JP4813450B2 - Lithium-containing composite oxide and non-aqueous secondary battery using the same - Google Patents

Description

  The present invention relates to a lithium-containing composite oxide that can be used as a positive electrode active material of a non-aqueous secondary battery, and a non-aqueous secondary battery that improves cycle characteristics and storage characteristics at high temperatures by using the lithium-containing composite oxide. .

In recent years, with the development of portable electronic devices such as mobile phones and laptop computers, and the practical application of electric vehicles, secondary batteries with small size and light weight and high capacity have been required. Currently, non-aqueous secondary batteries using LiCoO ₂ as a positive electrode material and a carbon-based material as a negative electrode active material are commercialized as high-capacity secondary batteries that meet this requirement. The non-aqueous secondary battery is attracting attention as a power source for portable electronic devices because it has a high energy density and can be reduced in size and weight. LiCoO ₂ used as a positive electrode material for this non-aqueous secondary battery is frequently used as a suitable active material because it is easy to manufacture and easy to handle. However, since LiCoO ₂ is manufactured using Co, which is a rare metal, as a raw material, it is expected that resource shortages will become serious in the future. Furthermore, since Co is expensive and has a large price fluctuation, development of a positive electrode material that is inexpensive and stable in supply is desired.

In view of the above reasons, a lithium manganese oxide-based composite oxide material containing Mn as a constituent element, for which the price of the constituent element is low and supply is stable, is considered promising. Among them, the spinel structure is can be charged and discharged in the voltage range of the or LiMn ₂ O ₄ in the vicinity of 4V, studies on LiMnO ₂ layered are actively conducted against Li, in particular, of the LiMnO ₂ Mn Lithium-containing composite oxides in which a part of these is substituted with Ni, Co, Al, or the like is expected as a material to replace LiCoO ₂ (see Patent Documents 1 to 3).

JP-A-8-37007 (paragraph numbers 0027-0029) Japanese Patent Laid-Open No. 11-25957 (paragraph numbers 0003-0008) JP 2000-223122 A (paragraph number 0002-0009)

However, as a result of detailed studies on the composite oxide in which a part of Mn of LiMnO ₂ is substituted by Ni, Co, or the like, the present inventors have found that the composition of the compound, particularly, the quantitative ratio between Li and other metal elements. In addition, it was found that the physical properties such as the structure and characteristics of the substituting element change significantly depending on the kind and amount ratio of the substituting elements and the synthesis process until the composite oxide is formed.

In particular, when substitution with Ni is performed, the physical properties of the composite oxide to be synthesized vary greatly depending on the quantitative ratio of Mn to Ni and the quantitative ratio of these elements to other substituted elements. If the amount ratio of Mn and Ni to other substitutional elements is within a certain range, and the average valence of Mn is not a value close to tetravalent, the compound is homogeneous and has excellent characteristics. It was clarified that the true density of the composite oxide greatly fluctuated depending on the amount ratio of Mn and other substituted elements to Li.

  Furthermore, it was also found that the characteristics of the battery are greatly influenced by the particle form of the lithium-containing composite oxide.

  The present invention has been made as a result of intensive studies to solve the above problems, and is a complex oxide having a layered structure in a limited composition range and a lithium-containing complex oxide having a specific particle form. Is used as an active material for the positive electrode to provide a non-aqueous secondary battery having high capacity, excellent durability against charge / discharge cycles, and excellent storage at high temperatures.

Lithium-containing composite oxide of the present invention have the general formula _{Li 1 + x + α Ni (} 1-xy + δ) / 2 Mn (1-xy-δ) / 2 M y O 2 [ however, 0 ≦ x ≦ 0.05, −0.05 ≦ x + α ≦ 0.05, 0 ≦ y ≦ 0.4, −0.1 ≦ δ ≦ 0.1 (when 0 ≦ y ≦ 0.2) or − 0.24 ≦ δ ≦ 0.24 (when 0.2 <y ≦ 0.4), and M is made of Mg, Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, Sn 1 or more elements selected from the group], and is a composite oxide in which primary particles aggregate to form secondary particles, and the average particle diameter of the primary particles is 0.3 to 3 μm. The average particle diameter of the secondary particles is 5 to 20 μm , the BET specific surface area is 0.3 to ² m ² / g, and the average valence of Mn is 3.3 to 4.

  The non-aqueous secondary battery of the present invention includes a positive electrode and a negative electrode using the lithium-containing composite oxide as an active material, and a non-aqueous electrolyte.

