The updated chemistry could mean better performance and longevity at a reduced cost.

We've been reading and sharing reports about Tesla's potential million-mile battery for some time now. This doesn't come as too much of a surprise since many EV batteries have already been proven to last a very long time. Moreover, Tesla CEO Elon Musk shared that the battery pack in the current Model 3 should already last some 300,000 to 500,000 miles.

Now, a new patent entitled ‘Dioxazolones and nitrile sulfites as electrolyte additives for lithium-ion batteries’ references adjustments to battery cell chemistry for the company's cars and energy storage products. The new chemistry aims to increase battery performance and longevity while reducing costs.

According to the patent application:

“This disclosure covers novel battery systems with fewer operative, electrolyte additives that may be used in different energy storage applications, for example, in vehicle and grid-storage. More specifically, this disclosure includes additive electrolyte systems that enhance performance and lifetime of lithium-ion batteries, while reducing costs from other systems that rely on more or other additives.”

"Improved battery systems have been developed for lithium-ion based batteries. The improved systems include a nonaqueous electrolyte including one or more lithium salts, one or more nonaqueous solvents, and an additive or additive mixture comprising one or more operative additives selected from a group of disclosed compounds, including 3-aryl substituted 1,4,2- dioxazol-5-ones and 3-phenyl-1,3,2,4-dioxathiazole 2-oxide."

More specifically, this patent refers to NMC battery chemistry:

"This work characterizes the high-temperature storage and long-term cycling performance of lithium-ion NMC/graphite pouch cells prepared with a recently developed electrolyte additive, MDO, and two new additives, PDO and BS. Differential capacity versus voltage indicates that both MDO and PDO form passive SEI layers on the graphite electrode surface during cell formation, whereas BS does not. The reduction features are generally consistent with DFT-predicted values, although the presence of multiple reduction peaks requires additional study to rationalize. As individual additives, PDO-containing cells show the best performance although these are nonetheless out-performed by VC-containing cells. The additives were also tested in binary blends with VC, DTD, and LFO. In long-term cycling tests, cells prepared with 2%PDO/l%DTD and 2%PDO/l%LFO additive blends outperform VC-containing cells. However, the high-temperature storage behavior of 2%PDO/l%LFO is superior than that of the 2%PDO/l%DTD blend."

Click on the 'Press Release' tab below to read the patent description. For access to the entire patent application, follow the PATENTSCOPE link below.

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DIOXAZOLONES AND NITRILE SULFITES AS ELECTROLYTE ADDITIVES FOR

LITHIUM-ION BATTERIES

 

CROSS-REFERENCE TO RELATED APPLICATIONS

 

This application claims priority from U.S. Patent Application No. 16/045,082 filed on July 25, 2018, and U.S. Provisional Patent Application No. 62/687,594 filed on June 20, 2018, the entire contents of which are hereby incorporated by reference herein.

 

TECHNICAL FIELD

 

[0001] The present disclosure relates to rechargeable battery systems, and more specifically to the chemistry of such systems, including operative electrolyte additives, for improving the properties of the rechargeable lithium-ion-battery systems.

 

BACKGROUND

[0002] Rechargeable batteries are an integral component of energy-storage systems for electric vehicles and for grid storage (for example, for backup power during a power outage, as part of a microgrid, etc.). Li-ion-based batteries are a common type of rechargeable battery.

[0003] Electrolyte additives have been shown to be operative and increase the lifetime and performance of Li-ion-based batteries. For example, in J. C. Bums et al., Journal of the Electrochemical Society, 160, A1451 (2013), five proprietary, undisclosed electrolyte additives were shown to increase cycle life compared to an electrolyte system with no or only one additive. Other studies have focused on performance gains from electrolyte systems containing three or four additives as described in U.S. 2017/0025706. However, researchers typically do not understand the interaction between different additives that allow them to work together synergistically with the electrolyte and specific positive and negative electrodes. Thus, the identity of certain systems is often based on trial and error and cannot be predicted beforehand. [0004] Prior studies have not identified two-additive electrolyte systems that can be combined into a lithium-ion battery system to yield a robust system with sufficient properties for grid or automobile applications. As discussed in U.S. 2017/0025706, two-additive systems studied (for example, 2% VC + 1% allyl methanesulfonate and 2% PES + 1% TTSPi) typically performed worse than the three- and four-additive electrolyte systems. (See, e.g., U.S. 2017/0025706 at Tables 1 and 2.) U.S. 2017/0025706 discloses that a third compound, often tris(-trimethly-silyl)-phosphate (TTSP) or tris(-trimethyl-silyl)-phosphite (TTSPi), was necessary in concentrations of between 0.25-3 wt% to produce a robust lithium-ion-battery system. (See, e.g, U.S. 2017/0025706 at†72.) However, because additives can be expensive and difficult to include within Li-ion batteries on a manufacture scale, more simple, yet effective battery systems are needed, including those with fewer additives.

[0005] To further progress the adoption of electric vehicles and grid energy storage applications, it is desirable to develop lithium-ion cell chemistries that offer longer lifetimes at high temperatures and high cell voltages, without significantly increasing cost. The introduction of sacrificial electrolyte additives on the order of a few weight percent is a practical method to form protective solid-electrolyte interphase (SEI) layers that limit electrolyte decomposition during cell storage and operation. In recent years, significant efforts have yielded a large number of such additives that may be used to improve cell performance for various applications. Examples are vinylene carbonate (VC), fluoroethylene carbonate (FEC), prop-l-ene-l,3-sultone (PES), ethylene sulfate (1, 3, 2-dioxathiolane-2, 2-dioxide, DTD), and lithium difluorophosphate (LFO).

[0006] The present application provides compositions for use as electrolyte additives in lithium-ion battery systems.

DEFINITIONS

[0007] "Cell" or "battery cell" generally refers to an electrochemical cell, which is a device capable of generating electrical energy from chemical reactions or facilitating chemical reactions through the introduction of electrical energy. An electrical battery can contain one or more cells.

