EP3782220A1 - An electrolyte composition for a lithium-ion battery and a lithium-ion battery - Google Patents

An electrolyte composition for a lithium-ion battery and a lithium-ion battery

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Publication number
EP3782220A1
EP3782220A1 EP19718371.8A EP19718371A EP3782220A1 EP 3782220 A1 EP3782220 A1 EP 3782220A1 EP 19718371 A EP19718371 A EP 19718371A EP 3782220 A1 EP3782220 A1 EP 3782220A1
Authority
EP
European Patent Office
Prior art keywords
lithium
carbonate
electrolyte
electrolyte composition
additive
Prior art date
Legal status (The legal status 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 status listed.)
Pending
Application number
EP19718371.8A
Other languages
German (de)
French (fr)
Inventor
Dominic BRESSER
Arefeh KAZZAZI
Stefano Passerini
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Karlsruher Institut fuer Technologie KIT
Original Assignee
Karlsruher Institut fuer Technologie KIT
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Filing date
Publication date
Application filed by Karlsruher Institut fuer Technologie KIT filed Critical Karlsruher Institut fuer Technologie KIT
Publication of EP3782220A1 publication Critical patent/EP3782220A1/en
Pending legal-status Critical Current

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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
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • 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 an electrolyte composition for a lithium-ion battery, specifically, a high-voltage lithium-ion battery, and a corresponding lithium-ion battery.
  • a lithium-ion battery specifically, a high-voltage lithium-ion battery, and a corresponding lithium-ion battery.
  • Lithium-ion batteries are widely used as an electrochemical device in applications covering various areas including but not limited to portable electronic devices, electric vehicles, hybrid electric vehicles, or stationary energy storage systems.
  • portable electronic devices electric vehicles, hybrid electric vehicles, or stationary energy storage systems.
  • an increase of the energy density and/or the power density of the lithium-ion battery is required.
  • high-voltage lithium-ion cathode materials appear to be promising since they allow for increasing the voltage which is applied across the electrochemical cells.
  • electrolytes are known to exhibit only a limited stability with respect to high voltages.
  • Lithium-ion batteries comprise at least one electrolyte which is designed for providing an ion conducting path between at least one first half-cell comprising at least one positive electrode and at least one second half-cell comprising at least one negative electrode of the electrochemical device.
  • the presently used electrolytes comprise non-aqueous organic solvents which are not sufficiently stable with respect to the application of a high voltage, in particular of 4.5 V or above. Therefore, it would be desirable to provide further kinds of electrolytes with an increased stability towards high voltages.
  • Silyl substituted electrolyte additives such as tris-(trimethylsilyl)-phosphite (TTSPi) have been developed in order to improve the cycling performance of various positive electrode materials at high voltage and/or at elevated temperatures.
  • US 2017/018806 Al discloses a flame-resistant electrolyte for rechargeable lithium secondary batteries, and a rechargeable lithium secondary battery.
  • the flame-resistant electrolyte can reduce the volatility of an organic solvent, and inhibit flammability to improve stability of a battery when a flame-resistant solvent, which includes a fluorinated phosphazene-based phosphorus compound and a phosphite-based compound for forming protective films on surfaces of negative and positive electrodes, is mixed with a lithium salt and a carbonate-based solvent, and thus has good lifespan characteristics and high battery charge vs. discharge efficiency even under high-temperature and high-voltage environments, and also has improved battery performance since an electrode interface is stabilized to inhibit side reaction with an electrolyte.
  • US 2013/164604 Al discloses a high performance secondary battery having good flame retardancy and cycling properties.
  • the present exemplary embodiment provides a secondary battery comprising an electrode assembly in which a positive electrode and a negative electrode are arranged to face each other, a liquid electrolyte and a package accommodating the electrode assembly and the liquid electrolyte, wherein the negative electrode is formed by binding a negative electrode active substance comprising a metal (a) capable of being alloyed with lithium, a metal oxide (b) capable of occluding and releasing lithium ions and a carbon material (c) capable of occluding and releasing lithium ions, to a negative electrode current collector, with a negative electrode binder, and the liquid electrolyte comprises a supporting salt and an electrolytic solvent, the electrolytic solvent comprising at least one phosphate ester compound selected from phosphite esters, phosphonate esters and bisphosphonate esters.
  • US 2013/236790 Al discloses an electrode assembly comprising a positive electrode, a negative electrode and a separator, wherein the positive electrode further comprises a first positive electrode active material layer, and a second positive electrode active material layer formed on one surface of the first positive electrode active material layer, wherein the first positive electrode active material layer further comprises a first positive electrode active material containing manganese (Mn), and wherein the second positive electrode active material layer further comprises a second positive electrode active material containing cobalt (Co), and a lithium battery.
  • Mn manganese
  • Co cobalt
  • KR 2016 0030765 A discloses a lithium secondary battery comprising a positive electrode; a negative electrode including porous silicon; and an electrolyte including a lithium salt, an organic solvent, and an additive.
  • the additive comprises fluoroalkylene carbonate and tris(trialkylsilyl)phosphite.
  • the lithium secondary battery has a stable solid electrolyte interphase (SEI) layer formed on the negative electrode surface so that electrochemical performance can be increased.
  • SEI solid electrolyte interphase
  • the terms“have”,“comprise” or“include” or any arbitrary grammatical variations thereof are used in a non-exclusive way.
  • these terms may refer to both a situation in which, besides the feature introduced by these terms, no further features are present in the entity described in this context and to a situation in which one or more further features are present.
  • the expressions“A has B”,“A comprises B” and“A includes B” may both refer to a situation in which, besides B, no other element is present in A (i.e. a situation in which A solely and exclusively consists of B) and to a situation in which, besides B, one or more further elements are present in entity A, such as element C, elements C and D or even further elements.
  • the present invention relates to an electrolyte for a lithium-ion battery.
  • the term“lithium-ion battery” refers to an electrochemical device, also denoted as an“electrochemical cell”, which may, in particular, be used for storing and providing electrical energy from chemical reactions which are performed within the electrochemical device.
  • the electrochemical device comprises at least one first half-cell comprising at least one positive electrode and at least one second half-cell comprising at least one negative electrode, wherein the two half-cells are separated from each other in order to avoid a short circuit.
  • the lithium-ion battery comprises a material in the anode and/or, preferably, in the cathode which allows generating lithium ions by application of a voltage the electrochemical cell, wherein the lithium ions move through the electrochemical cell during application of an electric voltage, i.e. during charging and discharging of the electrochemical cell.
  • particularly selected lithium-ion batteries may be capable of tolerating an application of a high voltage, wherein, as generally used, the term“high-voltage” refers to a voltage of 4.5 V or above, specifically to 4.5 V to 5.1 V, in particular, to 4.7 V to 5 V.
  • the term“high-voltage lithium-ion cathode material” refers to a lithium-ion cathode material as comprised by a “high-voltage lithium-ion battery” which is capable of tolerating an application of a high voltage as defined above, wherein the term“tolerating” relates to a property of a material with respect to withstanding the application of such a high voltage, specifically a repeated application thereof, without any substantial deterioration of the material.
  • the cathode material comprising lithium may be selected from the group consisting of lithium nickel manganese oxide (LiNio . 5Mn1 . 5O4, LNMO), a mixture of LNMO with an additional compound selected from at least one of Co, Al, and additional Li; a lithium nickel manganese cobalt oxide (LiNi x Mn y Co z 0 2 , NMC), a lithium-rich lithium nickel manganese cobalt oxide (x LiMn 2 0 3 NMC, x ⁇ 0.4); lithium iron phosphate (LiFeP0 4 , LFP); lithium manganese phosphate (LiMnP0 4 ); lithium cobalt phosphate (LiCoP0 4 , LCP); lithium metal phosphate (LiMP0 4 ), wherein M is selected from at least one of Fe, Mn, Co or Ni; lithium cobalt oxide (LiCo0 2 , LCO); lithium manganese oxide (LiMn 2 0 4 ),
  • lithium nickel manganese oxide LiNio . 5Mn1 . 5O4, LNMO
  • lithium nickel manganese oxide LiNio . 5Mn1 . 5O4, LNMO
  • lithium cobalt phosphate LiCoP0 4 , LCP
  • lithium metal phosphate LiMP0 4
  • M is selected from at least one of Co or Ni
  • lithium-rich NMC x LiMn 2 0 3 ⁇ NMC
  • lithium metal (Li) may be used as the anode material.
