WO2020021530A1 - Electrolyte solutions for high voltage lithium-ion cells - Google Patents

Electrolyte solutions for high voltage lithium-ion cells Download PDF

Info

Publication number
WO2020021530A1
WO2020021530A1 PCT/IL2019/050814 IL2019050814W WO2020021530A1 WO 2020021530 A1 WO2020021530 A1 WO 2020021530A1 IL 2019050814 W IL2019050814 W IL 2019050814W WO 2020021530 A1 WO2020021530 A1 WO 2020021530A1
Authority
WO
WIPO (PCT)
Prior art keywords
dmc
epe
lipf
electrolyte
fec
Prior art date
Application number
PCT/IL2019/050814
Other languages
French (fr)
Inventor
Shalom Luski
Doron Aurbach
Ortal YARIV
Original Assignee
Bar-Ilan University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Bar-Ilan University filed Critical Bar-Ilan University
Publication of WO2020021530A1 publication Critical patent/WO2020021530A1/en

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0568—Liquid materials characterised by the solutes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0034—Fluorinated solvents
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to high voltage lithium-ion cells. More particularly, the invention relates to improved electrolyte solutions for rechargeable lithium-ion batteries based on fluorinated solvents.
  • IOBs lithium-ion batteries
  • Improving high voltage batteries by way of enhancing power or energy density may be carried out, for example, by developing improved high voltage cathode materials, such as high-energy nickel cobalt manganese oxide (HENCM) or lithium-manganese-rich (LMR) cathodes.
  • HENCM high-energy nickel cobalt manganese oxide
  • LMR lithium-manganese-rich
  • the present invention relates to an electrolyte solution comprising:
  • the invention further relates to the electrolyte solution as described above wherein the electrolyte is LiPF 6 at a concentration of 1 M.
  • the invention additionally relates to the electrolyte solution according as described above, wherein the solvent is a combination of DMC, FEC and F-EPE (DMC:FEC:F-EPE) or a combination of DMC, F2EC and F-EPE (DMC:F2EC:F-EPE), at a volume ratio of 1:1:1.
  • the solvent is a combination of DMC, FEC and F-EPE (DMC:FEC:F-EPE) or a combination of DMC, F2EC and F-EPE (DMC:F2EC:F-EPE), at a volume ratio of 1:1:1.
  • the invention further relates to the electrolyte solution as described above, wherein the additive is TMSP, TMSPi or any combination thereof, wherein the total concentration of the additive in the electrolyte solution is 1 wt%.
  • the invention relates to an electrolyte solution, selected from the group consisting of:
  • the invention further relates to a battery comprising the electrolyte solutions as described above.
  • DMC dimethyl carbonate
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • FEC fluorinated ethylene carbonate
  • F2EC fluorinated ethylene carbonate
  • F-EPE 1,1,2,2-tetrafluoroethyl 2, 2,3,3,- tetrafluoropropyl ether
  • LiPF 6 lithium hexaflurophosphate
  • TMSP tris(trimethylsilyl)phosphate
  • TMSPi tris(trimethylsilyl)phosphite
  • Fig. 1 shows the temperature (T, °C) dependence of the specific conductivity (K, in millisiemens per meter) of the electrolyte solutions; a (1 M LiPF 6 /DMC:EC:EMC, 3:3:3), b (1 M LiPF 6 /DMC: FEC: F-EPE, 1:1:1), c (1 M LiPF 6 /DMC:FEC:F-EPE, 1:1:1 + 1% TMSP), d (1 M LiPF 6 /DMC:F2EC:F-EPE, 1:1:1), and e (1 M LiPF 6 /DMC:F2EC:F-EPE, 1:1:1 + 1% TMSP).
  • Fig. 2 shows the current density (I) as a function of the cell's potential (E) during 5 cycles (C1-C5) of aluminum current collector, measured by cyclic voltammetry (at a scan rate of 1 mV/s) in 1 M LiPF 6 /DMC:EC:EMC, 3:3:3 (a), 1 M LiPF 6 /DMC:FEC:F-EPE, 1:1:1 + 1% TMSP (b) and 1 M LiPF 6 /DMC:F2EC:F-EPE, 1:1:1 + 1% TMSP (c) solutions.
  • Fig. 3 shows the cycling performance of a Li/Lii. 2 Mn 0.56 Coo.o 8 Nio.i 6 0 2 cell in 1 M LiPF 6 /DMC:FEC:F-EPE, 1:1:1 electrolytes with and without 1% TMSP, between 3.0 and 4.7 V at a current rate of C/5.
  • Fig. 3 shows the cycling performance of a Li/Lii. 2 Mn 0.56 Coo.o 8 Nio.i 6 0 2 cell in 1 M LiPF 6 /DMC:FEC:F-EPE, 1:1:1 electrolytes with and without 1% TMSP, between 3.0 and 4.7 V at a current rate of C/5.
  • Fig. 3 shows the cycling performance of a Li/Lii. 2 Mn 0.56 Coo.o 8 Nio.i 6 0 2 cell in 1 M LiPF 6 /DMC:FEC:F-EPE, 1:1:1 electrolytes with and without 1% TMSP, between 3.0 and 4.7 V at
  • 4A shows the cyclic stability of a Li1.2Mrio.56Coo.08Nio.i6O2 cell in 1 M LiPF 6 /DMC: EC:EMC, 3:3:3 (a), 1 M LiPF 6 /DMC:FEC:F-EPE, 1:1:1 (b) and 1 M LiPF 6 /DMC:F2EC:F-EPE, 1:1:1 (c) electrolyte solutions, between 3.0 and 4.7 V at a current rate of C/5.
  • Fig. 4B shows the cyclic stability of a Li1.2Mn0.56Co0.08Ni0.i6O2 cell in 1 M LiPF 6 /DMC:FEC:F- EPE, 1:1:1 (a) 1 M LiPF 6 /DMC:FEC:F-EPE, 1:1:1 + 1% TMSPi (b), 1 M LiPF 6 /DMC:F2EC:F- EPE, 1:1:1 (c) and 1 M LiPF 6 /DMC:F2EC:F-EPE, 1:1:1 + 1% TMSPi (d) electrolyte solutions, between 3.0 and 4.7 V at a current rate of C/5.
  • Fig. 5 shows the cyclic stability of a full cell (Li1.2Mn0.56Co0.08Ni0.i6O2 vs. graphite) in 1 M LiPF 6 /DMC:FEC:DEC, 1:1:1 (a), 1 M LiPF 6 /DMC:FEC:F-EPE, 1:1:1 + 1% TMSP (b), 1 M LiPF 6 /DMC:F2EC:F-EPE, 1:1:1 (c) and 1 M LiPF 6 /DMC:F2EC:F-EPE, 1:1:1 + 1% TMSP (d) electrolyte solutions, between 3.0 and 4.7 V at a current rate of C/5.
  • Fig. 6A shows the cyclic stability of a Li1.2Mn0.56Co0.08Ni0.i6O2 cell in 1 M LiPF 6 /DMC: EC:EMC, 3:3:3 (a), 1 M LiPF 6 /DMC:FEC:F-EPE, 1:1:1 (b), 1 M LiPF 6 /DMC:FEC:F- EPE, 1:1:1 + 1% TMSPi (c) 1 M LiPF 6 /DMC:F2EC:F-EPE, 1:1:1 (d) and 1 M LiPF 6 /DMC:F2EC:F-EPE, 1:1:1 + 1% TMSPi (e) electrolyte solutions, between 3.0 and 4.7
  • FIG. 6B shows the capacity retention of solutions a-e.
  • Fig. 7A shows the voltage profile during the first cycle of an Lii.2Mno.56Coo.o 8 Nio.i 6 02 cell in 1 M LiPF 6 /DMC:EC: EMC, 3:3:3 (a), 1 M LiPF 6 /DMC:FEC:F-EPE, 1:1:1 (b), 1 M LiPF 6 /DMC:FEC:F-EPE, 1: 1:1 + 1% TMSP (c) 1 M LiPF 6 /DMC:F2EC:F-EPE, 1:1:1 (d) and 1 M LiPF 6 /DMC:F2EC:F-EPE, 1:1:1 + 1% TMSPi (e) electrolyte solutions, between 3.0 and 4.7
  • FIG. 7B shows the voltage profile during to 50 th cycle of Li1.2Mn0.56Co0.08Ni0.i6O2 cell in solutions a-e
  • Fig. 7C shows the voltage profile during to 100 th cycle of Li1.2Mn0.56Co0.08Ni0.i6O2 cell in solutions a-e.
  • FIG. 8A shows Nyquist impedance spectra plot of a Li 1.2 Mn 0.56 Co 0.08 Ni 0 .i 6 O 2 cell in 1 M LiPF 6 /DMC: EC:EMC, 3:3:3 (a), 1 M LiPF 6 /DMC:FEC:F-EPE, 1:1:1 (b) and 1 M LiPF 6 /DMC:FEC:F-EPE, 1: 1:1 + 1% TMSP (c) electrolyte solutions recorded at 3.3 V during the 4 th cycle;
  • Fig. 8B shows Nyquist impedance spectra plot of a Li 1.2 Mn 0.56 Co 0.08 Ni 0 .i 6 O 2 cell in electrolyte solutions a-c recorded at 3.3 V during the 100 th cycle.
  • Fig. 9 shows high resolution scanning electron microscope (HRSEM) images of a pristine lithium-manganese-rich cathode (a) or after 100 cycles in 1 M LiPF 6 /DMC:EC:EMC, 3:3:3 (b), 1 M LiPF 6 /DMC:FEC: F-EPE, 1:1:1 (c), 1 M LiPF 6 /DMC:FEC:F-EPE, 1:1:1 + 1% TMSP (d), 1 M LiPF 6 /DMC:F2EC:F-EPE, 1:1:1 (e) and 1 M LiPF 6 /DMC:F2EC:F-EPE, 1:1:1 + 1% TMSPi (f) electrolyte solutions.
  • HRSEM high resolution scanning electron microscope