 

[0008] "Rechargeable battery" generally refers a type of electrical battery which can be charged, discharged into a load, and recharged a number of times. In this disclosure, a number of examples are described based on Li-ion rechargeable batteries. Nevertheless, embodiments of the present invention are not limited to one type of rechargeable battery, and can be applied in conjunction with various rechargeable battery technologies.

SUMMARY

[0009] This disclosure covers novel battery systems with fewer operative, electrolyte additives that may be used in different energy storage applications, for example, in vehicle and grid-storage. More specifically, this disclosure includes additive electrolyte systems that enhance performance and lifetime of lithium-ion batteries, while reducing costs from other systems that rely on more or other additives. This disclosure also provides methods of preparing additives disclosed herein.

[0010] Certain embodiments described herein include a nonaqueous electrolyte for a lithium ion battery comprising at least one lithium salt, at least one nonaqueous solvent, and an additive component comprising at least one operative additive. The at least one operative additive is selected from

[0011] (a) the group consisting of 3-aryl substituted l,4,2-dioxazol-5-one compounds according to Formula (I):

 

 

[0012] wherein R is any aromatic substituent, any unsaturated aliphatic substituent, or any aliphatic substituent containing one or more fluorine atoms; or

[0013] (b) the group consisting of 3-CRR’R” substituted l,4,2-dioxazol-5-one compounds according to Formula (II):

 

[0014] wherein each of R, R’, and R” is hydrogen, alkyl substituents, or aromatic substituents; or

[0015] (c) the group consisting of R-substituted nitrile sulfite compounds according to

Formula (III):

 

 

[0016] wherein R is any alkyl or aromatic substituent.

[0017] In certain further embodiments, the at least one operative additive is in a range from 0.01 to 6 wt. %, based on the total weight of the electrolyte solution. In other embodiments, the at least one operative additive is in a range from 0.25 to 5 wt. %, based on the total weight of the electrolyte solution. In other embodiments, the concentration of the at least one operative additive is about 2% by weight.

 

[0018] In other embodiments, wherein the additive component includes ethylene sulfate, lithium difluorophosphate, vinylene carbonate, and/or fluoroethylene carbonate. In further embodiments the additive component includes 3-phenyl- 1, 4, 2-dioxazol-5-one.

[0019] In certain embodiments, the at least one nonaqueous is a carbonate solvent. In further embodiments, the carbonate solvent is ethylene carbonate or dimethyl carbonate. In yet further embodiments, the nonaqueous solvent includes at least 2 nonaqueous solvents.

[0020] In other embodiments, provided is a lithium-ion battery including a negative electrode;a positive electrode; and a nonaqueous electrolyte comprising a lithium salt dissolved in at least one nonaqueous solvent, and an additive component comprising at least one operative additive from

[0021] (a) the group consisting of 3-aryl substituted l,4,2-dioxazol-5-one compounds according to Formula (I):

 

[0022] wherein R is any aromatic substituent, any unsaturated aliphatic substituent, or any aliphatic substituent containing one or more fluorine atomsor

[0023] (b) the group consisting of 3-CRR’R” substituted 1 ,4,2-dioxazol-5-one compounds according to Formula (II):

 

 

[0024] wherein each of R, R’, and R” is hydrogen, alkyl substituents, or aromatic substituents; or

[0025] (c) the group consisting of R-substituted nitrile sulfite compounds according to

Formula (III):

 

 

[0026] wherein R is any alkyl or aromatic substituent.

[0027] In certain further embodiments, the at least one operative additive is in a range from 0.01 to 6 wt. %, based on the total weight of the electrolyte solution. In other embodiments, the at least one operative additive is in a range from 0.25 to 5 wt. %, based on the total weight of the electrolyte solution. In other embodiments, the concentration of the at least one operative additive is about 2% by weight.

[0028] In other embodiments, wherein the additive component includes ethylene sulfate, lithium difluorophosphate, vinylene carbonate, and/or fluoroethylene carbonate. In further embodiments the additive component includes 3-phenyl-l,4,2-dioxazol-5-one.

[0029] In certain embodiments, the at least one nonaqueous is a carbonate solvent. In further embodiments, the carbonate solvent is ethylene carbonate or dimethyl carbonate. In yet further embodiments, the nonaqueous solvent includes at least 2 nonaqueous solvents.

[0030] In other embodiments, the lithium-ion battery has 95% retention of initial capacity after 200 cycles between 3.0 V and 4.3 V at a charging rate of C/3 CCCV at 40°C. In further embodiments, the lithium-ion battery has 95% retention of initial capacity after 400 cycles between 3.0 V and 4.3 V at a charging rate of C/3 CCCV at 40°C.

[0031] In another aspect, provided is an electric vehicle with a rechargeable battery including a drive motor, a gear box, electronics, and a battery system. The battery system includes a negative electrode; a positive electrode; and a nonaqueous electrolyte comprising a lithium salt dissolved in at least one nonaqueous solvent, and an additive component comprising at least one operative additive from

[0032] (a) the group consisting of 3-aryl substituted l,4,2-dioxazol-5-one compounds according to Formula (I):

 

 

[0033] wherein R is any aromatic substituent, any unsaturated aliphatic substituent, or any aliphatic substituent containing one or more fluorine atoms; or

[0034] (b) the group consisting of 3-CRR’R” substituted 1,4,2-dioxazol-5-one compounds according to Formula (II):

 

[0035] wherein each of R, R’, and R” is hydrogen, alkyl substituents, or aromatic substituents; or

[0036] (c) the group consisting of R-substituted nitrile sulfite compounds according to

Formula (III):

 

 

[0037] wherein R is any alkyl or aromatic substituent.

[0038] In certain further embodiments, the at least one operative additive is in a range from 0.01 to 6 wt. %, based on the total weight of the electrolyte solution. In other embodiments, the at least one operative additive is in a range from 0.25 to 5 wt. %, based on the total weight of the electrolyte solution. In other embodiments, the concentration of the at least one operative additive is about 2% by weight.

