No abstract

Parasitic gas evolution in lithium ion battery (LIB) cells especially occurs within the first charge cycle, but can also take place during long-term cycling and storage, thereby, negatively affecting the cell performance. Gas formation is influenced by various factors, such as the cell chemistry and operating conditions, thus, demanding fundamental studies in terms of interphase and gas formation (gas volume and composition) and electrolyte consumption. Gas analyses in terms of mass spectrometry of gaseous products are regularly performed, however, usually using custom-made cell designs with a high excess of electrolyte. Here, a gas sampling port (GSP) is incorporated in a commercial small-scale multilayer pouch cell in a simple post-production process and systematically evaluated as proof-of-principle approach towards effective electrolyte additive research under practically relevant conditions, i.e., when applying a limited amount of electrolyte per cell capacity. The GSP-based LIB pouch cell design allows the voltage-dependent identification and separation of formed gases, while a clear correlation between electrolyte reduction peaks, observed in differential capacity profiles, and the onset of gas evolution is demonstrated. In summary, the novel GSP-based pouch cell setup benefits from the possibility of multiple time-, cell voltage- or state-of-charge-dependent gas measurements, without significantly influencing the original cell performance.

Silicon (Si) has attracted much attention to be applied as a negative electrode (N) material for lithium ion batteries (LIBs) with increased energy density. However, the huge volume changes during (de-)­lithiation of the Si, accompanied with the breakdown of the initially formed solid electrolyte interphase (SEI), result in the gradual consumption of active lithium and electrolyte and, hence, a poor cycling performance of LIBs with Si-based N. The addition of various electrolyte additives was proven to be able to reduce the active lithium consumption by the formation of a more effective/flexible and, therefore, better protecting SEI on the Si. Within this study, we synthesize the new electrolyte additive lactic acid O-carboxyanhydride (lacOCA), which is designed to incorporate two different moieties within its structure, that both show to function as effective SEI additives. The addition of small amounts of 2 wt % of lacOCA to the baseline electrolyte significantly improves the electrochemical performance of NMC-111||Si full cells in terms of discharge capacity retention and Coulombic efficiency. The lacOCA also outperforms the comparable additives lactide and diethyl dicarbonate, which are chosen to individually represent the moieties incorporated within the lacOCA structure, proving the synergistic effect of the two different moieties, when in one molecule. Ex situ investigations of the SEI by means of X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy reveal that the SEI formed by lacOCA is mainly composed of poly­(lactic acid) and lithium carbonate, which enables a significant reduced consumption of active lithium during charge/discharge cycling of the NMC-111||Si full cells.

Layered oxides, such as Li­[Ni0.5Co0.2Mn0.3]­O2 (NCM523), are promising cathode materials for operation at a high voltage, i.e., high-energy lithium-ion batteries. The instability-reasoned transition metal dissolution remains a major challenge, which initiates electrode cross-talk, alteration of the solid electrolyte interphase, and enhanced Li-metal dendrite formation at the graphite anode, consequently leading to rollover failure. In this work, relevant impacts on this failure mechanism are highlighted. For example, a conventional coating of NCM523 with aluminum oxide as a typical high-voltage modification improves kinetic aspects but can only postpone the rollover failure to later charge/discharge cycles. Interestingly, a similar effect on the rollover failure is observed merely after modification of the cell formation protocol, i.e., the first cycles. Further influences of specific test protocols are highlighted and show that the rollover failure even disappears at C-rates above 2C, which can be attributed to a more homogeneous distribution of Li-metal dendrite formation. It is worth noting that a variation of anode porosity can reveal similar effects, as, e.g., variations in anode processing also impact Li dendrite distribution and the appearance of rollover failure. Overall, the rollover failure is a valid but complex phenomenon, which sensitively depends on apparently inconspicuous parameters and should not be disregarded.

In order to further increase the energy density of lithium ion batteries (LIBs), it is of utmost importance to develop advanced electrode materials in combination with suitable electrolytes, which deliver either higher capacities and/or can be operated at high cell voltage with sufficient cycling stability. Here, we introduce (1H-imidazol-1-yl)(morpholino)methanone (MUI) as a cathode electrolyte interphase (CEI) forming electrolyte additive for LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NMC111) || graphite cells operated at high cell voltage of up to 4.6 V. The addition of MUI to the carbonate-based reference electrolyte leads to a superior cycling stability in comparison to those with the pure reference electrolyte. The working mechanism of MUI is comprehensively elucidated with various ex situ analytical techniques. A reduction of MUI at the graphite anode is observed starting at a potential of ≈0.9 V vs. Li/Li + , resulting in a slightly higher kinetic impairment of lithium ion intercalation/deintercalation into/from graphite. To prevent the unfavorable reduction of MUI at the graphite anode, Li 4 Ti 5 O 12 (LTO)-based composite anodes are also used to analyze the function of the additive at the cathode surface. We can clearly confirm that a protective film at the cathode surface is formed, helping to suppress parasitic side reactions at the cathode/electrolyte interface during long-term cycling.

