The instability of currently used electrolyte solutions and of the carbon support during charge-discharge in non-aqueous lithium-oxygen cells can lead to discharge products other than the desired Li2O2, such as Li2CO3, which is believed to reduce cycle-life. Similarly, discharge in an O2 atmosphere which contains H2O and CO2 impurities would lead to LiOH and Li2CO3 discharge products. In this work we therefore investigate the rechargeability of model cathodes pre-filled with four possible Li-air cell discharge products, namely Li2O2, Li2CO3, LiOH, and Li2O. Using Online Electrochemical Mass Spectrometry (OEMS), we determined the charge voltages and the gases evolved upon charge of pre-filled electrodes, thus determining the reversibility of the formation/electrooxidation reactions. We show that Li2O2 is the only reversible discharge product in ether-based electrolyte solutions, and that the formation of Li2CO3, LiOH, or Li2O is either irreversible and/or reacts with the electrolyte solution or the carbon during its oxidation.

The quality of metal oxide-based battery active materials is compromised by surface contamination from storage and handling at ambient conditions. We present a detailed analysis of the true nature and the quantity of the surface contaminants on two different cathode active materials, the widely used LiNi1/3Co1/3Mn1/3O2 (NCM111) and the Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811). We process these materials in three distinct conditions “wet” (excessive exposure to moisture), “dry” (standard drying of as-received materials), and “calcined” (heat-treatment of cathode powders). Surface contaminants are then quantified by thermogravimetric analysis coupled with mass spectrometry (TGA-MS), and their reactivity with an ethylene carbonate-based electrolyte is evaluated using on-line mass spectrometry (OMS). We demonstrate that not only the commonly assumed LiOH and Li2CO3 residues account for NCM performance deterioration upon storage in moisture and CO2 containing atmosphere, but also basic transition metal hydroxides/carbonates formed on the material surface. Eventually, we showcase a thermal treatment that removes these transition metal based surface contaminants and leads to superior cycling stability.

The electrochemical oxidation of LiPF 6-based electrolytes is reported to generate POF 3 gas. In order to enable a quantitative analysis of the LiPF 6 decomposition reactions, we aimed to establish calibration factors for POF 3 and PF 5 in on-line electrochemical mass spectrometry (OEMS). Thermal decomposition of dry LiPF 6 is expected to yield PF 5 , but instead all PF 5 is detected as POF 3 in our OEMS setup, rendering a differentiation of the two gases impossible and presenting an artefact which likely occurs with most on-line mass spectrometry systems due to the high reactivity of PF 5. However, we can still determine a cumulative calibration factor for POF 3 + PF 5 (referred to as "POF 3 "), which is then used to investigate the evolution of gases during the oxidation of an EC/LiPF 6 electrolyte on a carbon black electrode. Mechanistic experiments with protons or water added to EC/LiPF 6 electrolyte show that protons trigger the formation of PF 5 , while the kinetics for the hydrolysis of LiPF 6 with water at room temperature are too slow to be detectable. These findings let us conclude that the oxidation of EC generates highly acidic species, which cause the decomposition of PF 6 − to PF 5 and HF; the PF 5 is then detected as POF 3 in the OEMS.

In this study we report on the direct proportionality between cathode surface area and first discharge capacity of non-aqueous Li-O 2 cells using ether-based electrolytes. Seven different highly structured carbon blacks, characterized by different surface areas and porosities, were used to prepare non-catalyzed cathodes. Surface measurements and porosity analyzes were carried out on both raw materials and electrodes in order to estimate the fraction of cathode surface accessible by the electrolyte. The first specific discharge capacity of different cathodes was then normalized over its specific surface and a strong correlation between the two quantities was found. This result strongly supports a discharge mechanism for Li-O 2 batteries wherein the main factor limiting the capacity is the formation of a passivating layer of products on the surface of the cathode material, impeding ORR at carbon active sites. Also the cyclability of the cells was considered, demonstrating the effect of electrolyte degradation on the increased capacity upon cycling of ethereal electrolytes (e.g. DEGDME). The first discharge specific capacity and cyclability using TEGDME, commonly used in Li-air research, was found similar to reacting or degraded electrolytes, suggesting a much higher reactivity toward superoxide ion radical in comparison to its lighter homologues DEGDME and DME.

Lowering of the oxygen evolution reaction (OER) noble metal catalyst loading on the anode of a polymer electrolyte membrane water electrolysis (PEMWE) is a necessity for enabling the large-scale hydrogen production based on this technology. This study introduces a remarkably active OER catalyst that is based on the dispersion of Ir nanoparticles on a highly conductive oxide support. The catalyst was designed in a way to combine all characteristics that have been reported to enhance the OER activity on an Ir oxide-based catalyst, including high catalyst dispersion and controlling the Ir catalyst particle size, so that this design approach provides both high surface area to Ir mass ratio and at the same time ensures maximum synergetic interaction with the oxide support, termed strong metal−support interaction (SMSI). This was achieved through using a high surface area (50 m 2 /g) and highly conductive antimony-doped tin oxide support (2 S/cm), where combining a high catalyst dispersion and maximum SMSI resulted in a very high OER activity of the Ir/ATO catalyst (≈1100 A/g Ir , at 80 °C and 1.45 V RHE ). This enhanced activity will allow a significant reduction (ca. 75-fold) in the precious metal catalyst loading when this catalyst is implemented in the anode of a PEMWE.