Further, preferred embodiments of the positive electrode active material of the present invention have the general formula _{Li 1 + x + α Ni (} 1-xy + δ) / 2 Mn (1-xy-δ) / 2 M y O 2 [ however, 0 ≦ x ≦ 0.05, −0.05 ≦ x + α ≦ 0.05, 0 ≦ y ≦ 0.4, and −0.1 ≦ δ ≦ 0.1 (provided that 0 ≦ y ≦ 0.2) ) Or −0.24 ≦ δ ≦ 0.24 (when 0.2 <y ≦ 0.4), and M is Mg, Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, 1 or more elements selected from the group consisting of Sn], which is a composite oxide in which primary particles aggregate to form secondary particles, and the average particle size of the secondary particles is 5 to 20 μm. The average particle diameter of the secondary particles of the composite oxide A having the same composition as the lithium-containing composite oxide A having an average valence of Mn of 3.3 to 4 and the lithium-containing composite oxide A Less than average A lithium-containing composite oxide B having a particle size, wherein the average particle size of the composite oxide B is 3/5 or less of the average particle size of the secondary particles of the composite oxide A, The ratio of the composite oxide B is 10 to 40% by weight of the whole positive electrode active material .
Et al is the preferred embodiment of the nonaqueous secondary battery of the present invention is characterized by comprising a positive electrode and a negative electrode and a non-aqueous electrolyte having the positive electrode active material.

Hereinafter, the present invention will be described in more detail with reference to embodiments of the invention. Lithium-containing composite oxide of the present invention have the general formula _{Li 1 + x + α Ni (} 1-xy + δ) / 2 Mn (1-xy-δ) / 2 M y O 2 [ however, 0 ≦ x ≦ 0.05, −0.05 ≦ x + α ≦ 0.05, 0 ≦ y ≦ 0.4, −0.1 ≦ δ ≦ 0.1 (when 0 ≦ y ≦ 0.2) or − 0.24 ≦ δ ≦ 0.24 (when 0.2 <y ≦ 0.4), and M is made of Mg, Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, Sn 1 or more elements selected from the group], and is a composite oxide in which primary particles aggregate to form secondary particles, and the average particle diameter of the primary particles is 0.3 to 3 μm. The average particle diameter of the secondary particles is 5 to 20 μm , the BET specific surface area is 0.3 to ² m ² / g, and the average valence of Mn is 3.3 to 4.

  That is, the lithium-containing composite oxide of the present invention contains at least Ni and Mn as constituent elements and has a very limited composition range centering on a composition in which the quantity ratio of Ni and Mn is 1: 1. It is a complex oxide.

In the present invention, only the limited composition range as described above is selected for the following reason. That is, in the layered lithium-containing composite oxide having Ni and Mn, based on the composition represented by the general formula LiNi _1/2 Mn _1/2 O _{2 in} which the quantity ratio of Ni and Mn is 1: 1, Ni and Mn are each replaced by x / 2 with Li, the quantity ratio of Ni and Mn is shifted from ½ by δ / 2 and −δ / 2 respectively, the quantity ratio of Li has a width by α, and , Ni, and Mn are each replaced by y / 2 elements M (where M is one or more elements selected from Mg, Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, Sn) composition, i.e., the general formula _{Li 1 + x + α Ni (} 1-xy + δ) / 2 Mn (1-xy-δ) / 2 M y O 2 [ however, 0 ≦ x ≦ 0.05, - 0.05 ≦ x + α ≦ 0.05, 0 ≦ y ≦ 0.4, −0.1 ≦ δ ≦ 0.1 (when 0 ≦ y ≦ 0.2) or −0. 4 ≦ δ ≦ 0.24 (when 0.2 <y ≦ 0.4), and M is selected from the group consisting of Mg, Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, and Sn. In the composition range represented by the selected one or more elements], the crystal structure is stabilized, and the composite oxide is excellent in reversibility of charge / discharge in a potential region near 4 V and durability in charge / discharge cycles. Is obtained.

In the above composition range, by an average valence of Mn in the composite oxide takes a tetravalent near the value (approximately 3.3 to 4-valent), during doping and dedoping of Li in the charge and discharge, the crystal It is considered that the movement of Mn therein is suppressed and the durability at high temperature is excellent .

  Further, it was found that when y> 0 and at least Co is contained as the element M, the conductivity of the compound is improved and the load characteristics during large current discharge are improved.

According to further detailed compositional examination, the composition in which the quantity ratio of Ni, Mn and M is 1: 1: 1, that is, the composition represented by the general formula LiNi _1/3 Mn _1/3 M _1/3 O ₂ It was also found that the stability of the compound was improved in the vicinity.

