sodium-ion battery

Abstract

The present invention provides a sodium-ion secondary battery having a cathode and an anode, wherein the cathode comprises one or more cathode electrode active materials including at least one layered nickel-containing sodium oxide material; the anode comprises a layer of anode electrode active material disposed on an anode substrate, the anode electrode active material comprising one or more disordered carbon-containing materials, and the layer of anode electrode active material has a mass of 80 gm per square meter of the anode substrate. -2 and further, a ratio of the mass of the cathode electrode active material to the mass of the layer of the anode electrode active material is 0.1 to 10, and a thickness of the layer of the anode electrode active material on the anode substrate is less than 100 μm.

Description

[Technical Field]

[0001] This application relates to sodium-ion secondary batteries that exhibit excellent anode active material capacity and stable cycling characteristics. This application also provides methods for manufacturing these sodium-ion secondary batteries and batteries that include such sodium-ion secondary batteries. [Background technology]

[0002] Sodium-ion batteries are similar in many ways to the lithium-ion batteries commonly used today. Both are reusable secondary batteries that contain an anode (negative electrode), a cathode (positive electrode), and electrolyte materials, and both are capable of energy storage and can be charged and discharged via similar reaction mechanisms. When a sodium-ion (or lithium-ion) battery is charged, Na + (or Li + ) ions deintercalate from the cathode and insert into the anode, while charge-balancing electrons pass from the cathode through an external circuit that includes the charger and into the battery's anode. During discharge, the same process occurs in reverse.

[0003] Lithium-ion battery technology has attracted considerable attention in recent years, providing the preferred portable battery for most electronic devices in use today. However, lithium is not an inexpensive metal source, and concerns remain about its high cost for large-scale applications. Sodium-ion battery technology, on the other hand, is believed to offer many advantages. Sodium is significantly more abundant than lithium and is expected to provide a cheaper and more durable method for future energy storage, especially for large-scale applications such as storing energy on the power grid. Research is currently underway to commercialize sodium-ion batteries.

[0004] One area that requires more attention is the design of sodium-ion batteries to optimize their electrochemical performance.

[0005] WO 2017 / 073056 describes a method for passive voltage control in sodium-ion batteries as a way to achieve useful secondary sodium batteries. Specifically, the method involves controlling the ratio of the mass of negative electrode active material to the mass of positive electrode active material to be greater than 0.37 and less than 1.2. This corresponds to a cathode:anode active material mass ratio (referred to herein as the "C / A mass balance") in the range of 0.833 to 2.70. While not explicitly disclosed in WO 2017 / 073056, collaborations with the inventors of this technology have revealed that they have achieved a mass balance of 100 to 130 gm per square meter of anode substrate. -2 It is understood that the anode contains a negative electrode active material of the formula (I). Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a sodium-ion secondary battery that exhibits excellent anode and cathode active material capacities and stable cycling characteristics. Furthermore, the sodium-ion secondary battery of the present invention is cost-effective and easy to manufacture. To this end, Applicant has unexpectedly discovered that, while using a C / A mass ratio in the range of 0.833 to 2.70 is one way to provide a sodium-ion secondary cell with useful anode first sodium removal capacity, these anode capacities can be further increased by selecting the C / A ratio in combination with other selected cell construction parameters. Below, Applicant describes and demonstrates these surprising results. [Means for solving the problem]

[0007] Therefore, in the present invention, A sodium ion secondary battery having a cathode and an anode, the cathode comprises one or more positive electrode active materials, and the anode comprises a layer, preferably a uniform layer, of negative electrode active material disposed on an anode substrate; the negative electrode active material comprises one or more disordered carbon-containing materials; i) The mass of the layer of the negative electrode active material is expressed in units of m 2 Each serving is 80g or less, ii) the ratio of the mass of the layer of positive electrode active material to the mass of the layer of negative electrode active material is 0.1 to 10; iii) There is provided a sodium ion secondary battery, wherein the thickness of the layer of the negative electrode active material on the anode substrate is 100 μm or less, preferably 80 μm or less.

[0008] For clarity, the unit "gm -2 " (grams / square meter) is the mass per unit area of ​​the substrate (m 2 ) and is also referred to herein as "GSM."

[0009] In this application, "anode electrode active material" is equivalent to "negative electrode active material," and "cathode electrode active material" is equivalent to "positive electrode active material."

[0010] As shown in the specific examples below, the ratio of the mass of the cathode and anode electrode active materials is important. However, the applicant has recognized that the mass of the anode electrode active material exerts a greater control on the anode capacity results, and for a constant mass of the cathode electrode active material, as the mass of the anode active material decreases, significantly improved anode capacity results have been observed. Also, the applicant has noted that since problems with Na electrodeposition can occur, it is recommended to use a 80g -2It has been found that using a mass of anode active material exceeding 25 g / cm is undesirable. Na electrodeposition is highly undesirable for several reasons. First, once Na electrodeposition occurs during a charge cycle (anode sodiation), it is difficult to efficiently remove it during a discharge cycle for most commonly used sodium-ion electrolytes. This means that the cell's coulombic efficiency decreases with each such cycle, and the delivered cell capacity (due to sodium loss from the cathode) decreases significantly and gradually with each passing cycle during which Na electrodeposition occurs. Second, repeated Na electrodeposition during each charge cycle and inefficient removal during discharge cycles can cause the deposited Na metal on the anode to grow in a dendrite morphology, which can cause the battery to internally short-circuit and potentially result in an explosion. This can clearly be a serious safety hazard. Some of the most promising anode initial sodiation capacity results (e.g., values ​​of 270 mAh / g or greater) are due to the fact that the mass of the layer of negative active material per square meter of anode substrate is 25 g / cm . -2 Super, 80gm -2 The best anode initial sodium removal capacity results were obtained when the mass of the negative electrode active material layer per square meter of the anode substrate was 40 gm -2 From 75gm -2 , preferably 40gm -2 From 65gm -2 and at the same time, the highest cycling stability (i.e., minimum capacity fade per unit cycle) is obtained when the mass of negative electrode active material per square meter is within these latter two ranges.

[0011] In particularly preferred sodium-ion secondary batteries according to the present invention, the ratio of the mass of the positive electrode active material to the mass of the layer of negative electrode active material (i.e., C / A mass balance) is 0.5 to 10, preferably 1.0 to 10, more preferably 1 to 5, ideally 2.0 to 3.5, and particularly preferably 2.0 to 2.75. Sodium-ion batteries having a C / A mass balance within these preferred ranges exhibit extremely high anode first sodium removal capacity and provide the unexpected advantage of excellent cycling stability. The most preferred sodium-ion batteries have a C / A ratio in the range of 2.05 to 2.90 and an anode electrode active material mass within the described preferred ranges.

