JP2018067506A - Positive electrode active material for lithium secondary battery, positive electrode of lithium secondary battery, lithium secondary battery, and method of producing positive electrode active material for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a positive electrode active material for a lithium secondary battery, having a high capacity.SOLUTION: A positive electrode active material for a lithium secondary battery contains a salt of a polyoxometalate which contains Ni and Mo and which has the Anderson structure.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode for a lithium secondary battery, a lithium secondary battery, and a method for producing a positive electrode active material for a lithium secondary battery.

The positive electrode active material of a lithium ion battery is typically a layered composite oxide such as lithium cobaltate (LiCoO ₂ ). When the positive electrode active material is a layered composite oxide such as LiCoO ₂ , an intercalation reaction occurs in which lithium ions (Li ⁺ ) are desorbed from the positive electrode active material during charging and Li ⁺ is inserted into the positive electrode active material during discharging. be able to. For this reason, when the positive electrode active material is a layered composite oxide such as LiCoO ₂ , the positive electrode active material has high charge / discharge reversibility. The intercalation reaction is also called an insertion reaction. When the positive electrode active material is a layered composite oxide such as LiCoO ₂ , the capacity of the positive electrode active material is the intercalation reaction of atoms of transition metal elements such as cobalt (Co) contained in the layered composite oxide. Depends on the average valence change at.

For example, when the positive electrode active material of the lithium ion battery is LiCoO ₂ , during charging, the Co atom contained in the positive electrode active material changes from trivalent cobalt ion Co ³⁺ to tetravalent cobalt ion Co ⁴⁺ , and Co ³⁺ the number corresponding to the number of Co atoms and changed to ^{Co 4+} Li ⁺ is desorbed from the positive electrode active material from the time of discharge, Co atoms contained in the positive electrode active material is changed to ^{Co 3+} from ^{Co 4+,} Co from ^{Co 4+} A number of Li ⁺ corresponding to the number of Co atoms changed to ³⁺ is inserted into the positive electrode active material.

However, in order for the positive electrode active material of the lithium ion battery to have high reversibility, all of the Co atoms contained in the positive electrode active material cannot be changed in valence, and Co atoms contained in the positive electrode active material Only about half of the valence can be changed. This is because when about half or more of Co atoms contained in the positive electrode active material undergo a change in valence and about half or more of Li ⁺ contained in the positive electrode active material is desorbed from the positive electrode active material, the positive electrode active material This is because the crystal structure of this changes and Li ⁺ cannot be inserted into the positive electrode active material again.

Therefore, when the positive electrode active material of the lithium secondary battery is LiCoO ₂ , an oxidation-reduction reaction between LiCoO ₂ and Li _0.5 CoO ₂ expressed by the reaction formula (1) is caused during charge / discharge. The average valence change in the intercalation reaction of Co atoms is only 0.5. The capacity of the positive electrode active material reaches about 280 mAh / g when all the Co atoms contained in the positive electrode active material can be changed in valence, but in practice, the capacity is only about 140 mAh / g. Don't be.

^{_{Li 0.5 CoO 2 + 0.5Li + +}} 0.5e - ⇔LiCoO 2 ··· (1)

A problem similar to this problem also occurs when the positive electrode active material of the lithium secondary battery is a layered composite oxide other than LiCoO ₂ . In addition, a problem similar to this problem also occurs in lithium secondary batteries other than lithium ion batteries.

  Patent Document 1, Non-Patent Document 1 and Non-Patent Document 2 describe prior arts related to the present invention.

In the prior art described in Patent Document 1, Na ₃ [AlMo ₆ O ₂₄ H ₆ ] · 7H ₂ O and Li ₃ [, which are polyoxometalates having a Anderson structure as a positive electrode active material of a lithium secondary battery, are used. AlMo ₆ O ₂₄ H ₆ ] · 7H ₂ O. In the prior art, the theoretical capacity of the positive electrode active material is about 300 mAh / g, and the actual capacity of the positive electrode active material is equal to or greater than the theoretical capacity.

