Silica-based solid electrolyte for Li-ion microbatteries

The PhD thesis was embedded in the Energy for Smart Objects (EnSO) project, which is part of the Electronic Components and Systems for European Leadership (ECSEL) Joint Undertaking in collaboration with the European Union’s H2020 Framework Program (H2020/2014-2020) and National Authorities, with the aim to develop Autonomous Micro Energy Sources (AMES) for smart objects. In the framework of the EnSO project, the goal of the thesis was to develop a solid electrolyte for all-solid Li-metal microbatteries as energy storage device in AMES. Lithium metal is the anode material of choice because of its very high theoretical specific capacity of 3861 mAh/g, which is one of the important requirements for miniaturized batteries. However, inhomogeneous lithium depositions known as dendrites, which reduce the life time and can connect both electrodes and create a short circuit, are often observed when using Li-metal as anode. The aim is therefore to develop a solid electrolyte, which presents a high ionic conductivity for the Li ion transport and a high mechanical stability to hinder dendritic growth. Electrolyte solutions based on ionic liquids (ILs) with dissolved lithium salt can be confined into inorganic porous networks forming so called ionogels (IGs), which are investigated as quasi-solid electrolyte materials. In a first step, the synthesis in a one-pot sol-gel process for silica-based ionogels is developed and in a second step tested as quasi-solid electrolyte in Li/LiCoO2 systems. IGs were obtained by a sol-gel reaction between TMOS as silica precursor and TFA as catalyst in PYR13-FSI (IL) and LiTFSI (Li+ source). It was possible to synthesize transparent IG monoliths with gelation times of 2-3 h, which is a suitable time for the IG film preparation on the LCO cathodes. Four IGs with different compositions were prepared and characterized. Two types of silica matrices built of mostly threefold-condensed Si centers could be distinguished: a densely packed structure and an open-porous structure, the latter one corresponding to IG B with the molar ratios IL/TMOS=3, TFA/TMOS=0.3, H2O/TMOS=2.3. The ionic conductivity of the IGs could be linked to the silica matrix structure. Only the IG with the open-pore structure (IG B) has a good ionic conductivity (10−4 S/cm). Equally, the examination of the four IGs as thin film electrolytes in LCO/Li batteries show promising results for batteries containing IG B. However, the capacity lies under the theoretical value (89 mAh/g instead of 136 mAh/g) due to high cell resistance. Therefore, the ionic conductivity of IG B was improved by changing the synthesis process while keeping the composition unaltered. The new IG B∗ has a very good ionic conductivity (10−3 S/cm) but a poor mechanical stability due to a matrix structure of loosely connected silica particles. IG B∗ was not able to hinder dendritic growth. Thus, the PVDF-HFP polymer (20 wt.%) was added to B∗ (B∗-p), which enhanced the mechanical stability and the cyclability of the Li-ion batteries with B∗-p as electrolyte layer. No indication of dendrites was visible in the charge/discharge curve for minimum 30 cycles at C/5. The capacities are low (≤ 80 mAh/g) due to the decreased liquid (IL) to solid (SiO2 + PVDF-HFP) ratio, which results in a lower lithium ion mobility. In order to increase the battery capacity, the silica amount in the IG formulation was reduced, the LiTFSI lithium salt concentration was increased, and the Li+ source was modified by taking IL-based electrolyte solution with different concentrations of LiFSI. Indeed, the capacity increases with decreasing silica amount due to improved ion mobility. The change of the lithium concentration from 1M to 3M and 5M enhanced the capacity. A battery with the combination of the reduced silica amount (0.5 TMOS) and 5M electrolyte solution has a good capacity (> 100 mAh/g) for at least 10 cycles at C/5. The lithium salt LiFSI has a smaller anion than LiTFSI and thus, it can further improve the ion mobility in the IG electrolyte film. All IGs containing LiFSI have a higher ionic conductivity than the corresponding gels with LiTFSI. Overall the battery performance and reproducibility could be greatly improved. Batteries containing a solid electrolyte with 20 wt.% PVDF-HFP and the reduced TMOS amount with a 3M LiFSI solution are able to cycle without the appearance of dendrites for 13 cycles at C/5 followed by 12 cycles at C/2 with a rather good coulombic efficiency around 95%. However, the capacity remains under the theoretical maximum

Silica-based ionogels as a promising solution for all-solid-state Lithium-ion microbatteries

