JP2014086378A - Sodium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sodium secondary battery excellent in cost performance.SOLUTION: The present invention relates to a sodium secondary battery including: a positive electrode including a material capable of inserting/desorbing sodium ions; a negative electrode including metallic sodium, a sodium-containing material, or a material capable of inserting/desorbing sodium ions; and an electrolyte having sodium ion conductivity. The material capable of inserting/desorbing sodium ions included in the positive electrode is an azo compound, specifically methyl orange or methyl red sodium. The present invention also provides a method for manufacturing the sodium secondary battery.

Description

  The present invention relates to a sodium secondary battery. In particular, the present invention relates to a sodium secondary battery that includes an azo compound, particularly methyl orange or meryl red sodium salt, in the positive electrode of a sodium secondary battery, and is excellent in cost and cycle characteristics.

  Sodium secondary batteries using sodium ion insertion and desorption reactions are expected to be cost effective secondary batteries because of the superiority of sodium resources over the widely used lithium secondary batteries. ing. For this reason, research and development relating to the electrode material and the electrolyte material are underway.

Park et al. In Non-Patent Document 1 that NaTi ₂ (PO ₄ ) ₃ can be used as a positive electrode in an organic electrolyte and a negative electrode in an aqueous electrolyte, and a discharge with a current density of 2.0 mA / cm ² . In this case, both electrolytes have reported a relatively large discharge capacity of about 120 mAh / g.

Further, Patent Document 1 describes that NaCoO ₂ can be charged and discharged in a non-aqueous electrolyte and has a high discharge capacity maintenance rate of 94% although the number of cycles is as small as five.

JP 2007-35283 A

Sun Il Park et al., Journal of The Electrochemical Society, 158 (10) A1067-A1070 (2011)

  As described above, a discharge capacity at a level comparable to that of a lithium secondary battery has been reported so far, but in many cases, a material containing a rare metal is used as an electrode material as in the non-patent literature and patent literature, In addition to being disadvantageous in terms of cost, there were problems that sufficient cycle characteristics could not be obtained.

  An object of this invention is to provide the sodium secondary battery excellent in cost property and cycling characteristics with respect to said subject.

The present invention includes a positive electrode containing a substance capable of inserting and removing sodium ions,
A sodium secondary battery including a metal sodium, a sodium-containing material, or a negative electrode including a material capable of inserting and removing sodium ions, and an electrolyte having sodium ion conductivity;
The material capable of inserting and desorbing sodium ions from the positive electrode (hereinafter also simply referred to as positive electrode material) is methyl orange represented by the following formula (I), which is an azo compound.

  In the present invention, the positive electrode material of the positive electrode may be a methyl red sodium salt represented by the following formula (II) which is an azo compound.

  In the sodium secondary battery of the present invention, it is preferable that the positive electrode includes a positive electrode material that includes the methyl orange or methyl red sodium salt and carbon particles and is processed by a ball mill (in this specification, methyl A positive electrode material including a positive electrode material of orange or methyl red sodium salt and a conductive material such as carbon particles is also referred to as a positive electrode material).

  In the sodium secondary battery of the present invention, the electrolyte is preferably an organic electrolyte containing sodium ions.

Furthermore, this invention provides the manufacturing method of the said sodium secondary battery. In this manufacturing method, the sodium secondary battery is
A positive electrode comprising a substance capable of inserting and desorbing sodium ions and a positive electrode material comprising carbon particles;
A negative electrode containing metallic sodium, a sodium-containing substance, or a substance capable of inserting and removing sodium ions, and an electrolyte having sodium ion conductivity,
The substance capable of inserting and desorbing sodium ions is methyl orange represented by the following formula (I), or

Methyl red sodium salt represented by the following formula (II):

This manufacturing method is
(A) preparing the positive electrode;
(B) preparing the negative electrode;
(C) preparing the electrolyte;
(D) producing a sodium secondary battery from the positive electrode, the negative electrode and the electrolyte,
The step of preparing the positive electrode includes a step of preparing a positive electrode material by mixing the substance capable of inserting and desorbing sodium ions and carbon particles with a ball mill.

  ADVANTAGE OF THE INVENTION According to this invention, the sodium secondary battery excellent in cost performance and cycling characteristics can be provided.