[0039] In other embodiments, wherein the additive component includes ethylene sulfate, lithium difluorophosphate, and/or vinylene carbonate. In further embodiments the additive component includes 3-phenyl- 1, 4, 2-dioxazol-5-one.

[0040] In certain embodiments, the at least one nonaqueous is a carbonate solvent. In further embodiments, the carbonate solvent is ethylene carbonate or dimethyl carbonate. In yet further embodiments, the nonaqueous solvent includes at least 2 nonaqueous solvents.

 

[0041] In other embodiments, the battery system has 95% retention of initial capacity after 200 cycles between 3.0 V and 4.3 V at a charging rate of C/3 CCCV at 40°C. In further

embodiments, the battery system has 95% retention of initial capacity after 400 cycles between 3.0 V and 4.3 V at a charging rate of C/3 CCCV at 40°C.

 

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 is a schematic diagram of a vehicle containing a battery storage system.

[0043] FIG. 2 is a schematic diagram of an exemplary battery storage system.

[0044] FIG. 3 is a schematic diagram of a lithium-ion, battery-cell system.

[0045] FIG. 4 is a 1H NMR spectrum of 3-methyl- 1,4, 2-dioxazol-5-one (MDO), synthesized as described herein.

[0046] FIG. 5 is a 13C NMR spectrum of MDO, synthesized as described herein.

[0047] FIG. 6 is a FTIR spectrum of MDO, synthesized as described herein.

[0048] FIG. 7 is a *H NMR spectrum of 3-phenyl- 1,4,2 -dioxazol-5-one (PDO), synthesized as described herein.

[0049] FIG. 8 is a 13C NMR spectrum of PDO, synthesized as described herein.

[0050] FIG. 9 is a FTIR spectrum of PDO, synthesized as described herein.

[0051] FIG. 10 is a’H NMR spectrum of benzonitrile sulfite (BS) , synthesized as described herein.

[0052] FIG. 11 is a 13C NMR spectrum of BS, synthesized as described herein.

[0053] FIG. 12 is a FTIR spectrum of BS, synthesized as described herein.

[0054] FIG. 13 shows differential capacity (dQ/dV) plots of cell formation in NMC622B/graphite (left) and NMC532/graphite (right) cells. Electrolyte solutions contained (a) MDO-, (b) PDO-, or (c) BS-based additive blends. A‘control’ cell was prepared without any additives for comparison.

 

[0055] FIG. 14 illustrates cell volume change due to gas production during (a) 4.3 V storage for 500 hr at 60°C and (b) cell formation to 4.3 V in NMC622B/graphite (left) and NMC 532/graphite (right) cells. Electrolyte solutions contained MDO-, PDO-, or BS-based additive blends.

[0056] FIG. 15 illustrates cell voltage in NMC622/graphite (left) and NMC532/graphite (right) cells was measured during open circuit storage at 60°C for 500 hr. Electrolyte solutions contained (a) MDO-, (b) PDO-, or (c) BS-based additive blends, as indicated on the figure.

[0057] FIG. 16 illustrates Rct after formation (a) storage for 500 hr at 60°C and (b) cell formation to 4.3 V in NMC622/graphite (left) and NMC532/graphite (right) cells. Electrolyte solutions contained MDO-, PDO-, or BS-based additive blends, as indicated at the bottom of the figure.

[0058] FIG. 17 (a-c) illustrates normalized discharge capacity and (d-f) AV of

NMC622/graphite pouch cells cycled at 40°C and C/3 charge-discharge rate to 4.3 V. Electrolyte additive concentrations are as indicated.

[0059] FIG. 18 (a-c) illustrates normalized discharge capacity and (d-f) AV of

NMC532/graphite pouch cells cycled at 40°C and C/3 charge-discharge rate to 4.3 V. Electrolyte additive concentrations are as indicated.

[0060] FIG. 19 illustrates that the PDO-containing cells shown in FIG. l5b were charged to 4.3 V and stored at open circuit at 60°C for an additional 500 hr. The cell voltage in (a) NMC622/graphite and (b) NMC532/graphite cells was measured during open circuit storage at 60°C for 500 hr. The PDO-based additive blends are as indicated.

 

DETAILED DESCRIPTION OF THE DISCLOSURE

[0061] FIG. 1 illustrates the basic components of a battery powered electric vehicle (electric vehicle) 100. The electric vehicle 100 includes at least one drive motor (traction motor) 102A and/or 102B, at least one gear box 104 A and/or 104B coupled to a corresponding drive motor 102A and/or 102B, battery cells 106 and electronics 108. Generally, the battery cells 106 provide electricity to power electronics of the electric vehicle 100 and to propel the electric vehicle 100 using the drive motor 102 A and/or 102B. The electric vehicle 100 includes a large number of other components that are not described herein but known to one or ordinary skill. While the construct of the electric vehicle 100 of FIG. 1 is shown to have four wheels, differing electric vehicles may have fewer or more than four wheels. Further, differing types of electric vehicles 100 may incorporate the inventive concepts described herein, including motor cycles, aircraft, trucks, boats, train engines, among other types of vehicles. Certain parts created using embodiments of the present disclosure may be used in vehicle 100.

[0062] FIG. 2 illustrates a schematic view of an exemplary energy storage system 200 showing various components. The energy storage system 200 typically includes a modular housing with at least a base 202 and four side walls 204 (only two shown in the figure). The module housing is generally electrically isolated from the housed battery cells 206. This may occur through physical separation, through an electrically insulating layer, through the choice of an insulating material as the module housing, any combination thereof, or another through another method. The base 202 may be an electrically insulating layer on top of a metal sheet or a nonconductive/electrically insulating material, such as polypropylene, polyurethane, polyvinyl chlorine, another plastic, a nonconductive composite, or an insulated carbon fiber. Side walls 204 may also contain an insulating layer or be formed out of a nonconductive or electrically insulating material, such as polypropylene, polyurethane, polyvinyl chlorine, another plastic, a nonconductive composite, or an insulated carbon fiber. One or more interconnect layers 230 may be positioned above the battery cells 206, with a top plate 210 positioned over the interconnect layer 230. The top plate 210 may either be a single plate or be formed from multiple plates.