[0012] During the manufacture of secondary battery cells, it is common to form a layer of anode or cathode active electrode material on a substrate, such as a current collector foil, and then "calendar" the coated substrate by passing the coated substrate through a series of rollers to achieve a uniform thickness of electrode material on the substrate. In a typical sodium-ion battery, the calendered thickness of the anode active electrode material ranges from 100 μm to 140 μm, and the thickness of the cathode active electrode material ranges from 80 to 110 μm. Surprisingly, Applicant has found that for layers of anode active electrode material of similar density, there is a clear relationship between the ability of sodium ions to be transported into the anode active electrode material during intercalation and deintercalation and the thickness of the anode active electrode material. In particular, Applicant has observed that thin layers of anode active electrode material result in disproportionately and unexpectedly high anode first sodium desorption capacities compared to thicker layers of anode active electrode material having comparable densities. The thickness of the layer of negative electrode active material on the anode substrate used in the sodium ion secondary battery of the present invention is the aforementioned value, ie, ≦100 μm, preferably ≦80 μm.

[0013] Sodium-ion secondary batteries according to the present invention may have any known positive electrode active material capable of inserting and desorbing sodium ions. Suitable examples include metal sulfide compounds such as TiS, 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 where: A is one or more alkali metals selected from sodium, potassium, and lithium; M 1 has one or more redox-active metals in the oxidation state +2, preferably one or more redox-active metals in the oxidation state +2 selected from nickel, copper, cobalt, and manganese; M 2 has an oxidation state greater than 0 and a metal in an oxidation state of +4 or greater, M 3 has a metal in the +2 oxidation state, M 4 has a metal with an oxidation state greater than 0 and less than or equal to +4, M 5 has a metal in the +3 oxidation state, where: 0 ≤ δ ≤ 1; V>0; W ≥ 0; X ≥ 0; Y ≥ 0; At least one of W and Y is greater than 0, Z ≥ 0; C is in the range of 0≦c<2, where V, W, X, Y, Z and C are selected to maintain electrochemical neutrality.

[0014] Ideally, metal M 2 has one or more transition metals, preferably selected from manganese, titanium and zirconium; M 3 preferably has one or more transition metals selected from magnesium, calcium, copper, tin, zinc and cobalt; M 4 has one or more transition metals, preferably selected from manganese, titanium and zirconium; M 5 Preferably, the cathode active material has one or more selected from aluminum, iron, cobalt, tin, molybdenum, chromium, vanadium, scandium, and yttrium. Cathode active materials having any crystal structure may be used, preferably having the structure O3 or P2, or derivatives thereof. Specifically, the cathode material may have a mixture of phases, i.e., a heterogeneous structure containing several different crystal forms.

[0015] As mentioned above, the negative electrode active material (anode) is a carbon-based material with a disordered structure, which advantageously lends itself to the insertion and extraction of sodium ions during the charge / discharge process. While the exact structure of the preferred carbon material remains to be determined, it is generally ideal for it to have a non-graphitizable, non-crystalline, amorphous carbon structure. While hard or soft carbon may be used, anodes containing one or more "hard carbon" materials are particularly preferred. While "hard carbon" has layers, these layers are not stacked in an orderly fashion; instead, they have micropores / nanopores (micron- or nano-sized pores) formed between the randomly stacked carbon layers. At a macroscopic level, hard carbon is isotropic. Typically, hard carbon suitable for use in the anode may be made from a carbon-containing starting material (e.g., sucrose, biomass, corn starch, glucose, organic polymers (e.g., polyacrylonitrile or resorcinol-formaldehyde gel), cellulose, petroleum coke, coal tar, or pitch coke) that is first mixed with a thermoplastic binder such as a synthetic resin and then heated to about 1200°C. Commercially available hard carbons include those sold by Kureha Corporation, Kuraray Chemical Co., Ltd., and Kureha Corporation.

[0016] In sodium-ion cells according to the present invention, the disordered carbon-based anode material may be used alone or in combination with any other suitable negative electrode (anode) active material (referred to as additional material) capable of storing sodium ions. Such additional materials may include metals, metal-containing compounds, metal alloys, non-metals, and non-metal-containing compounds. These include Na 15 Sn4, Na3Sb, Na3Ge, and Na 15High-capacity anodes are defined as those containing Pb4 or a composite with one or more other materials, such as nonmetals, metals, or metal alloys, capable of storing sodium ions, as described above. The metal or nonmetal may be in elemental or compound form. Particularly preferred anode active materials include hard carbon / X composites, where X is one or more selected from phosphorus, sulfur, indium, antimony, tin, lead, iron, manganese, titanium, molybdenum, and germanium. This may be in elemental or compound form, and preferably contains one or more selected from oxygen, carbon, nitrogen, phosphorus, sulfur, silicon, fluorine, chlorine, bromine, and iodine. Preferably, X is one or more selected from P, S, Sn, SnO, SnO2, SnF2, Fe2O3, Fe3O4, MoO3, TiO2, Sb, Sb2O3, SnSb, and SbO.

[0017] Secondary carbon-containing materials may also be used in combination with the aforementioned anode active materials to improve anode conductivity. Examples include activated carbon materials, particulate carbon black materials, graphene, carbon nanotubes, and graphite, among others. Examples of particulate carbon black materials include carbon black having a BET nitrogen surface area of ​​about 62 m 2 / g, or a BET nitrogen surface area of ​​approximately <900 m 2 / g, preferably with a BET nitrogen surface area of ​​about 770 m 2 / g. These are commercially available from Imerys Graphite and Carbon Corporation as specialty carbons for rubber compositions. 2 Carbon nanotubes with a BET nitrogen surface area of ​​1000 m / g, typically about 2630 m 2 Graphene with a surface area of ​​>3000 m / g, and 2 Activated carbon materials having a BET nitrogen surface area of ​​1 / g may also be used.

[0018] Surprisingly, the anode substrate has a surface area of ​​≦80 gm per square meter. -2The positive effect on the anode first desorption capacity as a result of using a negative electrode active material mass of 0.1 to 10, a C / A mass balance in the range of 0.1 to 10, and a negative electrode active material thickness of ≤100 μm on the anode substrate is observed to persist regardless of the composition of the electrolyte used in the cell and regardless of the type of binder used in fabricating the anode electrode. These observations are verified in the specific examples provided below.

[0019] According to the present applicant, when the sodium ion secondary battery of the present invention is charged and the anode is sodiated, the potential (V) on the y-axis versus Na / Na + A graph of anode active material capacity (mAh / g) on ​​the x-axis versus Na / Na shows a steep negative slope "slope" region (starting at about 1.20-1.30 V at 0 mAh / g and increasing to 0.10 V vs. Na / Na + above 0 V), then it plateaus (typically about above 0 V to 0.10 V vs. Na / Na + ), it has been noted that a "plateau" region that is substantially parallel to the X-axis is obtained. Importantly, as the mass and thickness of the active material on the anode decreases, the capacity resulting from the "plateau" region increases significantly compared to the capacity resulting from the "slope" region. Furthermore, applicants have found that the relationship between decreasing anode active material mass and increasing anode specific capacity is linear. It is noteworthy that the thickness of the active material on the anode directly affects the reversible capacity of a sodium-ion battery, and this is believed to be the first time such a phenomenon has been recognized.