  • At least one electrolyte is used.
  • the term“electrolyte” refers to an ionically conducting solution, in which the dissolved salt is separated into ions which may freely disperse throughout the electrolyte solvent.
  • the solution is, as a whole, ionically neutral, an application of a certain voltage to the cell, comprising the electrolyte, is capable of moving the ions within the solvent and/or of ions which are, in addition, provided by the at least one of the electrodes of the electrochemical cell to the respective electrode of opposite charge.
  • the solvent can, thus, be used for moving ions from one of the electrodes to an electrode of opposing charge within the electrochemical cell.
  • various electrolytes may exhibit a different behavior with respect to the application of the electric voltage, such as with regard to the extent of the applied voltage.
  • the electrolyte which is proposed for being used in a lithium-ion battery, specifically in a high-voltage lithium-ion battery is an electrolyte composition which comprises
  • - additives comprising a silyl substituted phosphite as a first additive and a fluorinated carbonate as a second additive.
  • the first additive may, preferably, be present in the electrolyte in a concentration of 0.001 wt.% to 5 wt.%, preferably of 0.01 wt.% to 3 wt.%, specifically of 0.5 wt.% to 2.5 wt.%
  • the second additive may, preferably, be present in the electrolyte in a concentration of 0.001 wt.% to 5 wt.%, preferably of 0.01 wt.% to 3 wt.%, specifically of 0.05 wt.% to 2 wt.%, wherein the term“wt.%” refers to a percentage in weight of the respective additive with regard to a total weight of the whole electrolyte.
  • all substances as comprised by the electrolyte sum up to an amount of 100 wt.%.
  • the silyl substituted phosphite which is used as the first additive in the electrolyte composition according to the present invention may, preferably, be selected from the group consisting of tris(trimethylsilyl)phosphite (TTSPi), dimethyl trimethylsilyl phosphite, diethyl trimethylsilyl phosphite, diphenyl trimethylsilyl phos phite, and derivatives thereof.
  • TTSPi tris(trimethylsilyl)phosphite
  • dimethyl trimethylsilyl phosphite diethyl trimethylsilyl phosphite
  • diphenyl trimethylsilyl phos phite diphenyl trimethylsilyl phos phite
  • the fluorinated carbonate which is used as the second additive in the electrolyte composition according to the present invention may, preferably, be a linear fluorinated carbonate, and may, in particular, be selected from the group consisting of bis(2,2,2-trifluoroethyl)carbonate (TFEC), methyl-2, 2,3, 3-tetrafluoro- propyl carbonate, ethyl-2,2,3,3,3-pentafluoropropyl carbonate, 2,2,3,4,4,4-hexafluorobutyl methyl carbonate, ethyl(l-fluoroethyl) carbonate, and l-fluoroethyl(2,2,2-trifluoroethyl) carbonate, wherein TFEC, methyl-2, 2, 3, 3-tetrafluoro-propyl carbonate and ethyl-2, 2, 3,3,3- pentafluoropropyl carbon-ate are preferred, wherein TFEC and
  • the least one conducting lithium salt as comprised by the electrolyte composition according to the present invention may, preferably, be selected from the group consisting of hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClCfi), lithium hexafluoroarsenate (LiAsF 6 ), lithium bis(oxalato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).
  • LiPF 6 hexafluorophosphate
  • LiBF 4 lithium tetrafluoroborate
  • LiClCfi lithium perchlorate
  • LiAsF 6 lithium hexafluoroarsenate
  • LiBOB lithium bis(oxalato)borate
  • LiTFSI lithium bis(trifluoromethanes
  • a first conducting lithium salt thereof such as LiPF 6
  • a second conducting lithium salt thereof preferably LiBOB
  • an additional lithium source being present in a concentration of 10 wt.% or less, preferably 5 wt.% or less, most preferred 3 wt.% or less.
  • further kinds of compositions may also be feasible.
  • the at least one non-aqueous organic solvent as comprised by the electrolyte composition according to the present invention may, preferably, be selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), tetrahydrofuran (THF), 1 ,2-dimethoxyethane (DME), 2- methyltetrahydrofuran (2Me-THF), trimethyl phosphate, triethyl phosphate, dimethyl methyl phosphonate, and diethyl ethyl phosphonate.
  • PC propylene carbonate
  • EC ethylene carbonate
  • DMC dimethyl carbonate
  • DEC diethyl carbonate
  • EMC ethyl methyl carbonate
  • THF tetrahydrofuran
  • DME 1,2-dimethoxyethane
  • 2Me-THF 2- methyltetra
  • an electrolyte composition which is especially adapted for a high-voltage lithium-ion battery
  • the electrolyte composition comprises two specific kinds of additives which, as demonstrated below in more detail, function together in a fashion that a synergetic effect can be achieved which cannot be obtained by any of the two kinds of additives alone.
  • the electrolyte composition exhibits a high stability at high voltages and may, thus, be applicable in large-size lithium-ion batteries, which may, for example, be used in electric vehicles, hybrid electric vehicles and large- scale energy- storage systems.
  • the present invention relates to a lithium-ion battery, which comprises:
  • the electrolyte comprises an electrolyte composition as described elsewhere herein, or wherein the cathode comprises at least one high-voltage lithium-ion cathode material and the electrolyte comprises at least one non-aqueous organic solvent, a least one conducting lithium salt, and an additive selected from at least one of a silyl substituted phosphite or a fluorinated carbonate.
  • the at least one cathode may comprise a cathode material selected from the group consisting of lithium nickel manganese oxide (LiNio. 5 Mn 1.5 O 4 , LNMO), a mixture of LNMO with an additional compound selected from at least one of Co, Al, and additional Li; lithium nickel manganese cobalt oxide (LiNi x Mn y Co z 0 2 , NMC); lithium iron phosphate (LiFeP0 4 , LFP); lithium manganese phosphate (LiMnP0 4 ); lithium cobalt phosphate (LiCoP0 4 , LCP); lithium metal phosphate (LiMP0 4 ), wherein M is selected from at least one of Fe, Mn, Co or Ni; lithium cobalt oxide (L1C0O 2 , LCO); lithium manganese oxide (LiMn 2 0 4 or LLMnOi, LMO); lithium nickel cobalt aluminum oxide (LiNii_ x-y Co
  • the high-voltage lithium-ion battery may comprise:
  • At least one cathode comprising at least one high-voltage lithium-ion cathode material
  • the term“high-voltage” refers to a voltage of 4.5 V or above, specifically to 4.5 V to 5.1 V, in particular, to 4.7 V to 5 V.
  • the term“high-voltage lithium-ion cathode material” refers to a lithium-ion cathode material which is capable of tolerating an application of a high voltage as defined above, wherein the term“tolerating” relates to a property of a material with respect to withstanding the application of such a high voltage, specifically a repeated application thereof, without any substantial deterioration of the material.
  • the high-voltage lithium-ion cathode material may, thus, allow providing a lithium-ion battery, which exhibits a high stability with respect to an application, specifically a repeated application, of a high voltage to the electrochemical cell.
  • the high-voltage lithium-ion cathode material may be selected from the group consisting of lithium nickel manganese oxide (LiNio. 5 Mn 1.5 O 4 , LNMO), a mixture of LNMO with an additional compound selected from at least one of Co, Al, and additional Li; lithium cobalt phosphate (L1C0PO 4 , LCP); lithium metal phosphate (L1MPO 4 ), wherein M is selected from at least one of Co or Ni; and lithium-rich NMC (x LiMn 2 0 3 ⁇ NMC).
