JPWO2012035648A1 - Non-aqueous electrolyte secondary battery active material and non-aqueous electrolyte secondary battery - Google Patents

Abstract

An active material for a non-aqueous electrolyte secondary battery using a sodium salt and excellent in reversibility, and a non-aqueous electrolyte secondary battery using the same are provided. The positive electrode active material is a complex metal oxide containing Na, and the oxide containing Mn and Ni retains a stable crystal structure with Na having a large ionic radius, and the reversibility of the storage and release reaction of Na ions during charge and discharge. Further, the compound having at least one aromatic carboxylic acid sodium salt structure is less likely to cause metal precipitation of Na, and the reversibility of the charge / discharge reaction is preferable.

Description

  The present invention relates to an active material for a non-aqueous electrolyte secondary battery using a sodium salt, and a non-aqueous electrolyte secondary battery using the same.

  A lithium ion battery using a lithium salt as an electrolyte has a high output density such as a high energy density, and is therefore widely used as a power source for notebook personal computers and portable devices. In addition, against the background of environmental problems in recent years, development of electric vehicles and hybrid vehicles using lithium ion batteries is being promoted. Furthermore, in order to effectively use natural energy such as solar power generation and wind power generation, application to a storage system of a lithium ion battery is expected. However, since lithium, cobalt, and the like used in the lithium ion battery have a small amount of resources and are limited in the country of origin and region, it is necessary to develop a high performance secondary battery using a material that can be secured stably.

  As a non-aqueous electrolyte secondary battery using an alkali metal other than lithium, Patent Document 1 discloses a negative electrode active material using sodium / lead alloy and a positive electrode active material using sodium / cobalt oxide. .

JP-A-4-6759

  Since sodium is abundant in resources, secondary batteries using sodium as an ion carrier can be widely used in large-scale power storage devices and systems such as electric vehicles, hybrid vehicles, solar power generation and wind power generation. In these applications, extending the life of secondary batteries is the biggest issue.

  Accordingly, an object of the present invention is to provide a novel positive electrode active material and negative electrode active material capable of stably and reversibly occluding and releasing sodium ions having a larger ionic radius than lithium ions.

  As a result of intensive studies by the present inventors in order to solve the above-mentioned problems, by using a composite metal oxide containing Na, Mn and Ni as a positive electrode active material, it is possible to maintain Na having a large ionic radius and a stable crystal structure. It has been found that it is particularly excellent in reversibility of the absorption and release reaction of Na ions in charge and discharge. Further, by using sodium salt of aromatic conjugated carboxylic acid compound or sodium salt of compound having aromatic conjugated carboxylic acid as a structural unit as a negative electrode active material, Na metal precipitation is less likely to occur, and charge / discharge reaction It was found to be excellent in reversibility.

  That is, the present invention includes the following inventions.

(1) A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a composite metal oxide containing Na, Ni and Mn.

(2) The composite metal oxide has the general formula (I):
Na _α Ni _β-g Mn _γ-h M ′ _{g + h} O ₂ (I)
[Where
M ′ is at least one selected from the group consisting of Al, Mg and Co;
α is in the range of 0 <α ≦ 0.5,
β is in the range of 2/9 ≦ β ≦ 1/4,
γ is in the range of 3/4 ≦ γ ≦ 7/9,
g is in the range of 0 ≦ g ≦ 0.045,
h is in the range of 0 ≦ h ≦ 0.045,
β + γ + g + h is 1]
The positive electrode active material for nonaqueous electrolyte secondary batteries according to (1), represented by:

(3) The composite metal oxide has the general formula (II):
Na _4-a Ni _2-x Mn _7-y M ′ _{x + y} O ₁₈ (II)
[Where
M ′ is at least one selected from the group consisting of Al, Mg and Co;
a is in the range of 0 ≦ a <4,
x is in the range of 0 ≦ x ≦ 0.4,
y is in the range of 0 ≦ y ≦ 0.4]
The positive electrode active material for a non-aqueous electrolyte secondary battery according to (2), represented by:

(4) The composite metal oxide has the general formula (III):
Na _2-b Ni _1-p Mn _3-q M ′ _{p + q} O ₈ (III)
[Where
M ′ is at least one selected from the group consisting of Al, Mg and Co;
b is in the range of 0 ≦ b <2,
p is in the range of 0 ≦ p ≦ 0.1,
q is within the range of 0 ≦ q ≦ 0.1]
The positive electrode active material for a non-aqueous electrolyte secondary battery according to (2), represented by:

(5) Nonaqueous electrolyte solution 2 having a positive electrode containing the positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of (1) to (4) and a negative electrode that reversibly occludes and releases sodium ions. Next battery.

(6) The nonaqueous electrolyte secondary battery according to (5), wherein the negative electrode reversibly occluding and releasing sodium ions includes a compound having at least one aromatic carboxylic acid sodium salt structure as a negative electrode active material.

(7) A compound having at least one aromatic carboxylic acid sodium salt structure is represented by the general formula (IV):
C ₆ H ₄ (CO ₂ Na _{1 + c} ) ₂ (IV)
[Wherein c is in the range of 0 ≦ c ≦ 1]
The nonaqueous electrolyte secondary battery according to (6), represented by:

(8) A negative electrode active material for a nonaqueous electrolyte secondary battery comprising a compound having at least one aromatic carboxylic acid sodium salt structure.

(9) The compound having at least one aromatic carboxylic acid sodium salt structure is represented by the general formula (IV):
C ₆ H ₄ (CO ₂ Na _{1 + c} ) ₂ (IV)
[Wherein c is in the range of 0 ≦ c ≦ 1]
The negative electrode active material for a nonaqueous electrolyte secondary battery according to (8), represented by:

(10) A nonaqueous electrolyte secondary battery comprising a negative electrode comprising the negative electrode active material for a nonaqueous electrolyte secondary battery according to (8) or (9) and a positive electrode capable of reversibly occluding and releasing sodium ions.

  ADVANTAGE OF THE INVENTION According to this invention, the active material material for nonaqueous electrolyte secondary batteries excellent in the reversibility of charging / discharging using sodium as an ion carrier of a nonaqueous electrolyte, and a nonaqueous electrolyte secondary using the same Battery can be provided.

