Sodium ion battery pack

Abstract

The present invention relates to a sodium-ion battery pack including one or more sodium-ion cells and one or more voltage converters. Methods and uses of such a sodium-ion battery pack are also disclosed.

Description

Technical Field

[0001] The present invention relates to a sodium ion battery pack designed to enable efficient delivery of the available energy in sodium ion cells present within a battery pack to an electrical device. The present invention also relates to a method for efficiently delivering the available energy in a sodium ion cell, and to an electrical device employing a sodium ion battery pack according to the present invention. To avoid misunderstanding, supercapacitors are not included within the scope of the present invention.

Background Art

[0002] Sodium ion batteries are in many respects similar to currently commonly used lithium ion batteries; both are rechargeable secondary batteries containing an anode (negative electrode), a cathode (positive electrode), and an electrolyte material, both can store energy, and both charge and discharge via similar reaction mechanisms. During charging of a sodium ion (or lithium ion) battery, Na + (or Li + ) ions deintercalate from the cathode and are inserted into the anode. During this time, electrons that balance the charge enter the anode of the battery from the cathode through an external circuit containing a charger. During discharge, the same process occurs in the opposite direction.

[0003] Lithium ion battery technology has received much attention in recent years and provides a portable type battery that is favorable for most currently used electronic application devices. However, lithium is not an inexpensive metal as a source and is considered too expensive for use in large-scale applications. In contrast, sodium is much more abundant than lithium, and there are high expectations that sodium ion batteries will provide a less expensive and more durable method for storing energy in the future, particularly for large-scale applications such as storing energy in the power distribution network. Nevertheless, further research is needed to commercially realize sodium ion batteries.

[0004] In any rechargeable battery, the energy available for practical use is a function of the depth of discharge (DoD) and voltage of each cell. In the case of conventional lithium-ion batteries, for example, batteries using cells containing lithium cobalt oxide (LCO), lithium nickel manganese cobalt oxide (NMC), or lithium nickel cobalt aluminum oxide (NCA) cathode materials, carbon or silicon anodes, a copper anode current collector, and an aluminum-containing cathode current collector, problems can occur when such cells are stored in a fully discharged state or cycled down to 0 volts or near 0 volts. For example, the dissolution of copper from the negative (anode) electrode current collector tends to cause a decrease in the discharge capacity of the cathode, and the cycle time of the lithium-ion battery will gradually become shorter. However, the practical problem with cycling lithium-ion cells down to near 0 volts is that lithium-ion cells are unstable, prone to overheating, and have a risk of unexpected ignition. So far, attempts to eliminate copper dissolution by using aluminum instead of copper for the negative electrode current collector have not been successful. This is because an alloying reaction occurs between lithium and aluminum in a fully discharged cell. There are alternative negative (anode) electrode materials that operate at a sufficiently high potential relative to lithium so that a lithium / aluminum alloy does not form, but the possible negative electrode materials are only slightly known, such as Li4Ti5O 12 and so on.

[0005] To mitigate these issues, the established way to handle standard lithium-ion batteries is to require a state of charge of about 90% to about 30% (20% for LFP, LiFePO4 batteries), i.e., their depth of discharge (DoD) must be about 70% to 80% or less. Lithium-ion batteries are conditioned immediately after manufacture by fully charging them to at least about 40% charge after at least 2 or 3 charge / discharge cycles, and any storage state at or near 0 volts is avoided. However, as a result of these precautions, the energy remaining in standard lithium-ion batteries at a state of charge of about 30% (or about 20% for LFP) cannot be accessed and is thus wasted.

[0006] On the other hand, sodium-ion batteries are extremely stable when fully discharged and when cycled down to 0 volts, and the applicant has found that even at very low states of charge (e.g., S.O.C 0% to <30%), substantially all (e.g., >95%) of the energy within the sodium-ion cell can be accessed and repeatedly accessed without affecting the life of the sodium-ion cell. However, the design of commercially viable sodium-ion batteries is currently hindered by the fact that many electrical systems used for general purposes employ narrow legacy voltage limits designed to keep lead-acid cells and lithium-ion cells within a voltage window that maximizes cycle life and ensures battery safety. For example, a commercially available nominal 12V lead-acid battery (Yuasa NPC24-12I Industrial VRLA, employing 6 cells in series) operates only within a voltage window between 14.5V and 10.5V. Table 1 lists the voltage limits published for common cell chemistries.

[0007]

Table 1

[0008] As a result of these voltage windows, electronic components such as inverters and motors have also been designed to operate within these limits. With the exception of sodium ion cells, it can be seen that all other chemical components can only operate within a voltage range where the minimum voltage (Vmin) is > 60% of the cell Vmax. Only sodium ion cells can operate within a voltage range where Vmin is < 60% of the cell Vmax. Put another way, sodium ion cells are characterized by having a much wider voltage range than other types of rechargeable cells and thus much lower compatibility with existing electronic components.

Summary of the Invention

[0009] Accordingly, an object of the present invention is to provide a sodium ion battery pack designed to facilitate efficient and comprehensive access to the available energy from one or more sodium ion cells employed in a battery pack. Specifically, an object of the present invention is to enable practical access to all, or at least substantially all, of the energy from the sodium ion cells, thereby increasing the total available energy from the sodium ion cells. Another object is to enable such practical access to the energy from the sodium ion cells when the sodium ion cells are at a low cell voltage, i.e., a voltage lower than the typical lower limit of electronic components. Still another object is to provide a sodium ion battery pack capable of controlling the battery output voltage to match the requirements of any external electronic components connected to the battery pack. In addition to this, an object of the present invention is to increase the specific available energy of the sodium ion cells within the sodium ion battery pack (i.e., increase the available energy per unit mass in J / Kg), and / or increase the volumetric energy density of the sodium ion battery pack or the sodium ion cells to the maximum value achievable within the cost window. Further, the object is to design a sodium ion battery pack that does not affect any aspect of sodium ion cell performance such as safety, cycle life, and rate performance.

