JP6832186B2 - Lithium ion secondary battery - Google Patents

Description

The present specification discloses a lithium ion secondary battery.

A lithium ion secondary battery in which a non-aqueous electrolyte solution having lithium ion conductivity is interposed between a positive electrode and a negative electrode not only provides high voltage and high energy density, but also makes it possible to reduce the size and weight of a personal computer. It has already been put into practical use in the related fields of information and communication devices such as mobile phones and mobile phones. Further, in recent years, due to resource problems and environmental problems, studies are underway as a power source to be installed in electric vehicles and hybrid electric vehicles. As the positive electrode active material contained in the positive electrode of such a lithium ion secondary battery, for example, a composite oxide of lithium and a transition metal such as cobalt, nickel, or manganese is used. The _{layered lithium nickel-manganese composite oxide represented by LiNi 1-x} Mn _x O ₂ (0 <x ≦ 0.5) is one of these composite oxides, but it has high capacity and battery characteristics at high temperature. , It is said to be useful from the viewpoint of economic efficiency (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2003-34536

However, a lithium ion battery using a positive electrode containing a layered lithium nickel-manganese composite oxide has problems that the positive electrode generates heat during charging and the output characteristics in a low temperature region below 0 ° C. deteriorate.

The present disclosure has been made to solve such a problem, and its main purpose is to suppress heat generation of the positive electrode during charging and to improve output characteristics in a low temperature region.

The lithium ion secondary battery of the present disclosure is
A lithium ion secondary battery in which a non-aqueous electrolytic solution having lithium ion conductivity is interposed between a positive electrode and a negative electrode.
_{The positive electrode contains a layered lithium nickel manganese oxide represented by the composition formula LiNi 1-X} Mn _X O ₂ (in the formula, X is 0 <X ≦ 0.5) as a positive electrode active material, and garnet as a solid electrolyte. The ratio of the mass of the solid electrolyte to the sum of the mass of the positive electrode active material and the mass of the solid electrolyte is 5 to 40% by mass, which contains a type oxide.
It is a thing.

Compared with the case of using a positive electrode containing layered lithium nickel manganese oxide but not garnet type oxide, this lithium ion secondary battery suppresses heat generation of the positive electrode during charging and has output characteristics in a low temperature region. Is improved. The reason why such an effect can be obtained is presumed as follows. That is, in the lithium ion secondary battery, a non-aqueous solvent in which a lithium salt is dissolved is used as the electrolytic solution. It is presumed that by including the garnet-type oxide, which is a solid electrolyte, in the positive electrode this time, the content of the non-aqueous electrolyte solution in the positive electrode was reduced, and the calorific value of the positive electrode during charging could be suppressed. .. On the other hand, if the content of the non-aqueous electrolyte solution in the positive electrode decreases, the low temperature output characteristics are expected to decrease, but the low temperature output characteristics can be improved by appropriately adjusting the content ratio of the garnet type oxide. It is presumed that it was possible.

It is explanatory drawing which shows an example of the structure of the lithium ion secondary battery 10.

A preferred embodiment of the lithium ion secondary battery of the present disclosure will be described below. In the lithium ion secondary battery of the present embodiment, a non-aqueous electrolytic solution having lithium ion conductivity is interposed between the positive electrode and the negative electrode.

For the positive electrode, a positive electrode active material, a solid electrolyte, a conductive material, and a binder are mixed, and an appropriate solvent is added to form a paste-like positive electrode mixture, which is applied to the surface of the current collector, dried, and required. Therefore, it may be formed by compression in order to increase the electrode density.

The positive electrode active material contained in the positive electrode is _{a layered material represented by the composition formula LiNi 1-X} Mn _X O ₂ (in the formula, X is 0 <X ≦ 0.5, preferably 0.3 ≦ X ≦ 0.5). Lithium nickel manganese oxide is preferred. Such layered lithium nickel-manganese oxide is useful from the viewpoints of high capacity, battery characteristics at high temperature, economy, and the like. The layered lithium nickel manganese oxide may be doped with at least one of Zr, Al and Mg. By doing so, the heat generation of the positive electrode during charging is further suppressed, and the output characteristics in the low temperature region are further improved. The doping amount of Zr is preferably 0.2 to 0.5 mol% with respect to the total number of moles of Ni and Mn. The doping amount of Al is preferably 2 to 5 mol% with respect to the total number of moles of Ni and Mn. The amount of Mg added is preferably 2 to 5 mol% with respect to the total number of moles of Ni and Mn.