The composite oxide of the present invention has a large true density of 4.55 to 4.95 g / cm ³ , and becomes a material having a high volume energy density. The true density of the composite oxide containing Mn in a certain range varies greatly depending on its composition. However, since the structure is stabilized and a single phase is easily formed in the above narrow composition range, the true density of LiCoO ₂ is increased. It is thought that it becomes a close value. In particular, the value increases when the composition is close to the stoichiometric ratio, and a high-density composite oxide of approximately 4.7 g / cm ³ or more is obtained when −0.015 ≦ x + α ≦ 0.015.

The general formula _{Li 1 + x + α Ni (} 1-xy + δ) / 2 Mn (1-xy-δ) / 2 M y O 2 [ however, 0 ≦ x ≦ 0.05, -0.05 ≦ x + α ≦ 0.05, 0 ≦ y ≦ 0.4, −0.1 ≦ δ ≦ 0.1 (when 0 ≦ y ≦ 0.2) or −0.24 ≦ δ ≦ 0.24 (Where 0.2 <y ≦ 0.4), and M is one or more selected from the group consisting of Mg, Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, and Sn. Element], the amount ratio of Ni and Mn basically needs to be 1: 1, and the deviation from the median (δ / 2) is as small as −0.1 ≦ δ ≦ 0.1. Only allowed. However, in the composition range of 0.2 <y ≦ 0.4, the crystal structure becomes more stable and a single phase is easily formed. Obtainable. Therefore, in the above general formula, the possible range of δ is basically as narrow as −0.1 ≦ δ ≦ 0.1, but in the composition range of 0.2 <y ≦ 0.4, δ May be extended to a range of −0.24 ≦ δ ≦ 0.24.

  Here, the upper limit value of y was set to 0.4 because the composition of y> 0.4, that is, when the amount of substitution with the element M exceeds 0.4, a heterogeneous phase is formed in the target composite oxide. This is because problems such as deterioration of the stability of the compound are likely to occur.

Further, as a form of a complex oxide having the above composition, in which primary particles are aggregated to form secondary particles, the composite oxide is selected average particle size of the secondary particles is 5 to 20 [mu] m. This is because the primary particles are aggregated to form secondary particles, so that the reactivity in charge and discharge and the filling property of the composite oxide can be improved. The average particle size of the secondary particles is 5 to 20 μm. As a result, it is possible to increase the capacity of the electrode by increasing the filling property of the composite oxide. Moreover, the reactivity in charging / discharging can be improved and the load characteristic of a battery can be improved by making the average particle diameter of a primary particle into 0.3-3 micrometers.

Furthermore, the BET specific surface area of the composite oxide is desirably in the range of 0.3 to ² m ² / g. This is because the BET specific surface area of 0.3 m ² / g or more in which one is excellent in reactivity, 2m ² / g or less is that a large density of the particles themselves, the electrode mixture when forming the electrode This is because the agent density can be increased.

In the lithium-containing composite oxide in the form of particles described above, for example, an aqueous solution in which Ni and Mn, or a salt of Ni, Mn, and element M are dissolved is introduced into an alkaline aqueous solution, and Ni and Mn or Ni, Mn, and element M It can be obtained by synthesizing a coprecipitated hydroxide, calcining it with a lithium compound, and mechanically grinding and sieving the synthesized composite oxide as necessary. Firing is preferably performed in an atmosphere containing 10% by volume or more of oxygen, such as in air or oxygen gas. The firing temperature is approximately 700 ° C. to 1100 ° C., and the firing time is generally 1 to 24 hours. is there. Further, prior to the firing treatment, preheating is performed at a temperature lower than the firing temperature (approximately 250 to 850 ° C.) for about 0.5 to 30 hours, and further the firing treatment is performed. This is preferable because homogenization is promoted. Here, the primary particle size of the composite oxide can be controlled by adjusting the preheating or firing temperature and the treatment time, and the secondary particle size is controlled by the degree of mechanical grinding and sieving. be able to.

  By using the lithium-containing composite oxide described above as the positive electrode active material, for example, a non-aqueous secondary battery is produced as follows.

  The positive electrode was obtained by adding the above mixed oxide, if necessary, with a conductive additive such as flaky graphite and acetylene black and a binder such as polytetrafluoroethylene and polyvinylidene fluoride. The positive electrode material mixture is used as a molded body, or applied to a substrate that also functions as a current collector and integrated with the substrate. Here, as the substrate, for example, a metal net such as aluminum, stainless steel, titanium, or copper, a punching metal, an expanded metal, a foam metal, or a metal foil can be used.

