Novel battery systems based on two-additive electrolyte systems including 2-furanone, and method of formation process of same

Abstract

An improved battery system has been developed for lithium-ion based batteries. The improved battery system consists of a two-additive mixture in an electrolyte solvent. This battery system is manufactured by performing a forming process comprising assembling a positive and negative electrode into a sealed cell, removing residues from the sealed cell, filling the sealed cell with a non-aqueous electrolyte under an inert atmosphere, vacuum-sealing the sealed cell, and charging and discharging the sealed cell until the sealed cell reaches its initial capacity. The non-aqueous electrolyte comprises a mixture of lithium ions, a first non-aqueous solvent comprising a carbonate solvent, a second non-aqueous solvent comprising methyl acetate, and a first working additive of vinylene carbonate or fluoroethylene carbonate and a second working additive of 2-furanone. Gas formation in the battery system is suppressed during the forming process.

Description

Technology Field

[0001] The present invention relates to a rechargeable battery system, and more specifically, to the chemistry of such system comprising an operative, an electrolyte additive, and an electrode for improving the characteristics of a rechargeable lithium-ion battery system. The present invention relates to the manufacture of rechargeable battery cells, and more specifically, to post-assembly formation and a testing process of rechargeable battery cells. Background Technology

[0002] Rechargeable batteries are an essential component of energy storage systems for electric vehicles and grid storage (e.g., backup power as part of a microgrid during a power outage). Depending on the application, energy storage systems require different characteristics. Tradeoffs regarding the chemistry of the battery system may be necessary to create a system suitable for a specific application. For example, in automotive applications, particularly electric vehicles, the ability to charge and discharge quickly is a critical characteristic of the system. Electric vehicle owners need to accelerate rapidly in traffic situations, which requires the ability to discharge the system quickly. Furthermore, since fast charging and discharging locations demand such systems, the components of the system must also be selected to provide sufficient lifespan under these operating conditions.

[0003] The first charge and discharge of a Li-ion cell is performed at the factory by the manufacturer. This is referred to as the "formation process." The formation process can result in the creation of a solid-electrolyte-interface (SEI) at the anode, which acts as a passivation layer essential for controlling the charging process in general use. This formation charge / discharge process helps identify cells that do not meet quality standards before being placed in a battery pack. Furthermore, it is important to minimize gas generation during the formation process, which can lead to process simplification.

[0004] Furthermore, during the formation process, information regarding cell performance such as cell capacity, and after formation, open-circuit voltage (OCV), direct-current resistance (DCR), capacitance, and impedance can be collected for quality analysis. The spread of performance measurements can also indicate whether the formation process and upstream cell manufacturing process are being controlled.

[0005] For high-throughput manufacturing, large quantities of cells can be placed together in the forming process, typically on conveyance trays. Conventional high-volume forming facilities generally consist of power supplies and control modules connected to battery contact fixing devices that secure the cell trays and facilitate electrical connections to individually controlled cells. Such systems often require a large number of cables (typically four or more wires per battery cell), occupy significant space, and can be energy-inefficient. Consequently, inefficiencies from power electronics and long cables can lead to heat rejection into the room, which often requires large ducted air cooling systems and can result in cell temperature fluctuations, thereby increasing the potential for errors in the forming process. Furthermore, existing forming facilities are generally designed without optimization or full consideration of the support systems.

[0006] Furthermore, electrolyte additives have been shown to be operative and increase the lifespan and performance of Li-ion-based batteries. For example, JC Burns et al., Journal of the Electrochemical Society In , 160, A1451 (2013), five proprietary, undisclosed electrolyte additives were shown to increase cycle life compared to electrolyte systems with no additives or only a single additive. Other studies have focused on performance improvements from electrolyte systems containing three or four additives as described in US 2017 / 0025706. However, researchers generally do not understand the interactions between different additives that enable synergistic action with the electrolyte and specific anodes and cathodes. Therefore, the composition of additive blends for a particular system is often based on trial and error and cannot be predicted in advance.

[0007] Conventional research has not identified a two-additive electrolyte system that can be combined with a lithium-ion battery system to obtain a robust system with sufficient characteristics for grid or automotive applications. As discussed in US 2017 / 0025706, the two-additive systems studied (e.g., 2% VC + 1% allyl methanesulfonate and 2% PES + 1% TTSPi) generally performed worse than three- and four-additive electrolyte systems (see, e.g., Tables 1 and 2 of US 2017 / 0025706). US 2017 / 0025706 discloses that to manufacture robust lithium-ion battery systems, three compounds, often tris(-trimethylsilyl)-phosphate (TTSP) or tris(-trimethylsilyl)-phosphite (TTSPi), are required at concentrations of 0.25–3 wt% (see, e.g., page 72 of US 2017 / 0025706). However, additives are expensive and, at manufacturing scale, within Li-ion batteries Because it can be difficult to include, a simpler but more effective battery system containing fewer additives is needed. means of solving the problem

[0008] The present disclosure includes a novel battery system having fewer operating electrolyte additives that can be used in different energy storage applications, e.g., vehicles and grid storage devices. More specifically, the present disclosure includes a two-additive electrolyte system that reduces the amount of gas generated during the forming process and enhances the lifespan and performance of lithium-ion batteries, while reducing costs compared to other systems that rely on more additives. The present disclosure discloses an effective anode and cathode that work with the disclosed two-additive electrolyte system to provide more systematic improvements.

[0009] A two-acting, additive electrolyte system comprising vinylene carbonate (VC) combined with 2-furanone (FN) is disclosed. FN has the following formula (I):

[0010] (I)

[0011] In addition, a fluoroethylene carbonate (FEC) combined with FN is disclosed.

[0012] Because VC and FEC provide similar improvements (and are considered to function similarly), a mixture of VC and FEC can be regarded as merely a single-acting electrolyte. That is, another disclosed two-acting, additive electrolyte system comprises a mixture of VC and FEC combined with FN. When used as part of a larger battery system (including an electrolyte, electrolyte solvent, anode, and cathode), this two-acting, additive electrolyte system provides desirable characteristics for energy storage applications, including vehicle and grid applications.