It is the schematic which shows the structure of the sodium secondary battery of this invention. It is a figure which shows the structure of the positive electrode material of the secondary battery of this invention, (a) represents the structure of methyl orange, (b) represents the structure of methyl red sodium salt. It is the schematic which shows the structure of the sodium secondary battery of one Embodiment of this invention. It is a figure which shows the charging / discharging curve of the sodium secondary battery of embodiment of this invention shown in FIG.

The first of the present invention is a sodium secondary battery, in particular, a substance capable of inserting and removing sodium ions in the positive electrode is methyl orange (C ₁₄ H ₁₄ N ₃ NaO ₃ S represented by the following formula (I): ),

Alternatively, the present invention relates to a sodium secondary battery that is a methyl red sodium salt (C ₁₅ H ₁₄ N ₃ NaO ₂ ) represented by the following formula (II).

  In the sodium secondary battery of the present invention, the positive electrode preferably includes a positive electrode material including the methyl orange or methyl red sodium salt and carbon particles.

  In one embodiment, the positive electrode preferably includes a positive electrode material that has been ball milled.

  Such ball milling is performed because of the low electronic conductivity of the methyl orange and methyl red sodium salts described above, so that when used as a battery material, there is a concern that the discharge voltage decreases and the charging voltage increases. By. That is, in the present invention, in order to improve the conductivity of the positive electrode containing methyl orange and methyl red sodium salt (positive electrode material), methyl orange and methyl red sodium salt are mixed with a carbon material as a conductive material, Process. By performing such treatment, the positive electrode material is composited with the carbon material to improve the adhesion of the active material in the positive electrode material, improve the uniformity and dispersibility of the active material, and improve the conductivity. be able to. A more excellent sodium secondary battery can be produced.

  The second of the present invention relates to a method for producing the sodium secondary battery. In the production method of the present invention, methyl orange of (I) or methyl red sodium salt of formula (II) and conductive particles such as carbon particles are used as the positive electrode material, and these materials are ball milled and mixed. A positive electrode is prepared by including a procedure.

  First, an embodiment of the sodium secondary battery of the present invention will be described.

  The sodium secondary battery of the present invention includes at least a positive electrode, a negative electrode, and an electrolyte. The positive electrode contains a substance capable of inserting and removing sodium ions (positive electrode substance), and the negative electrode contains metallic sodium, a sodium-containing substance, or a substance capable of inserting and removing sodium ions, The electrolyte has sodium ion conductivity.

  In the present invention, the positive electrode contains a sodium-containing azo compound as a substance capable of inserting and removing sodium ions (positive electrode substance). In the present invention, the azo compound as the positive electrode material is methyl orange of the above formula (I) or methyl red sodium salt of the above formula (II).

  The methyl orange and methyl red sodium salts that can be used in the present invention can be obtained as commercial products.

  The positive electrode of the sodium secondary battery of the present invention preferably includes a mixture (positive electrode material) of methyl orange or methyl red sodium salt and a conductive material such as carbon powder. In one embodiment of the present invention, a positive electrode material obtained by pulverizing and mixing a conductive material such as methyl orange or methyl red sodium salt and carbon powder (for example, carbon blacks such as acetylene black powder) by ball milling is used as a positive electrode. It is particularly preferable to use it.

  The above-mentioned positive electrode can be prepared, for example, by the following means, but the present invention is not limited to these.

  First, carbon powder (for example, carbon blacks such as acetylene black powder), binder powder such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and methyl orange or methyl red sodium salt are mixed. Then, the positive electrode can be prepared by rolling with a roll press machine, cutting into a predetermined size, and forming into a pellet.

  Alternatively, after a mixture of the above-mentioned carbon powder, binder powder and methyl red or methyl red sodium salt is dispersed in a solvent such as an organic solvent (for example, N-methyl-2-pyrrolidone (NMP)) to form a slurry. The positive electrode can also be prepared by coating on a metal foil such as a copper foil and drying.

  In the present invention, as described above, since methyl orange and methyl red sodium salt do not have electronic conductivity, when used as a battery material, the discharge voltage may decrease and the charge voltage may increase. Therefore, in order to improve the conductivity of the positive electrode containing methyl orange or methyl red sodium salt (positive electrode material), it is preferable to mix the positive electrode material with the above-described carbon particles as a conductive material and perform ball mill treatment. By such ball mill treatment, the uniformity and dispersibility between the methyl orange or methyl red sodium salt in the positive electrode material and the carbon powder can be improved, and the performance of the secondary battery can be improved. A sodium secondary battery having characteristics can be obtained.