[0010] An object of the present invention is also to provide a method for delivering all, or at least substantially all, i.e., preferably at least 90%, more preferably at least 93%, still more preferably at least 95%, of the energy from a sodium ion battery in which the sodium ion battery and / or one or more sodium ion cells contained therein are operable at a cell Vmin in the range of 0 to <2.0V. A further object is to provide an electronic application device connected to the sodium ion battery pack according to the present invention.

[0011] As used herein, the term "operable" in this context means that a sodium ion cell can operate between a cell Vmax and a cell Vmin according to the present invention. Such cells are used in battery packs according to the present invention. In contrast, as described above, non-sodium ion cell chemical compositions are not operable (i.e., cannot operate) between a cell Vmax and a cell Vmin according to the present invention.

[0012] As described below, the sodium ion battery pack according to the present invention is designed to provide access to a much larger input voltage range than is available with conventional battery chemical compositions, thereby increasing the amount of usable energy. In particular, the present invention provides an efficient and cost-effective means of converting energy present at low voltages in sodium ion cells into energy that is available for use and would otherwise be wasted. Ideally, the sodium ion battery pack of the present invention is designed using components that do not unnecessarily increase the mass of the battery pack.

[0013] In the broadest sense, the present invention provides a sodium ion battery pack comprising one or more sodium ion cells and one or more voltage converters. Preferably, the sodium ion battery pack comprises two or more sodium ion cells.

[0014] One or more sodium ion cells are operable between a cell Vmin in the range of >0.0V to <2.0V and a cell Vmax in the range of >3.60V to <4.30V. As noted above, the ability of sodium ion cells to operate within these cell Vmin and cell Vmax voltage ranges (i.e., be operable) is a unique characteristic of sodium ion cells not shared by other cell chemical compositions.

[0015] Preferably, one or more sodium ion cells are operable between a cell Vmin in the range of >0.0V to ≦1.50V, ideally between a cell Vmin in the range of >0.0V to ≦1.0V. Preferably, one or more sodium ion cells have a cell Vmax in the range of >3.70V to ≦4.25V and are operable ideally between a cell Vmax in the range of >3.70V to ≦4.20V.

[0016] In some embodiments, one or more sodium ion cells, preferably all of the one or more sodium ion cells, are operable in a voltage range where the cell Vmin is >0% to 55% of the cell Vmax, preferably >0% to 50% of the cell Vmax, more preferably >0% to 45% of the cell Vmax. Again, as above, the ability of sodium ion cells to operate within these Vmin / Vmax percentages is a unique feature of sodium ion cells not shared by other cell chemistries.

[0017] Two or more cells have the same cell voltage, preferably the nominal cell voltage, and are all of 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.

[0018] Furthermore, the "nominal" (or "general") cell voltage as shown in Table 1 and used herein is intended to mean, for example, the cell voltage value assigned (specified) to a cell or battery by a manufacturer and is based on the electrochemistry of the cell.

[0019] The actual measured voltage of a cell or battery decreases as the cell or battery discharges. Further, it will be understood that variations from this nominal cell voltage value can occur, for example, during manufacturing or over the life of the cell or battery. The variations can be most pronounced during aging in use of the cell or battery. However, as will be understood by those skilled in the art, the nominal cell voltage assigned to a cell or battery remains constant, i.e., the assigned nominal voltage does not change even as the actual measured voltage decreases as described above.

[0020] Two or more sodium ion cells are also typically of the same electrochemical design. By "the same electrochemical design" is meant that they share the same cell structure and combination of cell chemical components. In particular, the electrode / electrolyte chemical components, power density (per unit mass or per unit volume), and energy density (per unit mass or per unit volume) of two or more sodium ion cells are thus substantially the same at the time of initial attachment to a battery.

[0021] As a result of two or more sodium ion cells all having the same electrochemical design and the same nominal voltage, they operate in unison within a sodium ion battery pack, i.e., two or more sodium ion cells all initially behave substantially the same. The advantage of this arrangement is that the life of the sodium ion battery pack is much longer.

[0022] As used herein, one or more voltage converters within the sodium ion battery pack of the present invention provide means for matching (preferably boosting) the output voltage (also known as the terminal voltage) of a sodium ion battery pack including sodium ion cells to a level acceptable to any electronic component external to the sodium ion battery pack. This is particularly useful for sodium ion cells including hard carbon anodes where full discharge of the cell occurs only over a wide voltage window.

[0023] In some embodiments, the present invention uses two or more voltage converters. These can be the same, similar, or completely different from each other with respect to, for example, physical and / or performance characteristics, and / or type, and / or operating mode.

[0024] In some embodiments, each of one or more voltage converters is separately connected to an individual cell. In addition or alternatively, each of one or more voltage converters can be connected to more than one cell. One or more voltage converters can be connected inside and / or outside a sodium ion battery including one or more sodium ion cells.

[0025] If the energy in a low-voltage cell is not converted to a higher voltage, it cannot be utilized for use, and thus this will have an adverse effect on the effective specific energy of the cell. The energy remaining (and thus wasted) in a sodium ion cell at a low voltage (<60 - 70% cell Vmax) can reach up to 14% of the total energy in the cell.

[0026] Thus, most preferably, one or more voltage converters are provided to raise the terminal voltage of a sodium ion battery pack to >60% (preferably >70%) battery Vmax when the voltage measured across both ends of one or more sodium ion cells connected in series in the sodium ion pack is ≦60% (preferably ≦70%) battery Vmax.

[0027] "Battery Vmax" is the product of cell Vmax multiplied by the number of series cells in the pack and is related to the total voltage of such cells in the absence of one or more voltage converters. Thus, this is the maximum operating voltage of the battery in the absence of one or more voltage converters.

[0028] "Cell Vmax" described with reference to Table 1 is the maximum operating voltage of the cell itself in the absence of one or more voltage converters. The terminal voltage of a sodium-ion battery pack corresponds to the voltage measured across one or more sodium-ion cells connected in series within the sodium-ion battery pack.