[0020] In this application, the "plateau capacity" is defined as the capacity at ∼0.15 V (vs. Na / Na) in the desodium curve of a hard carbon anode. + ) in a 3E cell at a constant current cycling rate of C / 10. On the other hand, the "gradient capacity" is defined as the capacity contribution from ~0.15 to 2 V vs. Na / Na in a 3E cell at a C / 10 rate. + The active capacity of the desodium-depleted hard carbon anode during

[0021] In particular, the sodium-ion secondary battery of the present invention preferably has a specific range of plateau:slope capacity ratio of 0 to 6:1, more preferably 0.5 to 5:1, and advantageously 1 to 5:1. The most preferred plateau:slope capacity ratio is 1.2 to 5.0:1, and ideally 1.4 to 4.75:1.

[0022] Thus, the sodium-ion secondary battery of the present invention is characterized by a plateau:slope reversible capacity ratio of the anode electrode active material. This is derived from a plot of anode active material capacity (mAh / g) (x-axis) versus cell potential (V) vs. Na / Na+ (y-axis) of 0 to 6:1, preferably 0.5 to 5:1, more preferably 1 to 5:1, particularly preferably 1.2 to 5.0:1, and ideally 1.4 to 4.75:1, measured in a three- or four-electrode full-cell configuration. A plateau reversible capacity of 0 mAh / g can be achieved by cycling the cell so that it does not reach the plateau region, for example, by selecting a light C / A mass balance and / or by de-rating the cell, for example, between 3.7 and 1.5 V. A P:S ratio of 0 means that all of the capacity contribution is due to the slope region.

[0023] In another aspect, the present invention provides a battery having at least two sodium-ion secondary cells as described above, preferably at least three sodium-ion cells.

[0024] In yet another embodiment, the present invention provides: A method for producing the sodium ion secondary battery according to any one of the preceding claims, a. assembling a cathode having one or more positive electrode active materials with an anode having an anode substrate coated with a layer of negative electrode active material, and an electrolyte to form a sodium ion battery; b. cycling the sodium-ion battery to a first voltage; and i) the mass of the layer of anode active material is 80 gm per square meter of the anode substrate; -2is as follows: ii) the ratio of the mass of the positive electrode active material to the mass of the layer of the negative electrode active material is 0.1 to 10; iii) The thickness of the layer of the negative electrode active material on the anode substrate is 100 μm or less.

[0025] Applicant has discovered another interesting and useful phenomenon that can be used to further improve the performance of sodium-ion secondary batteries. When a sodium-ion secondary battery undergoes its first charge / discharge cycle, an irreversible loss of approximately 20% in capacity is observed in hard carbon anodes. Similar irreversible capacity loss is also observed in layered oxide active cathode materials. This is known as the cell's "first cycle loss." Conventional cell preparation procedures apply a voltage (typically C / 10 at 4.20-1.00 V) during the first four cell formation cycles, and then employ a formation cycle that uses a lower or the same voltage in subsequent ("post" or "operation") cell cycles (e.g., C / 5 at 4.00-1.00 V, 4.10-1.00 V, or 4.20-1.00 V), thereby eliminating the "first cycle loss" effect (making it invisible in commercially available cells). Similar to addressing the first cycle loss, this procedure is known to extend cell life. Surprisingly, Applicants have found that an additional positive effect on post-formation cycle stability is observed. This is observed when the "post" formation cycle (i.e., while the cell is in operation) is "derated," i.e., the "post" formation cycle is performed at C / 5 from 4.00 to 1.00 V or 4.10 to 1.00 V instead of C / 5 from 4.20 to 1.00 V. Applicants have also observed that performing the formation cycle at C / 10 from 4.00 to 1.00 V (or C / 10 from 4.10 to 1.00 V) instead of C / 10 from 4.20 to 1.00 V results in significant improvements in the cathode and anode capacities during the "post-formation" (operation) cycle. Details of these observations are provided in the specific examples below.

[0026] As discussed above and demonstrated in the specific examples below, applicants have found that the low GSM effect of hard carbon does not result from changes in the active material (type of hard carbon), binder, or electrolyte, but rather occurs solely as a result of the GSM of the hard carbon used in the anode electrode, the C / A mass balance, and the thickness of the anode material.

[0027] In another embodiment of the present invention, there is provided a sodium ion secondary battery having a cathode and an anode, the cathode comprises one or more positive electrode active materials, and the anode comprises a layer, preferably a uniform layer, of a negative electrode active material disposed on an anode substrate; the layer of negative electrode active material comprises one or more disordered carbon-containing materials; (i) The mass of the layer of the negative electrode active material is expressed in units of m 2 Per unit, ≦80g, (ii) the ratio of the mass of the layer of the positive electrode active material to the mass of the layer of the negative electrode active material is 0.1 to 10; (iii) the thickness of the layer of the negative electrode active material on the anode substrate is ≦100 μm, preferably ≦80 μm; (iv) The layer of negative electrode active material has a volume-specific surface area (VSSA) of more than about 0.8, preferably more than 0.8 to 500, particularly preferably 0.8 to 400, ideally 0.8 to 300, and particularly 0.8 to 200.

[0028] In another aspect, the present invention provides a sodium ion secondary battery having a cathode and an anode, the cathode comprises one or more positive electrode active materials, and the anode comprises a layer, preferably a uniform layer, of a negative electrode active material disposed on an anode substrate; the layer of negative electrode active material comprises one or more disordered carbon-containing materials; The layer of the negative electrode active material has a volume specific surface area (VSSA) of more than 0.8, preferably more than 0.8 to 500, particularly preferably 0.8 to 400, ideally 0.8 to 300, and particularly 0.8 to 200, thereby providing a sodium ion secondary battery.

[0029] The present invention will now be described with reference to the drawings. [Brief explanation of the drawings]