In addition, although the said lithium containing complex oxide can be used independently as a positive electrode active material, the average particle diameter of a primary particle shall be 0.3-3 micrometers in this case. Further, the lithium-containing composite oxide (hereinafter, to. The lithium-containing complex oxide A), the average particle size smaller lithium-containing composite oxide than this (hereinafter referred to as lithium-containing complex oxide B.) And By mixing and using, the filling property of the active material is further improved, and the capacity of the electrode can be increased. In this, the average small lithium-containing composite oxide particle diameter B is by entering the voids between the particles of Lithium-containing composite oxide A, because the density of the positive electrode mixture is greater than 3.0 g / cm ³ is there.

  When the lithium-containing composite oxide of the present invention is A and the lithium-containing composite oxide having a small average particle size used by mixing is B, the average particle size of the lithium-containing composite oxide B is the lithium-containing composite oxide A. The average particle diameter of the secondary particles is preferably 3/5 or less. When the average particle diameter of B is larger than the above value, that is, when the difference between the average particle diameters of A and B is small, the above-described effect is reduced, and the difference from the case where A is used alone is reduced. Further, the lower limit value of the average particle diameter of B is considered to be about 0.1 μm, and if it is smaller than this, the characteristics as an active material are lowered, and the effect of using the mixture becomes difficult to occur. The average particle size of B is the average particle size when B is a primary particle, and the average particle size of secondary particles when the primary particles are aggregated to form secondary particles. Means. For the same reason as A, B is also preferably a composite oxide in which primary particles are aggregated to form secondary particles.

The lithium-containing composite oxide B may have the same composition as the lithium-containing composite oxide A or a different composition. When the composition is different from A, the general formula Li _{1 + a + b} R _1-a O ₂ [where 0 ≦ a ≦ 0.05, −0.05 ≦ a + b ≦ 0.05, and R is Mg , Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, and Sn]. In particular, when R contains at least Co, the conductivity of the electrode using the lithium-containing composite oxide A, which is inferior to LiCoO ₂ , can be improved.

  The ratio of the lithium-containing composite oxide B is desirably 10 to 40% by weight in the positive electrode active material. If the amount is less than this, the difference from the case where the lithium-containing composite oxide A is used alone is reduced. If the amount is more than this, the proportion of the lithium-containing composite oxide A is small, and the effect is reduced. is there.

The active material of the negative electrode facing the positive electrode is usually lithium or a lithium alloy such as Li—Al alloy, Li—Pb alloy, Li—In alloy, Li—Ga alloy, Si, Sn, Mg—Si alloy. Or an element that can be alloyed with lithium or an alloy of these elements. Furthermore, in addition to oxide materials such as Sn oxide, Si oxide, Li ₄ Ti ₅ O ₁₂ , carbonaceous materials such as graphite and fibrous carbon, lithium-containing composite nitride, and the like can be used. Moreover, what compounded said some material can also be made into an active material. The negative electrode is also produced by the same method as that for the positive electrode.

  The amount ratio of the active material in the positive electrode and the negative electrode varies depending on the type of the negative electrode active material, but in general, the positive electrode active material / negative electrode active material = 1.5 to 3.5 (mass ratio). Thus, the characteristics of the positive electrode active material can be utilized well.

  As the non-aqueous electrolyte in the non-aqueous secondary battery of the present invention, an organic solvent-based liquid electrolyte in which an electrolyte is dissolved in an organic solvent, that is, an electrolytic solution, a polymer electrolyte in which the electrolytic solution is held in a polymer, or the like is used. Can do. The organic solvent contained in the electrolytic solution or polymer electrolyte is not particularly limited, but it preferably contains a chain ester from the viewpoint of load characteristics. Examples of such chain esters include chain carbonates typified by dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and organic solvents such as ethyl acetate and methyl propionate. These chain esters may be used alone or in admixture of two or more. Particularly, for improving low-temperature characteristics, the above-mentioned chain esters occupy 50% by volume or more in the total organic solvent. In particular, it is preferable that the chain ester occupies 65% by volume or more of the total organic solvent.

However, as the organic solvent, in order to improve the discharge capacity, compared with the chain ester alone, an ester having a high dielectric constant ( dielectric constant : 30 or more) is mixed with the chain ester. Is preferred. Specific examples of such esters include, for example, cyclic carbonates represented by ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, ethylene glycol sulfite, and the like. A cyclic ester such as carbonate is preferred.

  Such an ester having a high dielectric constant is preferably contained in an amount of 10% by volume or more, particularly 20% by volume or more in the total organic solvent from the viewpoint of discharge capacity. Moreover, from the point of load characteristics, 40 volume% or less is preferable and 30 volume% or less is more preferable.

  Examples of the solvent that can be used together with the ester having a high dielectric constant include 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, 2-methyl-tetrahydrofuran, and diethyl ether. In addition, amine imide organic solvents, sulfur-containing or fluorine-containing organic solvents, and the like can also be used.