[0063] Individual battery cells 106 and 206 often are lithium-ion battery cells, with an electrolyte containing lithium ions and positive and negative electrodes. FIG. 3 illustrates a schematic of a lithium ion cell 300. Lithium ions 350 are dispersed throughout electrolyte 320, within container 360. Container 360 may be part of a battery cell. The lithium ions 350 migrate between positive electrode 330 and negative electrode 340. Separator 370 separates the negative electrode and positive electrode. Circuitry 310 connects the negative electrode and positive electrode.

[0064] The present disclosures provides novel electrolyte and battery systems for use in grid and electric vehicle applications, such as the ones described above, as well as newly identified compounds and compositions for use in such systems. Certain embodiments described herein include a nonaqueous electrolyte for a lithium ion battery comprising at least one lithium salt, at least one nonaqueous solvent, and an additive component comprising at least one operative additive. The at least one operative additive is selected from

[0065] (a) the group consisting of 3-aryl substituted l,4,2-dioxazol-5-one compounds according to Formula (I):

 

 

[0066] wherein R is any aromatic substituent, any unsaturated aliphatic substituent, or any aliphatic substituent containing one or more fluorine atomsor

[0067] (b) the group consisting of 3-CRR’R” substituted l,4,2-dioxazol-5-one compounds according to Formula (II):

 

 

[0068| wherein each of R, R’, and R” is hydrogen, alkyl substituents, or aromatic substituents; or

[0069] (c) the group consisting of R-substituted nitrile sulfite compounds according to

Formula (III):

 

 

[0070] wherein R is any alkyl or aromatic substituent.

[0071] Exemplary 3-aryl substituted l,4,2-dioxazol-5-one compounds according to certain embodiments include those shown in Table 1.

 

[0072] Chemical structures of other exemplary additives for the electrolyte solutions discussed herein include the formulas shown above: 3-methyl- 1, 4, 2-dioxazol-5-one (MDO) (Formula IV) and benzonitrile sulfite, 3-phenyl-l,3,2,4-dioxathiazole 2-oxide (BS) (Formula VI ).

[0073] MDO, or 3-methyl-l,4,2-dioxazol-5-one, has demonstrated ability to passivate graphite anodes against exfoliation in the presence of propylene carbonate (PC). See, e.g., Chem. Mater., 2017, 29 (18), pp 7733-7739.

[0074] In certain further embodiments, the additives to the electrolyte solutions described herein are in a range from 0.01 to 6 wt. %, based on the total weight of the electrolyte solution. In other embodiments, the at least one operative additive is in a range from 0.25 to 5 wt. %, 0.35 to 4.5 wt. %, 0.45 to 4 wt. %, 0.55 to 3.5 wt. %, 0.65 to 3 wt. %, 0.75 to 2.5 wt. %, 0.85 to 2 wt. %, 0.95 to 2 wt. %, 1.05 to 1.5 wt. %, 1 to 5 wt. %, 1 to 4 wt. %,l to 3 wt. %, 2 to 4 wt. %, 1 to 2 wt. %, 3 to 4 wt. %, 2 to 5 wt. %, or 2 to 4 wt. % based on the total weight of the electrolyte solution. In other embodiments, the concentration of the at least one operative additive is about 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.5%, 3%, 3.5%, 4% 4.5%, 5%, 5.5%, or 6% by weight.

[0075] The additive component may include a combination of additives of described herein. Additionally, the additive component may include ethylene sulfate, lithium difluorophosphate, vinylene carbonate, fluoroethylene carbonate and combinations thereof.

[0076] In certain embodiments, the at least one nonaqueous is a carbonate solvent. In further embodiments, the carbonate solvent is ethylene carbonate or dimethyl carbonate. In yet further embodiments, the nonaqueous solvent includes at least 2 nonaqueous solvents.

[0077] In other embodiments, the battery systems described herein have a 95% retention of initial capacity after 200 cycles between 3.0 V and 4.3 V at a charging rate of C/3 CCCV at 40°C. In further embodiments, the battery system has 95% retention of initial capacity after 300 cycles between 3.0 V and 4.3 V at a charging rate of C/3 CCCV at 40°C. In further embodiments, the battery system has 95% retention of initial capacity after 400 cycles between 3.0 V and 4.3 V at a charging rate of C/3 CCCV at 40°C.

[0078] The cell formation, long-term cycling performance, and high temperature storage behavior of MDO (Formula IV), 3-phenyl- 1, 4, 2-dioxazol-5-one (PDO, Formula V) and BS (benzonitrile sulfite; alternatively 3-phenyl-l,3,2,4-dioxathiazole 2-oxide, Formula VI), and binary blends thereof, in LiNi1-x-yMnxCoyO2 (NMC)/graphite pouch cells was studied. The results reported by others strongly suggest that MDO primarily acts by passivating the graphite electrode. It is, however, unknown whether these additives affect the positive electrode. Therefore, the studies described herein also tested each additive in binary additive mixtures with VC, DTD, and LFO, which are known to sometimes have beneficial effects at the positive electrode.

[0079] Differential capacity results indicate that MDO and PDO form passive solid-electrolyte interphase layers on the graphite electrode during cell formation, whereas BS does not. It is demonstrated that PDO is a highly promising new additive, especially when used as a binary blend with lithium difluorophosphate or ethylene sulfate.

Pre-Experimental Setup

[0080] Although the battery systems themselves may be packaged differently according to the present disclosure, the experimental setup typically used machine made“sealed cells” to systematically evaluate the battery systems using a common setup, including the two-additive

electrolyte systems and materials for use as the positive and negative electrodes. All percentages mentioned within this disclosure Eire weight percentages unless otherwise specified. A person of skill in the art will appreciate that the type of additive to be used and the concentration to be employed will depend on the characteristics which are most desirably improved and the other components and design used in the lithium ion batteries to be made and will be apparent from this disclosure.