  • the electrolyte solution for high voltage lithium-ion cells addresses the need for an electrolyte solution which is compatible with high voltage batteries.
  • the solution is thus a stable electrolyte solution, such that the components of the solution are less subject to decomposition at high voltage compared to components in conventional electrolyte solutions. Due to the increased stability of the components in the solution, capacity fading over multiple charge-discharge cycles of the battery is reduced. Moreover, the electrolyte solution described herein suppresses manganese dissolution from the cathode. Overall, the electrolyte solution of the invention enables the battery to maintain its functionality for a longer period of time compared to a battery employing conventional solutions.
  • an electrolyte solution that is based on non- fluorinated alkyl carbonates as solvents, such as ethylene carbonate (EC), dimethyl carbonate (DMC) and/or ethyl methyl carbonate (EMC) solvents.
  • EC ethylene carbonate
  • DMC dimethyl carbonate
  • EMC ethyl methyl carbonate
  • electrolyte refers to a substance (such as a soluble salt, acid or base), which produces an electrically conducting solution when dissolved in a polar solvent.
  • the dissolved electrolyte dissociates into cations and anions, which disperse uniformly throughout the solvent.
  • an electric potential is applied to such a solution, the cations and anions of the solution are drawn to the oppositely charged electrode, thus producing a current.
  • the electrolyte is lithium hexaflurophosphate (LiPF 6 ) at a concentration of 1 M.
  • Fluorinated alkyl carbonates demonstrate higher oxidation potential compared to non- fluorinated alkyl carbonates, and are thus less subject to decomposition by oxidation at the operating voltage of the cell.
  • the increased stability of fluorinated alkyl carbonates may be attributed to the strong electron-withdrawing effect of the fluorine atom.
  • electrolyte solutions based on fluorinated alkyl carbonates as solvents exhibit reduced irreversible capacity loss and consequently possess increased capacity retention. In other words, electrolyte solutions based on fluorinated alkyl carbonates as solvents maintain their discharge capacity upon a greater number of charge-discharge cycles of the battery when compared to conventional electrolyte solutions.
  • fluorinated alkyl carbonate solvents form a stable solid electrolyte interphase (SEI) film (i.e., passivation layer) on the surface of both the anode and the cathode.
  • SEI solid electrolyte interphase
  • the performance of lithium-ion batteries depends greatly on the stability of the SEI film formed on the surface of the negative electrode during the battery's first charge-discharge cycle.
  • the use of fluorinated alkyl carbonates as solvents in the electrolyte solution improves the performance of the battery and increases its shelf life.
  • the solvent in the electrolyte solution described herein comprises a combination of two fluorinated alkyl carbonates and one non-fluorinated alkyl carbonate.
  • the fluorinated alkyl carbonates used as solvents in the solution described herein is selected from the group consisting of fluorinated ethylene carbonate (FEC), 2- fluorinated ethylene carbonate (F2EC), and 1,1,2,2-tetrafluoroethyl 2, 2,3,3, - tetrafluoropropyl ether (F-EPE).
  • FEC fluorinated ethylene carbonate
  • F2EC 2- fluorinated ethylene carbonate
  • F-EPE 1,1,2,2-tetrafluoroethyl 2, 2,3,3, - tetrafluoropropyl ether
  • the solvent in the electrolyte solution described herein is a combination of DMC, FEC and F-EPE (DMC:FEC:F-EPE) or a combination of DMC, F2EC and F-EPE (DMC:F2EC:F-EPE), each at a volume ratio of 1:1:1.
  • the electrolyte solutions described herein may also comprise at least one additive.
  • the additive is tris(trimethylesilyl) phosphate (TMSP), tris(trimethylsilyl) phosphite (TMSPi) or any combination thereof, wherein the total concentration of the additive in the electrolyte solution is 1 wt%.
  • TMSP tris(trimethylesilyl) phosphate
  • TMSPi tris(trimethylsilyl) phosphite
  • a non-limiting example of a combination of additives is a combination of 0.5% TMSP and 0.5% TMSPi.
  • the stability and performance of an electrolyte solution also depend on the presence of various impurities. For example, the presence of small amounts of water in the solution, leads to the formation of hydrofluoric acid (HF).
  • HF hydrofluoric acid
  • additives such as TMSP and/or TMSPi, prevents the dissolution of Ni and Mn from the cathode, by removing the HF molecules that are present in the electrolyte solution.
  • the cyclic stability of the cathode e.g., Li1.2Mn0.56Co0.08Ni0.i6O2 cathode
  • the improvement is attributed to the formation of a highly stable and protective SEI film on the cathode particles due to the preferential oxidation of the additives.
  • the additives protect the cathode from degradation.
  • the electrolyte solution comprising at least one additive exhibits increased discharge capacity and enhanced cycling performance due to the increased cathode stability and decreased electrolyte decomposition.
  • the electrolyte solution is selected from the group consisting of:
  • the electrolyte solution comprises:
  • a high voltage battery comprising the electrolyte solution described herein.
  • the battery comprising said electrolyte solution exhibits improved performance in terms of increased discharge capacity, enhanced cycling stability and safety.
  • the fluorinated alkyl carbonate solvents used in the electrolyte solution described herein exhibit lower flammability compared to their corresponding non-fluorinated carbonates.
  • the non-flammability of the electrolyte solution renders the battery safe, for example, for transportation applications.
  • the high voltage battery is a lithium-ion battery.
  • the lithium-ion battery is based on Li 1.2 Mn 0.56 Co 0.08 Ni 0 .i 6 O 2 cathode.
  • Solvents, additives and salts used in the preparation of electrolyte solutions according to the inventions are shown in Table 1.
  • a mixture of DMC:EC:EMC, 3:3:3 ratio by weight, containing 1 M LiPF 6 was used as a standard electrolyte solution (reference solution).
  • Cathodes were made by mixing Li1.2Mn0.56Co0.08Ni0.i6O2 (HE5050, Tadiran) as an active material with super P-Li and polyvinylidene fluoride (PVDF) binder (86:6:8 by weight).
  • the active material loading was approximately 10.3 mg/cm 2 .
  • Coin cells 2325 coin cell parts from NRC, Canada were fabricated in an argon filled glove-box (0 2 and water under 1 ppm) with a polypropylene separator (PP2500 Cellgard). Lithium foil (99.9% purity) was used as the counter electrode. Electrochemical measurements
  • the coin cells were cycled 4 formation cycles with a current rate of C/10 between 3.0 and 4.8 V, followed by 100 cycles at a rate of C/5 between 3.0 and 4.7 V.
  • a scanning electron microscope (SEM, FEI Company, Oregon) was used to image the morphologies of the electrodes before and after cycling.
  • the contents of Mn and Ni deposited on Li foils were determined by inductively coupled plasma mass spectrometry (ICP-MS, U.S).
