Patent Application
20150333373
The present application relates to high voltage electrolytes and lithium ion batteries containing the high voltage electrolytes.
The ever-growing demand of energy for modern society has prompted the need to develop efficient storage of electricity, meaning that one needs to have battery systems with high energy and power density, long lifetime and minimum production/disposal cost. In the last decade, a number of different battery systems such as nickel-metal hydride, sodium-sulfur, and lithium ion systems were found to have high potential for electric vehicles. Among them, lithium ion battery is considered to be the most promising candidate for this demanding application.
Conventional lithium ion batteries utilizing carbonate electrolytes provide working voltage of around 3.2-3.8 V and stable charging voltage up to around 4.3 V. The electrolyte becomes unstable at elevated voltages and may result in reduced cycle life and decreased safety of the lithium ion battery. There is, therefore, a need for improved electrolytes stable at an elevated voltage, such as greater than 5 V. There is also a need for further improving the reliability and performance of the batteries at high charging voltages.
In one aspect, the present application provides a high voltage electrolyte including an electrolyte solvent which includes a mixture of a dinitrile solvent and a nitrile solvent. The electrolyte is stable at voltage of about 5 V or above.
In one embodiment, the high voltage electrolyte may further include one or more additives in an amount of about 0.1-10% by volume of the electrolyte solvent. The additives may be selected from the group consisting of vinyl carbonate (VC), 4-fluoro-1,3-dioxolan-2-one (FEC) and 4-vinyl-1,3-dioxolan-2-one (VEC).
In one embodiment, the dinitrile solvent may include at least one selected from the group consisting of malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile and sebaconitrile.
In one embodiment, the nitrile solvent may include at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, pivalonitrile and capronitrile.
In one embodiment, the mixture of the dinitrile solvent and the nitrile solvent may be present in an amount of about 10-40% of the total volume of the high voltage electrolyte. In a particular embodiment, the mixture of the dinitrile solvent and the nitrile solvent may be present in an amount of about 25% of the total volume of the high voltage electrolyte.
In one embodiment, the volume ratio of the dinitrile solvent to the nitrile solvent may be in the range of about 90:10 to 50:50. In a particular embodiment, the volume ratio of dinitrile solvent to nitrile solvent may be about 75:25.
In one embodiment, the mixture of the dinitrile solvent and the nitrile solvent may include adiponitrile and butylronitrile.
In another aspect, the present application provides a lithium ion battery including a cathode, an anode and an electrolyte. The electrolyte includes a mixture of a dinitrile solvent and a nitrile solvent. The lithium ion battery is stable at voltage of about 5 V or above.
In one embodiment, the electrolyte may further include one or more additives in an amount of about 0.1-10% by volume of the electrolyte solvent. The additives may be selected from the group consisting of vinyl carbonate (VC), 4-fluoro-1,3-dioxolan-2-one (FEC) and 4-vinyl-1,3-dioxolan-2-one (VEC).
In one embodiment, the dinitrile solvent may include at least one selected from the group consisting of malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile and sebaconitrile.
In one embodiment, the nitrile solvent may include at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, pivalonitrile and capronitrile.
In one embodiment, the mixture of the dinitrile solvent and the nitrile solvent may be present in an amount of about 10-40% of the total volume of the high voltage electrolyte. In a particular embodiment, the mixture of the dinitrile solvent and the nitrile solvent may be present in a concentration of about 25% of the total volume of the high voltage electrolyte.
In one embodiment, the volume ratio of the dinitrile solvent to the nitrile solvent may be in the range of about 90:10 to 50:50. In a particular embodiment, the volume ratio of dinitrile solvent to nitrile solvent may be about 75:25.
In one embodiment, the mixture of the dinitrile solvent and the nitrile solvent may include adiponitrile and butylronitrile.
In one embodiment, the lithium ion battery may have a cyclic performance of greater than about 300 cycles and with a capacity retention of greater than about 80%.
The embodiments of the present application are described with reference to the attached figures, wherein:
a and 1b show cyclic voltammetry measurement of Electrolyte A and Electrolyte B, respectively.
a and 2b show potentiodynamic scan and cycling test of a half cell in example 2 with no additive, respectively.
a and 3b show potentiodynamic scan and cycling test of a half cell in example 2 with additive vinylboronic acid pinacol ester (BO-2), respectively.
a and 4b show potentiodynamic scan and cycling test of a half cell in example 2 with additive 4-vinyl-1,3-dioxolan-2-one (VEC), respectively.
a shows reversibility of full cells in example 3 using 5% of vinyl ethylene carbonate (VEC) in adiponitrile (DN-6) with butylronitrile (25% by volume, volume ratio of DN-6 to butylronitrile is 75:25) with 1M LiNTf2+0.25M LiBF4 salts.