It is a figure which shows a cylindrical nonaqueous electrolyte secondary battery. It is a figure which shows a coin type non-aqueous electrolyte secondary battery. It is a figure which shows the maintenance factor with respect to the rated capacity in connection with progress of the charging / discharging cycle of the nonaqueous electrolyte secondary battery of a present Example. It is a figure which shows the maintenance factor with respect to the rated capacity in connection with progress of the charging / discharging cycle of the nonaqueous electrolyte secondary battery of a present Example. It is a figure which shows the maintenance factor with respect to the rated capacity in connection with progress of the charging / discharging cycle of the nonaqueous electrolyte secondary battery of a present Example.

  Hereinafter, the present invention will be described in detail.

1. Cathode Active Material The cathode active material for a non-aqueous electrolyte secondary battery according to the present invention is a composite metal oxide containing Na, Ni and Mn, and preferably has the general formula (I):
Na _α Ni _β-g Mn _γ-h M ′ _{g + h} O ₂ (I)
[Where
M ′ is at least one selected from the group consisting of Al, Mg and Co;
α is in the range of 0 <α ≦ 0.5,
β is in the range of 2/9 ≦ β ≦ 1/4,
γ is in the range of 3/4 ≦ γ ≦ 7/9,
g is in the range of 0 ≦ g ≦ 0.045,
h is in the range of 0 ≦ h ≦ 0.045,
β + γ + g + h is 1]
It is a complex metal oxide represented by.

  The value of α representing the amount of Na varies depending on charge / discharge. That is, the deintercalation of Na ions occurs due to charging, and the value of α decreases, and the intercalation of Na ions occurs due to discharge, and the value of α increases.

As one form of the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention, a general formula:
Na _4-a Ni _2-x Mn _7-y M ′ _{x + y} O ₁₈ (II)
[Where
M ′ is at least one selected from the group consisting of Al, Mg and Co;
a is in the range of 0 ≦ a <4,
x is in the range of 0 ≦ x ≦ 0.4,
y is in the range of 0 ≦ y ≦ 0.4]
The composite metal oxide represented by these can be mentioned.

  The value of a representing the amount of Na varies depending on charging and discharging. That is, Na ion deintercalation occurs due to charging, and the value of a increases, and Na ion intercalation occurs due to discharge, and the value of a decreases.

Na _{4 -a} Ni _{2 -x} Mn _{7 -y} M ' _{x + y} O ₁₈ is the diagonal of Na ₄ Mn ₄ Ti ₅ O ₁₈ reported in Acta Crystallographica Section B, Vol. 24, pages 1114 to 1120 (1968). Similar to crystal structure. This crystal is a complex oxide of trivalent and tetravalent metals and Na, and has a large tunnel space in the crystal structure. The positive electrode active material of the present invention is mainly a Ni-containing composite metal oxide to which Ni and Mn, and in some cases, a metal M ′ for stabilizing the crystal structure is added. ^Presumed to be divalent (Ni ²⁺ ) and tetravalent (Mn ⁴⁺ ). In the deintercalation of Na ions, which is a charging reaction, the valence of Ni is considered to change from divalent to tetravalent (Ni ⁴⁺ ). At this time, it is considered that Na ions move through the large tunnel space in the crystal structure and are released to the electrolyte side. On the other hand, in the discharge, it is considered that a reaction occurs in which the valence of Ni changes from tetravalent to divalent. On the other hand, the valence of tetravalent Mn does not change, and thus it is thought that this maintains a stable crystal structure that is not affected by large Na ions. Moreover, since the potential of Ni oxidation-reduction reaction (Ni ²⁺ ⇔Ni ⁴⁺ + 2e ⁻ ) is high and reversible, it is considered that a secondary battery having a high voltage and a long life can be obtained as a result.

M ′ is an additive element as described above, and is at least one selected from Al, Mg, and Co. In any case, the bonding strength with oxygen is large, and by substituting these with a part of the Ni or Mn site, the crystal structure becomes more stable, which is desirable. The values of x and y representing the substitution amount to the Ni or Mn site are preferably in the range of 0 ≦ x ≦ 0.4 and 0 ≦ y ≦ 0.4. When the value of x or y exceeds 0.4, impurities such as by-products and unreacted raw materials remain, and the reversibility is impaired. As a by-product, it is considered that a small amount of NaMO ₂ (M = Ni, Mn, Al, Co) is contained. This is a very small amount and may not be confirmed by a powder X-ray diffraction method. In this case, it can be confirmed by a transmission electron microscope. The value of x + y representing the added amount of M ′ is preferably in the range of 0 ≦ x + y ≦ 0.8, and more preferably in the range of 0 ≦ x + y ≦ 0.4. In order to stabilize the crystal structure and further improve the reversibility of charge / discharge, the range of 0 <x + y ≦ 0.8 is desirable, and the range of 0 <x + y ≦ 0.4 is more desirable. desirable.

  In synthesizing the positive electrode active material represented by the above general formula (II), there is a concern that sodium may be scattered in the course of mixing and firing each raw material. Therefore, in some cases, sodium carbonate, sodium oxide, sodium hydroxide, or the like, which is a sodium raw material, is slightly excessive with respect to the stoichiometric ratio in the charged composition of each raw material. However, since the above-mentioned by-products may be slightly generated due to these reasons, it is desirable to determine the raw material charge in consideration of the product composition after firing.

As another form of the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention, the general formula (III):
Na _2-b Ni _1-p Mn _3-q M ′ _{p + q} O ₈ (III)
[Where
M ′ is at least one selected from the group consisting of Al, Mg and Co;
b is in the range of 0 ≦ b <2,
p is in the range of 0 ≦ p ≦ 0.1,
q is within the range of 0 ≦ q ≦ 0.1]
The composite metal oxide represented by these can be mentioned.

  The value of b representing the amount of Na varies depending on charging and discharging. That is, deintercalation of Na ions occurs due to charging, the value of b increases, and intercalation of Na ions occurs due to discharge, and the value of b decreases.

