JP2004288501A - Positive electrode activator for lithium secondary battery, positive electrode of lithium secondary battery using the same, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode material of a lithium secondary battery capable of suppressing increase of impedance when charging and discharging at high temperature. <P>SOLUTION: The positive electrode activator for a lithium secondary battery is characterized by containing (1) a lithium-containing complex oxide expressed in formula (I): Li<SB>x</SB>Ni<SB>1-y</SB>M<SB>y</SB>O<SB>2-δ</SB>, (In the formula, M denotes an element chosen from elements of a 2nd to 14th group of the periodic table excluding Ni; x, y, δ denote the number fulfilling 1.0<x≤1.5, 0<y≤0.7, -0.1<δ<0.1 respectively), (2) Sb, Bi, and compound of those elements, and (3) oxide salt of an element of a 16th group excluding oxygen. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００６２】
上記表１の結果から、第１６族元素の酸化物塩である硫酸塩と第１５族元素物質であるＳｂを含有する置換型リチウムニッケル複合酸化物を正極に用いた電池は、これらを含まない正極活物質、又は硫酸塩あるいはＳｂのみ含む正極活物質を正極に用いた電池よりも高温サイクル後のインピーダンス増加が小さい事は明らかである。
【００６３】
【発明の効果】
本発明によれば、高温サイクル時のインピーダンス増加の小さい、特性の良好な電池あるいはそのための正極活物質を得ることができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a positive electrode material for a lithium secondary battery, a positive electrode for a lithium secondary battery and a lithium secondary battery using the same, and a method for producing the positive electrode material.
[0002]
[Prior art]
LiCoO having a layered structure₂, LiNiO₂, LiMnO₂And LiMn having a spinel structure₂O₄Since lithium-containing composite oxides and the like can insert and remove Li at a counter electrode Li potential near 3 to 4 V, they have been attracting attention and being put to practical use as positive electrode active materials for lithium secondary batteries.
[0003]
Among them, LiNiO₂That is, the lithium nickel composite oxide is made of LiCoO which has been generally used in the past.₂Has the advantage of being inexpensive and advantageous in resources as compared with lithium cobalt composite oxides such as₂O₄There is an advantage that the capacity is larger than that of the lithium manganese composite oxide. For this reason, recently, lithium nickel composite oxides have attracted particular attention as positive electrodes of lithium secondary batteries requiring a high-density and high-output power supply, such as mobile phones and electric vehicles.
[0004]
However, LiNiO₂It is known that the lithium-nickel composite oxide represented by the following basic composition has a large overvoltage and a large deterioration during a charge / discharge cycle of a battery. The reason for this is that the composite oxide Ni³⁺Is Ni²⁺Ni that is easily reduced to²⁺Is Li in the composite oxide⁺It is considered that one of the causes is that the ions enter the site and hinder the movement of Li ions.
[0005]
Therefore, when synthesizing a lithium nickel composite oxide, an excessive amount of Li raw material is charged, and Li⁺There is known a method for preventing a shortage of Li ions at a site (for example, see Non-Patent Document 1).
Also, Li_{x '}Ni_{1-y '}M_{y '}O₂(In the formula, M represents a transition metal other than Ni or Al, and a part of the Ni site represented by 1.0 <x ′, 0 <y ′ <1) is replaced with another element. Thus, there is known a lithium-containing composite oxide that has stabilized the crystal structure and consequently improved battery characteristics such as cycle characteristics of a lithium secondary battery (hereinafter, a part of Ni site is replaced by another element). The lithium-containing composite oxide thus obtained is sometimes referred to as a “substituted lithium-nickel composite oxide” (for example, see Non-Patent Document 2).
[0006]
However, even in the lithium secondary battery using the improved substituted lithium nickel composite oxide as described above, the resistance (during charge / discharge cycles at about 40 to 80 ° C. of the actual use temperature in electronic devices and automobiles, that is, the resistance ( Impedance) is reported to occur (for example, see Non-Patent Document 3).
In order to improve the cycle characteristics of the substituted lithium nickel composite oxide, a method of coating the surface of the composite oxide with a metal sulfide, selenide, telluride, or the like has been studied (for example, see Patent Document 1). However, this alone cannot suppress the aforementioned increase in impedance.
[0007]
This increase in impedance causes deterioration of battery characteristics such as deterioration of output characteristics of the battery and lowering of low-temperature output.
Therefore, it is very important to suppress an increase in impedance of the lithium-nickel composite oxide due to a charge / discharge cycle at a high temperature.
