Sodium ion cell

Abstract

The present invention relates to a process for providing a sodium-ion cell and / or a sodium-ion battery having a state of charge of about 20% or less. Sodium-ion cells and / or batteries are also disclosed.

Description

[Technical Field]

[0001] The present invention relates to a method for providing sodium ion cells and / or sodium ion batteries that can be safely transported and / or stored, for example, rechargeable sodium ion cells and / or sodium ion batteries. The present invention also relates to an energy storage device comprising one or more of these sodium ion cells, such as a battery, a battery module, a battery pack, an electrochemical device, and an electrochromic device. [Background technology]

[0002] Sodium-ion batteries are similar in many ways to lithium-ion batteries, which are commonly used today; they are both reusable secondary batteries containing an anode (negative electrode), cathode (positive electrode), and electrolyte material, both can store energy, and both charge and discharge via similar reaction mechanisms. When a sodium-ion (or lithium-ion) battery is being charged, Na+ (or Li+) ions deintercalate from the cathode and are inserted into the anode. Meanwhile, electrons that equilibrate the charge pass from the cathode through an external circuit containing the charger to the anode of the battery. The same process occurs during discharge, but in the reverse direction.

[0003] Lithium ion battery technology has received much attention in recent years, and provides preferred portable batteries for most electronic devices used today; however, lithium is not an inexpensive metal source, and is considered to be too expensive for use in large-scale applications. In contrast, sodium-ion battery technology is still in its relatively early stages, but is considered advantageous; sodium is far more abundant than lithium, and some researchers predict that this will provide a cheaper and more durable method for storing energy in the future, particularly for large-scale applications such as storing energy on the power grid. Nevertheless, there is still a great deal of research to be done before sodium-ion batteries can be commercialized.

[0004] An international PCT application published as International Publication No. 2016 / 027082 A1 discloses a process for producing a sodium-ion cell that can be safely stored and / or transported. This is carried out by discharging a charged / discharged sodium-ion cell at -0.1 to 1 V, thereby producing a sodium-ion cell having a state of charge (SOC) of 0% to 20%. While this process is clearly advantageous, it is somewhat limiting in the sense that discharging of the charged / discharged sodium-ion cell is preferably performed at a low C-rate (i.e., a rate of C / 100 is the most preferred discharge rate).

[0005] For the avoidance of doubt, C-rate is the discharge current divided by the theoretical current draw at which a sodium-ion cell would deliver its nominal rated capacity within a specified time.

[0006] In most situations, commercial manufacturers do not want to spend 100 hours preparing such cells. On the other hand, commercial manufacturers do not wish to prepare cells of inferior quality when operating the process over a short period of time (i.e., less than 100 hours). In some cases, manufacturers do not want to operate a process that adversely affects the electrochemical performance of the cells.

[0007] Accordingly, it is one object of the present invention to provide a process that provides a sodium ion cell and / or sodium ion battery, for example, at a state of charge of about 20% or less, that can be prepared in a relatively short time (i.e., less than 100 hours), and preferably does not substantially adversely affect the electrochemical performance of the cell and / or battery. Adverse effects include, for example, a reduction in the original charge capacity of the cell or battery.

[0008] Another factor to be considered is cell safety. For lithium ion cells, a fundamental problem is that their transport and / or storage is inherently dangerous. This is because, in most cases, lithium ion cells are not safe when (i) stored in a fully discharged state, or (ii) discharged to or near 0 volts. This is because copper from the current collector for the anode (negative) electrode dissolves into the electrolyte as copper ions, and during subsequent recharging, the dissolved copper ions deposit on the internal surfaces of the cell to form conductive paths. This not only reduces the capacity of the cell, but also leads to the formation of internal short circuits in the lithium ion cell and subsequent thermal runaway.

[0009] Discharging a lithium ion cell to or near 0 V, even when the cell is not recharged, can have serious consequences because the internal microstructure of the cell is already damaged by this point. For example, problems such as internal short circuits caused by the growth of metallic dendritic copper, reduced mechanical integrity of the separator, weakened adhesion of the anode to the copper current collector (resulting from dissolution of the copper current collector during overdischarge), reduced porosity in the cathode, and blockage of electrochemically active sites on the cathode not only lead to rapid capacity loss, but can also cause serious thermal hazards such as dangerous temperature spikes that can trigger thermal runaway.

[0010] Naturally, this is a major concern, especially for airlines, and to mitigate these safety concerns, in 2013 the International Civil Aviation Organization introduced very strict regulations on the mass air transport of lithium-based cells, implementing rules to control both the size (watt-hour rating and lithium content) of lithium-ion batteries permitted for transport and the number of batteries permitted in each consignment.

[0011] Therefore, the most well-known method for handling lithium-ion battery cells is to ensure that the lithium-ion batteries are properly conditioned immediately after manufacturing by a process that includes at least two or three charge / discharge cycles followed by a final charge to at least approximately 30-40%. This avoids any storage conditions of 0 volts or near 0 volts. The cells must then be degassed and finally resealed before being ready for storage and / or transport.

[0012] While the disclosure in International Publication No. 2016 / 027082 A1 demonstrates several clear advantages of sodium-ion cells over lithium-ion cells, the need to make sodium-ion cells safer remains. Therefore, another object of the present invention is to provide a process for providing sodium-ion cells (not half-cells) and / or sodium-ion batteries, wherein the resulting sodium-ion cells and / or sodium-ion batteries are provided in a safer state than sodium-ion cells and / or sodium-ion batteries produced according to one or more processes known in the art.

[0013] A recent report entitled "Thermal Stability of High Power 26650-Type Cylindrical Na-Ion Batteries," Chin. Phys. Lett. Vol.38, No.7(2021)076501, describes the safety test results for high-power 26650-type cylindrical sodium-ion batteries in a fully charged state. The tests included (a) external short-circuit testing, (b) overheating testing, (c) overcharge testing, (d) over-discharge testing, (e) crushing testing, and (f) nail penetration testing.

[0014] The report details that sodium-ion cells containing layered oxide cathodes and hard carbon anodes can be discharged to approximately -2.5V, recharged, and then cycled within the range of 4.0V to 1.5V. Because there is no apparent temperature change and capacity can be recovered after over-discharge events, the researchers conclude that this (along with results from overheating, overcharging, crushing, and nail-piercing tests) demonstrates the "good safety" of sodium-ion batteries.

[0015] However, regarding over-discharge testing, researchers have only established this "good safety" in the sense of a single discharge down to -2.5V. It has not been shown that discharging to -2.5V more than once has any effect on whether the sodium ion cell is prone to smoke, excessive heat, ignition, or explosion. Therefore, this prior art does not teach whether sodium ion cells discharged to -2.5V are safe for storage and / or transport and / or maintenance.

[0016] Furthermore, while the researchers claim that the capacity of the sodium ion cell "can be recovered after an over-discharge event," it is unclear to what extent the original discharge capacity was affected by the over-discharge event. Therefore, the researchers have not established any kind of effect that an over-discharge event has on the original or expected charge capacity of the sodium ion cell.

[0017] Finally, since their experimental data does not specify the charge / discharge C-rate, it is unclear from this report whether the discharge must be performed at a high or low speed. Therefore, it is not clear whether all or substantially all (80-100%) of the charge was actually dissipated as a result of the single over-discharge process they describe. Since the charge in the cell will not be completely or substantially dissipated without a slow discharge, and the researchers have not specified the charge / discharge C-rate, it is expected that the extent of the charge actually remaining in the cell after the discharge process, specifically whether it is less than 20%, will be unknown.

[0018] Therefore, the present invention aims to mitigate or eliminate one or more of the above-mentioned drawbacks of known technologies. [Prior art documents] [Patent Documents]

[0019] [Patent Document 1] International Publication No. 2016 / 027082 A1 [Non-patent literature]

[0020] [Non-Patent Document 1] "Thermal Stability of High Power 26650-Type Cylindrical Na-Ion batteries", Chin. Phys.Lett. Vol.38, No.7(2021)076501 [Overview of the project]

[0021] In one view, the present invention relates to a process for providing a sodium ion cell that is in a charged state of about 20% or less, and is preferably capable of safe storage and / or transport and / or maintenance, comprising the following steps: a) A step of providing a sodium ion cell which preferably includes a positive electrode containing a positive electrode material, a positive electrode current collector, a negative electrode containing a negative electrode material, a negative electrode current collector, and an electrolyte; and b) The sodium ion cell provided in step a) is subjected to one or more discharge operations, preferably at a discharge rate of C / <10, until it reaches a minimum cell operating voltage of less than -0.1V (i.e., cell Vmin); The process described above is provided, including the process described above.

[0022] As used herein, the term “charged state” is intended to be interpreted in its broadest sense and to mean either “instantaneous charge state” or “true charge state.” “Charged state” can be positive or negative, as defined below.

[0023] As used herein, the term “instantaneous charge state” is intended to mean the available capacity at the measured voltage as the capacitance ratio between V=0 and Vmax (e.g., 4.3V) and is measured by drawing current. Since Vmin according to the present invention has a voltage less than -0.1V, we define herein as “negative” instantaneous charge state existing if there is a non-zero capacitance between Vmin and V=0. This is observed and illustrated in the embodiments disclosed herein.

[0024] Where used herein, the term “true charge state” is intended to mean the capacity available at the open-circuit voltage (OCV) as the capacity ratio between V=0 and Vmax (e.g., 4.3V), measured without drawing any current. Thus, the OCV provides a “true” indication of the actual charge state, with a lower OCV indicating a lower charge state. However, if the OCV is a negative value, it may indicate damage to the cell or battery, which is obviously undesirable.

[0025] As used herein, the term "over-discharge" means discharging to below -0.1V. The sodium ion cells provided in step a) of the process of the present invention are preferably subjected to a conditioning process (also known as a “formation” process) that includes one or more charge and discharge (i.e., charge / discharge) operations prior to step b). That is, they are pre-charged sodium ion cells. The sodium ion cells provided in step a) may be subjected to a conditioning process prior to step b) that includes two or three charge and discharge operations, and optionally a subsequent degassing.

[0026] For the purposes of this disclosure, a cell that has been subjected to a conditioning process but is not subsequently used with an application device is described as "pristine." Similarly, a cell that has been subjected to a conditioning process and is subsequently used with an application device is described as "non-pristine." An application device is any device that utilizes a cell or battery. An electric vehicle or a mobile phone are examples of application devices.

[0027] Therefore, the actions involved in “discharging the sodium ion cell” in step b) are substantially the same whether step b) is performed on a sodium ion cell that has been subjected to the conditioning process but is not subsequently used with the application device ("pristine cell"), or whether step b) is performed on a sodium ion cell that has been subjected to the conditioning process and is subsequently used with the application device ("non-pristine cell").

[0028] If step b) is performed on sodium cells ("pristine cells") that have been subjected to the conditioning process but have not yet been used with the application device, then step b) can be conveniently performed immediately after step a).

[0029] Since the sodium ion cell provided in step a) of the process of the present invention can be subjected to a conditioning process, step b) can be performed on a sodium ion cell that is in a charged pristine state, a discharged pristine state, a charged non-pristine state, or an uncharged non-pristine state.

[0030] To avoid any doubt, it should be stated that if the cell voltage is below -0.1V, a copper dissolution reaction will occur, making it impossible to carry out the process of the present invention for pristine and / or non-pristine lithium-ion cells.

[0031] The act of “providing a sodium ion cell” in step a) may include constructing a sodium ion cell. Therefore, step a) may include constructing a sodium ion cell comprising a positive electrode containing positive electrode material, a positive electrode current collector, a negative electrode containing negative electrode material, a negative electrode current collector, and an electrolyte. Alternatively, step a) of the present invention may simply include providing and / or supplying a pre-constructed sodium ion cell. Therefore, step a) may or may not include any such construction and / or fabrication of a sodium ion cell.

[0032] Step b) of the process of the present invention is to dissipate the charge of the sodium ion cell provided in step a), resulting in a sodium ion cell with a charge of 20% or less. The resulting sodium ion cell is preferably in a charge state of about -20% to about 20%, more preferably about -10% to about 10%. Ideally, the process of the present invention provides a sodium ion cell in a charge state of about -5% to about 20%, more ideally about -5% to about 10%.

[0033] Step b) of the present invention's process involves discharging the sodium ion cell provided in step a) to a voltage (cell Vmin) of less than -0.1V. Ideally, this is less than -0.1V to about -5V, preferably less than -0.1V to about -2.5V, preferably less than -0.1V to about -2.0V, and preferably less than -0.1V to about -1.7V. These voltage (cell Vmin) ranges are particularly desirable at discharge rates of C / ≦5 to C / ≧0.1, very preferably C / ≦2 to C / ≧0.5.