Na _2-b Ni _1-p Mn _3-q M ′ _{p + q} O ₈ has a spinel crystal structure, mainly containing Ni and Mn, and in some cases, a metal M ′ for stabilizing the crystal structure. This is an added Na-containing composite metal oxide. Similarly to the above, in order to obtain a complex oxide with Na having a large ionic radius, it is desirable to combine Ni as a metal that forms a complex oxide with stable tetravalent Mn.

Ni is presumed to be mainly divalent (Ni ²⁺ ) in a discharged state, and it is considered that the ^{deintercalation of} Na ions, which is a charging reaction, changes from divalent to tetravalent (Ni ⁴⁺ ). In discharge, conversely, it is considered that a reaction occurs in which the valence of Ni changes from tetravalent to divalent. Such an oxidation-reduction reaction (Ni ²⁺ ⇔Ni ⁴⁺ + 2e ⁻ ) has a high reaction potential and excellent reversibility, and as a result, a secondary battery having a high voltage and a long life can be obtained. On the other hand, Mn is presumed to be tetravalent (Mn ⁴⁺ ), and is inactive in the charge / discharge reaction, so that it maintains tetravalence and thus contributes to stabilization of the crystal structure.

As described above, M ′ is an additive element and is at least one selected from Al, Mg and Co. In any case, the bonding strength with oxygen is large, and by substituting these with a part of the Ni or Mn site, the crystal structure becomes more stable, which is desirable. The values of p and q representing the substitution amount to the Ni or Mn site are desirably in the range of 0 ≦ p ≦ 0.1 and 0 ≦ q ≦ 0.1. When the value of p or q exceeds 0.1, impurities such as by-products and unreacted raw materials remain, and the reversibility is impaired. As a by-product, it is considered that a small amount of NaMO ₂ (M = Ni, Mn, Al, Co) is contained. This is a very small amount and may not be confirmed by a powder X-ray diffraction method. In this case, it can be confirmed by a transmission electron microscope. The value of p + q representing the amount of M ′ added is preferably in the range of 0 ≦ p + q ≦ 0.2. In order to stabilize the crystal structure and further improve the reversibility of charge / discharge, it is desirable that the range is 0 <p + q ≦ 0.2.

  When synthesizing the positive electrode active material represented by the above general formula (III), there is a concern that sodium is scattered in the process of mixing and firing each raw material, or that a deoxygenation reaction occurs when the temperature is lowered after firing. Is done. Therefore, in some cases, in the charge composition of each raw material, sodium carbonate, sodium oxide or sodium hydroxide, which is a sodium raw material, is slightly excessive with respect to the stoichiometric ratio, or oxidation with a high oxygen partial pressure. Firing is performed in a sexual atmosphere. However, since the above-mentioned by-products may be slightly generated due to these reasons, it is desirable to determine the raw material charge in consideration of the product composition after firing.

2. Nonaqueous electrolyte negative active material for a secondary battery according to the anode active material present invention is composed of a compound having at least one aromatic carboxylic acid sodium salt structure. Here, the “aromatic carboxylic acid sodium salt structure” means a structure in which a carboxyl group is directly bonded to an aromatic ring and the carboxyl group forms a sodium salt.

  The compound having at least one aromatic sodium carboxylate structure preferably has 1 to 10, more preferably 1 to 5, and particularly preferably one. preferable.

  Examples of the aromatic ring include aromatic hydrocarbon rings such as benzene, naphthalene, anthracene, phenanthrene, tetracene, and pyrene, and aromatic heterocycles such as pyridine, pyrazine, and pyrimidine.

  In the compound having at least one aromatic carboxylic acid sodium salt structure, an even number (particularly two) of sodium salts of carboxyl groups are preferably substituted on the aromatic ring. In addition, the distance between even number (particularly two) carboxyl groups (that is, the number of carbon atoms present between one carboxyl group and another carboxyl group) includes the carbon atoms substituted, An even number is preferable, and 2, 4, or 6 is particularly preferable.

The C═O part of a sodium salt of a carboxyl group (—C (═O) ONa) is conjugated with an aromatic ring, and binds and dissociates with Na. That is, the C = O part of the sodium salt of the carboxyl group and Na are bound and dissociated,
−C (═O) ONa + Na ⁺ + e ⁻ ⇔ = C (ONa) ₂
When this reaction occurs reversibly, Na ions are occluded and released. Since the reaction potential at this time is about 1.0 V noble potential from the equilibrium potential of Na metal, there is a feature that precipitation of Na hardly occurs. When used as a negative electrode active material, the reversibility becomes extremely worse when metal Na is deposited, but the negative electrode active material of the present invention does not cause such a side reaction and has excellent reversibility.

Examples of the compound having at least one aromatic carboxylic acid sodium salt structure include, for example, the following formula:

[Where
l is an integer of 1 or more, preferably an integer of 1 to 10, more preferably an integer of 1 to 5, particularly preferably 1.
R1 and R2 are independently of each other hydrogen, an alkyl group, an aryl group, or an alkoxyl group, preferably hydrogen, a _C1-3 alkyl group, a phenyl group, or a _C1-3 alkoxyl group, especially Preferred is hydrogen]

[Where
m is an integer of 1 or more, preferably an integer of 1 to 10, more preferably an integer of 1 to 5, particularly preferably 1.
R3 and R4, independently of each other, are hydrogen, an alkyl group, an aryl group, or an alkoxyl group, preferably hydrogen, a _C1-3 alkyl group, a phenyl group, or a _C1-3 alkoxyl group, particularly Preferred is hydrogen]

[Where
n is an integer greater than or equal to 1, Preferably it is an integer of 1-10, More preferably, it is an integer of 1-5, Most preferably, it is 1.
R5 and R6 are independently of each other hydrogen, an alkyl group, an aryl group, or an alkoxyl group, preferably hydrogen, a _C1-3 alkyl group, a phenyl group, or a _C1-3 alkoxyl group, especially Preferred is hydrogen]
The compound represented by these can be mentioned.

In particular, a negative electrode active material represented by the chemical formula C ₆ H ₄ (CO ₂ Na _{1 + c} ) ₂ (0 ≦ c ≦ 1) is particularly desirable because of its excellent reversibility and large Na storage / release capacity. Here, the value of c representing the amount of Na varies depending on charging and discharging. That is, the value of c is increased when Na ions are bound by charging, and the value of c is decreased when Na ions are dissociated by discharging.

3. Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery according to the present invention includes only one of a positive electrode including the positive electrode active material according to the present invention and a negative electrode including the negative electrode active material according to the present invention. You may have as a positive electrode or a negative electrode, and both the positive electrode and negative electrode may contain the active material which concerns on this invention.

It is not necessary to use a special electrolyte as the electrolyte used in the non-aqueous electrolyte secondary battery according to the present invention. For example, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), methyl acetate (MA), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), dimethoxyethane (DME), etc., and sodium hexafluorophosphate (NaPF) as an electrolyte _6), tetrafluoride sodium borate (NaBF _4), can be used after dissolved, sodium perchlorate (NaClO _4). The electrolyte concentration is preferably 0.5 to 1.5 M (mol / l).

  The use of the reversibly chargeable / dischargeable battery according to the present invention is not particularly limited. , Pager, handy terminal, portable copy, electronic notebook, calculator, LCD TV, electric shaver, electric tool, electronic translator, car phone, transceiver, voice input device, memory card, backup power supply, tape recorder, radio, headphone stereo, Power supplies for portable printers, handy cleaners, portable CDs, video movies, navigation systems, refrigerators, air conditioners, TVs, stereos, water heaters, microwave ovens, dishwashers, washing machines, dryers, game machines, lighting Equipment, toys, roadco Conditioners, medical equipment, automobiles, electric automobiles, golf carts, electric carts, can be used as a power source such as a power storage system. It can also be used for civilian use, military use, and space use.

  FIG. 1 is a diagram showing an outline of a cylindrical nonaqueous electrolyte secondary battery. In FIG. 1, 10 is a positive electrode, 11 is a separator, 12 is a negative electrode, 13 is a battery can, 14 is a positive electrode tab, 15 is a negative electrode tab, 16 is an inner lid, 17 is an internal pressure release valve, 18 is a gasket, and 19 is a PTC element. , 20 is an outer lid.

  FIG. 2 is a diagram showing an outline of a coin-type non-aqueous electrolyte secondary battery. In FIG. 2, 21 is a positive electrode, 22 is a negative electrode, 23 is a separator, 24 is a coin case, 25 is an upper lid, and 26 is a gasket.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, the technical scope of this invention is not limited to this.

<Preparation of positive electrode active material>
The composition of the positive electrode active material prepared in the following examples, comparative examples and reference examples was measured by an inductively coupled plasma method (ICP).

Example 1
Na ₂ CO ₃ , NiO, and MnO ₂ were used as raw materials for the Na ₄ Mn ₄ Ti ₅ O ₁₈ type orthorhombic positive electrode active material of this example. Na ₂ CO ₃ , NiO, and MnO ₂ were mixed at a weight ratio (wt%) of 21.9: 15.4: 62.7 and mixed at room temperature for 15 h using a ball mill. This was held at 150 ° C. for 1 h in the air atmosphere and further held at 470 ° C. for 5 h, and then fired in an oxygen atmosphere at 1050 ° C. for 20 h. The composition of the obtained positive electrode active material is Na ₄ Ni ₂ Mn ₇ O ₁₈ . Then, the positive electrode active material of Example 1 whose average particle diameter is 11 micrometers was obtained by grind | pulverizing with a ball mill and classifying with a sieve.

Example 2
Each of Al, Mg, and Co was added as a substitution element to the positive electrode active material synthesized in Example 1. In addition to Na ₂ CO ₃ , NiO, and MnO ₂ of Example 1, Al (OH) ₃ , MgO, or Co ₃ O ₄ was used as a raw material. First, Na ₂ CO ₃ , NiO, and MnO ₂ were combined at a weight ratio (wt%) of 22.7: 16.0: 61.4, and mixed at room temperature for 15 hours using a ball mill to prepare a mixed raw material. Next, this mixed raw material and Al (OH) ₃ , MgO, or Co ₃ O ₄ were mixed at a weight ratio (wt%) of 96.8: 3.2, 98.3: 1.7, or 96.7: 3.3, respectively, and three types The substitution element addition mixed raw material of this was prepared. Each was held at 150 ° C. for 1 h in the air atmosphere and further held at 470 ° C. for 5 h, and then calcined by holding at 1050 ° C. for 20 h in an oxygen atmosphere. The composition of the obtained three types of positive electrode active materials is Na ₄ Ni ₂ Mn _6.6 Al _0.4 O ₁₈ , Na ₄ Ni ₂ Mn _6.6 Mg _0.4 O ₁₈ , or Na ₄ Ni ₂ Mn _6.6 Co _0.4 O ₁₈ . Then, the positive electrode active material of Example 2 whose average particle diameter is 10 micrometers was obtained by grind | pulverizing with a ball mill and classifying with a sieve.

Example 3
A positive electrode active material was synthesized in the same manner as in Example 2. First, Na ₂ CO ₃ , NiO, and MnO ₂ were combined at a weight ratio (wt%) of 22.5: 12.7: 64.7, and mixed at room temperature for 15 hours using a ball mill to prepare a mixed raw material. Next, this mixed raw material and Al (OH) ₃ , MgO, or Co ₃ O ₄ were mixed at a weight ratio (wt%) of 96.8: 3.2, 98.3: 1.7, or 96.7: 3.3, respectively, and three types The substitution element addition mixed raw material of this was prepared. Each was held at 150 ° C. for 1 h in the air atmosphere and further held at 470 ° C. for 5 h, and then calcined by holding at 1050 ° C. for 20 h in an oxygen atmosphere. The composition of the obtained three types of positive electrode active materials is Na ₄ Ni _1.6 Mn ₇ Al _0.4 O ₁₈ , Na ₄ Ni _1.6 Mn ₇ Mg _0.4 O ₁₈ , or Na ₄ Ni _1.6 Mn ₇ Co _0.4 O ₁₈ . Then, the positive electrode active material of Example 3 whose average particle diameter is 11 micrometers was obtained by grind | pulverizing with a ball mill and classifying with a sieve.

