Environmental impact assessment and classification of 48 V plug-in hybrids with real-driving use case simulations

Plug-in hybrid electric vehicles (PHEVs) are commonly operated with high-voltage (HV) components due to their higher power availability compared to 48 V-systems. On the contrary, HV-powertrain components are more expensive and require additional safety measures. Additionally, the HV system can only be repaired and maintained with special equipment and protective gear, which is not available in all workshops. PHEVs based on a 48 V-system level can offer a reasonable compromise between the greenhouse gas (GHG) emission-saving potential and cost-effectiveness in small- and medium-sized electrified vehicles. In our study, the lifecycle emissions of the proposed 48 V PHEV system were compared to a conventional vehicle, 48 V HEV, and HV PHEV for individual driving use cases. To ensure a holistic evaluation, the analysis was based on measured real-driving cycles including Global Position System (GPS) map-matched slope profiles for a parallel hybrid. Optimal PHEV battery capacities were derived for the individual driving use cases. The analysis was based on lifecycle emissions for 2020 and 2030 in Europe. The impact analysis revealed that 48 V PHEVs can significantly reduce GHG emissions compared to vehicles with no charging opportunity for all use cases. Furthermore, the findings were verified for two vehicle segments and two energy mix scenarios. The 48 V PHEVs can therefore complement existing powertrain portfolios and contribute to reaching future GHG emission targets

Strategies towards enabling lithium metal in batteries: interphases and electrodes

Despite the continuous increase in capacity, lithium-ion intercalation batteries are approaching their performance limits. As a result, research is intensifying on next-generation battery technologies. The use of a lithium metal anode promises the highest theoretical energy density and enables use of lithium-free or novel high-energy cathodes. However, the lithium metal anode suffers from poor morphological stability and Coulombic efficiency during cycling, especially in liquid electrolytes. In contrast to solid electrolytes, liquid electrolytes have the advantage of high ionic conductivity and good wetting of the anode, despite the lithium metal volume change during cycling. Rapid capacity fade due to inhomogeneous deposition and dissolution of lithium is the main hindrance to the successful utilization of the lithium metal anode in combination with liquid electrolytes. In this perspective, we discuss how experimental and theoretical insights can provide possible pathways for reversible cycling of twodimensional lithium metal. Therefore, we discuss improvements in the understanding of lithium metal nucleation, deposition, and stripping on the nanoscale. As the solid–electrolyte interphase (SEI) plays a key role in the lithium morphology, we discuss how the proper SEI design might allow stable cycling. We highlight recent advances in conventional and (localized) highly concentrated electrolytes in view of their respective SEIs. We also discuss artificial interphases and three-dimensional host frameworks, which show prospects of mitigating morphological instabilities and suppressing large shape change on the electrode level

Are dye-sensitized nano-structured solar cells stable? an overview of device testing and component analyses

A review (71 refs.). The nano-structured dye-sensitized solar cell (DNSC) is considered as a promising technol. having the potential to significantly decrease the costs of solar energy. The breakthrough was achieved in 1991 with the demonstration of a DNSC system reaching more than 7% efficiency and after a decade of intense research the commercialization is in reach. Besides efficiency, stability is equally important for the step from research to the market. Therefore, the stability of such devices has been under close investigation since the DNSC was presented. In this contribution we summarize the literature about device testing and the attempts to understand the degrdn. mechanisms. Solar cells developed for energy prodn. are discussed as well as alternative systems for low power applications, e.g., DNSCs on plastic substrates. The components (substrate, nano-structured TiO2, dye, electrolyte, additive and counter electrode) are analyzed towards their stability and how it affects the durability of the entire system. From this anal., guidelines for testing and improving the stability of the DNSC are deduced

Are dye-sensitized nano-structured solar cells stable? An overview of device testing and component analyses

