Positive electrode active material, lithium secondary battery, compound, and method for producing compound

Abstract

The positive electrode active material contains a compound comprising Mn1-xZrxO2 (0 < x ≤ 0.05). The lithium secondary battery 100 comprises: a positive electrode layer 10 containing a positive electrode active material; a negative electrode layer 20 containing a negative electrode active material; and an electrolyte layer 30 disposed between the positive electrode layer 10 and the negative electrode layer 20. The method for producing a compound comprises: a preparation step for preparing a mixture by mixing an Mn precursor and a Zr precursor; and a synthesis step for synthesizing the mixture prepared in the preparation step for obtain Mn1-xZrxO2 (0 < x ≤ 0.05).

Description

Positive electrode active material, lithium secondary battery, compound, and method for producing the compound

[0001] The present invention relates to a positive electrode active material, a lithium secondary battery, a compound, and a method for producing the compound.

[0002] A lithium secondary battery comprises a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, and is charged and discharged by the movement of lithium ions between the positive electrode layer and the negative electrode layer.

[0003] Non-Patent Document 1 discloses β-MnO as a positive electrode active material used in the positive electrode layer of a lithium secondary battery. ２ Disclose.

[0004] Dan Zhan et al., Single-crystal β-MnO2 hollow bipyramids: synthesis and application in lithium ion batteries, RSC Advances, 2013, 3, 5141-5147

[0005] β-MnO described in Non-Patent Document 1 ２ Lithium batteries using a positive electrode active material containing β-MnO have a problem that when they are charged and discharged at high speed, the movement of lithium ions is restricted and the capacity decreases. ２ This is thought to be because the lithium diffusion tunnel for lithium ions to diffuse through the β-MnO ２ There is a need to improve the charge-discharge characteristics of positive electrode active materials containing

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a positive electrode active material, a lithium secondary battery, a compound, and a method for producing the compound, which have excellent charge / discharge characteristics.

[0007] In order to achieve the above object, the positive electrode active material according to the present invention comprises Mn １－ｘ Zr ｘ O ２ (0<x≦0.05).

[0008] According to the present invention, it is possible to provide a positive electrode active material, a lithium secondary battery, a compound, and a method for producing the compound, all of which have excellent charge / discharge characteristics.

[0009] FIG. 1 is a schematic cross-sectional view showing a lithium secondary battery according to an embodiment; FIG. 2 is a diagram showing a crystal structure of a compound according to an embodiment; FIG. 3 is a flowchart showing a method for producing a compound according to an embodiment; FIG. 4 is an XRD spectrum of compounds according to examples and comparative examples; FIG. 5 is a diagram showing a lattice constant a according to examples and comparative examples; FIG. 6 is a diagram showing a lattice constant c according to examples and comparative examples; FIG. 7 is a diagram showing the volume V of a unit cell according to examples and comparative examples; and FIG. 8 is a diagram showing a cycle test of lithium secondary batteries according to examples and comparative examples.

[0010] The positive electrode active material, lithium secondary battery, compound, and method for manufacturing the compound according to the embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or equivalent parts are designated by the same reference numerals.

[0011] 1 is a schematic cross-sectional view showing a lithium secondary battery 100 according to an embodiment. First, the lithium secondary battery 100, positive electrode active material, and compound according to this embodiment will be described. The lithium secondary battery 100 is a secondary battery that is charged and discharged by the movement of lithium ions between the positive electrode and the negative electrode.

[0012] 1, the lithium secondary battery 100 includes a positive electrode layer 10 having a positive electrode current collector layer 10A and a positive electrode active material layer 10B, a negative electrode layer 20 having a negative electrode current collector layer 20A and a negative electrode active material layer 20B, and an electrolyte layer 30, and may also include an exterior body, etc. The shape of the lithium secondary battery 100 is not particularly limited, and examples thereof include a cylindrical shape, a prismatic shape, a laminate shape, and a coin shape.

