WO2013153690A1 - 二次電池用正極活物質及びそれを使用した二次電池 - Google Patents
二次電池用正極活物質及びそれを使用した二次電池 Download PDFInfo
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G53/00—Compounds of nickel
- C01G53/40—Nickelates
- C01G53/42—Nickelates containing alkali metals, e.g. LiNiO2
- C01G53/44—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese
- C01G53/54—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese of the type [Mn2O4]-, e.g. Li(NixMn2-x)O4, Li(MyNixMn2-x-y)O4
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
- H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/50—Solid solutions
- C01P2002/52—Solid solutions containing elements as dopants
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- H—ELECTRICITY
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the present embodiment relates to a positive electrode active material for a lithium secondary battery and a secondary battery using the same.
- a lithium ion secondary battery using a non-aqueous electrolyte has a high energy density because a high voltage can be obtained, and is widely used as a power source for mobile phones, notebook computers, and the like.
- the use of the secondary battery for large-scale applications such as electric vehicles has attracted attention, and therefore, it is desired to solve problems such as improvement of safety, improvement of service life, and reduction of cost. .
- LiCoO 2 is well known as a positive electrode active material for lithium ion secondary batteries. LiCoO 2 is used in many lithium ion secondary batteries because it exhibits good characteristics. However, LiCoO 2 has a problem in that the raw material Co is expensive and resources are unevenly distributed, so that there are many fluctuation factors. In particular, for large-scale applications, consideration of alternative materials is indispensable because price and stable supply of resources are important in selecting materials.
- LiNiO 2 Another example of the positive electrode active material is LiNiO 2 .
- Ni is abundant in terms of resources compared to Co, but is a raw material with large price fluctuations due to demand balance.
- LiNiO 2 has a non-stoichiometric composition because trivalent Ni is unstable and easily becomes divalent, and synthesis control is possible because divalent Ni may enter the lithium site. Is difficult.
- LiNiO 2 is thermally unstable, it is difficult to ensure the safety of the secondary battery.
- LiMn 2 O 4 which is a lithium manganese composite oxide having a spinel crystal structure having a three-dimensional lithium diffusion path is promising.
- Mn which is a raw material of LiMn 2 O 4
- LiMn 2 O 4 suffers from problems such as deterioration due to cycling and elution of Mn into the electrolyte when stored at high temperatures. This is caused by the Jahn-Teller distortion of trivalent Mn that increases with the insertion of Li. This causes the crystal structure to become unstable, resulting in performance degradation associated with the cycle. It is considered to be.
- Patent Document 1 a composition formula Li x Mn (2-y) Al y O 4 (0.85 ⁇ x ⁇ 1.15, 0.02 ⁇ ) having a spinel structure and partially replacing Mn with Al. It is disclosed that the capacity maintenance rate during overdischarge can be improved by using a lithium manganese composite oxide of y ⁇ 0.5) as a positive electrode active material. Furthermore, the effect of life improvement etc. is confirmed by substituting with elements such as Mg, Ca (patent document 2), Ti (patent document 3), Co, Ni, Fe, Cr (patent document 4).
- the lithium manganese composite oxide is a so-called 4V class positive electrode having a discharge potential of 4.2 V or less and has a small discharge capacity, and therefore has a technical problem in terms of increasing the energy density.
- a method for improving the energy density of the lithium ion secondary battery a method for increasing the operating potential of the secondary battery is effective.
- a part of Mn of LiMn 2 O 4 can be replaced with Ni, Co, Fe, Cu, Cr, or the like, so that an operating potential of 5V class can be realized (for example, Patent Document 5, Non-patent document 1, Non-patent document 2). These are called 5V class positive electrodes.
- lithium manganese composite oxide in which a part of the Mn site is substituted with Ni has a flat discharge potential, and shows a high capacity in a region of 4.5 V or higher, and thus is expected as a high potential positive electrode active material.
- Mn exists in a tetravalent state, and discharge occurs due to the reaction of Ni 2+ ⁇ Ni 4+ instead of the reaction of Mn 3+ ⁇ Mn 4+ . Since the reaction of Ni 2+ ⁇ Ni 4+ has a high potential around 4.7 V, it functions as a high potential electrode material.