[0013] More specifically, there are a lithium nickel manganese cobalt oxide (NMC) anode, a graphite cathode, a lithium salt dissolved in an organic or non-aqueous solvent, and two additives for forming a battery system having desirable characteristics for different applications.

[0014] The electrolyte solvent may be the following solvents alone or in combination: ethylene carbonate (EC), ethyl methyl carbonate (EMC), methyl acetate, propylene carbonate, dimethyl carbonate, diethyl carbonate, other carbonate solvents (cyclic or acyclic), other organic solvents, and / or other non-aqueous solvents. The solvent is present at a concentration greater than that of the additive, generally greater than 6 wt%. The solvent may be combined with the disclosed two-additive pairs (VC and FN, FEC and FN, a mixture of VC and FEC and FN, or other combinations) to form a battery system having characteristics desirable for different applications. The anode may be coated with materials such as aluminum oxide (Al2O3), titanium dioxide (TiO2), or other coatings. Additionally, for cost reduction, the cathode may be formed from natural graphite, but depending on the price structure, in certain cases, synthetic graphite is cheaper than natural graphite.

[0015] The present disclosure is supported by experimental data demonstrating the symbiotic nature of a two-additive electrolyte system and a selected electrode. An exemplary battery system comprises two additives (e.g., FEC or VC, FN), a graphite anode (naturally occurring graphite or synthetic, synthetic graphite), an NMC cathode, a lithium electrolyte (e.g. formed from a lithium salt such as lithium hexafluorophosphate having the chemical composition LiPF6), and an organic or non-aqueous solvent.

[0016] An exemplary embodiment of the present application is a method for manufacturing a battery system comprising a sealed cell, the method comprising the steps of: assembling a positive electrode and a negative electrode to the sealed cell; removing residue from the sealed cell; filling the sealed cell with a non-aqueous electrolyte under an inert atmosphere; vacuum-sealing the sealed cell; and performing a forming process comprising charging and discharging the sealed cell until the sealed cell obtains an initial capacity.

[0017] The above-mentioned non-aqueous electrolyte comprises: lithium ions; a first non-aqueous solvent comprising a carbonate solvent; a second non-aqueous solvent comprising methyl acetate; and an additive mixture of a first working additive of either vinylene carbonate or fluoroethylene carbonate and a second working additive of 2-furanone having the following formula (I):

[0018] (I).

[0019] In some embodiments, this electrolyte formulation helps suppress gas formation in the battery system during the formation process.

[0020] In some embodiments, substantially all residue is removed. In some embodiments, all residue is removed.

[0021] In some embodiments, the initial capacity is a specified upper cutoff potential.

[0022] In some embodiments, the method does not include a gas release step after the forming process.

[0023] In another exemplary embodiment, gas generation during the formation process is suppressed by at least 50% compared to gas generation during the formation process of a battery system containing only the first operating additive.

[0024] In another exemplary embodiment, the forming process comprises charging a sealed cell to 4.2V at 11 mA, in this case corresponding to C / 20 (C / x), and discharging to 3.8V, where C / x indicates that the time for charging or discharging the cell at a selected current is x hours when the cell is at its initial capacity.

[0025] In another exemplary aspect, removing residue from a sealed cell involves opening the sealed cell under a heat seal and drying it at 100°C for 12 hours under vacuum.

[0026] In another exemplary embodiment, gas generation is completely suppressed during the formation process.

[0027] In another exemplary embodiment, the battery system has a capacity retention similar to that of a battery system containing only the first operating additive.

[0028] In another exemplary embodiment, the concentration of the first working additive is in the range of 0.25 to 6 weight percent.

[0029] In another exemplary embodiment, the concentration of the second working additive is in the range of 0.1 to 5 weight percent.

[0030] In another exemplary embodiment, the concentration of the first working additive is 2 weight%, and the concentration of the second working additive is 0.5 weight% to 1 weight%.

[0031] In another exemplary embodiment, the first working additive is fluoroethylene carbonate.

[0032] In another exemplary embodiment, the first working additive is vinylene carbonate.

[0033] In another exemplary embodiment, the non-aqueous solvent is a carbonate solvent.

[0034] In another exemplary embodiment, the non-aqueous solvent is at least one selected from ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0035] In another exemplary embodiment, the solvent additionally comprises a second non-aqueous solvent.

[0036] In another exemplary embodiment, the second non-aqueous solvent is methyl acetate.

[0037] In another exemplary embodiment, the anode is selected from NMC532, standard NMC532 and NMC622 having micrometer-sized particles.

[0038] In another exemplary embodiment, the cathode is selected from synthetic graphite and natural graphite. Brief explanation of the drawing