[0013] The positive electrode current collector layer 10A is a conductive plate- or foil-shaped member, and is made of, for example, a metal or a conductive resin, although it is not particularly limited thereto. Examples of metals that can be used include aluminum, nickel, iron, stainless steel, titanium, and copper. Alternatively, a clad material of nickel and aluminum, or a clad material of copper and aluminum may also be used. Examples of conductive resins include resins in which a conductive filler is added to a non-conductive polymer material.

[0014] The positive electrode active material layer 10B releases lithium ions during charging and absorbs lithium ions during discharging, and contains at least a positive electrode active material, and may further contain a solid electrolyte, a binder, a conductive material, etc. The thickness of the positive electrode active material layer 10B is not particularly limited, but is preferably 10 μm or more and 500 μm or less, and more preferably 50 μm or more and 200 μm or less.

[0015] The positive electrode active material is Mn １－ｘ Zr ｘ O ２ (0<x≦0.05). FIG. 2 shows the crystal structure of the compound. １－ｘ Zr ｘ O ２ As shown in FIG. 2, the compound consisting of (0<x≦0.05) has a rutile structure, and lithium diffusion tunnels DT are formed. The space group of the crystal structure of this compound is P42 / mnm. When the lithium secondary battery 100 is discharged, lithium ions enter the lithium diffusion tunnels DT. When the lithium secondary battery 100 is charged, lithium ions are released from the lithium diffusion tunnels DT. The number of Zr atoms relative to the number of Mn atoms is preferably 0.005 or more and 0.04 or less, more preferably 0.01 or more and 0.02 or less. This allows the Mn １－ｘ Zr ｘ O ２ (0<x≦0.05) can maintain the rutile structure. ２ By substituting a part of Mn with Zr, the lattice constant becomes larger, and the lithium diffusion tunneling DT becomes larger. ２This allows for easier movement of lithium ions. In particular, even when the battery is charged and discharged at high speed, the capacity can be prevented from decreasing. １－ｘ Zr ｘ O ２ The lithium secondary battery 100 using the compound having the formula (0<x≦0.05) as the positive electrode active material has excellent charge / discharge characteristics.

[0016] The negative electrode current collector layer 20A is a conductive plate- or foil-shaped member, and is made of, for example, a metal or a conductive resin, although it is not particularly limited thereto. Examples of metals that can be used include aluminum, nickel, iron, stainless steel, titanium, and copper. Alternatively, a clad material of nickel and aluminum, or a clad material of copper and aluminum may also be used. Examples of conductive resins include resins in which a conductive filler is added to a non-conductive polymer material.

[0017] The negative electrode active material layer 20B is configured to be able to absorb lithium (or precipitate lithium) during charging and release lithium ions during discharging, and includes at least a negative electrode active material, and may further include a solid electrolyte, a binder, a conductive material, etc. The thickness of the negative electrode active material layer 20B is not particularly limited, but is preferably 1 μm or more and 100 μm or less, and more preferably 5 μm or more and 80 μm or less.

[0018] The negative electrode active material is not particularly limited as long as it is an active material containing Li, and may be Li metal or a lithium alloy containing Li. Examples of lithium alloys include alloys of lithium and at least one metal selected from gold (Au), magnesium (Mg), aluminum (Al), calcium (Ca), zinc (Zn), tin (Sn), and bismuth (Bi). The lithium alloy may also be an alloy of lithium and two or more of the above-mentioned metals. Specific examples of lithium alloys include lithium-gold alloy (Li-Au), lithium-magnesium alloy (Li-Mg), lithium-aluminum alloy (Li-Al), lithium-calcium alloy (Li-Ca), lithium-zinc alloy (Li-Zn), lithium-tin alloy (Li-Sn), lithium-bismuth alloy (Li-Bi), and lithium-indium alloy (Li-In).

[0019] The electrolyte layer 30 is interposed between the positive electrode layer 10 and the negative electrode layer 20, and is in contact with the positive electrode active material layer 10B and the negative electrode active material layer 20B. The electrolyte layer 30 contains a solid electrolyte or a liquid electrolyte and may further contain a binder or the like. The solid electrolyte may partially contain a liquid electrolyte, a gel, a polymer electrolyte, or the like.

