JP4867153B2 - Positive electrode active material for non-aqueous electrolyte secondary battery, positive electrode for secondary battery, and non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery having a low cost and a high capacity, a positive electrode for a secondary battery, and a non-aqueous electrolyte secondary battery.

  Compared with Ni-Cd batteries and Ni-MH batteries, lithium ion secondary batteries generally have a higher operating voltage and outperform other battery systems in both unit volume and energy density per unit weight. Therefore, it is particularly suitable for reduction in size and weight and is widely used in mobile phones, digital cameras, notebook personal computers (sometimes referred to as notebook PCs) and the like, and greatly contributes to the development of today's mobile devices.

  On the other hand, in recent years, attention has been focused on the shift to a clean energy society and the establishment of environmental technology due to the growing awareness of environmental issues. For power storage, uninterruptible power supply (sometimes referred to as UPS), and mobile There is a need for early realization of high-performance secondary batteries suitable for power supply applications. Although the lithium ion secondary battery has been actively studied for the development of such a large battery due to the above-mentioned characteristic of high energy density, the current product is widely used for widespread use of the technology or products to which the technology is applied. Life cycle cost advantage over is essential, and low price is an indispensable element.

  In other words, if a charge / discharge current value can be increased using a low-priced material in a lithium ion secondary battery with a high operating voltage, a high-performance UPS or hybrid vehicle (sometimes referred to as HEV) can be realized. As a result, it can contribute to the construction of an advanced information society and a clean energy society.

Against this background, the reduction in price and increase in capacity of lithium ion secondary batteries are being actively studied. For example, conventionally, LiCoO ₂ has been mainly used for small portable applications, but attempts have been made to replace Co with other elements as LiCoO ₂ substitute materials, or development of olivine-based materials has been accelerated.

Currently, LiNi _0.5 Mn _0.5 O ₂ or LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ is attracting attention among such development trends. However, these materials have a weak impact on cost reduction, and have problems in development for HEV and UPS applications due to the low charge / discharge rate.

Therefore, various studies have been made with the aim of replacing with cheaper metals and improving the charge / discharge characteristics. For example, Patent Documents 1 to 3 disclose techniques for substituting a part of Ni with Mn or Fe as a result of improvement of LiNiO ₂ . The use of LiMO ₂ (M is a transition metal) as a positive electrode material for a non-aqueous electrolyte secondary battery is disclosed in Patent Document 4, but is specifically effective other than M = Co and Ni. The composition was not shown. Therefore, in Patent Documents 1 to 3, a system in which a part of Ni in LiNiO ₂ is substituted with Fe or Mn is studied, and an active material having a specific lattice constant (Patent Document 1), specific powder characteristics A combination with an active material (Patent Document 2) and a specific negative electrode (Patent Document 3) is disclosed as effective. On the other hand, the inventions disclosed in Patent Document 5 and Patent Document 6 attempted to improve characteristics by partially replacing Ni or Mn with LiFeO ₂ as an end composition. Patent Document 5 discloses a positive electrode active material having a median diameter defined, and Patent Document 6 discloses a method for producing a lithium battery. Furthermore, Patent Documents 7 to 9 also disclose the solid solution region composition of LiMnO ₂ —LiFeO ₂ —LiNiO ₂ .

  Similarly, reports on price reduction or characteristic improvement using Al as an additive element are also found in Patent Documents 8, 10, 11, and 12. However, all of them required further improvement in the impact of cost reduction, charge / discharge cycle characteristics, and rate characteristics.

Japanese Patent No. 3064655 Japanese Patent No. 3232984 Japanese Patent No. 3281829 US Pat. No. 4,302,518 Japanese Patent No. 3276451 Japanese Patent No. 3489771 JP 2003-048718 A JP 2002-145623 A JP 2002-060223 A JP 2000-223122 A JP 2002-234733 A Japanese Patent No. 3561607

  In view of the circumstances of such prior art, the present invention provides a positive electrode active material for a non-aqueous electrolyte secondary battery, a high capacity, excellent cycle life, and low cost, a positive electrode for a secondary battery, and a non-aqueous solution using these. An object is to provide an electrolyte secondary battery.

The present inventors have scrutinized the conventional technique, and as a composition region of M in LiMO ₂ , Mn = 50 to 60 mol%, Ni = 30 to 40 mol%, and Me = 10 to 20 mol% (Me is a trivalent cation). And the composition of the four components obtained by adding Li to the three components has not been studied in detail and has not been studied in detail, and it can withstand actual use in the composition region. The present invention has been completed by thoroughly examining whether there is a composition of active material that can be obtained.