[0008]
[Patent Document 1]
JP-A-8-250120
[Non-patent document 1]
Solid State Ionics, 1995, Vol. 80, p. 261
[Non-patent document 2]
Journal Electrochemical Society, 1994, vol. 141, no. 8, p. 2010
[Non-Patent Document 3]
Journal of Power Sources, 2001, Vol. 684, p. 97-98
[0009]
[Problems to be solved by the invention]
An object of the present invention is to provide a positive electrode material for a lithium secondary battery that can suppress an increase in impedance during a charge / discharge cycle at a high temperature.
[0010]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that in a substituted lithium nickel composite oxide, the purpose can be achieved by the presence of a specific element or a compound thereof, thereby completing the present invention. .
That is, the gist of the present invention is as follows: (1) The following formula (I)
[0011]
Embedded image
Li_xNi_1-yM_yO_{2- δ}                (I)
(In the formula, M is an element other than Ni selected from Group 2 to Group 14 elements of the periodic table, and x, y, and δ are 1.0 <x ≦ 1.5, 0 < It represents the number of y ≦ 0.7, −0.1 <δ <0.1.)
And (2) selected from Sb, Bi and these compounds, and (3) an oxide salt of a Group 16 element excluding oxygen. The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode for a lithium secondary battery using the same, a lithium secondary battery, and a method for producing the positive electrode active material.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
In the present invention, the substitution type lithium nickel composite oxide contained in the positive electrode active material has a basic composition of LiNiO 2.₂A part of the Ni site of the lithium nickel composite oxide represented by is replaced with an element other than Ni selected from Group 2 to Group 14 elements of the periodic table, and the composition thereof is (I ) Expression.
[0013]
In the formula (I), x is larger than 1.0, preferably 1.03 or more. The upper limit is 1.5 or less, preferably 1.1 or less. When x is 1.0 or less, Ni ions easily mix into the Li site, which adversely affects battery performance. When x exceeds 1.5, excessive Li may be a resistance component as lithium carbonate, lithium hydroxide, or the like, and the battery capacity per unit weight may be reduced. Hindered. Note that the composition of the substitutional lithium nickel composite oxide described in this specification is as a positive electrode active material before a battery is manufactured.
[0014]
M of the substitution element is an element other than Ni selected from Group 2 to Group 14 elements of the periodic table, and may be one or more. By substituting metal elements other than Ni for Ni sites, it is possible to prevent instability of the crystal structure when Li is removed during charging. In the present invention, M is preferably an element selected from the elements belonging to the third period and the fourth period. Among them, Co, Mn, Al, Fe, Cr, Ti , Zn and Mg are preferred.
[0015]
Further, y representing the substitution amount is larger than 0, preferably 0.1 or more, and more preferably 0.15 or more. The upper limit is 0.7 or less, preferably 0.5 or less, and more preferably 0.3 or less. If y is too small, the effect of stabilizing the crystal structure when Li is removed cannot be sufficiently obtained, and if it exceeds 0.7, the amount of Ni involved in charge and discharge decreases, and the capacity decreases.
[0016]
Δ corresponds to oxygen deficiency or oxygen excess, and represents a number of −0.1 <δ, preferably −0.05 <δ, and the upper limit is δ <0.1, preferably δ <0.05. Represents a number. If δ is too large or too small, the crystal structure becomes unstable.
A lithium secondary battery using the substituted lithium-nickel composite oxide represented by the formula (I) alone as an active material has a significantly improved battery characteristic at around room temperature, but has a high temperature of practical use, that is, During a durability test (especially charge / discharge cycle) at about 40 to 80 ° C., resistance (impedance) increases. The positive electrode active material for a lithium secondary battery according to the present invention includes the above-described substituted lithium nickel composite oxide, one selected from Sb, Bi, and these compounds (hereinafter, referred to as a “Group 15 element substance”), and An oxide salt of a group 16 element excluding oxygen (hereinafter, referred to as an "oxide salt of a group 16 element") is an essential component, and it can be substituted lithium nickel composite oxide even at a high temperature. It has the excellent property that the increase in resistance, which is a drawback of the product, is extremely small.
[0017]
The substituted lithium nickel composite oxide serving as the base material of the positive electrode active material according to the present invention is generally identified as a layered rock salt structure (hexagonal) by X-ray structural analysis. The lattice constant of the a-axis is preferably in the range of 0.285 to 0.288 nm, and more preferably in the range of 0.286 to 0.287 nm. The c-axis has a range of preferably 1.410 to 1.425 nm, more preferably 1.415 to 1.420 nm. If the ratio exceeds these ranges, the stability of the crystal tends to deteriorate and the capacity tends to decrease.