  • Fluorinated alkyl carbonates reduce conductivity of the electrolyte solution
  • the temperature dependence of the specific conductivity (K) of the electrolyte solutions are shown in Fig. 1.
  • the conductivity of LiPF 6 /DMC:EC:EMC solution (curve a in Fig. 1) exhibits higher conductivity than that of LiPF 6 /DMC:FEC:F-EPE solution (curve b in Fig. 1) in the temperature range of -28 °C to 60 °C.
  • the replacement of FEC by F2EC decreases conductivity in the complete temperature range.
  • the addition of TMSP to FEC and F2EC solutions has no effect on the conductivity of the solutions.
  • the anodic behavior of the aluminum current collector in different electrolyte solutions was investigated by cyclic voltammetry (CV) during 5 cycles.
  • CV cyclic voltammetry
  • the native oxide layer on the aluminum is broken down, and the exposed aluminum reacts with fluorine to form a passivation layer of AIF 3 on the aluminum surface.
  • the first polarization cycle has very low current densities evolving above 3.5 V for all the tested solutions. These currents are associated with the degradation of the fluorinated solvents and the products forming a protective layer on the aluminum surface.
  • a negligible current flow was observed between 4.0 and 5.0 V.
  • the peak observed at lower voltage is due to the breakdown of the native oxide layer on the aluminum.
  • the results indicate that mixtures of electrolyte solutions that contain two fluorinated solvents and additives reduce the corrosion current of the aluminum compared to conventional solutions, due to the formation of a stable passivation layer on the aluminum surface.
  • the formation of a stable passivation layer enables better performances and longer shelf life of the battery.
  • the residual discharge capacities were 195 mAh/gr for the electrolyte without TMSP and 249 mAh/gr for the electrolyte with 1% TMSP.
  • the capacity retentions at the 100th cycle were 79.9% without TMSP and 91.1% for 1% TMSP.
  • the cycling performance of the cell containing 1% TMSP is improved, at lease because the presence of TMSP stabilizes the interphase between Li1.2Mn0.56Ni0.13Co0.08lNi0.i6O2 cathode and electrolyte.
  • F2EC-based electrolytes improves anodic stability
  • Figs. 4A and 4B The cycling performance of Li/Lii. 2 Mno.56Coo.o8Nio.i602 cells with FEC- and F2EC-based electrolyte solutions is shown in Figs. 4A and 4B. Higher capacity retention and lower irreversible capacity loss were observed for the cells cycled with the F2EC-based electrolyte solution compared to those of cells cycled with the FEC-based solution. The F2EC-based solution had higher anodic stability compared to that of the FEC-based electrolyte.
  • Fig. 5 shows the cyclic stability of full cell (Li1.2Mn0.56Co0.08Ni0.i6O2 vs. graphite) in FEC- and F2EC-based electrolytes with and without 1% TMSP. When TMSP was added to the electrolytes, the cycling stability of the cathode after 600 cycles was significantly improved.
  • Fluorinated electrolyte solution in the presence of an additive improves cycling performance of lithium-ion batteries
  • TMSPi when TMSPi was added to the F2EC-based electrolyte solutions, the cycling stability of the cathode was significantly enhanced.
  • Fig. 6B shows that the capacity retention after 100 cycles of DMC:F2EC:F-EPE + 1% TMSPi solution was enhanced to 96.7%, suggesting that the electrolyte decomposition was suppressed by using TMSPI. Addition of TMSPi to the FEC-based electrolyte solutions also significantly enhances the cycling stability of the cathode (Fig. 6A).
  • Figs. 7A-7C describe the discharge voltage profiles of Li1.2Mn0.56Co0.08Ni0.i6O2 cell (vs lithium) in FEC- and F2EC- based electrolytes compared to standard electrolyte solution, between 3.0 and 4.7V at C/5.
  • the discharge voltage profiles are similar for all tested solutions. No significate changes were observed in the 50 th cycle (Fig. 7B).
  • the discharge voltage profile degraded severely while using conventional alkyl carbonate solution (EC: EMC: DMC) in contrast to electrolyte solutions which contain fluorinated alkyl carbonates.
  • ICP-MS Inductively coupled plasma mass spectrometry
  • the content of Mn was 0.004 pg per 1 mg of AM for the F2EC-based electrolyte solution without TMSP, and 0.007 pg per 1 mg of AM for the F2EC-based electrolyte solution with 1 wt% TMSP.
  • the content of Mn for the conventional electrolyte solution (DMC:EC:EMC) was 0.18 ppm.
  • electrochemical impedance spectra (EIS) of Li/HENCM cells were recorded at an open circuit voltage (OCV) of 3.3 V during the 4 th and 100 th cycle with an alternating current amplitude of 5 mV in the frequency range of between 100 kHz and 0.01 Hz in FEC-based electrolyte solution with or without 1% TMSP compared to the conventional solution.
  • OCV open circuit voltage
  • TMSP alternating current amplitude of 5 mV in the frequency range of between 100 kHz and 0.01 Hz
  • the Nyquist impedance spectra plot of HENCM cells in the FEC-based electrolyte with or without 1% TMSP consist of two semicicrcles in the 4 th cycle (Fig.
  • Fig. 8A a broad semicircle in the 100 th cycle at the high frequency region followed by a linear spike at the low frequency region
  • Fig. 8B a broad semicircle in the 100 th cycle at the high frequency region followed by a linear spike at the low frequency region
  • the curve is composed of two overlapping semicircles in the high-to-medium frequency range and a straight line in the low frequency range.
  • the semicircle of the SEI film resistance in the high frequency range is attributed to Li ion migration through the interphase film between the electrode and the electrolyte, while the semicircle in the medium frequency range is assigned to charge transfer resistance.
  • the cell containing 1% TMSP exhibits a higher interphase resistance than the cell without TMSP during the 4 th cycle, suggesting that an interphase film with high resistance was formed on the surface of the high-voltage Li1.2Mn0.56Co0.08Ni0.i6O2 cathode.
  • the Nyquist plot for the 100 th cycle shown in Fig. 8B consists of a broad semicircle due to combination of the capacitive and resistive elements of the cell.
  • the cell without TMSP shows a higher interphase resistance than the cell with 1% TMSP during the 100 th cycle, even though the resistance of both cells had increased.
  • the scanning electron microscope (SEM) images of the cathodes after 100 cycles in the fluorinated-based electrolyte solutions with or without TMSP or TMSPi additives, compared to the pristine electrode and conventional electrolyte solution are shown in Fig. 9. While the pristine cathode shows clean HENCM crystals and a carbon black network in between, the cycled cathode using fluorinated-based electrolyte solution without an additive shows a thick surface film on the Li-Mn-rich (LMR) particles as well as on the carbon black network. By contrast, the cycled cathode using fluorinated-based electrolyte solutions with an additive seems almost as clean as the pristine cathode.
  • LMR Li-Mn-rich