[0030] [Figure 1] Figure 1 shows the anodic profile for cycle 1 in a 3E full cell, in terms of potential (V vs. Na / Na+) versus the active specific capacity of the anode (mAh / g) using a nickelate-based NaNiMnMgTiO cathode and a commercial hard carbon anode (available from Kuraray Co., Ltd.). Several different masses of anode active material were used, as listed in Table 1. [Figure 2] Figure 1 shows the effect of using different electrolytes on the anodic profile for cycle 1 in a 3E full cell in terms of potential (V vs Na / Na+) versus the active specific capacity (mAh / g) of the anode for anodes with similar activity GSM values ​​using a nickelate-based NaNiMnMgTiO cathode and a commercial hard carbon anode (available from Kuraray). [Figure 3] Figure 1 shows the effect of using a commercially available hard carbon derived from anthracite on the anodic profile for cycle 1 in a 3E full cell in terms of potential (V vs Na / Na+) versus the active specific capacity of the anode (mAh / g) over a range of anode activity GSMs using a nickelate-based NaNiMnMgTiO cathode. [Figure 4]Figure 10 shows the effect of commercial biomass-derived hard carbon on the cycle 1 anodic profile in a 3E full cell in terms of potential (V vs Na / Na+) versus the active specific capacity of the anode (mAh / g) across two different anode active GSMs using a nickelate-based NaNiMnMgTiO cathode. [Figure 5] Figure 1 shows the effect of using an aqueous binder in a hard carbon anode on the anodic profile for cycle 1 in a 3E full cell in terms of the active specific capacity of the anode (mAh / g) versus potential (V vs Na / Na+) across two different anode active GSMs using a nickelate-based NaNiMnMgTiO cathode and a commercial hard carbon anode (available from Kuraray). [Figure 6] Figure 1 shows a plot of anode active specific capacity (mAh / g) versus cycle number to demonstrate long-term cycling performance in 3E full cells using a nickelate-based NaNiMnMgTiO cathode and a commercial hard carbon anode (available from Kuraray) with different anode active GSM and C / A mass balance. [Figure 7] Figure 1 shows a plot of cathode active specific capacity (mAh / g) versus cycle number to demonstrate long-term cycling performance in 3E full cells using a nickelate-based NaNiMnMgTiO cathode and a commercial hard carbon anode (available from Kuraray) with different anode active GSM and C / A mass balance. [Figure 8] Figure 1 shows a graph of anode active specific capacity (mAh / g) versus cycle number to illustrate the effect of derating and voltage window formation on the cathode (nickelate-based NaNiMnMgTiO) and anode active specific capacity and cycling stability using a commercial hard carbon anode (available from Kuraray). [Figure 9] Figure 1 shows a graph of potential (V vs Na / Na+) versus the active specific capacity of the anode (mAh / g) to illustrate the development of the anode profile in cycle 1 and cycle 4 at constant anode activity GSM and near-constant C / A mass balance values ​​using a 3E full cell with a nickelate-based NaNiMnMgTiO cathode and a commercial hard carbon anode (available from Kuraray). [Figure 10] Figure 1 shows the long-term cycling of a 1 Ah full cell FPC180905 with an anode having 54.20 GSM of anode electrode active material and a C / A mass balance of 2.71. The cathode is a nickelate-based NaNiMnMgTiO material, and the anode is a commercially available hard carbon (available from Kuraray). [Figure 11] FIG. 1 shows a graph of anode active specific capacity (mAh / g) versus anode active GSM using a 3E full cell with a nickelate-based NaNiMnMgTiO cathode and a commercial hard carbon anode (available from Kuraray Co., Ltd.), illustrating the effect of anode active GSM on initial cycle stability. [Figure 12] Figure 1 shows a graph of anode active specific capacity (mAh / g) versus C / A mass balance using a 3E full cell with a nickelate-based NaNiMnMgTiO cathode and a commercial hard carbon anode (available from Kuraray Co., Ltd.), illustrating the effect of C / A mass balance on initial cycle stability. [Figure 13] FIG. 1 shows a graph of cathode active specific capacity (mAh / g) versus cycle number for a sodium-ion battery having NaFeMnMgCuO cathode material and a commercial hard carbon (available from Kuraray Co., Ltd.) 40.25 GSM active anode. [Figure 14]Figure 1 shows a plot of potential (V vs. Na / Na+) versus anode active specific capacity (mAh / g) for two characteristic cells using HC / FeP anode active material and a nickelate-based NaNiMnMgTiO cathode. The anode active specific capacity of these cells is compared when the active anode material was used at a mass of 74.27 gm-2 in one cell (PCFA614) and 55.25 gm-2 in the other cell (711042). [Figure 15] Figure 1 shows a plot of anode active specific capacity (mAh / g) versus potential (V vs Na / Na+) for a 3E full cell performance using HC anode active material and a nickelate-based NaNiMnMgTiO cathode. The anode active material was used at a mass of 52.2 gm-2, and a 1.596 mass balance was used for the cell. [Figure 16] Figure 1 shows a plot of potential (V vs. Na / Na) versus anode active specific capacity (mAh / g) for the performance of a 3E full cell using HC anode active material and a presodiated TiS cathode. The anode active material was used at a mass of 62.9 gm, and a 0.918 mass balance was used for the cell. [Figure 17] Figure 1 shows a plot of anode active specific capacity (mAh / g) versus potential (V vs. Na / Na+) for the performance of a cell using HC anode active material and an oxygen-deficient nickelate-based NaNiMnMgTiO-δ cathode. The anode active material was used at a mass of 52.9 gm-2, and a 2.86 g mass balance was used for the cell. [Figure 18] FIG. 1 shows a plot of capacity retention (%) versus cycle number on first charge for two 3E full cells according to the invention (A3PC268 and AC3PC238) and two comparative 3E full cells (A3PC231 and A3PC225). DETAILED DESCRIPTION OF THE INVENTION

[0031] (Method of manufacturing a sodium-ion battery according to the present invention) A sodium-ion battery according to the present invention was fabricated using the following exemplary method.

[0032] The positive electrode was prepared by solvent casting a slurry of active material, conductive carbon, binder, and solvent onto a substrate. The conductive carbon used was commercially available from Timcal. Polyvinylidene fluoride (PVdF) was used as the binder, and N-methyl-2-pyrrolidone (NMP) was used as the solvent. The slurry was cast onto aluminum foil and heated until most of the solvent evaporated, forming an electrode film. The electrode was then dried under dynamic vacuum at approximately 120°C. The electrode film had the following composition, expressed by weight percent: 89% active material (doped nickelate-containing composition), 5% conductive carbon, and 6% PVdF binder.

[0033] The negative electrodes were prepared by solvent casting a slurry of hard carbon active material (e.g., commercially available from Kuraray), conductive carbon, binder, and solvent onto a substrate. The conductive carbon used was commercially available, e.g., from Timcal. PVdF was used as the binder (unless otherwise noted in a particular example), and N-methyl-2-pyrrolidone (NMP) was used as the solvent. The slurry was cast onto aluminum foil and heated until most of the solvent evaporated, forming an electrode film. The electrode was then further dried under dynamic vacuum at approximately 120°C. In all of the batteries evaluated in this study, the negative electrode film had the following composition, expressed in weight percent: 88% active material, 3% conductive carbon, and 9% PVdF binder, or 92% active material, 2% conductive carbon, and 6% PVdF binder. No practical electrochemical differences were observed between these electrode formulations.

[0034] Prior to cell fabrication, both the cathode and anode electrodes are calendered and again dried overnight under dynamic vacuum. Both electrodes are then placed in a pouch in an argon-filled glove box (the amount of O2 and HO present is less than 5 ppm). Three-electrode (3E) cells use two separator layers, while two-electrode (2E) cells use only one separator layer. All cells, except those listed in Table 1 below, use a common polyethylene separator, available from Asahi Kasei, for example. In the 3E cells, Na metal pieces are placed between the two separator layers and between the cathode and anode, ensuring that the Na pieces do not lie within the anode and / or cathode footprints. The cell assembly is then filled with electrolyte. The electrolyte is 0.5 m NaPF6 in a 1:2:1 weight ratio of EC:DEC:PC, except as listed in Table 1 below. All cells, except as listed in Table 1 below, contain the nickelate-based cathode active material Na. 0.833 Ni 0.317 Mn 0.467 Mg 0.1 Ti 0.117 O2 is used, and commercially available hard carbon (e.g., available from Kuraray) is used as the anode. Finally, the pouch is sealed in a glove box using a vacuum sealer. The cell is then subjected to electrochemical evaluation.