As an electrolyte to be dissolved in an organic solvent, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 ( SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2) are used alone or in combination of two or more. Among these, LiPF ₆ and LiC ₄ F ₉ SO ₃ that can obtain good charge / discharge characteristics are preferably used. The concentration of the electrolyte in the electrolytic solution is not particularly limited, but is preferably about 0.3 to 1.7 mol / dm ³ , particularly about 0.4 to 1.5 mol / dm ³ .

  Moreover, in order to improve the safety | security and storage characteristic of a battery, you may make an non-aqueous electrolyte contain an aromatic compound. As the aromatic compound, benzenes having an alkyl group such as cyclohexylbenzene or t-butylbenzene, biphenyl, or fluorobenzenes are preferably used.

  As the separator, a separator having sufficient strength and capable of holding a large amount of electrolyte solution is preferable. From such a viewpoint, the separator is made of polyolefin such as polypropylene, polyethylene, a copolymer of propylene and ethylene, with a thickness of 5 to 50 μm. A microporous film or non-woven fabric is preferably used. In particular, when a thin separator of 5 to 20 μm is used, the characteristics of the battery are likely to deteriorate during charge / discharge cycles, high-temperature storage, etc., and the safety is also lowered, but the battery using the composite oxide positive electrode of the present invention is Since it is excellent in stability and safety, the battery can function stably even if such a thin separator is used.

  Examples of the present invention will be described below. However, this invention is not limited only to those Examples. In the following examples, the primary particle size was measured based on a scanning electron micrograph of 10,000 times, and the secondary particle size was MICROTRAC HRA (Model: 9320-X100) manufactured by Microtrack. ) Using a laser diffraction particle size distribution measurement method. The BET specific surface area was measured using a BET specific surface area meter ASAP2000 manufactured by Micromeritics.

(Example 1)
A sodium hydroxide aqueous solution and aqueous ammonia were added to an aqueous solution containing nickel sulfate and manganese sulfate at a molar ratio of 1: 1, and a coprecipitated hydroxide containing Ni and Mn at 1: 1 was synthesized with vigorous stirring. After drying this, 0.2 mol of the coprecipitated hydroxide and 0.198 mol of LiOH.H ₂ O were weighed and mixed, and the mixture was dispersed in ethanol to form a slurry. And mixed for 40 minutes, and further dried at room temperature to prepare a uniformly mixed mixture. Next, this mixture is put in an alumina crucible, heated to 700 ° C. in an air stream at a flow rate of 1 dm ³ / min, preheated by holding at that temperature for 2 hours, and further heated to 900 ° C. The mixture was reacted for 12 hours to obtain a composite oxide. By pulverizing and further sieving the synthesized composite oxide, it is represented by the general formula LiNi _0.5 Mn _0.5 O _2. The average primary particle size is 1 μm, the average secondary particle size is 10 μm, and the BET specific surface area is 0. A lithium-containing composite oxide of .9 m ² / g was obtained.

(Example 2)
Represented by the general formula LiNi _0.5 Mn _0.5 O ₂ in the same manner as in Example 1 except that the firing temperature was 1000 ° C. and the firing time was 20 hours, the average particle diameter of primary particles: 3 μm, the average of secondary particles A lithium-containing composite oxide having a particle size of 10 μm and a BET specific surface area of 0.7 m ² / g was obtained.

(Examples 3-6 and Comparative Examples 1-3)
The composite oxide was synthesized by changing the firing temperature and firing time, and the composite oxide thus synthesized was pulverized and further sieved to obtain lithium-containing composite oxides shown in Table 1. In Example 5, a hydroxide containing Ni, Mn and Co at a ratio of 5: 5: 2 was used as the coprecipitated hydroxide. In Example 6, Ni, Mn and Co were 1: 1: 1. The hydroxide contained at a ratio of

(Comparative Example 4)
By a conventional method, LiCoO ₂ having an average primary particle size of 0.7 μm, an average secondary particle size of 7 μm, and a BET specific surface area of 0.6 m ² / g was obtained.

(Comparative Example 5)
According to a conventional method, LiMn ₂ O ₄ having an average primary particle size of 1 μm, an average secondary particle size of 12 μm, and a BET specific surface area of 1.8 m ² / g was obtained.