In the prior art described in Non-Patent Document 1, the positive electrode active material of a lithium secondary battery is TBA ₃ [PMo ₁₂ O ₄₀ ], which is polyoxometalate. “TBA” means tributylammonium. In the prior art, the theoretical capacity of the positive electrode active material is about 250 mAh / g, and the actual capacity of the positive electrode active material is equal to or greater than the theoretical capacity.

In the prior art described in Non-Patent Document 2, the positive electrode active material of the lithium secondary battery is Na ₃ [AlMo ₆ O ₂₄ H ₆ ], which is a polyoxometalate having an Anderson type structure. In the prior art, the theoretical capacity of the positive electrode active material is about 300 mAh / g, and the capacity of the positive electrode active material is equal to or greater than the theoretical capacity.

JP 2013-115028 A

Wang Heng and 6 others, "In-operndo X-ray Absorption Fine Structure Studies of Polyoxometalate: Research on X-ray Absorption Fine Structure of Polyoxometalate Molecular Cluster Batteries Molecular Cluster Batteries: Polyoxometalates as Electron Sponges), Journal of the American Chemical Society, (USA), March 14, 2012, Vol. 134, No. 10, p. 4918-4924 Erfu Ni and one other, "Anderson type polyoxomolybdate as cathode material of lithium battery and its reaction mechanism", Journal of・ Journal of Power Sources, (Netherlands), December 1, 2014, Vol. 267, p. 673-681

  An object of this invention is to solve the problem that the capacity | capacitance of the positive electrode active material of a lithium secondary battery resulting from a small average valence change being small. Therefore, the problem to be solved by the present invention is to obtain a positive electrode active material for a lithium secondary battery having a high capacity.

  The present invention produces a positive electrode active material of a lithium secondary battery, a positive electrode of a lithium secondary battery including the positive electrode active material, a lithium secondary battery including a positive electrode including the positive electrode active material, and a positive electrode active material of the lithium secondary battery On how to do. The positive electrode active material of the lithium secondary battery includes a salt of polyoxometalate containing Ni and Mo and having an Anderson type structure.

  According to the present invention, a positive electrode active material for a lithium secondary battery having a high capacity can be obtained.

  The objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

It is a schematic diagram illustrating the primary structure of the polyoxometalate constituting the salt contained in the positive electrode active material of the lithium secondary battery of the embodiment. It is a schematic diagram which illustrates the secondary structure of the polyoxometalate which comprises the salt contained in the positive electrode active material of the lithium secondary battery of embodiment. It is a flowchart which illustrates the procedure of the synthesis | combination of the positive electrode active material of the lithium secondary battery of embodiment. It is sectional drawing which illustrates the basic structure of the lithium secondary battery of embodiment. It is a disassembled perspective view which illustrates CR2032-type coin cell which is an example of the lithium secondary battery of embodiment. It is a figure which illustrates the X-ray-diffraction pattern of synthetic | combination Na-NM and Li-NM, and AHNM quoted from the database. It is a graph which shows the charging / discharging characteristic in case a positive electrode active material is ANM. It is a graph which shows the charging / discharging characteristic in case a positive electrode active material is AHNM. It is a graph which shows the charging / discharging characteristic in case a positive electrode active material is Na-NM. It is a graph which shows the charging / discharging characteristic in case a positive electrode active material is Li-NM.

1 Idea Table 1 shows the valence that each transition metal element can take for each transition metal element of manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and molybdenum (Mo). The number and the bond distance between the atom of each transition metal element and the oxygen atom are shown. The bond distances shown in Table 1 are calculated from Shannon's ion radius table. When the transition metal elements are Mn, Fe, Co, and Ni, the bond distance when the valence is tetravalent is 100. When the transition metal element is Mo, the bond distance is 100 when the valence is hexavalent.