 

Additive Synthesis

[0081] MDO, PDO, and BS were synthesized using the routes shown below.

 

[0082] Reaction a) shows synthesis of 3-methyl- 1, 4, 2-dioxazol-5-one (MDO), reaction b) shows synthesis of 3-phenyl-l,4,2-dioxazol-5-one (PDO), and reaction c) shows synthesis of benzonitrile sulfite (BS).

[0083] All solvents and starting materials were used as-received, without further purification. Thionyl chloride (1 M in CH2C12) and benzohydroxamic acid (98%) were purchased from Alfa Aesar. 1,1’-carbonyldiimidazole (CDI, ³ 98%) and acetohydroxamic acid (95%) were purchased from Oakwood Chemical Inc. Following preparation, additives were characterized by nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FTIR). Full details of the syntheses and the characterization results are provided below.

 

[0084] MDO and PDO were synthesized as follows. To a stirred solution of hydroxamic acid (5.00g, 36.5 mmol, leq) in dichloromethane (120 mL), 1,1’-carbonyldiimidazole (5.92g, 36.5 mmol, 1 eq) was added in one portion. The mixture was stirred for half an hour at room

temperature, quenched with 50 mL of IN H2SO4, extracted with dichloromethane (3x40 mL), and dried over Na2SO4. Volatiles were removed under reduced pressure to give 3-substituted

1.4.2-dioxazol-5-ones. The product (3-methyl-l,4,2-dioxazol-5-one) was recrystallized from diethyl ether using liquid nitrogen, or from a 10:1 mixture of cyclohexane:acetone (3 -phenyl - 1.4.2-dioxazol-5-one). The structure of 3-methyl-l,4,2-dioxazol-5-one (MDO) is shown below:

 

[0085] The structure of 3-phenyl-l,4,2-dioxazol-5-one (PDO) is shown below:

 

[0086] Additional 3 -substituted- 1, 4, 2-dioxazol-5-ones were also synthesized, including o-FDO, m-FDO, p-FDO, p-MODO, and TDO. These compounds were prepared by dissolving potassium carbonate (K2CO3, 3.32g, 24.0mmol, 2 eq) and hydroxylamine hydrochloride (HN2OH*HCl, 1.67 g, 24.0 mmol, 2eq) in 40 mL water (H2O), to which 60 mL of ethyl acetate was added. 12.0 mmol of the corresponding acyl chloride (c-FDO: 2-fluorobenzoyl chloride; m-FDO: 3-fluorobenzoyl chloride; p-FDO, 4fluorobenzoyl chloride; p-MODO: 4-methoxybenzoyl chloride; TDO: 2-thiophenecarbonyl chloride) was dissolved in 20 mL ethyl acetate, and this was added dropwise at 0°C with constant stirring by magnetic bar. The reaction was allowed to warm up to room temperature and left to proceed for 16 hr with constant stirring. The aqueous layer was extracted with ethyl acetate (3x30 mL), dried over anhydrous sodium sulfate (Na2SO4), and the solvent removed under reduced pressure. The residue from the previous step was added to 40 mL dichloromethane, and 1,1’-carbonyldiimidazole (l.95g, 12.0 mmol, 1 eq) was added in one portion. The reaction was allowed to proceed for 30 min with constant stirring by magnetic stir bar. The reaction was then quenched with 1M H2SO4 (25mL), extracted with dichloromethane (3x25 mL), and then dried over anhydrous sodium sulfate. Solvent was removed under reduced pressure to obtain the product.

[0087] Benzonitrile sulfite (BS, 5-phenyl- 1,3, 2, 4-dioxathiazole 2-oxide) was prepared as follows. To a solution of thionyl chloride (30 mL, 1M, 30 mmol, 3 eq), benzohydroxamic acid (1.4g, 10.0 mmol, 1 eq) was added. The mixture was stirred for 6 hr at room temperature. Excess thionyl chloride and solvent were removed under reduced pressure to yield 5-phenyl-l, 3, 2, 4-dioxathiazole 2-oxide (l.57g, 80%). The product was rescrystallised from diethyl ether using liquid nitrogen for purification. The structure of 5-phenyl-l, 3, 2, 4-dioxathiazole 2-oxide is shown below:

 

 

Additive Characterization

[0088] Following isolation, and purification, the MDO, PDO, and BS additives synthesized as described above were characterized by nuclear magnetic resonance spectroscopy (NMR) using a Bruker AV500 spectrometer controlled by ICON-NMR software. MDO was characterized using 1H NMR (CDCl3, 500 MHz): 2.35 (s, 3H), as shown in FIG. 4. MDO was characterized using 13C NMR (CDCl3, 125 MHz): 164.0, 154.2, 10.5, as shown in FIG. 5. PDO was characterized using 1H NMR (CDCl3, 300 MHz): 7.83-7.89 (m, 2H), 7.61-7.69 (m, 1H), 7.50-7.59 (m, 2H), as shown in FIG. 7. PDO was characterized using 13C NMR (CDCl3, 125 MHz): 163.7, 154.0, 133.9, 129.6, 126.7, 120.3, as shown in FIG. 8. BS was characterized using 1H NMR (CDCl3, 500 MHz): 7.90-7.96 (m, 2H), 7.56-7.64 (m, 1H), 7.47-7.55 (m, 2H), as shown in FIG. 10. BS was characterized using 13C NMR (CDCl3, 125 MHz): 157.3, 133.1, 129.3, 128.2, 120.8, as shown in FIG. 11. Chemical shifts are reported in ppm relative to the residual solvent peak.