  Using the lithium-containing composite oxides of Examples 1 to 6 and Comparative Examples 1 to 5 as the positive electrode active material, non-aqueous secondary batteries were produced. 94 parts by weight of a lithium-containing composite oxide and 3 parts by weight of carbon black are dry-mixed, and a binder solution in which polyvinylidene fluoride is dissolved in N-methyl-2-pyrrolidone is mixed with 3 parts by weight of polyvinylidene fluoride. In addition, N-methyl-2-pyrrolidone was further added and mixed well to prepare a paste. This paint was uniformly applied to both sides of an aluminum foil having a thickness of 20 μm, dried, and then pressure-formed by a roller press, and cut into a size of 280 mm × 38 mm to produce a strip-shaped positive electrode having a thickness of about 170 μm. . Moreover, the weight of the mixture layer of each produced positive electrode was measured, and the density of the mixture obtained from this value is also shown in Table 1.

As is clear from Table 1, the lithium-containing composite oxides of Examples 1 to 6 have the general formula Li _{1 + x + α} Ni _{(1-x-y + δ) / 2} Mn _{(1-xy-δ) / 2} M _y O ₂ [however, 0 ≦ x ≦ 0.05, a -0.05 ≦ x + α ≦ 0.05,0 ≦ y ≦ 0.4, -0.1 ≦ δ ≦ 0.1 ( where 0 ≦ y ≦ 0.2) or −0.24 ≦ δ ≦ 0.24 (provided that 0.2 <y ≦ 0.4), and M is Mg, Ti, Cr, Fe, Co, 1 or more elements selected from the group consisting of Cu, Zn, Al, Ge, Sn], a composite oxide in which primary particles aggregate to form secondary particles, The average particle size of the primary particles and secondary particles is within the range of 0.3 to 3 μm and 5 to 20 μm, respectively, which is the claim of the present invention, so that the mixture density when the positive electrode is configured is more versatile than before. Is nearly the same level of density and LiCoO ₂ in the Comparative Example 4 has, it was possible to improve the filling property. On the other hand, even if it has the above composition, the lithium-containing composite oxides of Comparative Examples 1 to 3 in which any of the average particle diameters of the primary particles and the secondary particles deviate from the claims of the present invention are the density of the mixture. As a result, only a filling property comparable to that of LiMn ₂ O ₄ of Comparative Example 5 was obtained.

  Next, a paste prepared by mixing 92 parts by weight of natural graphite, 3 parts by weight of low crystalline carbon, and 5 parts by weight of polyvinylidene fluoride was uniformly applied to both sides of a copper foil having a thickness of 10 μm, dried, and then a roller press machine. The strip-shaped negative electrode having a thickness of about 165 μm was manufactured by pressure molding and cutting into a size of 310 mm × 41 mm.

A separator made of a microporous polyethylene film having a thickness of 20 μm is disposed between the belt-like positive electrode and the belt-like negative electrode, wound into a spiral shape to form an electrode body, and then has a bottom with an outer diameter of 14 mm and a height of 51.5 mm. It inserted in the cylindrical battery case, and the positive electrode lead body and the negative electrode lead body were welded. Thereafter, 1.7 cm ^{3 of a} non-aqueous electrolyte solution in which LiPF ₆ was dissolved at 1.2 mol / l in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 2 was injected into the battery case. The mass ratio of the positive electrode to the negative electrode active material (positive electrode active material / negative electrode active material) was 1.9 in the electrode body using the lithium-containing composite oxide of Example 1.

  The opening of the battery case was sealed according to a conventional method to produce a cylindrical non-aqueous secondary battery, and the discharge capacity was measured. After charging to 4.2V at a constant current of 600 mA under an environment of 20 ° C., charging is performed by a constant voltage method so that the total charging time is 2.5 hours, and at a constant current of 120 mA. The discharge capacity when discharged to 3.0 V was measured. The results are shown in Table 2.

The batteries using the lithium-containing composite oxides of Examples 1 to 6 showed a large discharge capacity as in the battery of Comparative Example 4 using LiCoO ₂ due to the high packing density of the positive electrode mixture. On the other hand, since the batteries using the lithium-containing composite oxides of Comparative Examples 1 to 3 have low active material filling properties, only a low discharge capacity can be obtained as in the battery of Comparative Example 5 using LiMn ₂ O _4. It was.

  Further, for the batteries using the lithium-containing composite oxides of Example 1, Example 6, Comparative Example 4 and Comparative Example 5, at a temperature of 20 ° C., charging under the same conditions as above and a constant current of 600 mA. A charge / discharge cycle by discharging up to 3.0 V was performed, and the cycle characteristics at room temperature were evaluated by the ratio of the discharge capacity after 100 cycles [capacity maintenance (%)]. Furthermore, in order to investigate the cycle characteristics at high temperature, the above-described cycle test was also performed at a temperature of 60 ° C., and the cycle characteristics at high temperature were evaluated by the ratio of the discharge capacity after 20 cycles [capacity maintenance (%)].

