JP2014029782A - Cathode active material for nonaqueous electrolyte secondary battery, cathode for nonaqueous electrolyte secondary battery using the cathode active material, and nonaqueous electrolyte secondary battery using the cathode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which uses, as a cathode active material, an oxide containing lithium excess lithium-containing transition metal, the nonaqueous electrolyte secondary battery having high capacity and superior high-rate characteristics.SOLUTION: The cathode active material for the nonaqueous electrolyte secondary battery is characterized by including a lithium-containing transition metal oxide 9a represented by Li(LiMnNiCo)O, and erbium oxy-hydroxide 9b sticking on a part of a surface of the lithium-containing transition metal oxide 9a, a charging voltage of the battery being 4.6 V(vs.Li/Li) or higher.

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery.

  In recent years, mobile information terminals such as mobile phones, notebook computers, and smart phones have been rapidly reduced in size and weight, and batteries as driving power sources are required to have higher capacities. A non-aqueous electrolyte secondary battery that performs charge / discharge by moving lithium ions between the positive and negative electrodes along with charge / discharge has a high energy density and a high capacity. Widely used as a drive power source.

In addition, the mobile information terminal further increases power consumption with enhancement of functions such as a video playback function and a game function, and the terminal tends to be downsized. Therefore, the capacity of the non-aqueous electrolyte secondary battery is further increased. There is a strong need for a change.
Furthermore, in recent years, non-aqueous electrolyte secondary batteries have been rapidly developed as power sources for driving hybrid vehicles and electric vehicles and power sources for storing electric power. The non-aqueous electrolyte secondary battery in such applications has excellent high-rate characteristics, rapid charge / discharge, and excellent capacity maintenance rate of 70% or more even when the charge / discharge cycle is repeated for a long period of time. It is required to have a cycle characteristic.

Here, recently, as a positive electrode active material capable of realizing a high capacity, a lithium-containing transition metal having a layered structure containing manganese and containing excess lithium has been attracting attention. When this positive electrode active material is used, a discharge capacity of 250 mAh / g or more can be obtained by charging at 4.6 V (vs. Li / Li ⁺ ) or more. However, when the positive electrode active material is used, there are problems such as deterioration of cycle characteristics. Therefore, the following proposals have been made.
(1) An oxide such as ZrO ₂ , TiO ₂ , and Al ₂ O ₃ is unevenly distributed on the surface of Li (Li _w Mn _x Ni _y Co _z ) O ₂ , which is a positive electrode active material made of lithium-containing transition metal containing excess lithium. Proposal (see Patent Document 1).

(2) A lithium-excess lithium-containing transition metal containing additive elements such as Mg, Al, Ti, Cu, and Zr in the crystal structure is used as a positive electrode active material, and the amount of Li ₂ CO ₃ present on the surface is 0.05 The proposal which regulates to -0.20 wt% (refer patent document 2).

WO2012 / 057289 JP 2011-113792 A

However, the above proposal has the following problems.
When the lithium-rich positive electrode active material is coated with an oxide such as ZrO ₂ , TiO ₂ , or Al ₂ O ₃ as proposed in (1) above, the high rate characteristics deteriorate, and charge / discharge is performed when rapid charge / discharge is performed. There was a problem that the capacity decreased.
In the above proposal (2), not only the discharge capacity of the positive electrode active material is reduced by adding an additive element to the lithium-excess positive electrode active material, but also high rate characteristics are deteriorated by coating with Li ₂ CO _3. There was a problem.

  The present invention contains lithium, manganese, nickel and / or cobalt, and the molar amount of the lithium is 1.1 mol or more with respect to the total molar amount of the transition metal element and has a layered structure It has a transition metal oxide and a rare earth compound attached to a part of the surface of the lithium-containing transition metal oxide.

  According to the battery configuration of the present invention, there is an excellent effect that the high rate characteristic can be dramatically improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic longitudinal sectional view showing a schematic structure of a cylindrical nonaqueous electrolyte secondary battery according to an embodiment of the present invention. Explanatory drawing which shows the positive electrode active material which concerns on one Embodiment of this invention. Lithium-rich transition metal _oxides: X-ray diffraction chart of [chemical formula _{Li (Li 0.2 Ni 0.4 Mn 0.4} ) O 2 ]. The schematic diagram which shows schematic structure of a three-electrode type test cell.