[0018]
The average particle size of the substituted lithium nickel composite oxide is usually 0.1 μm or more, preferably 1 μm or more, more preferably 3 μm or more, and the upper limit is usually 50 μm or less, preferably 30 μm or less, more preferably 20 μm or less. It is. If the average particle size of the substitutional lithium nickel composite oxide falls below this lower limit, the density of the active material in the electrode does not increase, and the capacity density of the battery tends to decrease. Conversely, if the upper limit is exceeded, internal short-circuiting of the battery or the like tends to occur.
[0019]
The Group 15 elemental substance may be a simple substance, but is preferably a compound. The type of compound is not particularly limited, but a compound with Li or oxygen which is stable even in the air is preferable. Specifically, Sb₂O₃, Sb₂O₅, LiSbO₃, Li₃SbO₄, Bi₂O₃, Bi₂O₅, LiBiO₃, Li₃BiO₄And the like, but are not limited thereto. These Group 15 elemental substances may be used alone or in combination of two or more. Further, it is more preferable that the compound is contained in the lithium nickel composite oxide as a compound in an ionic state (an expensive number state) than the zero-valent element itself. Particularly preferred as the Group 15 element substance is a compound of Sb.
[0020]
The amount of the Group 15 element substance contained in the positive electrode active material is usually 0.1 mol% or more, preferably 0.5 mol% or more, and the upper limit is usually 3.0 mol based on the total molar amount of Ni and M. %, Preferably 2.0 mol% or less. When the content of the group 15 element substance is less than 0.1 mol%, the effect of improving the battery performance is small, and when it exceeds 3.0 mol%, the battery performance decreases such as a decrease in capacity. Note that the number of moles of the group 15 element substance is the number of moles (= the number of atoms) as a group 15 element.
[0021]
On the other hand, examples of the oxide salts of Group 16 elements include sulfates, sulfites, selenates, selenites, tellurates, tellurites, polonates, and polonates. Specifically, sulfates such as lithium sulfate, sodium sulfate, magnesium sulfate, calcium sulfate, nickel sulfate, and cobalt sulfate; lithium selenate, sodium selenate, magnesium selenate, calcium selenate, nickel selenate, and cobalt selenate Selenates such as lithium tellurate, sodium tellurate, magnesium tellurate, calcium tellurate, nickel tellurate, cobalt tellurate; lithium polonate, sodium polonate, magnesium polonate, calcium polonate And polonates such as nickel polonate and cobalt polonate. Among these salts, sulfates are particularly preferred because of their high performance improving effect.
[0022]
Since the oxide salts of these Group 16 elements can be usually extracted as ions from water from the positive electrode active material, their amounts can be quantified by analysis such as ion chromatography.
The amount of the Group 16 element oxide salt contained in the positive electrode active material is usually 0.1 mol% or more, preferably 0.5 mol% or more, and the upper limit is 3 mol, based on the total molar amount of Ni and M. 0.0 mol% or less, preferably 2.0 mol% or less. When the content of the oxide salt of the Group 16 element is less than 0.1 mol%, the effect of improving the battery performance is small, and when the content exceeds 3.0 mol%, the battery performance such as the capacity is reduced. Note that the number of moles of the oxide salt of the Group 16 element is also the number of moles (= the number of atoms) as the Group 16 element.
[0023]
The ratio of the Group 15 element substance to the Group 16 element oxide salt in the positive electrode active material is not particularly limited, but is usually about 1:10 to 10: 1 by mole, preferably 1: 2 to 2 in terms of molar ratio. : About 1.
The positive electrode active material according to the present invention includes (1) a substituted lithium nickel composite oxide represented by the above formula (I), (2) a Group 15 element material, and (3) an oxide salt of a Group 16 element. The three components are essential components, but there are no particular restrictions on the form in which they exist, and any of (1) to (3) may exist in a mixed state or may be in a complex form.
[0024]
The most common method for producing the positive electrode active material according to the present invention is a method of mixing the above (1) to (3) by a dry or wet method. As a more uniform mixing method, a method of dissolving or dispersing a Group 15 element substance or an oxide salt of a Group 16 element in an appropriate solvent and adding and mixing the same with the substituted lithium nickel composite oxide is more preferable.
The amount of the Group 15 element substance and the oxide salt of the Group 16 element is smaller than that of the substitutional lithium nickel composite oxide, and the particle diameter of the substitutional lithium nickel composite oxide is usually smaller than that of the substitutional lithium nickel composite oxide. Since the diameter of the mixture is larger than the diameter, the resulting mixture is usually a mixture of a substituted lithium nickel composite oxide as a core and an oxide salt of a Group 15 element substance and a Group 16 element adhered to its surface, that is, a substituted lithium nickel composite oxide. It has a structure in which a composite oxide is covered with a group 15 element substance and an oxide salt of a group 16 element.