[0035] (Cell evaluation) The cells are evaluated using galvanostatic cycling as follows.

[0036] The cells are cycled galvanostatically at a given current density between preset voltage limits. Commercially available battery cyclers from MTI (Richmond, CA, USA) or Maccor (Tulsa, OK, USA) are used. During charging, alkali ions are extracted from the cathode and inserted into the X / hard carbon anode material. During discharge, alkali ions are extracted from the anode and reinserted into the cathode active material.

[0037] A number of sodium-ion batteries were prepared using the above method. Table 1 below shows the 3E cycling results using a range of active anode GSMs, thicknesses, and C / A mass balances. The plateau capacity:slope capacity ratio (P:S ratio) is also shown. Two-electrode (2E) cell data is also shown.

[0038] [Table 1-1] [Table 1-2] [Table 1-3] Examples marked with an * are comparative examples, ie the compositions evaluated are not according to the invention.

[0039] (Effect of the mass of the anode active material on the capacity of the anode active material) As shown by the results shown in Table 1 above, the anode active first desodium specific capacity (mAh / g) in a sodium-ion battery including a 3E full cell was approximately 85 gm -2 From about 20gm -2 It is observed that the anode active material mass decreases over a range of 0.01 to 0.15 g. Furthermore, particularly high anode active first desodium specific capacities (500 mAh / g or greater) are obtained when low anode active material mass (low GSM) is combined with a high C / A mass balance ratio (e.g., a C / A ratio greater than 7). Surprisingly, the anode active material mass can be reduced to about 52 g. -2 (e.g., samples A3PC118, A3PC117, A3PC129, A3PC119, A3PC140, A3PC133, and A3PC103), the anode first sodium removal capacity increases from about 272 mAh / g to 379 mAh / g, which is seen as a result of increasing the C / A mass ratio from 2.31 to 3.41.

[0040] Figure 1 shows the anode profiles of 3E full cells using different masses of hard carbon material (GSM) (e.g., commercially available from Kuraray). The C / A mass balance for each cell is also shown. All cells use 0.5 m NaPF6 in a weight ratio of EC:DEC:PC = 1:2:1 as the electrolyte. The results confirm that the lighter GSM anodes provide significantly higher capacity than the heavier GSM anodes, and that the anode potentials of the lighter GSM anodes are significantly higher than those of the heavier GSM anodes when fully charged, under corresponding charged conditions. This point is very important not only from a performance standpoint but also from a safety standpoint. That is, the higher absolute anode potential in the fully charged state indicates that it is the "sodium deposition potential" (vs. Na / Na + This means that the GSM anode is further away from the positive electrode potential (below 0 V at 100 V), thus enhancing the safety of the battery. These facts indicate that the light GSM anode offers significant advantages over the heavy GSM anode from a commercial standpoint.

[0041] Figure 1 also shows that full cells using heavy GSM anodes and high C / A mass balances have drawbacks that lead to Na deposition, especially at low capacity values. -2 In a full cell using this active anode material, Na electrodeposition begins at a sodiation capacity of about 335 mAh / g during the first charge cycle of the full cell. The Na electrodeposition capacity is estimated to be about 68 mAh / g during the first sodiation process (this value corresponds to the Na / Na + (This corresponds to the portion of the anodic cycling curve where the potential was below 0 V vs. 0 V). This is evident from the characteristic overpotential spike indicated by the arrow in Figure 1. The initial sodium removal capacity observed for this cell is 335 mAh / g, but when Na electrodeposition capacity is taken into account, the initial effective sodium removal capacity due to sodium storage in the hard carbon active material drops to 267–300 mAh / g.

[0042] In contrast, as previously mentioned, Figure 1 confirms that the lighter GSM anode full cells achieve higher sodium removal capacities (364 or 450 mAh / g for 53.09 or 36.88 GSM anodes, respectively) at significantly higher fully charged anode potentials (approximately 80-83 mV). Therefore, it is concluded that high GSM hard carbon anodes tend to induce Na electrodeposition in sodium-ion full cells, which occurs at significantly lower capacity values ​​than sodium-ion cells using lower mass anode active materials.

[0043] (Effect of different electrolytes on the capacity of anode active materials) Experiments were conducted to evaluate whether the anode capacity increase of batteries using lower mass anode active materials was affected by the composition of the sodium-ion electrolyte used. Two cells (A3PC47 and A3PC80) were prepared. The former used an electrolyte containing 0.5 m NaPF6 in a 1:2:1 weight ratio of EC:DEC:PC, while the latter used an ether-based electrolyte containing 1 m NaBF4 in tetraethylene glycol dimethyl ether (tetraglyme).

[0044] As shown in Figure 2, the anode profiles of the two 3E full cells, A3PC47 and A3PC80, showed negligible differences. The former cell exhibited a first desodium anode capacity of 518 mAh / g against a 29.27 GSM active hard carbon electrode, and the latter cell exhibited a first desodium anode capacity of 520 mAh / g against a 24.90 GSM active hard carbon electrode.

[0045] Thus, the preferred anode capacity exhibited by cells containing lower mass anode electrode active material was found to be independent of the sodium ion electrolyte used.

[0046] (Effect of using different hard carbon materials on anode active material capacity) Two further experiments were performed to assess whether the initial sodium desodium capacity of the anode was affected by the nature (composition and / or source) of the anode electrode active material.

[0047] In the first of these experiments, three 3E full cells were prepared using a commercially available hard carbon anode material derived from anthracite (a type of coal) sold under the trade name "Welsh Anthracite" and available from Supaheat Full. One cell (A3PC64) contained 103.98 gm -2 The other cell (A3PC106) contained 62.16 gm of anode active material. -2 The final cell (A3PC107) contained 51.51 gm of anode active material. -2 The anode active material was used.

[0048] As shown in Figure 3, the lower mass of the anode material (51.51 gm, respectively) is consistent with the results previously described. -2 and 62.16 gm -2 For the two 3E full cells containing 3E, the first cycle anode capacity profiles (300 mAh / g and 240 mAh / g) and C / A mass balance values ​​(3.38 and 2.69, respectively) indicate that the anode active material has a high mass (103.98 gm -2 The anode capacity (196 mAh / g) and C / A mass balance value (1.83) of the 1000-kJ / cm3 cell were both higher than those of the 1000-kJ / cm3 cell.

[0049] In the second experiment, two 3E full cells were prepared using a commercially available biomass-derived hard carbon anode material, sold by BTR Corporation in China under the trade name "BHC-240." One cell (A3PC143) contained 81.36 gm -2 of anode electrode active material was used, and in the other cell (A3PC136), 42.58 gm -2 The anode electrode active material is used.

[0050] In Figure 4, a low mass anode material (42.58 gm -2For the 3E full cell containing a high C / A mass balance value (3.63), the first cycle anode capacity profile (410 mAh / g) is due to the high mass of anode material (81.36 gm -2 ) and a higher anode capacity (242 mAh / g) compared to the cell with a lower C / A mass balance value (1.87).