  As a specific procedure for obtaining a positive electrode including the above ball mill treatment, first, carbon powder (for example, carbon blacks such as acetylene black powder) and methyl orange or methyl red sodium salt are mixed, ball mill or the like. The above-mentioned pulverizer may be pulverized and mixed for a desired time, and the resulting ball mill (BM) treatment mixture may be further mixed with the binder powder as described above, followed by rolling as described above.

  When the cathode material is methyl orange, the desired pulverization and mixing time of the ball mill treatment is less than 6.5 hours, preferably 3 to 6.5 hours, more preferably 3 to 6 hours, and the cathode material is methyl red. In the case of a sodium salt, it is less than 10.5 hours, preferably 3 to 10.5 hours, more preferably 6 to 10.5 hours, and particularly preferably 6 to 10 hours.

  In the positive electrode of the present invention, an organic electrolyte containing sodium ions can be used as the electrolyte solution. Furthermore, the sodium secondary battery including the positive electrode of the present invention can also use a solid electrolyte or polymer electrolyte that allows sodium ions to pass therethrough as an electrolyte.

  The negative electrode is not particularly limited as long as it includes a sodium-containing material such as metallic sodium, a sodium-containing alloy, or a material capable of inserting and removing sodium ions. For example, examples of the negative electrode include a metal sodium sheet, or a metal sodium sheet bonded to a metal foil such as aluminum. The negative electrode of such a metal sodium sheet can be prepared by rolling metal sodium into a sheet shape with a press or the like and forming it into a desired shape. Further, a metal sodium sheet that has been pressure-bonded to a metal foil can be prepared by pressure-bonding the metal sodium sheet prepared as described above to a metal foil such as aluminum.

  Moreover, as a negative electrode material other than metallic sodium as described above, an alloy containing sodium as a main component as a negative electrode active material (for example, a sodium-tin alloy) (sodium-containing material), or insertion and removal of sodium ions is possible. Examples thereof include amorphous carbon and other materials (substances capable of inserting and removing sodium ions). The negative electrode containing these negative electrode active materials is, for example, a metal foil such as copper foil and a negative electrode active material and a binder such as polyvinylidene fluoride (PVDF), such as N-methyl-2-pyrrolidone (NMP). A slurry dispersed in a simple organic solvent can be applied and dried.

As long as the electrolyte of the sodium secondary battery of the present invention is a substance having sodium ion conductivity but not electronic conductivity, it is a solid state such as an organic electrolyte containing sodium, a solid electrolyte containing sodium ion, or a polymer electrolyte. The electrolyte can also be used. For example, metal salts containing sodium ions such as sodium bistrifluoromethanesulfonylimide (NaTFSI), sodium perchlorate (NaClO ₄ ), sodium hexafluorophosphate (NaPF ₆ ), such as ethylene carbonate (EC) and dimethyl carbonate. An organic electrolyte dissolved in a mixed solvent of (DMC) (volume ratio 1: 1), a mixed solvent such as EC and diethyl carbonate (DEC), or a single solvent such as propylene carbonate (PC). .

Other examples of the electrolyte include solid electrolytes that pass sodium ions [eg, 75Na ₂ S · 25P ₂ S ₅ , NASICON (Na ⁺ Super Ionic Conductor, Na ₃ Zr ₂ Si ₂ PO _12, etc.)], polymers that pass sodium ions Examples thereof include, but are not limited to, an electrolyte [for example, a composite of the above organic electrolyte and polyethylene oxide (polyethylene oxide (PEO) -based polymer electrolyte)]. In the present invention, any known solid electrolyte passing through sodium ions or polymer electrolyte passing through sodium ions used in sodium secondary batteries can be used.

  The sodium secondary battery of the present invention can also include other elements such as a structural material such as a separator and a battery case. Also for these elements, various materials used in conventionally known secondary batteries can be used, and there is no particular limitation.

  A battery using the positive electrode, the negative electrode, the electrolytic solution, or the like as described above can take a conventional shape such as a coin shape, a cylindrical shape, or a laminate shape.

  The sodium secondary battery of the present invention includes, for example, a positive electrode and a negative electrode as shown in FIG. 1 and an electrolyte in contact with both electrodes. In the present invention, a separator may be included between the positive electrode and the negative electrode. When using an organic electrolyte as the electrolyte solution, for example, a separator may be impregnated with the electrolyte solution. Further, the organic electrolyte may be impregnated in a polymer electrolyte or the like. Moreover, what is necessary is just to arrange | position so that both poles may contact | connect these, when using a solid electrolyte, a polymer electrolyte, etc.