Sulfide-based solid electrolytes (SE) are quite attractive for application in all-solid-state batteries (ASSB) due to their high ionic conductivities and low grain boundary resistance. However, limited chemical and electrochemical stability demands for protection on both cathode and anode side. One promising concept to prevent unwanted reactions and simultaneously improve interfacial contacting at the anode side consists in applying a thin polymer film as interlayer between Li metal and the SE. In the present study, we investigated the combination of polyethylene oxide (PEO) based polymer films with the sulfide-based SE Li 10 SnP 2 S 12 (LSPS). We analyzed their compatibility using both electrochemical and chemical techniques. A steady increase in the cell resistance during calendar aging indicated decomposition reactions at the interfaces. By means of X-ray photoelectron spectroscopy and further analytical methods, the formation of polysulfides, P-[S] n-P like bridged PS 4 3− units and sulfite, SO 3 2− , was demonstrated. We critically discuss potential reasons and propose a plausible mechanism for the degradation of LSPS with PEO. The main objective of this paper is to highlight the importance of understanding interfaces in ASSBs not only from an electrochemical perspective, but also from a chemical point of view.

The decomposition of lithium peroxide during the charging process of lithium-air batteries is investigated. A novel preparation method for electrodes in the discharged state, i.e., prefilled with Li2O2 using polyethylene oxide as a binder, is presented. The composition and reactivity of Li2O2-prefilled electrodes are examined by thermal analysis coupled with on-line mass spectrometry. Voltage profiles and gas evolution during the charging process of Li2O2-prefilled electrodes in battery cells are correlated with the thermal decomposition process of Li2O2 and its impact on other electrode compounds. It is found that both thermal Li2O2 decomposition and the electrochemical decomposition of Li2O2 during charging enhance the oxidation of the electrolyte, the binder, and/or carbon, which is suggested to be due to the formation of "nascent" oxygen during Li2O2 decomposition into O2 and Li2O (thermally) or into O2 and lithium ions (electrochemically).

The fluorinated phosphate lithium bis (2,2,2-trifluoroethyl) phosphate (LiBFEP) has been investigated as a film-forming additive employed to passivate the cathode and hinder continuous oxidation of the electrolyte. Cyclic voltammetry (CV) and linear sweep voltammetry coupled with online electrochemical mass spectrometry (LSV-OEMS) on a conductive carbon electrode (i.e., a C65/PVDF composite) showed that LiBFEP decreases electrolyte oxidation (CV and LSV) and LiPF 6 decomposition at high potentials. Incorporation of LiBFEP (0.1 and 0.5 wt%) into LiPF 6 in ethylene carbonate (EC)/ethyl methyl carbonate (EMC) (3:7 wt) results in improved coulombic efficiency and capacity retention for LNMO/graphite cells. Ex-situ surface analysis of the electrodes suggests that incorporation of LiBFEP results in the formation of a cathode electrolyte interface (CEI) and modification of the solid electrolyte interface (SEI) on the anode. The formation of the CEI mitigates electrolyte oxidation and prevents the decomposition of LiPF 6 , which in turn prevents HF-induced manganese dissolution from the cathode and destabilization of the SEI. The passivation of the cathode and stabilization of the SEI is responsible for the increased coulombic efficiency and capacity retention. Since their debut in 1991, lithium ion batteries (LIB) have become the universal power source for consumer electronics.1 Larger format LIBs such as those needed to power electric vehicles (EVs), an important future market, have amassed considerable interest; however higher specific energy densities are required for larger format LIBs.1,2 The practical way to increase energy density is to employ cathode materials with increased theoretical capacities and/or high discharge plateaus, and thus high energy (HE) or high voltage (HV) cathodes are required in order for LIBs to meet the demands of the EV market.3 While both HE and HV cathodes have been implemented, current research efforts are focused on overcoming the caveats associated with these materials. The oxidative instability of carbonate-based electrolytes is a central limitation for cells with various cathode chemistries operated above 4.4 V. [3][4][5][6][7] In addition to the instability of the electrolyte, cathodes such as nickel-rich layered oxides (LiNi x Mn y Co z O 2 ), lithium-rich layered oxides (0.6 Li 2 MnO 3 • 0.4 Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 ), and HV spinel (LiNi 0.5 Mn 1.5 O 4 ) (LNMO) all suffer from structural instability when operated at high potentials.5-11 While the layered oxides are capable of delivering higher practical energy densities, the lack of cobalt in LNMO alleviates the issues of cost and resource limitations.7 As the higher energy densities associated with HE materials can only be obtained at higher cutoff potentials, oxidation of the electrolyte is a universal problem to both HE and HV cathodes. This work focuses on improving the performance of LNMO/Graphite cells.The capacity fading observed in LNMO/Graphite cells is due to continuous oxidation of the electrolyte and transition...