[0051] These results are believed to indicate that the nature of the hard carbon used as the anode active material is not related to the anode capacity characteristics.

[0052] (Effect of Using Different Binders in the Anode on Anode Active Material Capacity) In this experiment, we investigated whether the anode capacity was affected by using an aqueous carboxymethyl cellulose (CMC):styrene butadiene rubber (SBR) binder instead of a non-aqueous PVdF binder in a 3E full cell. Two cells were prepared. One (A3PC120) contained 59.04 g of active anode material. -2 In the case of the A3PC141, a hard carbon anode with a C / A mass balance of 2.62 was used, while in the case of the A3PC141, the active anode material was 80.85 gm -2 A hard carbon anode with a mass balance of 1.92 was used. In all other respects, i.e., the use of an aqueous binder based on CMC and SBR, the selection of the cathode, and the selection of a commercially available hard carbon anode (e.g., available from Kuraray Co., Ltd.), the two cells were identical. As shown in Figure 5, -2 The heavier cell with 1000 mAh / g of anode active material was able to achieve 234 mAh / g in the first discharge cycle of the full cell, while the lighter mass of anode active material (59.04 gm -2 ), the capacity was 320 mAh / g. Therefore, the increased capacity of hard carbon in cells using lower mass anode active material is not affected by the type of binder used, and this trend is expected to be observed for any binder type.

[0053] (Long-term cycling results of the 3E complete cell of the present invention) Figures 6 and 7 show the long-term cycling characteristics of several 3E full cells with different masses of anode active material, as listed in Table 1. Specifically, Figure 6 shows capacity versus cycle life based on the specific capacity of the active anode, and Figure 7 shows the corresponding graph of the active cathode specific capacity. All cells underwent the first four cycles at C / 10 (the "formation" cycle) before cycling at C / 5 (the "post-formation" cycle). Note that Figures 6 and 7 report the last cycle capacity retention (relative to the fifth cycle capacity, or first "post" cycle capacity) for selected cells.

[0054] From the results shown in Figures 6 and 7 and Table 1, several trends can be identified: Light GSM anodes (e.g., GSM values ​​around 52 or 62) with low C / A mass balances (i.e., C / A mass balances between 1.9 and 2.56) significantly enhance cycling stability, as opposed to high C / A mass balances (i.e., C / A mass balances greater than 3.0). For the 52 GSM anode, the cycling stability of A3PC118 is compared to that of A3PC119, while for the 62 GSM anode, the cycling stability of A3PC110 and A3PC91 is compared to that of A3PC93. For any light GSM anode (e.g., GSM values ​​around 52 or 62), a decrease in C / A mass balance results in an increase in cathode specific capacity (A3PC118 compared to A3PC119, A3PC110 or A3PC91 compared to A3PC93). The above observations are based on the lower coulombic efficiency observed with light GSM anodes as a result of deeper sodiation of the hard carbon when heavier C / A mass balances are used. For this reason, cells with high C / A mass balances (greater than about 5) and very low GSM anodes (less than 30 GSM) tend to exhibit very low first-cycle coulombic efficiencies (less than 50-60%), which explains why such cells exhibit low cathode capacity and poor cycling stability. For example, an A3PC127 with a 17.11 GSM anode and a 7.09 C / A mass balance achieves a cathode capacity of only 72.8 mAh / g on the first discharge cycle.

[0055] (The effect of changing the rating of the voltage window formed on cycle stability and anode specific capacity) In this experiment, the effect of "de-rating" the formation voltage window on cycling stability and anode specific capacity is investigated.

[0056] 51.64g at 66µm thickness -2 Cell A3PC140, with active anode material of 1.0 V and a C / A mass balance of 3.27, was cycled four times at C / 10 from 4.20 to 1.00 V (during the formation cycle) and then cycled at C / 5 from 4.00 to 1.00 V ("post-formation cycle"). As shown in Figures 6 and 7, after "de-rating" the "post" cycle, this cell exhibited extremely high stability over 134 "post" cycles. The cathode capacity retention was 94%.

[0057] To further investigate the effect of derating and protocol formation, a 66 μm thick, 52.36 g -2Another similar cell, A3PC153, was fabricated with an active anode material of 100 V and a C / A mass balance of 3.32. It was then cycled four times at C / 10 from 4.00 to 1.00 V during the formation process. It was then cycled at C / 5 from the same voltage, 4.00 to 1.00 V, during the "post" cycle process. The rationale behind this experiment was to investigate the effect of four formation cycles from 4.20 to 1.00 V and four formation cycles from 4.00 to 1.00 V. Figures 8 and 9 show the resulting cathode and anode capacities versus cycle number, as well as the anode profiles for the first and fourth formation cycles. Figure 8 also shows the capacity retention at the 100th "post" cycle (relative to the first "post" cycle capacity). The results demonstrate the following: When these cells were then "post" cycled using four formation cycles from 4.00 to 1.00 V, the cathode and anode capacities were significantly improved at similar "post" cycling stability (approximately 93% or 94.5% retention at 100 "post" cycles) compared to four formation cycles from 4.20 to 1.00 V (cathode: 85.5 vs. 80.5 mAh / g; anode: 284.1 vs. 264.8 mAh / g). The anode profile in Figure 9 shows the detrimental effect of formation between 4.20 and 1.00 V on capacity. This is likely due to more pronounced anode sodiation in the fully charged state from 4.20 to 1.00 V, which adversely affects the coulombic efficiency of photo-GSM anodes. As shown in Figure 9, the coulombic efficiency of the A3PC140 cell increases from 75.5% in cycle 1 (which underwent four formation cycles between 4.20 and 1.00 V) to 96.2% in cycle 4, while the A3PC153 cell (which underwent four formation cycles between 4.00 and 1.00 V) exhibits a slightly higher coulombic efficiency (76.8%) in the first cycle but achieves a significantly improved efficiency of 99.2% in the fourth cycle. This last observation is likely a result of reduced Na loss from the cathode when the lower 4.00-1.00 V cell formation voltages were used, explaining why the initial high "post" discharge capacity of the cathode (and even the anode) was observed.

[0058] Based on the above results, it appears that derating lightweight GSM anodes offers a good strategy for enhancing cycling stability by first derating from 4.20 to 1.00 V (during the formation cycle), then from 4.00 to 1.00 V (during the "post" cycle), and then using 4.00 to 1.00 V for both the formation and "post" formation cycles. Cycling between 4.00 and 1.00 V is extremely stable, and the capacity obtained in the "post" cycle is higher when formation is performed between 4.00 and 1.00 V. Using such a derating cycling protocol allows for the use of heavier C / A mass balances (>3) even with light GSM anodes.

[0059] (Long-term cycling stability of the cell according to the present invention) Figure 10 is a graph of specific capacity versus cycle number for a 1 Ah full cell FPC180905. -2The cell has a mass of active anode material (e.g., commercially available from Kuraray) of 1000 mAh / g, a thickness of the anode material of 65 μm, and a C / A mass balance of 2.71. As shown in Figure 10, this cell has a high anode specific capacity of 325.71 mAh / g, 88.2% of which is retained after 90 cycles. Therefore, this cell has extremely high cycling stability.