[0089] Materials were also characterized by Fourier transform infrared spectroscopy (FTIR) using a Cary 630 FTIR (Agilent Technologies) equipped with a germanium crystal attenuated total reflectance (ATR) accessory, controlled by MicoLab PC software, and measured at 4 cm-1 resolution. The FTIR spectrum of 3-methyl- 1,4, 2-dioxazol-5-one (MDO) is shown in FIG. 6; the

spectrum of 3-phenyl-l,4,2-dioxazol-5-one (PDO) is shown in FIG. 9, and the spectrum of BS is shown in FIG. 12.

 

Lithium-ion Cells

[0090] Dry (no electrolyte), vacuum-sealed LiNio.sMno.3Coo.2O2 (NMC532)/graphite and LiNi0.6Mn0.2Co0.2O2 (NMC622)/graphite pouch cells, with capacity of -220 mAh and -230 mAh, respectively, were received from LiFun Technology (Tianyuan District, Zhuzhou, Hunan, China). The cells were cut below the heat seal in an argon-atmosphere glove box, dried under vacuum at 80°C for 14 h, and then returned to the glove box for filling. All solutions used 1.2 mol L-1 LiPF6 (BASF, ³ 99.9%) in a 3:7 solvent blend, by mass, of ethylene carbonate (EC) and dimethyl carbonate (DMC), as received from BASF (< 20 ppm H2O). The additives MDO (synthesized as described above), PDO (synthesized as described above), BS (synthesized as described above), VC (BASF, ³ 99.8%), DTD (Guangzhou Tinci Materials Tech. Co. Ltd., ³ 98%), and L1PO2F2 (abbreviated as“LFO”, Shenzhen CapChem Tech. Co. Ltd.) were added singly or as binary blends to this electrolyte solution in the indicated mass percentages. Cells were filled with 1.0 ± 0.1 g of solution, sealed at -90 kPa gauge pressure using a compact vacuum sealer (MSK-l 15 A, MTI Corp.) and immediately held at 1.5 V at room temperature (21 - 25°C) to prevent corrosion of the copper current collector during the -24 h wetting period that followed. Cells were then loaded into temperature-controlled boxes (40.0 ± 0.1 °C) and connected to a Maccor 4000 Series automated test system (Maccor Inc.). Because gas formation was expected to occur during formation, the pouch cells were clamped using soft rubber (at about 25 kPa gauge pressure), which had previously been observed to significantly improve the experimental precision.

 

Electrochemical Testing

[0091] SEI formation was performed by charging cells at C/20 to 4.3 V, holding at 4.3 V for 1 h, discharging at C/20 to 3.8 V, and then holding cells at 3.8 V for 1 h. Cells were weighed under water before and after formation, allowing the change in displacement volume to be determined using the Archimedes principle. Cells were then degassed by cutting the pouch open in an argon-atmosphere glove box, and resealed using the compact vacuum sealer. Cells were weighed again and electrochemical impedance spectroscopy (EIS) was then measured at 10.0 ± 0.1°C using a BioLogic VMP3 instrument (100 kHz - 10 mHz, ± 10 mV sinusoidal amplitude). Following formation, cells were either taken for storage or long-term cycling.

[0092] For storage, cells were maintained at 40. ± 0.1 °C while they were cycled between 2.8 - 4.3 V twice and then held at 4.3 V for 24 h. Cells were then increased in temperature to 60. ± 0.1 °C and the cell voltage was recorded at open circuit for 500 hr. Following storage, cells were charge-discharge cycled twice again and then charged to 3.8 V. EIS was then measured and cells were weighed under water again to determine gas evolution during storage.

[0093] For long-term cycling, cells were maintained at 40. ± 0.1 °C and cycled by charging at C/3 to 4.3 V, and holding the voltage at 4.3 V until the charge current decreased below C/20. Cells were then discharged at C/3 to 2.8 V before being charged again. A slow charge-discharge cycle at C/20 was performed every 50 cycles.

 

Density Functional Theory Calculations

[0094] Density functional theory (DFT) calculations were performed using Gaussian (G09.d01), as described in M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, et al., Gaussian 09, Gaussian, Inc., Wallingford, CT, USA, (2009). Geometry optimization and normal mode analyses were performed using the M062X hybrid functional, as described in Y. Zhao and D. G. Truhlar, Theor. Chem. Acc., 120, 215-241 (2007); the IEFPCM-UFF implicit solvation model (e = 20), as described in D. S. Hall, J. Self, and J. R. Dahn, J. Phys. Chem. C, 119, 22322-22330 (2015), J. Tomasi, B. Mennucci, and R. Cammi, Chem. Rev., 105, 2999-3094 (2005), and J. Tomasi, B. Mennucci, and E. Cances, J. Mol. Struct. THEOCHEM, 464, 211-226 (1999); and the 6-311++G(2df,2pd) basis set. Whereas the B3LYP hybrid functional generally provides an excellent balance of speed and accuracy, the M062X double hybrid functional typically offers superior accuracy for molecules with charge separation. The polarizable continuum model (PCM) was selected to balance calculation speed and accuracy. This choice comes with an inherent loss of accuracy, because implicit solvation models do not account for factors such as solvation sheath structure and preferential solvation in binary solvents. Standard electrode potentials were calculated according to the following reactions for (1) oxidation and (2) reduction of a molecular species, M\

 

[0095] The full details of the calculation of electrode half potentials from DFT-calculated free energies of reaction, including the conversion from the absolute to relative electrode potentials, is known in the art.

