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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 ...

Summary Incorporation of silicon into negative electrodes is pursued widely to increase the energy density of lithium ion batteries (LIBs). However, severe volume changes of silicon during (de)lithiation cause consumption of active lithium and electrolyte by continuous solid electrolyte interphase (SEI) formation, resulting in deterioration of cell performance. Electrolyte additives offer an unprecedented way to improve LIB cell performance by effective interphase formation. Here, we report a class of electrolyte additives based on substituted N-carboxyanhydrides (N-CAs) designed to effectively tailor the SEI formed in LiNi0.5Co0.2Mn0.3O2 (NCM523) ∥ SiOx/C full cells, which are evaluated in pouch cells with application-relevant electrolyte per-cell capacity ratios. The working mechanism is elucidated systematically by use of complementary postmortem techniques, correlating cycling and storage performance data, gas formation, SEI composition, and electrolyte degradation. With successful additive functionalization, several N-CAs even outperform the state-of-the-art additive fluoroethylene carbonate in terms of capacity retention.

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+).

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.

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 Mossbauer 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+).

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.