  First, a nonaqueous electrolyte secondary battery according to an embodiment of the present invention will be described with reference to FIG. The nonaqueous electrolyte secondary battery in FIG. 1 is a cylindrical nonaqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery includes a battery case 1, a gasket 3, a positive electrode 5, a positive electrode lead 5a, a negative electrode 6, a negative electrode lead 6a, a separator 7, an upper insulating plate 8a, a lower insulating plate 8b, and a sealing body (including the sealing plate 2). 17). The belt-like positive electrode 5 to which the positive electrode lead 5a is attached and the belt-like negative electrode 6 to which the negative electrode lead 6a is attached are wound in the longitudinal direction via the separator 7 to form a spiral electrode body. The spiral electrode body is housed in the battery case 1 with the lower insulating plate 8b disposed at the lower portion and the upper insulating plate 8a disposed at the upper portion. One end of the negative electrode lead 6 a is welded to the battery case 1, while one end of the positive electrode lead 5 a is connected to the sealing body 17. Further, a non-aqueous electrolyte is injected into the battery case 1, and the sealing body 17 is caulked and fixed to the opening end of the battery case 1 via the gasket 3.

The nonaqueous electrolyte secondary battery having the above structure can be produced, for example, as follows.
First, a spiral electrode body is manufactured by winding a separator 7 between the negative electrode 6 and the positive electrode 5. Next, in a state where the lower insulating plate 8 b is disposed at the bottom of the spiral electrode body, these are accommodated in the battery case 1, and the negative electrode lead 6 a is welded to the bottom of the battery case 1. Next, after inserting the core and installing the upper insulating plate 8a on the spiral electrode body, the groove 4 is formed in the battery case so as to be positioned on the upper insulating plate 8a. Thereafter, a nonaqueous electrolyte is injected into the battery case 1. The amount of the nonaqueous electrolyte can be appropriately set according to the size of the spiral electrode body. Finally, the sealing body 17 is caulked and fixed to the open end of the battery case 1. Thereby, the cylindrical non-aqueous electrolyte secondary battery sealed inside can be manufactured.

Here, the positive electrode active material used for the positive electrode 5 contains lithium, manganese, nickel and / or cobalt, and the molar amount of the lithium is 1.1 mol with respect to the total molar amount of the transition metal element. The lithium-containing transition metal oxide (lithium-excess transition metal oxide) having a layered structure as described above and a rare earth compound attached to a part of the surface of the lithium-containing transition metal oxide.
When a rare earth compound adheres to a part of the surface of the lithium-containing transition metal oxide, the ionic conductivity of the film formed on the surface of the lithium-containing transition metal oxide increases, and desolvation is achieved. The reaction can be promoted. Therefore, the high rate characteristics of the nonaqueous electrolyte secondary battery are improved.

As shown in FIG. 2, the positive electrode active material has a specific structure in which a rare earth compound (for example, erbium oxyhydroxide) 9b adheres to the surface of the secondary particles of the lithium-containing transition metal oxide 9a. It has become. However, the rare earth compound 9b may have a structure that enters not only the surface of the secondary particles but also the gap between the primary particles.
The rare earth compound is preferably a rare earth hydroxide, a rare earth oxyhydroxide, or a rare earth oxide, and in particular, a rare earth hydroxide or a rare earth oxyhydroxide. It is desirable. This is because when these are used, the above-described effects are further exhibited. In addition to these, the rare earth compound may contain a rare earth carbonate compound, a rare earth phosphate compound, and the like.

  Examples of rare earth elements contained in the rare earth compounds include yttrium, lanthanum, cerium, neodymium, samarium, europium, gadolinium, cerium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Samarium and erbium are preferable. This is because a neodymium compound, a samarium compound, and an erbium compound have a smaller average particle size than other rare earth compounds and are more likely to be deposited more uniformly on the surface of the lithium-containing transition metal oxide.

  Specific examples of the rare earth compound include neodymium hydroxide, neodymium oxyhydroxide, samarium hydroxide, samarium oxyhydroxide, erbium hydroxide, and erbium oxyhydroxide. Further, when lanthanum hydroxide or lanthanum oxyhydroxide is used as the rare earth compound, lanthanum is inexpensive, so that the manufacturing cost of the positive electrode can be reduced.