- Japanese Patent Laid-Open No. 04-28962 Japanese Unexamined Patent Publication No. 03-108261 Japanese Patent Laid-Open No. 08-17423 Japanese Unexamined Patent Publication No. 04-282560 Japanese Patent Laid-Open No. 09-147867 JP 2000-90923 A JP 2010-97845 A JP 2000-235857 A JP 2002-42814 A JP 2002-158008 A
- Patent Document 8 Patent Document 9, Patent Document 10, Non-Patent Document 3, Non-Patent Document 4
- 5V class positive electrodes in which a part of Mn is substituted with various elements such as Ni and Fe.
- the amount of substitution with Fe is very small, and further improvement is required for cost reduction.
- these documents do not mention the case where a part of Mn is substituted with three or more elements.
- An object of the present embodiment is to provide a positive electrode active material for a secondary battery capable of suppressing a reduction in capacity due to a cycle and a secondary battery using the same at low cost.
- the positive electrode active material for a secondary battery has the following formula (I) Li a (Fe x Ni y Mn 2-x-y-z A z) O 4 (I) (In formula (I), 0.2 ⁇ x ⁇ 1.2, 0 ⁇ y ⁇ 0.5, 0 ⁇ a ⁇ 1.2, 0 ⁇ z ⁇ 0.3.
- A is Li, B, And at least one selected from the group consisting of Na, Mg, Al, K, and Ca.
- the positive electrode active material for the secondary battery utilizes the change in valence of Ni and Fe as substitution elements, and has a high potential. It is characterized by ensuring the operation in
- Fe is a very advantageous material in terms of raw material costs and resources, but sufficient energy density is not obtained.
- Ni has a problem in terms of extending its life because the raw material cost fluctuates greatly and the electrolytic solution is easily decomposed by the catalytic action of Ni.
- the positive electrode active material for a secondary battery according to the present embodiment by substituting a part of Mn not only with Fe and Ni but also with the element A, it is possible to realize cost reduction and suppression of capacity reduction due to the cycle.
- the positive electrode active material for a secondary battery has the following formula (I) Li a (Fe x Ni y Mn 2-x-y-z A z) O 4 (I) (In formula (I), 0.2 ⁇ x ⁇ 1.2, 0 ⁇ y ⁇ 0.5, 0 ⁇ a ⁇ 1.2, 0 ⁇ z ⁇ 0.3.
- A is Li, B, And at least one selected from the group consisting of Na, Mg, Al, K, and Ca.
- the composition ratio x of Fe is 0.2 ⁇ x ⁇ 1.2.
- x is 0.2 or less, it is not preferable from the viewpoint of cost reduction and long life.
- x exceeds 1.2, the crystal structure becomes unstable and the capacity decreases, which is not preferable.
- the Fe composition ratio x is preferably 0.2 ⁇ x ⁇ 1.0, more preferably 0.2 ⁇ x ⁇ 0.6, and still more preferably 0.25 ⁇ x ⁇ 0. 4.
- the composition ratio y of Ni is 0 ⁇ y ⁇ 0.5.
- y 0, that is, when Ni is not included, it is not preferable from the viewpoint of increasing the capacity.
- y 0.5 or more, it is not preferable from the viewpoint of extending the life.
- the composition ratio y of Ni is preferably 0 ⁇ y ⁇ 0.4, more preferably 0 ⁇ y ⁇ 0.3, and further preferably 0.1 ⁇ y ⁇ 0. 3.
- Fe which is a substitution element of Mn
- Ni is preferably divalent.
- x + 2y 1 in the formula (I).
- the total substitution amount of Fe and Ni increases, Li and the transition metal element The cation mixing is likely to occur, and a single-phase spinel is difficult to obtain, which may lead to a decrease in capacity.
- the sum of the substitution amounts of Fe and Ni is preferably 0 ⁇ x + y ⁇ 0.7, more preferably 0 ⁇ x + y ⁇ 0.7, and 0.4 ⁇ x + y ⁇ 0.7. More preferably, 0.5 ⁇ x + y ⁇ 0.6 is particularly preferable.