[0034] If step b) is carried out with a sodium ion cell that can be charged to the conventional and / or expected charge capacity of the cell, it is particularly desirable that it have an endpoint (e.g., -2.5V or -1.7V). In one embodiment, step b) of the present invention comprises discharging the sodium ion cell provided in step a) to a voltage (cell Vmin) of less than -0.1V to about -1.5V, and optionally less than -0.1V to about -1.0V.

[0035] Step b) of the present invention involves discharging the sodium ion cell provided in step a) to a voltage (cell Vmin) preferably less than -0.5V to about -5V, more preferably less than -0.5V to about -2.5V, even more preferably less than -0.5V to about -2.1V, and most preferably less than -0.5V to about -1.7V. These voltage (cell Vmin) ranges are particularly desirable at discharge rates of C / ≦5 to C / ≧0.1, and very preferably C / ≦2 to C / ≧0.5.

[0036] In one embodiment, step b) of the present invention comprises discharging the sodium ion cell provided in step a) to a voltage (cell Vmin) of less than -0.1V, preferably about -0.2V or less, preferably about -0.5V or less, preferably about -0.9V or less, preferably about -1.0V or less, preferably about -1.4V or less, and preferably about -1.6V or less.

[0037] As described above, a desirable object of the present invention is to provide a process in which the resulting sodium ion cells and / or sodium ion batteries are safer than sodium ion cells and / or sodium ion batteries produced according to one or more processes known in the art. The phrase "safer" means that the charge state of the resulting sodium ion cells and / or sodium ion batteries is lower than that of a comparative sodium ion cell and / or sodium battery discharged to a voltage of -0.1V or higher (cell Vmin). Therefore, the effect resulting from the present invention, in particular the effect resulting from discharging the sodium ion cell to a voltage of less than -0.1V (cell Vmin) in step b), is that the charge state from the resulting sodium ion cell is lower than that of a comparative sodium ion cell discharged to a voltage of -0.1V or higher (cell Vmin). This is because the percentage of charge remaining in a sodium ion cell discharged to a voltage of less than -0.1V (cell Vmin) is lower than the percentage of charge remaining in a comparative cell discharged to a voltage of -0.1V or higher (cell Vmin). Therefore, the present invention provides a sodium ion cell that is safer than a sodium ion cell discharged to a voltage (cell Vmin) of -0.1V or higher. Furthermore, the sodium ion cell obtained from the process of the present invention surprisingly does not pose the risk of fire and explosion associated with discharging a comparable lithium ion cell to a voltage (cell Vmin) of less than -0.1V. Therefore, such a sodium ion cell is surprisingly capable of safe storage and / or safe transport and / or safe maintenance. Moreover, the estimated lifespan of the obtained sodium ion cell is also expected to be longer than that of a lithium ion cell. This is because such a sodium ion cell can withstand discharge to a voltage (cell Vmin) of less than -0.1V without affecting its conventional or expected charge capacity.

[0038] The sodium ion cell provided in step a) ideally has a maximum operating cell voltage (cell Vmax) based on the electrochemistry of the cell, for example, as assigned by the manufacturer. The sodium ion cell (pristine or non-pristine) provided in step a) preferably has an assigned cell Vmax of about 1.0V to about 5.0V, ideally 3.0V to 4.5V. For example, a very preferred sodium ion cell provided in step a) of the process of the present invention uses an alkali metal-containing oxide-based (cathode) chemistry and therefore can have a cell Vmax of about 4.0V to about 4.5V, ideally 4.0V to about 4.3V. Alternatively, the sodium ion cell provided in step a) of the process of the present invention can use a Prussian blue analog (including Prussian white) or phosphate-based (cathode) chemistry and therefore can have a cell Vmax of about 3.0V to about 3.9V.

[0039] Preferably, step a) includes a sodium ion cell that can be charged to the conventional and / or expected charge capacity of the cell. As used herein, “a sodium ion cell that can be charged to the conventional and / or expected charge capacity of the cell” is intended to mean a cell that can be charged to ≥50% to 100%, preferably ≥80% to 100%, of the cell Vmax.

[0040] It will be understood that a sodium ion cell that can be charged to its conventional and / or expected charge capacity can be a pristine sodium ion cell. Thus, such a sodium ion cell can be charged to ≥90% to 100% of its cell Vmax.

[0041] It will also be understood that a sodium ion cell that can be charged to its conventional and / or expected charge capacity may be a non-pristine sodium ion cell. During the lifespan of a sodium ion cell, fluctuations from the cell Vmax may occur, which may be most noticeable during the aging of the sodium ion cell in use (e.g., when used with an application device). Thus, such a sodium ion cell may be chargeable up to ≥50% to 100% of its cell Vmax.

[0042] A further benefit of the present invention, particularly in preferred embodiments where step a) includes a sodium ion cell that can be charged to the conventional and / or expected charge capacity of the cell, is that the electrochemical performance of the resulting sodium ion cell is substantially unaffected. Furthermore, after long-term storage and charging to their conventional and / or expected charge capacity, the resulting sodium ion cell can be cycled from cell Vmin at 0V to its conventional and / or expected charge capacity, for example, indefinitely, or at least 100 times, or at least 20 times, without causing any damage to the conventional charge capacity of the cell. Furthermore, the cycle from a 0V cell Vmin to a cell Vmax of approximately 1.0V to approximately 5.0V (preferably approximately 3.0V to approximately 4.5V) can also be performed without affecting the cell's charging capacity, using rest periods of at least 30 minutes, optionally at least 1 hour, optionally at least 4 hours, optionally at least 8 hours, optionally at least 12 hours, optionally at least 24 hours, and optionally at least 96 hours between each cycle, using a 0V cell Vmin or near it.

[0043] In one embodiment, step a) includes a sodium ion cell that cannot be charged to the conventional and / or expected charge capacity of the cell, also known as a “dead cell” or “defective cell”. As used herein, this is intended to mean a sodium ion cell that cannot be charged to ≥50% to 100%, preferably ≥80% to 100%, of the cell Vmax based on the electrochemistry of the cell, for example, as assigned by the manufacturer.

[0044] It will be understood that a sodium ion cell that cannot be charged to its conventional and / or expected charge capacity may be a pristine sodium ion cell. Therefore, such a cell may not be able to be charged to ≥50% to 100%, preferably ≥80% to 100%, of the cell Vmax.

[0045] It will also be understood that sodium ion cells that cannot be charged to their conventional and / or expected charge capacity may be non-pristine sodium ion cells. Thus, such cells may not be able to be charged to ≥50% to 100%, preferably ≥80% to 100%, of the cell Vmax.

[0046] A further effect of the present invention, particularly in embodiments in which step a) includes a sodium ion cell that cannot be charged to the conventional and / or expected charge capacity of the cell, is that the resulting sodium ion cell is in a safer state because the percentage of residual charge (if present) in the cell is lower. Thus, such a sodium ion cell can be safely stored and / or safely transported and / or safely maintained, and / or safely destroyed where appropriate.

[0047] As described above, another desirable object of the present invention is to provide a process for providing a sodium ion cell and / or sodium ion battery in a charge state of, for example, 20% or less, which can be provided in a relatively short time (i.e., less than 100 hours). While low discharge rates (C / 20 or C / 100) are more likely to result in a sodium ion cell from which all or substantially all of the charge has been dissipated, the methods of the prior art only teach that the sodium ion cell should be discharged to a voltage of -0.1V or higher (cell Vmin). Therefore, it is very beneficial to dissipate all or substantially all of the charge from the sodium ion cell at a high discharge rate (C / <10), and thus obtain a sodium ion cell in a charge state of 20% or less in a shorter time.

[0048] A preferred method for discharging the sodium ion cell in step b) of the present invention is to draw a constant current at a discharge rate of C / <10 until the sodium ion cell shows a voltage of less than -0.1V (cell Vmin). A discharge rate of C / <10 means that the entire sodium ion cell is discharged in less than 10 hours with a discharge current. As those skilled in the art will understand, a discharge rate of C / <10 can also be expressed as >0.1C (i.e., less than 1 ÷ 10 hours = >0.1C).

[0049] In one embodiment, the discharge carried out in step b) of the present invention is at discharge rates of C / <10 (i.e., greater than 0.1C (>0.1C)) to about 4000C, optionally about C / <10 to about 1000C, optionally about C / <10 to about 500C, optionally about C / <10 to about 200C, optionally about C / <10 to about 150C, and optionally about C / <10 to about 50C.

[0050] In one embodiment, the discharge carried out in step b) of the present invention is at a discharge rate of C / <10 to C / ≧0.1 (10C), preferably C / <10 to C / ≧0.33 (3C), and further preferably C / <10 to C / ≧0.5 (2C).

[0051] Therefore, a discharge rate of C / <10 to C / ≧0.1 (10C) means that the entire sodium ion cell is discharged over a period of 6 minutes or more (i.e., C / ≧0.1 × 60 minutes = 6 minutes) to less than 10 hours (i.e., C / <10).

[0052] The advantage of this preferred method is that, as described above, the cells in step b) can be safely discharged to a voltage of less than -0.1V (cell Vmin), allowing for the use of higher discharge rates to dissipate all, or substantially all, of the charge from the resulting sodium ion cells in a shorter time. Furthermore, it was found that the charge state of the resulting sodium ion cells discharged to a voltage of less than -0.1V (cell Vmin) at a discharge rate of C / <10 was closer to 0% than that of the comparative sodium ion cells discharged to a voltage of 0V (i.e., above -0.1V) (cell Vmin).

[0053] In one embodiment, the discharge carried out in step b) of the present invention is at a discharge rate of C / ≦8, optionally C / ≦6, optionally C / ≦4, optionally C / ≦2, optionally C / ≦1, and optionally C / ≦0.5.

[0054] In one embodiment, the discharge carried out in step b) of the present invention is at a discharge rate of C / <10 to C / ≧2. The discharge carried out in step b) of the present invention is preferably at a discharge rate of C / ≦5 to C / ≧0.1, more preferably at a discharge rate of C / ≦5 to C / ≧0.5. The discharge carried out in step b) of the present invention is very preferably at a discharge rate of C / ≦2 to C / ≧0.1, most preferably at a discharge rate of C / ≦2 to C / ≧0.5. As described above, a discharge rate of C / ≦2 to C / ≧0.5 means that the entire sodium ion cell is discharged with a discharge current for a period of 30 minutes or more (i.e., C / ≧0.5 × 60 minutes = 30 minutes or more) to 2 hours or less (i.e., C / ≦2).

[0055] In one embodiment, the discharge carried out in step b) of the present invention has a discharge rate of C / 2, and optionally C / 0.5(2C). In an embodiment in which step a) includes a sodium ion cell capable of being charged to a conventional and / or expected charge capacity, step b) of the present invention is preferably carried out at a discharge rate of C / <10 to C / ≧0.1 (10C), preferably C / <10 to C / ≧0.33 (3C), and more preferably C / <10 to C / ≧0.5 (2C). In such embodiments, a discharge rate of C / ≦5 to C / ≧0.1 is preferred, and C / ≦2 to C / ≧0.5 is very preferred.

[0056] In embodiments where step a) includes a sodium ion cell that cannot be charged to its conventional and / or expected charge capacity, step b) of the present invention is preferably carried out at a discharge rate of about 12C or higher (also expressed as C / ≦0.083). Thus, a discharge rate of 12C or higher means that the discharge current discharges the entire sodium ion cell within 5 minutes.

[0057] In an embodiment in which step a) includes a sodium ion cell that cannot be charged to a conventional and / or expected charge capacity, step b) of the present invention is preferably carried out at a discharge rate of about 12C to about 4000C, preferably about 12C to about 1000C, preferably about 12C to about 500C, preferably about 12C to about 200C, and preferably 12C to about 150C.

[0058] In an embodiment in which step a) can be charged to a conventional and / or expected charge capacity and includes a sodium ion cell containing an alkali metal-containing oxide cathode material, step b) of the present invention can be carried out at a preferred discharge rate of C / ≦5 to C / ≧0.1, very preferably C / ≦2 to C / ≧0.5.

[0059] In one embodiment, the process of the present invention may further include step c), which includes maintaining sodium ions at a voltage of 1 V or less. Thus, the sodium ion cell provided in step a) can be maintained at a voltage above the cell Vmin (as defined herein) of the sodium ion cell. Step c) can be performed immediately after step b).

