathodes in pouch cells. The LTO anode outperformed graphite with regards to capacity retention on extended cycling, pulsing impedance, and calendar life and was found to be more stable to thermal abuse from analysis of gases generated at elevated temperatures and calorimetric data. The safety, calendar life, and pulsing performance of LTO make it an attractive alternative to graphite for high power automotive applications, in particular when paired with LiMn₂O₄ cathode materials.     

Development of long life lithium ion battery for power storage

With the aim of developing lithium ion batteries with a long life and high efficiency for power storage, we experimentally evaluated combinations of cathode and anode active materials, in which batteries are able to obtain over 4000 cycles or 10 years of life. An acceleration method was evaluated using coin cells. We found that changing the current density was effective for evaluating battery life, since the logarithm of the cycle life showed a linear relationship to current density. Based on the current density increasing method, various combinations of cathode and anode active materials were tested. The cell system of LiCoO₂/Li_4/3Ti_5/3O₄ clearly showed a long life of about 4000 cycles. The energy density of the cell using the Li_4/3Ti_5/3O₄ anode is obviously smaller than that using a graphite anode, the cell with Li_4/3Ti_5/3O₄ anode was thought to have some merit especially in the large-scale-layer-built type battery by the applicability of the Al anode collector and a light weight battery case.     

In-situ synthesis of two-dimensional sheet-like MoO2/NPC@rGO as advanced anode for alkali metal ion batteries

MoO₂ anode displays excellent potential in the alkali ion batteries owing to its large capacity, high conductivity and stability. However, exploiting the stable and high performance MoO₂ anode endowed with triple roles for the storage of lithium/sodium/potassium ions is still a challenge. Herein, a two-dimensional sheet-like MoO₂/NPC@rGO composites were in-situ synthesized and utilized as anode materials for alkali metal ion batteries. Applied as an anode in lithium ion batteries (LIBs), superior cycling capability and rate performance were obtained, which kept a large reversible capacity of 1233.1 mAh/g in the 200th cycle at 100 mA/g. Impressively, it displayed superior long cycling performance over 1000 cycles with a 249.5 mAh/g capacity at a high current density of 10 A/g. Simultaneously, MoO₂/NPC@rGO displayed enhanced electrochemical performance both in sodium and potassium ion batteries (NIBs/KIBs). Furthermore, the ex-situ X-ray photoelectron spectroscopy results verified the reversible reaction during Li⁺ insertion-extraction process. The improved energy storage properties were attributed to the typical two dimensional structure and synergistic effects between various constituents, which suppressed the volume change, created more active sites, increased the conductivity and facilitated reaction kinetics. More significantly, our design provides a simple and green route to synthesize transition metal oxide anode and promote their applications in energy storage devices.     

Surface structural disordering in graphite upon lithium intercalation/deintercalation

We report on the origin of the surface structural disordering in graphite anodes induced by lithium intercalation and deintercalation processes. Average Raman spectra of graphitic anodes reveal that cycling at potentials that correspond to low lithium concentrations in Li_xC (0 ≤ x < 0.16) is responsible for most of the structural damage observed at the graphite surface. The extent of surface structural disorder in graphite is significantly reduced for the anodes that were cycled at potentials where stage-1 and stage-2 compounds (x > 0.33) are present. Electrochemical impedance spectra show larger interfacial impedance for the electrodes that were fully delithiated during cycling as compared to electrodes that were cycled at lower potentials (U < 0.15 V vs. Li/Li⁺). Steep Li⁺ surface-bulk concentration gradients at the surface of graphite during early stages of intercalation processes, and the inherent increase of the Li_xC d-spacing tend to induce local stresses at the edges of graphene layers, and lead to the breakage of C-C bonds. The exposed graphite edge sites react with the electrolyte to (re)form the SEI layer, which leads to gradual degradation of the graphite anode, and causes reversible capacity loss in a lithium-ion battery.     

Towards a high performing lithium polymer battery system (VARTA PoLiFlex™)

The design of a lithium polymer battery with excellent properties is presented. The focus is on cathode and anode active materials and their influence on cell properties like energy density and cycle behavior. Standard LiCoO₂ is compared with alternative cathode materials like Li–Co–Ni–Mn–O and high density LiCoO₂. Furthermore, several natural graphites and their mixtures with synthetic graphite are discussed as potential anode active material as natural graphite is attractive concerning price. The good performance of VARTA Microbattery's PoLiFlex™ lithium polymer battery results from an adequate combination of cathode and anode formulations.     