- the composition ratio a of Li is 0 ⁇ a ⁇ 1.2.
- the composition ratio a of Li is preferably 0.8 ⁇ a ⁇ 1.1.
- a part of Mn is substituted with the element A.
- the element A is at least one selected from the group consisting of Li, B, Na, Mg, Al, K, and Ca, which is a metal having a valence of 1 to 3 and being lighter than Mn. It is done.
- the element A it is possible to reduce the weight of the electrode and suppress the decrease in capacity due to the cycle while preventing a change in the valence of Mn and realizing a high operating potential. It is presumed that the effect of suppressing the capacity decrease accompanying the cycle is obtained because the crystal structure can be further stabilized by substituting Mn with element A.
- the element A is preferably at least one selected from the group consisting of Li, Mg and Al.
- the composition ratio z of the element A is 0 ⁇ z ⁇ 0.3.
- the composition ratio z of the element A is preferably 0.01 ⁇ z ⁇ 0.2.
- the positive electrode active material for a secondary battery in the present embodiment preferably has a charge / discharge region due to a change in the valence of trivalent and tetravalent Fe.
- the change in the valence of trivalent and tetravalent Fe occurs at 4.8 V or more with respect to the lithium reference potential.
- it can be judged from the discharge curve of the secondary battery using the positive electrode active material made into object whether it has this charging / discharging area
- the specific surface area of the positive electrode active material for a secondary battery in this embodiment is 0.01 m 2 / g or more, and preferably not more than 3m 2 / g, 0.05m 2 / g or more, or less 1 m 2 / g Is more preferable.
- the specific surface area is 3 m 2 / g or less, a large amount of binder is not necessary in the production of the positive electrode, which is advantageous from the viewpoint of the capacity density of the positive electrode.
- the specific surface area is a value measured by the BET method.
- the raw material of the positive electrode active material for a secondary battery according to the present embodiment is not particularly limited, for example, as the Li raw material, Li 2 CO 3, LiOH, Li 2 O, may be used Li 2 SO 4 and the like. Among these, Li 2 CO 3 and LiOH are preferable.
- the Mn raw material various Mn oxides such as electrolytic manganese dioxide (EMD), Mn 2 O 3 , Mn 3 O 4 , and CMD (chemical manganese dioxide), MnCO 3 , MnSO 4 and the like can be used.
- EMD electrolytic manganese dioxide
- Mn 2 O 3 , Mn 3 O 4 , and CMD (chemical manganese dioxide), MnCO 3 , MnSO 4 and the like can be used.
- Fe raw material Fe 2 O 3 , Fe 3 O 4 , Fe (OH) 2 , FeOOH, and the like can be used.
- NiO, Ni (OH), NiSO 4 , Ni (NO 3 ) 2 or the like can be used as the Ni raw material.
- a raw material for the element A an oxide, carbonate, hydroxide, sulfide, nitrate, or the like of the element A can be used. These may use only 1 type and may use 2 or more types together.
- the materials are weighed and mixed so as to have the desired metal composition ratio.
- Mixing can be performed by pulverizing and mixing with a ball mill, a jet mill or the like.
- the obtained mixed powder is fired in air or oxygen at a temperature of 400 ° C. to 1200 ° C. to obtain a positive electrode active material that is a lithium manganese composite oxide.
- the firing temperature is high. However, if the firing temperature is too high, oxygen deficiency may occur and battery characteristics may deteriorate. Therefore, the firing temperature is preferably 450 ° C to 1000 ° C.
- the composition ratio of each element in the formula (I) is a value calculated from the amount of raw material charged for each element.
- the positive electrode for a secondary battery according to this embodiment includes the positive electrode active material for a secondary battery according to this embodiment.
- the positive electrode for a secondary battery according to the present embodiment can be produced, for example, by the following method.
- the positive electrode active material according to this embodiment is mixed with a conductivity-imparting agent, and a binder is further mixed and applied onto the current collector.
- a carbon material such as acetylene black, carbon black, fibrous carbon, graphite, a metal substance such as Al, a conductive oxide powder, or the like can be used.