The nano-structured dye-sensitized solar cell (DNSC) is considered as a promising technology having the potential to significantly decrease the costs of solar energy. The breakthrough was achieved in 1991 with the demonstration of a DNSC system reaching more than 7% efficiency and after a decade of intense research the commercialization is in reach. Besides efficiency, stability is equally important for the step from research to the market. Therefore, the stability of such devices has been under close investigation since the DNSC was presented. In this contribution we summarize the literature about device testing and the attempts to understand the degradation mechanisms. Solar cells developed for energy production are discussed as well as alternative systems for low power applications, e.g., DNSCs on plastic substrates. The components (substrate, nano-structured TiO2, dye, electrolyte, additive and counter electrode) are analyzed towards their stability and how it affects the durability of the entire system. From this analysis, guidelines for testing and improving the stability of the DNSC are deduced

In Situ Optical Investigations of Lithium Depositions on Pristine and Aged Lithium Metal Electrodes

A custom-designed in situ optical cell is used to investigate the behavior of lithium (Li0) deposition in a symmetrical face-to-face setup. The experiment aims at monitoring the lithium deposition on both pristine and aged lithium foils, as a function of the waiting time between the lithium electrodes and the electrolyte (LP30: 1.0 M LiPF6 in EC: DMC (50/50 (v/v))). Constant current and electrochemical impedance spectroscopy measurements are applied at ∼28 °C. The experiments show that lithium metal deposits in a wide range of morphologies, which are cataloged in terms of forms, structures, textures and colors for better visualization and improved analysis. Pristine lithium electrodes show tree-like deposition morphologies over the entire range of applied waiting times, but aged samples provided fibrous, and spheroidal forms as dominant lithium deposition morphologies at waiting times ≥ 24 h. Gas-treated metal foils (artificially aged by exposing pristine lithium to N2 at 25 °C for 1 h) showed a similar deposition behavior as the aged-over-time foils. The storage of lithium has a measurable influence on the deposition behavior on lithium foils. The obtained results help to further understand the lithium deposition behavior under different realistic conditions, which is for instance applicable to rechargeable lithium metal batteries

In Situ Optical and Electrochemical Investigations of Lithium Depositions as a Function of Current Densities

The electrodeposition behavior of lithium metal as a function of the current density at room temperature was investigated in a symmetrical face‑to‑face in‑situ optical cell. After a defined initial contact time between electrode and electrolyte, various current densities in the range of 0.05 mA cm−2 to 10 mA cm−2 were tested. Constant current phases, electrochemical impedance spectroscopy measurements and in situ images of the working electrode were recorded and results were compared. Two regimes of lithium deposition with different optical and electrochemical characteristics were identified as a function of current density. The first regime, at low current densities (0.05 mA cm−2–0.5 mA cm−2), showed none to tiny lithium depositions with sporadic large lithium structures at the higher end of this range. The second regime, at high current densities (2 mA cm−2–10 mA cm−2), showed many smaller, deposited lithium structures. The experimental results are discussed in the context of the formation and presence of metal-electrolyte interphases presumably by chemical reactions between lithium and electrolyte, current density and their interactions with each other. The correlation of fundamental parameters of lithium metal deposition with current density must be taken into account for the development of lithium metal-based energy storage devices

Customizing Active Materials and Polymeric Binders: Stern Requirements to Realize Silicon-Graphite Anode Based Lithium-Ion Batteries.

Due to the well-balanced and synergistic advantageous features, the co-utilization of silicon (Si) and graphite (Gr) particles is hailed as enabling substitute to all-Gr and all–Si anodes for lithium-ion batteries (LIBs). The effect of Si to Gr and lithium poly(acrylic acid) (LiPAA) to sodium carboxymethyl cellulose (CMC) ratio on the electrochemistry and performance of Si-Gr composite (blended) anode based LIB cells is investigated. Besides regulating the ratio of Si to Gr active materials in the Si-Gr blend, it is found that the use of a mixture of polymeric binders and their optimization is of supreme importance. Thus, the co-use and appropriate dose optimization of LiPAA and CMC with specific compatibility to Si and Gr respectively, are evaluated. Among tested various ratios, a blend anode with 20 wt% Si and LiPAA to CMC ratio of 2.27:7.73 resulted in high performing half and full cells based on NMC622 cathode, in terms of cycle life, capacity retention, and coulombic efficiency. The systematic investigation approach implemented in this work presents to be of significant importance to enable the practical deployment of silicon-graphite blend anode based LIBs