Example 4
A positive electrode active material was synthesized in the same manner as in Example 2. Na ₂ CO ₃ , NiO, and MnO ₂ were combined at a weight ratio (wt%) of 21.9: 15.4: 62.7, and mixed for 15 h at room temperature using a ball mill to prepare a mixed raw material. Next, the mixed raw material and Co ₃ O ₄ were mixed at a weight ratio (wt%) of 96.7: 3.3 and 93.4: 6.6, respectively, to prepare two kinds of mixed element addition mixed raw materials. Each was held at 150 ° C. for 1 h in the air atmosphere and further held at 470 ° C. for 5 h, and then calcined by holding at 1050 ° C. for 20 h in an oxygen atmosphere. The composition of the obtained two types of positive electrode active materials is Na ₄ Ni _1.8 Mn _6.8 Co _0.4 O ₁₈ and Na ₄ Ni _1.6 Mn _6.6 Co _0.8 O ₁₈ . Then, the positive electrode active material of Example 4 whose average particle diameter is 9 micrometers was obtained by grind | pulverizing with a ball mill and classifying with a sieve.

Comparative Example 1
Na ₂ CO ₃ , NiO, and MnO ₂ were combined at a weight ratio (wt%) of 21.9: 15.4: 62.7, and mixed for 15 h at room temperature using a ball mill to prepare a mixed raw material. Next, this mixed raw material and Co ₃ O ₄ were mixed at a weight ratio (wt%) of 91.7: 8.3 to prepare a mixed element-added mixed raw material. After holding at 150 ° C. for 1 hour in an air atmosphere and further holding at 470 ° C. for 5 hours, firing was carried out by holding at 1050 ° C. for 20 hours in an oxygen atmosphere. The composition of the obtained positive electrode active material is Na ₄ Ni _1.5 Mn _6.5 Co _1.0 O ₁₈ . Then, the positive electrode active material of the comparative example 1 whose average particle diameter is 11 micrometers was obtained by grind | pulverizing with a ball mill and classifying with a sieve.

Example 5
Na ₂ CO ₃ , NiO, and MnO ₂ were used as raw materials for the spinel-type positive electrode active material of this example. Na ₂ CO ₃ , NiO, and MnO ₂ were mixed at a weight ratio (wt%) of 24.0: 16.9: 59.1 and mixed at room temperature for 15 h using a ball mill. This was held at 150 ° C. for 1 h in the air atmosphere and further held at 470 ° C. for 5 h, and then calcined by holding at 750 ° C. for 20 h in an oxygen atmosphere. The composition of the obtained positive electrode active material is Na ₄ Ni ₂ Mn ₇ O ₁₈ . Then, the positive electrode active material of Example 5 whose average particle diameter is 9 micrometers was obtained by grind | pulverizing with a ball mill and classifying with a sieve.

Example 6
Each of Al, Mg, and Co was added as a substitution element to the positive electrode active material synthesized in Example 5. In addition to Na ₂ CO ₃ , NiO, and MnO ₂ of Example 5, Al (OH) ₃ , MgO, or Co ₃ O ₄ was used as a raw material. First, Na ₂ CO ₃ , NiO, and MnO ₂ were combined at a weight ratio (wt%) of 24.5: 17.3: 58.3, and mixed at room temperature for 15 hours using a ball mill to prepare a mixed raw material. Next, this mixed raw material and Al (OH) ₃ , MgO, or Co ₃ O ₄ were mixed at a weight ratio (wt%) of 98.2: 1.8, 99.1: 0.9, or 98.2: 1.8, respectively, and three types were mixed. The substitution element addition mixed raw material of this was prepared. Each was held at 150 ° C. for 1 h in the air atmosphere and further held at 470 ° C. for 5 h, and then fired by holding at 750 ° C. for 20 h in an oxygen atmosphere. The composition of the obtained three types of positive electrode active materials is Na ₂ NiMn _2.9 Al _0.1 O ₈ , Na ₂ NiMn _2.9 Mg _0.1 O ₈ , or Na ₂ NiMn _2.9 Co _0.1 O ₈ . Then, the positive electrode active material of Example 6 whose average particle diameter is 8 micrometers was obtained by grind | pulverizing with a ball mill and classifying with a sieve.

Example 7
A positive electrode active material was synthesized in the same manner as in Example 6. First, Na ₂ CO ₃ , NiO, and MnO ₂ were combined at a weight ratio (wt%) of 24.4: 15.5: 60.1, and mixed at room temperature for 15 hours using a ball mill to prepare a mixed raw material. Next, this mixed raw material and Al (OH) ₃ , MgO, or Co ₃ O ₄ were mixed at a weight ratio (wt%) of 98.2: 1.8, 99.1: 0.9, or 98.2: 1.8, respectively, and three types were mixed. The substitution element addition mixed raw material of this was prepared. Each was held at 150 ° C. for 1 h in the air atmosphere and further held at 470 ° C. for 5 h, and then fired by holding at 750 ° C. for 20 h in an oxygen atmosphere. The composition of the obtained three types of positive electrode active materials is Na ₂ Ni _0.9 Mn ₃ Al _0.1 O ₈ , Na ₂ Ni _0.9 Mn ₃ Mg _0.1 O ₈ , or Na ₂ Ni _0.9 Mn ₃ Co _0.1 O ₈ . Then, the positive electrode active material of Example 7 whose average particle diameter is 9 micrometers was obtained by grind | pulverizing with a ball mill and classifying with a sieve.

Example 8
A positive electrode active material was synthesized in the same manner as in Example 6. Na ₂ CO ₃ , NiO, and MnO ₂ were combined at a weight ratio (wt%) of 24.0: 16.9: 59.1 and mixed at room temperature for 15 h using a ball mill to prepare a mixed raw material. Next, this mixed raw material and Co ₃ O ₄ were mixed at a weight ratio (wt%) of 96.4: 3.6 to prepare a mixed element-added mixed raw material. After holding at 150 ° C. for 1 hour in the air atmosphere and further holding at 470 ° C. for 5 hours, firing was carried out at 750 ° C. for 20 hours in an oxygen atmosphere. The composition of the obtained positive electrode active material is Na ₂ Ni _0.9 Mn _2.9 Co _0.2 O ₈ . Then, the positive electrode active material of Example 8 whose average particle diameter is 10 micrometers was obtained by grind | pulverizing with a ball mill and classifying with a sieve.