  The ratio of the rare earth compound is preferably 0.005% by mass or more and 0.8% by mass or less with respect to the lithium-containing transition metal oxide in terms of rare earth elements. When the proportion is less than 0.005% by mass, the effect of attaching the rare earth compound may not be sufficiently exhibited. On the other hand, when the proportion exceeds 0.8% by mass, the lithium-containing transition metal oxide particles The lithium ion permeability and electronic conductivity on the surface may be lowered, and the high rate characteristics may be deteriorated.

Examples of the lithium-containing transition metal oxides (lithium-rich transition metal oxides), the chemical _{formula: Li α (Li x Mn y} Me (1-x-y)) O 2 (0.99 ≦ α ≦ 1.05,0 0.1 ≦ x ≦ 0.4, 0 <y <1, Me is preferably an oxide represented by Ni and / or Co).
Specifically, Li (Li _0.2 Ni _0.4 Mn _0.4 ) O ₂ , Li (Li _0.12 Ni _0.374 Mn _0.374 Co _0.132 ) O ₂ , Li (Li _{0. 12} Ni _0.2 Co _0.25 Mn _0.43 ) O ₂ , Li (Li _0.11 Ni _0.17 Co _0.07 Mn _0.65 ) O ₂ , Li (Li _0.2 Ni _0.18 Co _0.10 Mn _0.52 ) O _{2 and the} like. The lithium-containing transition metal oxide may contain Fe, Cr, and the like.

The lithium-containing transition metal oxide is expressed as LiMeO ₂ (Me is a transition metal), an R-3M structure in which a lithium layer, a transition metal layer, and an oxygen layer are stacked in a uniaxial direction, and Li (Li _1/3 Me _2/3 ) A lithium-containing transition metal oxide represented by O ₂ and having a C2 / m structure in which a Li layer, a Li _1/3 Me _2/3 layer, and an oxygen layer are stacked.

As shown in FIG. 3, the X-ray diffraction pattern showing an example of the lithium-containing transition metal oxide has a peak derived from the R-3M structure in the initial discharge state (peak near 2θ = 18 °) and 2θ. = It has a low intensity peak derived from the C2 / m structure in the vicinity of 20 to 23 °.
In addition, although it is preferable to use such a lithium containing transition metal oxide, this invention is not limited to this.

The charging voltage is preferably 4.6 V (vsLi / Li ⁺ ) or higher. Lithium-containing lithium-containing transition metal oxides can be formed at a charging voltage of 4.6 V (vsLi / Li ⁺ ) or higher, and the discharge capacity can be 250 mAh / g or higher. It is.

  Here, the positive electrode 5 has a structure including a sheet-like positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector. For example, the positive electrode active material, carbon A positive electrode slurry containing a conductive agent such as black and a binder such as polyvinylidene fluoride is applied to at least one surface of a positive electrode current collector made of aluminum or the like, and then dried and rolled.

  As the conductive agent and the binder, known materials can be used without any particular limitation. Further, as the positive electrode current collector, a sheet of stainless steel, aluminum, titanium, or the like can be used. In the case where the positive electrode active material layers are formed on both surfaces of the positive electrode current collector, the total thickness of the two positive electrode active material layers is preferably 50 to 250 μm. If the total thickness of the positive electrode active material layer is less than 50 μm, sufficient capacity may not be obtained. On the other hand, when the total thickness of the positive electrode active material layer exceeds 250 μm, the internal resistance of the battery tends to increase.

  In addition, cellulose may be added to the positive electrode slurry in order to improve the slip properties of the positive electrode active material, the conductive agent, and the binder during rolling in the positive electrode manufacturing step. Any method may be used for adding the celluloses, but when the positive electrode slurry is prepared, it can be uniformly added by dissolving it in N-methylpyrrolidone or the like as the solvent of the positive electrode slurry. Therefore, it is preferable. Examples of the celluloses include carboxymethyl cellulose and methyl cellulose, but methyl cellulose is preferably used. If methylcellulose is used, not only the slipping property during rolling can be remarkably improved, but also methylcellulose has high stability in the voltage range applied to the positive electrode. Moreover, since celluloses can be used as a thickener, the dispersibility of the positive electrode slurry can be improved.