[0025]
The solvent used for dissolving or dispersing is not particularly limited as long as it can dissolve or disperse the Group 15 element substance or the oxide salt of the Group 16 element, and usually, water or alcohol is used. You.
As a device used for the mixing process, a V-type, biaxial conical-type, etc. container rotary type mixer (V blender, conical blender) or a vertical axis rotary type multi-stage blade mixer using a shear compression mixing action (Ver. Tikal granulators, high-speed mixers), horizontal-shaft rotary shovel blade mixers (Redige mixers), and particle-combining devices using compression shearing force (mechanofusion systems, hybridization systems). However, the present invention is not limited to this.
[0026]
Alternatively, a method of spraying a solution or slurry of a Group 15 element substance and an oxide salt of a Group 16 element onto the substitutional lithium nickel composite oxide by using a spray coating apparatus may be employed.
Even if the three components are mixed simultaneously, the two components can be mixed separately after mixing any two components.
[0027]
In the case where Sb or an Sb compound is used as the Group 15 element substance, this substance has a strong interaction with Li, and tends to lower the performance as an active material by replacing Li in the lithium composite oxide. Therefore, it is desirable to mix (1) with (3) and then with (2), or to mix the three simultaneously.
Alternatively, the positive electrode active material according to the present invention can be obtained by dissolving or dispersing the three components in an appropriate solvent to form a slurry, and drying the slurry by spray drying or another appropriate method.
[0028]
In any case, the obtained mixture is appropriately ground and classified to obtain a positive electrode active material having a desired particle size distribution.
As described above, the form of the oxide salt of the group 15 element substance or the group 16 element is preferably as fine as possible because it is desirable to perform more uniform mixing as used in the production of the positive electrode active material according to the present invention. Is preferred. In particular, when these are used in a solid state for mixing, usually those having a median diameter of 10 μm or less are used. It is preferably 5 μm or less, more preferably 1 μm or less.
[0029]
The mixture obtained by mixing the three components as described above can be used as it is as the positive electrode active material according to the present invention. However, it is preferable that the obtained mixture is heated and fired to obtain the positive electrode active material. By heating and sintering, the group 15 element substance and the oxide salt of the group 16 element are melted or reacted with the substituted lithium nickel composite oxide, so that a more preferable cathode active material is produced.
[0030]
The heating and calcination is performed at a temperature lower than the melting point or the decomposition temperature of the lithium nickel composite oxide so that the substitutional lithium nickel composite oxide does not deteriorate. For the above reason, it is preferable to perform the treatment at a temperature higher than the melting point of the Group 15 element substance or the oxide salt of the Group 16 element. The firing temperature depends on the type of the oxide salt of the group 15 element substance and the group 16 element and the composition of the substituted lithium nickel composite oxide, but is usually 120 ° C. or higher, preferably 300 ° C. or higher, more preferably 400 ° C. or higher. ° C or higher. The upper limit temperature is usually 1000 ° C. or lower, preferably 900 ° C. or lower, more preferably 800 ° C. or lower.
[0031]
The firing is usually performed in an air or oxygen atmosphere so that the substitutional lithium nickel composite oxide is not decomposed and deteriorated.
The baking time is usually 1 hour or more and preferably 10 hours or less. If it is too short, the desired performance will not be obtained, and if it is too long, the productivity will decrease.
The firing apparatus may be of any type as long as the atmosphere can be controlled, and examples thereof include a batch type atmosphere furnace and a continuous kiln furnace. Sintering should be such that local heating does not occur, and the material of the sintering apparatus should be one that does not react with the mixture used for sintering.
[0032]
In addition, in addition to the above-described manufacturing method, when synthesizing the substituted lithium nickel composite oxide, a raw material or an intermediate product is mixed with an oxide salt of a Group 15 element or a Group 16 element. Accordingly, these can be contained in the substitution-type lithium nickel composite oxide finally formed.
The specific surface area of the positive electrode active material according to the present invention by the nitrogen adsorption measurement method (BET method) is preferably 0.1 to 2.0 m.²/ G, more preferably 0.3 to 1.0 m²/ G. The particle size distribution of the positive electrode active material is preferably 3 to 20 μm, more preferably 6 to 12 μm in median diameter. The upper limit of the maximum particle size is usually 60 μm or less, preferably 50 μm or less, more preferably 40 μm or less.