As can be understood from Table 1, the redox couple Mn ²⁺ / Mn ⁴⁺ , which is a pair of divalent manganese ion (Mn ²⁺ ) and tetravalent manganese ion (Mn ⁴⁺ ), divalent iron ion (Fe ²⁺ ) And redox pair Fe ²⁺ / Fe ⁴⁺ , which is a pair of tetravalent iron ion (Fe ⁴⁺ ), and redox pair which is a pair of divalent cobalt ion (Co ²⁺ ) and tetravalent cobalt ion (Co ⁴⁺ ) When the redox couple Ni ²⁺ / Ni ^{4+, which} is a pair of Co ²⁺ / Co ⁴⁺ or a divalent nickel ion (Ni ²⁺ ) and a tetravalent nickel ion (Ni ⁴⁺ ), is used in the redox reaction The associated bond distance changes are 15%, 10%, 11%, or 11%, respectively. In addition, when the redox couple Mo ⁴⁺ / Mo ^6+, which is a pair of tetravalent molybdenum ions (Mo ⁴⁺ ) and hexavalent molybdenum ions (Mo ⁶⁺ ), is used, the bond distance changes due to the redox reaction. Becomes 3%. Thus, when the redox ^couple Mo ⁴⁺ / Mo ⁶⁺ is used, it is compared to the redox couple Mn ²⁺ / Mn ⁴⁺ , Fe ²⁺ / Fe ⁴⁺ , Co ²⁺ / Co ⁴⁺ or Ni ²⁺ / Ni ^4+. Thus, the change in the bond distance accompanying the redox reaction is reduced. From this, when the oxidation-reduction pair Mo ⁴⁺ / Mo ⁶⁺ is used, it is expected that the change in the crystal structure of the positive electrode active material of the lithium secondary battery due to the change in the valence of the Mo atom is less likely to occur. It is expected that the reversibility of the positive electrode active material is increased. For this reason, the redox ^couple Mo ⁴⁺ / Mo ⁶⁺ is promising as a redox center of a positive electrode active material having a high capacity.

  On the other hand, polyoxometalate (POM), which is a cluster anion, is known to cause electrochemical multi-electron transfer in solution. POM is also called polyacid.

  For these reasons, the positive electrode active material of a lithium secondary battery containing a Mo-based POM salt may have a high capacity. Thus, when a Mo-based POM salt was searched, it was found that the positive electrode active material had a high capacity when the positive electrode active material contained a POM salt containing Ni and Mo and having an Anderson type structure.

2 Cathode Active Material of Lithium Secondary Battery The schematic diagram of FIG. 1 illustrates the primary structure of polyoxometalate (POM) constituting the salt contained in the cathode active material of the lithium secondary battery of the embodiment.

In the primary structure illustrated in FIG. 1, POM 1000 includes one NiO ₆ octahedron 1020 and six MoO ₆ octahedrons 1040, 1041, 1042, 1043, 1044 and 1045. In one NiO ₆ octahedron 1020, six oxygen (O) atoms are six-coordinated to one nickel (Ni) atom. In each of the _six MoO ₆ octahedrons 1040, 1041, 1042, 1043, 1044 and 1045, six O atoms are six coordinated to one molybdenum (Mo) atom. Six MoO ₆ octahedrons 1040, 1041, 1042, 1043, 1044 and 1045 are annularly arranged around one NiO ₆ octahedron 1020. In two adjacent MoO ₆ octahedrons, one MoO ₆ octahedron and the other MoO ₆ octahedron share a ridge. The POM 1000 includes hydrogen ions (H ⁺ ) not shown in FIG. The POM 1000 having such a primary structure is called a POM having an Anderson type structure.

POM1000 is the chemical formula _{H 6} NiMo 6 O ₂₄ ^4- represented. H ⁺ contained in POM1000 may be substituted with alkali metal ions (X1 ⁺ ). For example, H ⁺ contained in POM1000 may be replaced with lithium ions (Li ⁺ ). When H ⁺ contained in POM1000 is substituted with X1 ⁺ , a POM represented by the chemical formula H _6-m X1 _m NiMo ₆ O ₂₄ ⁴⁻ is obtained. X1 is an alkali metal, typically lithium (Li). m is an integer from 1 to 6.

  The schematic diagram of FIG. 2 illustrates the secondary structure of the POM constituting the salt contained in the positive electrode active material of the lithium secondary battery of the embodiment.

In the secondary structure illustrated in FIG. 2, the POM salt 1060 includes POM1000, ammonium ions (NH ₄ ⁺ ) 1080 and water molecules (H ₂ O) 1081. POM1000 is an anion. Ammonium ion 1080 is the counter cation of POM1000. The water molecule 1081 is hydrated water.