[0060] A desirable object of the present invention is to produce sodium ion cells having the lowest possible percentage of charge, about 20% or less. Therefore, advantageously, step c) is useful for dissipating any remaining charge from the sodium ion cells, thus providing the resulting sodium ion cells with the lowest possible percentage of charge, preferably in the range of about -20% to 20%, and more preferably in the range of -10% to 10%. Ideally, this range is about -5% to about 20%, and even more ideally, about -5% to about 10%.

[0061] Assuming that the sodium ion cell obtained from the process of the present invention is stable for a long period of time, step c) can be carried out for a period of time, for example, for more than 1 minute. Step c) can be carried out for a long period of time, for example, for at least 30 minutes, optionally at least 1 hour, optionally at least 4 hours, optionally at least 8 hours, and optionally at least 24 hours.

[0062] In one embodiment, step c) includes maintaining the sodium ion cell at a voltage of 1V or less, preferably 0.5V or less, preferably 0V, preferably 0V or less, preferably -0.1V or less, and preferably less than -0.1V. In one embodiment, step c) includes maintaining the sodium ion cell at a voltage of about 1V to about -5.0V, preferably about 1V to about -2.5V, more preferably about 1V to about -2.0V, and more preferably about 1V to about -1.70V. Step c) may also include maintaining the sodium ion cell at a voltage of about 1V to about 0V.

[0063] In one embodiment, step c) may include maintaining the sodium ion cell at the above voltage using a removable short-circuit device as described below. Alternatively, or additionally, the process may further include step d), which includes removing the removable short-circuit device as described below.

[0064] In one embodiment, the process of the present invention may include an initial step of carrying out a conditioning cycle. That is, the present invention is a process for providing a sodium ion cell that is in a charge state of about 20% or less and is preferably safe to store and / or transport and / or maintain, and the steps are as follows: a) In the step of performing a conditioning cycle on a sodium ion cell, it is preferable that the sodium ion cell includes a positive electrode containing a positive electrode material, a positive electrode current collector, a negative electrode containing a negative electrode material, a negative electrode current collector, and an electrolyte; and b) The sodium ion cell provided in step a) is subjected to one or more discharge operations at a discharge rate of preferably C / <10, down to a voltage of less than -0.1V (i.e., cell Vmin); The process described above is provided, including the process described above.

[0065] As described above, a conditioning cycle is typically one or more charge and discharge operations (or as previously defined elsewhere). A typical conditioning cycle like step a) above is as follows: i) A step of providing a sodium ion cell that has not been subjected to a charging operation, wherein the sodium ion cell preferably comprises a positive electrode containing a positive electrode material, a positive electrode current collector, a negative electrode containing a negative electrode material, a negative electrode current collector, and an electrolyte; ii) The step of charging the sodium ion cell from a first voltage to a second voltage, wherein the second voltage is approximately 2V to approximately 4.5V, the charging is carried out at a rate of approximately C / 2 to approximately C / 50, and optionally the second voltage is maintained for approximately 5 minutes to approximately 10 hours, or until the current value of the cell decreases to a current value corresponding to C / 5 to C / 100; iii) The step of discharging the sodium ion cell from a second voltage to a third voltage, wherein the third voltage is approximately 0V to 3V, and the discharge is carried out at a rate of approximately C / 2 to approximately C / 50; and iv) A step in which steps ii) and iii) are repeated one or more times, if desired; It can include...

[0066] The first voltage is lower than the second voltage. Ideally, the first voltage is -0.5V or higher. Ideally, it is -0.35V to 1V. The charge / discharge rate is typically C / 10, but may be C / 2, C / 5, or C / 50. Ideally, it is C / 5 to approximately C / 10.

[0067] Those skilled in the art will know that different conditioning cycles may be used. For example, step ii) may alternatively include charging the sodium ion cell from a first voltage to a second voltage and maintaining the second voltage (e.g., 1.5V) for a certain period of time (e.g., 30 minutes or 30 hours; or 30 minutes to 30 hours). Such an alternative step ii) may be carried out alone as a conditioning cycle or used in conjunction with step iii) above. Furthermore, the conditioning process may also include further steps between steps ii) and iii), and / or as further steps after step iii), which include subjecting the cell to one or more charge / discharge operations between 0 and 4.2V.

[0068] The purpose of the conditioning process is to form a stable interface on the surface between the electrode and the electrolyte. In particular, one of the main objectives of this conditioning process is the formation of a stable interface layer on the anode, referred to in the literature as the "solid electrolyte interface" (SEI), or a stable interface layer on the cathode, referred to as the "cathode electrolyte interface" (CEI). Those skilled in the art will know that undesirable gas generation (reaction products in the process of forming the interface layer) may occur during the process of forming the interface layer. Therefore, after the conditioning process, an optional step is to remove this gas generation and then (if necessary) reseal the cell, and resealing depends on the type of cell used (for example, those skilled in the art will know that resealing may be necessary for pouch cells but not necessarily for prism or cylindrical cells).

[0069] In other words, the present invention provides a sodium ion cell according to the process of the present invention. In other words, the present invention provides an energy storage device comprising one or more sodium ion cells according to the process of the present invention.

[0070] In other words, the present invention provides a process for providing a sodium-ion battery that is charged to about 20% or less, and is preferably safe to store and / or transport and / or maintain, the process comprising the step of providing a sodium-ion battery comprising two or more sodium-ion cells, each of which is a sodium-ion cell according to the process of the present invention.

[0071] In other words, the present invention relates to a process for providing a sodium-ion battery that is in a charge state of about 20% or less and is preferably safe to store and / or transport and / or maintain, comprising the following steps: a) In the step of providing a sodium-ion battery, it is preferable that the sodium-ion battery comprises one or more sodium-ion cells comprising a positive electrode containing a positive electrode material, a positive electrode current collector, a negative electrode containing a negative electrode material, a negative electrode current collector, and an electrolyte; and b) The sodium-ion battery provided in step a) is subjected to one or more discharge operations at a discharge rate of preferably C / <10, down to a minimum battery operating voltage of less than -0.1V (i.e., battery Vmin); The process described above is provided, including the process described above.

[0072] It is preferable that all one or more sodium ion cells used to provide the sodium ion battery in step a) of the process of the present invention are subjected to a conditioning process (also known as a “formation” process) comprising one or more charge and discharge operations prior to step b). That is, all one or more sodium ion cells are pre-charged sodium ion cells. All one or more sodium ion cells used to provide the sodium ion battery in step a) may be subjected to a conditioning process prior to step b) comprising two or three charge and discharge operations, and optionally subsequent degassing. Such a conditioning process may be as described above.

[0073] For the purposes of this disclosure, a battery is described as “pristine” if all of the sodium ion cells forming the battery have been subjected to a conditioning process, but none of those cells are subsequently used with an application device. A battery is described as “non-pristine” if, after all of the sodium ion cells forming the battery have been subjected to a conditioning process, one or more of those cells are subsequently used with an application device. An application device is any device that utilizes a cell or battery. An electric vehicle or a mobile phone are examples of application devices.

[0074] Therefore, the actions involved in “discharging the sodium-ion battery” in step b) are substantially the same whether step b) is performed on a “pristine” sodium-ion battery or a “non-pristine” sodium-ion battery.

[0075] If step b) is performed on a "Pristine" sodium-ion battery, step b) can conveniently be performed immediately after step a). Since the sodium-ion battery provided in step a) preferably contains cells that have been subjected to a conditioning process, step b) can be performed on a sodium-ion battery that is in a charged pristine state, a discharged pristine state, a charged non-pristine state, or an uncharged non-pristine state.

[0076] To avoid any doubt, it should be stated that if the cell voltage is below -0.1V, a copper dissolution reaction will occur, making it impossible to carry out the process of the present invention for pristine and / or non-pristine lithium-ion batteries.

[0077] The act of “providing a sodium-ion battery” in step a) may include constructing a sodium-ion battery. Thus, step a) may include constructing a sodium-ion battery comprising one or more sodium-ion cells comprising a positive electrode comprising a positive electrode material, a positive electrode current collector, a negative electrode comprising a negative electrode material, a negative electrode current collector, and an electrolyte. In other embodiments, step a) of the present invention may simply include providing and / or supplying a pre-constructed sodium-ion battery. Thus, step a) may or may not include any such construction and / or fabrication of a sodium-ion battery.

[0078] Step b) of the process of the present invention is to dissipate the charge of the sodium-ion battery provided in step a), resulting in a sodium-ion battery with a charge of 20% or less. The resulting sodium-ion battery is preferably charged to about -20% to about 20%, more preferably to about -10% to about 10%. Ideally, the process of the present invention provides a sodium-ion battery with a charge of about -5% to about 20%, more ideally to about -5% to about 10%.

[0079] Step b) of the present invention's process involves discharging the sodium-ion battery provided in step a) to a voltage (cell Vmin) of less than -0.1V. Ideally, this is less than -0.1V to about -5V, preferably less than -0.1V to about -2.5V, preferably less than -0.1V to about -2.0V, and preferably less than -0.1V to about -1.7V. These voltage (cell Vmin) ranges are particularly desirable at discharge rates of C / ≦5 to C / ≧0.1, very preferably C / ≦2 to C / ≧0.5.

[0080] If step b) is carried out with a sodium-ion battery that can be charged to the conventional and / or expected charge capacity of the cell, it is particularly desirable that it have an endpoint (e.g., 2.5V or -1.7V). In one embodiment, step b) of the present invention comprises discharging the sodium-ion battery provided in step a) to a voltage (battery Vmin) of less than -0.1V to about -1.5V, and optionally less than -0.1V to about -1.0V.

[0081] Step b) of the present invention involves discharging the sodium-ion battery provided in step a) to a voltage (battery Vmin) preferably less than -0.5V to about -5V, more preferably less than -0.5V to about -2.5V, even more preferably less than -0.5V to about -2.1V, and most preferably less than -0.5V to about -1.7V. These voltage (battery Vmin) ranges are particularly desirable at discharge rates of C / ≦5 to C / ≧0.1, and very preferably C / ≦2 to C / ≧0.5.

[0082] In one embodiment, step b) of the present invention comprises discharging the sodium-ion battery provided in step a) to a voltage (battery Vmin) of less than -0.1V, preferably about -0.2V or less, preferably about -0.5V or less, preferably about -0.9V or less, preferably about -1.0V or less, preferably about -1.4V or less, and preferably about -1.6V or less.

[0083] As described above, a desirable object of the present invention is to provide a process in which the resulting sodium-ion cells and / or sodium-ion batteries are in a safer state than sodium-ion cells and / or sodium-ion batteries produced according to one or more processes known in the art. The phrase "safer state" means that the charge state of the resulting sodium-ion cells and / or sodium-ion batteries is lower than that of a comparative sodium-ion cell and / or sodium battery discharged to a voltage of -0.1V or higher (cell Vmin). Therefore, the effect resulting from the present invention, in particular the effect resulting from discharging the sodium-ion battery to a voltage of less than -0.1V (battery Vmin) in step b), is that the charge state from the resulting sodium-ion battery is lower than that of a comparative sodium-ion battery discharged to a voltage of -0.1V or higher (battery Vmin). This is because the percentage of charge remaining in a sodium-ion battery discharged to a voltage of less than -0.1V (battery Vmin) is lower than the percentage of charge remaining in a comparative battery discharged to a voltage of -0.1V or higher (battery Vmin). Therefore, the present invention provides a sodium-ion battery that is safer than a sodium-ion battery discharged to a voltage of -0.1V or higher (battery Vmin). Furthermore, the sodium-ion battery obtained from the process of the present invention surprisingly does not pose the risk of fire and explosion associated with discharging a comparable lithium-ion battery to a voltage of less than -0.1V (battery Vmin). Therefore, such a sodium-ion battery is surprisingly capable of safe storage and / or safe transport and / or safe maintenance. Moreover, the estimated lifespan of the obtained sodium-ion battery is also expected to be longer than that of a lithium-ion cell, because such a sodium-ion battery can withstand discharge to a voltage of less than -0.1V (cell Vmin) without affecting conventional or expected charge capacity.