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Inorganic Chemistry (AREA)
  • Secondary Cells (AREA)

Abstract

The present invention relates to improved electrolyte solutions for rechargeable lithium-ion batteries based on fluorinated solvents, comprising at least one electrolyte and a solvent comprising at least two fluorinated alkyl carbonate. The improved electrolyte solution may also comprise at least one additive.

Description

ELECTROLYTE SOLUTIONS FOR HIGH VOLTAGE LITHIUM-ION
CELLS
FIELD OF THE INVENTION
The present invention relates to high voltage lithium-ion cells. More particularly, the invention relates to improved electrolyte solutions for rechargeable lithium-ion batteries based on fluorinated solvents.
BACKGROUND OF THE INVENTION
During recent years, the popularity of electric vehicles and hybrid electric vehicles has markedly increased worldwide. However, the main disadvantage of electric vehicles is the limited driving range, due to low battery capacity. Hence, there is an on-going demand for producing improved high voltage batteries, such as lithium-ion batteries (LIBs), in order to increase their capacity. Improving high voltage batteries by way of enhancing power or energy density may be carried out, for example, by developing improved high voltage cathode materials, such as high-energy nickel cobalt manganese oxide (HENCM) or lithium-manganese-rich (LMR) cathodes.
Nonetheless, there are several challenges which may prevent utilization of high voltage cathode materials, such as capacity fading over charge-discharge cycles, manganese dissolution from the cathode and compatibility of electrolyte solutions. In particular, conventional electrolyte solutions, which are based on alkyl carbonates, are highly subjected to decomposition at high potentials of 4.5 V and above, and are therefore not compatible with high voltage cells, which require operation voltage of about 4.6 - 4.8 versus Li/Li+.
It is therefore an object of the present invention to provide an electrolyte solution compatible with high voltage batteries, having superior performances in terms of enhanced stability, reduced manganese dissolution from the cathode and reduced capacity fading upon cycling.
It is another object of the invention to provide a Li-ion battery comprising the electrolyte solution presenting the above-mentioned advantages.
Other objects and advantages of the invention will become apparent as the description proceeds.
SUMMARY OF THE INVENTION
The present invention relates to an electrolyte solution comprising:
(a) at least one electrolyte;
(b) a solvent comprising at least two fluorinated alkyl carbonate; and optionally
(c) at least one additive.
The invention further relates to the electrolyte solution as described above wherein the electrolyte is LiPF6 at a concentration of 1 M.
The invention additionally relates to the electrolyte solution according as described above, wherein the solvent is a combination of DMC, FEC and F-EPE (DMC:FEC:F-EPE) or a combination of DMC, F2EC and F-EPE (DMC:F2EC:F-EPE), at a volume ratio of 1:1:1.
The invention further relates to the electrolyte solution as described above, wherein the additive is TMSP, TMSPi or any combination thereof, wherein the total concentration of the additive in the electrolyte solution is 1 wt%.
Thus, the invention relates to an electrolyte solution, selected from the group consisting of:
1 M LiPF6 in DMC:FEC:F-EPE at a volume ratio of 1:1:1;
1 M LiPF6 in DMC:FEC:F-EPE at a volume ratio of 1:1:1 and 1 wt% TMSP; 1 M Li PF6 in DMC:FEC:F-EPE at a volume ratio of 1:1:1 and 1 wt% TMSPi;
1 M LiPF6 in DMC:F2EC:F-EPE at a volume ratio of 1:1:1;
1 M LiPF6 in DMC:F2EC:F-EPE at a volume ratio of 1:1:1 and 1 wt% TMSP; and
1 M LiPF6 in DMC:F2EC:F-EPE at a volume ratio of 1:1:1 and 1 wt% TMSPi.
The invention further relates to a battery comprising the electrolyte solutions as described above.
BRIEF DESCRIPTION OF THE DRAWINGS
Abbreviations used in the drawings: DMC (dimethyl carbonate); EC (ethylene carbonate); EMC (ethyl methyl carbonate); FEC (fluorinated ethylene carbonate); F2EC (2-fluorinated ethylene carbonate); F-EPE (1,1,2,2-tetrafluoroethyl 2, 2,3,3,- tetrafluoropropyl ether); LiPF6 (lithium hexaflurophosphate); TMSP (tris(trimethylsilyl)phosphate); TMSPi (tris(trimethylsilyl)phosphite).
Fig. 1 shows the temperature (T, °C) dependence of the specific conductivity (K, in millisiemens per meter) of the electrolyte solutions; a (1 M LiPF6/DMC:EC:EMC, 3:3:3), b (1 M LiPF6/DMC: FEC: F-EPE, 1:1:1), c (1 M LiPF6/DMC:FEC:F-EPE, 1:1:1 + 1% TMSP), d (1 M LiPF6/DMC:F2EC:F-EPE, 1:1:1), and e (1 M LiPF6/DMC:F2EC:F-EPE, 1:1:1 + 1% TMSP).
Fig. 2 shows the current density (I) as a function of the cell's potential (E) during 5 cycles (C1-C5) of aluminum current collector, measured by cyclic voltammetry (at a scan rate of 1 mV/s) in 1 M LiPF6/DMC:EC:EMC, 3:3:3 (a), 1 M LiPF6/DMC:FEC:F-EPE, 1:1:1 + 1% TMSP (b) and 1 M LiPF6/DMC:F2EC:F-EPE, 1:1:1 + 1% TMSP (c) solutions.
Fig. 3 shows the cycling performance of a Li/Lii.2Mn0.56Coo.o8Nio.i602 cell in 1 M LiPF6/DMC:FEC:F-EPE, 1:1:1 electrolytes with and without 1% TMSP, between 3.0 and 4.7 V at a current rate of C/5. Fig. 4A shows the cyclic stability of a Li1.2Mrio.56Coo.08Nio.i6O2 cell in 1 M LiPF6/DMC: EC:EMC, 3:3:3 (a), 1 M LiPF6/DMC:FEC:F-EPE, 1:1:1 (b) and 1 M LiPF6/DMC:F2EC:F-EPE, 1:1:1 (c) electrolyte solutions, between 3.0 and 4.7 V at a current rate of C/5.
Fig. 4B shows the cyclic stability of a Li1.2Mn0.56Co0.08Ni0.i6O2 cell in 1 M LiPF6/DMC:FEC:F- EPE, 1:1:1 (a) 1 M LiPF6/DMC:FEC:F-EPE, 1:1:1 + 1% TMSPi (b), 1 M LiPF6/DMC:F2EC:F- EPE, 1:1:1 (c) and 1 M LiPF6/DMC:F2EC:F-EPE, 1:1:1 + 1% TMSPi (d) electrolyte solutions, between 3.0 and 4.7 V at a current rate of C/5.
Fig. 5 shows the cyclic stability of a full cell (Li1.2Mn0.56Co0.08Ni0.i6O2 vs. graphite) in 1 M LiPF6/DMC:FEC:DEC, 1:1:1 (a), 1 M LiPF6/DMC:FEC:F-EPE, 1:1:1 + 1% TMSP (b), 1 M LiPF6/DMC:F2EC:F-EPE, 1:1:1 (c) and 1 M LiPF6/DMC:F2EC:F-EPE, 1:1:1 + 1% TMSP (d) electrolyte solutions, between 3.0 and 4.7 V at a current rate of C/5.
Fig. 6A shows the cyclic stability of a Li1.2Mn0.56Co0.08Ni0.i6O2 cell in 1 M LiPF6/DMC: EC:EMC, 3:3:3 (a), 1 M LiPF6/DMC:FEC:F-EPE, 1:1:1 (b), 1 M LiPF6/DMC:FEC:F- EPE, 1:1:1 + 1% TMSPi (c) 1 M LiPF6/DMC:F2EC:F-EPE, 1:1:1 (d) and 1 M LiPF6/DMC:F2EC:F-EPE, 1:1:1 + 1% TMSPi (e) electrolyte solutions, between 3.0 and 4.7
V at a current rate of C/5; Fig. 6B shows the capacity retention of solutions a-e.
Fig. 7A shows the voltage profile during the first cycle of an Lii.2Mno.56Coo.o8Nio.i602 cell in 1 M LiPF6/DMC:EC: EMC, 3:3:3 (a), 1 M LiPF6/DMC:FEC:F-EPE, 1:1:1 (b), 1 M LiPF6/DMC:FEC:F-EPE, 1: 1:1 + 1% TMSP (c) 1 M LiPF6/DMC:F2EC:F-EPE, 1:1:1 (d) and 1 M LiPF6/DMC:F2EC:F-EPE, 1:1:1 + 1% TMSPi (e) electrolyte solutions, between 3.0 and 4.7