[0039] Figure 1 is a schematic diagram of a vehicle containing a battery storage system. Figure 2 is a schematic diagram of an exemplary battery storage system. Figure 3 is a schematic diagram of a lithium-ion battery-cell system. FIG. 4 illustrates an exemplary configuration of a contact module and an electrical circuit module for cell formation according to one embodiment of the present invention. Figures 5a-5c illustrate the gas formation and filling profiles of various electrolytes. FIG. 5a illustrates the gas formation and filling profile of an electrolyte composition containing 2% FEC as a first electrolyte additive. FIG. 5b illustrates the gas formation and filling profiles of an electrolyte composition comprising 2% FEC as a first electrolyte additive and 0.5% FN as a second electrolyte additive. FIG. 5c illustrates the gas formation and filling profile of an electrolyte composition comprising 2% FEC as a first electrolyte additive and 1% FN as a second electrolyte additive. Figures 6a-6b illustrate the passivation impact of various electrolyte compositions on different types of cells. Figure 6a illustrates the passivation effect of EC:EMC with ethylene carbonate (EC):ethyl methyl carbonate (EMC) (control), and 2% VC, 0.5% FN, 1% FN, 2% VC + 1% FN, 2% FEC + 1% FN, and 1% LFO (LiPO2F2) + 1% FN on a cell having a coated NMC532 anode and an artificial graphite cathode. FIG. 6b illustrates the passivation effect of EC:EMC having ethylene carbonate (EC):ethyl methyl carbonate (EMC) and 2% VC, 0.5% FN, 1% FN, 2% VC + 1% FN, and 2% FEC + 1% FN in a lithium-ion battery cell. Figures 7a-7b show gas formation and electrochemical impedance spectroscopy (EIS) spectra in different electrolyte compositions for different types of cells. FIG. 7a shows the gas formation and EIS spectra in an electrolyte composition comprising 2% VC, 2% FEC, 1% LFO, 0.5% FN, 1% FN, 2% VC + 1% FN, 2% FEC + 1% FN, and 1% LFO + 1% FN in a cell having a coated NMC532 anode and an artificial graphite cathode. FIG. 7b shows the gas formation and EIS spectra in an electrolyte composition comprising 2% VC, 0.5% FN, 1% FN, 2% VC + 1% FN, and 2% FEC + 1% FN in a lithium-ion battery cell. Figures 8a-8e show typical experimental data from long-term cycling studies at 40°C and C / 3 CCCV, demonstrating the advantages of including FN as an additive in an electrolyte system containing VC or FEC. FIG. 8a shows the discharge capacity, normalized capacity, and voltage hysteresis of an electrolyte system containing 2% VC, 2% FEC, 0.5% FN, and 1% FN in a cell containing a coated NMC532 anode and an artificial graphite cathode. FIG. 8b shows the discharge capacity, normalized capacity, and voltage hysteresis of an electrolyte system containing 2% VC, 2% FEC, 2% VC + 1% FN, and 2% FEC + 1% FN in a cell containing a coated NMC532 anode and an artificial graphite cathode. FIG. 8c illustrates the discharge capacity, normalized capacity, and voltage hysteresis of an electrolyte system containing 1% LFO and 1% LFO + 1% FN in a cell containing a coated NMC532 anode and an artificial graphite cathode. Figure 8d shows the discharge capacity, normalized capacity, and voltage hysteresis of an electrolyte system comprising an EC:EMC:DMC electrolyte having 2% VC, 2% FEC, 0.5% FN, and 1% FN as additives to a lithium-ion battery cell. FIG. 8e illustrates the discharge capacity, normalized capacity, and voltage hysteresis of an electrolyte system comprising an EC:EMC:DMC electrolyte having 2% VC + 1% FN, 2% FEC + 1% FN, 2% VC, and 2% FEC in a lithium-ion battery cell. Specific details for implementing the invention

[0040] "Cell" or "battery cell" generally refers to an electrochemical cell, which is a device capable of utilizing a chemical reaction through the introduction of electrical energy or generating electrical energy from a chemical reaction. A battery may include one or more cells.

[0041] "Rechargeable battery" generally refers to a type of electric battery capable of charging, discharging under load, and recharging multiple times. In this disclosure, a number of examples are described based on lithium-ion rechargeable batteries. Nevertheless, embodiments of the present invention are not limited to a single type of rechargeable battery and may be applied in conjunction with various rechargeable battery technologies.

[0042] The following description is provided to enable a person skilled in the art to make and use embodiments, and is provided in the context of a specific application and its requirements. Various modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of this disclosure. Accordingly, the present invention is not limited to the embodiments shown but follows the broadest scope consistent with the principles and features disclosed herein.

[0043] 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) (402A and / or 402B), at least one gearbox (404A and / or 404B) connected in correspondence with the drive motor (402A and / or 402B), a battery cell (406), and an electronic device (408). Generally, the battery cell (406) supplies electricity to the power electronics of the electric vehicle (100) and uses the drive motor (402A and / or 402B) to propel the electric vehicle (100). The electric vehicle (100) includes a large number of other parts that are not described herein but are known to those skilled in the art. Although the structure of the electric vehicle (100) in FIG. 1 is depicted as having four wheels, other electric vehicles may have fewer than four or more than four wheels. Additionally, other types of electric vehicles (100) may include, among other types of vehicles, motorcycles, aircraft, trucks, boats, train engines, and the progressive concepts described herein. Specific parts created using aspects of the present disclosure may be used in the vehicle (100).

[0044] FIG. 2 illustrates a schematic diagram of an exemplary energy storage system (200) illustrating various components. The energy storage system (200) generally comprises a modular housing having at least a base (202) and four side walls (204) (only two are shown in the drawing). The modular housing is generally electrically isolated from the housingd battery cell (206). This can be achieved through physical isolation, through an electrical insulation layer, through the selection of an insulating material as the modular housing, any combination thereof, or other methods. The base (202) may be an electrical insulation layer on top of a metal sheet or a non-conductive / electrical insulating material such as polypropylene, polyurethane, polyvinyl chloride, other plastics, non-conductive composites, or insulated carbon fiber. Additionally, the sidewall (204) may include an insulating layer or be formed of a non-conductive or electrically insulating material such as polypropylene, polyurethane, polyvinyl chloride, other plastics, non-conductive composites, or insulated carbon fibers. One or more interconnect layers (230) may be placed on a battery cell (206) having an upper plate (210) placed on top of the interconnect layer (230). The upper plate (210) may be a single plate or formed from multiple plates. Each battery cell (106 and 206) is often a lithium-ion battery cell having an electrolyte containing lithium ions and a positive and a negative electrode.

[0045] FIG. 3 illustrates a schematic diagram of a lithium-ion cell (300). Lithium ions (350) are dispersed throughout the electrolyte (320) within a container (360). The container (360) may be part of a battery cell. Lithium ions (350) move between a positive electrode (330) and a negative electrode (340). A separator (370) separates the negative electrode and the positive electrode. A circuit (310) connects the negative electrode and the positive electrode.