[0084] The sodium-ion battery provided in step a) ideally has a maximum operating cell voltage (battery Vmax) based on the electrochemistry of the battery, for example, as assigned by the manufacturer. Furthermore, each sodium-ion cell used to provide the sodium-ion battery may ideally have a maximum operating cell voltage (cell Vmax) based on the electrochemistry of the cell, for example, as assigned by the manufacturer. Each of the one or more sodium-ion cells used to provide the sodium-ion battery is preferably assigned a cell Vmax of about 1.0V to about 5.0V, ideally 3.0V to 4.5V. For example, a very preferred sodium-ion cell uses an alkali metal-containing oxide-based (cathode) chemistry and therefore may have a cell Vmax of about 4.0V to about 4.5V, ideally 4.0V to about 4.3V. Alternatively, a sodium-ion cell may use a Prussian blue analog (including Prussian white) or phosphate-based (cathode) chemistry and therefore may have a cell Vmax of about 3.0V to about 3.9V.

[0085] Preferably, step a) includes a sodium-ion battery that can be charged to the conventional and / or expected charge capacity of the battery. As used herein, this is intended to mean a sodium battery that can be charged to ≥50% to 100%, preferably ≥80% to 100%, of its battery Vmax.

[0086] It will be understood that a sodium-ion battery that can be charged to its conventional and / or expected charge capacity may be a pristine sodium-ion battery. Therefore, such a sodium-ion battery may be chargeable up to ≥90% to 100% of its battery Vmax. It will also be understood that a sodium-ion battery that can be charged to its conventional and / or expected charge capacity may be a non-pristine sodium-ion battery. During the lifespan of a sodium-ion battery, fluctuations from the battery Vmax may occur, which may be most pronounced during the aging of the sodium-ion battery in use. Therefore, such a sodium-ion battery may be chargeable up to ≥50% to 100% of its battery Vmax.

[0087] A further benefit of the present invention, particularly in preferred embodiments where step a) includes a sodium-ion battery that can be charged to the conventional and / or expected charge capacity of the battery, is that the electrochemical performance of the resulting sodium-ion battery is substantially unaffected.

[0088] In one embodiment, step a) includes a sodium-ion battery that cannot be charged to its conventional and / or expected charge capacity, also known as a “dead cell” or “defective cell.” As used herein, this is intended to mean a sodium-ion battery that cannot be charged to ≥50% to 100%, preferably ≥80% to 100%, of the battery Vmax based on the battery's electrochemistry, for example, as assigned by the manufacturer.

[0089] It will be understood that a sodium-ion battery that cannot be charged to the conventional and / or expected charge capacity of its cells may be a pristine sodium-ion battery. Therefore, such a sodium-ion battery may not be able to be charged to ≥50% to 100%, preferably ≥80% to 100%, of the battery Vmax.

[0090] It will also be understood that sodium-ion batteries that cannot be charged to their conventional and / or expected charge capacity may be non-pristine sodium-ion batteries. Therefore, such sodium-ion batteries may not be able to be charged to ≥50% to 100%, preferably ≥80% to 100%, of the battery Vmax.

[0091] A further effect of the present invention, particularly in embodiments in which step a) includes a sodium-ion battery that cannot be charged to its conventional and / or expected charge capacity, is that the resulting sodium-ion battery is in a safer state because it has a lower percentage of residual charge (if any) in the battery. Thus, such a sodium-ion battery can be safely stored and / or safely maintained and / or safely transported, and / or safely destroyed where appropriate.

[0092] Preferably, step a) includes providing a sodium-ion battery comprising two or more sodium-ion cells (as defined herein, in particular, such as those using alkali metal-containing oxide-based (cathode) chemistry). The two or more cells may have the same cell voltage profile, preferably the same nominal cell voltage profile, and may have the same electrochemical design. As used herein, the terms “same cell voltage profile” or “same cell nominal voltage profile” mean the same voltage-to-capacity relationship. As described above, each of the two or more cells may have a cell Vmax of about 1.0V to about 5.0V, ideally 3.0V to 4.5V. Similarly, as described above, all of the two or more cells may be subjected to a conditioning process (also known as a “formation” process) comprising one or more charge and discharge operations prior to step b).

[0093] In one embodiment, step a) includes sodium-ion batteries in a parallel or series configuration. As described above, another desirable object of the present invention is to provide a process for providing a sodium-ion cell and / or sodium-ion battery in a charge state of, for example, 20% or less, which can be provided in a relatively short time (i.e., less than 100 hours). While low discharge rates (C / 20 or C / 100) are more likely to result in a sodium-ion battery from which all or substantially all of the charge has been dissipated, the methods of the prior art merely teach that the sodium-ion battery should be discharged to a voltage of -0.1V or higher (cell Vmin). Therefore, it is very beneficial to dissipate all or substantially all of the charge from the sodium-ion battery at a high discharge rate (C / <10), and thus obtain a sodium-ion battery in a charge state of 20% or less in a shorter time.

[0094] A preferred method for discharging the sodium-ion battery in step b) of the present invention is to draw a constant current at a discharge rate of C / <10 until the sodium-ion battery shows a voltage of less than -0.1V. A discharge rate of C / <10 means that the entire sodium-ion battery is discharged in less than 10 hours with a discharge current. As those skilled in the art will understand, a discharge rate of C / <10 can also be expressed as >0.1C (i.e., less than 1 ÷ 10 hours = >0.1C).

[0095] In one embodiment, the discharge carried out in step b) of the present invention is at discharge rates of C / <10 to about 4000C, optionally about C / <10 to about 1000C, optionally about C / <10 to about 500C, optionally about C / <10 to about 200C, optionally about C / <10 to about 150C, and optionally about C / <10 to about 50C.

[0096] In one embodiment, the discharge carried out in step b) of the present invention is at a discharge rate of C / <10 to C / ≧0.1 (10C), preferably C / <10 to C / ≧0.33 (3C), and further preferably C / <10 to C / ≧0.5 (2C).

[0097] Therefore, a discharge rate of C / <10 to C / ≧0.1 (10C) means that the entire sodium-ion battery is discharged over a period of 6 minutes or more (i.e., C / ≧0.1 × 60 minutes = 6 minutes or more) to less than 10 hours (i.e., C / <10).

[0098] The advantage of this preferred method is that, as described above, the battery in step b) can be safely discharged to a voltage of less than -0.1V (battery Vmin), allowing for the use of a higher discharge rate to dissipate all, or substantially all, of the charge from the resulting sodium-ion battery in a shorter time. Furthermore, it was found that the charge state of the resulting sodium-ion battery discharged to a voltage of less than -0.1V at a discharge rate of C / <10 was closer to 0% than that of the comparative sodium-ion battery discharged to a voltage of 0V (i.e., above -0.1V).

[0099] In one embodiment, the discharge carried out in step b) of the present invention is at a discharge rate of C / ≦8, optionally C / ≦6, optionally C / ≦4, optionally C / ≦2, optionally C / ≦1, and optionally C / ≦0.5.

[0100] In one embodiment, the discharge carried out in step b) of the present invention is at a discharge rate of C / <10 to C / ≧2. The discharge carried out in step b) of the present invention is preferably at a discharge rate of C / ≦5 to C / ≧0.1, more preferably at a discharge rate of C / ≦5 to C / ≧0.5. The discharge carried out in step b) of the present invention is very preferably at a discharge rate of C / ≦2 to C / ≧0.1, most preferably at a discharge rate of C / ≦2 to C / ≧0.5. As described above, a discharge rate of C / ≦2 to C / ≧0.5 means that the entire sodium-ion battery is discharged with a discharge current for a period of 30 minutes or more (i.e., C / ≧0.5 × 60 minutes = 30 minutes or more) to 2 hours or less (i.e., C / ≦2).

[0101] In one embodiment, the discharge carried out in step b) of the present invention is at a discharge rate of C / 2, and optionally C / 0.5. In an embodiment in which step a) includes a sodium-ion battery that can be charged to a conventional and / or expected charge capacity, step b) of the present invention is preferably carried out at a discharge rate of C / <10 to C / ≧0.1 (10C), preferably C / <10 to C / ≧0.33 (3C), and more preferably C / <10 to C / ≧0.5 (2C). In such embodiments, a discharge rate of C / ≦5 to C / ≧0.1 is preferred, and C / ≦2 to C / ≧0.5 is very preferred.

[0102] In embodiments in which step a) includes a sodium-ion battery that cannot be charged to its conventional and / or expected charge capacity, step b) of the present invention is preferably carried out at a discharge rate of 12C or higher (also expressed as C / ≦0.083). Thus, a discharge rate of 12C or higher means that the discharge current discharges the entire sodium-ion cell within 5 minutes.

[0103] In an embodiment in which step a) includes a sodium-ion battery that cannot be charged to a conventional and / or expected charge capacity, step b) of the present invention is preferably carried out at a discharge rate of about 12C to about 4000C, preferably about 12C to about 1000C, preferably about 12C to about 500C, preferably about 12C to about 200C, and preferably 12C to about 150C.

[0104] In an embodiment in which step a) includes a sodium-ion battery comprising one or more cells having an alkali metal-containing oxide as a positive electrode material, which can be charged to a conventional and / or expected charge capacity, step b) of the present invention can be carried out at a preferred discharge rate of C / ≦5 to C / ≧0.1, very preferably C / ≦2 to C / ≧0.5.

[0105] In one embodiment, the process of the present invention may further include step c), which includes maintaining the sodium-ion battery at a voltage of 1V or less, preferably for 1 minute or more. Thus, the sodium-ion battery can be maintained at a voltage above the battery Vmin (as defined herein) of the sodium-ion battery. Step c) can be performed immediately after step b).

[0106] A desirable object of the present invention is to produce a sodium-ion battery having the lowest possible percentage of charge, about 20% or less. Therefore, advantageously, step c) is useful for dissipating any remaining charge from the sodium-ion battery, thus providing a sodium-ion battery with the lowest possible percentage of charge, preferably in the range of about -20% to 20%, and more preferably -10% to 10%. Ideally, this range is about -5% to about 20%, and even more ideally, about -5% to about 10%.

[0107] Assuming that the sodium-ion battery obtained from the process of the present invention is stable for a long period of time, step c) can be carried out for a period of time, for example, for more than 1 minute. Step c) can be carried out for a long period of time, for example, for at least 30 minutes, optionally at least 1 hour, optionally at least 4 hours, optionally at least 8 hours, and optionally at least 24 hours.

[0108] In one embodiment, step c) includes maintaining the sodium-ion battery at a voltage of 1V or less, preferably 0.5V or less, preferably 0V, preferably 0V or less, preferably -0.1V or less, and preferably less than -0.1V. In one embodiment, step c) includes maintaining the sodium-ion battery at a voltage of about 1V to about -5.0V, preferably about 1V to about -2.5V, more preferably about 1V to about -2.0V, and more preferably about 1V to about -1.70V. Step c) may also include maintaining the sodium-ion battery at a voltage of about 1V to about 0V.

[0109] In one embodiment, step c) may include maintaining the sodium-ion battery at the above voltage using a removable short-circuit device as described below. Alternatively, or additionally, the process may further include step d), which includes removing the removable short-circuit device as described below.

[0110] In other words, the present invention provides a sodium battery according to the process of the present invention. In other words, the present invention provides a sodium ion cell which is preferably capable or incapable of being charged to a conventional or expected charge capacity of the cell, preferably suitable for safe storage and / or transport and / or maintenance, and which comprises a positive electrode comprising a positive electrode material, a positive electrode current collector, a negative electrode comprising a negative electrode material, a negative electrode current collector, and an electrolyte, wherein the sodium ion cell is in a charge state of 20% or less, and the sodium ion cell is maintained at a voltage of less than -0.1V (i.e., cell Vmin).

[0111] In other words, the present invention provides a sodium ion cell which is preferably capable or incapable of being charged to a conventional or expected charge capacity of the cell, preferably suitable for safe storage and / or transport and / or maintenance, and which comprises a positive electrode comprising a positive electrode material, a positive electrode current collector, a negative electrode comprising a negative electrode material, a negative electrode current collector, and an electrolyte, wherein the sodium ion cell is in a charge state of 20% or less, and the potential difference between the positive electrode and the negative electrode is less than -0.1V.

[0112] In one embodiment, the sodium ion cell is a pristine and / or non-pristine cell. In one embodiment, the sodium ion cell is charged to about -20% to about 20%, more preferably to about -10% to about 10%. Ideally, the sodium ion cell is charged to about -5% to about 20%, more ideally to about -5% to about 10%.

[0113] In one embodiment, the sodium ion cell has or is maintained at a voltage (cell Vmin) of approximately -0.2V or less, preferably approximately -0.5V or less, preferably approximately -0.9V or less, preferably approximately -1.0V or less, preferably approximately -1.4V or less, and preferably approximately -1.6V or less.