[0029] Preferably, the efficiency of one or more voltage converters is such that the energy obtained during conversion is greater than the energy lost in one or more voltage converters by resistive heating and switching, i.e., the energy efficiency of voltage conversion must be high. Further, the mass of one or more voltage converters is preferably such that the effect of the mass of one or more voltage converters does not exceed an additional contribution to the specific energy from "up-conversion". A similar argument applies to the total volume of the pack and one or more voltage converters.

[0030] A preferred voltage converter is a DC / DC converter, which is a type of power converter generally including an electronic circuit or an electro-chemical device that converts a DC source of one voltage level to another voltage level. Particularly preferably, the DC / DC converter is a bidirectional DC / DC converter that allows power to flow in both forward and reverse directions. Typical DC / DC converters include boost converters and buck / boost converters, but the present invention is not limited to these two types. Generally speaking, a boost converter raises the voltage from a DC power source, while a buck / boost converter raises and lowers the output voltage.

[0031] Depending on the voltage converter circuitry, one or more voltage converters (e.g., DC / DC converters) provide a constant output voltage or reproduce an existing or known voltage profile. One or more voltage converters can be part of a stand-alone circuit configuration (as used in the examples below), especially when at least one is a DC / DC converter, or can be incorporated or connected to another component such as a battery management system (BMS). Thus, in some aspects, the present invention further includes a battery management system (BMS).

[0032] As used herein, the term "battery management system" (BMS) in this context generally also encompasses a management system for energy storage devices. A battery management system is an electronic system that manages a rechargeable battery (cell or battery or energy storage device) by, for example, protecting it from operation outside a safe operating range, monitoring the state of the battery (energy storage device), calculating secondary data, reporting that data, and using it, for example, by charge balancing within each cell, to control the performance of the battery (energy storage device). Since the sodium ion cells used in the sodium ion battery pack of the present invention can be safely discharged to at least 0 volts without degrading the charge / discharge performance of the cells, the associated battery management system does not need to be involved in monitoring the lower limit of the safe operating range or in implementing means for equalizing the charge at these low levels. Nevertheless, it is important to manage the sodium ion cells at maximum charge. Thus, the BMS typically monitors the individual cell voltages, currents, and temperatures, controls the battery safety system, and preferably employs cell balancing.

[0033] Advantageously, one or more voltage converters do not unnecessarily increase the mass of at least one sodium ion cell or battery pack, and thus the available specific energy of the sodium ion battery pack is surely higher than the available specific energy of at least one sodium ion cell alone. The present invention preferably employs one or more highly efficient voltage converters that are lightweight and have a very low amount of energy lost due to resistive heating and switching.

[0034] A DC / DC converter is known to be used in combination with a lithium-ion cell so that the output voltage of the lithium-ion cell reliably meets the voltage requirements of a particular application / device, and also to be used within an electronic application device. However, to date, there has been no prior disclosure of a battery pack including one or more sodium-ion cells and one or more voltage converters (at least one of which is preferably a DC / DC converter) for providing means to match the output voltage of a sodium-ion battery pack to an acceptable level for external electronic components (e.g., an electronic application device) of the sodium-ion battery pack. Further, to date, there has been no prior art disclosure describing that a particular design of a sodium-ion battery pack can provide an increase in the total energy available from at least one sodium-ion cell employed in the battery pack, nor a disclosure describing that a particular design of a sodium-ion battery pack can provide an increase in the specific energy available from the sodium-ion battery pack, nor a disclosure of a particular design of a sodium-ion battery pack capable of achieving an increase in volumetric energy density.

[0035] Accordingly, the present invention provides (including its use) a sodium-ion battery pack including one or more sodium-ion cells and one or more voltage converters (at least one of which is preferably a DC / DC converter as described above), wherein the specific energy deliverable by the sodium-ion battery pack satisfies the following condition: (Energy difference between battery V max and 0V) × (efficiency of one or more voltage converters) / (mass of one or more sodium-ion cells + mass of one or more voltage converters) > (energy difference between battery Vmax and 60 - 70% battery V max and) / mass of one or more sodium-ion cells; The battery V max is determined as the maximum output voltage of a sodium-ion battery pack including one or more sodium-ion cells in the absence of one or more voltage converters.

[0036] Preferably, the specific energy deliverable by the sodium ion battery pack satisfies the following conditions: (Energy difference between battery V max and 0V) × (efficiency of one or more voltage converters) / (mass of one or more sodium ion cells + mass of one or more voltage converters) > (energy difference between battery Vmax and 60 - 65% battery V max and) / mass of one or more sodium ion cells; The battery V max is determined as the maximum output voltage of a sodium ion battery pack including one or more sodium ion cells in the absence of one or more voltage converters.

[0037] To avoid misunderstanding, as used herein, the maximum output voltage of a sodium ion battery pack including one or more sodium ion cells in the absence of one or more voltage converters, i.e., battery V max is defined as the initial design maximum voltage of the sodium ion battery pack. The fact that such an initial design maximum voltage typically decreases over the cycle life of the pack is, strictly speaking, ignored in the applicant's definition of battery V max herein.

[0038] In another aspect, the present invention provides a sodium ion battery pack (including its use) including one or more sodium ion cells and one or more voltage converters (at least one of which is preferably a DC / DC converter as described above), wherein the volumetric energy density satisfies the following conditions: (Energy difference between battery V max and 0V) × (efficiency of one or more voltage converters) / (volume of at least one sodium ion cell + volume of one or more voltage converters) > (energy difference between battery V max and 60 - 70% battery V max and) / volume of at least one sodium ion cell; The battery Vmax is determined as the maximum output voltage of a sodium ion battery pack including one or more sodium ion cells in the absence of one or more voltage converters.

[0039] Preferably, the volumetric energy density satisfies the following condition: (Energy difference between battery V max and 0V) × (efficiency of one or more voltage converters) / (volume of one or more sodium ion cells + volume of one or more voltage converters) > (energy difference between battery V max and 60 - 65% battery V max and) / volume of one or more sodium ion cells; The battery V max is determined as the maximum output voltage of a sodium ion battery pack including one or more sodium ion cells in the absence of one or more voltage converters.