[0033]
If the specific surface area is too small or the particle size is too large, the diffusion of Li ions during the battery reaction will be slow, and the battery characteristics may be degraded. Conversely, if the specific surface area is too large or the particle size is too small, side reactions other than the insertion and release of the original Li ions of the battery, such as the reaction with the electrolytic solution, may increase, which may cause battery deterioration. .
[0034]
When the positive electrode active material according to the present invention is used in a battery, the positive electrode active material may take any form, but usually takes the form of an electrode sheet.
The electrode sheet is a thin film obtained by adding a binder and, if desired, various auxiliaries to a positive electrode active material, and for example, adding a positive electrode active material and a binder to an appropriate solvent to prepare a coating for an electrode (slurry). ), Which is applied to a current collector and dried. Other known positive electrode active materials can be used in combination with the positive electrode active material as long as the effects of the present invention are not hindered. In this case, the content of the positive electrode active material according to the present invention is preferably 50% by weight or more, especially 70% by weight or more, and more preferably 80% by weight or more, because the effect of the present invention can be remarkably exhibited.
[0035]
The lower limit of the proportion of the active material in the positive electrode layer obtained by drying is usually 70% by weight or more, preferably 80% by weight or more, more preferably 90% by weight or more, and the upper limit is usually 99.9% by weight or less, preferably Is 99% by weight or less. If the amount of the active material is too large, the mechanical strength of the electrode tends to be inferior. If the amount is too small, battery performance such as capacity tends to be inferior.
[0036]
Examples of the binder (binding agent) include polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), and NBR (acrylonitrile). Butadiene rubber), fluorine rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, CMC (carboxymethyl cellulose) and the like. The lower limit of the proportion of the binder in the positive electrode layer is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 2% by weight or more, and the upper limit is usually 30% by weight or less, more preferably 20% by weight. Or less, more preferably 10% by weight or less. If the proportion of the binder is too low, the active material cannot be sufficiently retained, the mechanical strength of the positive electrode becomes insufficient, and the battery performance such as cycle characteristics may be deteriorated. May be lowered.
[0037]
Furthermore, it is usually preferable that the positive electrode layer contains a conductive agent in order to increase conductivity. Examples of the conductive agent include carbon materials such as graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke. The lower limit of the proportion of the conductive agent in the positive electrode is usually 0.1% by weight or more, preferably 2% by weight or more, more preferably 2% by weight or more, and the upper limit is usually 30% by weight or less, preferably 20% by weight or less. , More preferably 10% by weight or less. If the proportion of the conductive agent is too low, the conductivity may be insufficient, while if it is too high, the battery capacity may be reduced.
[0038]
The solvent used for preparing the electrode coating material is not particularly limited as long as it dissolves or disperses the binder, but usually an organic solvent or water is used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, water and the like can be mentioned.
[0039]
The thickness of the positive electrode layer is usually about 1 to 500 μm, preferably about 5 to 100 μm. If it is too thick, the conductivity tends to decrease, and if it is too thin, the capacity tends to decrease.
As a material of the current collector used for the positive electrode, aluminum, stainless steel, nickel-plated steel, or the like is used, and aluminum is preferable. The thickness of the current collector is usually about 1 to 500 μm, preferably about 5 to 20 μm. If the thickness is too thick, the capacity of the lithium secondary battery as a whole decreases, and if it is too thin, the mechanical strength may be insufficient.
[0040]
The positive electrode layer obtained by coating and drying is preferably compacted by a roller press or the like in order to increase the filling density of the active material and secure a conductive path between the active materials. Although depending on the composition of the electrode, the density of the positive electrode layer is usually 2.0 g / cc or more and 3.5 g / cc or less.
The lithium secondary battery according to the present invention comprises at least the positive electrode obtained as described above, a negative electrode opposed thereto, and a non-aqueous electrolyte (or solid electrolyte) as an ion conductor. Usually, a separator is interposed between the positive electrode and the negative electrode.
[0041]
As the active material of the negative electrode, any material can be used as long as it can occlude and release lithium, but a carbonaceous material is usually preferable. For example, thermal decomposition products of organic substances under various thermal decomposition conditions, artificial graphite, natural graphite and the like can be mentioned. Preferably artificial graphite, graphitized mesophase microspheres, graphitized mesophase pitch-based carbon fibers, other artificial graphite and purified natural graphite, or the like, produced by high-temperature heat treatment of graphitic pitch obtained from various raw materials. A material obtained by subjecting graphite to surface treatment with a pitch or the like is used. These carbonaceous materials preferably have a lattice plane (002 plane) d value (interlayer distance) of 0.335 to 0.34 nm, preferably 0.335 to 0.337 nm, determined by X-ray diffraction by the Gakushin method. Is more preferable. The crystallite size (Lc) determined by X-ray diffraction according to the Gakushin method is preferably 30 nm or more, more preferably 50 nm or more, and even more preferably 100 nm or more. These carbonaceous materials may be further mixed with other active materials capable of inserting and extracting lithium. Examples of the active material capable of occluding and releasing lithium other than the carbonaceous material include metal oxide materials such as tin oxide and silicon oxide, as well as lithium metal and various lithium alloys. These negative electrode materials may be used as a mixture of two or more kinds.