[0020] The solid electrolyte may be, for example, a sulfide solid electrolyte, an oxide solid electrolyte, a halogen solid electrolyte, or an oxyhalogen solid electrolyte, and it is preferable to use a sulfide solid electrolyte. The thickness of the solid electrolyte layer 30 is not particularly limited, but is preferably 5 μm or more and 100 μm or less, and more preferably 20 μm or more and 60 μm or less.

[0021] Examples of sulfide solid electrolytes include LiI-Li ２ S-SiS ２ , LiI-Li ２ S-P ２ O ５ , LiI-Li ３ P.O. ４ -P ２ S ５ , Li ２ S-P ２ S ５ , Li２ S-P ２ S ５ -Z ｍ S ｎ (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li ２ S-GeS ２ , Li ２ S-SiS ２ -Li ３ P.O. ４ , Li ２ S-SiS ２ -Li ｘ MO ｙ (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In). ２ S-P ２ S ５ " The statement Li ２ S and P ２ S ５ The same applies to the other descriptions above. In addition, sulfide glass or the like may be used as the sulfide solid electrolyte.

[0022] As the oxide solid electrolyte, for example, a compound having a NASICON structure can be used. Examples of the compound having a NASICON structure include compounds represented by the general formula Li １＋ｘ Al ｘ Ge ２－ｘ (P.O. ４ ) ３ (0≦x≦2) (LAGP), a compound represented by the general formula Li １＋ｘ Al ｘ Ti ２－ｘ (P.O. ４ ) ３ (0≦x≦2) (LATP) and the like can be used. In addition, other oxide solid electrolytes include LiLaTiO (for example, Li ０．３４ La ０．５１ TiO ３ ), LiPON (e.g., Li ２．９ P.O. ３．３ N ０．４６ ), LiLaZrO (e.g., Li ７ La ３ Zr２ O １２ ) etc. can be used.

[0023] The liquid electrolyte may be an electrolytic solution containing a solvent and a lithium salt.

[0024] The type of solvent is not particularly limited, and examples thereof include non-aqueous solvents, such as carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, and aprotic solvents.

[0025] Examples of carbonate solvents include cyclic carbonate solvents and chain carbonate solvents, such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and butylene carbonate.

[0026] Examples of ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, and caprolactone.

[0027] Examples of ether solvents include dibutyl ether, tetraglyme, triglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran.

[0028] An example of the ketone solvent is cyclohexanone.

[0029] Examples of alcohol-based solvents include ethyl alcohol and isopropyl alcohol.

[0030] Aprotic solvents include nitriles, amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes.

[0031] The solvent preferably contains ethylene carbonate and diethyl carbonate. The content of the solvent in the electrolytic solution is not particularly limited, but is preferably 50 to 99% by mass, more preferably 85 to 98% by mass, based on the total mass of the electrolytic solution, in terms of achieving a more excellent effect.

[0032] The type of lithium salt is not particularly limited, and LiPF ６ , LiBF ４ , LiClO ４ , LiAsF ６ , LiC(CF ３ SO ２ ) ３ , Li ２ SiF ６ , LiOSO ２ CkF ２ｋ＋１ [k is an integer from 1 to 8], LiN(SO ２ C ｋ F ２ｋ＋１ ) 2 (k is an integer from 1 to 8), LiPF ｎ (C ｋ F ２ｋ＋１ ) ６－ｎ [n is an integer of 1 to 5, k is an integer of 1 to 8], LiPF ４ (C2O ２ ), and LiPF ２ (C ２ O ２ ) ２ Examples include:

[0033] The content of the lithium salt in the liquid electrolyte is not particularly limited, but is preferably 0.2 to 3.0 mol / L, and more preferably 0.4 to 2.0 mol / L, in terms of achieving a more excellent effect.

[0034] The liquid electrolyte may contain components other than the solvent and the lithium salt. The method for preparing the liquid electrolyte is not particularly limited as long as it is a method that can mix the solvent, the lithium salt, and any optional components added as needed, and can uniformly dissolve or disperse each component.