  The average particle size of the rare earth compound is desirably 1 nm or more and 100 nm or less. When the average particle size of the rare earth compound exceeds 100 nm, the particle size of the rare earth compound is too large relative to the particle size of the lithium-containing transition metal oxide particles, so that the surface of the lithium-containing transition metal oxide particles is a rare earth compound. Will not be covered precisely. Therefore, the area in which the lithium-containing transition metal oxide particles and the nonaqueous electrolyte and their reductive decomposition products are in direct contact with each other increases, so that the oxidative decomposition of the nonaqueous electrolyte and its reductive decomposition products increases, and the charge / discharge characteristics deteriorate. To do.

  On the other hand, when the average particle size of the rare earth compound is less than 1 nm, the surface of the lithium-containing transition metal oxide particle is too densely covered with the rare earth hydroxide or the like. This is because the occlusion / release performance of the battery deteriorates and the charge / discharge characteristics deteriorate. In consideration of this, the average particle size of the rare earth compound is more preferably 10 nm or more and 50 nm or less.

  In order to attach the rare earth compound such as erbium oxyhydroxide to the lithium-containing transition metal oxide, it can be obtained by mixing, for example, an aqueous solution in which an erbium salt is dissolved in a solution in which the lithium-containing transition metal oxide is dispersed. As another method, there is a method in which an aqueous solution in which an erbium salt is dissolved is sprayed and then dried while mixing a lithium-containing transition metal oxide.

  Among them, it is preferable to use a method of mixing an aqueous solution in which a rare earth salt such as an erbium salt is dissolved in a solution in which a lithium-containing transition metal oxide is dispersed. This is because the rare earth compound can be more uniformly dispersed and adhered to the surface of the lithium-containing transition metal oxide. At this time, it is preferable to make the pH of the solution in which the lithium-containing transition metal oxide is dispersed constant. Particularly, in order to uniformly disperse fine particles of 1 to 100 nm on the surface of the lithium-containing transition metal oxide, It is preferable to regulate the pH to 6-10.

When the pH is less than 6, the transition metal of the lithium-containing transition metal oxide may be eluted. On the other hand, when the pH exceeds 10, the rare earth compound may be segregated.
In order to reduce the internal resistance and perform the reaction uniformly, the positive electrode lead 5a is preferably disposed at a position close to the central portion of the positive electrode.

  The negative electrode 6 has a structure including a sheet-like negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector. For example, a negative electrode active material such as carbon particles; A negative electrode slurry is prepared by dispersing a binder, a thickener added as necessary, and various other additives in water, and the negative electrode slurry is placed on at least one surface of the negative electrode current collector. After coating, it is obtained by drying and rolling.

  In the negative electrode active material layer produced as described above, a negative electrode active material, a binder, a thickener and other various additives, and gaps formed between the negative electrode active materials, that is, void portions, It has.

  As the negative electrode active material, a carbon material or an element capable of forming an alloy with lithium can be used. As the carbon material, natural graphite, non-graphitizable carbon, graphite such as artificial graphite, coke, etc. can be used, and the element capable of forming an alloy with lithium is preferably silicon or tin. Silicon oxide or tin oxide in which these are combined with oxygen can also be used. Furthermore, what mixed the said carbon material and the compound of silicon or tin can also be used. In addition, although the energy density is decreased, a negative electrode material having a higher charge / discharge potential than that of a carbon material or the like for lithium metal such as lithium titanate can be used.

The ratio of the binder to the total amount of the negative electrode active material layer is preferably 0.5 to 10% by mass, and particularly preferably 0.8 to 2% by mass.
The binder for the negative electrode is not particularly limited. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), styrene butadiene latex, And vinylidene fluoride-hexafluoropropylene copolymer.

The negative electrode current collector is not particularly limited. For example, a sheet or foil made of stainless steel, copper, or the like can be used. The negative electrode lead 6a is protected by an insulating tape after being connected to the negative electrode current collector by welding or the like.
Note that the binder and thickener in the negative electrode active material layer are not essential, and when forming the negative electrode active material layer using a method such as vapor deposition or CVD, the binder is unnecessary. There are many cases.