  Further, although not explicitly shown in FIG. 1, a battery case covering a positive electrode, a negative electrode, an electrolyte, a separator, and the like can be included. In the present invention, it is particularly preferable to use methyl orange or methyl red sodium salt as the positive electrode material.

  As a more specific embodiment, the present invention can be applied as a coin cell type secondary battery as shown in FIG. As shown in FIG. 3, the coin cell type secondary battery includes a positive electrode 1 and a negative electrode 3, and further includes a separator 2 impregnated with an electrolyte between these electrodes. Further, the secondary battery structure may include a positive electrode case 4, a gasket 5, and a negative electrode case 6.

  In the present invention, a solid electrolyte, a polymer electrolyte, or the like as described above can be used instead of or in addition to the separator.

  Next, the manufacturing method (2nd invention) of the sodium secondary battery of this invention is demonstrated.

  In the manufacturing method of the sodium secondary battery of the present invention using the positive electrode, the negative electrode, the electrolytic solution and the like as described above, the sodium secondary battery can be manufactured in a conventional shape such as a coin shape, a cylindrical shape, and a laminate shape. it can. And the manufacturing method of these secondary batteries can also use the method similar to the past.

  For example, in a sodium secondary battery as shown in FIG. 1, a positive electrode, a negative electrode, and an electrolyte in contact with both electrodes are prepared. What is necessary is just to prepare these materials according to the adjustment method of each material mentioned above. In the present invention, when an organic electrolyte is used as an electrolytic solution, for example, a separator (not shown) can be used by impregnating the electrolytic solution. Further, the organic electrolyte may be impregnated in a polymer electrolyte or the like. Moreover, what is necessary is just to arrange | position so that both poles may contact | connect these, when using a solid electrolyte, a polymer electrolyte, etc.

  Further, although not clearly shown in FIG. 1, it can include a battery case that covers a positive electrode, a negative electrode, an electrolyte, a separator, and the like. The positive electrode, the negative electrode, the electrolyte, the separator, and the like are arranged in this battery case. A sodium secondary battery can be manufactured by fixing.

  As a more specific embodiment, a coin cell type secondary battery as shown in FIG. 3 can be manufactured. For example, the positive electrode 1, the negative electrode 3, and the separator 2 impregnated with the electrolytic solution are disposed in the positive electrode case 4 and the negative electrode case 6 as desired, and both cases in which the respective components are disposed are fixed. A battery can be manufactured.

  A specific method of manufacturing the sodium secondary battery of the present invention is as follows.

A method for manufacturing a sodium secondary battery, comprising:
The sodium secondary battery is
A positive electrode comprising a substance capable of inserting and desorbing sodium ions and a positive electrode material comprising carbon particles;
A negative electrode containing metallic sodium, a sodium-containing substance, or a substance capable of inserting and removing sodium ions, and an electrolyte having sodium ion conductivity,
The substance capable of inserting and desorbing sodium ions from the positive electrode is methyl orange represented by the above formula (I) or methyl red sodium salt represented by the above formula (II),
The method
(A) preparing the positive electrode;
(B) preparing the negative electrode;
(C) preparing the electrolyte;
(D) producing a sodium secondary battery from the positive electrode, the negative electrode and the electrolyte,
The step of preparing the positive electrode includes a step of preparing a positive electrode material by pulverizing and mixing the substance capable of inserting and desorbing sodium ions and carbon particles with a ball mill.

  The steps (a) to (c) can be prepared according to the bipolar electrode and electrolyte preparation method described in the first invention. Moreover, what is necessary is just to arrange | position a battery case, for example, arrange | positions a positive electrode, a negative electrode, and electrolyte to a battery case. A more specific procedure is as described above with reference to FIGS.

  In the production method of the present invention, the above-described solid electrolyte, polymer electrolyte, or the like can be used as the electrolyte.

  In the production method of the present invention, it is preferable to improve the conductivity of the positive electrode containing methyl orange or methyl red sodium salt (positive electrode material). For this reason, in the step of preparing the positive electrode in step (a), a substance capable of inserting and removing sodium ions (methyl orange or methyl red sodium salt) and carbon particles are pulverized and mixed by a ball mill (ball mill treatment). And preparing a positive electrode material.