[0042]
Like the positive electrode, the negative electrode is usually used in the form of an electrode sheet. As a method of manufacturing an electrode sheet, a slurry containing a negative electrode active material, a binder, and, if desired, a thickener or a conductive agent is further prepared using a solvent, as in the case of the positive electrode, and the slurry is applied to a current collector. -There is a drying method. Examples of the solvent include organic solvents such as N-methylpyrrolidone (NMP) and dimethylformamide (DMF), and water. Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, styrene / butadiene rubber, isoprene rubber, and butadiene rubber. Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein. Examples of the conductive agent include metal materials such as copper and nickel, graphite, and carbon black.
[0043]
Examples of the negative electrode current collector include metals or alloys such as copper, nickel, and stainless steel, and preferably copper.
The negative electrode layer obtained by coating and drying is preferably compacted by a roller press or the like in order to increase the packing density of the active material. Although depending on the composition, the density of the negative electrode layer is usually from 1.0 g / cc to 2.0 g / cc.
[0044]
The material and shape of the separator are not particularly limited, but it is preferable to use a porous sheet or a nonwoven fabric or the like made of a polyolefin such as polyethylene or polypropylene as a material that is stable to an electrolytic solution and has excellent liquid retention properties. .
Examples of the non-aqueous electrolyte include those in which various electrolyte salts are dissolved in a non-aqueous solvent. As the non-aqueous solvent, for example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, halogenated hydrocarbons, amines, esters, amides, phosphate compounds and the like can be used. it can. Representative examples include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, and the like.
[0045]
As the electrolyte salt, any of conventionally known electrolyte salts can be used.₄  , LiAsF₆  , LiPF₆  , LiBF₄  And the like.
Also, CO₂  , NO₂, CO, SO₂  Or an additive such as vinylene carbonate, catechol carbonate, or the like that forms a good film that enables efficient charge and discharge of lithium ions on the surface of the negative electrode may be added to the electrolyte at an arbitrary ratio.
[0046]
Further, a solid polymer electrolyte may be used instead of or together with the electrolytic solution.
The method for producing the lithium secondary battery is not particularly limited, and can be appropriately selected from commonly employed methods. The shape of the battery is not particularly limited, and a cylinder type in which a sheet electrode and a separator are formed in a spiral shape, a stacked type in which an electrode and a separator are stacked, and the like can be used. The use of the battery is not particularly limited, and it can be widely used from electronic devices such as personal computers and mobile phones to batteries for automobiles.
[0047]
In a lithium secondary battery, the capacity balance between the active material of the positive electrode and the active material of the negative electrode is important. This is because the negative electrode can absorb Li ions without precipitating Li metal, or the positive electrode can store Li ions. Designed based on capacity that can be released.
The capacity of the negative electrode capable of storing Li ions without depositing Li metal is Qa (mAh / g), the capacity of the positive electrode capable of releasing Li ions is Qc (mAh / g), and the active materials of the negative electrode and the positive electrode are each Wa. (G) and Wc (g), the capacity balance ratio R is represented by R = (Qa × Wa) / (Qc × Wc). Usually, the lower limit of R is set to 1 or more, preferably 1.2 or more, and the upper limit is set to 2 or less, preferably 1.5 or less. If R is too small, the negative electrode cannot receive Li ions from the positive electrode during charging, and Li metal will precipitate on the negative electrode, causing deterioration and safety problems. Conversely, if R is too large, the capacity per weight of the battery will decrease.
[0048]
Although there are various methods for measuring Qc to Qa, in the following examples, the positive electrode and the negative electrode are each made of a counter electrode Li metal in an electrolytic solution at a current density as low as possible, for example, 20 mA / g (active material) or less. The negative electrode was determined by measuring the discharge (Li occlusion) capacity from the natural potential to the lower limit of 5 mV, and the positive electrode was determined by measuring the charge capacity from the natural potential to 4.2 V.