[0040] In a further aspect, the present invention provides for using one or more voltage converters (preferably a DC / DC converter as described above) in combination with one or more sodium ion cells to produce a sodium ion battery pack having a deliverable specific energy or a deliverable volumetric energy density that is at least 3% (preferably at least 5%) higher than the deliverable specific energy or the deliverable volumetric energy density when it is possible to have a sodium ion battery pack including one or more sodium ion cells in the absence of one or more voltage converters.

[0041] In another further aspect, the present invention provides for the use of a sodium ion battery pack according to the present invention to increase the terminal voltage of the sodium ion battery pack to > 60% (preferably > 70%) battery Vmax when the voltage measured across both ends of one or more sodium ion cells connected in series in the sodium ion battery pack is ≦ 60% (preferably ≦ 70%) battery Vmax.

[0042] As described above, "Battery Vmax" is the product of the cell Vmax and the number of series cells in the pack, and is related to the total voltage of such cells. In addition to or alternatively, one or more voltage converters are provided to raise the terminal voltage of the sodium ion battery pack to >60% (preferably >70%) Battery Vmax when the cell voltage of one or more sodium ion cells of the sodium ion pack is ≦60% (preferably ≦70%) cell Vmax. Similarly, as described above, "cell Vmax" is the maximum operating voltage of the cell itself.

[0043] To summarize the above, in another further aspect, the present invention provides for the use of a sodium ion battery pack as described above to raise the terminal voltage of the sodium ion battery pack to >60% Battery Vmax when the voltage measured across one or more sodium ion cells connected in series in the sodium ion battery pack is ≦60% Vmax. Vmax in this former case should be interpreted as Battery Vmax and / or cell Vmax.

[0044] In another preferred aspect, the present invention provides a method of accessing the available energy, preferably the specific energy, from a battery comprising one or more sodium ion cells, the method comprising the following steps: a) providing a sodium ion battery pack comprising one or more voltage converters and one or more sodium ion cells, the one or more sodium ion cells being operable between a cell Vmin in the range of >0.0 to <2.0 V and a cell Vmax in the range of >3.60 V to <4.30 V; further, if the sodium ion battery pack comprises two or more sodium ion cells, all of the two or more sodium ion cells have the same cell nominal voltage profile and the same electrochemical design; b) associating or integrating the battery pack with an electronic application device; and c) Operating at least one of the voltage converters with a value of 1 or more directly or indirectly to adjust the output voltage of the sodium ion battery pack to a voltage higher than 60% of battery V, preferably higher than 70% of battery V; max wherein battery V max is determined as the maximum output voltage of a sodium ion battery pack including one or more sodium ion cells in the absence of one or more voltage converters. The battery V max is determined as the maximum output voltage of a sodium ion battery pack including one or more sodium ion cells in the absence of one or more voltage converters.

[0045] In this method, one or more voltage converters can be operated directly or indirectly. In indirect operation, for example, signals generated in response to the power requirements of the application device (e.g., by a BMS or other computer software) can be used. In addition, one or more voltage converters can be operated continuously or intermittently according to the required output voltage profile over a part, all, or outside (e.g., below the minimum operating voltage) of the operating voltage range of the electronic application device.

[0046] Preferably, one or more voltage converters are operated when the output voltage of one or more sodium ion cells is 70% or less of V max Very preferably, one or more voltage converters are operated when the output voltage of one or more sodium ion cells is 60% or less of V max .

[0047] Those skilled in the art will be well aware that one or more voltage converters (at least one of which is preferably a DC / DC converter) have a response time, and as the converter consumes energy, a part of the voltage is lost in one or more converters. Therefore, in order to ensure that one or more converters raise the voltage to less than 60% of Vmax, for example, in a discharge cycle, it is beneficial that at least one of the one or more converters is switched on slightly before reaching the desired voltage, for example, slightly before the voltage reaches 60% of Vmax.

[0048] In another preferred embodiment, the present invention provides for the use of a sodium ion battery pack according to the present invention to increase the specific energy available and / or deliverable and / or the volumetric energy density deliverable by one or more sodium ion cells in the absence of one or more voltage converters by at least 3% (preferably at least 5%).

[0049] Preferably, one or more voltage converters (preferably including at least one DC-DC converter) can efficiently, cost-effectively, and without unnecessary mass convert all or substantially all (preferably at least 90%, very preferably at least 95%) of the energy available at a low voltage (e.g., <3.5 to <2.5 volts) into energy available within a predetermined, narrow, and higher voltage window (e.g., 4.2V to 3.5V or 4.2 to 2.5V). Advantageously, the present invention achieves converting 94 to 95% of the cell energy available at a minimum cell voltage of 1.5V into energy available within a voltage window of 2.4V to 4.2V. The present invention is ideally suitable for use in static storage systems and mobile systems.

[0050] In a further preferred embodiment, the present invention provides a sodium ion battery pack that is particularly suitable for use in electronic applications applicable to static or fixed applications (such as large-scale energy storage), backup power supplies, and portable (mobile) applications (such as mobile phones, computers, tablets, etc., as well as applications in starting, lighting, and ignition (SLI) batteries for electric vehicles and motor drives), especially when the battery pack output voltage of such electronic applications is at a low voltage (e.g., ≦70% of the battery Vmax, preferably ≦60%). Accordingly, the present invention provides an electronic application device integrated or associated with the sodium ion battery pack according to the present invention.

[0051] As used herein, the term "sodium ion cell" is defined to mean any secondary sodium ion electrochemical cell, and suitable examples include, but are not limited to, non-aqueous sodium ion cells, aqueous sodium ion cells, sodium air cells, and sodium oxygen cells. A plurality of such electrochemical cells can be utilized in any small-scale or large-scale energy storage device, such as, but not limited to, batteries, battery modules, electrochemical devices, and electrochromic devices. The term "sodium ion battery pack" according to the present invention encompasses any such small-scale or large-scale energy storage device that is associated with, integrated with, or used in combination with one or more voltage converters as described above. Typically, the pack includes a container and preferably a safety system and a battery management system.