  The solvent of the non-aqueous electrolyte used in the present invention is not limited, and solvents conventionally used for non-aqueous electrolyte secondary batteries can be used. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, propionic acid Compounds containing esters such as ethyl and γ-butyrolactone, compounds containing sulfone groups such as propane sultone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 1,4 -Compounds containing ethers such as dioxane and 2-methyltetrahydrofuran, butyronitrile, valeronitrile, n-heptanenitrile, succinonitrile, glutaronitrile, adiponitrile, pimeronite Le, 1,2,3-propanetriol-carbonitrile, 1,3,5-pentanetricarboxylic carbonitrile compounds containing nitrile such as nitrile or can be used compounds comprising an amide such as dimethylformamide. In particular, a solvent in which a part of these H is substituted with F is preferably used. Further, these can be used alone or in combination, and a solvent in which a cyclic carbonate and a chain carbonate are combined, and a solvent in which a compound containing a small amount of nitrile or an ether is further combined with these is preferable. .

Examples of lithium salts include inorganic lithium fluorides and lithium imide compounds. Examples of the inorganic lithium fluoride include LiPF ₆ and LIBF ₄ , and examples of the lithium imide compound include a lithium salt having an oxalato complex as an anion in addition to LiN (CF ₃ SO ₂ ) _{2 and the} like. As a lithium salt having this oxalato complex as an anion, in addition to LiBOB [lithium-bisoxalate borate], a lithium salt having an anion in which C ₂ O ₄ ²⁻ is coordinated to the central atom, for example, Li [M (C ₂ O ₄ ) _x R _y ] (wherein M is a transition metal, an element selected from groups IIIb, IVb, and Vb of the periodic table, R is selected from a halogen, an alkyl group, and a halogen-substituted alkyl group) Group, x is a positive integer, and y is 0 or a positive integer.). Specifically, there are Li [B (C ₂ O ₄ ) F ₂ ], Li [P (C ₂ O ₄ ) F ₄ ], Li [P (C ₂ O ₄ ) ₂ F ₂ ], and the like. However, it is most preferable to use LiBOB in order to form a stable film on the surface of the negative electrode even in a high temperature environment.
In addition, the said solute may be used not only independently but in mixture of 2 or more types. Further, the concentration of the solute is not particularly limited, but is preferably 0.8 to 1.7 mol per liter of the electrolytic solution.

As the separator 7, a microporous film made of general polyethylene, polypropylene, or the like can be used. Preferably, a separator including an aramid layer on polyethylene or polypropylene is used. This is because the aramid layer is excellent in durability and heat resistance, can prevent shrinkage of the separator, and can improve the safety of the nonaqueous electrolyte secondary battery.
Moreover, it is preferable that the thickness of the separator 7 is 10-25 micrometers. If the thickness of the separator 7 is less than 10 μm, an OCV defect is likely to occur because the distance between the positive electrode and the negative electrode is narrow. When large particles slide off due to rubbing between the electrode plate and the separator during winding, the large particles may break through the separator and cause a short circuit between the positive and negative electrodes. On the other hand, if the thickness of the separator 7 is larger than 25 μm, the battery capacity cannot be increased and the high rate characteristics may be deteriorated.

  Hereinafter, the positive electrode active material for a nonaqueous electrolyte secondary battery according to the present invention will be described below. In addition, the positive electrode active material for nonaqueous electrolyte secondary batteries in this invention is not limited to what was shown in the following Example, It can implement by changing suitably in the range which does not change the summary.

(Example)
(A) Preparation of positive electrode 3 liters of Li (Li _0.2 Mn _0.54 Ni _0.13 Co _0.13 ) O ₂ particles 1000 g as a lithium-containing transition metal oxide (lithium-excess transition metal oxide) Was added to pure water and stirred. Next, a solution in which 5.31 g of erbium nitrate pentahydrate was dissolved was added to this solution. At this time, a 10% by mass aqueous sodium hydroxide solution was appropriately added to adjust the pH of the solution containing Li (Li _0.2 Mn _0.54 Ni _0.13 Co _0.13 ) O ₂ to 9. Next, after suction filtration and washing with water, the powder obtained at 250 ° C. is dried to contain erbium on the surface of Li (Li _0.2 Mn _0.54 Ni _0.13 Co _0.13 ) O _2. A positive electrode active material to which a compound (erbium oxyhydroxide) was uniformly attached was obtained. In addition, the adhesion amount of the said erbium oxyhydroxide was 0.20 mass% with respect to the said lithium containing transition metal oxide in conversion of the erbium element.