The salt 1060 of POM is a polyacid compound and is represented by a chemical formula (NH ₄ ) ₄ POM (H ₂ O) ₄ . POM is the polyoxometalate described so far. NH ₄ ⁺ contained in the POM salt 1060 may be substituted with an alkali metal ion (X2 ⁺ ). For example, NH ₄ ⁺ contained in the salt 1060 of POM may be replaced with sodium ion (Na ⁺ ). When NH ₄ ⁺ contained in the POM salt 1060 is substituted with X 2 ⁺ , a salt of POM represented by the chemical formula (NH ₄ ) _4-n X2 _n POM (H ₂ O) ₄ is obtained. X2 is an alkali metal, typically sodium (Na). n is an integer of 1 or more and 4 or less.

3 Synthesis of Positive Electrode Active Material A salt of POM represented by the chemical formula (NH ₄ ) ₄ (H ₆ NiMo ₆ O ₂₄ ) (H ₂ O) ₄ (hereinafter referred to as “ANMH”) is a heptamolybdate ion Mo ₇ It is synthesized by reacting a salt containing O ₂₄ ⁶⁻ and a salt containing nickel ion Ni ²⁺ in solution. For example, ANMH prepares a first aqueous solution by dissolving hexaammonium hexamolybdate tetrahydrate ((NH ₄ ) ₆ Mo ₇ O ₂₄ (H ₂ O) ₄ ) in water, and nickel sulfate (NiSO ₄ ) Is dissolved in water to prepare a second aqueous solution, the second aqueous solution is mixed with the first aqueous solution to prepare a mixed aqueous solution, and ANMH is precipitated from the mixed aqueous solution. The first aqueous solution, the second aqueous solution, and the mixed aqueous solution are heated as necessary. A recrystallization operation may be performed on the deposited ANMH. For example, the precipitated ANMH may be dissolved in water to prepare an aqueous solution for recrystallization, and ANMH may be precipitated from the aqueous solution for recrystallization. When ANMH is precipitated by the recrystallization operation, for example, a poor solvent is mixed with an aqueous solution for recrystallization.

  FIG. 3 is a flowchart illustrating a procedure for synthesizing the positive electrode active material of the lithium secondary battery according to the embodiment.

The procedure shown by the flowchart of FIG. 3 is included in a salt of POM (hereinafter referred to as “Li-NM”) in which hydrogen ions (H ⁺ ) contained in AHNM are replaced with lithium ions (Li ⁺ ) and AHNM. This is suitably used when a POM salt (hereinafter referred to as “Na-NM”) in which ammonium ions (NH ₄ ⁺ ) are replaced with sodium ions (Na ⁺ ) is synthesized.

In step S101 of FIG. 3, a salt of POM represented by the chemical formula (NH ₄ ) ₆ (NiMo ₉ O ₃₂ ) (H ₂ O) ₆ (hereinafter referred to as “ANM”) is synthesized. The POM represented by the chemical formula NiMo ₉ O ₃₂ ⁶⁻ is called POM having an Allman-Waugh type structure. When ANM is synthesized, for example, hexammonium hexamolybdate tetrahydrate ((NH ₄ ) ₆ Mo ₇ O ₂₄ (H ₂ O) ₄ ) is dissolved in water to prepare a first aqueous solution. Nickel sulfate (NiSO ₄ ) and sodium sulfate (Na ₂ SO ₄ ) are dissolved in water to prepare a second aqueous solution, and the second aqueous solution is mixed with the first aqueous solution to prepare a mixed aqueous solution, ANM is precipitated from the mixed aqueous solution. The first aqueous solution, the second aqueous solution, and the mixed aqueous solution are heated as necessary.

  In step S102 of FIG. 3, ANM is dissolved in an aqueous alkali solution containing alkali metal ions to prepare an aqueous solution. The alkaline aqueous solution containing alkali metal ions is, for example, a lithium hydroxide (LiOH) aqueous solution when Li-NM is synthesized, and is a sodium hydroxide (NaOH) aqueous solution when Na-NM is synthesized.

  In step S103 of FIG. 3, Li-NM or Na-NM is precipitated from an aqueous solution, and a positive electrode active material is obtained.