- a binder polyvinylidene fluoride (PVDF) or the like can be used.
- PVDF polyvinylidene fluoride
- the current collector a metal thin film mainly composed of Al or the like can be used.
- the addition amount of the conductivity imparting agent is preferably 1 to 10% by mass with respect to the positive electrode active material. By making the addition amount of the conductivity imparting agent 1% by mass or more, the conductivity can be made sufficient. Moreover, since the content rate of a positive electrode active material becomes large by making the addition amount of an electroconductivity imparting agent into 10 mass% or less, the capacity
- the amount of the binder added is preferably 1 to 10% by mass with respect to the positive electrode active material. Electrode peeling can be suppressed by making the addition amount of a binder into 1 mass% or more. Moreover, since the content rate of a positive electrode active material becomes large by making the addition amount of a binder into 10 mass% or less, the capacity
- the secondary battery according to the present embodiment includes the secondary battery positive electrode according to the present embodiment.
- a secondary battery positive electrode according to the present embodiment As an example of the secondary battery according to the present embodiment, a secondary battery positive electrode according to the present embodiment, an electrolytic solution, and a negative electrode disposed to face each other with the electrolytic solution interposed therebetween are provided.
- Specific configurations of the secondary battery according to the present embodiment include, for example, a positive electrode for a secondary battery according to the present embodiment, a negative electrode including a negative electrode active material capable of occluding and releasing lithium, the positive electrode, and the negative electrode.
- a separator sandwiched between the positive electrode and the negative electrode and a lithium ion conductive electrolyte in which the positive electrode, the negative electrode and the separator are immersed are sealed in a battery case. Can be configured.
- the form of the secondary battery according to the present embodiment is not particularly limited.
- a positive electrode facing the separator a winding type winding the negative electrode, a positive electrode facing the separator, a stacked type stacking the negative electrodes, etc.
- a coin type or a laminate pack can be used for the cell.
- As the cell shape, a square cell, a cylindrical cell, or the like can be used.
- FIG. 1 shows a laminate type secondary battery as an example of the secondary battery according to this embodiment.
- a separator 5 is interposed between a positive electrode composed of a positive electrode active material layer 1 containing a positive electrode active material according to this embodiment and a positive electrode current collector 3, and a negative electrode composed of a negative electrode active material layer 2 and a negative electrode current collector 4. It is sandwiched.
- the positive electrode current collector 3 is connected to the positive electrode lead terminal 8
- the negative electrode current collector 4 is connected to the negative electrode lead terminal 7.
- An exterior laminate 6 is used for the exterior, and the inside of the secondary battery is filled with an electrolytic solution.
- Electrode As the electrolytic solution, a solution in which a lithium salt is dissolved as an electrolyte in a solvent can be used.
- Solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC).
- Chain carbonates such as dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, ⁇ -lactones such as ⁇ -butyrolactone, 1,2-diethoxyethane (DEE), chain ethers such as ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylform Amide, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, And apro
- propylene carbonate, ethylene carbonate, ⁇ -butyrolactone, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferably used alone or in combination.
- lithium salt examples include LiPF 6 , LiAsF 6 , LiAlCl 4 , LiClO 4 , LiBF 4 , LiSbF 6 , LiCF 3 SO 3 , LiC 4 F 9 CO 3 , LiC (CF 3 SO 2 ) 2 , LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, LiB 10 Cl 10, lower aliphatic lithium carboxylate, chloroborane lithium, lithium tetraphenylborate, LiBr, include LiI, LiSCN, LiCl, imides and the like It is done. These can be used alone or in combination of two or more.
- the electrolyte concentration of the electrolytic solution can be, for example, 0.5 mol / l to 1.5 mol / l. If electrolyte concentration is 1.5 mol / l or less, the increase in the density and viscosity of electrolyte solution can be suppressed. Moreover, if electrolyte concentration is 0.5 mol / l or more, the electrical conductivity of electrolyte solution can be made enough. A polymer electrolyte may be used instead of the electrolytic solution.
- the negative electrode can be produced, for example, by the following method.
- a negative electrode active material is mixed with a conductivity imparting agent, and a binder is further mixed and imparted onto the current collector.