[0046] FIG. 4 illustrates an exemplary configuration of an electrical circuit module and a contact module for cell formation according to one embodiment of the present invention. In this example, the contact module (102) and the electrical circuit module (104) are located adjacent to each other. A cell undergoing formation charge / discharge cycling may be placed in contact with a contact pin at one of the receptacles on the contact module (102). The circuit module (104) may accommodate a plurality of electrical circuits, each corresponding to a receptacle on the contact module (102) for accommodating a cell. Each cell-specific circuit may be configured to supply a well-controlled voltage to the cell accommodated in the receptacle and to collect measurements for the cell. It should be noted that this compact configuration of the contact module (102) and the circuit module (104), which jointly form a cell interface block, can eliminate the need for a large amount of cabling as in conventional formation systems. Large amounts of cabling are expensive, take up space, require long installation and repair times, can be a cause of inefficiency, and may reduce accuracy.

[0047] Since the contact module (102) may include a plurality of pogo pins in the receptacle, the contact module (102) may also be called a "pogo board." In one embodiment, the contact module (102) and the circuit module (104) may be attached together with spacers (103) so that the two modules can form a single rigid entity. Additionally, the contact module (102) may provide 32 receptacles to accommodate 32 cells at a time. Other numbers of receptacles are also possible.

[0048] To facilitate expandable automatic operation, a contact module / circuit module combination may be attached to an upper platform (108), and a formed cell may be fixed to a lower platform (110). Both the upper platform (108) and the lower platform (110) may be accommodated in a frame (106). In one embodiment, the upper platform (108) and the lower platform (110) may be operated to move vertically in a "clamshell" manner. Specifically, an actuator (122) may move the lower platform (110) upward, and an actuator (124) may move the upper platform downward. Thus, the frame (106) may be referred to as a "clamshell structure." After the cell is placed on the lower platform (110), the upper platform (108) and the lower platform (110) can be actuated to move toward each other, so that the upper part of the cell can come into contact with a pin located inside the respective receptacle of the cell contact module (similar to the contact module (102)). It is also possible to fix the vertical position of the lower platform (110) and move only the upper platform (108) downward to come into contact with the cell, and vice versa. This one-side actuating configuration has specific advantages. By using only one set of actuating mechanisms, the complexity of the clamping fixture can be eliminated, and the total space required for the clamping fixture can be reduced by about one-third. Furthermore, the top-only cell connection configuration can eliminate cables to the bottom of the cell and also obtain the aforementioned advantages. The contact and circuit modules also help eliminate the need to disconnect power electronics modules and long cable runs.

[0049] In the example shown in FIG. 4, the clamshell structure (106) can accommodate eight cell interface blocks (each including a contact module and a circuit module), and each block can accommodate 32 cells. Thus, the entire clamshell structure can handle 32 × 8 = 256 cells simultaneously. Different numbers of cells and different numbers of blocks per block are also possible. This dense cell packing can reduce operational efficiency (operational expenditure, OPEX) and total CAPEX per cell, which could not be achieved in conventional forming systems where the contact board and the power supply and control modules are separated from each other and require complex and space-consuming cabling to connect the two.

[0050] To further improve cell-packing density, a number of clamshell structures, such as structure (106), can be accommodated in a larger rack, such as rack (112). In this example, rack (112) can accommodate 7 clamshell structures, and the total number of cells formed is 1,792. Other numbers of clamshell structures are also possible. Bulky electrical components (parts), such as system control and AC / DC power conversion modules (114), can be provisioned per clamshell structure and placed near each clamshell structure. In a further embodiment, AC / DC power conversion modules can be centrally provisioned on a rack-by-rack basis.

[0051] New research by the inventors has identified novel electrolyte and battery systems for use in grid and electric vehicle applications. These systems are based on two-additive electrolyte systems having a solvent and electrodes comprising vinylene carbonate (VC) combined with 2-furanone (FN) and fluoroethylene carbonate (FEC) combined with FN. These two-additive electrolyte systems have the composition LNi x Mn y Co z It is paired with a cathode prepared from lithium nickel manganese cobalt oxide having O2 (generally abbreviated as NMC or NMCxyz, where x, y, and z are the molar ratios of nickel, manganese, and cobalt, respectively, and x + y + z = 1). In certain embodiments, the cathode is formed from NMC111, NMC532, NMC811, or NMC622. In certain embodiments, an NMC532 cathode formed from a single crystal, micrometer-sized particle, which produces an electrode having a continuous crystal lattice (or particle) of micrometer-sized, has been shown to be particularly robust, partly because the material and processing conditions produce larger grain sizes than those using conventional materials and processing conditions.

[0052] Typical processing conditions produce NMC electrodes in which nanometer-sized particles are packed into larger micrometer-sized aggregates, creating grain boundaries at the nanometer scale. Since grain boundaries are defects that tend to reduce desirable properties (e.g., electrical properties), it is generally desirable to reduce the particle count and increase the grain size. Processing can create larger domains at the micrometer scale, thereby reducing the number of grain boundaries in the NMC electrode and increasing electrical properties. This increase in properties results in a more robust battery system. In certain embodiments, other NMC electrodes can be processed to create larger domain sizes (beyond the micrometer scale), for example, to produce NMC111, NMC811, NMC622, or other NMC compounds, thereby creating a more robust system.

[0053] The anode can be coated with materials such as aluminum oxide (Al2O3), titanium dioxide (TiO2), or other coatings. Coating the anode is advantageous because it helps reduce interfacial phenomena at the anode that can degrade the system, such as parasitic reactions, thermal abuse, or other phenomena. The cathode can be manufactured from natural graphite, synthetic graphite, graphite / SiO2 mixtures, or other materials.