[0052] Typically, the sodium ion cells used in the battery pack of the present invention have: i) a negative electrode including a negative electrode material and a negative electrode current collector; and ii) a positive electrode including a positive electrode material and a positive electrode current collector. Suitable negative electrode materials include amorphous carbon, hard carbon, silicon, and any other materials such as alloying metals like tin, germanium, or antimony, and their structures are adapted to allow insertion / removal of sodium ions during charging / discharging. Advantageously, the negative electrode current collector and the positive electrode current collector are stable under conditions of low voltage (i.e., within the above-preferred cell voltage range) and / or low state of charge (e.g., less than 20% state of charge), do not dissolve in sodium, or alloy with sodium, and include one or more conductive materials. Preferably, the one or more conductive materials do not alloy and / or react with sodium in other forms, and can be in pure form, or in impure form as an alloy or mixture, either alone or in combination with one or more other elements in various amounts. More preferably, at least one of the one or more conductive materials includes one or more metals selected from copper, aluminum, and titanium. Ideally, one or both of the current collectors include aluminum, either in pure form or in impure form as an alloy or mixture, either alone or in combination with one or more other elements in various amounts. For example, low-grade aluminum from an impure or household-grade source is particularly preferred, thereby achieving clearly significant commercial advantages. Carbon-coated negative electrode current collectors are also useful as they produce benefits such as better adhesion between the active negative electrode material and the negative electrode current collector, and thus lower contact resistance. Current collectors including a carbon coating have also been found to improve rate performance, thereby allowing the 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 carbon-coated positive and negative electrode current collectors are particularly electrically efficient.

[0053] As the positive electrode (cathode) material used in the sodium ion cell of the present invention, any material that enables sodium ions to intercalate and deintercalate (enter and exit their lattice or layered structure) during charging and discharging can be mentioned. Suitable examples include metal sulfide compounds such as TiS2, metal oxide compounds, phosphate-containing compounds, polyanion-containing compounds, Prussian blue analogs, and nickelate or non-nickelate compounds of the following 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; M 1 includes one or more redox-active metals in the +2 oxidation state, preferably one or more redox-active metals in the +2 oxidation state selected from nickel, copper, cobalt, and manganese; M 2 includes a metal in an oxidation state greater than 0 and less than or equal to +4; M 3 includes a metal in the +2 oxidation state; M 4 includes a metal in an oxidation state greater than 0 and less than or equal to +4; M 5 includes a metal in the +3 oxidation state; 0≦δ≦1; V is >0; W≧0; X is ≧0; Y is ≧0; at least one of W and Y is >0, Z is ≧0; C is in the range of 0≦c<2, V, W, X, Y, Z, and C are selected to maintain electrochemical neutrality].

[0054] Ideally, the metal M 2 includes 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 preferably includes one or more transition metals selected from manganese, titanium, and zirconium; M 5 is preferably one or more selected from aluminum, iron, cobalt, tin, molybdenum, chromium, vanadium, scandium, and yttrium. A cathode active material having any crystalline structure can be used, and the structure is preferably O3 or P2 or derivatives thereof. In particular, it is also possible that the cathode material contains a mixture of phases, that is, has a heterogeneous structure composed of several different crystalline forms. A layered metal oxide cathode material is particularly preferred.

Brief Description of the Drawings

[0055] Here, the present invention will be described with reference to the following drawings:

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

[0056] In the following experiments, one of two types of buck / boost DC / DC converters was employed in the battery pack according to the present invention, namely, either the MeanWell SD-1000L-48 converter available from Mean Well Enterprises Co., Ltd., or a converter available from Vicor Corporation. These converters were chosen for their ease of availability and not for their specific performance and / or physical characteristics. It will be understood that any suitable voltage converter having appropriate mass, efficiency, volume, and voltage characteristics can be used in the sodium-ion battery pack according to the present invention. Complementary to this, the MeanWell SD-1000L-48 converter is a wide-input-voltage buck / boost converter with an input voltage range of 19V to 72V and has a mass of 1.675 kg. The dimensions of this converter are 295 mm × 125 mm × 41 mm.

[0057] The converter available from Vicor Corporation has an input window of 16V to 50V and a weight of 255 g. The dimensions of this converter are 85.93 mm × 35.50 mm × 9.4 mm.

Example

[0058] General experimental method As the test medium, a 300 Wh sodium-ion battery pack containing 14 sodium-ion cells in series together with a safety system, BMS, etc. was selected. All the cells in this pack have the same cell nominal voltage profile and the same electrochemical design, which means that they all behave substantially similarly initially. After charging this pack up to 56V, it was discharged through a 295W electronic load. The fuse attachment and wiring of the pack were designed to carry a maximum current of 25 amperes. The voltage of the pack during discharge was measured and recorded using the data stream from the BMS. The results are shown in Figures 2, 4, and 6. The total energy output was also measured. All the data collected for each experiment are shown in Table 2 below.

[0059] Reference experiment 1 - Discharge of the pack without a DC / DC converter until the pack voltage reaches a lower limit of 35V. As shown in Figure 1, a 14S 1P 300Wh sodium-ion battery pack designed to discharge from 56V to 35V was directly connected to a 295W electronic load. The discharge voltage was measured over time. The results are shown in Figure 2. This experiment (without a DC / DC converter) provides a reference or benchmark for comparison with the results of Experiments 2 and 3 below. Note that in these experiments, the electronic load drops the voltage as the battery pack discharges and the load draws an increasing current to maintain a constant power output. As shown in Table 2 below, the total output energy of Reference Experiment 1, i.e., the energy available for use by the electronic load, is 322Wh.