V at a current rate of C/5; Fig. 7B shows the voltage profile during to 50th cycle of Li1.2Mn0.56Co0.08Ni0.i6O2 cell in solutions a-e; Fig. 7C shows the voltage profile during to 100th cycle of Li1.2Mn0.56Co0.08Ni0.i6O2 cell in solutions a-e. Fig. 8A shows Nyquist impedance spectra plot of a Li1.2Mn0.56Co0.08Ni0.i6O2 cell in 1 M LiPF6/DMC: EC:EMC, 3:3:3 (a), 1 M LiPF6/DMC:FEC:F-EPE, 1:1:1 (b) and 1 M LiPF6/DMC:FEC:F-EPE, 1: 1:1 + 1% TMSP (c) electrolyte solutions recorded at 3.3 V during the 4th cycle; Fig. 8B shows Nyquist impedance spectra plot of a Li1.2Mn0.56Co0.08Ni0.i6O2 cell in electrolyte solutions a-c recorded at 3.3 V during the 100th cycle.
Fig. 9 shows high resolution scanning electron microscope (HRSEM) images of a pristine lithium-manganese-rich cathode (a) or after 100 cycles in 1 M LiPF6/DMC:EC:EMC, 3:3:3 (b), 1 M LiPF6/DMC:FEC: F-EPE, 1:1:1 (c), 1 M LiPF6/DMC:FEC:F-EPE, 1:1:1 + 1% TMSP (d), 1 M LiPF6/DMC:F2EC:F-EPE, 1:1:1 (e) and 1 M LiPF6/DMC:F2EC:F-EPE, 1:1:1 + 1% TMSPi (f) electrolyte solutions.
DETAILED DESCRIPTION OF THE INVENTION
The electrolyte solution for high voltage lithium-ion cells according to the present invention addresses the need for an electrolyte solution which is compatible with high voltage batteries. The solution is thus a stable electrolyte solution, such that the components of the solution are less subject to decomposition at high voltage compared to components in conventional electrolyte solutions. Due to the increased stability of the components in the solution, capacity fading over multiple charge-discharge cycles of the battery is reduced. Moreover, the electrolyte solution described herein suppresses manganese dissolution from the cathode. Overall, the electrolyte solution of the invention enables the battery to maintain its functionality for a longer period of time compared to a battery employing conventional solutions.
The terms "conventional electrolyte solution" and "standard electrolyte solution" as used interchangeably herein refer to an electrolyte solution that is based on non- fluorinated alkyl carbonates as solvents, such as ethylene carbonate (EC), dimethyl carbonate (DMC) and/or ethyl methyl carbonate (EMC) solvents. In one aspect of the invention, there is provided an electrolyte solution comprising:
(a) at least one electrolyte;
(b) a solvent comprising at least two fluorinated alkyl carbonates; and optionally
(c) at least one additive.
The term "electrolyte" as used herein refers to a substance (such as a soluble salt, acid or base), which produces an electrically conducting solution when dissolved in a polar solvent. The dissolved electrolyte dissociates into cations and anions, which disperse uniformly throughout the solvent. When an electric potential is applied to such a solution, the cations and anions of the solution are drawn to the oppositely charged electrode, thus producing a current.
According to a specific embodiment of the invention, the electrolyte is lithium hexaflurophosphate (LiPF6) at a concentration of 1 M.
Fluorinated alkyl carbonates demonstrate higher oxidation potential compared to non- fluorinated alkyl carbonates, and are thus less subject to decomposition by oxidation at the operating voltage of the cell. The increased stability of fluorinated alkyl carbonates may be attributed to the strong electron-withdrawing effect of the fluorine atom. Due to their enhanced stability, electrolyte solutions based on fluorinated alkyl carbonates as solvents exhibit reduced irreversible capacity loss and consequently possess increased capacity retention. In other words, electrolyte solutions based on fluorinated alkyl carbonates as solvents maintain their discharge capacity upon a greater number of charge-discharge cycles of the battery when compared to conventional electrolyte solutions.
Furthermore, fluorinated alkyl carbonate solvents form a stable solid electrolyte interphase (SEI) film (i.e., passivation layer) on the surface of both the anode and the cathode. The performance of lithium-ion batteries depends greatly on the stability of the SEI film formed on the surface of the negative electrode during the battery's first charge-discharge cycle. Hence, the use of fluorinated alkyl carbonates as solvents in the electrolyte solution improves the performance of the battery and increases its shelf life.
In some embodiments, the solvent in the electrolyte solution described herein comprises a combination of two fluorinated alkyl carbonates and one non-fluorinated alkyl carbonate.
The fluorinated alkyl carbonates used as solvents in the solution described herein is selected from the group consisting of fluorinated ethylene carbonate (FEC), 2- fluorinated ethylene carbonate (F2EC), and 1,1,2,2-tetrafluoroethyl 2, 2,3,3, - tetrafluoropropyl ether (F-EPE).
In a specific embodiment, the solvent in the electrolyte solution described herein is a combination of DMC, FEC and F-EPE (DMC:FEC:F-EPE) or a combination of DMC, F2EC and F-EPE (DMC:F2EC:F-EPE), each at a volume ratio of 1:1:1.
The electrolyte solutions described herein may also comprise at least one additive.
In a specific embodiment of the invention, the additive is tris(trimethylesilyl) phosphate (TMSP), tris(trimethylsilyl) phosphite (TMSPi) or any combination thereof, wherein the total concentration of the additive in the electrolyte solution is 1 wt%. A non-limiting example of a combination of additives is a combination of 0.5% TMSP and 0.5% TMSPi.
The stability and performance of an electrolyte solution also depend on the presence of various impurities. For example, the presence of small amounts of water in the solution, leads to the formation of hydrofluoric acid (HF). The use of additives, such as TMSP and/or TMSPi, prevents the dissolution of Ni and Mn from the cathode, by removing the HF molecules that are present in the electrolyte solution. By introducing additives into fluorinated electrolyte solutions, the cyclic stability of the cathode (e.g., Li1.2Mn0.56Co0.08Ni0.i6O2 cathode) is significantly enhanced. The improvement is attributed to the formation of a highly stable and protective SEI film on the cathode particles due to the preferential oxidation of the additives. Thus, the additives protect the cathode from degradation.
Moreover, the electrolyte solution comprising at least one additive exhibits increased discharge capacity and enhanced cycling performance due to the increased cathode stability and decreased electrolyte decomposition.
According to a specific embodiment of the invention, the electrolyte solution is selected from the group consisting of:
1 M LiPF6 in DMC:FEC:F-EPE at a volume ratio of 1:1:1;
- 1 M LiPFg in DMC:FEC:F-EPE at a volume ratio of 1:1:1 and 1 wt% TMSP;
1 M LiPF6 in DMC:FEC:F-EPE at a volume ratio of 1:1:1 and 1 wt% TMSPi;
- 1 M LiPFg in DMC:F2EC:F-EPE at a volume ratio of 1:1:1;
1 M LiPFg in DMC:F2EC:F-EPE at a volume ratio of 1:1:1 and 1 wt% TMSP; and
- 1 M LiPFg in DMC:F2EC:F-EPE at a volume ratio of 1:1:1 and 1 wt% TMSPi.
According to a further specific embodiment of the invention, the electrolyte solution comprises:
(a) 1 M LiPFg;
(b) DMC:F2EC:F-EPE, at a volume ratio of 1:1:1; and
(c) 1 wt% TMSP.