That is, the present invention which has solved the above problems, the content ratio of the metal element (molar ratio) is represented by the following formula (1), and satisfies the lithium manganese-based composite oxide represented by the following formula (2) A positive electrode active material for a non-aqueous electrolyte secondary battery.
[Mn]: [Ni]: [Me] = 5: 3: 1 (molar ratio) (1)
[Li] / [Mn + Ni + Me] = 1.22 (molar ratio) (2)
(In the above formula, Me represents Fe or Al .)
Moreover, the present invention that has solved the above problems is a lithium manganese composite oxide in which the content ratio (molar ratio) of the metal element is represented by the following formula (1) and satisfies the condition represented by the following formula (2). And the value of the following formula (1) and the value of the following formula (2) are in the range of ± 2.5% with respect to the respective values. It is an active material.
[Mn]: [Ni]: [Me] = 5: 3: 1 (molar ratio) (1)
[Li] / [Mn + Ni + Me] = 1.22 (molar ratio) (2)
(In the above formula, Me represents Fe or Al.)
The lithium manganese-based composite oxide is preferably a lithium manganese-based composite oxide represented by the following following formula (3).
Li [Mn _0.5 Ni _0.3 Me _0.1 Li _0.1 ] O ₂ (3)
(In the above formula, Me represents Fe or Al .)

  Furthermore, the present invention that has solved the above problems includes a non-electrode including a negative electrode capable of inserting / extracting lithium, and a positive electrode using a positive electrode active material disposed opposite to the negative electrode via a non-aqueous electrolyte. In the water electrolyte secondary battery, the positive electrode active material is a positive electrode active material for the nonaqueous electrolyte secondary battery of the present invention.

Furthermore, the present invention that has solved the above problems is a positive electrode for a secondary battery using the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention, wherein the positive electrode for the secondary battery is constituted. A positive electrode for a secondary battery, wherein the mixture, excluding the electric metal foil, has a density of 2.55 to 3.05 g / cm ³ .
Furthermore, this invention which solved the said subject is a nonaqueous electrolyte secondary battery using the positive electrode for secondary batteries of the said this invention.

Positive electrode active material for a nonaqueous electrolyte secondary battery of the present invention, the content ratio of the metal element (molar ratio) is represented by the following formula (1), and, under following formula (2)
[Mn]: [Ni]: [Me] = 5: 3: 1 (molar ratio) (1)
[Li] / [Mn + Ni + Me] = 1.22 (molar ratio) (2)
(In the above formula, Me represents Fe or Al .)
In the initial state before charging, manganese (Mn) in the lithium manganese composite oxide is in the vicinity of tetravalent nickel (Ni). Is a divalent metal element, Me has a trivalent stable oxidation degree, and the structure is stabilized. In other words, the ratio of each element of lithium (Li), Mn, Ni, and Me is not a solid solution in an arbitrary composition range, but is substantially [Li]: [Mn]: [Ni]: [Me]. = Stabilization of the structure by setting the metal element content ratio very close to 1.1: 0.5: 0.3: 0.1.

In the lithium manganese composite oxide in the present invention, Li is essential at both the A site and the B site in the layered crystal structure expressed as ABO _2, and the lithium manganese composite oxide in the present invention Since the initial valence of the constituent elements and the ratio thereof are limited, in the charge / discharge reaction mechanism, the ratio of the cation exhibiting a valence change at the time of insertion / extraction of Li is 20% or less.

That is, the lithium manganese composite oxide in the present invention has a valence balance between cations, and the ratio of cations that are oxidized / reduced with charge / discharge is 20% or less with respect to all cations, There is little increase or decrease in volume due to charge / discharge, and reliability is high. Moreover, since expensive cobalt (Co) is not included and the ratio of Ni is relatively small, the price of the positive electrode active material can be kept low. In addition, since the ratio of Li, which is a light element, is high, there is also an advantage that a high capacity density per weight can be obtained.
That is, by using a lithium manganese composite oxide having the above-described metal element content ratio, the present invention realizes a high-capacity and low-priced secondary battery. In applications such as HEV and UPS, The battery pack / module is reduced in size, weight and cost.