[0060] Experiment 2 - Discharge of the pack through a DC / DC converter until the pack voltage reaches a lower limit of 35V. This test was the same as Experiment 1, except that a MeanWell SD-1000L-48 DC / DC converter that provides a constant output of 48V was introduced between the pack and the load. For a schematic diagram of the sodium-ion battery pack designed to be tested in Experiment 2, refer to Figure 3. After charging the battery pack to 56V, it was discharged to 35V. The battery voltage profile was measured over time. The results are shown in Figure 4 together with the voltage discharge curve of Reference Experiment 1. It can be seen from Figure 4 that there is an energy loss caused by the use of the DC / DC converter over the same voltage window. In this case, the battery pack energy input to the DC / DC converter was 322Wh and the total output energy was 297.5Wh. From these results, it can be seen that the energy efficiency of the DC / DC converter over this voltage window is 92.38%. Note: In this test, the electronic load was made to be constant at 48 volts throughout the discharge and draws a constant current from the DC / DC converter.

[0061] Experiment 3 - Discharge with a DC / DC converter, setting the lower limit of the pack voltage to 18V. The test setup was the same as in Experiment 2, except that the lower limit of the pack voltage was set to 18V here. Refer to the schematic diagram shown in Figure 5. After charging the battery pack to 56V, it was discharged to 18V. The battery voltage profile was measured over time. The results are shown in Figure 6. Also shown are the benchmark discharge voltage curves from Reference Experiment 1 (without a converter) and the discharge voltage curves from Experiment 2 with a cut-off voltage of 35V. It can be seen from Figure 6 that the driving time of the electronic load increased for Experiments 1 and 2. Since the load was at a constant power, the additional energy was a function of this added driving time.

[0062] In this Experiment 3, the battery pack energy input to the DC / DC converter was 390.55 Wh, and the total output energy available to the electronic load was 353.4 Wh. Compared with Reference Experiment 1, the use of this DC / DC converter resulted in a 9.75% increase in the available energy. Over this voltage window, the energy efficiency of the DC / DC converter was 90.49%.

[0063] Note: In this test, the electronic load was made to be constant at 48 volts throughout the discharge and drew a constant current from the DC / DC converter.

[0064] Summary and analysis of results Increase in available energy As shown by the results presented in Table 2 below, the use of a commercial DC / DC converter enabled access to a wider cell voltage window compared to setting the minimum cell voltage to the same as the minimum voltage acceptable to the system or application.

[0065] In the case of Experiment 2, the decrease in available energy (-7.61%) was due to the converter consuming energy during its operation. In the case of Experiment 3, the total energy benefit is an increase in available energy of approximately 10% ((353.4 - 322) / 322). Such a significant increase in available energy would make it possible to obtain important commercial advantages that have not been achieved so far in the use of sodium-ion cells.

[0066]

Table 2

[0067] Simulation model 1 - Calculation A Using a more efficient DC / DC converter is expected to increase the percentage of available energy improvement. For example, if a commercially available converter is used under the conditions of Experiment 3 and the average efficiency of the converter is 97%, it can be calculated that the total energy increase will be 17.5%.

[0068] Simulation model 2 - Calculation B (The DC / DC converter is operated only when the battery pack voltage approaches the minimum operating voltage of the application device powered by the battery pack.) This simulation experiment models the amount of energy that is expected to be accessible when the DC / DC converter in the same battery pack used in Experiment 3 is operated only when the battery pack voltage approaches the cut-off voltage to reduce the parasitic load of the battery pack. A schematic diagram of this simulation model battery pack is shown in Figure 7.

[0069] Assuming that the application device powered by the battery pack has a minimum operating voltage of 35V and the battery pack is designed to have an apparent voltage lower limit of 38V (slightly higher than 35V to prevent switching out), this can be achieved if the battery is first operated like Experiment 1 (without a converter) until it reaches the limit of 38V, and then the DC / DC converter is operated to take over and supply a constant voltage at the 38V load terminal until the battery reaches the limit of 18V.

[0070] As described above, the battery pack used in this simulation experiment is the same as that in Experiment 3. Therefore, since the battery pack operates within the same voltage window of 56V to 18V, the output energy of the battery pack is 390.55 Wh.

[0071] Also, from the data collected in Experiment 3, the battery output energy between 56V and 38V is 299.9 Wh. Since the DC / DC converter does not operate within this voltage window, there is no energy loss.

[0072] Assuming the efficiency of the DC / DC converter is approximately 90%, it is expected that the battery output voltage will be boosted to 38V at voltages below 38V. An example of a converter suitable for this embodiment is the Vicor Corporation DCM3414x50M53C2yzz, which has an efficiency of approximately 90%. Figure 8 shows the discharge profile of the simulation model of the Na-ion battery pack based on this calculation B.

[0073] From the results shown in Table 2 above for Experiment 3, the available energy from the battery (with a DC / DC converter) between 38V and 18V is (390.55 Wh - 299.9 Wh) = 90.65 Wh. Therefore, the additional available energy for the load is 90.65 Wh × 90% = 81.6 Wh As a result, the total energy output of the battery pack and the part-time DC / DC converter system is (299.9 Wh + 81.6 Wh) = 381.5 Wh, and the overall efficiency (average of 56V to 18V) is 97.7% Therefore, the total output energy of this simulation model shows an 18.47% increase compared to the reference Experiment 1. This is also an increase over Simulation Model A.

[0074] Simulation model 3 - Similarly calculation B, but using a DC / DC converter with reduced mass to increase the available specific energy density of the battery pack The increase in the available specific energy density (Wh / Kg) can be obtained as a result of reducing the weight of the DC / DC converter. The Mean Well converter is not the optimal converter for this purpose due to its large mass (see calculation C), but the converter from Vicor Corporation (DCM3414x50M53C2yzz) is lightweight and has an efficiency comparable to that of the Mean Well converter in the low voltage range. Therefore, it can be calculated that operating the Vicor Power converter only in the range below 38V and 18V will result in an approximately 15% increase in the available pack specific energy density between 56V and 38V. From Table 2 above: ((41.9 - 36.5) / 36.5)×100)

[0075] Simulation model 4 - Calculation D (Investigation using a DC / DC converter with reduced mass to increase the available cell specific energy density) It is preferable to ensure an increase in the available cell specific energy and the available pack specific energy. This is because it will thereby bring greater flexibility in pack design. Comparing the single cell of Experiment 1, which had a weight of 4.90 kg, with the same cell connected to a Vicor Power converter that was used only in the range below 38V and 18V and had an overall weight of 5.16 kg, the available cell specific energy density between 56V and 38V increased from 65.7 Wh / kg (322 / 4.9) to 74 Wh / kg (381.5 / 5.16), an increase of 13%.