This specific electrolyte solution provided in a HENCM Graphite cell (full lithium-ion cell) demonstrates breakthrough results regarding prevention of manganese dissolution from the cathode and number of cycles. In particular, only 25% capacity fading was observed after 1000 charge-discharge cycles.
Thus, the extraordinary electrochemical stability of this electrolyte solution makes it a preferable candidate for other high voltage batteries.
In another aspect of the invention, there is provided a high voltage battery comprising the electrolyte solution described herein.
The battery comprising said electrolyte solution exhibits improved performance in terms of increased discharge capacity, enhanced cycling stability and safety.
The fluorinated alkyl carbonate solvents used in the electrolyte solution described herein exhibit lower flammability compared to their corresponding non-fluorinated carbonates. The non-flammability of the electrolyte solution renders the battery safe, for example, for transportation applications.
In one embodiment of the invention, the high voltage battery is a lithium-ion battery.
According to a specific embodiment of the invention, the lithium-ion battery is based on Li1.2Mn0.56Co0.08Ni0.i6O2 cathode.
The invention will now be described with reference to specific examples and materials. The following examples are representative of techniques employed by the inventors in carrying out aspects of the present invention. It should be appreciated that while these techniques are exemplary of specific embodiments for the practice of the invention, those of skill in the art, in light of the present disclosure, will recognize that numerous modifications can be made without departing from the spirit and intended scope of the invention. EXAMPLES
Materials and methods
Preparation of electrolyte solutions based on fluorinated solvents
Solvents, additives and salts used in the preparation of electrolyte solutions according to the inventions are shown in Table 1.
Table 1. Structural formulas of solvents, additives and salts
Figure imgf000011_0001
Figure imgf000012_0001
The following six different electrolyte solutions were prepared:
1. a mixture of DMC:FEC:F-EPE, 1:1:1 ratio by volume, containing 1 M LiPF6;
2. a mixture of DMC:FEC:F-EPE, 1:1:1 ratio by volume, containing 1 M LiPF6 with 1 wt% TMSP;
3. a mixture of DMC:FEC:F-EPE, 1:1:1 ratio by volume, containing 1 M LiPF6 with 1 wt% TMSPi;
4. a mixture of DMC:F2EC:F-EPE, 1:1:1 ratio by volume, containing 1 M LiPF6;
5. a mixture of DMC:F2EC:F-EPE, 1:1:1 ratio by volume, containing 1 M LiPF6 with 1 wt% TMSP; and
6. a mixture of DMC:F2EC:F-EPE, 1:1:1 ratio by volume, containing 1 M LiPF6 with 1 wt% TMSPi.
A mixture of DMC:EC:EMC, 3:3:3 ratio by weight, containing 1 M LiPF6 was used as a standard electrolyte solution (reference solution).
Fabrication of cathodes electrodes and coin cells
Cathodes were made by mixing Li1.2Mn0.56Co0.08Ni0.i6O2 (HE5050, Tadiran) as an active material with super P-Li and polyvinylidene fluoride (PVDF) binder (86:6:8 by weight). The active material loading was approximately 10.3 mg/cm2.
Coin cells (2325 coin cell parts from NRC, Canada) were fabricated in an argon filled glove-box (02 and water under 1 ppm) with a polypropylene separator (PP2500 Cellgard). Lithium foil (99.9% purity) was used as the counter electrode. Electrochemical measurements
All the electrochemical measurements were performed at 30 °C in galvanostatic (constant current) mode experiments, using multi-channel computerized analyzers from Arbin and Maccor Inc, USA. The test voltage ranged from 3.0 to 4.8 V for the HENCM/Li cell.
The coin cells were cycled 4 formation cycles with a current rate of C/10 between 3.0 and 4.8 V, followed by 100 cycles at a rate of C/5 between 3.0 and 4.7 V.
Analytical measurements
A scanning electron microscope (SEM, FEI Company, Oregon) was used to image the morphologies of the electrodes before and after cycling. The contents of Mn and Ni deposited on Li foils were determined by inductively coupled plasma mass spectrometry (ICP-MS, U.S).
Example 1:
Fluorinated alkyl carbonates reduce conductivity of the electrolyte solution
The temperature dependence of the specific conductivity (K) of the electrolyte solutions are shown in Fig. 1. The conductivity of LiPF6/DMC:EC:EMC solution (curve a in Fig. 1) exhibits higher conductivity than that of LiPF6/DMC:FEC:F-EPE solution (curve b in Fig. 1) in the temperature range of -28 °C to 60 °C. The replacement of FEC by F2EC (curve d in Fig. 1) decreases conductivity in the complete temperature range. The addition of TMSP to FEC and F2EC solutions (curves c and e in Fig. 1, respectively) has no effect on the conductivity of the solutions.
Example 2:
Addition of F-EPE as a third fluorinated solvent reduces current density
The anodic behavior of the aluminum current collector in different electrolyte solutions was investigated by cyclic voltammetry (CV) during 5 cycles. During the first cycle of the cell, the native oxide layer on the aluminum is broken down, and the exposed aluminum reacts with fluorine to form a passivation layer of AIF3 on the aluminum surface. As shown in Tables 2 and 3, as well as in Fig. 2, the first polarization cycle has very low current densities evolving above 3.5 V for all the tested solutions. These currents are associated with the degradation of the fluorinated solvents and the products forming a protective layer on the aluminum surface. In the following cycles, a negligible current flow was observed between 4.0 and 5.0 V. The peak observed at lower voltage is due to the breakdown of the native oxide layer on the aluminum. The results indicate that mixtures of electrolyte solutions that contain two fluorinated solvents and additives reduce the corrosion current of the aluminum compared to conventional solutions, due to the formation of a stable passivation layer on the aluminum surface. The formation of a stable passivation layer enables better performances and longer shelf life of the battery.
Table 2. Current density of 5 electrolyte solutions at a cell's potential of 4.5 V during 5 cycles
Figure imgf000014_0001
Table 3. Current density of 5 electrolyte solutions at a cell's potential of 5 V during 5 cycles
Figure imgf000014_0002
Figure imgf000015_0001
Example 3:
Addition of TMSP improves cycling performance of lithium-ion batteries in coin cell
The cycling performance of Li/Ui.2Mn0.56Coo.o8Nio.i602 cells containing the electrolytes 1 M Li PF6 in DMC:FECF-EPE (1:1:1 by volume) with and without 1% TMSP is shown in Fig. 3. All the cells with different electrolytes were first subjected to four formation cycles with a current rate of C/10. The following cycles were cycled at a current rate of C/5. At the fifth cycle, the discharge capacity of the cell without TMSP was 224 mAh/gr and the discharge capacity of the cell with TMSP was 274 mAh/gr. Moreover, at the 100th cycle, the residual discharge capacities were 195 mAh/gr for the electrolyte without TMSP and 249 mAh/gr for the electrolyte with 1% TMSP. The capacity retentions at the 100th cycle were 79.9% without TMSP and 91.1% for 1% TMSP. As compared with the electrolyte without TMSP, the cycling performance of the cell containing 1% TMSP is improved, at lease because the presence of TMSP stabilizes the interphase between Li1.2Mn0.56Ni0.13Co0.08lNi0.i6O2 cathode and electrolyte.