Li nuclear magnetic resonance studies of hard carbon and graphite/hard carbon hybrid anode for Li ion battery

The hard carbon is attractive for the Li ion battery because of its higher capacity than the theoretical value of 372 Ah kg⁻¹ based on the composition of stage 1 Li-intercalated graphite, LiC₆. However, since the Li-doping reaction occurs at the potential of around 0 V versus Li/Li⁺ reference electrode, it is often pointed out the possibility of Li metal deposition on the surface of anode. From the viewpoint of the safety, it may be a moot point. In the present study, ⁷Li NMR measurement was performed to estimate the degree of Li metal deposition on the surface of graphite and hard carbon anode. As a result, it is clarified that the Li metal deposition does not occur up to 110% over-discharge of the reversible capacity of hard carbon, whereas in the case of graphite anode, Li metal deposition occurred above 105% over-discharge of the capacity. From the ⁷Li NMR spectroscopy, the safety limit of hard carbon is rather superior to that of graphite.     

Electrode structure analysis and surface characterization for lithium-ion cells simulated low-Earth-orbit satellite operation: I. Electrochemical behavior and structure analysis

Lithium-ion cells for satellite applications operate under a special condition, and are expected to behave differently from those for commercial purposes. To understand the performance-degradation mechanism of lithium-ion cells experienced cycle-life testing in a simulated low-Earth-orbit (LEO) satellite operation, we conducted the structure analysis and surface characterization of the aged LiCoO₂ cathode and graphite anode obtained from a lithium-ion cell with 4350-cycle LEO simulation experience. The analysis results were compared with a fresh cell which served as control. This paper provides a review of testing results on electrochemical and structure analysis. The capacity-verification and impedance measure results indicated that the LiCoO₂ cathode, rather than graphite anode, was responsible for the performance degradation of the aged cell. This conclusion was confirmed by the structure analysis. The qualitative analysis of the XRD spectra disclosed that the aged cathode exhibited a much larger structure change than the aged anode. We also detected the lithium ions that were irreversibly reserved in graphite anode in XRD and ⁷Li nuclear magnetic resonance (NMR) analysis of aged graphite anode. These results lead us to deduce that the serious structure change in LiCoO₂ cathode was primarily responsible for the performance degradation of the aged cell.     

In situ X-ray diffraction studies of mixed LiMn2O4-LiNi1/3Co1/3Mn1/3O2 composite cathode in Li-ion cells during charge-discharge cycling

The structural changes of the composite cathode made by mixing spinel LiMn₂O₄ and layered LiNi_1/3Co_1/3Mn_1/3O₂ in 1:1 wt% in both Li-half and Li-ion cells during charge/discharge are studied by in situ XRD. During the first charge up to ∼5.2 V vs. Li/Li⁺, the in situ XRD spectra for the composite cathode in the Li-half cell track the structural changes of each component. At the early stage of charge, the lithium extraction takes place in the LiNi_1/3Co_1/3Mn_1/3O₂ component only. When the cell voltage reaches at ∼4.0 V vs. Li/Li⁺, lithium extraction from the spinel LiMn₂O₄ component starts and becomes the major contributor for the cell capacity due to the higher rate capability of LiMn₂O₄. When the voltage passed 4.3 V, the major structural changes are from the LiNi_1/3Co_1/3Mn_1/3O₂ component, while the LiMn₂O₄ component is almost unchanged. In the Li-ion cell using a MCMB anode and a composite cathode cycled between 2.5 V and 4.2 V, the structural changes are dominated by the spinel LiMn₂O₄ component, with much less changes in the layered LiNi_1/3Co_1/3Mn_1/3O₂ component, comparing with the Li-half cell results. These results give us valuable information about the structural changes relating to the contributions of each individual component to the cell capacity at certain charge/discharge state, which are helpful in designing and optimizing the composite cathode using spinel- and layered-type materials for Li-ion battery research.     

Cresyl diphenyl phosphate effect on the thermal stabilities and electrochemical performances of electrodes in lithium ion battery