The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention has a metal element content ratio (molar ratio) substantially represented by the following formula (1) and a condition represented by the following formula (2). It contains lithium manganese complex oxide satisfying the above.
[Mn]: [Ni]: [Me] = 5: 3: 1 (molar ratio) (1)
[Li] / [Mn + Ni + Me] = 1.22 (molar ratio) (2)
(In the above formula, Me represents a metal element that becomes a trivalent cation.)

  In the lithium manganese based composite oxide, the content ratio (molar ratio) of the metal elements is substantially represented by the above formula (1), but the value in the molar ratio of each metal element is ± 2 with respect to these values. The content ratio of each of the metal elements of [Li] and [Mn], [Ni], and [Me] substantially represented by the above formula (2) is acceptable as long as it is within the allowable range of 5%. As long as it is within the allowable range of ± 2.5% with respect to the ratio (molar ratio) value 1.22 of the total value (which may be expressed as [Mn + Ni + Me]).

The lithium manganese composite oxide is preferably a lithium manganese composite oxide substantially represented by the following formula (3).
Li [Mn _0.5 Ni _0.3 Me _0.1 Li _0.1 ] O ₂ (3)
(In the above formula, Me represents a metal element that becomes a trivalent cation.)

  Examples of the metal element Me (sometimes referred to as Me) that becomes a trivalent cation include iron (Fe), aluminum (Al), other scandium (Sc), chromium (Cr), gallium (Ga), yttrium ( Y), indium (In), and the like. Of these, Fe and Al are particularly preferable. The reason is that an increase in capacity can be achieved effectively and at a low cost.

  The valence of Mn in the lithium manganese composite oxide is around tetravalent, specifically, preferably 3.8 or more, more preferably 3.9 or more. By doing so, the operating potential can be maintained more stably and high, the elution of Mn into the electrolytic solution can be more effectively prevented, and the decrease in capacity during repeated use can be suppressed. The valence of Mn can be calculated based on the valence and composition ratio of each constituent element other than Mn.

  In the lithium manganese composite oxide in the present invention, as described above, the valence of Mn is preferably 3.8 or more, more preferably 3.9 or more, and Ni is preferably divalent, Me is preferably trivalent. In a state in which such a relationship is maintained, the valence balance between cations is balanced, and the ratio of cations that are oxidized / reduced with charge / discharge is 20% or less with respect to all cations. There is little increase or decrease in volume, and the reliability is high and the capacity can be increased. Further, by satisfying the condition expressed by the above formula (2), the ratio of Li can be kept high, the battery weight can be reduced, and the capacity density per weight can be easily kept high.

  The non-aqueous electrolyte secondary battery according to the present invention includes, as main components, a positive electrode using a positive electrode active material containing the above lithium manganese composite oxide, and a negative electrode having a negative electrode active material capable of occluding and releasing lithium. A separator which does not cause an electrical connection is sandwiched between the positive electrode and the negative electrode so that they are immersed in a lithium ion conductive nonaqueous electrolyte solution, facing each other through the nonaqueous electrolyte solution. It is in a state of being sealed inside. When a voltage is applied to the positive electrode and the negative electrode, lithium ions are desorbed from the positive electrode active material, and the lithium ions are occluded in the negative electrode (active material), resulting in a charged state. In addition, by causing electrical contact between the positive electrode and the negative electrode outside the battery, lithium ions are released from the negative electrode active material, and lithium ions are occluded in the positive electrode active material, which is opposite to that during charging.

Next, a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery will be described. As a raw material for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, Li ₂ CO ₃ , LiOH, Li ₂ O, Li ₂ SO _{4 and the} like can be used as the Li raw material, but Li ₂ CO ₃ , LiOH or the like is suitable. As the Mn raw material, various manganese oxides such as electrolytic manganese dioxide (EMD) / Mn ₂ O ₃ , Mn ₃ O ₄ , CMD, MnCO ₃ , MnSO _{4 and the} like can be used. NiO, Ni (OH) ₂ , NiSO ₄ , Ni (NO ₃ ) _2, etc. can be used as the Ni raw material. In addition, an oxide, carbonate, hydroxide, sulfide, nitrate, or the like of Me is used as a raw material for the metal element Me that becomes a trivalent cation. Ni raw materials, Mn raw materials, and metal element raw materials that become trivalent cations may be difficult to cause element diffusion during firing. After firing the raw materials, Ni oxide, Mn oxide, and Me oxide remain as different phases. May end up. For this reason, Ni raw material, Mn raw material, Me raw material are dissolved and mixed in an aqueous solution, and then precipitated in the form of hydroxide, sulfate, carbonate, nitrate, etc., Ni containing Ni, Mn composite precursor and Me It is possible to use a Mn composite precursor as a raw material. It is also possible to use Ni, Mn composite oxide or Ni, Mn, Me composite oxide obtained by firing such composite precursor. When such a complex precursor or complex oxide is used as a raw material, Mn, Ni and Me are preferably diffused well at the atomic level.