The lower limit is usually 2.0 V or higher, preferably 2.5 V or higher, more preferably 3.0 V or higher. The upper limit is usually 4.3 V or less, preferably 4.2 V or less, more preferably 4.1 V or less. If the upper limit value is too large or the lower limit value is too small, battery deterioration may increase.
[0049]
【Example】
Hereinafter, specific embodiments of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded.
(Substitution type lithium nickel composite oxide)
Lithium-nickel composite oxide serving as a base material of a positive electrode active material includes Li_1.06Ni_0.81Co_0.14Al_0.05O₂A composition having the following composition was used. According to X-ray diffraction measurement, the compound belonged to a hexagonal system, and the lattice constant was 0.286 nm for the a-axis and 1.418 nm for the c-axis. The specific surface area is about 0.5m²/ G, the median diameter measured by particle size distribution measurement was about 11 μm, and the maximum particle size was 30 μm.
[0050]
(Preparation of positive electrode)
A slurry was prepared by mixing 85% by weight of a positive electrode active material, 10% by weight of acetylene black as a conductive agent, and 5% by weight of polyvinylidene fluoride (PVdF) as a binder in an N-methylpyrrolidone solvent to form a slurry. A 20 μm aluminum foil was coated on one side, dried, and then rolled by a press machine, and punched to a diameter of 12 mm to obtain a positive electrode. The positive electrode layer density was 2.2 to 2.5 g / cc.
[0051]
(Negative electrode active material)
A graphite-based carbon material was used as the negative electrode active material. The plane distance measured by X-ray diffraction was 0.336 nm. Specific surface area is about 4m²/ G, and the median diameter as measured by particle size distribution was about 11 μm.
(Preparation of negative electrode)
92.5% by weight of the negative electrode active material and 7.5% by weight of PVdF as a binder were mixed in an N-methylpyrrolidone solvent to form a slurry, which was then applied to one side of a copper foil having a thickness of 20 μm and dried. Then, the product rolled by a press was punched out to a diameter of 12 mm. The negative electrode layer density was 1.3 to 1.6 g / cc.
The capacity balance ratio R between the positive electrode and the negative electrode was designed to be 1.2 to 1.5.
[0052]
(Assembly of coin cell battery)
The electrode was vacuum-dried at 120 ° C. for about 1 to 3 hours, and a lithium secondary battery was produced using a CR2032 type coin cell in a dry box in an argon atmosphere. That is, the positive electrode was placed in a positive electrode can, one porous polyethylene film having a pore size of 25 μm was placed thereon as a separator, pressed with a polypropylene gasket, and then the negative electrode was placed. After placing a spacer for thickness adjustment on the negative electrode, an electrolytic solution was added to allow the battery to sufficiently permeate the battery, and finally, the negative electrode can was placed thereon to seal the battery. For the electrolyte, a mixed solvent of ethylene carbonate (EC) + dimethyl carbonate (DMC) + ethyl methyl carbonate (EMC) (volume ratio 1: 1: 1) was mixed with LiPF.₆Was used so as to be 1 mol / L.
[0053]
(Evaluation of battery characteristics)
A charge / discharge cycle test was performed at an upper limit voltage of 4.1 V and a lower limit voltage of 3.0 V. As the 1C current value,
1C (mA) = active material amount of positive electrode (g) x 175 (mAh / g)
Values were used. This value is obtained based on a capacity confirmation test using the counter electrode Li of the substitutional lithium nickel composite oxide used for producing the positive electrode active material.
[0054]
First, as a conditioning (preliminary charge / discharge), a constant current-constant voltage charge and constant current discharge of 0.2 C were performed at room temperature (25 ° C.) for several cycles, and based on the obtained capacity, the charge depth was increased to 60%. After the adjustment, the resistance of the battery before the high-temperature cycle was measured by the AC impedance method.
Next, the battery was moved to an atmosphere of 60 ° C., and a high-temperature cycle test was performed in a pattern of 1 cycle at 0.2 C constant current → 100 cycles at 1 C constant current → 2 cycles at 0.2 C.
[0055]
After returning to room temperature (25 ° C.), the charge depth was adjusted to 60% based on the discharge capacity of 0.2 C at the end of the 60 ° C. cycle test to confirm the increase in resistance after the high-temperature cycle. A measurement was made.
The AC impedance was measured at room temperature using a frequency analysis device (1255B) and a potentiostat (1287) manufactured by Solartron with a swing width of 10 mV and a measurement frequency range of 0.01 to 100 kHz. The value of the total impedance at 0.1 Hz was adopted as the resistance value.