[0060] (Effect of C / A anode mass balance changes on specific energy) The following table provides various relative energy densities for all 1 Ah cells evaluated using a light GSM anode (approximately 50-54 active anode GSM) compared against a 97.23 heavy GSM anode. The energy densities listed are the energy densities at the first "post" cycle (after four formation cycles). As indicated, different cells were cycled at different voltage windows. As these results show, the energy densities of the cells of the present invention with a light GSM anode are significantly higher than those of the heavy (>80 gm -2 ) mass of anode active material.

[0061] [Table 2] (Further study on the influence of anode active material mass and C / A anode mass balance on early cycle stability) Considering the above experimental results, it is clear that cells containing low mass anodes are highly advantageous in providing high anode capacity. However, such cells do not necessarily provide the best initial cycle stability during the formation process. This observation is clearly illustrated in Figure 11, which shows that extremely low mass anodes, particularly those with a mass of approximately 30 gm -2For cells with a C / A mass balance of less than 1.5, the cells exhibit the lowest cycling stability over the first three cycles, while the high mass anodes are fairly stable. Furthermore, as shown in Figure 12, the C / A mass balance also influences the initial cycling stability over the first three cycles. For the same cells evaluated in Figure 11, the cells with a mass balance of approximately 7.5 and 6.0 (anode mass of approximately 30 g) exhibited the lowest cycling stability over the first three cycles. -2 Cells with a mass balance of about 3.5 or less show the poorest initial cycle stability, while cells with a mass balance of about 3.5 or less show improved stability.

[0062] 11 and 12 may also be used to identify optimal ranges for anode mass and C / A mass balance to produce cells with high anode capacity (preferably at least 270 mAh / g) and good initial cycling stability. Specifically, for 45 gm -2 ~75gm -2 Particularly preferred are cells having an anode mass of about 1.0 to 3.5 and a C / A mass balance of about 2.0 to 3.5.

[0063] (Investigation of the performance of cells with non-nickelate cathode active materials) As shown in Table 1 above, cell 811023 contained Na as the cathode active material. 0.833 Fe 0.200 Mn 0.483 Mg 0.0417 Cu 0.225 O2 and mass 40.25gm -2 and a C / A mass balance of 3.13. Figure 13 shows a graph of specific capacity versus cycle number, which shows that the non-nickelate cathode active material when used in a cell according to the present invention very successfully achieved a first desodium capacity of 336.45 mAh / g and retained 97.2% of this after 20 cycles.

[0064] This result illustrates that the positive effect of increasing anode specific capacity with decreasing anode GSM is independent of the type of cathode used.

[0065] (Study on the influence of hard carbon / Fe2P anode on anode properties) We investigated whether hard carbon composite anodes (hard carbon mixed with the aforementioned "X") would exhibit a trend of increasing anode specific capacity with decreasing anode GSM. In this example, we used another type of hard carbon (called "Farazion Hard Carbon") prepared from cornstarch. Table 1 above lists the hard carbons, each containing 74.27 gm -2 and 55.25 gm -2 Figure 14 shows the composition of cells PCFA614 and 711042 using different amounts of HC / Fe2P anode active material. The cycle 104 performance of these two cells is plotted as anode specific capacity (mAh / g) versus potential (V vs. Na / Na + ) plots. This figure not only confirms the general trend described above of lower mass anodes producing higher anode capacity, but also shows that such hard carbon / FeP (HC / X) anodes produce cells with extremely high cycling stability. From these results, it is clear that the trend of increasing anode capacity with decreasing anode GSM is exhibited by different types of hard carbon / X composite anodes.

[0066] (Consideration of cathode / anode mass balance less than 1.0 and the effect of non-nickelate cathode materials) As shown in Figures 15 and 16, the anode profiles for the 3E full cells use a low mass (GSM) of hard carbon material (e.g., commercially available from Kuraray) and a low C / A mass balance (C / A = 1.596 for Sample 50 and C / A = 0.918 for Sample 51). In both cells, the electrolyte was 0.5 m NaPF6 with a mass ratio of EC:DEC:PC = 1:2:1. These results confirm that such light GSM anodes provide excellent capacity and that other non-nickelate materials, such as sodiated metal sulfide materials (TiS2), can be used as active cathode materials. This example also reiterates that the C / A mass balance, when used in such cells, is highly dependent on the cathode and anode active materials used (thus, the respective capacities of the cathode and anode active materials actually determine which range of C / A mass balances can be used).

[0067] (Study on the effect of using oxygen-deficient nickelate cathode materials) Figure 17 shows the anode specific capacity (mAh / g) versus potential (V vs. Na / Na) for cells using oxygen-deficient nickelate cathode materials. + ) plot. In other cells according to the invention, the anode GSM is ≦80 / m 2 (i.e., 52.9) and the C / A ratio is in the range of 0.1 to 10 (i.e., 2.86), and as observed, the cell with the oxygen-deficient nickelate cathode material performs in a similar manner to the cell using the fully oxygenated nickelate cathode material.

[0068] (Study to demonstrate the charge tolerance of low GSM anode cells) Figure 17 shows the capacity retention versus cycle number for 3E full cells when charged at various rates and discharged at a constant C / 5 rate, as indicated. These cells use either low GSM (samples 54 and 56) or comparative GSM anodes (samples 53 and 55) made from either hard carbon commercially available from Kuraray or hard carbon commercially available from BTR (grade BHC-240). Comparing the two hard carbon-containing cells, it is observed that the low GSM anode cell of the present invention (A3PC268) exhibits better capacity retention than the comparative GSM cell (A3PC231) at fast charge rates, such as 2C. This trend is also observed with the hard carbon material available from BTR. Furthermore, the low GSM cell of the present invention (A3PC238) can be cycled in a more stable manner than the corresponding comparative GSM anode cell (A3PC225) when charged at fast rates, such as 2C.

[0069] In this example, another surprising, important and commercially relevant result for low GSM anodes is evident: cells of the present invention can be charged more quickly than comparative cells having a GSM of anode material greater than 80.

[0070] (Study on the relationship between the weight (GSM) of the anode material and I) the porosity of the anode material, and II) the volume-specific surface area of ​​the anode material) X-ray computed tomography (CT) is a useful tool for non-destructively constructing a 3D image of the interior of a battery electrode. CT allows for the visualization and quantification of the morphology of battery materials at the electrode level by constructing such a 3D map image. In particular, it can reveal two important physical parameters of a battery electrode. The first is its porosity, which can be determined in %, and is defined as the ratio of the void volume within the electrode to the total volume of the electrode. The second is its volume-specific surface area, VSSA, which is expressed in m 2 / m 3 can be determined in units of

[0071] As the above results show, the low GSM effect of hard carbon is not a result of changes in the active material (type of hard carbon), binder, or electrolyte, but is solely a result of the GSM of the hard carbon used in the anode electrode (when the anode material thickness is less than 100 μm and C / A is in the range of 0.1 to 10). The applicant investigated how the porosity and VSSA of a hard carbon electrode change with its GSM, and obtained interesting and completely unexpected results, as will be shown below.