The positive electrode active material is preferably one synthesized by the coprecipitation method. This is because the metal elements can be uniformly mixed at the atomic level, and more suitable performance can be obtained. In the coprecipitation method, a precursor in which metal ions coexist in one particle may be prepared, mixed with a lithium salt, and calcined.

The solid electrolyte is preferably a garnet-type oxide. The garnet-type oxide is not particularly limited as long as it can conduct lithium ions, but the composition formula Li _{5 + Y} La ₃ (Zr _Y , A _2-Y ) O ₁₂ (in the formula, A is One or more elements selected from the group consisting of Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga and Ge, where Y is represented by 1.4 ≤ Y <2). preferable. Since Y satisfies 1.4 ≦ Y <2, such a garnet-type oxide _{has higher lithium ion conductivity than the known garnet-type oxide Li 7} La ₃ Zr ₂ O ₁₂ (that is, Y = 2). And the activation energy becomes smaller. Therefore, if this oxide is used, lithium ions are easily conducted, the resistance is lowered, and the output of the battery is improved. Further, since the activation energy is small, that is, the rate of change in conductivity with respect to temperature is small, the output of the battery is stable. Further, when Y satisfies 1.6 ≦ Y ≦ 1.95, the conductivity is higher and the activation energy is lower, which is more preferable. Further, when Y satisfies 1.65 ≦ Y ≦ 1.9, the conductivity is substantially maximized and the activation energy is substantially minimized, which is more preferable. As A, Nb having the same ionic radius as Ta or Ta is preferable.

Here, the garnet-type oxide capable of conducting lithium ions may mainly have a garnet-type structure, for example, a part of other structures may be contained or the peak position of X-ray diffraction may be shifted. It may include a structure that is distorted when viewed from the garnet. Further, as shown in the composition formula, the garnet-type oxide capable of conducting lithium ions may partially contain other elements and structures.

The ratio of the mass of the solid electrolyte to the sum of the mass of the positive electrode active material and the mass of the solid electrolyte is preferably 5 to 40% by mass. Within this range, the amount of heat generated by the positive electrode in the charged state can be suppressed, and the low temperature output characteristics can be improved. The mass ratio of this solid electrolyte is more preferably 6 to 38% by mass.

The conductive material contained in the positive electrode is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance of the positive electrode. For example, graphite such as natural graphite (scaly graphite, scaly graphite), artificial graphite, or acetylene black. , Carbon black, Ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.), etc., or a mixture of two or more thereof can be used. Among these, carbon black and acetylene black are preferable as the conductive material from the viewpoint of electron conductivity and coatability.

The binder contained in the positive electrode plays a role of binding the active material particles and the conductive material particles, and is, for example, a fluororesin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and fluororubber. Alternatively, a thermoplastic resin such as polypropylene or polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR) or the like can be used alone or as a mixture of two or more kinds. Further, an aqueous dispersion of cellulose-based binder or styrene-butadiene rubber (SBR), which is an aqueous binder, can also be used.

Examples of the solvent for dispersing the positive electrode active material, the conductive material, and the binder include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methylethylketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N, N-dimethylaminopropylamine. , Ethylene oxide, tetrahydrofuran and other organic solvents can be used. Further, a dispersant, a thickener or the like may be added to water, and the active material may be slurried with a latex such as SBR. As the thickener, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or as a mixture of two or more kinds. Examples of the coating method include roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, and the like, and any of these can be used to obtain an arbitrary thickness and shape. As the current collector, aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, etc., as well as aluminum, copper, etc. for the purpose of improving adhesiveness, conductivity, and oxidation resistance. The surface of the above can be treated with carbon, nickel, titanium, silver or the like. For these, it is also possible to oxidize the surface. Examples of the shape of the current collector include foil, film, sheet, net, punched or expanded, lath, porous body, foam, and fiber group forming body. As the thickness of the current collector, for example, one having a thickness of 1 to 500 μm is used.