  In this specification, the ball mill treatment (BM treatment) is a compound in which methyl orange or methyl red sodium salt (positive electrode material) and conductive particles such as carbon particles are pulverized and mixed for a predetermined time in the presence of balls. It means to become. Specifically, methyl orange or methyl red sodium salt and conductive particles such as carbon particles are first mixed for about several minutes in a mixer, and, for example, zirconia balls are added to the mixture and pulverized for a predetermined time. Mix. In the BM treatment, the mixture ratio of the positive electrode material-conductive particles and the ball is preferably a weight ratio of the positive electrode material-conductive particle mixture: ball = 1: 9 to 2: 8. Moreover, it is preferable that the rotational speed of the mixer at the time of mixing the material at the time of BM processing is 200-1000 rpm.

  When the positive electrode material is methyl orange, the predetermined time for pulverizing and mixing by the ball mill treatment is less than 6.5 hours, preferably 3 to 6.5 hours, more preferably 3 to 6 hours, and the positive electrode material is methyl In the case of a red sodium salt, it is less than 10.5 hours, preferably 3 to 10.5 hours, more preferably 6 to 10.5 hours, and particularly preferably 6 to 10 hours.

  Hereinafter, embodiments of the sodium secondary battery of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to what was shown to the following Example, In the range which does not change the meaning and scope of this invention, it can change suitably and can implement.

  Examples 1 to 10 are shown below. Examples 1 and 2 are examples in which a sodium secondary battery was prepared using an organic electrolyte using an organic solvent, and Examples 3 to 10 were sodium secondary batteries using a positive electrode material subjected to ball milling. This is an example of manufacturing a battery.

(Example 1 and Example 2)
This example is an example using methyl orange as a positive electrode material (Example 1) and an example using methyl red sodium as a positive electrode material (Example 2).

(I) Production of sodium secondary battery A sodium secondary battery was produced by the following procedure.

  The positive electrode is a commercially available reagent, methyl range powder (manufactured by Kishida Chemical) [Example 1] or methyl red sodium salt powder (manufactured by Merck) [Example 2], acetylene black powder (manufactured by Denki Kagaku Kogyo Co., Ltd.), and polytetrafluoro Ethylene (PTFE) powder (manufactured by Daikin) at a weight ratio of 70: 25: 5 is sufficiently pulverized and mixed using a roughing machine, and then roll-molded to form a sheet pellet-shaped electrode (thickness: 0.5 mm). This sheet-like electrode was cut out into a circle having a diameter of 15 mm. The negative electrode was produced by pressing a sodium reagent (manufactured by Kanto Chemical Co., Ltd.), which is a commercially available reagent, to a thickness of 0.8 mm and molding it into a circular sheet having a diameter of 15 mm. The electrolyte was sodium bistrifluoromethane at a concentration of 1 mol / L in a mixed solvent prepared by mixing ethylene carbonate (EC) (manufactured by Kishida Chemical) and dimethyl carbonate (DMC) (manufactured by Kishida Chemical) at a volume ratio of 1: 1. It was prepared by dissolving methanesulfonylimide (NaTFSI) (manufactured by Kishida Chemical). The separator was made of polypropylene (made by Celgard) for lithium secondary batteries.

  As the sodium secondary battery, a 2320 coin type battery as shown in FIG. 3 was manufactured. For the positive electrode, the above-mentioned pellet electrode was set in the positive electrode case 4, covered with a titanium mesh (manufactured by Niraco) (not shown), and the peripheral edge thereof was fixed by spot welding. The negative electrode was prepared by fixing a titanium mesh (manufactured by Niraco) (not shown) to the negative electrode case 6 by spot welding and fixing a sodium sheet thereon by pressure bonding. Next, the separator 2 is set in the positive electrode case to which the pellet is fixed, the electrolytic solution is injected into the separator 2, and the negative electrode case to which the sodium sheet is fixed is covered, and the positive electrode case 4 and the negative electrode case 6 are covered with a coin cell caulking machine. By crimping, a coin cell including a polypropylene gasket 5 was produced. The sodium secondary battery was produced in an argon atmosphere glove box having a dew point of −85 ° C. or lower.

(Ii) Charge / Discharge Test The charge / discharge test of the sodium secondary battery was conducted by applying 0.5 mA / cm ² at a current density per effective area of the positive electrode using a commercially available charge / discharge measurement system (made by Hokuto Denko). The charge / discharge test was performed in a voltage range of a charge end voltage of 3.5 V and a discharge end voltage of 2.0 V (or 1.5 V). The battery charge / discharge test was performed in a thermostatic chamber at 25 ° C. (atmosphere was in a normal living environment).