[0072] CT measurements were performed on two samples.

[0073] As detailed in Table 3 below, the sample designated as Comparative Sample 57 utilizes a GSM anode activity of 99.09 and a coating thickness of 113 μm. The sample designated as Sample 58 is in accordance with the present invention and has a GSM anode activity of 52.91 and a coating thickness of 60 μm. To avoid confusion, it is noted that for both these samples, the CT measurements were carried out on hard carbon electrodes (not in an electrochemical cell).

[0074] Table 3 below summarizes the results of the CT scans.

[0075] [Table 3] As the above results show, Sample 58 exhibits a VSSA value (1.92) that is nearly twice that of Comparative Sample 57. This improved VSSA value helps explain the significantly higher capacity observed for all of the low GSM hard carbon electrodes according to the present invention. It is clear that the high capacity of the low GSM anodes is due to their increased surface area per unit volume. This simply means that more hard carbon active material is accessible for sodium storage. In other words, the electrolyte-hard carbon interfacial area increases for the low GSM anodes, and this access to "more" hard carbon active material per given volume results in the electrode's higher sodium storage capacity.

[0076] It is important to note that while the VSSA of Samples 57 and 58 are significantly different, the two samples do not differ significantly in porosity. This is a highly unexpected result, as literature studies tend to attribute differences in porosity (obtained by techniques such as BET on hard carbon powders) to why different hard carbons have different capacities (and different plateau:slope capacity ratios). However, Applicant's results from the aforementioned CT experiments indicate that the important feature is not porosity, but VSSA, which largely determines the capacity and plateau:slope capacity ratio achieved by a hard carbon electrode. Those skilled in the art will recognize that the porosity of a hard carbon electrode remains important in determining certain electrochemical performance aspects, such as first-cycle efficiency, electrode density, etc. However, as seen in this example, VSSA is also a critical parameter, and this has been demonstrated for the first time in this application.

[0077] Based on simple linear extrapolation, for an anode active GSM of 80 GSM (the threshold GSM value for samples used in the cells of the present invention), the VSSA value is 0.993. However, it should be understood that this VSSA value may have some error, which may vary slightly or significantly depending on the type of hard carbon. It is also expected that the type of carbon additive and binder may affect the VSSA value. It is also expected that such VSSA value may be significantly affected. Therefore, the present invention relates to any negative active material (preferably disordered carbon, and more preferably hard carbon)-containing electrode in which the active material layer has a VSSA value greater than 0.80.

Claims

1. Cathode, anode, and sodium tetrafluoroborate (NaBF 4 ) or sodium hexafluorophosphate (NaPF 6 A sodium ion secondary battery having an electrolyte containing the cathode has one or more layers of positive electrode active material disposed on a cathode substrate, and the anode has one or more layers of negative electrode active material disposed on an anode substrate; the layer of negative electrode active material comprises one or more hard carbon materials, i) the mass of the layer of negative electrode active material is more than 25 g and not more than 65 g per square meter of the anode substrate; ii) the ratio of the mass of the layer of positive electrode active material to the mass of the layer of negative electrode active material is 0.1 to 10; iii) the thickness of the layer of the negative electrode active material on the anode substrate is 80 μm or less; One or more of the positive electrode active materials is represented by the general formula A 1±δ M 1 V M 2 W M 3 X M 4 Y M 5 Z O 2-c is a compound of where: A is one or more alkali metals selected from sodium, potassium, and lithium; M 1 has one or more redox-active metals in the oxidation state +2, M 2 has a metal with an oxidation state greater than 0 and less than or equal to +4, M 3 has a metal in the +2 oxidation state, M 4 has a metal with an oxidation state greater than 0 and less than or equal to +4, M 5 has a metal in the oxidation state +3, where: 0 ≤ δ ≤ 1; V＞0； W≧0； X≧0； Y≧0； At least one of W and Y is greater than 0, Z≧0； C is in the range of 0≦c<2, where V, W, X, Y, Z and C are selected to maintain electrochemical neutrality.

2. The mass of the layer of the negative electrode active material per square meter of the anode substrate is 40 gm －２ ~75gm －２ 2. The sodium ion secondary battery according to claim 1, wherein

3. 2. The sodium ion secondary battery according to claim 1, wherein a ratio of the mass of the positive electrode active material to the mass of the layer of the negative electrode active material is 0.5 to 10.

4. the negative electrode active material has a hard carbon / X composite, 2. The sodium-ion secondary battery of claim 1, wherein X is one or more selected from phosphorus, sulfur, indium, antimony, tin, lead, iron, manganese, titanium, molybdenum, and germanium, in either elemental or compound form.

5. 2. The sodium-ion secondary battery of claim 1, wherein the negative electrode active material comprises one or more additional materials capable of storing sodium ions and selected from non-metals, non-metal-containing compounds, metals, metal-containing compounds, and metal-containing alloys.

6. having a cathode and an anode, the cathode comprises one or more positive electrode active materials, and the anode comprises a layer of negative electrode active material disposed on an anode substrate; the layer of negative electrode active material comprises one or more disordered carbon-containing materials; 10. The sodium-ion secondary battery of claim 1, wherein the layer of negative electrode active material has a volume-specific surface area (VSSA) greater than about 0.

8.

7. A method for producing the sodium ion secondary battery according to any one of claims 1 to 6, a. A cathode having one or more layers of positive electrode active material is combined with an anode having an anode substrate coated with a layer of negative electrode active material, and sodium tetrafluoroborate (NaBF 4 ) or sodium hexafluorophosphate (NaPF 6 ) to form a sodium-ion battery, wherein the layer of negative electrode active material comprises one or more hard carbon materials; b) cycling the sodium-ion battery to a first voltage; and i) the mass of the layer of negative electrode active material per square meter of the anode substrate is 25 gm －２ Super, 65gm －２ is as follows: ii) the ratio of the mass of the layer of the positive electrode active material to the mass of the layer of the negative electrode active material is 0.1 to 10; iii) the thickness of the layer of the negative electrode active material on the anode substrate is 80 μm or less; One or more of the positive electrode active materials is represented by the general formula A 1±δ M 1 V M 2 W M 3 X M 4 Y M 5 Z O 2-c is a compound of where: A is one or more alkali metals selected from sodium, potassium, and lithium; M 1 has one or more redox-active metals in the oxidation state +2, M 2 has a metal with an oxidation state greater than 0 and less than or equal to +4, M 3 has a metal in the +2 oxidation state, M 4 has a metal with an oxidation state greater than 0 and less than or equal to +4, M 5 has a metal in the oxidation state +3, where: 0 ≤ δ ≤ 1; V＞0； W≧0； X≧0； Y≧0； At least one of W and Y is greater than 0, Z≧0； C is in the range of 0≦c<2, wherein V, W, X, Y, Z and C are selected to maintain electrochemical neutrality.

8. A battery comprising at least two sodium ion secondary batteries according to any one of claims 1 to 6.

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