  By the recrystallization operation performed in steps S102 and S103, the POM having the Allman-Waugh type structure is changed to the POM having the Anderson type structure.

4 Basic Structure of Lithium Secondary Battery The schematic diagram of FIG. 4 illustrates the basic structure of the lithium secondary battery of the embodiment.

  In the basic structure illustrated in FIG. 4, a lithium secondary battery 1100 includes a positive electrode 1120, a negative electrode 1121, and an electrolyte solution 1122. The positive electrode 1120, the negative electrode 1121, and the electrolyte 1122 are changed according to the specifications of the lithium secondary battery 1100, and additional products such as a current collector, a container, and a separator that are further added to the basic structure are also specified for the lithium secondary battery 1100. Will be changed according to

  The positive electrode 1120 includes the positive electrode active material described so far, and preferably further includes a conductive agent and a binder. When the positive electrode 1120 includes a conductive agent and a binder, a large number of powder particles contained in a mixture in which the positive electrode active material powder and the conductive agent powder are mixed with each other are bound to each other by the binder.

  The conductive agent has electronic conductivity and is made of ketjen black, acetylene black, vapor grown carbon fiber (VGCF), carbon nanotube, or the like.

  The binder is made of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyimide, or the like.

The negative electrode 1121 includes a negative electrode active material. The negative electrode active material is metallic lithium or a lithium alloy. Materials that form an alloy with lithium (Li) include magnesium (Mg), calcium (Ca), aluminum (Al), silicon (S), germanium (Ge), tin (Sn), lead (Pb), arsenic ( As), antimony (Sb), bismuth (Bi), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg), and the like. The negative electrode active material may be a material capable of inserting lithium ions (Li ⁺ ) into the negative electrode active material during charging and detaching Li ⁺ from the negative electrode active material during discharge. For example, the negative electrode active material may be carbon predoped with Li ⁺ .

The electrolytic solution 1122 has lithium ion conductivity and is in contact with the positive electrode 1120 and the negative electrode 1121. The solvent of the electrolytic solution 1122 includes a carbonate ester or the like. Examples of the carbonate ester include ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). The solute of the electrolytic solution 1122 contains a lithium salt. The lithium salt is composed of LiPF ₆ , LiBF ₄ , LiClO ₄ , Li (CF ₃ SO ₂ ) ₂ N (LiTFSI), LiN (SO ₂ C ₂ F ₅ ) ₂ (LiBETI), LiC ₄ BO ₈ (LiBOB), and the like. . The electrolytic solution 1122 may contain an additive. The additive is vinylene carbonate (VC), fluoroethylene carbonate (FEC), LiC ₄ BO ₈ (LiBOB), or the like. The electrolyte solution 1122 that is a liquid electrolyte may be replaced with a solid electrolyte.

When the lithium secondary battery 1100 is charged, Li ⁺ moves from the positive electrode 1120 to the negative electrode 1121 via the electrolytic solution 1122. When the lithium secondary battery 1100 is discharged, Li ⁺ moves from the negative electrode 1121 to the positive electrode 1120 through the electrolytic solution 1122.

  The lithium secondary battery 1100 is produced in the same manner as a conventional lithium secondary battery except that the positive electrode active material is different.

5 CR2032-type coin cell The schematic diagram of FIG. 5 is an exploded perspective view illustrating a CR2032-type coin cell which is an example of the lithium secondary battery of the embodiment.

  5 includes a positive electrode can 1160, a spring 1161, a spacer 1162, a positive electrode current collector 1163, a positive electrode 1164, a gasket 1165, a separator 1166, a separator 1167, an electrolyte, a lithium metal negative electrode 1168, and a negative electrode can. 1169. The electrolyte is not shown in FIG.

  Positive electrode can 1160 is coupled to negative electrode can 1169. As a result, the positive electrode can 1160 and the negative electrode can 1169 constitute a coin-shaped container in which an accommodation space is formed. A gap between the positive electrode can 1160 and the negative electrode can 1169 is sealed with a gasket 1165. Thereby, the accommodation space becomes an airtight space.