- the negative electrode active material as a material capable of occluding and releasing lithium, carbon materials such as graphite, hard carbon, and soft carbon, Li metal, Si, Sn, Al, SiO, SnO, Li 4 Ti 5 O 12 and the like alone Or can be used in combination.
- the conductivity-imparting agent include carbon materials such as acetylene black, carbon black, fibrous carbon, graphite, and conductive oxide powder.
- the binder polyvinylidene fluoride (PVDF) or the like can be used.
- PVDF polyvinylidene fluoride
- As the current collector a metal foil mainly composed of Al, Cu or the like can be used.
- a laminate in which the positive electrode and the negative electrode for the secondary battery according to the present embodiment are stacked via a separator is used. It can be produced by being housed in a can. Further, the laminate can be produced by sealing with a flexible film or the like in which a synthetic resin and a metal foil are laminated. In addition, what wound this laminated body can also be used instead of this laminated body.
- Example 1 As a raw material of the positive electrode active material, MnO 2 , Fe 2 O 3 , NiO, Li 2 CO 3 , and B 2 O 3 as a raw material of B, CaO as a raw material of Ca, K 2 O as a raw material of K, MgO as the Mg raw material, Na 2 O as the Na raw material, and Al 2 O 3 as the Al raw material were weighed so as to have the metal composition ratio shown in Table 1, and pulverized and mixed. The powder after mixing the raw materials was fired at 800 ° C. for 8 hours to prepare a positive electrode active material.
- the prepared positive electrode active material and carbon (trade name: VGCF, manufactured by Showa Denko KK), which is a conductivity-imparting agent, are mixed, and polyvinylidene fluoride (PVDF), which is a binder, is dissolved in N-methylpyrrolidone.
- PVDF polyvinylidene fluoride
- the resulting solution was dispersed into a slurry.
- the mass ratio of the positive electrode active material, the conductivity imparting agent, and the binder was 92/4/4.
- the slurry was applied on an Al current collector. Then, it was dried in vacuum for 12 hours to obtain an electrode material.
- the electrode material was cut into a circle having a diameter of 12 mm.
- Li metal foil was used for the negative electrode.
- a polypropylene (PP) film was used as the separator.
- the positive electrode and the negative electrode were placed opposite to each other with a separator interposed therebetween, placed in a laminate cell, filled with an electrolytic solution, and sealed.
- the battery characteristics of the secondary battery produced as described above were evaluated. During the evaluation, the battery was charged to 5.2 V at a charging rate of 0.1 C and discharged to 3 V at a 0.1 C rate. Table 1 shows discharge capacity, discharge average voltage with respect to lithium metal, and discharge energy per positive electrode active material mass with respect to lithium metal potential.
- the negative electrode was produced as follows. Graphite as a negative electrode active material is mixed with carbon (trade name: VGCF, manufactured by Showa Denko KK) as a conductivity imparting agent, and dispersed in a solution of polyvinylidene fluoride (PVDF) dissolved in N-methylpyrrolidone. To make a slurry. The mass ratio of the negative electrode active material, the conductivity-imparting agent, and the binder was 90/1/9. The slurry was applied on a Cu current collector. Then, it was dried in vacuum for 12 hours to obtain an electrode material. The electrode material was cut into a circle having a diameter of 13 mm.
- PVDF polyvinylidene fluoride
- Cycle characteristics were evaluated by charging to 5.1 V at a charging rate of 1 C in a constant temperature bath at 20 ° C., and then performing constant voltage charging at 5.1 V. The total charging time was 150 minutes. Next, the battery was discharged to 3 V at a rate of 1C. This was repeated to evaluate the capacity maintenance rate after 500 cycles. The results are shown in Table 1.
- Examples 2 to 16, Comparative Examples 1 to 9 A secondary battery was produced in the same manner as in Example 1 except that the positive electrode active material having the composition shown in Table 1 was prepared in the same manner as in Example 1, and discharge capacity, discharge average voltage evaluation, and cycle characteristic evaluation were performed. The results are shown in Table 1.