Comparative Example 2
Na ₂ CO ₃ , NiO, and MnO ₂ were combined at a weight ratio (wt%) of 24.0: 16.9: 59.1 and mixed at room temperature for 15 h using a ball mill to prepare a mixed raw material. Next, this mixed raw material and Co ₃ O ₄ were mixed at a weight ratio (wt%) of 92.7: 7.3 to prepare a mixed element-added mixed raw material. After holding at 150 ° C. for 1 hour in the air atmosphere and further holding at 470 ° C. for 5 hours, firing was carried out by holding at 750 ° C. for 20 hours in an oxygen atmosphere. The composition of the obtained positive electrode active material is Na ₂ Ni _0.8 Mn _2.8 Co _0.4 O ₈ . Then, the positive electrode active material of the comparative example 2 whose average particle diameter is 10 micrometers was obtained by grind | pulverizing with a ball mill and classifying with a sieve.

Reference example 1
Na ₂ CO ₃ and Co ₃ O ₄ were combined at a weight ratio (wt%) of 30.7: 69.3, and mixed at room temperature for 15 h using a ball mill to prepare a mixed raw material. After holding at 150 ° C. for 1 h in the air atmosphere and further holding at 470 ° C. for 5 h, firing was carried out at 650 ° C. for 20 h in an oxygen atmosphere. The composition of the obtained positive electrode active material is Na _0.67 CoO ₂ . Then, the positive electrode active material of the reference example 1 whose average particle diameter is 10 micrometers was obtained by grind | pulverizing with a ball mill and classifying with a sieve.

<Preparation of positive electrode>
In each of Examples 1 to 8, Comparative Examples 1 and 2, and Reference Example 1, a conductive material, graphite, and a binder, polyvinylidene fluoride (PVDF), were weighed to a weight ratio of 88: 7: 5. The mixture was mixed with a paddle for 1 hour to prepare each positive electrode mixture slurry. Then, each positive mix slurry was apply | coated to the single side | surface or both surfaces of 15-micrometer-thick aluminum foil, and it dried sufficiently at 120 degreeC. The dry-coated electrode was press-molded at a pressure of 100 MPa to obtain positive electrodes of Examples 1 to 8, Comparative Examples 1 and 2, and Reference Example 1.

<Production of negative electrode>
Example 9
As the negative electrode active material, disodium terephthalate (chemical formula: C ₆ H ₄ (CO ₂ Na) ₂ , manufactured by Aldrich) was used. To this, acetylene black as a conductive material and PVDF as a binder were weighed to a weight ratio of 88: 7: 5 and mixed with a rake machine for 30 minutes to prepare a negative electrode mixture slurry. Thereafter, each negative electrode mixture slurry was applied to one side or both sides of a 10 μm thick copper foil and sufficiently dried at 120 ° C. The dry coated electrode was press-molded at a pressure of 100 MPa to obtain a negative electrode of Example 9.

Example 10
1,5-naphthalenedicarboxylic acid (chemical formula: C ₁₀ H ₆ (CO ₂ H) ₂ , manufactured by Aldrich) was added to an aqueous solution containing an excess of 5% sodium hydroxide in terms of equivalent amount, and Na ion exchange was performed. This solution was added to a large excess of methanol to reprecipitate sodium 1,5-naphthalenedicarboxylate. Further, it was thoroughly washed with methanol and vacuum-dried at 80 ° C. Using this as a negative electrode active material, a negative electrode of Example 10 was obtained in the same manner as Example 9.

Example 11
A negative electrode of Example 11 was obtained in the same manner as Example 9 using 2,6-naphthalenedicarboxylic acid (chemical formula: C ₁₀ H ₆ (CO ₂ H) ₂ , manufactured by Aldrich).

Reference example 2
A negative electrode of Reference Example 2 was obtained in the same manner as Example 9 using amorphous carbon (manufactured by Kureha Chemical, Carbotron P (registered trademark)) as the negative electrode active material.

<Production of battery>
Example 12
A coin-type non-aqueous electrolyte secondary battery shown in FIG. 2 is manufactured by the following procedure by combining the positive electrode coated on one side with the positive electrode active material prepared in Example 1 and the negative electrode coated on one side prepared in Reference Example 2. did. The positive electrode and the negative electrode were each punched out to a diameter of 15 mm and dried under the conditions of 120 ° C. and vacuum. A microporous polypropylene film was used for the separator, and the positive electrode, the separator, and the negative electrode were placed in a coin case in this order. As a solvent for the non-aqueous electrolyte, a mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 3, NaPF ₆ as a sodium salt, and a sodium concentration of 1 mol / l were prepared. After sufficiently impregnating the above positive electrode, separator, and negative electrode, the upper lid of the coin case was caulked and completely sealed to obtain a nonaqueous electrolyte secondary battery of Example 12. Using this, charge and discharge cycles were repeated under a charging condition with a constant current of 0.5 mA and 4.0 V and a termination condition of 5 hours with a constant current of 0.5 mA and a discharge condition of 2.0 V with a termination condition of 0.5 mA. Sex was evaluated. As with the lithium ion battery, the negative electrode side reaction occurs in the initial cycle, so the fifth cycle is defined as the rated capacity. FIG. 3 shows the change in the maintenance rate with respect to the rated capacity as the cycle progresses. The nonaqueous electrolyte secondary battery of Example 12 showed excellent reversibility, and the capacity retention rate after 50 cycles was 75%.

Example 13
The coin-type non-aqueous electrolyte secondary battery shown in FIG. 2 was combined with the positive electrode on which the positive electrode active material prepared in Example 5 was applied on one side and the negative electrode on the single side applied in Reference Example 2 as in Example 12. It produced similarly. Further, in the same manner as in Example 12, the change in the maintenance ratio with respect to the rated capacity with the progress of the cycle was examined. As shown in FIG. 3, the nonaqueous electrolyte secondary battery of Example 13 exhibited excellent reversibility, and the capacity retention rate after 50 cycles was 79%.