To improve the safety of lithium ion battery, cresyl diphenyl phosphate (CDP) is used as a flame-retardant additive in a LiPF₆ based electrolyte. The electrochemical performances of LiCoO₂/CDP-electrolyte/Li and Li/CDP-electrolyte/C half cells are evaluated. The thermal behaviors of Li_0.5CoO₂ and Li_0.5CoO₂-CDP-electrolyte, and Li_xC₆ and Li_xC₆-CDP-electrolyte are examined using a C80 micro-calorimeter. For the LiCoO₂/CDP-electrolyte/Li cells, the onset temperature of single Li_0.5CoO₂ is put off and the heat generation is decreased greatly except the one corresponding to 5% CDP-containing electrolyte. When Li_0.5CoO₂ coexists with CDP-electrolyte, the thermal stability is enhanced. CDP improves the thermal stability of lithiated graphite anode effectively and the addition of 5% CDP inhibits the decomposition of solid electrolyte interphase (SEI) films significantly. The electrochemical tests on LiCoO₂/CDP-electrolyte/Li and Li/CDP-electrolyte/C cells show that when less than 15% CDP is added to the electrolyte, the electrochemical performances are not worsen too much. Therefore, the addition of 5-15% CDP to the electrolyte almost does not worsen the electrochemical performance of LiCoO₂ cathode and graphite anode, and improves theirs thermal stability significantly; thus, it is a possible choice for electrolyte additive.     

Lithium-ion rechargeable cells with polyacenic semiconductor (PAS) and LiCoO2 electrodes

Polyacenic semiconductor (PAS), heat-treated at 700°C, has a lithium intercalation capacity as high as 438 mAh g⁻¹ which is higher than the theoretical capacity of 372 mAh g⁻¹ for graphite. The electrochemical behaviour of PAS is examined by studying Li/PAS and Li/graphite cells. In a PAS or graphite anode, three reactions are distinguished: (i) reaction of lithium with the Teflon binder; (ii) decomposition of electrolyte, and (iii) intercalation of Li⁺ ions. Two laboratory cells with liquid organic electrolyte or polymer electrolyte and PAS as the anode demonstrate that PAS is a promising anode material for lithium-ion batteries.     

Properties of the lithium and graphite-lithium anodes in N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide

The ternary [Li⁺]_0.09[MePrPyr⁺]_0.41[NTf₂⁻]_0.50 room temperature ionic liquid was obtained by dissolution of solid lithium bis(trifluoromethanesulfonyl)imide (LiNTf₂) in liquid N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([MePrPyr⁺][NTf₂⁻]), and studied as an electrolyte for lithium-ion batteries. The graphite-lithium (C₆Li) anode, working together with vinylene carbonate as an additive showed ca. 90% of its initial discharge capacity after 50 cycles. The addition of vinylene carbonate to the neat ionic liquid results in the formation of the protective coating (SEI) on both the lithium and graphite anodes. The SEI formation increases the rate of the charge transfer reaction as well as protects the anode from chemical passivation (corrosion). The graphite-lithium (C₆Li) anode shows good cyclability and Coulombic efficiency in the presence of 10 wt.% of vinylene carbonate as an additive to the ionic liquid.     

Mitigation of the irreversible capacity and electrolyte decomposition in a LiNi0.5Mn1.5O4/nano-TiO2 Li-ion battery

Nanosized titanium oxides can achieve large reversible specific capacity (above 200 mAh g⁻¹) and good rate capabilities, but suffer irreversible capacity losses in the first cycle. Moreover, due to the intrinsic safe operating potential (1.5 V), the use of titanium oxide requires to couple it with high-potential cathodes, such as lithium nickel manganese spinel (LNMO) in order to increase the energy density of the final cell. However the use of the 4.7 V vs. Li⁺/Li⁰ LNMO cathode material requires to tackle the continuous electrolyte decomposition upon cycling. Coupling these two electrodes to make a lithium ion battery is thus highly appealing but also highly difficult because the cell balancing must account not only for the charge reversibly exchanged by each electrode but also for the irreversible charge losses. In this paper a LNMO-nano TiO₂ Li-ion cell with liquid electrolyte is presented: two innovative approaches on both the cathode and the anode sides were developed in order to mitigate the electrolyte decomposition upon cycling. In particular the LNMO surface was coated with ZnO in order to minimize the surface reactivity, and the TiO₂ nanoparticles where activated by incorporating nano-lithium in the electrode formulation to compensate for the irreversible capacity loss in the first cycle. With these strategies we were able to assemble balanced Li-ion coin cells thus avoiding the use of electrolyte additives and more hazardous and expensive ex-situ SEI preforming chemical or electrochemical procedures.     

LiAsF6 in propylene carbonate—acetonitrile for primary lithium batteries

1M LiAsF₆ in 50% v/v propylene carbonate—acetonitrile (PC-AN) is an electrolyte solution which offers improved cathode utilization, improved energy efficiency and more stable discharge voltages when used in primary lithium batteries with MnO₂, TiS₂, Cu₂S, CuS, MoO₃, V₂O₅, V₆O₁₃ and NbSe₃ cathodes. Incorporation of solvated Li⁺ into the cathodic material may be part of the cathodic process, and the lower viscosity and lower molar volume of acetonitrile, which is a solvator of Li⁺ in PC/AN mixtures, are thought to be responsible for the major improvement over LiAsF₆ in PC as electrolyte solution for these cells.     