[0054] The electrolyte may be a lithium salt (e.g., LiPF6) dissolved in a combination of organic or non-aqueous solvents, including ethylene carbonate (EC), ethyl methyl carbonate (EMC), methyl acetate (MA), propylene carbonate, dimethyl carbonate (DMC), diethyl carbonate, other carbonate solvents (cyclic or acyclic), other organic solvents, and / or other non-aqueous solvents. The solvent is present at a higher concentration than the additive, generally at a concentration of about 5 wt% or more, or about 6 wt% or more. Experimental data for NMC / graphite cells were generated using electrolyte solvents containing EC and EMC (with or without DMC and / or MA), but these solvents are merely examples of other carbonate solvents and other non-aqueous solvents. EC and EMC solvents were used in experiments to control the tested system to understand the effects of the additive and the electrode. Accordingly, the electrolyte system may use other carbonate solvents and / or non-carbonate solvents, including propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, other carbonate solvents (cyclic or acyclic), other organic solvents, and / or other non-aqueous solvents. The solvent is present at a higher concentration than the additive, generally exceeding 5 wt% or 6 wt%.

[0055] In the two-additive mixture FEC and FN, the concentration of FEC is preferably 0.5 to 6 weight% and the concentration of FN is preferably 0.2 to 5 weight%. In the two-additive mixture VC and FN, the concentration of VC is preferably 0.5 to 6 weight% and the concentration of FN is preferably 0.1 to 5 weight%, 0.15 to 5 weight%, 0.2 to 5 weight%, and 0.25 to 5 weight%.

[0056] This novel battery system can be used in energy-storage applications and automotive applications (including energy storage devices in electric vehicles) where charge / discharge speed and lifespan are important during rapid charging and discharging.

[0057] Pre-Experimental Setup

[0058] Although the battery system itself may be packaged differently according to the present disclosure, the experimental setup generally used mechanically manufactured "sealed cells" to systematically evaluate battery systems using a general setup comprising a two-additive electrolyte system and specific materials for the use of the anode and cathode. All percentages mentioned in the present disclosure are weight percentages unless otherwise noted. Those skilled in the art will understand that the type of additive to be used and the concentration to be applied will vary depending on the characteristics most preferably improved and other components and designs used in the lithium-ion battery to be manufactured.

[0059] Sealed Cells

[0060] The NMC / graphite sealed cell used in the experimental setup contained 1 M LiPF6 in an additive solvent. The electrolyte consisted of 1 M LiPF6 in 1.2 M LiPF6 at 30% EC and 70% EMC. The concentration of the electrolyte components can be modified to include MA and / or DMC. For this electrolyte, the additive components were added at specified weight percentages.

[0061] The sealed lithium-ion battery cells used in the experimental setup contained an electrolyte solvent composed of 1.2 M LiPF6 added to EC, EMC, and DMC in a volume ratio of 25:5:70. For this electrolyte, the additive components were added in specified weight percentages.

[0062] Sealed NMC / graphite cells used a positive electrode made of NMC532 with micrometer-sized particles (sometimes referred to as single-crystal NMC532) and a negative electrode made of synthetic graphite, unless otherwise specified. To test specific battery systems, other positive electrodes and negative electrodes (containing natural graphite) including standard NMC532 (which has particles smaller than those of NMC with micrometer-sized particles) and NMC622 are used.

[0063] Before charging with electrolyte, the sealed cell was cut open under the heat seal and dried under vacuum at 100°C for 12 hours to remove any residue. Afterward, the cell was immediately transferred to an argon-filled glove box for charging and vacuum sealing, and charged with electrolyte. After charging, the cell was vacuum sealed.

[0064] After sealing, the sealed cells were placed in a temperature box at 40.0 + / - 0.1 °C and maintained at 1.5 V for 24 hours to complete wetting. Subsequently, the sealed cells underwent a formation process. Unless otherwise described, the formation process of the NMC / graphite cells involved charging the sealed cells to 4.2 V and discharging to 3.8 V at 11 mA (C / 20). C / x indicates that the time taken to charge or discharge the cell at the selected current is x hours when the cell is at its initial capacity. For example, C / 20 indicates that charging or discharging takes 20 hours. After formation, the cells were transferred to a glove box, cut open to release any generated gases, vacuum-sealed again, and subjected to appropriate experiments.

[0065] The formation process of the lithium-ion battery cell for the cycling and storage experiment consisted of the following steps: charging at C / 2 and 40°C for 1 hour; storing at 60°C for 22 hours; and charging the cell to 4.2 V and discharging it to 3.8 V at C / 2 and 40°C. After formation, the cell was transferred to a glove box, cut open to release any generated gas, then vacuum-sealed again and subjected to appropriate experiments.

[0066] The formation process of the lithium-ion battery cell for charging, profiling, and gas volume measurement experiments consisted of the steps of: charging the sealed cell at C / 20 and 40 ℃ for 1 hour; storing it at 60 ℃ for 22 hours; and charging the cell to 4.2 V and discharging it to 3.8 V at C / 20 and 40 ℃. After formation, the cell was transferred to a glove box, cut open to release any generated gas, then vacuum-sealed again and appropriate experiments were performed.

[0067] Charging Profile and Gas Volume Measurements

[0068] The formation process is performed before cells are used in their intended applications, such as in-vehicle grid storage or energy storage in electric vehicles. During formation, cells undergo precisely controlled charge and discharge cycles, which are intended to activate the electrodes and electrolytes for use in their intended applications. Gas is generated during formation. If a sufficient amount of gas is produced (depending on specific tolerances allowed by the cell and cell packaging), it may need to be released after the formation process and before application. This typically requires an additional step of breaking and resealing the seal. While such steps are common in many battery systems, it is desirable to eliminate them by selecting a system that produces less gas whenever possible.