[0114] In one embodiment, the sodium ion cell has or is maintained at a voltage (cell Vmin) of less than -0.1V to about -5.0V, optionally less than -0.1V to about -2.5V, and optionally less than -0.1V to about -1.0V.

[0115] The voltage (cell Vmin) can be maintained using a removable short-circuit device, as described below. In other words, the present invention provides a sodium-ion battery which is preferably capable or incapable of being charged to a conventional or expected charge capacity of the battery, preferably suitable for safe storage and / or transport and / or maintenance, and which comprises one or more sodium-ion cells comprising a positive electrode comprising a positive electrode material, a positive electrode current collector, a negative electrode comprising a negative electrode material, a negative electrode current collector, and an electrolyte, wherein the sodium-ion cells are in a charge state of 20% or less, and the sodium-ion battery is maintained at a voltage of less than -0.1V (battery Vmin).

[0116] In other words, the present invention provides a sodium-ion battery which is preferably capable or incapable of being charged to a conventional or expected charge capacity of the battery, preferably suitable for safe storage and / or transport and / or maintenance, and which comprises one or more sodium-ion cells comprising a positive electrode comprising a positive electrode material, a positive electrode current collector, a negative electrode comprising a negative electrode material, a negative electrode current collector, and an electrolyte, wherein the sodium-ion cells are in a charge state of 20% or less, and the potential difference between the positive electrode and the negative electrode is less than -0.1V.

[0117] In one embodiment, the sodium-ion battery is a pristine and / or non-pristine battery. In one embodiment, the sodium ion cell is charged to about -20% to about 20%, more preferably to about -10% to about 10%. Ideally, the sodium ion cell is charged to about -5% to about 20%, more ideally to about -5% to about 10%.

[0118] In one embodiment, the sodium-ion battery has or maintains a voltage (battery Vmin) of approximately -0.2V or less, preferably approximately -0.5V or less, preferably approximately -0.9V or less, preferably approximately -1.0V or less, preferably approximately -1.4V or less, and preferably approximately -1.6V or less.

[0119] In one embodiment, the sodium-ion battery has or is maintained at a voltage (battery Vmin) of less than -0.1V to about -5.0V, optionally less than -0.1V to about -2.5V, and optionally less than -0.1V to about -1.0V.

[0120] The voltage (battery Vmin) can be maintained using a removable short-circuit device, as described below. In other words, the present invention provides sodium ion cells as described above for storage and / or transport, and / or sodium ion cells produced according to the process of the present invention as described above.

[0121] In other words, the present invention provides a sodium-ion battery as described above for storage and / or transport, and / or a sodium-ion battery produced according to the process of the present invention as described above.

[0122] In other words, the present invention provides a sodium-ion battery comprising one or more sodium-ion cells as described above, and / or storage and / or transport and / or maintenance of a sodium-ion battery comprising one or more sodium-ion cells produced according to the process of the present invention as described above.

[0123] In other words, the present invention provides storage and / or transport and / or maintenance of sodium ion cells and / or energy storage devices, the energy storage devices comprising one or more sodium ion cells as described above and / or one or more sodium ion cells produced according to the process of the present invention as described above.

[0124] In other words, the present invention provides an energy storage device comprising one or more sodium ion cells according to the process of the present invention and / or as described above. The energy storage device of the present invention comprises one or more sodium ion cells as described above. Examples of such energy storage devices include batteries, battery modules, battery packs, electrochemical devices, and electrochromic devices. In a preferred energy storage device according to the present invention, some or all of these one or more sodium ion cells are connected in series.

[0125] Preferably, the present invention in any of the above aspects also provides a sodium ion cell and / or energy storage device (such as a sodium ion battery as described herein), the energy storage device comprising, in at least one of one or more sodium ion cells, a removable short-circuit device, for example, between a cathode electrode and an anode electrode. Preferably, the removable short-circuit device is connected to the terminals of the cathode electrode and the anode electrode.

[0126] The removal of a short-circuit device encompasses any procedure including disconnecting the connection between the cathode and anode electrodes. Therefore, the removal of a short-circuit device does not necessarily have to involve physically removing the short-circuit device from the sodium ion cell or energy storage device. In alternative arrangements, the connection between electrodes can be disconnected without physically removing the short-circuit device from the sodium ion cell or energy storage device.

[0127] The short-circuit device conveniently provides a physical and / or electrical short circuit (a low-impedance or low-resistance connection that provides electrical conductivity) between the cathode electrode and the anode electrode to ensure that the amount of electrical energy in one or more sodium ion cells is maintained at 20% or less (or as defined in the preferred range above) while the sodium ion cell or energy storage device is being stored and / or transported and / or maintained, i.e., that the cell is in a very safe state.

[0128] A short-circuit device can be an internal or external manual or automatic device, and may be one of several different short-circuit devices known in the art, such as using inductance or resistance or a combination thereof in a triggered or latched manner. It may be active or passive. Like physical devices, a short-circuit device can be an electronic device.

[0129] Preferably, the short-circuit device is easily removable, perhaps by having at least a portion of it outside the sodium ion cell or energy storage device, and as a result, the short-circuit device can be removed from the sodium ion cell or energy storage device before use.

[0130] In a preferred configuration, the short-circuit device is located outside the cell housing or packaging and is a low-impedance / resistive short circuit between a positive tab and a negative tab, which are connected to the positive and negative electrodes inside the housing or packaging.

[0131] Furthermore, in energy storage devices, it is expected that some or all of the individual sodium ion cells used therein may be short-circuited, or that the entire energy storage device (e.g., a sodium ion battery) may be short-circuited. It is also expected that the removable short-circuit device may be reused to short-circuit the sodium ion cell / energy storage device more than once, or to short-circuit other sodium ion cells or energy storage devices. The removable short-circuit device may be provided by any convenient means, such as a short-circuit tab, or a conductive gel or other conductive material that provides a connection between the anode and cathode in one or more of the sodium ion cells.

[0132] Typically, the sodium ion cell of the present invention (including the sodium ion cell used in the sodium ion battery of the present invention) comprises a positive electrode containing a positive electrode material, a positive electrode current collector, a negative electrode containing a negative electrode material, a negative electrode current collector, and an electrolyte.

[0133] Preferably, the sodium ion cell of the present invention is asymmetric. The term "asymmetric" means that the positive electrode active material is not the same as the negative electrode active material. Suitable negative electrode (active material) materials include amorphous carbon, hard carbon, soft carbon, silicon, and any other materials, such as alloying metals like phosphorus, tin, germanium, or antimony, materials that store sodium via conversion (and / or alloying reactions) such as Sb2O3 and Fe2O3, and some titanates / sodium titanates, the structures of which are adapted to allow insertion / removal of sodium ions during charging / discharging. These suitable negative electrode materials can be used alone or in combination with each other. Hard carbon is particularly advantageous and preferred.

[0134] Advantageously, the negative and positive electrode current collectors each contain one or more conductive materials that are stable at voltages below -0.1V (or within the preferred voltage range described herein) and / or under conditions of 20% or less, preferably about -20% to about 20%, and preferably about -10% to about 10%. Ideally, about -5% to about 20%, and more ideally about -5% to about 10% (or within the preferred charge range described herein). In this context, “stable” means that under certain conditions (e.g., below -0.1V), one or more conductive materials do not react with sodium or form a solid solution with sodium. A “solid solution” as defined herein is a solid mixture containing a major component and a trace component, wherein the trace component is uniformly distributed within the crystal lattice of the major component. For example, sodium does not form a solid solution with aluminum under these conditions.

[0135] It is preferable that one or more conductive materials do not alloy with and / or otherwise react with sodium. Those skilled in the art will understand from general knowledge that aluminum does not alloy with sodium. However, it is possible for sodium to be present in aluminum as an impurity to achieve grain boundary effects, or for sodium to be used in aluminum as a modifier at very low concentrations (e.g., 0.015%). However, this does not change the understanding herein that aluminum does not alloy with sodium.

[0136] In one embodiment, one or more conductive materials may exist in pure form, in impure form, as an alloy, or as a mixture, alone or in combination with one or more other elements in varying amounts.

[0137] More preferably, at least one of the one or more conductive materials includes a lower-grade material, such as an industrial-grade or household-grade material. Advantageously, the one or more conductive materials may include one or more metals selected from copper, aluminum, and titanium, most preferably aluminum.

[0138] The negative electrode current collector, the positive electrode current collector, or both the negative and positive electrode current collectors may contain aluminum or an aluminum alloy (e.g., an alloy of aluminum with one or more of Mg, Mn, Cr, Zn, Si, Fe, and Ni). Very preferably, both the negative and positive electrode current collectors contain aluminum current collectors. Advantageously, conductive materials of the same composition are selected for both the positive and negative electrode current collectors. Furthermore, it is particularly preferable that at least one of the one or more conductive materials for both the positive and negative electrode current collectors contains aluminum in pure form, in impure form, as an alloy, or as a mixture, alone, or in combination with one or more other elements in varying amounts.

[0139] The applicant has found, surprisingly, that it is possible to use low-grade aluminum from, for example, impure or household sources as a conductive material for one or both current collectors, or within them, thereby achieving clearly significant commercial advantages. Furthermore, at the operating electrode potential, impurities in the low-grade aluminum (e.g., zinc or copper) are under cathode protection and therefore do not dissolve in the electrolyte phase. This is in contrast to the usual requirements of high-purity aluminum used in cathode current collectors for lithium-ion and sodium-ion batteries currently in use.

[0140] Household-grade aluminum (e.g., sold as "kitchen foil," "tin foil," or "oven foil") includes aluminum materials with an aluminum content of 92-99%, for example, 92-99%. Impure aluminum may contain less than 92% aluminum.

[0141] Accordingly, the present invention provides a sodium ion cell for use in a sodium ion cell itself and / or an energy storage device (e.g., a sodium ion battery as defined herein), comprising a negative electrode having one or more negative electrode materials and negative electrode current collectors, and a positive electrode having one or more positive electrode materials and positive electrode current collectors, wherein one or more positive electrode current collectors and / or negative electrode current collectors comprise one or more conductive materials that are stable in the range of less than -0.1V (or within the preferred voltage or charging range described herein).

[0142] Advantageously, one or more conductive materials do not form solid solutions with sodium under certain conditions (e.g., less than -0.1V). Preferably, one or more conductive materials do not alloy with sodium and / or otherwise react with it. One or more conductive materials may include one or more metals. These may exist in pure form, in impure form, as alloys or mixtures, alone or in combination with one or more other elements in varying amounts. Particularly preferably, one or more current collectors include one or more metals selected from copper, aluminum, and titanium, most preferably aluminum.

[0143] The applicant has found that when the sodium ion cell of the present invention is used on its own or as part of an energy storage device, it is particularly advantageous when at least one of the positive electrode current collector and the negative electrode current collector, preferably the negative electrode current collector, includes a carbon coating. This results in advantages such as better adhesion between the active negative electrode material and the negative electrode current collector, and consequently lower contact resistance. Current collectors including a carbon coating have also been found to improve speed performance, which allows current to be charged / discharged rapidly. Similar advantages are obtained when the sodium ion cell includes a positive electrode current collector including a carbon coating. Sodium ion cells including a positive electrode current collector including a carbon coating, in addition to a negative electrode current collector including a carbon coating, are particularly electrically efficient.

[0144] A current collector containing a carbon coating preferably contains one or more carbon-coated materials that are stable at less than -0.1V. The carbon-coated material preferably includes a carbon-coated metal (the metal may be conductive, but does not need to be conductive itself, as the carbon coating provides conductivity). The carbon coating can be applied to the selected material (the one used to provide the conductive material) using any suitable technique such as spray coating, solution casting, or dipping. Alternatively, a suitable carbon-coated material may be commercially available. Carbon-coated metals, such as carbon-coated copper and / or carbon-coated aluminum and / or carbon-coated titanium, are preferred, and carbon-coated aluminum of grade SDX supplied by Showa Denko Inc. is particularly preferred. Carbon-coated low-grade aluminum (e.g., from impure or household sources) is extremely preferred. As described above, carbon-coated low-grade aluminum has low production costs, and impurities present in the low-grade aluminum do not leach out or cause problems with cell performance.

[0145] The negative electrode and positive electrode (active material) materials used in the sodium ion cell of the present invention (including the sodium ion cell used in the sodium ion battery of the present invention) are any materials capable of intercalating and deintercalating (inserting and removing) sodium ions during charging and discharging.

[0146] The positive electrode may contain one or more positive electrode active materials, which can insert and extract alkali metals, and are preferably selected from oxide-based materials, polyanionic materials, and Prussian blue analog-based materials (including Prussian white materials).