Example 14
The coin-type non-aqueous electrolyte secondary battery shown in FIG. 2 was combined with the negative electrode with a single-side coating produced in Example 9 and the positive electrode with a single-sided coating of the positive electrode active material produced in Reference Example 1 together with Example 12 It produced similarly. The negative electrode produced in Example 9 has a feature that Na precipitation is unlikely to occur because the reaction potential of occlusion and release of Na ions is about 1.0 V noble potential from the equilibrium potential of Na metal. Since the operating potential is different from that of Example 12, the charging / discharging conditions were changed to charging at 0.5 mA and 3.5 V constant current constant voltage for 5 hours and discharging at 0.5 mA constant current at 1.0 V termination. Other than that, in the same manner as in Example 12, the change in the maintenance ratio with respect to the rated capacity as the cycle progressed was examined. As shown in FIG. 4, the nonaqueous electrolyte secondary battery of Example 14 showed excellent reversibility, and the capacity retention rate after 50 cycles was 83%.

Example 15
The coin-type non-aqueous electrolyte secondary battery shown in FIG. 2 was combined with the negative electrode with a single-side coating produced in Example 10 and the positive electrode with a single-sided coating of the positive electrode active material produced in Reference Example 1 as in Example 12. It produced similarly. The negative electrode produced in Example 10 has a feature that Na precipitation is unlikely to occur because the reaction potential of occlusion and release of Na ions is about 1.0 V noble potential from the equilibrium potential of Na metal. Hereinafter, in the same manner as in Example 14, the change in the maintenance ratio with respect to the rated capacity with the progress of the cycle was examined. As shown in FIG. 4, the nonaqueous electrolyte secondary battery of Example 15 showed excellent reversibility, and the capacity retention rate after 50 cycles was 78%.

Example 16
The coin-type non-aqueous electrolyte secondary battery shown in FIG. 2 is combined with the negative electrode with the single-side coating prepared in Example 11 and the positive electrode with the single-side coating of the positive electrode active material manufactured in Reference Example 1 as in Example 12. It produced similarly. The negative electrode produced in Example 11 has a feature that the reaction potential of the storage and release of Na ions is about 1.0 V noble potential from the equilibrium potential of Na metal, so that precipitation of Na hardly occurs. Hereinafter, in the same manner as in Example 14, the change in the maintenance ratio with respect to the rated capacity with the progress of the cycle was examined. As shown in FIG. 4, the nonaqueous electrolyte secondary battery of Example 16 showed excellent reversibility, and the capacity retention rate after 50 cycles was 80%.

Example 17
The coin-type non-aqueous electrolyte secondary battery shown in FIG. 2 was combined with the positive electrode obtained by applying the positive electrode active material prepared in Example 1 on one side and the single-sided negative electrode prepared in Example 9 with Example 12. It produced similarly. Further, in the same manner as in Example 14, the change in the maintenance ratio with respect to the rated capacity with the progress of the cycle was examined. As shown in FIG. 5, the nonaqueous electrolyte secondary battery of Example 17 showed excellent reversibility, and the capacity retention rate after 100 cycles was 70%.

Example 18
The coin-type non-aqueous electrolyte secondary battery shown in FIG. 2 is combined with the positive electrode on which the positive electrode active material manufactured in Example 5 is applied on one side and the negative electrode on the single side applied in Example 9 as in Example 12. It produced similarly. Further, in the same manner as in Example 14, the change in the maintenance ratio with respect to the rated capacity with the progress of the cycle was examined. As shown in FIG. 5, the nonaqueous electrolyte secondary battery of Example 18 exhibited excellent reversibility, and the capacity retention rate after 100 cycles was 79%.

Example 19
A positive electrode formed by adding one substitution element to each of three types of Examples 2 and 3, two types of Example 4, and a total of eight types of positive electrode active materials, and a single-sided negative electrode prepared in Example 9 In combination, the coin-type non-aqueous electrolyte secondary battery shown in FIG. Further, a charge / discharge test was conducted in the same manner as in Example 14 to examine the maintenance ratio relative to the rated capacity after 100 cycles.

Comparative Example 3
A coin-type non-aqueous electrolyte secondary solution shown in FIG. 2 is formed by combining the positive electrode active material of Comparative Example 1 coated on one side and the single-sided coated negative electrode fabricated in Reference Example 2 produced by adding a substitution element in excess. A battery was produced in the same manner as in Example 12. Further, a charge / discharge test was conducted in the same manner as in Example 12, and the maintenance rate relative to the rated capacity after 50 cycles was examined.

  Table 1 shows a comparison of the maintenance rates with respect to the rated capacities after the elapse of cycles of the eight types of nonaqueous electrolyte secondary batteries of Example 19 and the nonaqueous electrolyte secondary battery of Comparative Example 3. It was found that all of the eight types of nonaqueous electrolyte secondary batteries of Example 19 had a higher retention rate after 100 cycles than Example 17 and were desirable. On the other hand, the non-aqueous electrolyte secondary battery of Comparative Example 3 was found to have a lower maintenance rate after 50 cycles than Example 12. That is, reversibility can be further improved by adding a substitution element in an appropriate range.

Example 20
A positive electrode formed by adding one substitution element to each of three types of Examples 6 and 7, one type of Example 8, and a total of seven types of positive electrode active materials, and a single-sided negative electrode prepared in Example 9 In combination, the coin-type non-aqueous electrolyte secondary battery shown in FIG. Further, a charge / discharge test was conducted in the same manner as in Example 14 to examine the maintenance ratio relative to the rated capacity after 100 cycles.

Comparative Example 4
A coin-type non-aqueous electrolyte secondary shown in FIG. 2 is formed by combining the positive electrode active material of Comparative Example 2 coated on one side and the single-sided coated negative electrode fabricated in Reference Example 2 prepared by adding a substitution element in excess. A battery was produced in the same manner as in Example 12. Further, a charge / discharge test was conducted in the same manner as in Example 12, and the maintenance rate relative to the rated capacity after 50 cycles was examined.