  A charge / discharge curve of the sodium secondary battery produced in this example is shown in FIG. From the figure, both Example 1 and Example 2 had small irreversible capacity (difference between charge capacity and discharge capacity), and the sodium secondary battery according to the present invention could be charged and discharged.

  In Example 1 using methyl orange, the initial discharge capacity was 73 mAh / g (normalized per weight of methyl orange powder), and in Example 2 using methyl red sodium salt, the initial discharge capacity was 87 mAh / g. g (normalized per weight of methyl red sodium salt powder). The average discharge voltage was 2.5 V in Example 1 and 2.4 V in Example 2. Table 1 shows the discharge capacity retention rates at the 20th and 50th cycles. From the table, it can be seen that only about 0.4% capacity reduction per cycle is seen, and that stable cycle characteristics are obtained.

  As mentioned above, it turned out that the sodium secondary battery by Example 1 and Example 2 is excellent in cycling characteristics, and can be charged / discharged. However, the decrease in discharge voltage during energization from the open circuit was great in both examples. This is thought to be due to the low conductivity of methyl orange and methyl red sodium salts.

(Examples 3 to 6)
In this example, methyl orange powder and acetylene black powder were pulverized and mixed with a ball mill (BM) (ball mill treatment) to improve battery performance.

  Methyl orange powder and acetylene black powder (weight ratio 70:25) were mixed in a mixer for about several minutes. A zirconia ball having a diameter of 7 mm was added to this mixture, and BM treatment was performed for 3 hours (Example 3), 6 hours (Example 4), 6.5 hours (Example 5), and 10 hours (Example 6). went. In any BM treatment, the mixing ratio of the methyl orange-acetylene black mixture and the ball was 1:10 by weight, and the rotation speed during the BM treatment was 500 rpm.

  A PTFE binder was further added to the obtained methyl orange-acetylene black mixture after the BM treatment, and the mixture was mixed with a rake machine to produce positive electrode pellets in the same manner as in Examples 1 and 2. Using this pellet, a coin cell was produced in the same manner as in Examples 1 and 2 above. The charge / discharge test was also performed in the same manner as in Examples 1 and 2 above.

  The results of the charge / discharge test are shown in Table 2 (in Table 2, the results of Example 1 are also shown for reference). The characteristics improved until the BM treatment time was 6 hours (6 hours). In addition, in the BM treatment for 6 hours, the discharge capacity retention rate after 50 cycles achieved a high value of 95% and a high discharge voltage. This is presumably because the BM treatment improved the contact between the methyl orange powder and the acetylene black powder, and the interfacial resistance between the powders decreased. On the other hand, the battery performance such as the discharge capacity deteriorated in the BM treatment exceeding 6 hours. This is presumably because methyl orange was decomposed due to local heat generation during BM treatment. Thus, in this invention, it became clear by carrying out BM treatment of the active material of positive electrode material, the fall of the discharge voltage at the time of electricity supply was suppressed, and the battery performance regarding discharge voltage and discharge capacity improved. However, with regard to the BM treatment, the optimum conditions differ depending on the particle size of the sample and the material and size of the ball to be used. Therefore, it is considered that optimization is necessary in each case.

(Examples 7 to 10)
An attempt was made to improve battery performance by pulverizing and mixing methyl red sodium salt powder and acetylene black powder with a ball mill (BM) (ball mill treatment).

  Methyl red sodium salt powder and acetylene black powder (weight ratio 70:25) were mixed in a mixer for several minutes. To this mixture, a zirconia ball having a diameter of 7 mm was added, 3 hours (Example 7), 6 hours (Example 8), 10 hours (Example 9), 10.5 hours (Example 10), 12 hours ( The BM treatment of Example 11) was performed. In any BM treatment, the mixing ratio of the methyl red sodium salt-acetylene black mixture and the ball was 1:10 by weight, and the rotation speed during the BM treatment was 300 rpm.

  The obtained BM-treated methyl red sodium salt-acetylene black mixture was added with a PTFE binder and mixed with a coarse machine to produce positive electrode pellets in the same manner as in Examples 1 and 2. Using this pellet, a coin cell was produced in the same manner as in Examples 1 and 2, and a charge / discharge test was performed.