  • LNMO lithium nickel manganese oxide
  • LNMO lithium nickel manganese oxide
  • LNMO lithium cobalt phosphate
  • L1MPO 4 lithium metal phosphate
  • M is selected from at least one of Co or Ni
  • lithium-rich NMC x LiMn 2 0 3 ⁇ NMC
  • the at least one anode may comprise an anode material selected from the group consisting of graphite, silicon, a silicon/graphite composite, metallic lithium, lithium titanate (LhTfO ⁇ , LTO), tin, germanium, magnesium, aluminum, zinc, and other elements, which are known to electrochemically alloy with lithium, as well as a transition metal-doped zinc oxide or tin oxide.
  • anode material selected from the group consisting of graphite, silicon, a silicon/graphite composite, metallic lithium, lithium titanate (LhTfO ⁇ , LTO), tin, germanium, magnesium, aluminum, zinc, and other elements, which are known to electrochemically alloy with lithium, as well as a transition metal-doped zinc oxide or tin oxide.
  • the electrolyte may, as indicated above, comprise a silyl substituted phosphite as a first additive, a fluorinated carbonate as a second additive, or a silyl substituted phosphite as a first additive and a fluorinated carbonate as a second additive.
  • the first additive and/or the second additive may, preferably, be present in the electrolyte in a concentration as indicated above in more detail.
  • silyl substituted phosphite and the fluorinated carbonate may, preferably, be selected from the materials as presented above in more detail, wherein the silyl substituted phosphite may, specifically, be tris(trimethylsilyl)phosphite (TTSPi) and wherein the fluorinated carbonate may, preferably be a linear fluorinated carbonate, specifically bis(2,2,2-trifluoroethyl)carbonate (TFEC).
  • TTSPi tris(trimethylsilyl)phosphite
  • TFEC bis(2,2,2-trifluoroethyl)carbonate
  • a high-voltage lithium-ion battery wherein the electrolyte comprises at least one kind of additive, wherein, as demonstrated below in more detail, the electrolyte exhibits a high stability at high voltages and may, thus, be applicable in large- size lithium-ion batteries, which may, for example, be used in electric vehicles, hybrid electric vehicles and large-scale stationary energy- storage systems.
  • Figures 1 A and 1B show a behavior of the specific capacity (Figure 1A) and of the coulombic efficiency ( Figure 1B), respectively, of a lithium cobalt phosphate (F1C0PO 4 , FCP) high-voltage cathode in a half-cell configuration versus cycle number;
  • Figure 2 shows a behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right), respectively, of a graphite anode in a half-cell configuration versus cycle number;
  • Figures 3 A and 3B show a behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right) of a lithium cobalt phosphate (F1C0PO4, FCP)/graphite full electrochemical cell versus cycle number for different kinds of electrolytes;
  • Figure 4 shows a behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right), respectively, of a lithium nickel manganese oxide (LiNio.5Mn1.5O4, LNMO) high- voltage cathode in half-cell configuration versus cycle number;
  • Figures 5A and 5B show a behavior of the specific capacity (Figure 5A) and of the coulombic efficiency (Figure 5B), respectively, of a lithium nickel manganese oxide (LiNio . 5Mn1 . 5O4, LNMO)/graphite full electro- chemical cell versus cycle number for different kinds of electrolytes;
  • a lithium nickel manganese oxide LiNio . 5Mn1 . 5O4, LNMO
  • Figures 6A and 6B show a behavior of the specific capacity of LNMO half-cells having an electrolyte composition comprising LP30 and TTSPi and methyl- 2, 2,3, 3-tetrafluoropropyl carbonate as additives ( Figure 6A), and the corresponding coulombic efficiency in comparison with an LNMO half-cell comprising pure LP30 as the electrolyte; and
  • Figure 7 shows a behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right) of LNMO/graphite full-cells having different electrolyte compositions.
  • a lithium cobalt phosphide (L1C0PO4, LCP) or lithium nickel manganese oxide (LiNio . 5Mn1 . 5O4, LNMO) high-voltage cathode was provided for a half-cell configuration or for a full electrochemical cell.
  • a graphite anode (MEG2) was provided for a half-cell configuration or for a full electrochemical cell.
  • a lab-scale cell in particular of a pouch-bag-type, a coin-cell-type or a Swagelok-three-electrode-type configuration, comprising at least one of the high-voltage cathodes and the anode selected from graphite or lithium metal (the latter in case of half-cell configuration) was assembled inside an argon- filled glove box (0 2 and FLO content of less than 0.1 ppm) or a dry-room (remaining humidity ⁇ 0.1% at 20 °C).
  • LiPF 6 lithium hexafluorophosphate
  • EC:DMC ethylene carbonate/dimethyl carbonate
  • LP30 ethylene carbonate/dimethyl carbonate
  • the specific capacity of a lithium cobalt phosphate (LiCoP0 4 , LCP) high-voltage cathode in a half-cell configuration versus cycle number shows a different behavior depending on the electrolyte.
  • the coulombic efficiencies of the lithium cobalt phosphate (LiCoPCF, LCP) high-voltage cathode in the half-cell configuration shows a different behavior versus cycle number depending on the electrolyte.
  • TTSPi tris(trimethylsilyl)phosphite
  • TFEC bis(2,2,2-trifluoroethyl)carbonate
  • Figure 2 presents the behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right) of a graphite anode in a half-cell configuration versus cycle number.
  • the electrolyte composition according to the present invention which, specifically, comprises LP30 with 2 wt.% TTSPi and 0.3 wt.% TFEC as additives, was found to be beneficial also for graphite anodes with respect to an enhanced specific capacity, an improved rate capability, and enhanced capacity retention and cycling stability, and a higher coulombic efficiency.
  • Figure 3A shows a behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right) of a lithium cobalt phosphate (LiCoP0 4 , LCP)/graphite full electrochemical cell versus cycle number for different kinds of electrolytes.
  • the electrolyte composition according to the present invention led to higher specific capacities and to an enhanced coulombic efficiency in full electrochemical cells.
  • Figure 3B shows a behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right) of a further lithium cobalt phosphate (FiCoP0 4 , FCP)/graphite full electrochemical cell versus cycle number for different kinds of electrolytes.
  • using the electrolyte composition according to the present invention is beneficial for the cycling stability and to the coulombic efficiency, also compared to the addition of TTSPi only, even with respect to the lower amount of 0.05 % for TFEC.
  • Figure 4 shows a behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right) of a further high-voltage cathode in a half-cell configuration versus cycle number depending on the electrolyte.
  • electrolyte composition according to the present invention led to increased specific capacities (increase approx. 13%) and enhanced first cycle coulombic efficiency also for this other kind of high-voltage cathode, demonstrating that this electrolyte composition is versatile and not limited to specific active materials.
  • DEMS data indicate an occurrence of substantially reduced electrolyte decomposition at the LNMO cathode for an electrolyte composition comprising the LP30 electrolyte and the additives comprising the silyl substituted phosphite and the fluorinated carbonate, compared to a pure LP30 electrolyte.
  • Figures 5A shows a behavior of the specific capacity and Figure 5B of the coulombic efficiency, respectively, of a lithium nickel manganese oxide (FiNio . 5Mn1 . 5O4, FNMO)/ graphite full electrochemical cell versus cycle number for different kinds of electrolytes.
  • a lithium nickel manganese oxide FiNio . 5Mn1 . 5O4, FNMO
  • results as presented there illustrate the superior performance of FNMO/graphite full- cells when both additives TTSPi and TFEC are added to the electrolyte composition, providing higher specific capacities, enhanced cycling stability, increased capacity retention after 100 cycles (14.1% for FP30, 75.8% for TTSPi, and 80.7% for TTSPi+TFEC) and higher average coulombic efficiencies (97.5% for FP30, 99.0% for TTSPi, and 99.1% for TTSPi and TFEC).
  • X-ray photoelectron spectroscopy (XPS) data show a synergistic effect of the two additives, demonstrating a contribution of TFEC to the SEI on the anode and on the cathode in a case in which TTSPi is added, while no evidence can be found for a contribution of TFEC in absence of TTSPi.