Example 4:
F2EC-based electrolytes improves anodic stability
The cycling performance of Li/Lii.2Mno.56Coo.o8Nio.i602 cells with FEC- and F2EC-based electrolyte solutions is shown in Figs. 4A and 4B. Higher capacity retention and lower irreversible capacity loss were observed for the cells cycled with the F2EC-based electrolyte solution compared to those of cells cycled with the FEC-based solution. The F2EC-based solution had higher anodic stability compared to that of the FEC-based electrolyte. Fig. 5 shows the cyclic stability of full cell (Li1.2Mn0.56Co0.08Ni0.i6O2 vs. graphite) in FEC- and F2EC-based electrolytes with and without 1% TMSP. When TMSP was added to the electrolytes, the cycling stability of the cathode after 600 cycles was significantly improved.
Example 5:
Fluorinated electrolyte solution in the presence of an additive improves cycling performance of lithium-ion batteries
As shown in Fig. 6A, when TMSPi was added to the F2EC-based electrolyte solutions, the cycling stability of the cathode was significantly enhanced. Fig. 6B shows that the capacity retention after 100 cycles of DMC:F2EC:F-EPE + 1% TMSPi solution was enhanced to 96.7%, suggesting that the electrolyte decomposition was suppressed by using TMSPI. Addition of TMSPi to the FEC-based electrolyte solutions also significantly enhances the cycling stability of the cathode (Fig. 6A). The capacity retention after 100 cycles of DMC:FEC:F-EPE solution was enhanced compared to non-fluorinated electrolytes to 79.9%, while addition of 1% TMSPi further enhanced the capacity retention to 91.06%. These results indicate that a protective solid electrolyte interface (SEI) film is formed due to the preferential oxidation of TMSPi. Subsequently, the SEI film suppresses the successive electrolyte decomposition and protects Li1.2Mn0.56Co0.08Ni0.i6O2 from degradation.
Figs. 7A-7C describe the discharge voltage profiles of Li1.2Mn0.56Co0.08Ni0.i6O2 cell (vs lithium) in FEC- and F2EC- based electrolytes compared to standard electrolyte solution, between 3.0 and 4.7V at C/5. During the first cycle (Fig. 7A) the discharge voltage profiles are similar for all tested solutions. No significate changes were observed in the 50th cycle (Fig. 7B). However, after 100 cycles (Fig. 7C), the discharge voltage profile degraded severely while using conventional alkyl carbonate solution (EC: EMC: DMC) in contrast to electrolyte solutions which contain fluorinated alkyl carbonates. The results are in accordance with the inferior electrochemical stability of non-fluorinated alkyl carbonates, such as EC (ethylene carbonate), EMC (ethyl methyl carbonate) and DMC (dimethyl carbonate) compared to fluorinated alkyl carbonates.
Inductively coupled plasma mass spectrometry (ICP-MS) was carried out to further analyze the chemical composition of the slurry on the lithium metallic anode after cycling for 100 cycles. The two lithium electrodes cycled in each of the tested electrolyte solutions were first dissolved in 10 ml deionized water. The content of Co, Mn and Ni in the deionized water was then investigated. As shown in Table 4, the content of Mn was 0.01 pg per 1 mg of active material of the electrode (AM) for the FEC-based electrolyte solution without TMSP. The content of Mn for the FEC-based electrolyte solution with 1 wt% TMSP was 0.013 pg per 1 mg of AM. The content of Mn was 0.004 pg per 1 mg of AM for the F2EC-based electrolyte solution without TMSP, and 0.007 pg per 1 mg of AM for the F2EC-based electrolyte solution with 1 wt% TMSP. The content of Mn for the conventional electrolyte solution (DMC:EC:EMC) was 0.18 ppm. These results indicate that TMSP prevents the dissolution of Mn and Ni from the cathode by removing HF molecules from the electrolyte at a high charge potential of 4.8 V. Moreover, the use of electrolyte solutions based on fluorinated solvents compared the conventional electrolyte solution also prevents dissolution of Mn and Ni from the cathode.
Table 4. Mn, Co and Ni content in 10 ml deionized water after 100 cycles of lithium electrodes
Figure imgf000017_0001
Figure imgf000018_0001
In order to understand the effect of electrolyte additives, electrochemical impedance spectra (EIS) of Li/HENCM cells were recorded at an open circuit voltage (OCV) of 3.3 V during the 4th and 100th cycle with an alternating current amplitude of 5 mV in the frequency range of between 100 kHz and 0.01 Hz in FEC-based electrolyte solution with or without 1% TMSP compared to the conventional solution. The Nyquist impedance spectra plot of HENCM cells in the FEC-based electrolyte with or without 1% TMSP consist of two semicicrcles in the 4th cycle (Fig. 8A) and a broad semicircle in the 100th cycle at the high frequency region followed by a linear spike at the low frequency region (Fig. 8B). As shown in Fig. 8B, the curve is composed of two overlapping semicircles in the high-to-medium frequency range and a straight line in the low frequency range. The semicircle of the SEI film resistance in the high frequency range is attributed to Li ion migration through the interphase film between the electrode and the electrolyte, while the semicircle in the medium frequency range is assigned to charge transfer resistance. Fig. 8A clearly shows that the cell containing 1% TMSP exhibits a higher interphase resistance than the cell without TMSP during the 4th cycle, suggesting that an interphase film with high resistance was formed on the surface of the high-voltage Li1.2Mn0.56Co0.08Ni0.i6O2 cathode. On the contrary, the Nyquist plot for the 100th cycle shown in Fig. 8B consists of a broad semicircle due to combination of the capacitive and resistive elements of the cell. The cell without TMSP shows a higher interphase resistance than the cell with 1% TMSP during the 100th cycle, even though the resistance of both cells had increased. The scanning electron microscope (SEM) images of the cathodes after 100 cycles in the fluorinated-based electrolyte solutions with or without TMSP or TMSPi additives, compared to the pristine electrode and conventional electrolyte solution are shown in Fig. 9. While the pristine cathode shows clean HENCM crystals and a carbon black network in between, the cycled cathode using fluorinated-based electrolyte solution without an additive shows a thick surface film on the Li-Mn-rich (LMR) particles as well as on the carbon black network. By contrast, the cycled cathode using fluorinated-based electrolyte solutions with an additive seems almost as clean as the pristine cathode. These results clearly demonstrate the stability of TMSP against oxidation on the cathode surface. Moreover, high resolution SEM (HRSEM) images of the HENCM electrode cycled in the conventional electrolyte solution provide clear visual evidence for the mechanism of their capacity fading.