b shows reversibility of full cells in example 3 using 4-chloro-1,3-dioxolan-2-one (CIEC) in adiponitrile (DN-6) with butylronitrile (25% by volume, volume ratio of DN-6 to butylronitrile is 75:25) with 1M LiNTf2+0.25M LiBF4 salts.
a and 6b show cyclic performance of a LiCoO2/graphite full cell utilizing 5% of vinyl ethylene carbonate (VEC) in adiponitrile (DN-6) with butylronitrile (25% by volume, volume ratio of DN-6 to butylronitrile is 75:25) with 1M LiNTf2+0.25M LiBF4 salts.
a and 7b show SEM images of SEI layers formed on the graphite electrode surface in electrolyte with and without VC additives, respectively.
c and 7d are SEM images described in the literature (Journal of the Electrochemical Society, 2004, 151, A1659-A1669).
a and 8b respectively show C1s XPS spectra before and after SEI layers formed on composite graphite with VC additives in electrolyte solvent.
c and 8d respectively show O1s XPS spectra before and after SEI layers formed on composite graphite with VC additives in electrolyte solvent.
In the following detailed description, numerous specific details are described in order to provide a thorough understanding of the application. However the present application may be practiced without these specific details. In other instances, well known methods, procedures, components have not been described in detail so as not to obscure the present application. Further, exemplary sizes, values and ranges may be given, but it should be understood that the present application is not limited to these specific examples.
An electrolyte has an important role in a battery especially with respect to the stability and charge-discharge cycling of the battery. The electrolyte may include a non-aqueous solvent, lithium salt and optionally one or more additives. To stabilize the battery under high working voltage, the solvent is selected to provide stability with respect to oxidation. One or more additives may be added to further stabilize the electrolyte during high charging voltage of the lithium batteries.
In one aspect, the present application provides a high voltage electrolyte which remains stable at a high voltage of about 5 V or greater.
The electrolyte of the present application may be determined through computational molecular orbital calculation and experimental determination. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy values of electrolyte solvents and additive compounds may provide useful guidelines in the following experimental verification.
The electrolyte includes a non-aqueous solvent, a lithium salt and optionally one or more additives. In certain embodiments, the electrolyte may include a mixture of dinitrile and nitrile solvents, and a lithium salt. One or more additives may also be included to improve the stability and safety of the electrolytes as well as lithium ion batteries utilizing the electrolyte.
It has been surprisingly found that an electrolyte including a mixture of dinitrile solvent and nitrile solvent would still be stable at high charging voltage of about 5 V or higher. One or more additives may be added to further improve the stability and safety of the electrolyte as well as a lithium battery utilizing the electrolyte. The additives may be provided in a concentration of about 0.1 to 10% by volume of the electrolyte solvent.
It has also been found that a lithium ion battery utilizing the electrolyte can safely and stably be used at high voltage of about 5 V or higher, without a substantial decomposition of the electrolyte.
Various dinitriles may be used, such as those possessing the desired characteristics such as high anodic stability limits (>5 V (vs. Li+/Li)), low melting point (e.g. glutaronitrile, Tm=−29° C.), high flash point (e.g. adiponitrile, Tf=163° C.) and high boiling point (e.g. adiponitrile, 295° C.). Another attractive characteristic of dinitriles is their relatively low cost.
In certain embodiments of the present application, the dinitriles may include one or more selected from the group consisting of malononitrile (DN-3), succinonitrile (DN-4), glutaronitrile (DN-5), adiponitrile (DN-6), pimelonitrile (DN-7), suberonitrile, azelanitrile and sebaconitrile.
Various nitriles may be used, such as those possessing the desired characteristics such as high boiling point and high oxidation resistance.
In some embodiments of the present application, the nitriles may include one or more selected form the group consisting of acetonitrile, propionitrile, butyronitrile, pivalonitrile and capronitrile.
The mixture of dinitrile and nitrile solvents provides other desired characteristics such as low electrolyte viscosity and high ionic conductivity.
In certain embodiments, the mixture/combination of dinitrile and nitrile solvents may be selected from the group consisting of glutaronitrile (DN-5), adiponitrile (DN-6), butyronitrile and pivalonitrile.
In certain embodiments, the mixture of dinitrile and nitrile solvents may be present in an amount of about 10-40% of the total volume of the electrolyte.
In certain embodiments, the volume ratio of the dinitrile solvent to the nitrile solvent may be in the range of about 90:10 to 50:50. In some embodiments, the volume ratio of dinitrile solvent to nitrile solvent may be about 75:25.
In certain embodiments, a mixture of adiponitrile (DN-6) with butylronitrile may be present in an amount of about 20-40% of the total volume of the electrolyte. In some embodiments, the amount of the mixture of adiponitrile (DN-6) with butylronitrile may be about 25% of the total volume of the electrolyte.