- Examples 1 to 16 are positive electrode active materials having the composition of the formula (I)
- Comparative Examples 1 and 2 are positive electrode active materials in which a part of Mn is replaced with only one element
- Examples 3 to 9 show the results when the positive electrode active materials in which a part of Mn is substituted with two kinds of elements are used.
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Abstract
Description
Lia(FexNiyMn2-x-y-zAz)O4 (I)
(式(I)中、0.2<x≦1.2、0<y<0.5、0≦a≦1.2、0<z≦0.3である。Aは、Li、B、Na、Mg、Al、K及びCaからなる群から選択される少なくとも一種である。)で表される。
Mnを他元素で置換する技術は4V級正極において数多くの開示例がある。しかしながら、これらが結晶構造の安定性を高めることを目的としているのに対し、本実施形態に係る二次電池用正極活物質では置換元素であるNiとFeの価数変化を利用し、高電位での動作を確保することを特徴とする。
Lia(FexNiyMn2-x-y-zAz)O4 (I)
(式(I)中、0.2<x≦1.2、0<y<0.5、0≦a≦1.2、0<z≦0.3である。Aは、Li、B、Na、Mg、Al、K及びCaからなる群から選択される少なくとも一種である。)で表される。
本実施形態に係る二次電池用正極は、本実施形態に係る二次電池用正極活物質を含む。本実施形態に係る二次電池用正極は、例えば以下の方法により作製することができる。本実施形態に係る正極活物質を導電性付与剤と混合し、更に結着剤を混合して集電体上に塗布する。
本実施形態に係る二次電池は、本実施形態に係る二次電池用正極を備える。
本実施形態に係る二次電池の一例としては、本実施形態に係る二次電池用正極と、電解液と、該電解液を介して対向配置される負極とを備える。本実施形態に係る二次電池の具体的な構成としては、例えば、本実施形態に係る二次電池用正極と、リチウムを吸蔵放出可能な負極活物質を含む負極と、該正極と該負極との間に挟まれ該正極と該負極との電気的接続を起こさないセパレータと、該正極、該負極及び該セパレータが浸漬されるリチウムイオン伝導性の電解液と、が電池ケースの中に密閉された構成とすることができる。
前記電解液には、溶媒に電解質としてリチウム塩を溶解させた溶液を用いることが出来る。溶媒としては、プロピレンカーボネート(PC)、エチレンカーボネート(EC)、ブチレンカーボネート(BC)、ビニレンカーボネート(VC)等の環状カーボネート類、ジメチルカーボネート(DMC)、ジエチルカーボネート(DEC)、エチルメチルカーボネート(EMC)、ジプロピルカーボネート(DPC)等の鎖状カーボネート類、ギ酸メチル、酢酸メチル、プロピオン酸エチル等の脂肪族カルボン酸エステル類、γ-ブチロラクトン等のγ-ラクトン類、1,2-ジエトキシエタン(DEE)、エトキシメトキシエタン(EME)等の鎖状エーテル類、テトラヒドロフラン、2-メチルテトラヒドロフラン等の環状エーテル類、ジメチルスルホキシド、1,3-ジオキソラン、ホルムアミド、アセトアミド、ジメチルホルムアミド、アセトニトリル、プロピルニトリル、ニトロメタン、エチルモノグライム、リン酸トリエステル、トリメトキシメタン、ジオキソラン誘導体、スルホラン、メチルスルホラン、1,3-ジメチル-2-イミダゾリジノン、3-メチル-2-オキサゾリジノン、プロピレンカーボネート誘導体、テトラヒドロフラン誘導体、エチルエーテル、1,3-プロパンスルトン、アニソール、N-メチルピロリドン、フッ素化カルボン酸エステル等の非プロトン性有機溶媒等が挙げられる。これらは一種又は二種以上を混合して使用できる。これらの中でも、プロピレンカーボネート、エチレンカーボネート、γ-ブチロラクトン、ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネートを単独で又は混合して用いることが好ましい。