For the negative electrode, a negative electrode active material, a conductive material, and a binder are mixed, and an appropriate solvent is added to form a paste-like negative electrode mixture, which is applied to the surface of the current collector and dried. It may be formed by compression to increase the density. The negative electrode active material is not particularly limited as long as it can store and release lithium ions, but a carbonaceous material is preferable from the viewpoint of safety. Examples of the carbonaceous material include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers and the like. Of these, graphites such as artificial graphite and natural graphite have an operating potential close to that of metallic lithium and can be charged and discharged at a high operating voltage. When a lithium salt is used as the electrolyte salt, self-discharge is suppressed. Moreover, it is preferable because the irreversible capacity at the time of charging can be reduced. Further, as the conductive material, the binder, the solvent and the like used for the negative electrode, those exemplified for the positive electrode can be used. The current collector of the negative electrode includes copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., as well as improved adhesiveness, conductivity and reduction resistance. For the purpose, for example, one in which the surface of copper or the like is treated with carbon, nickel, titanium, silver or the like can also be used. For these, it is also possible to oxidize the surface. The shape of the current collector can be the same as that of the positive electrode.

The non-aqueous electrolyte solution may contain a non-aqueous solvent and a supporting salt. Examples of the non-aqueous solvent include carbonates, esters, ethers, nitriles, furans, sulfolanes, dioxolanes and the like, and these can be used alone or in combination. Specifically, cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate; dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, Chain carbonates such as di-i-propyl carbonate and t-butyl-i-propyl carbonate; cyclic esters such as γ-butyl lactone and γ-valerolactone; methyl formate, methyl acetate, ethyl acetate, methyl butyrate and the like. Chain esters; Ethers such as dimethoxyethane, ethoxymethoxyethane, diethoxyethane; Nitriles such as acetonitrile and benzonitrile; Francs such as tetrahydrofuran and methyl tetrahydrofuran; Sulfolans such as sulfolane and tetramethylsulfolane; 1, Examples thereof include dioxolanes such as 3-dioxolane and methyldioxolane. Of these, a combination of cyclic carbonates and chain carbonates is preferable. According to this combination, not only the cycle characteristics that represent the battery characteristics by repeated charging and discharging are excellent, but also the viscosity of the electrolytic solution, the electric capacity of the obtained battery, the battery output, etc. can be balanced. it can.

Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiSbF ₆ , LiSiF _{6 , LiAlF 4} , LiSCN, and the like. Examples thereof include LiClO ₄ , LiCl, LiF, LiBr, LiI, and LiAlCl _4. Of these, from the group consisting _{of inorganic salts such as LiPF 6} , LiBF ₄ , LiAsF ₆ , and LiClO ₄ , and organic salts such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiC (CF ₃ SO ₂ ) _3. It is preferable to use one or a combination of two or more selected salts from the viewpoint of electrical characteristics. The concentration of this supporting salt in the non-aqueous electrolytic solution is preferably 0.1 mol / L or more and 5 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less. When the concentration of the supporting salt is 0.1 mol / L or more, a sufficient current density can be obtained, and when the concentration of the supporting salt is 5 mol / L or less, the electrolytic solution can be made more stable. Further, a flame retardant such as phosphorus or halogen may be added to this non-aqueous electrolytic solution.

The lithium ion secondary battery of the present embodiment may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the lithium ion secondary battery. For example, a polymer non-woven fabric such as a polypropylene non-woven fabric or a polyphenylene sulfide non-woven fabric, or a thin olefin resin such as polyethylene or polypropylene is used. Examples include microporous membranes. These may be used alone or in combination of two or more.

