CONDUCTIVITY OF LITHIUM PERCHLORATE SALT DIS- SOLVED IN DIFFERENT TYPES OF SOLVENT. Tomas Gottwald, Jiří Vondrák Doctoral Degree Programme (III.), FEEC BUT E-mail: xgottw03@stud.feec.vutbr.cz Supervised by: Marie Sedlaříková E-mail: sedlara@feec.vutbr.cz Abstract: Lithium perchlorate (LiClO4) is usable crystalline salt for electrolyte in a rechargeable lithium ion battery (LIB). LiClO4 is an inorganic compound with white color. In the present study the conductivity and the electrochemical behavior of electrolytes based on LiClO4 was examined by using impedance spectroscopy (EIS) and linear voltametry (LSV) measurement at a room tem- perature. The resistance (conductivity) of electrolytes with different molar concentration of LiClO4 dissolved in different types of the solvent was measured in the first part of this work. In the second part electrochemical behavior of two electrolytes with the highest conductivity was measured and evaluated by using a potential window. At the end the sodium perchlorate NaClO4 (for NIBs) was measured in this study too. Keywords: Lithium perchlorate, LiClO4, Sodium perchlorate, NaClO4, Electrolyte, Li-ion battery 1 INTRODUCTION “Li-ion batteries are one of the most successes of modern electrochemistry. These batteries, which became a commercial reality about a decade ago, are conquering the markets with increasingly wider applications. Present challenges are to extend their use to high power and large size appli- cations (e.g., propulsion, EV). The current systems use graphitic carbons as the anode material, LiCoO2 as the major cathode materials, mixtures of alkyl carbonates including ethylene carbonate (a mandatory component for sufficient negative electrode passivation), dimethyl, diethyl, and ethyl- methyl carbonates (EC, DMC, DEC, EMC, respectively), and LiPF6 as the electrolyte solution. The alkyl carbonates were chosen due to their acceptable anodic stability for the 4 V cathodes used in Li-ion batteries, as well as lithiated graphite, together with other properties, such as high po- larity (i.e., good conductivity of their solutions), a reasonable temperature range between freezing and boiling points, sufficiently low toxicity, and accept able safety features. The LiPF6 salt is, to some extent, also a compromise” [1]. “A lithium ion accumulator directly converts electrical energy and chemical energy reversibly by use of lithium ions in a chemical redox reaction. However, with respect to the high energy density in lithium ion cells, there are still challenges regarding safety, high voltage applications, and long- term stability. Therefore, a broad research on electrolytes, cathode, and anode materials is per- formed from numerous scientific groups and companies. Major interest lies in the study of addi- tives to the electrolytes which are applied for a specific and selective purpose. Numerous classes of different compounds are already identified which result in highly selective effects in a Li-ion based cell [2]. In this study a series of six aprotic solvents in a liquid electrolyte mixture based on LiClO4 salt (for LIBs) were studied with respect to the usability in Li-ion cells. Namely, Propylene carbonate (PC), Dimethylformamide (DMF), Diethoxyethane (DEE), Dimethoxyethane (DMC), Ethylene carbonate (EC), Dimethyl carbonate (DMC) and Diethyl carbonate (DEC). This salt (LiClO4) instead of (LiPF6) was chosen because I am looking for the eqvivalent liquid electrolyte to NaClO4 (for 522 NIBs)- Genrally, sodium perchlorate is well soluble in many organic solvents. It the next study will be examinated differences in the intercalation and deintercalation process into the graphite structure used in sodium + graphite system and lithium + graphite system. I have the experience that the oth- er usable salt for NIBs electrolyte like a NaBF4 and NaPF6 are so bad soluble under the conditions known for us. 2 EXPERIMENTAL PART 2.1 MEASURING WORKSTATION AND METHODS For the experimental part a lithium perchlorate (LiClO4) and a sodium perchlorate (NaClO4) salt from company Sigma Aldrich (used as received) were selected. The main electrolyte parameters (conductivity of electrolyte and electrochemical stability) were examined. Experiments were car- ried out in AtmosBag (Sigma Aldrich). On the field of liquid electrolytes was examining behavior of aprotic electrolytes which were prepared from the suitable salt which was dissolved in organic solvent (see table 1). Electrochemical measurements were made on the station BioLogic VMP3 and the results were evaluated by calculation software EC-Lab V10.39. Parameters of measuring meth- ods (see table 2). Solvent Salt Diethoxyethane LiClO4 Dimethoxyethane Dimethylformamide Ethylene carbonate + Diethyl carbonate; 1:1 weight ratio Ethylene carbonate + Dimethyl carbonate; 1:1 weight ratio Propylene carbonate Table 1: List of solvents and salt used. For the measurement of conductivity was used commercial conductivity cell KC 503 from compa- ny THETA ’90. On the beginning the salt LiClO4 was weighed on the laboratory digital weight and put in to the small glass vials. After