前記負極は、例えば以下の方法により作製することができる。負極活物質を導電性付与剤と混合し、更に結着剤を混合して集電体上に付与する。
本実施形態に係る二次電池の作製方法としては、例えば、乾燥空気又は不活性ガス雰囲気において、本実施形態に係る二次電池用正極及び負極を、セパレータを介して積層した積層体を、電池缶に収容して作製することができる。また、該積層体を合成樹脂と金属箔とを積層した可とう性フィルム等によって封口して作製することができる。なお、該積層体の代わりに、該積層体を捲回したものを用いることもできる。
正極活物質の原料として、MnO2、Fe2O3、NiO、Li2CO3、ならびに、Bの原料としてはB2O3、Caの原料としてはCaO、Kの原料としてはK2O、Mgの原料としてはMgO、Naの原料としてはNa2O、およびAlの原料としてはAl2O3を表1に示す金属組成比になるように秤量し、粉砕混合した。原料混合後の粉末を800℃で8時間焼成して正極活物質を作製した。
作製した正極活物質と導電性付与剤である炭素(商品名:VGCF、昭和電工(株)製)とを混合し、N-メチルピロリドンに結着剤であるポリフッ化ビニリデン(PVDF)を溶解させた溶液に分散させ、スラリーとした。正極活物質、導電性付与剤、結着剤の質量比は92/4/4とした。Al集電体上に該スラリーを塗布した。その後、真空中で12時間乾燥させて、電極材料とした。該電極材料を直径12mmの円に切り出した。その後、3t/cm2で加圧成形した。これにより正極を作製した。負極にはLi金属箔を用いた。セパレータにはポリプロピレン(PP)のフィルムを使用した。セパレータを介して正極と負極とを対向配置させ、ラミネートセル内に配置し、電解液を満たして密閉した。電解液には、溶媒EC/DMC=4/6(vol.%)に電解質LiPF6を1mol/lの濃度で溶解させた溶液を使用した。
前記正極を使用して、サイクル特性を評価した。負極は以下のようにして作製した。負極活物質としてのグラファイトに、導電性付与剤である炭素(商品名:VGCF、昭和電工(株)製)を混合し、N-メチルピロリドンにポリフッ化ビニリデン(PVDF)を溶解させた溶液に分散させ、スラリーとした。負極活物質、導電性付与剤、結着剤の質量比は90/1/9とした。Cu集電体上に該スラリーを塗布した。その後、真空中で12時間乾燥させて、電極材料とした。該電極材料を直径13mmの円に切り出した。その後、1.5t/cm2で加圧成形した。これにより負極を作製した。セパレータにはPPのフィルムを使用した。セパレータを介して正極と負極とを対向配置させ、コインセル内に配置し、電解液を満たして密閉し、二次電池を作製した。電解液には、溶媒EC/DMC=4/6(vol.%)に電解質LiPF6を1mol/lの濃度で溶解させた溶液を使用した。
表1に示す組成の正極活物質を実施例1と同様に調製した以外は実施例1と同様に二次電池を作製し、放電容量、放電平均電圧評価及びサイクル特性評価を行った。結果を表1に示す。
2 負極活物質層
3 正極集電体
4 負極集電体
5 セパレータ
6 外装ラミネート
7 負極リード端子
8 正極リード端子
Claims (7)
- 下記式(I)
Lia(FexNiyMn2-x-y-zAz)O4 (I)
(式(I)中、0.2<x≦1.2、0<y<0.5、0≦a≦1.2、0<z≦0.3である。Aは、Li、B、Na、Mg、Al、K及びCaからなる群から選択される少なくとも一種である。)
で表される二次電池用正極活物質。 - 前記式(I)のxが、0.2<x≦0.6である請求項1に記載の二次電池用正極活物質。
- 前記式(I)のyが、0<y≦0.3である請求項1または2に記載の二次電池用正極活物質。
- 前記式(I)のAが、Li、Mg及びAlからなる群から選択される少なくとも一種である請求項1~3のいずれか1項に記載の二次電池用正極活物質。
- Feの3価と4価の価数変化による充放電領域を有する請求項1から4のいずれか1項に記載の二次電池用正極活物質。
- 請求項1から5のいずれか1項に記載の二次電池用正極活物質を含む二次電池用正極。
- 請求項6に記載の二次電池用正極を備える二次電池。
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