The electrolyte may include one or more electrolyte additives. Additives have been found to improve the cycling performance of the high voltage batteries. In general, the additives can be classified as lithium salt additives and organic non-ionic additives. Examples for additives may be selected from solid electrolyte interface (SEI) forming additives, cathode protecting agents, salt stabilizers, overcharge protecting additives, lithium depositing additives, solvation enhancers, as well as corrosion inhibitors and wetting agents. The additives may be further selected based on their reduction potentials.
In certain embodiments, the additives may be one or more selected from the group consisting of 4-vinyl-1,3-dioxolan-2-one (VEC), 4-fluoro-1,3-dioxolan-2-one (FEC), vinyl carbonate (VC), ally methyl carbonate (AMC), dimethyl dicarbonate (DMDC), allyl ethyl carbonate (AEC), diallyl carbonate (DAC), 4-chloro-1,3-dioxolan-2-one (CIEC), glycol sulfite (ES), dimethyl sulfite (DMS), 1,3,2-dioxathiolane 2,2-dioxide (132 DOT), dimethyl carbonate (DMC), propylene sulfate (PSO4), ethyl fluoroacetate (EFA), methyl fluroracetate (MFA), trifluoromethyl maleic anhydride (TFMMA), methyl phenyl carbonate (MPC), N,N-dimethyltrifluoroacetamide 2-MTFA, ethyl 3-furoate (E-3-F), 1,3-propylene sulfite (1,3-PSF).
In certain embodiments, the additives may be one or more selected from the group consisting of vinyl carbonate (VC), 4-fluoro-1,3-dioxolan-2-one (FEC) and 4-vinyl-1,3-dioxolan-2-one (VEC).
In certain embodiments, the additives may be added in an amount of about 0.1-10% of the total volume of the electrolyte.
The lithium salt provides the lithium ions that are active at both of the battery electrodes of a secondary battery. The lithium salt dissolves into the non-aqueous solvents. The selection of the particular salt can be based on appropriate solubility, ion mobility and stability. The selection of salts can be influenced by the stability of the resulting electrolyte.
Various electrolyte salts may be used, including lithium salts that are generally used in the field. In some embodiments, lithium salts may be selected from the group consisting of lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiNTf2), lithium trifluoromethanesulfonate, lithium tetrachlorogallate, lithium tetrachloroaluminate and lithium hexafluoroarsenate (V) and any combinations thereof. The electrolyte may include the electrolyte salts in a concentration ranging from about 1M to 1.5 M.
In another aspect, the present application provides a lithium ion battery utilizing the above described electrolyte, which may be stable at voltages of greater than about 5 V. The battery may include a cathode, an anode, and the above described electrolyte. A separator between the cathode and anode may also be included.
Various cathode materials may be used, including the materials that are generally used in the field. In certain embodiments, the cathode material may include those selected from the group consisting of cobalt oxide, manganese oxide, nickel oxide, nickel cobalt aluminum oxide, iron phosphate, nickel manganese oxide and nickel cobalt manganese oxide.
Various anode materials may be used, including the materials that are generally used in the field. In certain embodiments, the anode material may include those selected from the group consisting of graphite, hard carbon, tin, germanium and silicon.
The lithium ion battery can ensure overcharge safety of a high voltage battery. Not only the lithium ion battery has stable cycle performance at normal temperature and small changes of internal resistance, the preparation process for the high-voltage lithium ion battery electrolyte is simple and easy to implement and has good market prospects.
In certain embodiments, the lithium ion battery has a cyclic performance of greater than about 300 cycles and with capacity retention of greater than about 80%.
Hereinafter the present application will be further illustrated by the following non-limitative examples.
The measurement was performed in a coin cell. A graphite electrode was used as the working electrode and lithium metal was used as both the counter electrode and the reference electrode. A separator was placed between the lithium metal electrode and the graphite electrode.
The working electrode tapes were fabricated at room temperature using MCMB (MesoCarbon MicroBeads) graphite powder as the active material, polyvinylidene difluoride (PVDF) resin, and conductive carbon black (SuperP) with 80:10:10 wt. % loading. Freestanding electrodes were dried at 90° C. in an oven before being transferred to a helium filled glove box with H2O and O2<1 ppm.
Stainless steel CR2032-type coin cells were used. The cell was comprised of a disk of the working electrode, glass fiber separators saturated with electrolyte, and Li foil. These cells were examined on an Arbin battery tester in the potentiodynamic (cyclic voltammetry) mode at a fixed temperature of 25° C. Each step was 0.5 mV/s. The cells were swept from the 3.0 V to 8.0 V to 0.0 V to 3.0 V (vs. Li) for one cycle to examine the stability of dinitrile solvents at different voltages.