The intermetallic compound EuAu3Al2 has been prepared by reaction of the elements in tantalum ampules. The structure was refined from single-crystal data, indicating that the title compound crystallizes in the orthorhombic crystal system (a = 1310.36(4), b = 547.87(1), c = 681.26(2) pm) with space group Pnma (wR2 = 0.0266, 1038 F(2) values, 35 parameters) and is isostructural to SrAu3Al2 (LT-SrZn5 type). Full ordering of the gold and aluminum atoms was observed. Theoretical calculations confirm that the title compound can be described as a polar intermetallic phase containing a polyanionic [Au3Al2](δ-) network featuring interconnected strands of edge-sharing [AlAu4] tetrahedra. Magnetic measurements and (151)Eu Mössbauer spectroscopic investigations confirmed the divalent character of the europium atoms. Ferromagnetic ordering below TC = 16.5(1) K was observed. Heat capacity measurements showed a λ-type anomaly at T = 15.7(1) K, in line with the ordering temperature from the susceptibility measurements. The magnetocaloric properties of EuAu3Al2 were determined, and a magnetic entropy of ΔSM = -4.8 J kg(-1) K(-1) for a field change of 0 to 50 kOe was determined. Band structure calculations found that the f-bands of Eu present at the Fermi level of non-spin-polarized calculations are responsible for the ferromagnetic ordering in this phase, whereas COHP chemical bonding coupled with Bader charge analysis confirmed the description of the structure as covalently bonded polyanionic [Au3Al2](δ-) network interacting ionically with Eu(δ+).

The title compound is synthesized from the elements (Ta ampule, 1300 K for 10 min and 825 K for 2—8 h) and characterized by single crystal XRD, Moessbauer spectroscopy, magnetic measurements, and DFT calculations.

Lithium ion batteries (LIBs), as the state-of-the-art energy storage technique, possess high energy and power density. The target to decrease the emission of carbon dioxide, released by the combustion of fossil fuels promotes the market of electric vehicles (EVs) or hybrid electric vehicles (HEVs), resulting in a high demand for LIBs. LIBs are expected to be the most promising candidate to replace the fossil fuels in conventional means of transportation [1]. LiNixMnyCo1-x-yO2 (x ≤ 0.5) has been widely applied as the state-of-the-art cathode material for lithium ion batteries, with the application in E-bikes or xEVs. However, the application in competitive xEVs requires high specific capacity as well as high working potential (> 4.5 V vs. Li/Li+). Therefore, Ni-rich or high-voltage NMC cathode materials will be established as future cathode materials, offering higher discharge capacities at equivalent cut-off potentials. Certainly, as the operation voltage or Ni content increases, not only the intrinsic stability of the layered oxides decreases due to the higher delithiation degree, but also the oxidative decomposition of the electrolyte by e.g. chemical reaction with highly reactive Ni4+ species on the cathode surface becomes more severe. These side reactions can promote the loss of active material (Ni4+ → Ni2+) and the formation of a thick layer of decomposition products on the electrode surface, resulting in an overall impedance increase. Furthermore, Ni-rich layered oxides particles tend to form micro-cracks, revealing the pristine active material and further accelerating capacity fading, due to ongoing electrolyte decomposition. The use of electrolyte additives to prevent these cathode fading mechanisms is one promising approach to improve the capacity retention and cell performance [2,3]. A variety of electrolyte additives to act as a film forming agent to hinder the fading of different cathode materials have been reported in literature so far. These additives are oxidized prior to the blank electrolyte components and in situ form a protective layer on the surface of the electrode [4]. Within this work, several new compounds were synthesized and evaluated as possible electrolyte additives for NMC/graphite cells, to address the previously mentioned fading mechanisms. The novel compounds were characterized towards their reductive and oxidative stability on active electrode materials, as opposed to commonly used inactive materials (e.g. Pt, or glassy carbon).The addition of these nitrogen-based electrolyte additives lead to an increased Coulombic efficiency and enhanced capacity retention during long-term cycling in comparison to the baseline electrolyte. The working mechanism was tried to elucidate using different ex situ analytical techniques. Post-mortem investigations of the extracted electrolyte and the cathode surface were performed to study the cathode electrolyte interphase (CEI) layer formed by the addition of these additives. The improved cycling performance of these additives in LIB full cells can be correlated to the formation of a passivation film on the cathode surface. References [1] J.M. Tarascon, M. Armand, Issues and challenges facing rechargeable lithium batteries, Nature 414 (2001) 359–367. [2] R. Jung, M. Metzger, F. Maglia, C. Stinner, H.A. Gasteiger, Oxygen Release and Its Effect on the Cycling Stability of LiNixMnyCozO2 (NMC) Cathode Materials for Li-Ion Batteries, J. Electrochem. Soc. 164 (2017) A1361-A1377. [3] J. Kasnatscheew, M. Evertz, B. Streipert, R. Wagner, S. Nowak, I. Cekic Laskovic, M. Winter, Changing Established Belief on Capacity Fade Mechanisms, J. Phys. Chem. C 121 (2017) 1521–1529. [4] Y. Dong, B.T. Young, Y. Zhang, T. Yoon, D.R. Heskett, Y. Hu, B.L. Lucht, Effect of Lithium Borate Additives on Cathode Film Formation in LiNi0.5Mn1.5O4/Li Cells, ACS Appl. Mater. Interfaces 9 (2017) 20467–20475.