  • ex-situ XPS data obtained for the graphite anode in FNMO/graphite full-cells after five cycles demonstrate that an introduction of TTSPi and TFEC prevents a dissolution of manganese from the cathode and a deposition thereof on the graphite anode. In fact, such manganese deposition on the anode is considered highly detrimental for the cycling performance, thus, explaining, at least in part, the inferior performance of the additive-free full-cells.
  • Figures 6A shows a behavior of the specific capacity of FNMO half-cells having an electrolyte composition comprising FP30 and TTSPi and methyl-2, 2, 3, 3-tetrafluoropropyl carbonate as additives while Figure 6B illustrates the corresponding coulombic efficiency in comparison with an FNMO half-cell comprising pure FP30 as the electrolyte.
  • additional fluorinated linear carbonates replacing TFEC in combination with TTSPi, have been used.
  • methyl-2, 2, 3, 3-tetrafluoropropyl carbonate has demonstrated a superior electrochemical performance compared to pure FP30 in combination with TTSPi, accompanied by a superior coulombic efficiency of 99.4% in average compared to 99.2% for pure LP30. Similar results have been obtained for ethyl-2,2,3,3,3-pentafluoropropyl carbonate (not depicted here).
  • fluorinated linear carbonates bearing a phenyl group e.g., 9-fluorenylmethyl pentafluorophenyl carbonate or methyl pentafluorophenyl carbonate
  • fluorinated linear carbonates bearing a phenyl group e.g., 9-fluorenylmethyl pentafluorophenyl carbonate or methyl pentafluorophenyl carbonate
  • Figure 7 shows a behavior of the specific capacity, being expressed by full symbols, and of the coulombic efficiency, being expressed by open symbols, of LNMO/graphite full electrochemical cells having different electrolyte compositions,
  • the electrolyte further LiPF 6 as a first conducting lithium salt and lithium bis(oxalate)borate (LiBOB) in a concentration of 1 wt.% as a second conducting lithium salt, leading to a further improved performance of the full electrochemical cell.

Abstract

The present invention relates to an electrolyte composition for a lithium-ion battery, specifically for a high-voltage lithium-ion battery, and a corresponding lithium-ion battery. The electrolyte composition for the lithium-ion battery comprises at least one non-aqueous organic solvent, a least one conducting lithium salt, and additives comprising at least one of a silyl substituted phosphite or a fluorinated carbonate. The electrolyte composition exhibits, compared to known electrolytes, an increased stability with respect to high voltages and is, therefore, particularly suited for the use in high-voltage lithium-ion batteries.

Description

An electrolyte composition for a lithium-ion battery and a lithium-ion battery
Field of the invention
The present invention relates to an electrolyte composition for a lithium-ion battery, specifically, a high-voltage lithium-ion battery, and a corresponding lithium-ion battery. Related art
Lithium-ion batteries are widely used as an electrochemical device in applications covering various areas including but not limited to portable electronic devices, electric vehicles, hybrid electric vehicles, or stationary energy storage systems. However, in order to further improve their performance, in particular, in electric or hybrid electric vehicles, an increase of the energy density and/or the power density of the lithium-ion battery is required. For this purpose, high-voltage lithium-ion cathode materials appear to be promising since they allow for increasing the voltage which is applied across the electrochemical cells. However, presently used electrolytes are known to exhibit only a limited stability with respect to high voltages.
Lithium-ion batteries comprise at least one electrolyte which is designed for providing an ion conducting path between at least one first half-cell comprising at least one positive electrode and at least one second half-cell comprising at least one negative electrode of the electrochemical device. In general, the presently used electrolytes comprise non-aqueous organic solvents which are not sufficiently stable with respect to the application of a high voltage, in particular of 4.5 V or above. Therefore, it would be desirable to provide further kinds of electrolytes with an increased stability towards high voltages. Silyl substituted electrolyte additives such as tris-(trimethylsilyl)-phosphite (TTSPi) have been developed in order to improve the cycling performance of various positive electrode materials at high voltage and/or at elevated temperatures. Mai et al, Electrochim. Acta 147 (2014) 565, showed that adding only 0.5 wt.% of TTSPi in 1M LiPF6 in ethylene carbonate/dimethyl carbonate (EC:EMC, 1 :2 by volume) significantly improved the impedance and capacity retention of lithium nickel manganese cobalt oxide (NMC)/Li half cells at 4.5 V, which they ascribed to a preferential oxidation of TTSPi that formed a protective SEI on the NMC electrode. Further, Sinha et al, J. Electrochem. Soc. 161 (2014), A1084, studied the effect of TTSPi in NMC/graphite pouch cells with 1M LiPF6 in (EC:EMC, 3:7 by weight) at 4.2 V and showed that TTSPi not only increased the coulombic efficiency but also reduced the cell impedance significantly.
Xia et al, J. Electrochem. Soc.20l6 (163) 8, A1637 describe the effects of four fluorinated carbonates including fluoroethylene carbonate, difluoroethylene carbonate, bis(2,2,2- trifluoroethyl) carbonate (TFEC) and 2,2,3,4,4,4-hexafluorobutyl methyl carbonate as electrolyte additives in NMC/graphite pouch cells. Cells containing difluoroethylene carbonate showed the highest coulombic efficiency and lowest charge end point capacity slippage rate at both 4.2 and 4.4 V, however, the performance was not as good as that of cells containing a state of the art additive blend. Long-term cycle-hold-rest tests showed that at 4.4 V ah cells with fluorinated additives apart that gave promising capacity retention from difluoroethylene carbonate generated unacceptable quantities of gas. The authors suggest that a use of these fluorinated additives in NMC/graphite pouch cells with ethylene carbonate-based electrolytes is not competitive to alternative approaches.
US 2017/018806 Al discloses a flame-resistant electrolyte for rechargeable lithium secondary batteries, and a rechargeable lithium secondary battery. The flame-resistant electrolyte can reduce the volatility of an organic solvent, and inhibit flammability to improve stability of a battery when a flame-resistant solvent, which includes a fluorinated phosphazene-based phosphorus compound and a phosphite-based compound for forming protective films on surfaces of negative and positive electrodes, is mixed with a lithium salt and a carbonate-based solvent, and thus has good lifespan characteristics and high battery charge vs. discharge efficiency even under high-temperature and high-voltage environments, and also has improved battery performance since an electrode interface is stabilized to inhibit side reaction with an electrolyte.
US 2013/164604 Al discloses a high performance secondary battery having good flame retardancy and cycling properties. The present exemplary embodiment provides a secondary battery comprising an electrode assembly in which a positive electrode and a negative electrode are arranged to face each other, a liquid electrolyte and a package accommodating the electrode assembly and the liquid electrolyte, wherein the negative electrode is formed by binding a negative electrode active substance comprising a metal (a) capable of being alloyed with lithium, a metal oxide (b) capable of occluding and releasing lithium ions and a carbon material (c) capable of occluding and releasing lithium ions, to a negative electrode current collector, with a negative electrode binder, and the liquid electrolyte comprises a supporting salt and an electrolytic solvent, the electrolytic solvent comprising at least one phosphate ester compound selected from phosphite esters, phosphonate esters and bisphosphonate esters.
US 2013/236790 Al discloses an electrode assembly comprising a positive electrode, a negative electrode and a separator, wherein the positive electrode further comprises a first positive electrode active material layer, and a second positive electrode active material layer formed on one surface of the first positive electrode active material layer, wherein the first positive electrode active material layer further comprises a first positive electrode active material containing manganese (Mn), and wherein the second positive electrode active material layer further comprises a second positive electrode active material containing cobalt (Co), and a lithium battery.
KR 2016 0030765 A discloses a lithium secondary battery comprising a positive electrode; a negative electrode including porous silicon; and an electrolyte including a lithium salt, an organic solvent, and an additive. The additive comprises fluoroalkylene carbonate and tris(trialkylsilyl)phosphite. In addition, the lithium secondary battery has a stable solid electrolyte interphase (SEI) layer formed on the negative electrode surface so that electrochemical performance can be increased.