[0069] Gas volume experiments were conducted as follows: Ex-situ (static) gas measurements were used to measure gas generation during formation and cycling. Measurements were taken using Archimedes' principle with a cell suspended from a balance while submerged in a liquid. Before and after the test, the change in weight of the cell suspended in the fluid is directly related to the change in volume due to the change in buoyancy. The change in mass Δm of the cell suspended in a fluid of density ρ is related to the change in cell volume Δv according to Δv = -Δm / ρ. Gas generated during the charge-discharge period and the high potential holding period was measured using an in-situ gas measurement device described in Aiken et al. (CP Aiken, J. Xia, David Yaohui Wang, DA Stevens, S. Trussler and JR Dahn, J. Electrochem. Soc. 2014 volume 161, A1548-A1554).

[0070] In a specific embodiment, a two-additive electrolyte system, with each additive concentration of about 0.25–6%, forms part of a battery system. FIGS. 5a–5c illustrate the gas formation and charging profiles of various electrolytes tested in a lithium-ion battery cell.

[0071] As shown in FIGS. 5a-5c, the charge profile of the battery cell is independent of the additives present in the electrolyte composition. Furthermore, as shown in FIG. 5c, the charge profile of the electrolyte composition containing EC:EMC:DMC is similar to the charge profile of the electrolyte composition containing 80% EC:EMC:DMC + 20% MA, indicating that the charge profile is independent of the electrolyte composition itself.

[0072] Figures 5a-5c also illustrate gas formation in various electrolyte systems. Surprisingly, the inventors discovered that the presence of FN in the electrolyte composition significantly suppresses gas generation during cell formation compared to an electrolyte composition containing only 2% FEC as an additive. The suppression of gas generation observed after the addition of FN is unrelated to the amount of FN, provided that at least 0.5% of FN is present, as illustrated in Figures 5b-5c. Negligible amounts of gas were generated in cells containing 2% FEC + 1% FN as an additive (Figure 5c), as well as in an electrolyte composition containing 2% FEC + 0.5% FN as an additive (Figure 5b). As also illustrated in Figure 5c, the suppression of gas generation is independent of the main components of the electrolyte composition. The negligible amount of gas generation is not affected even when 20% MA is added to the electrolyte composition. Due to the unexpectedly excellent effect of FN-containing electrolyte compositions, which significantly reduce gas generation during the formation process, the manufacturing process of battery systems can be made more efficient and cost-effective by eliminating the post-formation gas release step. The post-formation gas release step typically requires the opening and resealing of the battery system, which increases manufacturing time and reduces efficiency due to potential solvent evaporation.

[0073] Passivation Impact

[0074] Figures 6a-6b illustrate the passivation impact of various electrolytes in different types of cells and plot the differential capacity (dQ / dV) with respect to cell voltage during the formation process. As can be seen from the data in Figures 6a-6b, FN exhibits a passivation peak at 2.4 V, which dominates the contributions of VC and EC at 2.85 V and 3 V, respectively. Figure 6a illustrates the passivation effect of ethylene carbonate (EC):ethyl methyl carbonate (EMC) (control), and EC:EMC with 2% VC, 0.5% FN, 1% FN, 2% VC + 1% FN, 2% FEC + 1% FN, and 1% LFO and 1% FN on a cell having a coated NMC532 anode and an artificial graphite cathode. Figure 6b illustrates the passivation effect of ethylene carbonate (EC):ethyl methyl carbonate (EMC) (control) and EC:EMC with 2% VC, 0.5% FN, 1% FN, 2% VC + 1% FN, and 2% FEC + 1% FN on a lithium-ion battery cell.

[0075] Cell Impedance

[0076] The two-additive electrolyte system and the novel battery system disclosed herein have low cell impedance. Minimizing cell impedance is desirable because cell impedance reduces the energy efficiency of the cell. Conversely, low impedance leads to a higher charge rate and higher energy efficiency.

[0077] Cell impedance was measured using electrochemical impedance spectroscopy (EIS).

[0078] Unless otherwise described, the sealed cells used a single-crystal NMC532 anode and an artificial cathode, and EIS measurements were performed after formation. The cells were charged or discharged at 3.80 V before being moved to a temperature box at 10.0 + / - 0.1 °C. AC impedance spectra were collected at 10 points per decade from 100 kHz to 10 mHz with a signal amplitude of 10 mV at 10.0 + / - 0.1 °C. In a specific embodiment, a two-electrolyte system with a concentration of approximately 0.25–6% of each additive forms part of the battery system.

[0079] The effect of FN on impedance is illustrated in FIGS. 7a-7b, which is generally higher than the impedance of a cell that does not contain FN in the electrolyte composition. However, the benefits associated with gas generation during the formation process, which is significantly low (Fig. 7a) or negligible (Fig. 7b), outweigh the increase in impedance observed in a cell containing FN as an additive in the electrolyte composition.

[0080] Ultrahigh Precision Cycling and Storage Experiments

[0081] Ultra-high precision cycling (UHPC) was performed to study the efficacy of the battery system of the present disclosure, comprising working electrolyte additives and electrodes. A standard UHPC procedure consists of cycling a cell at 40°C and 4.3 V using a current corresponding to C / 3 to generate data.

[0082] UPHC is applied to measure Coulomb efficiency, charge endpoint capacity slippage, and other parameters with an accuracy of 30 ppm. Details of the UHPC procedure are provided by TM Bond, JC Burns, DA Stevens, HM Dahn, and JR Dahn. Journal of the Electrochemical Society, 160, A521 (2013), the entirety of which is incorporated into this specification.