Claims

1. An electrolyte solution comprising:
(a) at least one electrolyte;
(b) a solvent comprising at least two fluorinated alkyl carbonate; and optionally
(c) at least one additive.
2. The electrolyte solution according to claim 1, wherein the electrolyte is LiPF6 at a concentration of 1 M.
3. The electrolyte solution according to claim 1 or 2, wherein the solvent is a combination of DMC, FEC and F-EPE (DMC:FEC:F-EPE) or a combination of DMC, F2EC and F-EPE (DMC:F2EC:F-EPE), at a volume ratio of 1:1:1.
4. The electrolyte solution according to any one of claims 1-3, wherein the additive is TMSP, TMSPi or any combination thereof, wherein the total concentration of the additive in the electrolyte solution is 1 wt .
5. The electrolyte solution according to claim 1, selected from the group consisting of:
1 M LiPF6 in DMC:FEC:F-EPE at a volume ratio of 1:1:1;
1 M LiPF6 in DMC:FEC:F-EPE at a volume ratio of 1:1:1 and 1 wt% TMSP;
1 M LiPF6 in DMC:FEC:F-EPE at a volume ratio of 1:1:1 and 1 wt% TMSPi;
1 M LiPF6 in DMC:F2EC:F-EPE at a volume ratio of 1:1:1;
1 M LiPF6 in DMC:F2EC:F-EPE at a volume ratio of 1:1:1 and 1 wt% TMSP; and 1 M LiPF6 in DMC:F2EC:F-EPE at a volume ratio of 1:1:1 and 1 wt% TMSPi.
6. A battery comprising the electrolyte solution according to any one of claims 1-5.
PCT/IL2019/050814 2018-07-23 2019-07-21 Electrolyte solutions for high voltage lithium-ion cells WO2020021530A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IL260745A IL260745A (en) 2018-07-23 2018-07-23 Electrolyte solutions for high voltage lithium-ion cells
IL260745 2018-07-23

Publications (1)

Publication Number Publication Date
WO2020021530A1 true WO2020021530A1 (en) 2020-01-30

Family

ID=66624526

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IL2019/050814 WO2020021530A1 (en) 2018-07-23 2019-07-21 Electrolyte solutions for high voltage lithium-ion cells

Country Status (2)

Country Link
IL (1) IL260745A (en)
WO (1) WO2020021530A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111326799A (en) * 2020-03-09 2020-06-23 天津中电新能源研究院有限公司 Flame-retardant high-voltage electrolyte for lithium ion battery and preparation method thereof
CN112234251A (en) * 2020-09-28 2021-01-15 中国电子科技集团公司第十八研究所 Wide-temperature-range organic electrolyte applied to lithium battery and preparation method thereof

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7494746B2 (en) * 2006-11-20 2009-02-24 Samsung Sdi Co., Ltd. Electrolyte for rechargeable lithium battery, and rechargeable lithium battery including same
US20140302401A1 (en) * 2013-04-04 2014-10-09 E I Du Pont De Nemours And Company Nonaqueous electrolyte compositions
US20160118690A1 (en) * 2013-05-02 2016-04-28 Solvay Fluor Gmbh Fluorinated carbonates as solvent for lithium sulfonimide-based electrolytes

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7494746B2 (en) * 2006-11-20 2009-02-24 Samsung Sdi Co., Ltd. Electrolyte for rechargeable lithium battery, and rechargeable lithium battery including same
US20140302401A1 (en) * 2013-04-04 2014-10-09 E I Du Pont De Nemours And Company Nonaqueous electrolyte compositions
US20160118690A1 (en) * 2013-05-02 2016-04-28 Solvay Fluor Gmbh Fluorinated carbonates as solvent for lithium sulfonimide-based electrolytes

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
CHOON-KI KIM ET AL.: "Synergistic Effect of Partially Fluorinated Ether and Fluoroethylene Carbonate for High- Voltage Lithium-Ion Batteries with Rapid Chargeability and Dischargeability", ACS APPL. MATER. INTERFACES, vol. 9, no. 50, 28 November 2017 (2017-11-28), pages 44161 - 44172, XP055681118 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111326799A (en) * 2020-03-09 2020-06-23 天津中电新能源研究院有限公司 Flame-retardant high-voltage electrolyte for lithium ion battery and preparation method thereof
CN112234251A (en) * 2020-09-28 2021-01-15 中国电子科技集团公司第十八研究所 Wide-temperature-range organic electrolyte applied to lithium battery and preparation method thereof

Also Published As

Publication number Publication date
IL260745A (en) 2019-01-31

Similar Documents

Publication Publication Date Title
KR102004069B1 (en) Lithium metal oxide cathode powder for high-voltage lithium-ion batteries
JP6085456B2 (en) Electrolyte for lithium ion secondary battery and lithium ion secondary battery
JP5306749B2 (en) Electrochemical devices
KR101798259B1 (en) Lithium secondary battery using ionic liquid
JP5754358B2 (en) Nonaqueous electrolyte secondary battery and manufacturing method thereof
US10347942B2 (en) Electrolyte for lithium based energy accumulators
JPH07505740A (en) Li↓1↓＋↓xMn↓2O↓4 High-pressure stable electrolyte for carbon secondary batteries
JP2001043895A (en) Nonaqueous electrolytic solution and lithium secondary battery using same
Ji et al. Electrochemical behavior of suberonitrile as a high-potential electrolyte additive and Co-solvent for Li [Li0. 2Mn0. 56Ni0. 16Co0. 08] O2 cathode material
WO2016034936A1 (en) Wound electrode body lithium ion battery having active electrode material layers of different widths
JP6926942B2 (en) Manufacturing method of positive electrode
CN108292568A (en) Electrochemical apparatus and its manufacturing method
Murmann et al. Lithium-cyclo-difluoromethane-1, 1-bis (sulfonyl) imide as a stabilizing electrolyte additive for improved high voltage applications in lithium-ion batteries
TW201823256A (en) Electrolyte solutions and electrochemical cells containing same
WO2017098682A1 (en) Nonaqueous electrolyte secondary battery
JP6250941B2 (en) Nonaqueous electrolyte secondary battery
JP2021511640A (en) Mixtures of potassium and lithium salts and their use in batteries
JP2013069442A (en) Lithium-ion secondary battery
JP2007053080A (en) Non-aqueous electrolytic solution, and electrochemical energy accumulating device using the same
WO2020021530A1 (en) Electrolyte solutions for high voltage lithium-ion cells
Li et al. Using a lithium difluoro (sulfato) borate additive to improve electrochemical performance of electrolyte based on lithium bis (oxalate) borate for LiNi0. 5Mn1. 5O4/Li cells
JP6656623B2 (en) Non-aqueous electrolyte for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and method for producing non-aqueous electrolyte secondary battery
JP6587101B2 (en) Non-aqueous electrolyte secondary battery
Swiderska-Mocek Properties of LiMn 2 O 4 cathode in electrolyte based on ionic liquid with and without gamma-butyrolactone
CN113871698B (en) Electrolyte and lithium battery containing same

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 19841281

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 19841281

Country of ref document: EP

Kind code of ref document: A1