Further electrolytes comprising TTSPi in FEC:TFEC = 1 :1 are disclosed in Jian Xia et al, J. Electrochem. Soc. 163 (10), 2016, pp. A2399-A2406 and Xia Jian et al, The effectiveness of electrolyte additives in fluorinated electrolytes for high voltage Li[Nio.4Mno.4Coo.2] 02/graphite pouch Li-ion cells, J. Power Sources 330, 2016, pp. 175- 185.
Problem to be solved
It is therefore an objective of the present invention to provide an electrolyte for a lithium- ion battery and a lithium-ion battery comprising this kind of electrolyte, which at least partially overcome the above-mentioned problems of the state of the art. It is a particular objective of the present invention to provide an electrolyte which exhibits, compared to known electrolytes, an increased stability with respect to high voltages, in particular of 4.5 V or above, specifically for a use in lithium-ion batteries which comprise at least one high-voltage lithium-ion cathode material.
Summary of the invention
This problem is solved by an electrolyte composition for a lithium-ion battery and a lithium-ion battery, specifically a high-voltage lithium-ion battery, with the features of the independent claims. Preferred embodiments, which might be realized in an isolated fashion or in any arbitrary combination, are listed in the dependent claims.
As used in the following, the terms“have”,“comprise” or“include” or any arbitrary grammatical variations thereof are used in a non-exclusive way. Thus, these terms may refer to both a situation in which, besides the feature introduced by these terms, no further features are present in the entity described in this context and to a situation in which one or more further features are present. As an example, the expressions“A has B”,“A comprises B” and“A includes B” may both refer to a situation in which, besides B, no other element is present in A (i.e. a situation in which A solely and exclusively consists of B) and to a situation in which, besides B, one or more further elements are present in entity A, such as element C, elements C and D or even further elements.
Further, as used in the following, the terms "preferably", "more preferably", "particularly", "more particularly", or similar terms are used in conjunction with optional features, without restricting alternative possibilities. Thus, features introduced by these terms are optional features and are not intended to restrict the scope of the claims in any way. The invention may, as the skilled person will recognize, be performed by using alternative features. Similarly, features introduced by "in an embodiment of the invention" or similar expressions are intended to be optional features, without any restriction regarding alternative embodiments of the invention, without any restrictions regarding the scope of the invention and without any restriction regarding the possibility of combining the features introduced in this way with other features of the invention.
In a first aspect, the present invention relates to an electrolyte for a lithium-ion battery. As indicated above, the term“lithium-ion battery” refers to an electrochemical device, also denoted as an“electrochemical cell”, which may, in particular, be used for storing and providing electrical energy from chemical reactions which are performed within the electrochemical device. For this purpose, the electrochemical device comprises at least one first half-cell comprising at least one positive electrode and at least one second half-cell comprising at least one negative electrode, wherein the two half-cells are separated from each other in order to avoid a short circuit. Specifically, the lithium-ion battery comprises a material in the anode and/or, preferably, in the cathode which allows generating lithium ions by application of a voltage the electrochemical cell, wherein the lithium ions move through the electrochemical cell during application of an electric voltage, i.e. during charging and discharging of the electrochemical cell.
Herein, particularly selected lithium-ion batteries may be capable of tolerating an application of a high voltage, wherein, as generally used, the term“high-voltage” refers to a voltage of 4.5 V or above, specifically to 4.5 V to 5.1 V, in particular, to 4.7 V to 5 V. Thus, the term“high-voltage lithium-ion cathode material” refers to a lithium-ion cathode material as comprised by a “high-voltage lithium-ion battery” which is capable of tolerating an application of a high voltage as defined above, wherein the term“tolerating” relates to a property of a material with respect to withstanding the application of such a high voltage, specifically a repeated application thereof, without any substantial deterioration of the material.
In particular, the cathode material comprising lithium may be selected from the group consisting of lithium nickel manganese oxide (LiNio.5Mn1.5O4, LNMO), a mixture of LNMO with an additional compound selected from at least one of Co, Al, and additional Li; a lithium nickel manganese cobalt oxide (LiNixMnyCoz02, NMC), a lithium-rich lithium nickel manganese cobalt oxide (x LiMn203 NMC, x < 0.4); lithium iron phosphate (LiFeP04, LFP); lithium manganese phosphate (LiMnP04); lithium cobalt phosphate (LiCoP04, LCP); lithium metal phosphate (LiMP04), wherein M is selected from at least one of Fe, Mn, Co or Ni; lithium cobalt oxide (LiCo02, LCO); lithium manganese oxide (LiMn204 or Li2Mn03, LMO); lithium nickel cobalt aluminum oxide (LiNii_x-yCoxAly02, NCA);. Herein, lithium nickel manganese oxide (LiNio.5Mn1.5O4, LNMO), a mixture of LNMO with an additional compound selected from at least one of Co, Al, and additional Li; lithium cobalt phosphate (LiCoP04, LCP); lithium metal phosphate (LiMP04), wherein M is selected from at least one of Co or Ni; and lithium-rich NMC (x LiMn203 · NMC) are known as high-voltage lithium-ion cathode materials. However, other kinds of materials comprising lithium may also be feasible for this purpose. Alternatively or in addition, lithium metal (Li) may be used as the anode material. In order to provide an ionically conducting path between the two different types of the electrodes in the electrochemical cell, in particular by generating a transport of ions, in general, at least one electrolyte is used. As generally used, the term“electrolyte” refers to an ionically conducting solution, in which the dissolved salt is separated into ions which may freely disperse throughout the electrolyte solvent. Although, the solution is, as a whole, ionically neutral, an application of a certain voltage to the cell, comprising the electrolyte, is capable of moving the ions within the solvent and/or of ions which are, in addition, provided by the at least one of the electrodes of the electrochemical cell to the respective electrode of opposite charge. As a result, the solvent can, thus, be used for moving ions from one of the electrodes to an electrode of opposing charge within the electrochemical cell. As indicated above, various electrolytes may exhibit a different behavior with respect to the application of the electric voltage, such as with regard to the extent of the applied voltage.
According to the present invention, the electrolyte which is proposed for being used in a lithium-ion battery, specifically in a high-voltage lithium-ion battery, is an electrolyte composition which comprises
- at least one non-aqueous organic solvent,
- a least one conducting lithium salt, and
- additives comprising a silyl substituted phosphite as a first additive and a fluorinated carbonate as a second additive.
Herein, the first additive may, preferably, be present in the electrolyte in a concentration of 0.001 wt.% to 5 wt.%, preferably of 0.01 wt.% to 3 wt.%, specifically of 0.5 wt.% to 2.5 wt.%, whereas the second additive may, preferably, be present in the electrolyte in a concentration of 0.001 wt.% to 5 wt.%, preferably of 0.01 wt.% to 3 wt.%, specifically of 0.05 wt.% to 2 wt.%, wherein the term“wt.%” refers to a percentage in weight of the respective additive with regard to a total weight of the whole electrolyte. As generally, all substances as comprised by the electrolyte sum up to an amount of 100 wt.%.
In a particularly preferred embodiment, the silyl substituted phosphite which is used as the first additive in the electrolyte composition according to the present invention may, preferably, be selected from the group consisting of tris(trimethylsilyl)phosphite (TTSPi), dimethyl trimethylsilyl phosphite, diethyl trimethylsilyl phosphite, diphenyl trimethylsilyl phos phite, and derivatives thereof. In a further particularly preferred embodiment, the fluorinated carbonate which is used as the second additive in the electrolyte composition according to the present invention may, preferably, be a linear fluorinated carbonate, and may, in particular, be selected from the group consisting of bis(2,2,2-trifluoroethyl)carbonate (TFEC), methyl-2, 2,3, 3-tetrafluoro- propyl carbonate, ethyl-2,2,3,3,3-pentafluoropropyl carbonate, 2,2,3,4,4,4-hexafluorobutyl methyl carbonate, ethyl(l-fluoroethyl) carbonate, and l-fluoroethyl(2,2,2-trifluoroethyl) carbonate, wherein TFEC, methyl-2, 2, 3, 3-tetrafluoro-propyl carbonate and ethyl-2, 2, 3,3,3- pentafluoropropyl carbon-ate are preferred, wherein TFEC and methyl-2, 2, 3, 3-tetrafluoro- propyl carbonate are more preferred, wherein TFEC is specifically, preferred.