The emerging market of the Internet of Things, smart objects, wearables and others increases the demand for micro energy sources. Rechargeable lithium-ion batteries are a well-known technology for energy storage. However, safety issues and high production costs constrain progress. Electrolyte solutions based on ionic liquids (ILs) with dissolved lithium salts can be confined into inorganic porous networks forming so-called ionogels, which are investigated as solid electrolytes. Ionogels combine low hazard and good ionic conductivity. However, the growth of lithium dendrites may be observed during cycling, which reduce battery lifetime. In this project, we try to prepare a silica-ionogel to prevent dendritic growth by mechanical hindrance. The ionogel composition was studied to obtain a fast gelation and the correlation between the physical properties of the silica matrix and the electrochemical performances of the ionogel was evaluated

Structural influence of silica-based ionogels on their performance as electrolytes for all-solid-state Lithium-ion microbatteries

The emerging market of the Internet of Things, smart objects and others increase the demand for micro energy sources. Rechargeable Li-ion batteries are a well-known technology for energy storage. However, safety issues and high production costs constrain progress. Research on solid electrolytes, such as LiPON, was performed to evade leakage. But LiPON suffers from low ionic conductivity and a cost and time intensive production process. Another approach is the substitution of volatile and flammable organic electrolyte solvents with ionic liquids (IL), which display negligible vapor pressure and wide chemical, electrochemical, and thermal stability. Electrolyte solution based on ILs can be confined into inorganic porous networks forming so-called ionogels (IG), which are investigated as solid electrolyte materials. IGs combine low hazard and good ionic conductivity [1]. Silica-based IGs compatible with Li/LiCoO2 systems were prepared in a one-pot sol-gel process. The composition of the IG precursor solution and the influence of trifluoroacetic acid as catalyst were studied to obtain a fast condensation. Homogeneous and transparent IGs were obtained with a gelation time of less than 4 h. The physical properties of the host matrix were characterized by N2 sorption, Hg porosimetry and SEM. The silica host matrices were 3D networks predominantly built from 3-fold condensed silicon centres. The influence of its structural changes on the electrochemical behaviour was studied by varying the catalyst amount and by increasing the IL amount in the gel. The electrochemical performances of the IG were measured with complex impedance spectroscopy and galvanostatic cycling. Results show that IGs with IL amounts nIL/nSiO2~3 may be successfully used as solid electrolyte in Li/LiCoO2 cells. Batteries were prepared, which cycle more than 100 cycles at a rate of C/2 with no evidence of dendritic growth. Impedance characterization reveals the high internal resistivity of these batteries due to the dense structure of the silica matrix

Silica-based thin film solid-state electrolytes for Lithium-ion microbatteries

The emerging market of the Internet of Things, smart objects, wearables and others increases the demand for micro energy sources. Rechargeable lithium-ion batteries are a well-known technology for energy storage. However, safety issues and high production costs constrain progress. Electrolyte solutions based on ionic liquids (ILs) with dissolved lithium salts can be confined into inorganic porous networks forming so-called ionogels, which are investigated as solid electrolytes [1]. Ionogels combine low hazard and good ionic conductivity. However, the growth of lithium dendrites may be observed during cycling, which reduce battery lifetime. In this project, we try to prepare a silica-ionogel to prevent dendritic growth by mechanical hindrance. The ionogel composition was studied to obtain a fast gelation and the correlation between the physical properties of the silica matrix and the electrochemical performances of the ionogel was evaluated.Energy for smart object

Haemoplasmosis in cats: European guidelines from the ABCD on prevention and management

peer reviewedOverview: Haemoplasmas are haemotropic bacteria that can induce anaemia in a wide range of mammalian species. Infection in cats: Mycoplasma haemofelis is the most pathogenic of the three main feline haemoplasma species known to infect cats. ‘Candidatus Mycoplasma haemominutum’ and ‘Candidatus Mycoplasma turicensis’ are less pathogenic but can result in disease in immunocompromised cats. Male, non-pedigree cats with outdoor access are more likely to be haemoplasma infected, and ‘Candidatus M haemominutum’ is more common in older cats. All three haemoplasma species can be carried asymptomatically. Transmission: The natural mode of transmission of haemoplasma infection is not known, but aggressive interactions and vectors are possibilities. Transmission by blood transfusion can occur and all blood donors should be screened for haemoplasma infection. Diagnosis and treatment: PCR assays are the preferred diagnostic method for haemoplasma infections. Treatment with doxycycline for 2–4 weeks is usually effective for M haemofelis-associated clinical disease (but this may not clear infection). Little information is currently available on the antibiotic responsiveness of ‘Candidatus M haemominutum’ and ‘Candidatus M turicensis’. © 2018, © Published by SAGE on behalf of ISFM and AAFP 2018