The shape of the lithium ion secondary battery of the present embodiment is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Further, a plurality of such lithium ion secondary batteries may be connected in series and applied to a large-sized battery used for an electric vehicle or the like. FIG. 1 is a schematic view showing an example of the lithium ion secondary battery 10 of the present embodiment. The lithium ion secondary battery 10 includes a positive electrode sheet 13 having a positive electrode mixture 12 formed on a current collector 11, a negative electrode sheet 18 having a negative electrode mixture 17 formed on the surface of the current collector 14, and a positive electrode sheet 13 and a negative electrode. It is provided with a separator 19 provided between the sheets 18 and a non-aqueous electrolytic solution 20 that fills the space between the positive electrode sheet 13 and the negative electrode sheet 18. In the lithium ion secondary battery 10, a separator 19 is sandwiched between the positive electrode sheet 13 and the negative electrode sheet 18, and these are wound and inserted into the cylindrical case 22, and the positive electrode terminal 24 and the negative electrode sheet connected to the positive electrode sheet 13 are connected. It is formed by disposing the negative electrode terminal 26 connected to the above. In the lithium ion secondary battery 10, the positive electrode mixture 12 is _{a layered lithium nickel represented by the composition formula LiNi 1-X} Mn _X O ₂ (in the formula, X is 0 <X ≦ 0.5) as the positive electrode active material. It contains manganese oxide and garnet-type oxide as a solid electrolyte, and the ratio of the mass of the solid electrolyte to the sum of the mass of the positive electrode active material and the mass of the solid electrolyte is in the range of 5 to 40 mass%.

In the lithium ion secondary battery of the present embodiment described in detail above, heat generation of the positive electrode during charging is suppressed as compared with the case of using a positive electrode containing a layered lithium nickel manganese oxide but not containing a garnet type oxide. At the same time, the output characteristics in the low temperature region are improved.

It goes without saying that the present invention is not limited to the above-described embodiment, and can be implemented in various aspects as long as it belongs to the technical scope of the present invention.

Preferable examples of the present invention will be described below, but the present invention is not limited to the following examples.

[Experimental Example 1]
(Synthesis of _{LiNi 0.5} Mn _0.5 O ₂₎
LiNi _0.5 Mn _0.5 O ₂ was prepared by the oxalate coprecipitation method as follows. Nickel acetate and manganese acetate are dissolved in ion-exchanged water from which an inert gas has been aerated in advance to remove dissolved oxygen so that the molar ratio of Ni element and Mn element is 0.5: 0.5, and these metal elements. A mixed aqueous solution was prepared so that the total molar concentration of the above was 0.5 mol / L. On the other hand, 0.5 mol / L oxalic acid aqueous solution and 0.5 mol / L ammonia water were prepared using ion-exchanged water from which dissolved oxygen had been removed in the same manner. Ion-exchanged water from which dissolved oxygen has been removed is placed in a reaction tank set to a temperature of 80 ° C. in the tank, and the mixture is stirred at 400 rpm. Ammonia water is added dropwise thereto, and the pH is based on a liquid temperature of 25 ° C. Was adjusted to be 6. A mixed aqueous solution, an oxalic acid aqueous solution, and aqueous ammonia were added to the reaction vessel while controlling the pH to 6, and stirring was continued for 5 hours to obtain a oxalate of a coprecipitation product. After completion of the reaction, the oxalate was filtered, washed with water and taken out, and dried in an oven at 120 ° C. overnight to obtain a powder sample of the oxalate. The obtained oxalate powder is heated at 600 ° C. to prepare a nickel-manganese composite oxide, and the powder and lithium hydroxide powder are mixed with the number of moles of lithium Mol (Li) and the transition metal element (Ni, Mn). The mixture was mixed so that the ratio (Mol (Li) / Mol (Me)) to the total number of moles of Mol (Me) was 1.10. This mixed powder is pressure-molded into pellets having a diameter of 2 cm and a thickness of about 5 mm at a pressure of 6 MPa, heated to a temperature of 1000 ° C. in an air atmosphere in an electric furnace in 2 hours, and the mixture is calcined at that temperature for 13 hours. As a result, the target sample was obtained. After firing, the heater was turned off and allowed to cool naturally. After about 8 hours, it was confirmed that the temperature in the furnace was 100 ° C. or lower, and the pellets were taken out to obtain _{LiNi 0.5} Mn _0.5 O _2.

The above-mentioned oxalate coprecipitation method was adopted because it is effective for uniformly mixing transition metal elements at the atomic level, but other methods may be used for synthesis.