In a further preferred embodiment, the least one conducting lithium salt as comprised by the electrolyte composition according to the present invention may, preferably, be selected from the group consisting of hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClCfi), lithium hexafluoroarsenate (LiAsF6), lithium bis(oxalato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI). However, further conducting lithium salts may also be feasible. In a preferred embodiment, a first conducting lithium salt thereof, such as LiPF6, may be used as a dominant lithium source, while a second conducting lithium salt thereof, preferably LiBOB, may be used as an additional lithium source being present in a concentration of 10 wt.% or less, preferably 5 wt.% or less, most preferred 3 wt.% or less. However, further kinds of compositions may also be feasible.
In a further preferred embodiment, the at least one non-aqueous organic solvent as comprised by the electrolyte composition according to the present invention may, preferably, be selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), tetrahydrofuran (THF), 1 ,2-dimethoxyethane (DME), 2- methyltetrahydrofuran (2Me-THF), trimethyl phosphate, triethyl phosphate, dimethyl methyl phosphonate, and diethyl ethyl phosphonate.
Summarizing, an electrolyte composition which is especially adapted for a high-voltage lithium-ion battery is proposed, wherein the electrolyte composition comprises two specific kinds of additives which, as demonstrated below in more detail, function together in a fashion that a synergetic effect can be achieved which cannot be obtained by any of the two kinds of additives alone. As a result, the electrolyte composition exhibits a high stability at high voltages and may, thus, be applicable in large-size lithium-ion batteries, which may, for example, be used in electric vehicles, hybrid electric vehicles and large- scale energy- storage systems.
In a further aspect, the present invention relates to a lithium-ion battery, which comprises:
- at least one cathode;
- a least one anode; and
- an electrolyte,
wherein the electrolyte comprises an electrolyte composition as described elsewhere herein, or wherein the cathode comprises at least one high-voltage lithium-ion cathode material and the electrolyte comprises at least one non-aqueous organic solvent, a least one conducting lithium salt, and an additive selected from at least one of a silyl substituted phosphite or a fluorinated carbonate.
As indicated above, the at least one cathode may comprise a cathode material selected from the group consisting of lithium nickel manganese oxide (LiNio.5Mn1.5O4, LNMO), a mixture of LNMO with an additional compound selected from at least one of Co, Al, and additional Li; lithium nickel manganese cobalt oxide (LiNixMnyCoz02, NMC); lithium iron phosphate (LiFeP04, LFP); lithium manganese phosphate (LiMnP04); lithium cobalt phosphate (LiCoP04, LCP); lithium metal phosphate (LiMP04), wherein M is selected from at least one of Fe, Mn, Co or Ni; lithium cobalt oxide (L1C0O2, LCO); lithium manganese oxide (LiMn204 or LLMnOi, LMO); lithium nickel cobalt aluminum oxide (LiNii_x-yCoxAly02, NCA); and lithium-rich NMC (xLiMn203-NMC). However, other kinds of electrode materials, such as those known by the skilled person, may also be feasible for being used as one of the electrodes in the lithium-ion battery according to the present invention.
In the particularly preferred embodiment in which the at least one cathode may comprise at least one high-voltage lithium-ion cathode material, the high-voltage lithium-ion battery may comprise:
- at least one cathode comprising at least one high-voltage lithium-ion cathode material;
- a least one anode; and
- an electrolyte comprising an additive selected from at least one of a silyl substituted phosphite or a fluorinated carbonate. As already indicated above, the term“high-voltage” refers to a voltage of 4.5 V or above, specifically to 4.5 V to 5.1 V, in particular, to 4.7 V to 5 V. Further, the term“high-voltage lithium-ion cathode material” refers to a lithium-ion cathode material which is capable of tolerating an application of a high voltage as defined above, wherein the term“tolerating” relates to a property of a material with respect to withstanding the application of such a high voltage, specifically a repeated application thereof, without any substantial deterioration of the material. Together with a suitable electrolyte, which is also capable of tolerating the application of such a high voltage, in particular the electrode which comprises at least one additive selected from a silyl substituted phosphite and/or a fluorinated carbonate, the high-voltage lithium-ion cathode material may, thus, allow providing a lithium-ion battery, which exhibits a high stability with respect to an application, specifically a repeated application, of a high voltage to the electrochemical cell.
Specifically, the high-voltage lithium-ion cathode material may be selected from the group consisting of lithium nickel manganese oxide (LiNio.5Mn1.5O4, LNMO), a mixture of LNMO with an additional compound selected from at least one of Co, Al, and additional Li; lithium cobalt phosphate (L1C0PO4, LCP); lithium metal phosphate (L1MPO4), wherein M is selected from at least one of Co or Ni; and lithium-rich NMC (x LiMn203 · NMC).
As further indicated above, the at least one anode may comprise an anode material selected from the group consisting of graphite, silicon, a silicon/graphite composite, metallic lithium, lithium titanate (LhTfO^, LTO), tin, germanium, magnesium, aluminum, zinc, and other elements, which are known to electrochemically alloy with lithium, as well as a transition metal-doped zinc oxide or tin oxide.
In the particularly preferred embodiment in which the at least one cathode may comprise at least one high-voltage lithium-ion cathode material, the electrolyte may, as indicated above, comprise a silyl substituted phosphite as a first additive, a fluorinated carbonate as a second additive, or a silyl substituted phosphite as a first additive and a fluorinated carbonate as a second additive. Herein, the first additive and/or the second additive may, preferably, be present in the electrolyte in a concentration as indicated above in more detail. Further, the silyl substituted phosphite and the fluorinated carbonate may, preferably, be selected from the materials as presented above in more detail, wherein the silyl substituted phosphite may, specifically, be tris(trimethylsilyl)phosphite (TTSPi) and wherein the fluorinated carbonate may, preferably be a linear fluorinated carbonate, specifically bis(2,2,2-trifluoroethyl)carbonate (TFEC).
For further details concerning the lithium-ion battery, reference may be made to the description of the electrolyte composition.
Summarizing, a high-voltage lithium-ion battery is proposed, wherein the electrolyte comprises at least one kind of additive, wherein, as demonstrated below in more detail, the electrolyte exhibits a high stability at high voltages and may, thus, be applicable in large- size lithium-ion batteries, which may, for example, be used in electric vehicles, hybrid electric vehicles and large-scale stationary energy- storage systems.
Short description of the Figures
Further optional features and embodiments of the invention will be disclosed in more detail in the subsequent description of preferred embodiments, preferably in conjunction with the dependent claims. Therein, the respective optional features may be realized in an isolated fashion as well as in any arbitrary feasible combination, as the skilled person will realize. It is emphasized here that the scope of the invention is not restricted by the preferred embodiments.
In the Figures:
Figures 1 A and 1B show a behavior of the specific capacity (Figure 1A) and of the coulombic efficiency (Figure 1B), respectively, of a lithium cobalt phosphate (F1C0PO4, FCP) high-voltage cathode in a half-cell configuration versus cycle number;
Figure 2 shows a behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right), respectively, of a graphite anode in a half-cell configuration versus cycle number;
Figures 3 A and 3B show a behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right) of a lithium cobalt phosphate (F1C0PO4, FCP)/graphite full electrochemical cell versus cycle number for different kinds of electrolytes; Figure 4 shows a behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right), respectively, of a lithium nickel manganese oxide (LiNio.5Mn1.5O4, LNMO) high- voltage cathode in half-cell configuration versus cycle number;
Figures 5A and 5B show a behavior of the specific capacity (Figure 5A) and of the coulombic efficiency (Figure 5B), respectively, of a lithium nickel manganese oxide (LiNio.5Mn1.5O4, LNMO)/graphite full electro- chemical cell versus cycle number for different kinds of electrolytes;
Figures 6A and 6B show a behavior of the specific capacity of LNMO half-cells having an electrolyte composition comprising LP30 and TTSPi and methyl- 2, 2,3, 3-tetrafluoropropyl carbonate as additives (Figure 6A), and the corresponding coulombic efficiency in comparison with an LNMO half-cell comprising pure LP30 as the electrolyte; and
Figure 7 shows a behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right) of LNMO/graphite full-cells having different electrolyte compositions.