[0147] Particularly preferably, the one or more positive electrode active materials include one or more selected from alkali metal-containing oxide-based materials and alkali metal-containing polyanion materials, wherein the alkali metal is one or more alkali metals selected from sodium and / or potassium, preferably sodium, and may optionally be combined with lithium. Certain positive electrode active materials contain lithium as a minor alkali metal component, that is, the amount of lithium is less than 50% by weight, preferably less than 10% by weight, ideally less than 5% by weight of the total alkali metal content.

[0148] The most preferred positive electrode active material has the general formula: A 1±δ M 1 V M 2 W M 3 X M 4 Y M 5 Z O 2-c wherein: A is one or more alkali metals selected from sodium, potassium and lithium, preferably sodium; M 1 comprises one or more redox-active metals in the +2 oxidation state, M 2 comprises a metal in an oxidation state greater than 0 and not more than +4; M 3 comprises a metal in the +2 oxidation state; M 4 comprises a metal in an oxidation state greater than 0 and not more than +4; M 5 comprises a metal in the +3 oxidation state; wherein, 0≦δ≦1; V>0; W≧0; X≧0; Y≧0; at least one of W and Y is >0, Z≧0; C is in the range of 0≦c<2, V, W, X, Y, Z, and C are selected to maintain electrochemical neutrality.

[0149] Ideally, metal M 2 It contains one or more transition metals, preferably selected from manganese, titanium and zirconium; M 3 is preferably one or more selected from magnesium, calcium, copper, tin, zinc, and cobalt; M 4 It preferably comprises one or more transition metals selected from manganese, titanium and zirconium; and M 5 Preferably, it is one or more selected from aluminum, iron, cobalt, tin, molybdenum, chromium, vanadium, scandium, and yttrium.

[0150] Particularly preferred cathode electrode active materials are nickelate-based materials and / or nickel-free layered oxides (e.g., iron, copper, and manganese-based layered oxides). Any positive electrode active material having a crystalline structure can be used, but preferably the structure is O3 or P2 or a derivative thereof. Specifically, the positive electrode active material may have a heterogeneous structure consisting of a mixture of phases, i.e., several different crystalline forms. For example, the positive electrode active material contains a compound having the general formula detailed above in a mixture of O3 phase and P2 phase. The ratio of O3 phase to P2 phase is preferably 1 to 99:99 to 1.

[0151] A highly preferred cathode active material includes sodium and / or potassium-containing transition metal-containing compounds, with sodium transition metal nickelate compounds being particularly preferred. Particularly preferred examples include alkali metal layered oxides, single-phase and mixed-phase O3, P2 and P3 alkali metal layered oxides, alkali metal-containing polyanionic materials, oxymetalates, Prussin blue analogs, and Prussian white analogs. A specific example is O3 / P2-A 0.833 Ni 0.317 Mn 0.467 Mg 0.1 Ti 0.117O2, O3-A 0.95 Ni 0.3167 Mn 0.3167 Mg 0.1583 Ti 0.2083 O2, P2 type A 2 / 3 Ni 1 / 3 Mn 1 / 2 Ti 1 / 6 O2, P2-A 2 / 3 (Fe 1 / 2 Mn 1 / 2 )O2, P'2-A 2 / 3 MnO2, P3, or P2-A 0.67 Mn 0.67 Ni 0.33 O2, A3V2(PO4)3, AVPO4F, AVPO4F, A3V2(PO4)3A3V2(PO4)2F3, A3V2(PO4)2F3, A x Fe y Mn y (CN)6·nH2O(0≦x, y, z≦2; 0≦n≦10), O3, P2 and / or P3-A x Mn y Ni z Examples include O2 (0≦x≦1 and 0≦y, z≦1). A2Fe2(SO4)3, A2Ni2SbO6 and A3Ni2SbO6 [wherein "A" in these compounds is one or more alkali metals selected from Li, Na and K, preferably Na and / or K, most preferably Na].

[0152] Advantageously, the sodium ion cell according to the present invention (including the sodium ion cell used in the sodium ion battery of the present invention) can use an electrolyte in any form, i.e., a solid, liquid, or gel composition can be used. Non-aqueous electrolytes, such as those described in International Publication No. 2020 / 240290 A1, may be particularly preferred.

[0153] The electrolyte may include one or more sodium-containing salts, such as sodium tetrafluoroborate (NaBF4) and / or sodium hexafluorophosphate (NaPF6).

[0154] The electrolyte may contain one or more fluorosulfonyl-containing salts, such as NaTFSI. Suitable examples include: 1) liquid electrolytes, e.g., ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) (preferably as an EC:DEC:PC mixture in a 1:2:1 weight / weight ratio), gamma-butyrolactone (GBL) sulfonate, diglyme, triglyceride, tetraglyceride, dimethyl sulfoxide (DMSO), dioxolane, and mixtures thereof, in one or more solvents, >0 to 10 moles of alkali metal salts, e.g., NaPF6, NaBF4, sodium bis(oxalate) (NaBOB), 1) Sodium triflate (NaOTf), NaTFSI, NaFSI, LiPF6, LiAsF6, LiBF4, LiBOB, LiClO4, LiFSi, Li-triflate and mixtures thereof, all containing / not containing diluents such as various types of hydrofluoroethers, including 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, 1,1,2,3,3,3-hexafluoropropyl 2,2,2-trifluoroethyl ether, or 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether. 2) Gel electrolytes based on any one of the following matrix materials used alone or in combination with each other; or 3) Solid electrolytes, e.g., Na3Zr2Si2PO 12 NASICON type, sulfide type such as Na3PS4 or Na3SbS4, Na2B 10 H 10 -Na2B 12 H 12 These include hydride systems, or β-alumina systems such as Na2O.(8-11)Al2O3, or related β"-alumina systems such as Na2O.(5-7)Al2O3.

[0155] Known electrolyte additives such as 1,3-propanediol cyclic sulfate (PCS), P123 surfactants, tris(trimethylsilyl) phosphite (TMSP), tris(trimethylsilyl) borate (TMSB), 1-propene-1,3-sultone, and 1,3-propanesultone can also be incorporated into the electrolyte, as can binders such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), poly(methyl methacrylate) (PMMA), sodium carboxymethylcellulose (CMC), and styrene-butadiene rubber (SBR).

[0156] As used herein, the term “sodium ion cell” should be interpreted as meaning any electrochemical cell, and preferred examples (though the present invention is not limited to these examples) include non-aqueous sodium ion cells, aqueous sodium ion cells, sodium air cells, sodium oxygen cells, rechargeable sodium metal-based cells, and anode-free sodium cells. Such electrochemical cells can be used in any small or large energy storage device, for example, but not limited to batteries, battery modules, battery packs, electrochemical devices, and electrochromic devices. Batteries, battery modules, and battery packs typically contain one or more sodium ion cells, some or all of which can be connected in series. [Brief explanation of the drawing]

[0157] The present invention will now be described with reference to the following drawings: [Figure 1] Figure 1 shows the discharge profile of a full sodium ion cell (A3PC802) discharged from 4.2 to 0V at a rate of C / 5 and a rate of 2C, as described in Example 1. [Figure 2]Figure 2 shows the discharge profiles of a full sodium ion cell (A3PC798) discharged from 4.2 to 0V at a rate of C / 2, and a full sodium ion cell (A3PC798) discharged from 4.2 to -2V at a rate of 2C, as described in Example 2. [Figure 3] Figure 3 shows the discharge profiles of a full sodium ion cell (A3PC800) discharged from 4.2 to 0V at a rate of C / 2, and a full sodium ion cell (A3PC802) discharged from 4.2 to -1.58V at a rate of 2C, as described in Example 3. [Figure 4] Figure 4 shows the discharge profiles of a full sodium ion cell (A3PC802) discharged from 4.2 to 0V at a rate of 2C, as described in Example 3, and a full sodium ion cell (A3PC802) discharged from 4.2 to -1.58V at a rate of 2C. [Figure 5] Figure 5 shows the discharge profile of a full sodium ion cell (A3PC765) discharged at a rate of C / 2 from 4.2 to approximately 2.5 times its rated capacity (in terms of the capacity that can be delivered to 0V), as described in Example 4. [Figure 6] Figure 6 shows the discharge profile of a full sodium ion cell (A3PC765) that was discharged from 4.2 to 0V at a rate of C / 2 after the discharge shown in Figure 5, as described in Example 4. [Modes for carrying out the invention]

[0158] Electrochemical results The sodium ion electrochemical test cell is configured as follows: The positive electrode is made of active material (doped nickelate-containing O3 / P2 Na). 0.833 Ni 0.317 Mn 0.467 Mg 0.1 Ti 0.117The electrode is prepared by solution casting a slurry of O2, conductive carbon, binder, and solvent onto a substrate. The conductive carbon used is commercially available from Timcal Limited. Polyvinylidene fluoride (PVdF) is used as the binder, and N-methyl-2-pyrrolidone (NMP) is used as the solvent. The slurry is cast onto carbon-coated aluminum foil and heated until most of the solvent evaporates and an electrode film is formed. The electrode is then dried under dynamic vacuum at approximately 120°C. The electrode film contained the following components, expressed by weight percentage: 89% active material, 5% conductive carbon, and 6% PVdF binder.

[0159] The negative electrode is prepared by solution casting a slurry of hard carbon active material (e.g., commercially available from Kuraray Corporation), conductive carbon, binder, and solvent onto a substrate. The conductive carbon used is commercially available, for example, from Timcal Limited. PVdF is used as the binder (unless otherwise specified in the specific example), and N-methyl-2-pyrrolidone (NMP) is used as the solvent. The slurry is cast onto carbon-coated aluminum foil and heated until most of the solvent evaporates and an electrode film is formed. The electrode is then further dried under dynamic vacuum at approximately 120°C. The negative electrode film contains the following components, expressed by weight percentage: 88% active material (hard carbon), 3% conductive carbon, and 9% PVdF binder.

[0160] The carbon-coated aluminum material used as the negative and / or positive electrode current collector is supplied by Showa Denko Inc. TM The material is an En'Safe® current collector supplied by ARMOR. General procedure for preparing pouch cells A sodium ion pouch cell was constructed using an active material electrode, a separator, and an electrolyte; an aluminum tab was connected to each electrode, and the cell was placed in a polymer-coated aluminum pouch. The three-electrode Na ion pouch cell used herein has a square negative electrode (4.8 cm²). 2 ) and a square positive pole (4.0cm 2 These include, and are separated by either a two-layer polyolefin separator (such as Asahi Kasei's ND525 grade or Celgard® 2500 grade) or a one-layer polyolefin separator and a one-layer glass fiber (Whatman GF / A grade) separator, with a third Na reference electrode inserted between them. Then, appropriate Na + The base electrolyte is added to the cell (such as the type described in International Patent Application Publication No. 2020 / 240209 A1). The cell assembly is then hermetically sealed under vacuum in an Al laminated pouch material that is ready for electrochemical testing. Cell test The cells are tested using constant current cycling technology (applying a constant voltage, 4.2V in this specification, when fully charged) as follows:

[0161] The cell is subjected to a cycle at a predetermined current density between preset voltage limits. A commercially available battery cycler from Maccor Inc. (Tulsa, Oklahoma, USA) is used. During charging, alkaline ions are extracted from the cathode active material. During discharge, alkaline ions are reinserted into the cathode active material. In the following examples, the first cycle between 4.2 and 0V at either ±C / 10 or ±C / 5 (detailed below) is an example of a conditioning / formation cycle. [Examples]

[0162] Example 1 (not based on the present invention) The effect of different discharge rates from 4.2V to 0V on the cell's "true state of charge" (SOC). Experiments were conducted to test the effect of different discharge rates on the true state of charge (SOC) of a sodium ion cell after a 30-minute pause during discharge from 4.2V to 0V.

[0163] A single cell (A3PC802) was prepared according to the general procedure described above. In one discharge, the cell was discharged from 4.2V to 0V at a rate of C / 5 (0.2C or 5-hour discharge), and in the other discharge, the cell was discharged from 4.2V to 0V at a rate of 2C (C / 0.5 or 30-minute discharge).

[0164] As illustrated by the results shown in Figure 1, mAh / g delivered at 0V cathode It can be observed that the specific capacity per unit (weight based on the amount of active material in the cathode) was lower at a rate of 2C compared to the same discharge performed at a rate of C / 5.

[0165] This (kinetic) effect stems from the fact that at slower discharge rates (i.e., a rate of C / 5) more Na+ ions may be inserted from the anode to the cathode compared to faster discharge rates (i.e., a rate of 2C).