  Furthermore, the storage characteristics were evaluated as follows. After the charge / discharge cycle was performed 5 times under the same charge / discharge conditions as the measurement of the cycle characteristics, the battery was charged under the charge conditions and stored at a temperature of 60 ° C. for 20 days. After this storage, the battery was discharged under the above conditions, and the ratio of the capacity remaining after storage to the capacity before storage [capacity maintenance (%)] was measured. After the measurement, one charge / discharge cycle was performed, and the ratio of the capacity after storage to the capacity before storage [capacity recovery (%)] was measured. The storage characteristics at high temperature were evaluated based on the ratio of capacity maintenance and capacity recovery. These results are shown in Table 3.

As is clear from Table 3, by using the lithium-containing composite oxides of Example 1 and Example 6 for the positive electrode, batteries having excellent cycle characteristics and storage characteristics could be constructed. However, LiCoO ₂ and LiMn ₂ O ₄ In the case of using, the cycle characteristics and storage characteristics were inferior to the lithium-containing composite oxide of the present invention. In order to investigate this cause, the following experiment was conducted. The positive electrode using the lithium-containing composite oxides of Example 1, Comparative Example 4 and Comparative Example 5 was cut to a diameter of 15 mm in an argon atmosphere, immersed in 5 ml of an electrolytic solution, and held at 60 ° C. for 5 days. The electrolytic solution thus obtained was subjected to ICP spectroscopic analysis, and the concentrations of Mn and Co eluted in the electrolytic solution were quantified. Table 4 shows values obtained by converting the elution amount per 1 g of the composite oxide.

In the lithium-containing composite oxide of Example 1, the elution amount of Mn is one order of magnitude smaller than that of LiMn ₂ O ₄ of Comparative Example 5, and even when stored at a high temperature, dissolution of Mn in the electrolyte is sufficiently suppressed. I found out. The elution amount of Mn in Example 1 is smaller than the Co elution amount of LiCoO _{2 in} Comparative Example 4, and it can be seen that the material is excellent in durability at high temperatures. It is known that LiMn ₂ O ₄ dissolves Mn at a high temperature, and the capacity deterioration is significant when it is charged and discharged at a high temperature or stored at a high temperature. Is backed up. On the other hand, LiCoO ₂ is a material that does not easily cause such a problem, but it is clear that the lithium-containing composite oxide of the present invention is a material further superior to this LiCoO ₂ .

(Example 7)
The lithium-containing composite oxide synthesized in Example 1 was pulverized and sieved until the average secondary particle size reached 5 μm, and lithium-containing composite oxide B was obtained. Next, the lithium of Example 1 represented by the general formula LiNi _0.5 Mn _0.5 O ₂ and having an average primary particle diameter of 1 μm, an average secondary particle diameter of 10 μm, and a BET specific surface area of 0.9 m ² / g. The non-aqueous secondary battery similar to the above was produced by mixing the containing composite oxide A and the lithium containing composite oxide B at a weight ratio of 60:40 and using this as a positive electrode active material.

(Example 8)
A nonaqueous secondary battery was produced in the same manner as in Example 7 except that the average particle size of the secondary particles of the lithium-containing composite oxide B was 3 μm.

Example 9
A nonaqueous secondary battery was produced in the same manner as in Example 8, except that the weight ratio of the lithium-containing composite oxide A and the lithium-containing composite oxide B was 80:20.

(Example 10)
A nonaqueous secondary battery was produced in the same manner as in Example 8 except that the weight ratio of the lithium-containing composite oxide A and the lithium-containing composite oxide B was 95: 5.

(Example 11)
A nonaqueous secondary battery was produced in the same manner as in Example 7 except that the average particle size of the secondary particles of the lithium-containing composite oxide B was 7 μm.

  Also in Examples 7 to 11, the density of the positive electrode mixture before battery assembly and the discharge capacity of the nonaqueous secondary battery were measured in the same manner as described above. The results are shown in Table 5 together with the results of Example 1. As is clear from this, the lithium-containing composite oxide A of the present invention was used by mixing with the lithium-containing composite oxide B having an average particle size of 3/5 or less of the average particle size of the secondary particles. In the nonaqueous secondary batteries of Examples 7 to 9, the density of the positive electrode mixture was increased, the active material filling property was improved, and the discharge capacity of the battery could be increased. On the other hand, Example 10 in which the average particle size of lithium-containing composite oxide B is sufficiently small but the mixing ratio thereof is small, and Example in which the average particle size of lithium-containing composite oxide B is not so different from lithium-containing composite oxide A In the non-aqueous secondary battery of No. 11, the density of the positive electrode mixture and the discharge capacity were about the same as in Example 1 in which the lithium-containing composite oxide A was used alone, and the effect of mixing the active material was not clear.