Detailed description of the embodiments
A lithium cobalt phosphide (L1C0PO4, LCP) or lithium nickel manganese oxide (LiNio.5Mn1.5O4, LNMO) high-voltage cathode was provided for a half-cell configuration or for a full electrochemical cell. Alternatively or in addition, a graphite anode (MEG2) was provided for a half-cell configuration or for a full electrochemical cell. A lab-scale cell, in particular of a pouch-bag-type, a coin-cell-type or a Swagelok-three-electrode-type configuration, comprising at least one of the high-voltage cathodes and the anode selected from graphite or lithium metal (the latter in case of half-cell configuration) was assembled inside an argon- filled glove box (02 and FLO content of less than 0.1 ppm) or a dry-room (remaining humidity < 0.1% at 20 °C). 1M lithium hexafluorophosphate (LiPF6) dissolved in ethylene carbonate/dimethyl carbonate (EC:DMC) solution in a ratio of 1 :1 per weight was utilized as a reference electrolyte, which can also be denoted by the term“LP30”. Electrochemical investigations, in particular of the specific capacity and/or of the coulombic efficiency, of the half-cell configurations or of the full electrochemical cells were performed at 20 ± 1 °C by employing a commercially available battery tester. Hereby, different cut-off potentials as indicated below were used.
As illustrated in Figure 1A, the specific capacity of a lithium cobalt phosphate (LiCoP04, LCP) high-voltage cathode in a half-cell configuration versus cycle number shows a different behavior depending on the electrolyte. Herein, the cathode had a composition of LCP : sodium carboxymethyl cellulose (CMC) : conductive carbon = 85 : 5 : 10 or of LCP : CMC + latex : conductive carbon = 89 : 5 : 6, and a mass loading of approx. 1.3 or of 11.2 mg/cm2. Cut-off potentials of 4.0-4.95 V vs. Li/Li+ were used; herein a discharge/charge rate of 1C = 167 mA g 1 was applied. Compared to the reference electrolyte LP30, an addition of tris(trimethylsilyl)phosphite (TTSPi) and/or bis(2,2,2- trifluoroethyl)carbonate (TFEC) as additive to the reference electrolyte led to enhanced cycling stabilities which is expressed in Figure 1A by a slower reduction of the specific capacity versus cycle number. As can be derived from Figure 1, the addition of TTSPi proved to be particularly advantageous whereas the best performance was obtained when an electrolyte composition comprising 2 wt.% TTSPi and 0.3 wt.% TFEC as additives was used.
Similarly, as illustrated in Figure 1B, the coulombic efficiencies of the lithium cobalt phosphate (LiCoPCF, LCP) high-voltage cathode in the half-cell configuration shows a different behavior versus cycle number depending on the electrolyte. Compared to the reference electrolyte LP30, an addition of tris(trimethylsilyl)phosphite (TTSPi) and/or bis(2,2,2-trifluoroethyl)carbonate (TFEC) to the reference electrolyte led to improved coulombic efficiencies which is expressed here by an increase of the coulombic efficiency versus cycle number to a larger value. Herein, the addition of TFEC proved to be particularly advantageous for the initial cycles whereas the addition of TTSPi proved to be particularly advantageous for the following cycles. Again, the best performance was obtained when the electrolyte composition comprising the two additives 2 wt.% TTSPi and 0.3 wt.% TFEC was used.
Experimental results for the reversible capacity and the coulombic efficiency for selected values from Figures 1 A and 1B for the electrolyte LP30 with various kinds of additives are presented in Table 1 below, wherein the term“n.a.” means“not applicable”:
Additional experiments (not depicted here) showed that similar improvements could be obtained for 4.95 V or 5.1 V as an anodic cut-off potential, thus, demonstrating the capability of the electrolytes for use with the high-voltage cathode.
Figure 2 presents the behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right) of a graphite anode in a half-cell configuration versus cycle number. Herein, the anode had a composition of MEG2 : conductive carbon : CMC : SBR (styrene-butadiene rubber) = 94 : 2 : 2 : 2, a mass loading of approx. 4.1 mg/cm2, and a coating density of : approx. 1.3 g/cc. Cut-off potentials of 1.5 - 0.02 V were used; herein a discharge/charge rate of 1C = 372 mA g 1 or an indicated portion thereof was applied. Again, this presentation shows a different behavior of the measured quantities depending on the electrolyte. In particular, the electrolyte composition according to the present invention which, specifically, comprises LP30 with 2 wt.% TTSPi and 0.3 wt.% TFEC as additives, was found to be beneficial also for graphite anodes with respect to an enhanced specific capacity, an improved rate capability, and enhanced capacity retention and cycling stability, and a higher coulombic efficiency. Figure 3A shows a behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right) of a lithium cobalt phosphate (LiCoP04, LCP)/graphite full electrochemical cell versus cycle number for different kinds of electrolytes. Herein, the cathode had a composition of LCP : sodium carboxymethyl cellulose (CMC) : Super P = 85 : 5 : 10 and a mass loading of approx. 1.27 mg/cm2, wherein a discharge/charge rate of 1C = 167 mA g 1 was applied. Further, the anode had a composition of MEG2 : conductive carbon : CMC : SBR = 94 : 2 : 2 : 2, a mass loading of approx. 4.1 mg/cm2, and a coating density of : approx. 1.3 g/cc. Cut-off potentials of 3.2- 4.85 V vs. Li/Li+ were used. Compared to the reference electrolyte LP30 without additives, the electrolyte composition according to the present invention led to higher specific capacities and to an enhanced coulombic efficiency in full electrochemical cells.
Experimental results for the reversible capacity and the coulombic efficiency for selected values from Figure 2 for the reference electrolyte LP30 and for the electrolyte composition according to the present invention are indicated in Table 2 below:
Figure 3B shows a behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right) of a further lithium cobalt phosphate (FiCoP04, FCP)/graphite full electrochemical cell versus cycle number for different kinds of electrolytes. Herein, the cathode had a composition of FCP : conductive carbon : conductive graphite : CMC : latex = 89 : 4.5 : 1.5 : 2 : 3 and a mass loading of approx. 11.2 mg/cm2, wherein a discharge/charge rate of 1C = 167 mA g 1 was applied. Further, the anode had a composition of MEG2 : conductive carbon : CMC : SBR = 94 : 2 : 2 : 2, a mass loading of approx. 4.1 mg/cm2, and a coating density of : approx. 1.3 g/cc. Cut-off potentials of 3.2-4.85 V vs. Fi/Fi+ were used. Herein, using the electrolyte composition according to the present invention is beneficial for the cycling stability and to the coulombic efficiency, also compared to the addition of TTSPi only, even with respect to the lower amount of 0.05 % for TFEC.
Experimental results for the reversible capacity and the coulombic efficiency for selected values from Figures 3A and 3B for the electrolyte LP30 with different additives are illustrated in Table 3 below:
Figure 4 shows a behavior of the specific capacity (full symbols, left) and of the coulombic efficiency (open symbols, right) of a further high-voltage cathode in a half-cell configuration versus cycle number depending on the electrolyte. Herein, a lithium nickel manganese oxide (LiNio.5Mn1.5O4, LNMO) cathode was used which had a composition of LNMO : conductive carbon : CMC : citric acid = 85 : 10 : 4 : 1 +1 wt.% (active material) phosphoric acid, and a mass loading of approx. 11.2 mg/cm2. Cut-off potentials of 3.5-4.8 V vs. Li/Li+ were used; herein a discharge/charge rate of 1C = 147 mA g 1 was applied.