[0083] Metrics measured and / or determined from UHPC measurements of particular interest include: Coulomb efficiency, normalized Coulomb inefficiency, normalized charge endpoint capacity slippage, normalized discharge capacity (or fade rate), and Delta V. Coulomb efficiency is the discharge capacity (Q d ) the charge capacity of the previous cycle (Q c It is the value divided by ). This tracks parasitic reactions occurring in the Li-ion cell and includes contributions from both the anode and the cathode. A higher CE value indicates less electrolyte degradation in the cell. Coulomb Inefficiency per hour (CIE / h) is the normalized Coulomb Inefficiency (per hour), defined as 1 - CE. It is calculated by taking 1 - CE and dividing CE by the time of the measured cycle. End-of-charge capacity movement (or slippage) tracks parasitic reactions occurring in the anode, as well as anode material mass loss, if present. Less movement is better and is associated with less electrolyte oxidation. Normalized discharge capacity, or fade rate, is another important indicator; a lower fade rate is desirable and generally indicates a battery system with a longer lifespan. ΔV is calculated as the difference between the average charge voltage and the average discharge voltage. Since cycling is desirable, a lower ΔV change is closely related to polarization growth. UHPC measurements are particularly suitable for comparing electrolyte compositions because they can track matrices with high accuracy and precision and evaluate various degradation mechanisms in a relatively rapid manner.

[0084] In a specific embodiment, a two-additive electrolyte system, with a concentration of about 0.25–6% of each additive, forms part of the battery system. Additionally, the battery system may include a cathode made of NMC111, NMC532, NMC811, NMC622, or other NMC compositions (NMCxyz). In a specific embodiment, a cathode made of NMC532 having micrometer-sized particles appears to be particularly robust because the processing conditions produce a larger crystal grain size than generally produced by processing conditions.

[0085] Typical process conditions result in NMC electrodes with nanometer-sized particles filled with larger micrometer-sized aggregates, creating grain boundaries at the nanometer scale. Since grain boundaries are defects that tend to reduce desirable properties (e.g., electrical properties), it is generally desirable to reduce the number of particles and increase the grain size. Current treatment can create larger domains on the micrometer scale, thereby reducing the number of grain boundaries in the NMC electrode and increasing electrical properties. The increase in properties results in a more robust battery system. In certain embodiments, other NMC electrodes can be processed to create larger domain sizes (beyond the micrometer scale), e.g., NMC111, NMC811, NMC622, or other NMC compounds, to create a more robust system.

[0086] In a specific embodiment, a lithium-ion battery cell containing a graphite-SiO electrode was used.

[0087] Long Term Cycling

[0088] Battery system lifespan is a critical characteristic. Charge and discharge rates can affect lifespan. Long-term cycling experiments help determine how resilient a battery system is over time under expected operating conditions. It is important to select a battery system with a lifespan sufficient for the desired application.

[0089] An aspect of the present disclosure illustrates long-term cycling desirable for different applications, including grid and automotive storage.

[0090] In particular, two-additive electrolyte systems of VC + FN and FEC + FN, in which EC is used as a solvent, are particularly relevant for automotive applications (especially energy storage inside electric vehicles), where the charge-discharge rate is generally higher than that of grid-storage applications.

[0091] In long-term cycling experiments, single-crystal NMC532 was generally used as the anode (unless otherwise described), and synthetic graphite was used as the cathode (unless otherwise described). In other embodiments, lithium-ion battery cells were used. Prior to the long-term cycling experiments, the sealed cells underwent a forming process as previously described. Typically, after the forming process, the cells are transferred to a glove box, cut open to release gases generated during the forming process, and then vacuum-sealed again. However, for cells containing FN as an additive, these additional steps are not necessary due to negligible gas generation during cell forming. After forming, the cells were cycled in a Neware charging system. The cells were stored in a temperature-controlled box at 40 °C + / - 0.2 °C or 20 °C + / - 0.2 °C. The cell was cycled between 3.0 V and the top of charge (4.2 V or 4.3 V) with a current of C / 3 (a half-cycle of 3 hours), and performed a constant voltage step at the top of charge until the current dropped below C / 20. Every 50 cycles, the cell underwent one full cycle at C / 20.

[0092] In certain embodiments, a two-additive electrolyte system, with a concentration of approximately 0.25–6% of each additive, forms part of a battery system. Figures 8a–8e illustrate general experimental data studying long-term cycling at 40°C and C / 3 CCCV, illustrating the advantages of including FN as an additive to an electrolyte system containing VC or FEC. Long-term cycling results using coated NMC532 as the anode and a synthetic graphite cathode are shown in Figures 8a–8c, and long-term cycling results using commercially available lithium-ion battery cells are shown in Figures 8d–8e. As shown in these figures, the addition of FN to the electrolyte composition does not significantly affect the long-term cycling characteristics of the battery system. Along with a significant reduction in gas generation during the formation process, battery systems including FN as an additive sometimes exhibit unexpectedly superior characteristics compared to standard battery systems (see Figure 8c).

[0093] The foregoing disclosure is not intended to limit the present disclosure to the exact form disclosed or to a particular field. As such, various alternative embodiments and / or modifications of the present disclosure, whether expressly described or implied herein, are considered possible in light of the present disclosure. Accordingly, although embodiments of the present disclosure have been described, those skilled in the art will recognize that forms and details may change without departing from the scope of the present disclosure. Accordingly, the present disclosure is limited only by the claims. References to additives in this specification generally relate to operative additives unless otherwise stated herein.

[0094] In the foregoing specification, the present disclosure has been described with reference to specific embodiments. However, as will be recognized by those skilled in the art, the various embodiments disclosed herein may be modified or otherwise implemented in various other ways without departing from the spirit and scope of the present disclosure. Accordingly, this description should be regarded as illustrative and is intended to teach those skilled in the art how to manufacture and use the various embodiments of the battery system disclosed herein. The forms of the disclosure shown and described herein should be understood as being taken as representative embodiments. Equivalent components or materials may substitute for those representatively illustrated and described herein. Furthermore, as will be apparent to those skilled in the art after taking advantage of this description of the present disclosure, specific features of the present disclosure may be used independently of the use of other features. Expressions such as “including,” “comprising,” “incorporating,” “consisting of,” “have,” and “is” used to describe and claim the present disclosure are intended to be interpreted as allowing items, configurations, or components not explicitly described to be presented in a non-exclusive manner. References to the singular should also be interpreted as relating to the plural. References to “about” or “approximately” should be interpreted as meaning plus or minus 10%. Similarly, references to any percentage of an additive are interpreted as meaning plus or minus 10%.