  The results of the charge / discharge test are shown in Table 3 (in Table 3, the results of Example 2 above are also described for reference). When the BM treatment time was 3 hours, the same effect as in Example 2 was observed. After 6 hours, the characteristics were improved, and the discharge capacity retention ratio after 50 cycles achieved a high value of 94% and a high discharge voltage. This is presumably because the contact property between the methyl red sodium salt powder and the acetylene black powder was improved by the BM treatment, and the interfacial resistance between the powders was reduced. On the other hand, in the BM treatment exceeding 10 h, battery performance such as discharge capacity was lowered. This is presumably because methyl red sodium salt was denatured due to local heat generation during BM treatment. Thus, in this invention, it became clear by carrying out BM treatment of the active material of positive electrode material, the fall of the discharge voltage at the time of electricity supply was suppressed, and the battery performance regarding discharge voltage and discharge capacity improved. However, with regard to the BM treatment, the optimum conditions differ depending on the particle size of the sample and the material and size of the ball to be used. Therefore, it is considered that optimization is necessary in each case.

(Example 12 and Example 13)
NASICON (Na ₃ Zr ₂ Si ₂ PO ₁₂ ) as a solid electrolyte, amorphous carbon as a negative electrode material, and a methyl orange-acetylene black mixture (Example 12) produced under the conditions of Examples 4 and 9 as a positive electrode, and methyl red A sodium salt-acetylene black mixture (Example 13) was used, respectively.

The NASICON disk was prepared by the following procedure. First, ZrO (NO ₃ ) ₂ · 8H ₂ O (Kanto Chemical Co., Inc.), NH ₄ H ₂ PO ₄ (Kanto Chemical Co., Ltd.), and Na ₂ SiO ₃ · 9H ₂ O (Kanto Chemical Co., Ltd.) : Zr: Si: P = 3: 2: 2: 1 were mixed at a molar ratio, and calcined at 850 ° C. The obtained powder was molded into a disk shape by a pellet molding machine and subjected to main firing at 1100 ° C. for 24 hours.

  A coin cell was fabricated in the same manner as in Example 1. The solid electrolyte was produced in a disk (thickness: about 1 mm) shape so as to be accommodated in the coin cell, and set in the separator 2 part of FIG. Also, a disc-shaped spacer made of the same material as the coin cell of an arbitrary thickness was welded to the coin cell case so that no gap was formed at each interface of the positive electrode / solid electrolyte / negative electrode.

In the battery discharge test, in the same manner as in Example 1, 0.5 mA / cm ² was applied at a current density per effective area of the positive electrode using a commercially available discharge charge measurement system, and the charge end voltage was 3.5 V. A charge / discharge test was conducted in a voltage range of a discharge end voltage of 2.0V.

  Table 4 shows the results of the charge / discharge test. Compared with Examples 4 and 9, the contact resistance at the positive electrode / electrolyte and negative electrode / electrolyte interface increases, so the voltage shows a decrease of 0.3 to 0.5 V, and the discharge capacity also decreases slightly. did. However, there was no change in the cycle stability indicated by the discharge capacity. According to this example, it was confirmed that the sodium secondary battery of the present invention including the solid electrolyte was operable.

(Example 14 and Example 15)
Methyl orange-acetylene black mixture (Example 14) prepared as a polymer electrolyte using PEO polymer electrolyte membrane, amorphous carbon as negative electrode material, and Examples 4 and 9 as positive electrode, and methyl red sodium salt-acetylene A black mixture (Example 15) was used respectively.

  A PEO-based electrolyte membrane (thickness: about 2 mm) was prepared by the following procedure.

First, PEO (Aldrich, Mw = 6 × 10 ⁵ ) and LiTFSI (Kishida Chemical) as a solute are 10 wt% BaTiO ₃ filler (BaTiO ₃ manufactured by Aldrich) so that Li / O = 1/18. Reagent (with particle size: <2 μm)) was added to the acetonitrile solvent (Kishida Chemical). After stirring overnight, the resulting solution was applied on a PTFE plate to completely volatilize acetonitrile. Then, it dried at 90 degreeC under vacuum for 12 hours.

  A coin cell was fabricated in the same manner as in Example 1. The polymer electrolyte was cut out in a disk shape so as to fit in the coin cell, and set in the separator 2 part of FIG. Also, a disc-shaped spacer made of the same material as the coin cell of an arbitrary thickness was welded to the coin cell case so that no gap was formed at each interface of the positive electrode / solid electrolyte / negative electrode.