A study on lithium/air secondary batteries—Stability of the NASICON-type lithium ion conducting solid electrolyte in alkaline aqueous solutions

The stability of the high lithium ion conducting glass ceramics, Li_1+x+yTi_2−xAl_xSi_yP_3−yO₁₂ (LTAP) in alkaline aqueous solutions with and without LiCl has been examined. A significant conductivity decrease of the LTAP plate immersed in 0.057 M LiOH aqueous solution at 50 °C for 3 weeks was observed. However, no conductivity change of the LTAP plate immersed in LiCl saturated LiOH aqueous solutions at 50 °C for 3 weeks was observed. The pH value of the LiCl-LiOH-H₂O solution with saturated LiCl was in a range of 7-9. The molarity of LiOH and LiCl in the LiOH and LiCl saturated aqueous solution were estimated to be 5.12 and 11.57 M, respectively, by analysis of Li⁺ and OH⁻. The high concentration of LiOH and the low pH value of 8.14 in this solution suggested that the dissociation of LiOH into Li⁺ and OH⁻ is too low in the solution with a high concentration of Li⁺. These results suggest that the water stable LTAP could be used as a protect layer of the lithium metal anode in the lithium/air cell with LiCl saturated aqueous solution as the electrolyte, because the content of OH⁻ ions in the LiCl saturated aqueous solution does not increase via the cell reaction of Li + 1/2O₂ + H₂O → 2LiOH, and LTAP is stable under a deep discharge state.     

Thermal and electrochemical behaviour of C/LixCoO2 cell during safety test

Thermal and electrochemical processes in a 1000 mAh lithium-ion pouch cell with a graphite anode and a Li_xCoO₂ cathode during a safety test are examined. In overcharge tests, the forced current shifts the cell voltage to above 4.2 V. This causes a cell charged at the 1 C rate to lose cycleability and a cell charged at the 3 C rate to undergo explosion. In nail penetration and impact tests, a high discharge current passing through the cells gives rise to thermal runaway. These overcharge and high discharge currents promote joule heat within the cells and leads to decomposition and release of oxygen from the de-lithiated Li_xCoO₂ and combustion of carbonaceous materials. X-ray diffraction analysis reveals the presence of Co₃O₄ in the cathode material of a 4.5 V cell heated to 400 °C. The major cathode product formed after the combustion process cells abused by forced current is Co₃O₄ and by discharge current the products are LiCoO₂ and Co₃O₄. The formation of a trace quantity of CoO through the reduction of Co₃O₄ by virtue of the reducing power of the organic solvent is also discussed.     

Improved lithium manganese oxide spinel/graphite Li-ion cells for high-power applications

The degradation mechanism of lithium manganese oxide spinel/graphite Li-ion cells using LiPF₆-based electrolyte was investigated by a Mn-dissolution approach during high-temperature storage, and by ac impedance measurement using a reference electrode-equipped cell. Through these studies, we confirmed that Mn ions were dissolved from the spinel cathode in the electrolyte and were subsequently reduced on the lithiated graphite electrode surface, due to the chemical activity of the lithiated graphite, and caused a huge increase in the charge-transfer impedance at the graphite/electrolyte interface, which consequently deteriorated cell performance. To overcome the significant degradation of the spinel/graphite Li-ion cells, we investigated a new electrolyte system using lithium bisoxalatoborate (LiBoB, LiB(C₂O₄)₂) salt not having fluorine species in its chemical structure. Superior cycling performance at elevated temperature was observed with the spinel/graphite cells using LiBoB-based electrolyte, which is attributed to the inert chemical structure of LiBoB that does not generate HF. Mn-ion leaching experiments showed that almost no Mn ions were dissolved from the spinel powder after 55 °C storage for 4 weeks. Through optimization of organic solvents for the LiBoB salt, we developed an advanced Li-ion cell chemistry that used lithium manganese oxide spinel, 0.7 M LiBoB/EC:PC:DMC (1:1:3), and graphite as the cathode, electrolyte, and anode, respectively. This cell provides excellent power characteristics, good calendar life, and improved thermal safety for hybrid electric vehicle applications.     