[0035] Next, a method for producing the compound according to this embodiment will be described.

[0036] 3 is a flowchart showing a method for producing a compound. As shown in FIG. 3, the method for producing a compound includes a preparation step (step S101) and a synthesis step (step S102). Here, the compound Mn １－ｘ Zr ｘ O ２ A method for producing (0<x≦0.05) will be described.

[0037] In the preparation step (step S101), a Mn precursor and a Zr precursor are mixed to prepare a mixture. Preferably, the Mn precursor, the Zr precursor, and an acid are dissolved in water to prepare the mixture. The Mn precursor is a Mn compound, such as KMnO. ４ The Zr precursor is a Zr compound including a Zr salt, for example, ZrCl ４ , ZrO(CH ３ COO) ２ , ZrOCl ２ , ZrO(NO ３ ) ２ , Zr(SO ４ ) ２ , Zirconium (IV) Propoxide. Preferably, ZrCl ４ The acid is preferably an inorganic acid, for example, HCl, H ２ SO ４ , HNO ３ The amount of the Zr precursor is adjusted depending on the number of Zr atoms relative to the number of Mn atoms. The ratio of the number of Zr atoms to the number of Mn atoms is preferably 0.005 or more and 0.04 or less, and more preferably 0.01 or more and 0.02 or less. The mixture prepared as described above is preferably stirred.

[0038] Next, in the synthesis step (step S102), Mn １－ｘ Zr ｘ O ２ Specifically, the mixture prepared in the preparation step (step S101) is subjected to hydrothermal synthesis using an autoclave to synthesize Mn １－ｘ Zr ｘ O ２(0<x≦0.05) is synthesized. The heating temperature is preferably 180°C or higher and 240°C or lower. The heating time is preferably 10 hours or higher and 20 hours or lower. After the hydrothermal synthesis, it is preferable to recover the product and wash it with pure water. As a result, the compound Mn １－ｘ Zr ｘ O ２ (0<x≦0.05) is obtained.

[0039] As described above, in the positive electrode active material and the lithium secondary battery 100 according to the present embodiment, Mn １－ｘ Zr ｘ O ２ By using a compound consisting of MnO (0<x≦0.05), excellent charge / discharge characteristics are obtained. ２ This is thought to be because the lithium diffusion tunnel DT is widened by substituting a part of the Mn in the lithium ion-containing electrolyte with Zr, which facilitates the movement of lithium ions. In particular, the capacity decrease can be suppressed even when the electrolyte is charged and discharged at high speed. １－ｘ Zr ｘ O ２ When the number of Zr atoms relative to the number of Mn atoms in the compound (positive electrode active material) consisting of (0<x≦0.05) is 0.005 or more and 0.04 or less, the charge-discharge characteristics are excellent, and when it is 0.01 or more and 0.02 or less, the charge-discharge characteristics are even more excellent. １－ｘ Zr ｘ O ２ The compound having the formula (0<x≦0.05) can be used as a positive electrode active material for a lithium secondary battery. １－ｘ Zr ｘ O ２ (0<x≦0.05) can be prepared.

[0040] (Modifications) The configurations shown in the above embodiments are merely examples, and can be modified or applied as desired.

[0041] In the above embodiment, the positive electrode active material is Mn １－ｘ Zr ｘ O ２ (0<x≦0.05) has been described, but Mn １－ｘ Zr ｘ O２ The composition may further contain a compound other than (0<x≦0.05). For example, the composition may contain other compounds used as positive electrode active materials in lithium secondary batteries. Even in this case, the composition can have excellent charge / discharge characteristics.

[0042] In the above embodiment, an example has been described in which the anode layer 20 and the electrolyte layer 30 are in direct contact with each other. The lithium secondary battery 100 may further include an anode intermediate layer between the anode layer 20 and the electrolyte layer 30. The anode intermediate layer is a layer provided in a lithium deposition-type solid-state battery for the purpose of protecting the electrolyte layer 30, etc. The presence of the anode intermediate layer protects the electrolyte layer 30 from metallic lithium. The anode intermediate layer can be realized, for example, by a layer containing metal particles such as silver, carbon particles, and a binder resin.