[0076] Simulation model 5 - Calculation E (Investigation using a DC / DC converter with reduced volume to increase the available volumetric energy density of the battery pack) To ensure an increase in volumetric energy density as a result of using a DC / DC converter, it is necessary to use a converter with a small volume. The converter from Vicor Corporation (DCM3414x50M53C2yzz) has a small volume and good efficiency. Comparing the pack alone in Experiment 1 with a volume of 6.696 L and the same pack connected to a Vicor Power converter used only in the range below 38V and 18V, with a total volume of 6.725 L, the available volumetric energy density between 56 and 38V increased from 48.1 Wh / L (322 / 6.696) in Experiment 1 to 56.7 Wh / L (381.5 / 6.725), and the increase in available pack volumetric energy is a 18% increase.

[0077] Simulation model 6 - Calculation F (Investigation using a DC / DC converter with reduced volume to increase the available cell volumetric energy density) It is preferable to ensure an increase in available cell volumetric energy density and available pack volumetric energy density. This is because it brings greater flexibility in pack design. Comparing the cell alone in Experiment 1 with a volume of 4.416 liters and the same cell connected to a Vicor Power converter only in the range below 38V and 18V, with a total volume of 4.445 liters, the available volumetric energy density between 56 and 38V increased from 72.9 Wh / liter (322 / 4.416) in Experiment 1 to 85.8 Wh / L (381.5 / 4.445), and the increase in available cell specific energy density is a 18% increase.

[0078] As demonstrated in the above live battery pack and simulation model experiments, including a DC / DC converter results in an unexpected increase in available energy, specific energy density, and volumetric energy density, not only for the sodium-ion battery pack but also for the individual sodium-ion cells contained in such a battery pack. What is particularly surprising is that even when weight (and volume) is added to the sodium-ion cells by including a DC / DC converter, these improved results can be obtained. Nevertheless, as shown by the calculations of the above simulation model, when a DC / DC converter with optimized mass and efficiency is used, an even further increase in specific energy density is expected. The sodium-ion battery pack according to the present invention has the potential to be lightweight and compact in order to reduce the energy retained within the cell and thus wasted, increase the time between charge cycles, and reduce the number of cells required for any particular application, and these results are therefore highly advantageous commercially. The present invention includes the following aspects. [1] A sodium-ion battery pack including one or more sodium-ion cells and one or more voltage converters; the one or more sodium-ion cells are operable between a minimum operating voltage (cell Vmin) in the range of >0.0V to <2.0V and a maximum operating voltage (cell Vmax) in the range of >3.60V to <4.30V; further, when the sodium-ion battery pack includes two or more sodium-ion cells, all of the two or more sodium-ion cells have the same cell nominal voltage profile and the same electrochemical design. [2] The sodium-ion battery pack according to 1, further including a battery management system (BMS). [3] The sodium-ion battery pack according to 1 or 2, wherein all of the one or more sodium-ion cells are operable in a voltage range where cell Vmin is >0% to 55% of cell Vmax, preferably >0% to 50% of cell Vmax, more preferably >0% to 45% of cell Vmax. [4] The sodium-ion battery pack according to any one of 1 to 3, wherein one or more sodium-ion cells are operable between a cell Vmax in the range of >3.70 V to ≦4.25 V, preferably between a cell Vmax in the range of >3.8 V to ≦4.20 V. [5] The sodium-ion battery pack according to any one of 1 to 4, wherein each of one or more voltage converters is connected to more than one sodium-ion cell. [6] The sodium-ion battery pack according to 1, wherein at least one of one or more voltage converters is a DC / DC converter. [7] The sodium-ion battery pack according to 6, wherein at least one DC / DC converter is a bidirectional DC / DC converter. [8] The sodium-ion battery pack according to 7, wherein the bidirectional DC / DC converter is selected from a boost converter and / or a buck / boost converter. [9] The sodium-ion battery pack according to any one of 1 to 8, wherein at least one of one or more voltage converters is part of a stand-alone circuit configuration, or is incorporated into or connected to a battery management system (BMS).

[10] Use of the sodium-ion battery pack according to any one of 1 to 9 for delivering a specific ratio of energy to meet the following conditions: (Energy difference between battery Vmax and 0 V) × (efficiency of one or more voltage converters) / (mass of one or more sodium-ion cells + mass of one or more voltage converters) > (energy difference between battery Vmax and 60 - 70% of battery Vmax) / mass of one or more sodium-ion cells; The battery Vmax is determined as the maximum output voltage of a sodium-ion battery pack containing one or more sodium-ion cells in the absence of one or more voltage converters.

[11] Use of the sodium-ion battery pack according to any one of 1 to 9 to raise the terminal voltage of the sodium-ion battery pack to >60% battery Vmax when the voltage measured across both ends of one or more sodium-ion cells connected in series in the sodium-ion battery pack is ≦60% Vmax.

[12] A method for accessing the available energy from a battery containing one or more sodium-ion cells, the method comprising the following steps: a) Providing a sodium-ion battery pack including one or more voltage converters and one or more sodium-ion cells, the one or more sodium-ion cells being operable between a minimum operating voltage (cell Vmin) in the range of >0 V to <2.0 V and a maximum operating voltage (cell Vmax) in the range of >3.6 V to <4.30 V; further, when the sodium-ion battery pack includes two or more sodium-ion cells, all of the two or more sodium-ion cells have the same cell nominal voltage profile and the same electrochemical design b) Associating or integrating the sodium-ion battery pack with an electronic application device, and c) Operating at least one of the one or more voltage converters directly or indirectly to increase the output voltage of the sodium-ion battery pack to more than 60% of battery Vmax; The battery Vmax is determined as the design maximum output voltage of a sodium-ion battery pack including one or more sodium-ion cells in the absence of one or more voltage converters.