Improved performance of Li hybrid solid polymer electrolyte cells

The seminal research by Wright et al. on polyethylene oxide (PEO) solid polymer electrolyte (SPE) generated intense interest in all solid-state rechargeable lithium batteries. Following this a number of researchers have studied the physical, electrical and transport properties of thin film PEO electrolyte containing Li salt. These studies have clearly identified the limitations of the PEO electrolyte. Chief among the limitations are a low cation transport number (t₊), high crystallinity and segmental motion of the polymer chain, which carries the cation through the bulk electrolyte. While low t₊ leads to cell polarization and increase in cell resistance high T_g reduces conductivity at and around room temperatures. For example, the conductivity of PEO electrolyte containing lithium salt is <10⁻⁷ S cm⁻¹ at room temperature. Although modified PEO electrolytes with lower T_g exhibited higher conductivity (∼10⁻⁵ S cm⁻¹ at RT) the t₊ is still very low ∼0.25 for lithium ion. Numerous other attempts to improving t₊ have met with limited success. The latest approach involves integrating nano domains of inorganic moieties, such as silcate, alumosilicate, etc. within the polymer component. This approach yields an inorganic–organic component (OIC) based polymer electrolyte with higher conductivity and t₊ for Li⁺_. This paper describes the improved electrical and electrochemical properties of OIC-based polymer electrolyte and cells containing Li anode with either a TiS₂ cathode or Mag-10 carbon electrode. Several solid polymer electrolytes derived from silicate OIC and salt-in-polymer constituent based on Li triflate (LiTf) and PEO are studied. A typical composition of the SPE investigated in this work consists of 600 kDa PEO, lithium triflate (LiTf, LiSO₃CF₃) and 55% of silicate based on (3-glycidoxypropyl)trimethoxysilane and tetramethoxysilane at molar ratio 4:1 and 0.65 mol% of aluminum(tri-sec-butoxide) (GTMOS-Al1-900k-55%). Several pouch cells consisting of Li/OIC-based–SPE/cathode containing OIC-based–SPE–LiTf binder were fabricated and tested, these cells are called modified cells. The charge/discharge and impedance characteristics of the new cells (also called modified cells) are compared with that of the pouch cells containing the conventional PEO–LiTf electrolyte as the cathode binder, these cells are called non-modified cells. The new cells can be charged and discharged at 70 °C at higher currents. However, the old cells can be charged and discharged only at 80 °C or above and at lower currents. The cell impedance for the new cells is much lower than that for the old cells.     

New electrolytes for lithium ion batteries using LiF salt and boron based anion receptors

The thermal and electrochemical stability, as well as compatibility with various bench mark cathode and anode materials of two new lithium fluoride salt (LiF) based electrolytes have been studied. These two new electrolytes are formed by using boron-based anion receptors, tris(pentafluorophenyl) borane (TPFPB), or tris(2H-hexafluoroisopropyl) borate (THFPB) as additives, which were designed and synthesized at Brookhaven National Laboratory (BNL), to dissolve the LiF salt in carbonate solvents. The transference number of Li⁺ for these electrolytes is as high as 0.7 and the room-temperature conductivity is around 2 × 10⁻³ S cm⁻¹. The electrolytes containing propylene carbonate (PC) show superior low-temperature conductivity properties. The electrochemical window is approaching 5.0 V. It was also found that the new electrolytes work well with LiCoO₂ or LiMn₂O₄ cathodes. However, when PC containing electrolytes were used, PC co-intercalation is still a problem for graphite anodes. The formation of a stable solid electrolyte interface layer on the surface of anode in this type of electrolyte needs to be studied further.     

Predicting electrical and thermal abuse behaviours of practical lithium-ion cells from accelerating rate calorimeter studies on small samples in electrolyte

An accelerating rate calorimeter (ARC) is used to measure the thermal stability of de-intercalated Li_1+xMn_2−xO₄ in LiPF₆ EC:DEC (33:67) electrolyte. Self-heating is detected well after the 80°C onset of self-heating measured for lithium intercalated mesocarbon microbead (MCMB) electrodes in LiPF₆ EC:DEC (33:67) electrolyte. As a result, the initial self-heating measured in a practical carbon/Li_1+xMn_2−xO₄ lithium-ion cell is caused by reactions at the anode. In previous work, we have proposed a model for the reactions that cause self-heating in MCMB electrodes in electrolyte. By assuming that a cell self-heats only because reactions occur at the anode, the model can be used to predict the power generated by the amount of MCMB in practical cells with an inert cathode. The calculated chemically generated power can be combined with power loss measurements, due to the transfer of heat to the environment, to predict the short-circuit behaviour and the oven exposure behaviour for a cell containing an MCMB anode and an inert cathode. The results agree qualitatively with short-circuit and oven exposure results measured on NEC Moli energy 18650 cells containing an Li_1+xMn_2−xO₄ cathode.