(Test battery)
The positive electrode sheet was prepared as follows. _{85% by mass of LiNi 0.5} Mn _0.5 O ₂ as the positive electrode active material, 10% by mass of carbon black as the conductive material, 5% by mass of polyvinylidene fluoride as the binder, and an appropriate amount of N-methyl-2-pyrrolidone as the solvent. By adding and dispersing the positive electrode active material and the like, a slurry-like mixture was obtained. This slurry-like mixture was uniformly applied to a 15 μm-thick aluminum foil current collector and dried by heating to prepare a coating sheet. After that, the coated sheet was passed through a roll press to increase the density, and cut into a shape having a width of 120 mm and a length of 100 mm to obtain a positive electrode sheet.

The negative electrode sheet was prepared as follows. 95% by mass of graphite was mixed as the negative electrode active material, and 5% by mass of polyvinylidene fluoride was mixed as the binder to prepare a slurry-like mixture similar to the positive electrode. These slurry-like mixture materials were uniformly applied to a copper foil current collector having a thickness of 10 μm and dried by heating to prepare a coating sheet. After that, the coated sheet was passed through a roll press to increase the density, and cut into a shape having a width of 122 mm and a length of 102 mm to obtain a negative electrode sheet.

A laminated electrode body was produced by facing the positive electrode sheet and the negative electrode sheet with a polyethylene separator having a thickness of 25 μm sandwiched between them. This electrode body was sealed in an aluminum laminated bag, impregnated with a non-aqueous electrolytic solution, and then sealed to prepare a lithium ion secondary battery. _{As the non-aqueous electrolytic solution, one in which LiPF 6} was dissolved at a concentration of 1 M in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a ratio of 30:70 vol% was used.

[Experimental Example 2]
(Synthesis of garnet type solid electrolyte)
_{Li 6.75} La ₃ Zr _1.75 Ta _0.25 O ₁₂ , which is a cubic garnet-type oxide, was synthesized as follows. _{Li 2} CO ₃ , La (OH) ₃ , ZrO ₂ , and Ta ₂ O ₅ were used as starting materials. The starting materials were weighed to a stoichiometric ratio and ball milled in ethanol. After drying the mixed powder of the starting material, it was calcined in an alumina crucible at 950 ° C. for 10 hours in the air. _{Then, Li 2} CO ₃ corresponding to 10 atom% of the Li-charged composition was excessively added to the calcined powder, and the mixed powder was ball-milled in ethanol. The obtained powder was reheated in air at 950 ° C. for 10 hours, and after compaction molding, it was calcined at 1200 ° C. for 36 hours to prepare a solid electrolyte. Then, the synthetic powder was ball-milled to control the particle size. The particle size was 2 μm when it was measured using ethanol as a dispersant using a laser diffraction type particle size distribution measuring device (SALD-2200 manufactured by Shimadzu Corporation) and calculated as the median size.

(Test battery)
_{When preparing the positive electrode, 6% by mass of the garnet-type solid electrolyte Li 6.75} La ₃ Zr _1.75 Ta _0.25 O ₁₂ with a particle size of 2 μm synthesized by the above method was added to the total of the positive electrode active material and the solid electrolyte to form a slurry. A lithium ion secondary battery was produced in the same manner as in Experimental Example 1 except that the material was mixed.

[Experimental Example 3]
_{When preparing the positive electrode, a garnet-type solid electrolyte Li 6.75} La ₃ Zr _1.75 Ta _0.25 O ₁₂ having a particle size of 2 μm synthesized by the method described in Experimental Example 2 was added to the total amount of 20 mass of the positive electrode active material and the solid electrolyte. A lithium ion secondary battery was produced in the same manner as in Experimental Example 1 except that the mixture was made into a slurry-like mixture.

[Experimental Example 4]
_{When producing a positive electrode, a garnet-type solid electrolyte Li 6.75} La ₃ Zr _1.75 Ta _0.25 O ₁₂ having a particle size of 2 μm synthesized by the method described in Experimental Example 2 was added to the total amount of 38 mass of the positive electrode active material and the solid electrolyte. A lithium ion secondary battery was produced in the same manner as in Experimental Example 1 except that a slurry-like mixture was added.