 

Results and Discussion

[0096] During the initial portion of the first charging step, the potential of the positive electrode increases very slowly, whereas the potential at the negative electrode surface decreases relatively quickly. As a result, it is during this‘formation’ step that the negative electrode SEI is produced, primarily by the electrochemical reduction of EC and/or electrolyte additives at the graphite surface. The differential capacity versus voltage (dQ/dV vs. V) plots of the first charging step, shown in FIG. 13, may therefore be used to consider whether the additives in this work directly produce negative SEI layers. The introduction of MDO into a cell leads to a broad reduction feature that onsets at ~2.1 Vcell for both cell types (FIG. 13). Given the positive electrode potentials are initially ~3.5 ± 0.1 V vs Li/Li+, it is therefore estimated that this reduction feature onsets at ~ 1.4 V vs Li/Li+. It is noted that the reduction feature is quite small and only visible for cells that contained 2% MDO (see inset). An additional reduction feature is observed at ~2.6 Vcell (~ 0.9 V vs Li/Li+) the origin of which is not clear. However, the reduction potential of MDO was calculated using DFT and found to be closer in value to this second feature, E0red,calc = 0.67 V vs Li/Li+ (Table 2). Finally, there is a small feature at 2.85 Vceii, attributable to reduction of the EC cosolvents. FIG. 13 includes the formation of a‘control’ cell, which was prepared with no additives for comparison. The feature at 2.85 Vceii has a larger area for the 1% MDO cell, indicating incomplete graphite passivation, whereas it is quite small in the 2% MDO cells. The results support the previous observation reported by others that MDO passivates graphite electrode surfaces.

[0097] Cells prepared with PDO display two clear features in the differential capacity plot (FIG. 13). The first reduction feature onsets at ~2.1 Vcell in NMC622/graphite cells (-1.4 V vs. Li/Li+) and -2.0 V (see inset) in NMC532/graphite cells (-1.5 V vs Li/Li+). The second feature onsets at -2.35 Vcell in both cell types (-1.15 V vs Li/Li+). As with MDO, the latter of these is the closer match with the DFT-calculated reduction potential, 1.18 V vs Li/Li+ (Table 2). The EC reduction feature is again weakly present in PDO-containing cells and its area is greater in l%PDO than it is in 2%PDO cells. Moreover, the area of the EC feature is very small for all

PDO-containing cells compared to additive-free cells. This demonstrates that PDO leads to the formation of a passive, or at least a partially passive, SEI on the graphite electrode.

[0098] Finally, cells prepared with BS also display two prominent features in the differential capacity plot (FIG. 13). The area of these features, which is directly proportional to the charge associated with the corresponding reduction, is significantly greater than observed for MDO and PDO reduction. There is also more variability in the onset potential of these features, which range from 2.2 - 2.4 Vcell (—1.1 - 1.3 V vs Li/Li+) and 2.4 - 2.6 Vcell (~0.9 - 1.1 V vs Li/Li+) between the two cell types and various additive blends. For BS, both features are comparable to the DFT-calculated reduction potential, 1.16 V vs Li/Li+ (Table 2). The area of the EC reduction feature is not significantly decreased for cells prepared with BS as a standalone additive. The differential capacity results therefore indicate that BS reduction indeed occurs but that it does not produce a passivating SEI at the graphite surface.

[0099] Table 2:

 

[00100] Shown in Table 2 are the standard reduction and oxidation potentials of the three additives. These were calculated with DFT using M06-2X/6-311++g(2df,2pd)/IEF-PCM(e=20). The experimental reduction potentials, estimated from FIG. 13, are provided for comparison.

[00101] The quantity of gas produced following the iull formation cycle to 4.3 V is summarized in FIG. 14. Whereas some gas production during formation is largely inevitable, it is desirable to develop solution chemistries that do not produce gas excessively. It is observed that PDO-containing cells produced the least amount of gas, whereas MDO-containing cells produced the most. It is interesting that the passivation behavior of MDO at the negative

electrode, as discussed above, does not limit gas production. Since cells with control electrolyte produce about 1.2 mL of gas during formation due to EC reduction and cells with 2% MDO produce about 2 mL, it is clear that MDO must react with Li+ + e- to produce gaseous products. FIG. 14 shows that DTD mitigates gas production from MDO. Prior studies have shown that cells with 1% DTD or 2% DTD as sole additives (in NMC1 l l/graphite cells), yield 0.8 and 1.0 mL of gas during formation. Others have also shown that significant gas is also produced during formation in NMC532/graphite cells that contain just DTD and that this gas is primarily ethylene. Therefore it is believed that there is some synergy in the behavior of MDO and DTD that acts to limit gas production.

[00102] Following the formation and degassing protocols, cells were apportioned into two groups and taken for either high-temperature storage or long-term cycling. For the former, the terminal voltage was measured automatically every 6 hr for 500 hr while the cells were maintained at 60°C (FIG. 15). Some degree of self-discharge under such harsh conditions is inevitable, which provides a practical opportunity to compare the performance of various cell chemistries on a relatively short timescale. FIG. 15 shows that MDO, PDO, and BS all display poor storage behavior when used as standalone additives. For all three additives, the performance was not improved by the introduction of DTD, whereas LFO offered some improvements for PDO and BS. During storage at high voltage and temperature, the production of significant gas volumes is often of concern. FIG. 14 shows that significant gas evolution occurs in cells prepared with MDO, whereas PDO-containing cells produced the least gas in this work. EIS was also measured to observe whether there was significant impedance growth during storage. However, the results summarized in FIG. 16 indicate that impedance growth is not a significant concern for any of the cells tested in this work. Overall, the best storage performance was observed in cells that contained VC as a co-additive and the storage results suggest that PDO is the most promising of the three additives.

[00103] The remainder of the cells in this work were tested via long-term cycling at 40°C and at C/3 charge-discharge rate to 4.3V. In NMC622/graphite cells, MDO-containing cells performed worse than cells made with 2%VC, which is a common additive that offers a good ‘standard’ comparison (FIG. 17). This is the opposite result than was reported in S. Roser, A. Lerchen, L. Ibing, X. Cao, J. Kasnatscheew, F. Glorius, M. Winter, and R. Wagner, Chem. Mater., 29, 7733-7739 (2017), which found that 2% MDO outperformed either 2% VC or 2%

FEC. This difference may be ascribed to the very different electrolyte solutions employed in that work, 1M LiPF6 in PC versus the 1.2M LiPF6 in 25EC:5EMC:70DMC used in the present study. The capacity retention of NMC622/graphite cells prepared with 2%PDO (including binary blends) is comparable to or better than the 2%VC cells. Of these, 2%PDO + 1%DTD is the best-performing blend, which is in contrast to the poor storage behavior of this cell chemistry, relative to 2% VC (FIG. 17). Finally, the cycling performance of BS in NMC622/graphite cells (FIG. 17) is only comparable to the 2%VC cell for the 2%BS + 2%VC blend. Of particular issue is the steep slope of AV versus cycle number (AV is the difference between average charge and average discharge voltages) for BS-containing cells (FIG. 17). This is often a negative sign for the longer-term performance of a cell. These results therefore support the previous observation that PDO is the most promising of the three additives developed in this work.