that, appropriate amount of specific solvent was added. For the mixing was used electromagnetic stirrer. At the end of this process were prepared 4 ml solutions from all types of solvent with LiClO4 and two types with NaClO4 (see table 4) salt in molar concen- trations 0.1 ; 0.25 ; 0.5 ; 0.75 ; 1.00 and 1.25 mol/l (see table 3). EIS LSV Uss = 0 V Ubegin = 0 V Ua = 5 mV Uend = 3,5 V f = 100 kHz – 100 Hz α =0.5 mV/s Note .: potential Uss, Ubegin, Uend measured against counter electrode Table 2: Parameters of the measuring methods EIS and LSV. 523 2.2 DISCUSSION OF MEASURED AND CALCULATED DATA Electric conductivity and potential window were measured. It is possible to see that the highest electric conductivity is globally somewhere in the interval from 0.75 to 1.25 M concentration for all solvents. The best electric conductivity was achieved by DMF solvent, exactly 1.25 M LiClO4 dissolved in DMF. The second best electric conductivity by 1 M LiClO4 electrolyte dissolved in EC/DMC 1:1 weight ratio (see table 3 and picture 1) was measured. The conductivity of NaClO4 liquid electrolyte (see table 4 and picture 2) is similar with the LiClO4 liquid electrolyte. LiClO4 γ [mS/cm] c [mol/l] 0.10 0.25 0.50 0.75 1.00 1.25 PC 1.14 2.32 3.14 3.47 3.42 3.11 DMF 3.33 6.67 10.64 12.50 12.99 13.16 DEE 0.29 0.57 1.21 1.51 1.60 1.73 DME 0.18 0.73 1.82 N1) N1) N1) EC/DMC 1:1 hm. 1.86 3.31 5.00 5.46 5.68 5.59 EC/DEC 1:1 hm. 1.44 2.41 3.34 3.75 3.72 3.11 1) Salt of this concentration is not dissolve. Table 3: Conductivity of liquid electrolytes. NaClO4 γ [mS/cm] c [mol/l] 0.10 0.25 0.50 0.75 1.00 1.25 PC 1.24 2.46 3.50 3.37 3.95 3.97 DMF 3.94 7.58 11.76 14.93 15.87 15.63 Table 4: Conductivity of liquid electrolytes. Picture 1: Liquid electrolytes conductivity depending on LiClO4 concentration. 0 3 6 9 12 15 0,00 0,25 0,50 0,75 1,00 1,25 1,50 γ [mS/cm] c [mol/l] PC DMF DEE DME EC/DMC 1:1 EC/DEC 1:1 524 Picture 2: Liquid electrolytes conductivity depending on NaClO4 concentration. 2.3 POTENTIAL WINDOW For these experiment were mixtured 1.25 M LiClO4/DMF electrolyte and 1 M LiClO4/EC/DMC 1:1 weight ratio electrolyte according to table 3. Experiment was measured in the ECC-ESD cell in AtmosBag with the argon atmosphere. It was 2-electrode measure- ment with the working electrode and counter electrode bouth made of steel. In to this ECC- ESD cell was put in the glass fibre separator (type: Z-4, Papírna Perštejn s.r.o.) and was droped in 100 µl of electrolyte by the pipette. The LSV curves you can see on picture 3 and the potential for Imax = 5µA (see table 5). LiClO4 U [V] 1.25 M DMF 1.11 1 M EC/DMC 1:1 weight ratio 1.54 Ucell [V] 1.25 M DMF 2.22 1 M EC/DMC 1:1 weight ratio 3.08 Note.: potential U was measured for Imax = 5µA Table 5: Decomposition potential of electrolytes. 0 3 6 9 12 15 18 0 0,25 0,5 0,75 1 1,25 1,5 γ [mS/cm] c [mol/l] PC DMF 525 Picture 3: LSV of two chosen electrolytes with highest conductivity. 3 CONCLUSION The best conductivity 13.16 mS/cm was measured by 1.25 M LiClO4/DMF electrolyte. All concen- tration of LiClO4 dissolved in DMF aprotic solvent are much more conductive than others electro- lytes with the same salt but different type of solvent. However, there can be suspiction to presence of the H2O particles in DMF solvent. This can be the reason why is possible to see some cureent flow at low potential (1V) on LSV curve of 1.25 M LiClO4/DMF electrolyte . It will be the subject of the next examination. Further will be proven that the reversible cycling 1.25 M LiClO4/DMF electrolyte with commercially available active materials is possible or isn't. ACKNOWLEDGEMENT This research work has been carried out in the Centre for Research and Utilization of Renewable Energy (CVVOZE). Authors gratefully acknowledge financial support from the Ministry of Edu- cation, Youth and Sports of the Czech Republic under NPU I programme (project No. LO1210) REFERENCES [1] Aubrach, D., Talyosef, Y., Makarovsky, B., Markewich, E., Zinigrad, E., Asraf, L., Granaraj, J., Design of electrolyte solutions for Li and Li-ion batteries: a review. Electrochimica Acta, 2004, 50(2-3), 247-254. DOI: 10.1016/j.electacta.2004.01.090. ISSN 00134686. [2] Hofmann, A., Schulz, M., & Hanemann, T. (2013). Effect of conducting salts in ionic liquid based electrolytes: viscosity, conductivity, and Li-ion cell studies. International Journal of Electrochemical Science, 8, 10170-10189. [3] SHEN, Y., Gang-Hua D., Chuanqi G., Yuhuan T., Guorong W., Xueming Y., Junrong Z. a Kaijun Y., Solvation structure around the Li+ ion in succinonitrile–lithium salt plastic crys- talline electrolytes. Phys. Chem. Chem. Phys [online]. 2016, 18(22), 14867-14873 [cit. 2017- 03-09]. DOI: 10.1039/C6CP02878K. ISSN 1463-9076. [4] Ellis, L., Brian, F., Linda and Nazar, Current Opinion in Solid State and Materials Science, 16(4), 168, (2012). [5] Woo, H.,Seung, L., Yadgarov, R., Rosentsveig, Y., Park, D., Song, R., Tenne and S. Hong, Israel Journal of Chemistry, 55(5), 599, (2015). 0,0 50,0 100,0 150,0 200,0 250,0 0,00 0,50 1,00 1,50 2,00 2,50 3,00 3,50 4,00 4,50 5,00 I [µA] U [V] 1.25M DMF 1M EC/DMC 526