  Next, 4 parts by mass of carbon black as a carbon conductive agent and 2 parts by mass of polyvinylidene fluoride as a binder are mixed with 100 parts by mass of the positive electrode active material, and further NMP (N-methyl-2- A positive electrode slurry was prepared by adding an appropriate amount of pyrrolidone). Next, the positive electrode slurry was applied to both sides of a positive electrode current collector made of aluminum and dried. Finally, it cut out to the predetermined electrode size, rolled using the roller, and also the positive electrode lead was attached, and the single electrode cell (positive electrode) was produced. The packing density of the positive electrode active material in the single electrode cell was 3.0 g / cc.

(B) Production of three-electrode test cell While using the positive electrode as the working electrode 11, the three-electrode test cell 10 as shown in FIG. Produced. As the non-aqueous electrolyte solution 14, a solution obtained by dissolving LiPF ₆ to a concentration of 1 mol / liter in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 was used. .
The cell thus produced is hereinafter referred to as cell A.

(Comparative Example 1)
Except that the compound containing erbium did not adhere to the surface of Li (Li _0.2 Mn _0.54 Ni _0.13 Co _0.13 ) O ₂ when producing the positive electrode active material, A cell was produced in the same manner.
The cell thus fabricated is hereinafter referred to as cell Z1.

(Comparative Example 2)
When producing the positive electrode active material, a cell was produced in the same manner as in the above example except that 27.8 g of aluminum nitrate nonahydrate was used instead of erbium nitrate and the heat treatment temperature was 400 ° C. In the positive electrode active material thus manufactured, an oxide containing aluminum (aluminum oxide) adheres to the surface of Li (Li _0.2 Mn _0.54 Ni _0.13 Co _0.13 ) O _2. It was. In addition, the adhesion amount of the said aluminum oxide was 0.20 mass% with respect to the said lithium containing transition metal oxide in conversion of the aluminum element. The cell thus fabricated is hereinafter referred to as cell Z2.

(Experiment)
Since the cells A, Z1, and Z2 were charged / discharged under the following conditions, the initial charge / discharge capacity, high-rate discharge characteristics (discharge capacity at 1.0 It), and cycle characteristics (discharge capacity at the 30th cycle) were examined. The results are shown in Table 1. In all the cells, the experiment was conducted with 1.0 It being 260 mAh / g. Further, since the initial charge / discharge efficiency was calculated from the initial charge / discharge capacity, the results are also shown in Table 1.

-Charging / discharging conditions when investigating the initial charge / discharge capacity In a 25 ° C environment, the battery was charged with a constant current of 0.05 It until the voltage became 4.8 V (vs. Li ^/ Li ⁺ ), and then continuously charged at 4.8 V. Charging was performed at a constant voltage until the current became 0.01 It, and the initial charge capacity was measured. Thereafter, discharging was performed at a constant current of 0.05 It until the voltage became 2.0 V (vs. Li ^/ Li ⁺ ), and the initial discharge capacity was measured.

-Charging / discharging conditions for investigating high-rate discharge characteristics In a 25 ° C environment, charging was performed at a constant current of 0.2 It until the voltage reached 4.8 V (vs. Li ^/ Li ⁺ ), and then a constant voltage of 4.8 V was maintained. Charging was performed until the current was 0.05 It at voltage. Thereafter, discharging was performed at a constant current of 1.0 It until the voltage became 2.0 V (vs. Li ^/ Li ⁺ ). The capacity at the time of discharge was measured to obtain a discharge capacity at 1.0 It.

-Charging / discharging conditions when investigating cycle characteristics In a 25 ° C environment, charging was performed at a constant current of 0.2 It until the voltage reached 4.8 V (vs. Li ^/ Li ⁺ ), and then a constant voltage of 4.8 V The battery was charged until the current reached 0.05 It. Thereafter, discharging was performed at a constant current of 0.05 It until the voltage became 2.0 V (vs. Li ^/ Li ⁺ ). Such charge / discharge was repeated 30 times, and the discharge capacity at the 30th cycle was measured.

  As apparent from Table 1, in the cell Z1, the initial charge capacity is increased, so that the initial charge / discharge efficiency is lowered. It can also be seen that the discharge capacity at 1.0 It is low and the discharge capacity at the 30th cycle is greatly reduced. This is considered to be due to the following reasons. In the positive electrode active material of the cell Z1, no compound adheres to the surface of the lithium-containing transition metal oxide (the surface of the lithium-containing transition metal oxide is completely exposed). The decomposition reaction of the electrolytic solution occurs on the surface of the contained transition metal oxide. For this reason, it is considered that the initial charge capacity is increased and the discharge capacity at 1.0 It is decreased. In addition, as the amount of decomposition reaction of the electrolytic solution increases as the charge / discharge cycle elapses, the deterioration of the lithium-containing transition metal oxide becomes significant. For this reason, it is considered that the discharge capacity at the 30th cycle is greatly reduced.