  As described above, in the present invention, by using a lithium-containing composite oxide that has high filling properties and excellent cycle durability at high temperatures and stability at high temperature storage, high capacity, cycle durability and It is possible to provide a non-aqueous secondary battery that is excellent in storability at high temperatures. Furthermore, the lithium composite oxide used in the present invention is suitable for mass production because it uses Mn and Ni, which are more abundant and cheaper than Co, as the main constituent elements, and also reduces the cost of the battery. It can contribute.

Claims (16)

Formula _{Li 1 + x + α Ni (} 1-xy + δ) / 2 Mn (1-xy-δ) / 2 M y O 2 [ however, 0 ≦ x ≦ 0.05, -0.05 ≦ x + α ≦ 0.05, 0 ≦ y ≦ 0.4, −0.1 ≦ δ ≦ 0.1 (when 0 ≦ y ≦ 0.2) or −0.24 ≦ δ ≦ 0.24 ( Where 0.2 <y ≦ 0.4), and M is one or more elements selected from the group consisting of Mg, Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, Sn The primary particles have a mean particle size of 0.3 to 3 μm, and the secondary particles have a mean particle size of 5 to 20 μm. A lithium-containing composite oxide characterized by having a BET specific surface area of 0.3-2 m ² / g and an average valence of Mn of 3.3-4.   2. The lithium-containing composite oxide according to claim 1, wherein in the general formula, y> 0, and M is one or more elements including at least Co.   3. The lithium-containing composite oxide according to claim 1, wherein 0.2 <y ≦ 0.4 and −0.1 ≦ δ ≦ 0.1 in the general formula.   The lithium-containing composite oxide according to any one of claims 1 to 3, wherein in the general formula, the amount ratio of Ni and Mn is 1: 1.   4. The lithium-containing composite oxide according to claim 3, wherein in the general formula, the quantitative ratio of Ni, Mn, and M is 1: 1: 1.   In the said general formula, M is Co, The lithium containing complex oxide in any one of Claims 1-5.   The nonaqueous secondary battery provided with the positive electrode and negative electrode which use the lithium containing complex oxide in any one of Claims 1-6 as an active material, and the nonaqueous electrolyte. Formula _{Li 1 + x + α Ni (} 1-xy + δ) / 2 Mn (1-xy-δ) / 2 M y O 2 [ however, 0 ≦ x ≦ 0.05, -0.05 ≦ x + α ≦ 0.05, 0 ≦ y ≦ 0.4, −0.1 ≦ δ ≦ 0.1 (when 0 ≦ y ≦ 0.2) or −0.24 ≦ δ ≦ 0.24 ( Where 0.2 <y ≦ 0.4), and M is one or more elements selected from the group consisting of Mg, Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, Sn The secondary particles have a mean particle size of 5 to 20 μm, and the average valence of Mn is 3.3 to 4. A lithium-containing composite oxide A, and a lithium-containing composite oxide having the same composition as the lithium-containing composite oxide A and having an average particle size smaller than the average particle size of secondary particles of the composite oxide A B and A mixture containing
The average particle diameter of the composite oxide B is 3/5 or less of the average particle diameter of the secondary particles of the composite oxide A;
The positive electrode active material whose ratio of the said complex oxide B is 10 to 40 weight% of the whole positive electrode active material. The positive electrode active material according to claim 8, wherein the composite oxide B is a composite oxide in which primary particles aggregate to form secondary particles. In the general formula representing the composite oxide A, a y> 0, the positive active material of claim 8 or 9 M is one or more elements including at least Co. The positive electrode active material according to any one of the above general formula representing the composite oxide A, 0.2 <y ≦ 0.4 and claims 8-10 is -0.1 ≦ δ ≦ 0.1. In formula representing the composite oxide A, the amount ratio between Ni and Mn is 1: 1 positive active material according to any one of claims 8-11 is. The positive electrode active material according to claim 11 , wherein in the general formula representing the composite oxide A, the quantitative ratio of Ni, Mn, and M is 1: 1: 1. The average particle diameter of primary particles of the composite oxide A is, the positive electrode active material according to any one of claims 8-13 is 0.3 to 3 m. Nonaqueous secondary battery comprising a positive electrode and a negative electrode and a non-aqueous electrolyte having a positive electrode active material according to any of claims 8-14. Said positive electrode, said has a positive electrode active material, conductive additive and a positive electrode mixture comprising a binder, according to claim 15 in which the density of the positive electrode mixture, being greater than 3.0 g / cm ³ A non-aqueous secondary battery according to 1.