Establishing Li-acetylide (Li2C2) as functional element in solid-electrolyte interphases in lithium-ion batteries

Previously, lithium-acetylide (Li2C2) had been identified as electrolyte degradation product on lithium-metal based electrodes using Raman spectroscopy. This raised the question, if Li2C2 is also be formed on graphitic electrodes in lithium-ion batteries without lithium metal present. In order to shed light on this research question, we performed a series of in situ Raman experiments with graphitic electrodes in half- and full-cell configuration. The recorded cell potential dependent spectra clearly prove the presence of Li2C2 in the lithiated state of the electrodes, but the according peak vanishes when delithiating. This observation indicates a somewhat reversible process involving Li2C2. Several chemical/electrochemical reactions are in question to contribute to this effect. With respect to its properties and potential role in the solid-electrolyte interphase (SEI) DFT calculations of Li2C2-nanoclusters were performed, which revealed an exceptionally low energy band gap, hence a remarkable electric conductivity. In conjunction with a relatively high ionic conductivity, Li2C2 appears to play a key role in the degradation of lithium-ion batteries, which had not yet been revealed nor taken into account in simulations of the interphase

Long-Term Stability of Redox Mediators in Carbonate Solvents

Scanning electrochemical microscopy (SECM) used in the feedback mode is one of the most powerful versatile analytical tools used in the field of battery research. However, the application of SECM in the field of lithium-ion batteries (LIBs) faces challenges associated with the selection of a suitable redox mediator due to its high reactivity at low potentials at lithium metal or lithiated graphite electrodes. In this regard, the electrochemical/chemical stability of 2,5-di-tert-butyl-1,4-dimethoxybenzene (DBDMB) is evaluated and benchmarked with ferrocene. This investigation is systematically carried out in both linear and cyclic carbonates of the electrolyte recipe. Measurements of the bulk current with a microelectrode prove that while DBDMB decomposes in ethyl methyl carbonate (EMC)-containing electrolyte, bulk current remains stable in cyclic carbonates, ethylene carbonate (EC) and propylene carbonate (PC). Ferrocene was studied as an alternative redox mediator, showing superior electrochemical performance in ethyl methyl carbonate-containing electrolytes in terms of degradation. The resulting robustness of ferrocene with SECM is essential for a quantitative analysis of battery materials over extended periods. SECM approach curves depict practical problems when using the decomposing DBDMB for data acquisition and interpretation. This study sheds light towards the use of SECM as a probing tool enabled by redox mediator

Tuning the Reactivity of Electrolyte Solvents on Lithium Metal by Vinylene Carbonate

Organic solvents undergo degradation reactions when in contact with lithium metal. These reactions form a layer of decomposition products that partly prevents further electrolyte decomposition—passivation. Still, the chemical processes in this system are complex and have not yet been fully understood though it is of high relevance for lithium metal batteries. Scanning Electrochemical Microscopy (SECM) in feedback mode as well as GC-MS are used for analyzing the interface as well as soluble decomposition products. SECM data show that the native interface thickness on metallic lithium from ethylene carbonate (EC) and ethyl methyl carbonate (EMC) electrolyte solutions is reduced by approx. 98% by adding 5 wt% vinylene carbonate (VC) to the solution. The addition of VC changed significantly the dynamics of the growth of the deposition layer. GC-MS studies of the EC:EMC electrolyte solution proof an ongoing reaction of the metallic lithium with the electrolyte even after several days. In comparison, the addition of VC appears to stabilize the interface and no decomposition products could be identified. It is concluded that the addition of VC to the electrolyte solution from EC:EMC prevents the trans-esterification of EMC by surface passivation and not by scavenging alkoxides as claimed in literature