  Table 2 shows a comparison of the maintenance ratio with respect to the rated capacity after the cycle of the seven types of nonaqueous electrolyte secondary batteries of Example 20 and the nonaqueous electrolyte secondary battery of Comparative Example 4. It was found that all of the seven types of nonaqueous electrolyte secondary batteries of Example 20 had a higher maintenance rate than Example 18 and were desirable. On the other hand, the nonaqueous electrolyte secondary battery of Comparative Example 4 was found to have a lower maintenance rate than Example 13. That is, reversibility can be further improved by adding a substitution element in an appropriate range.

Example 21
The cylindrical non-aqueous electrolyte secondary battery shown in FIG. 1 is manufactured by the following procedure by combining the positive electrode coated on both sides of the positive electrode active material prepared in Example 5 and the negative electrode coated on both sides manufactured in Example 9. did. The positive electrode and the negative electrode were formed into strips, and the positive electrode tab and the negative electrode tab were welded to one end of each, and further dried under conditions of 120 ° C. and vacuum. A microporous polypropylene film was used as a separator, and the film was wound in the order of a positive electrode, a separator, a negative electrode, and a separator, and inserted into a battery can. The negative electrode tab was welded to the battery can, and the positive electrode tab was welded to the inner lid. As a solvent for the non-aqueous electrolyte, a mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 3, NaPF ₆ as a sodium salt, and a sodium concentration of 1 mol / l were prepared. After sufficiently impregnating the above positive electrode, separator, and negative electrode, the battery lid was caulked and completely sealed to obtain a nonaqueous electrolyte secondary battery having a diameter of 14 mm and a height of 50 mm.

  Using the non-aqueous electrolyte battery of Example 21, the following tests were conducted.

<Pulse charge / discharge cycle test>
A pulse charge / discharge cycle test was conducted under the following conditions.

(1) Charging / discharging center voltage: 2.4V
(2) Discharge pulse: current 12CA (0.083 hour rate current), time 30 seconds.

(3) Charge pulse: Current 6CA (0.167 hour rate current), time 15 seconds.

(4) Pause time between discharge and charge: 30 seconds.

(5) Since the center voltage fluctuates, constant voltage charge or constant voltage discharge is performed at 2.4 V every 1000 pulses, and the center voltage is adjusted to 2.4 V.

(6) The ambient temperature was 50 ° C.

<Measurement of DC resistance and output density>
The direct current resistance and power density of the battery were determined by the following method. In an environment of 50 ° C., discharge was performed for 10 seconds in the order of currents 4CA, 8CA, 12CA, and 16CA. The relationship between the discharge current at that time and the voltage at 10 seconds was plotted, and the DC resistance was determined from the slope of the obtained straight line. Also, the current value at 1.0 V on the straight line was obtained, and the power density was obtained by dividing the battery weight by the product of 1.0 V and the current value.

  The initial power density and the rate of increase in resistance after 50,000 pulse cycles (initial resistance was taken as 100) were 2300 W / k and 108%, respectively, and it was found that they had high output and excellent life characteristics.

  All publications, patents and patent applications cited herein are incorporated herein by reference in their entirety.

DESCRIPTION OF SYMBOLS 10 Positive electrode 11 Separator 12 Negative electrode 13 Battery can 14 Positive electrode tab 15 Negative electrode tab 16 Inner cover 17 Internal pressure release valve 18 Gasket 19 PTC element 20 Outer cover 21 Positive electrode 22 Negative electrode 23 Separator 24 Coin case 25 Upper cover 26 Gasket

Claims (10)

  A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a composite metal oxide containing Na, Ni and Mn. The composite metal oxide is represented by the general formula (I):
Na _α Ni _β-g Mn _γ-h M ′ _{g + h} O ₂ (I)
[Where
M ′ is at least one selected from the group consisting of Al, Mg and Co;
α is in the range of 0 <α ≦ 0.5,
β is in the range of 2/9 ≦ β ≦ 1/4,
γ is in the range of 3/4 ≦ γ ≦ 7/9,
g is in the range of 0 ≦ g ≦ 0.045,
h is in the range of 0 ≦ h ≦ 0.045,
β + γ + g + h is 1]
The positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 1 represented by these. The composite metal oxide has the general formula (II):
Na _4-a Ni _2-x Mn _7-y M ′ _{x + y} O ₁₈ (II)
[Where
M ′ is at least one selected from the group consisting of Al, Mg and Co;
a is in the range of 0 ≦ a <4,
x is in the range of 0 ≦ x ≦ 0.4,
y is in the range of 0 ≦ y ≦ 0.4]
The positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 2 represented by these. The composite metal oxide has the general formula (III):
Na _2-b Ni _1-p Mn _3-q M ′ _{p + q} O ₈ (III)
[Where
M ′ is at least one selected from the group consisting of Al, Mg and Co;
b is in the range of 0 ≦ b <2,
p is in the range of 0 ≦ p ≦ 0.1,
q is within the range of 0 ≦ q ≦ 0.1]
The positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 2 represented by these.   The nonaqueous electrolyte secondary battery which has a positive electrode containing the positive electrode active material for nonaqueous electrolyte secondary batteries in any one of Claims 1-4, and the negative electrode which occludes / releases sodium ion reversibly.   The nonaqueous electrolyte secondary battery according to claim 5, wherein the negative electrode reversibly occluding and releasing sodium ions includes a compound having at least one aromatic carboxylic acid sodium salt structure as a negative electrode active material. A compound having at least one aromatic carboxylic acid sodium salt structure is represented by the general formula (IV):
C ₆ H ₄ (CO ₂ Na _{1 + c} ) ₂ (IV)
[Wherein c is in the range of 0 ≦ c ≦ 1]
The nonaqueous electrolyte secondary battery according to claim 6 represented by:   A negative electrode active material for a non-aqueous electrolyte secondary battery, comprising a compound having at least one aromatic carboxylic acid sodium salt structure. A compound having at least one aromatic carboxylic acid sodium salt structure is represented by the general formula (IV):
C ₆ H ₄ (CO ₂ Na _{1 + c} ) ₂ (IV)
[Wherein c is in the range of 0 ≦ c ≦ 1]
The negative electrode active material for nonaqueous electrolyte secondary batteries according to claim 8, represented by:   A nonaqueous electrolyte secondary battery comprising a negative electrode comprising the negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 8 and a positive electrode capable of reversibly occluding and releasing sodium ions.

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