[0043] The effects of the positive electrode active material and the lithium secondary battery are demonstrated below by way of examples. These examples illustrate one embodiment of the present disclosure, and the present disclosure is not limited thereto in any way.

[0044] First, the Mn precursor KMnO ４ and Zr precursor ZrCl ４ and HCl, an acid, were dissolved in water to prepare the mixtures of Examples 1 to 4. ４ and HCl, an acid, were dissolved in water to prepare the mixture of Comparative Example 1. For example, the mixtures of Examples 1 to 4 were prepared by dissolving 0.8593 g of KMnO ４ and Zr precursor ZrCl ４ and 36%, 11.25 ml of HCl in 176.25 ml of water. ４ The amount of each of the above-prepared mixtures of Examples 1 to 4 and Comparative Example 1 was adjusted according to the number of Zr atoms relative to the number of Mn atoms.

[0045] Next, the mixtures of Examples 1 to 4 and Comparative Example 1 were subjected to hydrothermal synthesis at 180°C for 10 hours using an autoclave. The hydrothermally synthesized mixtures were collected and washed with pure water to obtain Mn of Examples 1 to 4. １－ｘ Zr ｘ O ２(0<x≦0.05) (positive electrode active material) and MnO of Comparative Example 1 ２ The values ​​of x in Examples 1 to 4 and the number of Zr atoms relative to the number of Mn atoms in Examples 1 to 4 and Comparative Example 1 are shown in Table 1.

[0046]

[0047] Next, X-ray diffraction (XRD) measurements were performed on the compounds of Examples 1 to 4 and Comparative Example 1 under the following conditions: incident light: CuKα1 (monochromatic, λ = 0.15405 nm) and diffraction angles: 10° to 60°. Figure 4 shows the XRD spectra of the compounds of Examples 1 to 4 and Comparative Example 1. As shown in Figure 4, the XRD spectra of the compounds of Examples 1 to 4 and Comparative Example 1 have similar peaks, indicating that they have similar rutile crystal structures. The space group of this crystal structure was P42 / mnm. It was also found that the rutile structure can be maintained when the number of Zr atoms relative to the number of Mn atoms is 0.005 to 0.04. Table 2 also shows the lattice constants a and c and the unit cell volume V determined from the XRD spectra. Note that 1 Å = 0.1 nm. Figure 5 shows the lattice constant a of Examples 1 to 4 and Comparative Example 1. Figure 6 shows the lattice constant c of Examples 1 to 4 and Comparative Example 1. 7 is a diagram showing the volume V of the unit cell of Examples 1 to 4 and Comparative Example 1. It was found that the lattice constants a and c and the unit cell volume V of the compound of Example 1 were larger than those of the compound of Comparative Example 1. It was also found that the lattice constants a and c and the unit cell volume V of the compounds of Examples 2 to 4 were larger than those of the compound of Example 1.

[0048]

[0049] Next, positive electrode mixtures were prepared using the positive electrode active materials of Examples 1 to 4 and Comparative Example 1 synthesized as described above. Specifically, the positive electrode active material (80% by mass), PTFE (Polytetrafluoroethylene) (4% by mass), and carbon (16% by mass) were mixed in a mortar, punched into a Φ4 mm diameter, and molded at 100 MPa for 1 minute.

[0050] Next, an electrolyte solution for a lithium secondary battery was prepared. The electrolyte solution was prepared using 1.0 M LiPF as a lithium salt. ６ The solvent used was EC (Ethylene Carbonate):DEC (Diethyl Carbonate) = 1:1.

[0051] The positive electrode mixture and electrolyte solution prepared as described above were used to fabricate lithium secondary batteries of Examples 1 to 4 and Comparative Example 1. Li metal was used as the negative electrode active material, and glass fiber was used as the separator.