[0056]
Example 1
Lithium nickel composite oxide (Li_1.06Ni_0.81Co_0.14Al_0.05O₂) Is stirred in a fluidized tank while lithium sulfate (Li₂SO₄・ H₂The aqueous solution of O) was sprayed. Lithium sulfate was used in an amount of about 1 mol% with respect to the total molar amount of Ni, Co, and Al.
[0057]
Antimony trioxide (Sb) was added to the resulting mixture.₂O₃: 0.8 μm in particle median diameter) and shaken and mixed well in a polyethylene bottle. Sb₂O₃Was added so as to be 0.7 mol% as an antimony element with respect to the total molar amount of Ni, Co and Al.
Next, this mixture was transferred into an alumina crucible and fired at 680 ° C. for 2 hours in an oxygen atmosphere.
[0058]
The amount of sulfate in the obtained compound was determined by sulfate ion (SO₄ ^2-) Was determined (ion chromatography), and the amount of Sb was determined by atomic absorption analysis. As a result of analysis, as a result of elemental analysis of sulfate and Sb, the charged amount was almost maintained.
Using this as a positive electrode active material, a positive electrode was prepared by the method described above, and a coin cell battery assembly and battery characteristics evaluation were performed.
[0059]
Comparative Example 1
Lithium nickel composite oxide (Li_1.06Ni_0.81Co_0.14Al_0.05O₂) Was used as it was, a positive electrode was prepared in the same manner as in Example 1, a coin cell battery was assembled, and battery characteristics were evaluated.
Comparative Example 2
Lithium nickel composite oxide (Li_1.06Ni_0.81Co_0.14Al_0.05O₂), A positive electrode was prepared in the same manner as in Example 1 except that only lithium sulfate was not added, and a coin cell battery assembly and battery characteristics evaluation were performed.
[0060]
Comparative Example 3
Lithium nickel composite oxide (Li_1.06Ni_0.81Co_0.14Al_0.05O₂), A positive electrode was prepared in the same manner as in Example 1 except that antimony trioxide was not added, and coin cell batteries were assembled and battery characteristics were evaluated.
Table 1 below shows the results of the above battery test.
[0061]
[Table 1]

[0062]
From the results in Table 1 above, batteries using a substituted lithium nickel composite oxide containing a sulfate which is an oxide salt of a Group 16 element and a Sb which is a Group 15 element as a positive electrode do not include these. It is apparent that the impedance increase after the high-temperature cycle is smaller than that of the battery using the positive electrode active material or the positive electrode active material containing only sulfate or Sb for the positive electrode.
[0063]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the battery which has a small impedance increase at the time of a high temperature cycle, and has favorable characteristics, or its positive electrode active material can be obtained.

Claims (10)

(1) The following formula (I)

(In the formula, M is an element other than Ni selected from Group 2 to Group 14 elements of the periodic table, and x, y, and δ are 1.0 <x ≦ 1.5, 0 < It represents the number of y ≦ 0.7, −0.1 <δ <0.1.)
(2) a compound selected from Sb, Bi and these compounds, and (3) an oxide salt of a Group 16 element excluding oxygen. Active material for lithium secondary batteries. The positive electrode active material for a lithium secondary battery according to claim 1, wherein Sb, Bi, and / or a compound selected from these compounds are Sb and / or a compound thereof. 3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the oxide salt of a Group 16 element excluding oxygen is a sulfate. 4. The ratio of one selected from Sb, Bi, and these compounds to the total number of moles of Ni and M is 0.1 to 3.0 mol%. Positive electrode active material for lithium secondary batteries. The ratio of an oxide salt of a Group 16 element excluding oxygen to the total number of moles of Ni and M is 0.1 to 3.0 mol%, according to any one of claims 1 to 4, The positive electrode active material for a lithium secondary battery according to the above. A positive electrode for a lithium secondary battery, comprising the positive electrode active material according to claim 1 as a positive electrode active material. A lithium secondary battery comprising the positive electrode active material according to claim 6. The following formula (I)

(In the formula, M is an element other than Ni selected from Group 2 to Group 14 elements of the periodic table, and x, y, and δ are 1.0 <x ≦ 1.5, 0 < It represents the number of y ≦ 0.7, −0.1 <δ <0.1.)
A lithium-containing composite oxide represented by the formula: Sb, Bi and those selected from these compounds, and an oxide salt of a Group 16 element excluding oxygen, and heating the mixture. A method for producing a positive electrode active material. The method for producing a positive electrode active material for a lithium secondary battery according to claim 8, wherein Sb, Bi and a compound selected from these compounds are Sb and / or a compound thereof. The method for producing a positive electrode active material for a lithium secondary battery according to claim 8, wherein the oxide salt of a Group 16 element excluding oxygen is a sulfate.