[0166] However, what was particularly interesting in this experiment was observing the open-circuit voltage of the cell at the end of a 30-minute rest period under open-circuit conditions immediately after the discharge operation down to 0V (i.e., constant-current discharge event). This voltage can be called the "bounce back" open-circuit voltage (OCV).

[0167] As shown in the inset in Figure 1, the "rebound" OCV was greater for cells discharged to 0V at a rate of 2C than for cells discharged to 0V at a rate of C / 5. Therefore, the true SOC of cells discharged to 0V at a rate of C / 5 was found to be lower than the true SOC of cells discharged to 0V at a rate of 2C (i.e., 1.70V vs. 1.94V, respectively).

[0168] Therefore, since 1.70V is closer to 0V, we can conclude that a cell discharged to 0V at a rate of C / 5 is more likely to achieve a safe state than a comparison cell discharged to 0V at a rate of 2V. In other words, a cell discharged to 0V at a rate of C / 5 has a lower true state of charge (SOC) than a cell discharged to 0V at a rate of 2C. Example 2 (According to the present invention) The effect of over-discharge on the true SOC of sodium ion cells Table 1 below shows some relevant cycle metrics for three-electrode cells discharged from 4.2V to 0V or over-discharge voltage. These cells were subjected to the following cycles: Cycle 1 = ±C / 10 (Conditioning / Formation Cycle). Cycles 2-5: ±C / 2, 4.2-0V, followed by a 30-minute rest after the fifth discharge (D5) down to 0V. The 30-minute rest period is to measure the "rebound" effect of the cell voltage. Cycles 6-9: ±C / 2 for 4.2°C to over-discharge, followed by a 30-minute rest period after each over-discharge event. Cycles 10-13: To compare cycle stability after over-discharge cycles, the voltage is again set to ±C / 2 at 4.2-0V.

[0169] The main metrics in Table 1 are as follows: D6 Overdisch V: This indicates the voltage of the full cell at the end of the overdischarge state. D6-D5 Cap: Shows the increase in capacity that can be obtained from the Na ion cell when it is over-discharged to a negative voltage compared to when it is discharged to exactly 0V. D5-D6 OCV: This compares the OCV of the cell after a 30-minute rest following the D5 (down to 0V) and D6 (down to over-discharge V) discharge events. Negative values ​​indicate that the "true SOC" decreased during the over-discharge event.

[0170] [Table 1]

[0171] As shown in the results in Table 1 above, for each case, a negative voltage was observed (column 10) by subtracting the voltage observed after a 30-minute rest period following a discharge operation to 0V at a rate of ±C / 2 (D5, column 8) from the voltage observed after a 30-minute rest period following a discharge operation to the above over-discharge voltage (column 6) at ±C / 2 (D6, column 9). Therefore, it was found that the true SOC of each cell decreased as a result of discharging the cell to a voltage of less than -0.1V.

[0172] Therefore, the effect of the present invention, in particular from discharging the sodium ion cell to a voltage of less than -0.1V, is that the true charge state from the resulting sodium ion cell is lower than that when a comparative sodium ion cell is discharged to a voltage of -0.1V or higher (i.e., to a voltage of 0V).

[0173] Furthermore, when the cells are discharged from 4.2V to 0V after an over-discharge event, the capacity values ​​(D10, column 12) show very little capacity degradation compared to the capacity values ​​before the over-discharge event (D5, column 3). Moreover, the capacity values ​​remained very similar throughout the four over-discharge cycles of each cell (as can be seen from the comparison of D6, column 4 and D9, column 11). Clearly, discharging the cells to a voltage below -0.1V does not cause any substantial degradation of cell performance. The results based on the 3-electrode sodium ion cells in Table 1 are directly transferable to, for example, 2-electrode sodium ion cells used in any commercial application, and therefore the same conclusions can be drawn.

[0174] Figure 2 shows the D5 and D6 discharge cycle profiles of cell A3PC798 shown in Table 1. The inset shows the OCV "bouncing" effect over a 30-minute rest period under open-circuit conditions. Over-discharge of cell A3PC798 to -2.01V (Table 1, column 6) is 5.54 mAh / g cathodeThis resulted in an increase in capacity (Table 1, column 7), and it can be seen that the "true SOC" of the cell after the over-discharge event was approximately 0.166V lower. Furthermore, a closer examination of the capacity values ​​for D6 (column 4) and D9 (column 11) in Table 1 shows that the sodium ion cell exhibits stable cycling when over-discharged to negative voltages such as -1V or even -2V (since these are 3-electrode cells, Table 1 also provides the cathode and anode potentials at the end of the over-discharge D6 cycle).

[0175] To our great advantage, in each case, subtracting the capacity achieved by discharging the cell from 4.2V to 0V (column 3) from the capacity achieved by discharging the cell from 4.2V to the over-discharge voltage (column 4) gives an increase in cell capacity, i.e., approximately 1-5.5mAh / g cathode This was observed (7th column), which is approximately 1 to 4.6% of the cell capacity. In other words, at Vmin of each over-discharged cell (when current is still being drawn), these cells showed negative instantaneous SOC values ​​of approximately -1 to -4.6% SOC. Example: For A3PC798: (5.54 / 121.76) × 100% = -4.55% SOC Therefore, another effect resulting from the present invention, particularly from discharging the sodium ion cell to a voltage of less than -0.1V, is that the capacity from the resulting sodium ion cell is greater than that obtained when a comparative sodium ion cell is discharged to a voltage of -0.1V or higher (i.e., to a voltage of 0V).

[0176] The applicant argues that this increase in capacity was present in the anode but could not "approach" the normal operating window of the sodium ion cell (e.g., 4.2-0V). + It is understood that this is due to the following. Therefore, by over-discharging the cell according to the present invention (i.e., to a voltage of less than -0.1V), these Na + It is moved back and forth from the anode to the cathode, and therefore contributes to the reversible capacitance.

[0177] Thus, a further effect resulting from the present invention, particularly from discharging the sodium ion cell to a voltage of less than -0.1V, is the ability to achieve a negative charge state. Cell capacities that were previously inaccessible are now achievable through the present invention.

[0178] Therefore, the applicant has surprisingly discovered that by discharging the sodium ion cell to a voltage of less than -0.1V, the cell becomes safer, and subsequently, its performance, such as cycle stability, is not impaired. Approaching further cell capacity is also achieved according to the present invention. Example 3 (According to the present invention) Investigation of discharge rate for sodium ion cells The objective of this experiment was to determine whether sodium ion cells could be made to reach a lower "true state of charge" at a faster discharge rate. These three-electrode cells were subjected to the following cycle: Cycle 1 = ±C / 5 (Conditioning / Formation Cycle). Cycles 2-4: ±C / 2 (charge) / -2C (discharge) from 4.2V to 0V, with a 30-minute rest period after each discharge cycle down to 0V. The 30-minute rest period is to measure the "rebound" effect of the cell voltage. Cycles 5-7: ±C / 2 (charge) / -2C (discharge) to 4.2 to over-discharge, with a 30-minute rest after each over-discharge event. Using data from these cycles, the OCV of the cell in the relaxed state (open circuit condition) after an over-discharge event can be compared to the OCV after a 30-minute rest following discharge at 0V. The lower OCV after over-discharge provides evidence that the cell's "true SOC" decreases after over-discharge. Cycles 8-10: To compare cycle stability after over-discharge cycles, the voltage was again set to +C / 2C (charge) / -2C (discharge) at 4.2-0V (with a 30-minute rest period after each discharge cycle).

[0179] [Table 2]

[0180] From a closer examination of Table 2, we can conclude again, similar to the results shown in Table 1, that discharging the sodium ion cells to a voltage below -0.1V results in sodium ion cells with a lower true charge state than comparative sodium ion cells discharged to a voltage above -0.1V (i.e., to a voltage of 0V). This is evidenced by the observation of negative voltages in each cell in column 10. This value was similarly calculated by subtracting the voltage observed after a 30-minute rest period following the discharge operation to 0V (D4, column 8) from the voltage observed after a 30-minute rest period following the discharge operation to the over-discharge voltage (column 6) (D5, column 9).

[0181] However, the difference between the results shown in Table 1 and Table 2 is that the cells in Table 1 were discharged at a rate of C / 2 (0.5C or 2 hours), while the cells in Table 2 were discharged at a rate of 2C (C / 0.5 or 30 minutes). Therefore, the cells in Table 2 were discharged four times faster than the cells discharged in Table 1.

[0182] When a cell is discharged from 4.2V to 0V after an over-discharge event at a rate of 2C, the capacity value (D8, column 12) shows very little capacity degradation compared to the capacity value before the over-discharge event (D4, column 3). Furthermore, the capacity values ​​remained very similar throughout the three over-discharge cycles for each cell (as can be seen by comparing D5, column 4 and D7, column 11). Therefore, it is clear that discharging a cell to a voltage below -0.1V at a rate of C / <2 (e.g., 2C) does not cause any substantial degradation of cell performance. This is particularly advantageous as it means that safe cells can be prepared quickly.

[0183] The results based on the three-electrode sodium ion cell in Table 2 can be directly transferred to, for example, a two-electrode sodium ion cell used in any commercial application, and therefore the same conclusions can be drawn.

[0184] Furthermore, by comparing sodium ion cells with similar cell designs (such as C / A mass balance) between Table 1 and Table 2, we can gain a better understanding of the application of faster discharge rates up to the over-discharge voltage.

[0185] As an example, Figure 3 compares a sodium ion cell discharged from 4.2V to 0V at a discharge rate of C / 2 (cell A3PC800 shown in Table 1: completely discharged in 112.3 minutes) with a comparative sodium ion cell discharged from 4.2V to -1.58V at a discharge rate of 2C (cell A3PC802 in Table 2: completely discharged in exactly 27.7 minutes).

[0186] At 0V, it was expected that the A3PC802 would exhibit a lower capacitance than the A3PC800 due to the kinetic effect shown in Example 1. However, surprisingly, when the A3PC802 was discharged to -1.58V at a discharge rate of 2C, the resulting capacitance was comparable to that of the A3PC800 discharged to 0V at a discharge rate of C / 2: A3PC800 - 123.07mAh / g cathode (Table 1, 3rd column), A3PC802 - 120.05mAh / g cathode (Table 2, 4th column).

[0187] However, particularly surprisingly, as shown in the inset in Figure 3, the “true SOC” of cell A3PC802 (i.e., 1.831V after 30 minutes - Table 2, column 9) was equivalent to that of cell A3PC800 (i.e., 1.83V after 30 minutes - Table 1, column 8).

[0188] Therefore, in addition to the remarkable finding that sodium ion cells can be safely discharged to voltages below -0.1V, as described above and supported by Example 2, even more remarkably, as supported by Example 3, faster discharge rates can also be safely used to dissipate all or substantially all of the charge from the resulting sodium ion cell. Thus, a sodium ion cell discharged to a voltage below -0.1V at a discharge rate of 2C is safer than, or at least equally safe, a comparative sodium ion cell discharged to a voltage of 0V (i.e., above -0.1V) at a discharge rate of C / 2. In other words, a cell discharged to -1.58V at a rate of 2C has a lower or equivalent true SOC than a cell discharged to 0V at a rate of C / 2. Therefore, commercial manufacturers can prepare, for example, cells that are particularly safe for storage and / or transport and / or maintenance without performing the process over long periods of time.

[0189] Some further conclusions can also be drawn by referring to Figure 4. Figure 4 compares the discharge of the A3PC802 from 4.2V to 0V at a discharge rate of 2C with the discharge of the A3PC802 from 4.2V to -1.58V at the same discharge rate of 2C.

[0190] As illustrated in Figure 4, the "true SOC" for discharge from 4.2V to 0V was found to be 1.94V, while the "true SOC" for discharge from 4.2V to -1.58V was found to be 1.83V. Therefore, these findings lead to the conclusion that a sodium ion cell discharged to a voltage below -0.1V at a discharge rate of C / <2 is safer than, or at least equally safe, a comparative sodium ion cell discharged to a voltage of 0V (i.e., above -0.1V).

[0191] The implications of these results are crucial, as they demonstrate that when a sodium ion cell should be brought to a safe state quickly, it is substantially beneficial to discharge the sodium ion cell at a faster rate to the over-discharge voltage (negative voltage) rather than discharging it to just 0V. Example 4 (According to the present invention) Examination of the risks associated with severe overcharging of sodium ion cells Examples 2 and 3 demonstrate that the sodium ion cell has the ability to be over-discharged to a voltage of less than -0.1V without impairing its future cell performance. However, the applicant found that the sodium ion cell cannot be over-discharged indefinitely under certain circumstances, and beyond that point, the future performance of the sodium ion cell is impaired to a considerable extent.