[0052] Next, cycle tests were carried out on the lithium secondary batteries of Examples 1 to 4 and Comparative Example 1 under the following conditions: Charging conditions: 0.05 C, 4.0 V vs. Li / Li ＋ Cut-off discharge conditions: CC (Constant Current) discharge at each rate: 0.05C, 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, 2.0V vs. Li / Li ＋ Cut off at

[0053] FIG. 8 shows cycle tests of lithium secondary batteries. As shown in FIG. 8 , the capacity retention rates of the lithium secondary batteries of Examples 1 to 4 were found to be superior to that of the lithium secondary battery of Comparative Example 1. This is thought to be because, as described above, the lattice constants a and c and the unit lattice volume V of the positive electrode active material used in the lithium secondary batteries of Examples 1 to 4 were larger than those of Comparative Example 1, resulting in a wider lithium diffusion tunnel. Furthermore, the capacity retention rates of the lithium secondary batteries of Examples 2 and 3 were greater than those of the lithium secondary batteries of Examples 1 and 4. This revealed that the lithium secondary batteries of Examples 2 and 3 had the best cycle characteristics, followed by the lithium secondary batteries of Examples 1 and 4. The capacity retention rate of the lithium secondary battery of Comparative Example 1 was approximately 0 at 2C and 5C. This is thought to be because, as described above, the lattice constants a and c and the unit lattice volume V of the positive electrode active material used in the lithium secondary battery of Comparative Example 1 were smaller, resulting in a narrower lithium diffusion tunnel.

[0054] As described above, the lithium secondary batteries of Examples 1 to 4 contain Mn１－ｘ Zr ｘ O ２ It was found that the use of a positive electrode active material containing a compound consisting of MnO (0<x≦0.05) provides excellent charge-discharge characteristics. ２ This is thought to be because the lithium diffusion tunnel was widened by replacing part of the Mn with Zr, making it easier for lithium ions to move. It was found that the capacity decrease was suppressed even when the material was charged and discharged at high speeds. １－ｘ Zr ｘ O ２ It was found that when the number of Zr atoms relative to the number of Mn atoms in a positive electrode active material containing a compound consisting of (0<x≦0.05) is 0.005 or more and 0.04 or less, the charge-discharge characteristics are excellent, and when it is 0.01 or more and 0.02 or less, the charge-discharge characteristics are even more excellent.

[0055] The present invention allows various embodiments and modifications without departing from the broad spirit and scope of the present invention. Furthermore, the above-described embodiments are intended to explain the present invention and do not limit the scope of the present invention. In other words, the scope of the present invention is defined by the claims, not by the embodiments. Various modifications made within the scope of the claims and the meaning of the disclosure equivalent thereto are considered to be within the scope of the present invention.

[0056] 10...positive electrode layer, 10A...positive electrode current collector layer, 10B...positive electrode active material layer, 20...negative electrode layer, 20A...negative electrode current collector layer, 20B...negative electrode active material layer, 30...electrolyte layer, 100...lithium secondary battery, DT...lithium diffusion tunnel.

Claims

1. Mn １－ｘ Zr ｘ O ２ (0<x≦0.05).

2. The positive electrode active material according to claim 1, wherein the number of Zr atoms is 0.005 or more and 0.04 or less relative to the number of Mn atoms.

3. The positive electrode active material according to claim 1, wherein the number of Zr atoms is 0.01 or more and 0.02 or less relative to the number of Mn atoms.

4. A lithium secondary battery comprising: a positive electrode layer containing the positive electrode active material according to any one of claims 1 to 3; a negative electrode layer containing a negative electrode active material; and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer.

5. Mn １－ｘ Zr ｘ O ２ (0<x≦0.05).

6. A preparation step of mixing a Mn precursor and a Zr precursor to prepare a mixture; and synthesizing the mixture prepared in the preparation step to obtain Mn. １－ｘ Zr ｘ O ２ (0<x≦0.05) 7. The Mn precursor is KMnO ４ The method for producing the compound according to claim 6 , comprising:

8. In the synthesis step, the compound is hydrothermally synthesized at 180°C or higher and 240°C or lower to form Mn １－ｘ Zr ｘ O ２ 8. A method for producing the compound according to claim 6 or 7, wherein (0<x≦0.05) is obtained.

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