[13] The method according to 12, wherein at least one of the one or more voltage converters is intermittently operated over part or all of the operating voltage range of the electronic application device.

[14] The method according to 12 or 13, wherein at least one voltage converter is operated when the output voltage of at least one sodium-ion cell of the sodium-ion pack is 60% or less of Vmax.

[15] Use of the sodium-ion battery pack according to any one of 1 to 9 for increasing the available and / or deliverable specific energy of a sodium-ion battery pack including one or more sodium-ion cells in the absence of one or more voltage converters by at least 3%.

[16] Use of the sodium-ion battery pack according to any one of 1 to 9 for increasing the available and / or deliverable volumetric energy density of a sodium-ion battery pack including one or more sodium-ion cells in the absence of one or more voltage converters by at least 3%.

[17] An electronic application device integrated or associated with the sodium-ion battery pack according to any one of 1 to 9.

Claims

1. A sodium-ion battery pack including one or more sodium-ion cells and one or more voltage converters; the one or more sodium-ion cells are operable between a minimum operating voltage (cell Vmin) in the range of >0.0 V to <2.0 V and a maximum operating voltage (cell Vmax) in the range of >3.60 V to <4.30 V; further, when the sodium-ion battery pack includes two or more sodium-ion cells, all of the two or more sodium-ion cells have the same cell nominal voltage profile and the same electrochemical design.

2. The sodium-ion battery pack according to claim 1, further including a battery management system (BMS).

3. The sodium-ion battery pack according to claim 1 or 2, wherein all of the one or more sodium-ion cells are operable in a voltage range where cell Vmin is >0% to 55% of cell Vmax.

4. The sodium-ion battery pack according to any one of claims 1 to 3, wherein all of the one or more sodium-ion cells are operable in a voltage range where cell Vmin is >0% to 50% of cell Vmax.

5. The sodium-ion battery pack according to any one of claims 1 to 4, wherein all of the one or more sodium-ion cells are operable in a voltage range where cell Vmin is >0% to 45% of cell Vmax.

6. The sodium-ion battery pack according to any one of claims 1 to 5, wherein the one or more sodium-ion cells are operable between cell Vmax in the range of >3.70 V to ≦4.25 V.

7. The sodium-ion battery pack according to any one of claims 1 to 6, wherein the one or more sodium-ion cells are operable between cell Vmax in the range of >3.8 V to ≦4.20 V.

8. The sodium-ion battery pack according to any one of claims 1 to 7, wherein each of the one or more voltage converters is connected to more than one sodium-ion cell.

9. The sodium-ion battery pack according to claim 1, wherein at least one of the one or more voltage converters is a DC / DC converter.

10. The sodium-ion battery pack according to claim 9, wherein at least one DC / DC converter is a bidirectional DC / DC converter.

11. The sodium ion battery pack according to claim 10, wherein the bidirectional DC / DC converter is selected from a boost converter and / or a buck / boost converter.

12. The sodium ion battery pack according to any one of claims 1 to 11, wherein at least one of the one or more voltage converters is part of a stand-alone circuit configuration, or is incorporated into or connected to a battery management system (BMS).

13. Use of the sodium ion battery pack according to any one of claims 1 to 12 for delivering a specific energy in an amount satisfying the following conditions: (Energy difference between battery Vmax and 0 V) × (efficiency of one or more voltage converters) / (mass of one or more sodium ion cells + mass of one or more voltage converters) > (energy difference between battery Vmax and 60 - 70% of battery Vmax) / mass of one or more sodium ion cells; The battery Vmax is determined as the maximum output voltage of a sodium ion battery pack including one or more sodium ion cells in the absence of one or more voltage converters.

14. Use of the sodium ion battery pack according to any one of claims 1 to 12 to increase the terminal voltage of the sodium ion battery pack to > 60% battery Vmax when the voltage measured across both ends of one or more sodium ion cells connected in series in the sodium ion battery pack is ≦ 60% Vmax.

15. A method for accessing the available energy from a battery including one or more sodium ion cells, the method comprising the following steps: a) providing a sodium ion battery pack including one or more voltage converters and one or more sodium ion cells, the one or more sodium ion cells being operable between a minimum operating voltage (cell Vmin) in the range > 0 to < 2.0 V and a maximum operating voltage (cell Vmax) in the range > 3.6 V to < 4.30 V; and further, if the sodium ion battery pack includes two or more sodium ion cells, all of the two or more sodium ion cells have the same cell nominal voltage profile and the same electrochemical design b) associating or integrating the sodium ion battery pack with an electronic application device, and c) operating at least one of the voltage converters, directly or indirectly, to increase the output voltage of the sodium ion battery pack to more than 60% of the battery Vmax; The battery Vmax is determined as the design maximum output voltage of a sodium ion battery pack including one or more sodium ion cells in the absence of one or more voltage converters. **Claim 16** The method according to claim 15, wherein at least one of the voltage converters is intermittently operated over part or all of the operating voltage range of the electronic application device. **Claim 17** The method according to claim 15 or 16, wherein at least one voltage converter is operated when the output voltage of at least one sodium ion cell of the sodium ion pack is 60% or less of Vmax. **Claim 18** Use of a sodium ion battery pack according to any of claims 1 to 12 for increasing the available and / or deliverable specific energy of a sodium ion battery pack including one or more sodium ion cells in the absence of one or more voltage converters by at least 3%. **Claim 19** Use of a sodium ion battery pack according to any of claims 1 to 12 for increasing the available and / or deliverable volumetric energy density of a sodium ion battery pack including one or more sodium ion cells in the absence of one or more voltage converters by at least 3%. **Claim 20** An electronic application device integrated or associated with a sodium ion battery pack according to any of claims 1 to 12.

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