[Experimental Example 5]
A lithium ion secondary battery was produced in the same manner as in Experimental Example 2 except that the positive electrode active material was LiNi _0.7 Mn _0.3 O _2. LiNi _0.7 Mn _0.3 O ₂ was synthesized in the same manner as _{LiNi 0.5} Mn _0.5 O _{2 of} Experimental Example 1 except that the molar ratio of Ni element and Mn element was 0.7: 0.3.

[Experimental Example 6]
A lithium ion secondary battery was produced in the same manner as in Experimental Example 3 except that the positive electrode active material was LiNi _0.7 Mn _0.3 O _2.

[Experimental Example 7]
A lithium ion secondary battery was produced in the same manner as in Experimental Example 4 except that the positive electrode active material was LiNi _0.7 Mn _0.3 O _2.

[Experimental Example 8]
A lithium ion secondary battery was produced in the same manner as in Experimental Example 3 except that the positive electrode active material was LiNi _0.5 Mn _0.5 O _{2 doped with Zr.} Zr-doped LiNi _0.5 Mn _0.5 O ₂ was _{synthesized by mixing LiNi 0.5} Mn _0.5 O ₂ with lithium hydroxide powder and ZrO ₂ powder, pressure-molding the pellets, and firing. The _{amount of ZrO 2} used was adjusted to be 0.2 mol% with respect to the total number of moles of transition metal elements (Ni, Mn). The amount of lithium hydroxide used was adjusted to be 1.10 times the total number of moles of Ni, Mn, and Zr.

[Experimental Example 9]
When producing the positive electrode active material, _{lithium was prepared in the same manner as in Experimental Example 8 except that the mixing amount of ZrO 2} was adjusted to 0.5 mol% with respect to the total number of moles of transition metal elements (Ni, Mn). An ion secondary battery was manufactured.

[Experimental Example 10]
A lithium ion secondary battery was produced in the same manner as in Experimental Example 3 except that the positive electrode active material was LiNi _0.5 Mn _0.5 O _{2 doped with Al.} Al-doped LiNi _0.5 Mn _0.5 O ₂ was _{synthesized by mixing LiNi 0.5} Mn _0.5 O ₂ with lithium hydroxide powder and Al (OH) ₃ powder, pressure-molding the pellets, and firing. The amount of Al (OH) ₃ used was adjusted to be 2 mol% with respect to the total number of moles of transition metal elements (Ni, Mn). The amount of lithium hydroxide used was adjusted to be 1.10 times the total number of moles of Ni, Mn, and Al.

[Experimental Example 11]
When the positive electrode active material was prepared, _{the mixing amount of Al (OH) 3} was adjusted to be 5 mol% with respect to the total number of moles of the transition metal elements (Ni, Mn) in the same manner as in Experimental Example 10. A lithium ion secondary battery was manufactured.

[Experimental Example 12]
A lithium ion secondary battery was produced in the same manner as in Experimental Example 3 except that the positive electrode active material was LiNi _0.5 Mn _0.5 O _{2 doped with Mg. LiNi 0.5} Mn _0.5 O ₂ doped with Mg was synthesized by mixing LiNi _0.5 Mn _0.5 O ₂ with lithium hydroxide powder and Mg (OH) ₂ powder, pressure-molding the pellets, and firing. The mixing amount of Mg (OH) ₂ was adjusted to be 2 mol% with respect to the total number of moles of transition metal elements (Ni, Mn). The amount of lithium hydroxide used was adjusted to be 1.10 times the total number of moles of Ni, Mn, and Mg.

[Experimental Example 13]
When producing the positive electrode active material, _{the mixing amount of Mg (OH) 2} was adjusted to be 5 mol% with respect to the total number of moles of the transition metal elements (Ni, Mn) in the same manner as in Experimental Example 12. A lithium ion secondary battery was manufactured.