  Further, in the cell Z2 in which the aluminum compound is adhered to the surface of the lithium-containing transition metal oxide, the decomposition reaction of the electrolytic solution is suppressed by the presence of the aluminum compound, so that the discharge capacity at the 30th cycle is large, but 1.0 It It can be seen that the discharge capacity at is significantly reduced. This is considered to be due to the following reasons. First, since the initial charge / discharge efficiency is high in the cell Z2, it is considered that the amount of the coating formed on the surface of the lithium-containing transition metal oxide is small. However, the resistance of the coating itself is considered high. For this reason, combined with the high resistance of the aluminum compound, it is considered that the discharge capacity at 1.0 It was greatly reduced. In addition, it is recognized that the initial discharge capacity is reduced due to the reduction of the initial charge capacity.

  On the other hand, in the cell A in which the erbium compound is attached to the surface of the lithium-containing transition metal oxide, the decomposition reaction of the electrolytic solution is suppressed due to the presence of the erbium compound, and thus the discharge capacity at the 30th cycle is large. In addition, it is recognized that the discharge capacity at 1.0 It is also increased. This is considered to be due to the following reasons. In the cell A, an erbium compound is attached to the surface of the lithium-containing transition metal oxide, but the compound is considered to have a high resistance of the attached substance itself, like the aluminum compound. However, the state of the coating differs between the coating formed when the aluminum compound is adhered to the surface of the lithium-containing transition metal oxide and the coating generated when the rare earth compound (erbium compound) is present. Specifically, the coating produced when the rare earth compound is present has higher ionic conductivity of the coating and facilitates desolvation. From this, it is considered that the discharge capacity at 1.0 It increased in cell A. Note that it is recognized that the cell A has a larger initial charge / discharge capacity than the cell Z2.

  The nonaqueous electrolyte secondary battery according to the present invention is used not only as a driving power source in portable electronic devices such as mobile phones and notebook personal computers, but also as a driving power source and power storage power source in hybrid cars and electric vehicles. Can be preferably used.

DESCRIPTION OF SYMBOLS 1 Battery case 5 Positive electrode 6 Negative electrode 7 Separator 11 Working electrode 12 Counter electrode 13 Reference electrode 14 Nonaqueous electrolyte

Claims (8)

Lithium-containing transition metal oxide containing lithium, manganese, nickel and / or cobalt, wherein the molar amount of lithium is 1.1 mol or more with respect to the total molar amount of the transition metal element and has a layered structure When,
A rare earth compound attached to a part of the surface of the lithium-containing transition metal oxide;
A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising:   2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the rare earth compound is at least one selected from the group consisting of a rare earth hydroxide, a rare earth oxyhydroxide, and a rare earth oxide. Positive electrode active material.   3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the rare earth element in the rare earth compound is one selected from the group consisting of neodymium, samarium, and erbium.   The non-reactive compound according to any one of claims 1 to 3, wherein the rare earth compound is 0.005 mass% or more and 0.8 mass% or less with respect to the lithium-containing transition metal oxide in terms of rare earth elements. Positive electrode active material for water electrolyte secondary battery. The lithium-containing transition metal oxide has the chemical formula Li _α (Li _x Mn _y Me _(1-xy) ) O ₂ (0.99 ≦ α ≦ 1.05, 0.1 ≦ x ≦ 0.4, 0 The positive electrode active material for nonaqueous electrolyte secondary batteries according to any one of claims 1 to 4, wherein <y <1, Me is an oxide represented by Ni and / or Co). A sheet-like positive electrode current collector;
A positive electrode active material layer formed on at least one surface of the positive electrode current collector and containing the positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 5,
A positive electrode for a nonaqueous electrolyte secondary battery. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 6,
A negative electrode containing a negative electrode active material;
A separator disposed between the positive electrode and the negative electrode;
A non-aqueous electrolyte,
A non-aqueous electrolyte secondary battery comprising: The nonaqueous electrolyte secondary battery according to claim 7, wherein the charging voltage is 4.6 V (vs. Li ^/ Li ⁺ ) or higher.

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