[0095] Furthermore, the various aspects disclosed herein are to be taken for illustrative and descriptive purposes only and should not be interpreted as limiting the content of the disclosure. Any mentions of joiners (e.g., attachment, fixation, joining, connection, etc.) are intended solely to aid the reader's understanding of the disclosure and are not intended to create any limitations, particularly regarding the location, orientation, or use of the systems and / or methods disclosed herein. Therefore, mentions of joiners, even if present, should be interpreted broadly. Moreover, such mentions of joiners do not necessarily imply that two components are directly connected to each other.

[0096] Additionally, all numeric terms, e.g., "first," "second," "third," "primary," "secondary," "major," or any other general terms and / or numeric terms, are to be taken solely as identifiers to aid the reader’s understanding of the various components, modes, variations, and / or modifications of the present disclosure, and may not create any limitations, particularly of any component, mode, variation, and / or modification, over or in order or preference toward other components, modes, variations, and / or modifications.

[0097] You will understand that one or more components depicted in the figure / drawing may also be implemented in a more separate or integrated manner, as useful depending on the specific application, or may be removed or considered inoperable in certain cases.

Claims

Claim 1 An energy storage device comprising: a positive electrode; a negative electrode; and a non-aqueous electrolyte; wherein the non-aqueous electrolyte comprises a lithium salt; a first non-aqueous solvent comprising a carbonate solvent; a second non-aqueous solvent comprising methyl acetate; and an additive mixture comprising a first working additive and a second working additive; wherein the first working additive comprises vinylene carbonate, fluoroethylene carbonate, or a combination thereof; and wherein the second working additive comprises 2-furanone having the following formula (I): (I); an energy storage device wherein the concentration of each of the first non-aqueous solvent and the second non-aqueous solvent exceeds 6 weight%; the concentration of the first operating additive is in the range of 0.25 to 6 weight%; and the concentration of the second operating additive is in the range of 0.1 to 5 weight%. Claim 2 In claim 1, the energy storage device comprises a capacity retention rate equivalent to that of an energy storage device comprising only a first operating additive. Claim 3 An energy storage device according to claim 1, wherein the non-aqueous electrolyte is configured such that gas formation is suppressed compared to gas generation during the formation process of an energy storage device comprising only a first operating additive. Claim 4 An energy storage device according to claim 1, wherein the concentration of the first operating additive is 2 weight% and the concentration of the second operating additive is 0.5 to 1 weight%. Claim 5 An energy storage device according to claim 1, wherein the first operating additive comprises fluoroethylene carbonate. Claim 6 An energy storage device according to claim 1, wherein the first non-aqueous solvent is a carbonate solvent. Claim 7 An energy storage device according to claim 6, wherein the first non-aqueous solvent is at least one selected from ethylene carbonate, ethyl methyl carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate. Claim 8 An energy storage device according to claim 7, comprising ethylene carbonate at a concentration of 25 to 30 volume%. Claim 9 An energy storage device according to claim 7, comprising ethyl methyl carbonate at a concentration of 5 to 70 volume%. Claim 10 An energy storage device according to claim 7, comprising dimethyl carbonate at a concentration of 70 volume%. Claim 11 An energy storage device according to claim 1, wherein the lithium salt comprises lithium hexafluorophosphate. Claim 12 An energy storage device according to claim 1, wherein the second non-aqueous solvent is methyl acetate. Claim 13 An energy storage device according to claim 1, wherein the positive electrode comprises a lithium nickel manganese cobalt oxide (NMC) cathode active material. Claim 14 An energy storage device according to claim 13, wherein the lithium nickel manganese cobalt oxide (NMC) is selected from the group consisting of NMC111, NMC532, NMC811, and NMC622. Claim 15 An energy storage device according to claim 1, wherein the cathode comprises an anode active material selected from the group consisting of artificial graphite, natural graphite, and graphite / SiO blends. Claim 16 An energy storage device according to claim 1, wherein the energy storage device is configured to have a retention rate of at least 95% of the initial capacity after 200 cycles at 3.0 V to 4.3 V with a charging rate of C / 3 CCCV at 40℃. Claim 17 An energy storage device according to claim 1, wherein the energy storage device is configured to have a retention rate of at least 95% of the initial capacity after 600 cycles at 3.0 V to 4.3 V with a charging rate of C / 3 CCCV at 40℃. Claim 18 An energy storage device according to claim 1, wherein the non-aqueous electrolyte is configured such that at least 50% less gas is generated during the formation process compared to the gas generated during the formation process of an energy storage device comprising only a first operating additive. Claim 19 An energy storage device according to claim 1, wherein the energy storage device is a battery. Claim 20 An electric vehicle comprising a rechargeable battery, the electric vehicle comprising: a drive motor; a gearbox; electronic devices; and an energy storage device as described in claim 1. Claim 21 An electric vehicle according to claim 20, wherein the first operating additive comprises fluoroethylene carbonate. Claim 22 An electric vehicle according to claim 21, wherein the first operating additive further comprises vinylene carbonate. Claim 23 An energy storage device comprising: a positive electrode; a negative electrode; and a non-aqueous electrolyte; wherein the non-aqueous electrolyte comprises a lithium salt; a first non-aqueous solvent comprising a carbonate solvent; a second non-aqueous solvent comprising methyl acetate; and an additive mixture comprising a first working additive and a second working additive; wherein the first working additive comprises vinylene carbonate; and the second working additive comprises 2-furanone having the following formula (I): (I); an energy storage device wherein the concentration of each of the first non-aqueous solvent and the second non-aqueous solvent exceeds 6 weight%; the concentration of the first operating additive is in the range of 0.25 to 6 weight%; and the concentration of the second operating additive is in the range of 0.1 to 5 weight%.

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