[Experimental Example 14]
A lithium ion secondary battery was produced in the same manner as in Experimental Example 3 except that the positive electrode active material was LiNi _0.5 Mn _0.5 O _{2 doped with Zr and Mg. LiNi 0.5} Mn _0.5 O ₂ doped with Zr and Mg is obtained by mixing Lithium hydroxide powder, ZrO ₂ powder, and Mg (OH) ₂ powder with LiNi _0.5 Mn _0.5 O ₂ and press-molding the pellets. It was synthesized by firing. The mixing amounts of ZrO ₂ and Mg (OH) ₂ were adjusted to be 0.2 mol% and 2 mol%, respectively, with respect to the total number of moles of transition metal elements (Ni, Mn).

[Evaluation]
For the lithium ion secondary batteries of Experimental Examples 1 to 14, the calorific value and low temperature output characteristics of the following charged positive electrodes were measured. The results are shown in Table 1.

(The amount of heat generated by the charging positive electrode)
The battery was charged to 4.1 V and the laminated battery was opened in the glove box. A small amount of positive electrode was cut out from the battery and sealed in a stainless steel DSC pan without washing with an organic solvent or the like. The DSC measurement was performed with argon gas flowing through the measurement system, and the heat generation / endothermic behavior when the temperature was raised to the upper limit temperature of 400 ° C. at 5 ° C./min was measured. The calorific value (J / g) was calculated from the area of the region surrounded by the exothermic peak and the baseline obtained at this time. In the column of the calorific value of the charged positive electrode in Table 1, the numerical value standardized by the calorific value of Experimental Example 1 (relative value when the calorific value of Experimental Example 1 is "1") is shown.

(Low temperature output characteristics)
After adjusting to 50% of the battery capacity (SOC = 50%) at −30 ° C., currents were applied at various current values, and the battery voltage after 2 seconds was measured. The applied current and voltage were linearly interpolated to obtain the current value when the voltage after 2 seconds became 3.0 V, and the product of the current and voltage was taken as the output power in the low temperature region. In the column of low temperature output characteristics in Table 1, the numerical values standardized by the output power of Experimental Example 1 (relative values when the output power of Experimental Example 1 is "1") are shown.

From Table 1, by containing a garnet-type oxide as a solid electrolyte in the positive electrode in the range of 5 to 40% by weight as in Experimental Example 2-14, the garnet-type oxide was formed in the positive electrode as in Experimental Example 1. It was found that not only the amount of heat generated by the positive electrode during charging can be suppressed but also the low temperature output characteristics of the battery can be improved as compared with the case where it is not contained. In particular, as shown in Experimental Examples 8-14, it was found that more preferable characteristics were exhibited by doping the positive electrode active material with at least one of Zr, Al, and Mg. Further, it was found that when two elements of Zr and Mg were doped, more preferable characteristics were exhibited as compared with the case where one element was doped.

Of the above-mentioned Experimental Examples 1 to 14, Experimental Example 1 corresponds to Comparative Example and Experimental Examples 2 to 14 correspond to Examples.

10 Lithium-ion secondary battery, 11 current collector, 12 positive electrode mixture, 13 positive electrode sheet, 14 current collector, 17 negative electrode mixture, 18 negative electrode sheet, 19 separator, 20 non-aqueous electrolyte, 22 cylindrical case, 24 positive electrode Terminal, 26 Negative terminal.

Claims (4)

A lithium ion secondary battery in which a non-aqueous electrolytic solution having lithium ion conductivity is interposed between a positive electrode and a negative electrode.
The positive electrode is a layered lithium nickel manganese oxide represented by the composition formula LiNi _1-X Mn _X O ₂ (in the formula, X is 0 <X ≦ 0.5) which is not doped with other elements as the positive electrode active material. , And garnet-type oxide as a solid electrolyte, and the ratio of the mass of the solid electrolyte to the sum of the mass of the positive electrode active material and the mass of the solid electrolyte is 5 to 40% by mass.
Lithium-ion secondary battery. The garnet-type oxide is composed of Li _{5 + Y} La ₃ (Zr _Y , A _2-Y ) O ₁₂ (in the formula, A is Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, One or more elements selected from the group consisting of Ga and Ge, Y is represented by 1.4 ≦ Y <2).
The lithium ion secondary battery according to claim 1. A in the composition formula is Ta or Nb.
The lithium ion secondary battery according to claim 2. X is in the range of 0.3 ≤ X ≤ 0.5,
The lithium ion secondary battery according to any one of claims 1 to 3.

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