  The positive electrode 1164 is held by the positive electrode current collector 1163. The spring 1161, the spacer 1162, the positive electrode current collector 1163 holding the positive electrode 1164, the separator 1166, the separator 1167, and the lithium metal negative electrode 1168 are stacked in the order described, and the spring 1161 contacts the positive electrode can 1160 and the lithium metal negative electrode 1168. Is accommodated in the accommodating space so as to be in contact with the negative electrode can 1169. The spring 1161, the spacer 1162, and the positive electrode current collector 1163 are made of a material having electron conductivity. The negative electrode can 1169 is made of a material having electronic conductivity. Accordingly, the positive electrode can 1160, the spring 1161, the spacer 1162, and the positive electrode current collector 1163 are electrically connected to each other and constitute a charge / discharge path to the positive electrode 1164. The negative electrode can 1169 constitutes a charge / discharge path to the lithium metal negative electrode 1168.

  The positive electrode current collector 1163 is made of a mesh made of a metal such as aluminum or nickel or an alloy such as stainless steel. The positive electrode current collector 1163 made of a mesh may be replaced with a positive electrode current collector made of a foil. The positive electrode current collector 1163 made of a metal or alloy mesh may be replaced with a positive electrode current collector made of carbon paper.

The separators 1166 and 1167 are made of a polyolefin microporous film, a glass filter, or the like, and transmit Li ⁺ . The polyolefin constituting the polyolefin microporous film is polyethylene (PE), polypropylene (PP), or the like.

  The electrolytic solution is filled in the accommodation space.

6 Experiment 6.1 Synthesis of positive electrode active material ANM, AHNM, Na-NM and Li-NM were synthesized.

  In the synthesis of ANM, a first aqueous solution was prepared by dissolving hexaammonium hexamolybdate tetrahydrate in 25 ml of distilled water, and heated to 95 ° C. using an oil bath while stirring the first aqueous solution. Next, 25 ml of a second aqueous solution prepared by dissolving nickel sulfate and sodium sulfate in distilled water was added to the first aqueous solution to obtain a mixed aqueous solution. The mixed aqueous solution was heated to 100 ° C. and stirred for 20 minutes. Next, the mixed aqueous solution was subjected to suction filtration to obtain a filtrate, and the filtrate was cooled to room temperature to precipitate ANM from the filtrate.

  In the synthesis of AHNM, hexammonium heptamolybdate tetrahydrate was dissolved in 25 ml of distilled water to prepare a first aqueous solution, and the first aqueous solution was heated to 95 ° C. using an oil bath while stirring. Next, 25 ml of a second aqueous solution prepared by dissolving nickel sulfate in distilled water was added to the first aqueous solution to obtain a mixed aqueous solution. The mixed aqueous solution was heated to 100 ° C. and stirred for 20 minutes. Next, the mixed aqueous solution was subjected to suction filtration to obtain a filtrate. The filtrate was cooled to room temperature, and AHNM was precipitated from the filtrate. Next, 0.15 g of AHNM was dissolved in 10 ml of distilled water while stirring to obtain a solution for recrystallization. Next, 100 ml of ethanol was added to an aqueous solution for recrystallization while stirring to recrystallize AHNM. Next, the recrystallized AHNM was isolated by centrifugation. The isolated AHNM became nanoparticles.

  In the synthesis of Na-NM, an aqueous solution for recrystallization was prepared by dissolving ANM in 10 ml of an aqueous sodium hydroxide solution having a pH of 10 over 5 minutes while stirring. Next, 100 ml of ethanol was added to an aqueous solution for recrystallization while stirring to recrystallize Na-NM. Na-NM became nanoparticles by recrystallization operation.

  The synthesis of Li-NM was performed in the same manner as the synthesis of Na-NM except that a lithium hydroxide aqueous solution was used instead of the sodium hydroxide aqueous solution. Li-NM became nanoparticles by the recrystallization operation.

6.2 X-ray diffraction pattern of Na-NM and Li-NM FIG. 6 is a diagram illustrating the X-ray diffraction pattern of synthesized Na-NM and Li-NM and reference AHNM.