In the battery discharge test, in the same manner as in Example 1, 0.5 mA / cm ² was applied at a current density per effective area of the positive electrode using a commercially available discharge charge measurement system, and the charge end voltage was 3.5 V. A charge / discharge test was conducted in a voltage range of a discharge end voltage of 2.0V.

  Table 5 shows the results of the charge / discharge test. Compared with Examples 4 and 9, the contact resistance at the positive electrode / electrolyte and negative electrode / electrolyte interface increases, so the voltage shows a decrease of 0.1 to 0.2 V, and the discharge capacity also decreases slightly. did. However, there was no change in the cycle stability indicated by the discharge capacity. This example confirmed that the sodium secondary battery of the present invention containing a polymer electrolyte was operable.

(Comparative example)
As a comparative example, a sodium secondary battery using a positive electrode material containing a rare metal was produced. NaCoO ₂ was evaluated as a positive electrode material. NaCoO ₂ was synthesized by mixing Na ₂ CO ₃ and Co ₃ O ₄ at a predetermined molar ratio (3: 2) and firing at 1000 ° C.

Coin cells using NaCoO ₂ were produced and evaluated in the same manner as in Examples 1 and 2 above. The results are shown in Table 6 in comparison with Examples 4 and 9.

  Compared with Examples 4 and 9, the battery according to this comparative example showed excellent characteristics in terms of voltage and discharge capacity. However, the capacity decrease due to the charge / discharge cycle was significant, and only about 30% of the initial discharge capacity was obtained after 100 cycles.

On the other hand, in the case of Examples 4 and 9, the initial performance is inferior to that of the comparative example (however, the characteristics as a secondary battery are sufficient), but the discharge capacity is about 88% after 100 cycles. It was found that the stability was high. In the case of NaCoO ₂ , the elution of Co, which is a transition metal, has occurred, which is considered to have caused a decrease in capacity.

  As described above, it was found that the sodium secondary battery according to the present invention is a high-performance battery having excellent cost performance and excellent charge / discharge cycle characteristics.

  According to the present invention, a sodium secondary battery having excellent cost performance and cycle characteristics can be manufactured, and the sodium secondary battery of the present invention can be used as a drive source for various electronic devices.

1 Positive electrode 2 Separator (impregnated with electrolyte)
3 Negative electrode 4 Positive electrode case 5 Gasket 6 Negative electrode case

Claims (5)

A positive electrode containing a substance capable of inserting and removing sodium ions;
A sodium secondary battery comprising a negative electrode containing metallic sodium, a sodium-containing substance, or a substance capable of inserting and removing sodium ions, and an electrolyte having sodium ion conductivity,
A substance capable of inserting and removing sodium ions from the positive electrode is represented by the following formula (I):

A sodium secondary battery characterized by being methyl orange represented by A positive electrode containing a substance capable of inserting and removing sodium ions;
A sodium secondary battery comprising a negative electrode containing metallic sodium, a sodium-containing substance, or a substance capable of inserting and removing sodium ions, and an electrolyte having sodium ion conductivity,
A substance capable of inserting and removing sodium ions from the positive electrode is represented by the following formula (II):

A sodium secondary battery characterized by being a methyl red sodium salt represented by the formula:   2. The sodium secondary battery according to claim 1, wherein the positive electrode is a material including the methyl orange and carbon particles and subjected to a ball mill treatment.   3. The sodium secondary battery according to claim 2, wherein the positive electrode is a material that includes the methyl red sodium salt and carbon particles and is ball milled. A method for manufacturing a sodium secondary battery, comprising:
The sodium secondary battery is
A positive electrode comprising a substance capable of inserting and desorbing sodium ions and a positive electrode material comprising carbon particles;
A negative electrode containing metallic sodium, a sodium-containing substance, or a substance capable of inserting and removing sodium ions, and an electrolyte having sodium ion conductivity,
The substance capable of inserting and desorbing sodium ions in the positive electrode is methyl orange represented by the following formula (I), or

Methyl red sodium salt represented by the following formula (II):

The method
(A) preparing the positive electrode;
(B) preparing the negative electrode;
(C) preparing the electrolyte;
(D) producing a sodium secondary battery from the positive electrode, the negative electrode and the electrolyte,
The step of preparing the positive electrode includes a step of preparing a positive electrode material by mixing the substance capable of inserting and desorbing sodium ions and a carbon particle with a ball mill. .

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