Different dinitrile solvent candidates were tested by scanning the potential at an inert electrode and observing the anodic current. The onset oxidation potentials and the boiling points of different dinitrile solvent candidates have been measured (Table 1). The dinitriles with oxidation potential >5 V are the potential candidates such as DN-3, DN-4, DN-5, DN-6, DN-7 and ethylene bis(cyanoacetate) (DN-8-O4) to be solvents in the high voltage electrolyte system. In the mixed-solvent electrolyte solutions, two electrolytes were studied and shown as examples (
The measurement was performed in a coin cell. A graphite electrode was used as the working electrode and lithium metal was used as both the counter electrode and the reference electrode. A separator was placed between the lithium metal electrode and the graphite electrode.
The working electrode tapes were fabricated at room temperature using MCMB (MesoCarbon MicroBeads) graphite powder as the active material, polyvinylidene difluoride (PVDF) resin, and conductive carbon black (SuperP) with 80:10:10 wt. % loading. Freestanding electrodes were dried at 90° C. in an oven before being transferred to a helium filled glove box with H2O and O2<1 ppm.
Stainless steel CR2032-type coin cells were used. The cell was comprised of a disk of the working electrode, glass fiber separators saturated with electrolyte, and Li foil. These cells were examined on an Arbin battery tester in the potentiodynamic (cyclic voltammetry) mode at a fixed temperature of 25° C. Each step was 0.5 mV/s. The cells were swept from the 2.5 V to 0.0 V to 2.5 V (vs. Li) for two cycles to examine the effectiveness of additives on stabilizing the interface of the MCMB electrode and electrolyte.
Different additive candidates (in 5 volume %) were added into the cell and tested by scanning the potential at an inert electrode and observing the cathodic current. Examples of cyclic voltammetry scans are shown in
Using improper additives (e.g. vinylboronic acid pinacol ester (BO-2)), the first and the second cycles behave lesser degree of overlapping as shown in
The measurement was performed in a coin cell. Stainless steel CR2032-type coin cells were used. It was assembled with disks of both the positive and negative electrodes and glass fiber separators saturated with electrolyte. The LiCoO2 cathode was fabricated at room temperature using LiCoO2 powder as the active material, polyvinylidene difluoride (PVDF) resin, and conductive carbon black (SuperP) with 80:10:10 wt. % loading. The graphite anode was fabricated at room temperature using MCMB (MesoCarbon MicroBeads) graphite powder as the active material, polyvinylidene difluoride (PVDF) resin, and conductive carbon black (SuperP) with 80:10:10 wt. % loading. Freestanding electrodes were dried at 90° C. in an oven before being transferred to a helium filled glove box with H2O and O2<1 ppm.
In the actual battery performance test, different additive compounds were used to fabricate full coin cells using adiponitrile (DN-6) with butylronitrile (25% by volume, volume ratio of DN-6 to butylronitrile is 75:25) as the electrolyte solvent. The electrolyte contained 1 M of LiNTf2 and 0.25 M of LiBF4 salts. The charge/discharge rates were 0.5 C. Examples of charging-discharging performance of the full cells using 5% of vinyl ethylene carbonate (VEC) and 4-chloro-1,3-dioxolan-2-one (CIEC) as the additives in the electrolyte are shown in
a shows the cycling performance of the lithium ion battery utilizing the electrolyte solvents (i.e. adiponitrile (DN-6) and butylronitrile with a volume ratio of 75:25, and in an amount of 25% by volume of the total volume of the electrolyte). With appropriate additives (VEC), the electrolyte solvents showed ability to support reversible intercalation thereby resulting in good cycling behavior. This was consistent with the aforementioned potentiodynamic scan (
The SEI layer formed on the graphite electrode surface of the above full coin cell using vinyl carbonate (VC) as additive and adiponitrile (DN-6) with butylronitrile as electrolyte solvent is compared with the one free of VC additive.
a-8d showed the C1s and O1s XPS spectra for the SEI layers formed on the composite graphite after the first lithium-intercalation-deintercalation. The graphite anode samples were obtained from a half cell. The electrode pieces were mounted on the XPS sample holder in an Ar glove box and transported to the analysis chamber under an Ar-atmosphere to avoid air-exposure. The SEI layer (
Certain features of the application have been described with reference to example embodiments. However, the description is not intended to be construed in a limiting sense. Various modifications of the example embodiments, as well as other embodiments of the application, which are apparent to persons skilled in the art to which the application pertains are deemed to lie within the spirit and scope of the application.
This application claims the benefit of U.S. Provisional Patent Application No. 61/996,746 filed on May 15, 2014, the entire content of which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61996746 | May 2014 | US |