  As shown in FIG. 6, the X-ray diffraction patterns of the synthesized Na-NM and Li-NM are similar to the X-ray diffraction pattern of the reference AHNM, but the synthesized Na-NM and Li-NM The peak angle in the NM X-ray diffraction pattern is slightly different from the peak angle in the reference AHNM X-ray diffraction pattern. From this, the crystal structure of synthesized Na-NM and Li-NM approximates the crystal structure of AHNM, but the lattice constant of synthesized Na-NM and Li-NM is the same as that of AHNM. You can see the difference. That is, it can be understood that the lattice constant of the crystal to be deposited is slightly different depending on the type of metal salt used in the recrystallization operation.

6.3 Production of Coin Cell and Evaluation of Charge / Discharge Characteristics The above-described CR2032 type coin cell was produced using synthesized ANM, AHNM, Na-NM, and Li-NM as positive electrode active materials, respectively. Moreover, the charge / discharge characteristic of the produced coin cell was evaluated.

  7, 8, 9 and 10 are graphs showing charge / discharge characteristics in the case where the positive electrode active material is ANM, AHNM, Na-NM and Li-NM, respectively.

The theoretical capacity when redox couple Mo ⁴⁺ / Mo ⁶⁺ is utilized is about 300 mAh / g, but from FIGS. 7, 8, 9 and 10 the positive electrode active materials are ANM, AHNM, Na—NM and Li— It can be understood that in any case of NM, a capacity equal to or higher than the theoretical capacity can be obtained. Further, when the positive electrode active material is Li-NM, a capacity that is much higher than the theoretical capacity of about 600 mAh can be obtained. The reason is unknown, but it is considered that the molybdenum (Mo) atom has been reduced to tetravalent or less.

  Although the invention has been shown and described in detail, the above description is illustrative in all aspects and not restrictive. Accordingly, it is understood that numerous modifications and variations can be devised without departing from the scope of the invention.

1000 Polyoxometalate (POM)
1060 Salt of polyoxometalate (POM) 1080 Ammonium ion (NH ⁴⁺ )
1081 Water molecule (H ₂ O)
1100 Lithium secondary battery 1120 Positive electrode 1121 Negative electrode 1122 Electrolyte 1140 CR2032 type coin cell

Claims (10)

  A positive electrode active material for a lithium secondary battery comprising a polyoxometalate salt containing Ni and Mo and having an Anderson structure. The positive electrode active material of the lithium secondary battery according to claim 1, wherein an anion in the polyoxometalate is represented by a chemical formula H ₆ NiMo ₆ O ₂₄ ⁴⁻ The anion in the polyoxometalate is represented by the chemical formula H _6-m X1 _m NiMo ₆ O ₂₄ ^4-
X1 is an alkali metal,
The positive electrode active material for a lithium secondary battery according to claim 1, wherein m is an integer of 1 to 6. X1 is lithium, The positive electrode active material of the lithium secondary battery of Claim 3. The salt is represented by the chemical formula (NH ₄ ) ₄ POM (H ₂ O) ₄ ,
5. The positive electrode active material for a lithium secondary battery according to claim 1, wherein POM is the polyoxometalate. The salt is represented by the chemical formula (NH ₄ ) _4-n X2 _n POM (H ₂ O) ₄ ,
POM is the polyoxometalate,
X2 is an alkali metal,
n is an integer of 1 or more and 4 or less, The positive electrode active material of the lithium secondary battery in any one of Claim 1 to 4. X2 is sodium, The positive electrode active material of the lithium secondary battery of Claim 6.   The positive electrode of the lithium secondary battery containing the positive electrode active material of the lithium secondary battery in any one of Claim 1-7. A positive electrode containing a positive electrode active material of any of the lithium secondary batteries according to claim 1;
A negative electrode,
An electrolyte having lithium ion conductivity and in contact with the positive electrode and the negative electrode;
A lithium secondary battery comprising: a) preparing a salt of a polyoxometalate represented by the chemical formula (NH ₄ ) ₆ (NiMo ₉ O ₃₂ ) (H ₂ O) ₆ ;
b) preparing an aqueous solution by dissolving the salt in an aqueous alkali solution containing alkali metal ions;
c) depositing a salt of polyoxometalate containing Ni and Mo and having an Anderson structure from the aqueous solution to obtain a positive electrode active material of a lithium secondary battery;
A method for producing a positive electrode active material for a lithium secondary battery.

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