[0192] Figure 5 shows the three-electrode cycle curve for cell A3PC765, which has the same cell design as cells A3PC794 to A3PC798 shown in Table 1 (the C / A mass balance for A3PC765 was 2.28). Cell A3PC765 was subjected to cycles from 4.2V to approximately 2.5 times its rated capacity at a discharge rate of C / 2 to simulate extreme over-discharge conditions.

[0193] As shown in the figure, above 0V, the anode potential steadily continued to rise, reaching a very high potential of over 5.2V vs Na / Na+: such a potential far exceeds the oxidative stability limit of the carbonate ester electrolyte, and it is not surprising that the anode potential remained at such a high value due to continuous discharge (due to continuous decomposition of the electrolyte).

[0194] Simultaneously, the cathode potential steadily continued to decrease, and its cycle profile was significantly disrupted. Oxidizing electrolyte species generated at the high-potential anode may have migrated to the cathode, causing such disruption. As shown in the inset of Figure 5, the OCV of the cell was measured after it had been left to stand for approximately 13 hours following the over-discharge event. As can be seen, extreme over-discharge resulted in a negative true charge state, which was maintained for up to 16 hours after the extreme over-discharge event.

[0195] Figure 6 further shows the cycle curve of the A3PC765 from 4.2V to 0V at a discharge rate of C / 2 after the over-discharge event shown in Figure 5. As can be seen from Figure 6, when the A3PC765 was subsequently cycled at a discharge rate of C / 2 between 4.2 and 0V, the cathode was only able to deliver 13.4 mAh / g, which is just about 11% of the capacity (118.6 mAh / g) that it could deliver when cycled at a discharge rate of C / 2 between 4.2 and 0V before the over-discharge event in Figure 5.

[0196] Therefore, these results from Example 4 lead to the conclusion that the sodium ion cell can be over-discharged to a negative voltage, but beyond that point, there is a limit beyond which the future performance of the sodium ion cell will be impaired if it is over-discharged to a considerable extent. The over-discharge limit can be, for example, -5V, optionally -4.5V, or optionally -2.5V, as disclosed herein.

[0197] Needless to say, those skilled in the art will understand that a lower limit (i.e., above -5V, for example) can be achieved by different cell designs (e.g., including the cathode or anode active material used therein). Such different cell designs are intended to be within the scope of the present invention. The present invention includes the following embodiments. [1] A process for providing a sodium ion cell that is in a charge state of approximately 20% or less and can be safely stored and / or transported and / or maintained, a) A step of providing a sodium ion cell comprising a positive electrode containing a positive electrode material, a positive electrode current collector, a negative electrode containing a negative electrode material, a negative electrode current collector, and an electrolyte, wherein the positive electrode current collector and the negative electrode current collector each contain one or more conductive materials that are stable at voltages less than -0.1V; and b) A step in which the sodium ion cell provided in step a) is subjected to one or more discharge operations at a discharge rate of C / <10 until the minimum cell operating voltage (cell Vmin) is less than -0.1V; The process including the process described above. [2] The process described in [1], wherein step b) comprises discharging the sodium ion cell provided in step a) to cell Vmin of less than -0.1V to about -5.0V. [3] The process described in [1], wherein step b) discharges the sodium ion cell provided in step a) to cell Vmin of less than -0.1V to about -2.5V. [4] The process described in [1], wherein step b) discharges the sodium ion cell provided in step a) to cell Vmin of less than -0.1V to about -1.7V. [5] Step a) is a process according to any one of [1] to [4], comprising a sodium ion cell to which a maximum operating voltage (cell Vmax) of approximately 1V to approximately 5.0V is applied. [6] Step a) the process according to any one of [1] to [5], comprising a sodium ion cell that can be charged to the conventional and / or expected charge capacity of the cell. [7] The process described in [6] allows a sodium ion cell to be charged to ≥80% to 100% of the cell Vmax, which is approximately 1V to approximately 5.0V. [8] The process according to any one of [1] to [7], wherein step a) includes a sodium ion cell that cannot be charged to the conventional and / or expected charge capacity of the cell. [9] The sodium ion cell cannot be charged to ≥80% to 100% of the cell Vmax of approximately 1V to approximately 5.0V, as described in [8].

[10] The process according to any one of [1] to [9], wherein step a) comprises a sodium ion cell subjected to one or more charge and discharge operations.

[11] The process according to

[10] , wherein step a) comprises pristine or non-pristine cells.

[12] The process described in any one of [1] to

[11] , wherein the discharge in step b) is at a discharge rate of C / <10 to C / ≧0.1.

[13] The process according to any one of [1] to

[12] , further comprising step c), wherein step c) comprises maintaining a sodium ion cell at a voltage of 1V or less.

[14] The process described in

[13] , wherein step c) is to maintain the sodium ion cell at a voltage of approximately -1.7V to approximately 1V.

[15] Step c) the process described in

[13] or

[14] , which includes the use of a removable short-circuit device.

[16] The process described in any one of [1] to

[15] , wherein the positive and / or negative current electrode collectors are made of aluminum.

[17] A process for providing a sodium-ion battery that is in a charge state of approximately 20% or less and can be safely stored and / or transported and / or maintained, a) A step of providing a sodium-ion battery comprising one or more sodium-ion cells according to step a) of [1]; and b) A step in which the sodium-ion battery provided in step a) is subjected to one or more discharge operations at a discharge rate of C / <10 to a minimum battery operating voltage (battery Vmin) of less than -0.1V; The process including the process described above.

[18] The process described in

[17] , wherein step b) discharges the sodium-ion battery to a battery Vmin of less than -0.1V to approximately -5.0V.

[19] The process described in

[17] , wherein step b) discharges the sodium-ion battery to a battery Vmin of less than -0.1V to approximately -2.5V.

[20] The process described in

[17] , wherein step b) discharges the sodium-ion battery to a battery Vmin of less than -0.1V to approximately -1.7V.

[21] The process according to any one of

[17] to

[20] , wherein step a) includes a sodium-ion battery that can be charged to the conventional and / or expected charge capacity of the battery.

[22] The process described in

[21] allows a sodium-ion battery to be charged to ≥80% to 100% of the battery Vmax.

[23] The process according to any one of

[17] to

[20] , wherein step a) includes a sodium-ion battery that cannot be charged to the conventional and / or expected charge capacity of the battery.

[24] The sodium-ion battery cannot be charged to ≥80% to 100% of the battery Vmax, as described in

[23] .

[25] The process according to any one of

[17] to

[24] , wherein one or more sodium ion cells provided in step a) are subjected to one or more charge and discharge operations.

[26] The process according to

[25] , wherein step a) includes a pristine or non-pristine battery.

[27] The process described in any one of

[17] to

[26] , wherein the discharge in step b) is at a discharge rate of C / <10 to C / ≧0.1.

[28] The process according to any one of

[17] to

[27] , further comprising step c), wherein step c) comprises maintaining a sodium-ion battery at a voltage of 1V or less.

[29] The process described in

[28] , which includes step c) maintaining the sodium-ion battery at a voltage of approximately -1.7V to approximately 1V.

[30] Step c) the process described in

[28] or

[29] , which includes the use of a removable short-circuit device.

[31] The process according to any one of

[17] to

[30] , wherein the current electrode collectors of the positive and / or negative electrodes of one or more sodium ion cells are made of aluminum.

Claims

1. A process for providing a sodium ion cell that is in a charge state of 20% or less and can be safely stored and / or transported and / or maintained, a) A step of providing a sodium ion cell comprising a positive electrode containing a positive electrode material, a positive electrode current collector, a negative electrode containing a negative electrode material, a negative electrode current collector, and an electrolyte, wherein the positive electrode current collector and the negative electrode current collector contain aluminum; b) A step of subjecting the sodium ion cell provided in step a) to one or more discharge operations at a discharge rate of C / <10 to a minimum cell operating voltage (cell Vmin) of less than -0.1V; and c) The step of maintaining the sodium ion cell at a voltage of 1V or less. The process including the process described above.

2. The process according to claim 1, wherein step b) comprises discharging the sodium ion cell provided in step a) to a cell Vmin of less than -0.1 V to -5.0 V.

3. The process according to claim 1, wherein step b) includes discharging the sodium ion cell provided in step a) to a cell Vmin of less than -0.1V to -2.5V.

4. The process according to claim 1, wherein step b) includes discharging the sodium ion cell provided in step a) to a cell Vmin of less than -0.1 V to -1.7 V.

5. The process according to any one of claims 1 to 4, wherein step a) includes a sodium ion cell to which a maximum operating voltage (cell Vmax) of 1V to 5.0V is applied.

6. The process according to any one of claims 1 to 4, wherein step a) includes a sodium ion cell that can be charged to the expected charge capacity of the cell.

7. The process according to claim 6, wherein the sodium ion cell can be charged to ≥80% to 100% of the cell Vmax of 1V to 5.0V.

8. The process according to any one of claims 1 to 4, wherein step a) includes a sodium ion cell that cannot be charged to the expected charge capacity of the cell.

9. The process according to claim 8, wherein the sodium ion cell cannot be charged to ≥80% to 100% of the cell Vmax of 1V to 5.0V.

10. The process according to any one of claims 1 to 4, wherein step a) includes a sodium ion cell subjected to one or more charge and discharge operations.

11. The process according to claim 10, wherein step a) includes a pristine or non-pristine cell, wherein the pristine cell is a cell that has been subjected to a conditioning process but has not been used with the application device, and the non-pristine cell is a cell that has been subjected to a conditioning process but has been used with the application device.

12. The process according to any one of claims 1 to 4, wherein the discharge in step b) is at a discharge rate of C / < 10 to C / ≥ 0.

1.

13. The process according to any one of claims 1 to 4, wherein step c) comprises maintaining a sodium ion cell at a voltage of -1.7V to 1V.

14. The process according to any one of claims 1 to 4, wherein step c) includes the use of a removable short-circuit device.

15. A process for providing a sodium-ion battery that is in a charge state of 20% or less and is capable of safe storage and / or transport and / or maintenance, a) A step of providing a sodium-ion battery comprising one or more sodium-ion cells according to step a) of claim 1; b) A step of subjecting the sodium-ion battery provided in step a) to one or more discharge operations at a discharge rate of C / <10 to a minimum battery operating voltage (battery Vmin) of less than -0.1V; and c) The step of maintaining the sodium ion cell at a voltage of 1V or less. The process including the process described above.

16. The process according to claim 15, wherein step b) includes discharging the sodium-ion battery to a battery Vmin of less than -0.1V to -5.0V.

17. The process according to claim 15, wherein step b) includes discharging the sodium-ion battery to a battery Vmin of less than -0.1V to -2.5V.

18. The process according to claim 15, wherein step b) includes discharging the sodium-ion battery to a battery Vmin of less than -0.1V to -1.7V.

19. The process according to any one of claims 15 to 18, wherein step a) includes a sodium-ion battery that can be charged to an expected charge capacity.

20. The process according to claim 19, wherein the sodium-ion battery can be charged to ≥80% to 100% of the battery Vmax.

21. The process according to any one of claims 15 to 18, wherein step a) includes a sodium-ion battery that cannot be charged to its expected charge capacity.

22. The process according to claim 21, wherein the sodium-ion battery cannot be charged to ≥80% to 100% of battery Vmax.

23. The process according to any one of claims 15 to 18, wherein one or more sodium ion cells provided in step a) are subjected to one or more charge and discharge operations.

24. The process according to claim 23, wherein step a) includes a pristine or non-pristine battery, wherein the battery is pristine when all sodium ion cells forming the battery have been subjected to a conditioning process, but none of such cells are subsequently used with the application device, and the battery is non-pristine when all sodium ion cells forming the battery have been subjected to a conditioning process, but one or more of such cells are subsequently used with the application device.

25. The process according to any one of claims 15 to 18, wherein the discharge in step b) is at a discharge rate of C / < 10 to C / ≥ 0.

1.

26. The process according to any one of claims 15 to 18, wherein step c) comprises maintaining the sodium-ion battery at a voltage of -1.7V to 1V.

27. The process according to any one of claims 15 to 18, wherein step c) includes the use of a removable short-circuit device.

28. The process according to claim 1, wherein step c) is carried out for at least one hour.

29. The process according to claim 1, wherein step c) is carried out for at least four hours.

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