Experimental results for the reversible capacity and the coulombic efficiency for selected values from Figure 4 for the reference electrolyte LP30 and for the electrolyte composition according to the present invention for a discharge/charge rate of 1C except where otherwise indicated are presented in Table 4 below:
As a result, using the electrolyte composition according to the present invention led to increased specific capacities (increase approx. 13%) and enhanced first cycle coulombic efficiency also for this other kind of high-voltage cathode, demonstrating that this electrolyte composition is versatile and not limited to specific active materials.
Further, differential electrochemical mass spectrometry (DEMS) data indicate an occurrence of substantially reduced electrolyte decomposition at the LNMO cathode for an electrolyte composition comprising the LP30 electrolyte and the additives comprising the silyl substituted phosphite and the fluorinated carbonate, compared to a pure LP30 electrolyte.
Figures 5A shows a behavior of the specific capacity and Figure 5B of the coulombic efficiency, respectively, of a lithium nickel manganese oxide (FiNio.5Mn1.5O4, FNMO)/ graphite full electrochemical cell versus cycle number for different kinds of electrolytes. The results as presented there illustrate the superior performance of FNMO/graphite full- cells when both additives TTSPi and TFEC are added to the electrolyte composition, providing higher specific capacities, enhanced cycling stability, increased capacity retention after 100 cycles (14.1% for FP30, 75.8% for TTSPi, and 80.7% for TTSPi+TFEC) and higher average coulombic efficiencies (97.5% for FP30, 99.0% for TTSPi, and 99.1% for TTSPi and TFEC).
X-ray photoelectron spectroscopy (XPS) data (not depicted here) show a synergistic effect of the two additives, demonstrating a contribution of TFEC to the SEI on the anode and on the cathode in a case in which TTSPi is added, while no evidence can be found for a contribution of TFEC in absence of TTSPi. Moreover, ex-situ XPS data obtained for the graphite anode in FNMO/graphite full-cells after five cycles demonstrate that an introduction of TTSPi and TFEC prevents a dissolution of manganese from the cathode and a deposition thereof on the graphite anode. In fact, such manganese deposition on the anode is considered highly detrimental for the cycling performance, thus, explaining, at least in part, the inferior performance of the additive-free full-cells.
Figures 6A shows a behavior of the specific capacity of FNMO half-cells having an electrolyte composition comprising FP30 and TTSPi and methyl-2, 2, 3, 3-tetrafluoropropyl carbonate as additives while Figure 6B illustrates the corresponding coulombic efficiency in comparison with an FNMO half-cell comprising pure FP30 as the electrolyte. Herein, additional fluorinated linear carbonates, replacing TFEC in combination with TTSPi, have been used. In particular, methyl-2, 2, 3, 3-tetrafluoropropyl carbonate has demonstrated a superior electrochemical performance compared to pure FP30 in combination with TTSPi, accompanied by a superior coulombic efficiency of 99.4% in average compared to 99.2% for pure LP30. Similar results have been obtained for ethyl-2,2,3,3,3-pentafluoropropyl carbonate (not depicted here). However, an incorporation of fluorinated linear carbonates bearing a phenyl group, e.g., 9-fluorenylmethyl pentafluorophenyl carbonate or methyl pentafluorophenyl carbonate, has led to a rather rapid fading, indicating that such functional group in the fluorinated linear carbonates does not allow for a superior cycling (not depicted here).
Figure 7 shows a behavior of the specific capacity, being expressed by full symbols, and of the coulombic efficiency, being expressed by open symbols, of LNMO/graphite full electrochemical cells having different electrolyte compositions, Herein, the electrolyte further LiPF6 as a first conducting lithium salt and lithium bis(oxalate)borate (LiBOB) in a concentration of 1 wt.% as a second conducting lithium salt, leading to a further improved performance of the full electrochemical cell.

Claims

Claims
1. An electrolyte composition for a lithium-ion battery, comprising
- at least one non-aqueous organic solvent,
- a least one conducting lithium salt, and
- an additive comprising a silyl substituted phosphite as a first additive and a fluorinated carbonate as a second additive.
2. The electrolyte composition according to the preceding claim, wherein the first additive is present in a concentration of 0.001 wt.% to 5 wt.% and wherein the second additive is present in a concentration of 0.001 wt.% to 5 wt.%.
3. The electrolyte composition according to the preceding claim, wherein the first additive is present in a concentration of 0.01 wt.% to 3 wt.% and wherein the second additive is present in a concentration of 0.01 wt.% to 3 wt.%.
4. The electrolyte composition according to the preceding claim, wherein the first additive is present in a concentration of 0.5 wt.% to 2.5 wt.% and wherein the second additive is present in a concentration of 0.05 wt.% to 2 wt.%.
5. The electrolyte composition according to any one of the preceding claims, wherein the silyl substituted phosphite is selected from the group consisting of tris(trimethylsilyl)phosphite (TTSPi), dimethyl trimethylsilyl phosphite, diethyl trimethylsilyl phosphite, diphenyl trimethylsilyl phosphite, and derivatives thereof.
6. The electrolyte composition according to any one of the preceding claims, wherein the fluorinated carbonate is selected from the group consisting of and bis(2,2,2- trifluoroethyl)carbonate (TFEC), methyl-2, 2, 3, 3-tetrafluoropropyl carbonate, ethyl- 2,2,3,3,3-pentafluoropropyl carbonate, 2,2,3,4,4,4-hexafluorobutyl methyl carbonate, ethyl(l-fluoroethyl) carbonate, and l-fluoroethyl(2,2,2-trifluoroethyl) carbonate.
7. The electrolyte composition according to any one of the preceding claims, wherein the at least one lithium salt is selected from the group consisting of from the group consisting of hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (L1CIO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(oxal- ato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).
The electrolyte composition according to any one of the preceding claims, wherein the at least one non-aqueous organic solvent is selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), tetrahydrofuran (THF), 1,2- dimethoxyethane (DME), 2-methyltetrahydrofuran (2Me-THF), trimethyl phosphate, triethyl phosphate, dimethyl methyl phosphonate, and diethyl ethyl phosphonate.
A lithium-ion battery, comprising
- at least one cathode,
- a least one anode, and
- an electrolyte,
wherein the electrolyte comprises an electrolyte composition according to any one of the preceding claims, or wherein the cathode comprises at least one high-voltage lithium-ion cathode material and the electrolyte comprises at least one non-aqueous organic solvent, a least one conducting lithium salt, and an additive selected from at least one of a silyl substituted phosphite or a fluorinated carbonate.
10. The lithium-ion battery according to the preceding claim, wherein the cathode comprises at least one high-voltage lithium-ion cathode material and the electrode comprises the electrolyte composition according to any one of claims 1 to 8.
11. The lithium-ion battery according to any one of the two preceding claims, wherein the high-voltage lithium-ion cathode material is selected from the group consisting of lithium nickel manganese oxide, a mixture thereof with an additional compound selected from at least one of Co, Al, and additional Li; lithium cobalt phosphate; lithium metal phosphate, wherein M is selected from at least one of Co or Ni; and a lithium-rich lithium nickel manganese cobalt oxide.
12. The lithium-ion battery according to any one of the three preceding claims, wherein the anode comprises at least one anode material selected from the group consisting of graphite, silicon, a silicon/graphite composite, metallic lithium, lithium titanate, an alloy of lithium with at least one of tin, germanium, magnesium, aluminum, and zinc; and a transition metal-doped zinc oxide or tin oxide.
EP19718371.8A 2018-04-20 2019-04-18 An electrolyte composition for a lithium-ion battery and a lithium-ion battery Pending EP3782220A1 (en)

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WO2012029420A1 (en) 2010-09-02 2012-03-08 日本電気株式会社 Secondary battery
KR20130104088A (en) 2012-03-12 2013-09-25 삼성에스디아이 주식회사 Electrode assembly and lithium recheabable battery comprising the same
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