[00104] MDO-containing cells cycle considerably better in the NMC532/graphite cells, with comparable capacity retention to the 2%VC cells for 1%MD0, 2%MDO+1%DTD, and 2%MDO+2%VC (FIG. 18). However, there is considerable growth in AV versus cycle number for all of the MDO-containing cells. This indicates impedance growth and is often an early indication that a cell will eventually exhibit severe capacity fade and fail. Cells prepared with PDO as a standalone additive exhibit worse cycling performance than the 2%VC cells, in terms of both discharge capacity and AV (FIG. 18). However, the PDO-based blends all outperform 2%VC in terms of capacity retention. 2%PDO+l%DTD and 2%PDO+l%LFO additionally exhibit very little increase in AV versus cycle number, indicating these are both potentially good solution chemistries in NMC532/graphite cells. Finally, all of the BS-containing cells underperform 2%VC in this cell type.

[00105] Finally, it was considered whether the storage performance of PDO-containing cells improves or deteriorates over multiple charge-store cycles. FIG. 19 shows the open circuit voltage of PDO-containing cells that had already been stored at 60°C for 500 hr (FIG. 15b) and that were then charged back to the 4.3 V upper voltage limit and stored for an additional 500 hr. The results demonstrate a significantly smaller voltage drop during this second storage period, relative to the first. This finding is significant because it suggests that PDO performs well in storage but requires a sufficient SEI growth and maturation period. The long-term evolution of additive-derived SEI layers is a complex area of study that merits additional investigation to understand how the processes may be modeled for accurate cell lifetime and performance evolution predictions.

[00106] The cycling, gas evolution and storage performance therefore indicate that PDO is a promising new electrolyte additive, especially when used in combination with DTD and LFO co-additives.

Conclusions

[00107] This work characterizes the high temperature storage and long-term cycling performance of lithium-ion NMC/graphite pouch cells prepared with a recently developed electrolyte additive, MDO, and two new additives, PDO and BS. Differential capacity versus voltage indicates that both MDO and PDO form passive SEI layers on the graphite electrode surface during cell formation, whereas BS does not. The reduction features are generally consistent with DFT-predicted values, although the presence of multiple reduction peaks requires additional study to rationalize. As individual additives, PDO-containing cells show the best performance although these are nonetheless out-performed by VC-containing cells. The additives were also tested in binary blends with VC, DTD, and LFO. In long-term cycling tests, cells prepared with 2%PDO/l%DTD and 2%PDO/l%LFO additive blends outperform VC-containing cells. However, the high temperature storage behavior of 2%PDO/l%LFO is superior than that of the 2%PDO/l%DTD blend. A person of skill in the art will understand that compositions described herein may be further optimized, for example, by adjusting the ratio of primary and secondary additives or through introducing ternary blends.

[00108] The foregoing disclosure is not intended to limit the present disclosure to the precise forms or particular fields of use disclosed. As such, it is contemplated that various alternative embodiments and/or modifications to the present disclosure, whether explicitly described or implied herein, are possible in light of the disclosure. Having thus described embodiments of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made in form and detail without departing from the scope of the present disclosure. Thus, the present disclosure is limited only by the claims. Reference to additives in the specification are generally to operative additives unless otherwise noted in the specification.

[00109] In the foregoing specification, the disclosure has been described with reference to specific embodiments. However, as one skilled in the art will appreciate, various embodiments disclosed herein can be modified or otherwise implemented in various other ways without departing from the spirit and scope of the disclosure. Accordingly, this description is to be considered as illustrative and is for the purpose of teaching those skilled in the art the manner of making and using various embodiments of the disclosed battery system. It is to be understood that the forms of disclosure herein shown and described are to be taken as representative

embodiments. Equivalent elements, or materials may be substituted for those representatively illustrated and described herein. Moreover, certain features of the disclosure may be utilized independently of the use of other features, all as would be apparent to one skilled in the art after having the benefit of this description of the disclosure. Expressions such as “including”, “comprising”,“incorporating”,“consisting of’,“have”,“is” used to describe and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. Reference to“about” or“approximately” is to be construed to mean plus or minus 10%. Similarly, reference to any percentage of an additive is construed to mean plus or minus 10%.

[00110] Further, various embodiments disclosed herein are to be taken in the illustrative and explanatory sense, and should in no way be construed as limiting of the present disclosure. All joinder references ( e. g ., attached, affixed, coupled, connected, and the like) are only used to aid the reader's understanding of the present disclosure, and may not create limitations, particularly as to the position, orientation, or use of the systems and/or methods disclosed herein. Therefore, joinder references, if any, are to be construed broadly. Moreover, such joinder references do not necessarily infer that two elements are directly connected to each other.

[00111] Additionally, all numerical terms, such as, but not limited to,“first”,“second”, “third”,“primary”,“secondary”,“main” or any other ordinary and/or numerical terms, should also be taken only as identifiers, to assist the reader’s understanding of the various elements, embodiments, variations and/ or modifications of the present disclosure, and may not create any limitations, particularly as to the order, or preference, of any element, embodiment, variation and/or modification relative to, or over, another element, embodiment, variation and/or modification.

[00112] It will also be appreciated that one or more of the elements depicted in the drawings/figures can also be implemented in a more separated or integrated manner, or even removed or rendered as inoperable in certain cases, as is useful in accordance with a particular application.