  These raw materials are weighed and mixed so as to have a target metal composition ratio. The mixing is performed by pulverizing and mixing with a ball mill, a jet mill or the like. The mixed powder is fired in air or oxygen at a temperature of 600 ° C. to 950 ° C. to obtain a positive electrode active material containing a lithium manganese composite oxide. The firing temperature is preferably a high temperature for diffusing each element, but if the firing temperature is too high, oxygen deficiency may occur, which may adversely affect battery characteristics. For this reason, it is preferable that a calcination temperature shall be about 700 to 850 degreeC. A positive electrode active material synthesized by a liquid system method such as a sol-gel process or hydrothermal synthesis can also be used in the same manner if the final composition is a predetermined one.

The specific surface area of the obtained lithium manganese composite oxide is preferably 1.5 m ² / g or less, more preferably 0.8 m ² / g or less. This is because the larger the specific surface area, the more binders are required, which tends to be disadvantageous in terms of the capacity density of the positive electrode active material.

  The obtained positive electrode active material, conductivity imparting agent, binder and other mixture raw materials are dispersed in an organic solvent and applied on a current collector and dried, or the positive electrode active material and conductivity imparted A mixture material such as a binder and a binder is mixed to prepare a mixture, which is pressure-bonded to a current collector to form a positive electrode for a secondary battery. Examples of the conductivity-imparting agent include carbon materials, metal substances such as Al, and conductive oxide powders. As the binder, polyvinylidene fluoride or the like is used. As the current collector, a metal thin film mainly composed of metal such as Al can be used.

Preferably, the addition amount of the conductivity imparting agent is about 1 to 10% by mass with respect to the mass of the mixture, and the addition amount of the binder is also about 1 to 10% by mass with respect to the mass of the mixture. This is because the capacity per unit weight increases as the proportion of the positive electrode active material for the non-aqueous electrolyte secondary battery increases. If the ratio between the conductivity-imparting agent and the binder is too small, the conductivity may not be maintained, or a problem of electrode peeling may occur. Moreover, it is preferable that the density of the mixture which comprises the formed secondary battery positive electrode except the electrical power collector shall be 2.55-3.05 g / cm < ³ >. When the density of the mixture is the above value, the discharge capacity at the time of use at a high discharge rate is preferably improved.

  As an electrolytic solution in the present invention, propylene carbonate (may be represented as PC), ethylene carbonate (may be represented as EC), butylene carbonate (may be represented as BC), and vinylene carbonate (may be represented as VC). ), Etc., dimethyl carbonate (sometimes represented as DMC), diethyl carbonate (sometimes represented as DEC), ethyl methyl carbonate (sometimes represented as EMC), dipropyl carbonate (sometimes represented as DPC). Linear carbonates such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, and 1,2-ethoxyethane (DEE). ), Ethoxymethoxyethane (sometimes referred to as EME) Chain ethers such as tetrahydrofuran, cyclic ethers such as 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid Triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane Aprotic organic solvents such as sultone, anisole, N-methylpyrrolidone and fluorinated carboxylic acid esters can be used singly or in combination. Of these, propylene carbonate, ethylene carbonate, γ-butyl lactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and the like are preferably used alone or in combination.

Lithium salts are dissolved in these organic solvents. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ CO ₃ , LiC (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic carboxylic acid lithium carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, imides, etc. can give. Further, a polymer electrolyte may be used instead of the electrolytic solution. The electrolyte concentration is, for example, 0.5 mol / l to 1.5 mol / l. If the concentration is too high, density and viscosity increase. If the concentration is too low, the electrical conductivity may decrease.

  As the negative electrode active material, as a material capable of inserting and extracting lithium, a carbon material, Li metal, Si, Sn, Al, SiO, SnO, or the like can be used alone or in combination.

  Disperse raw materials for the negative electrode active material, conductivity imparting agent, binder and the like in an organic solvent, apply this on a current collector and dry it, or negative electrode active material, conductivity imparting agent, binder A mixture material such as an agent is mixed to prepare a mixture, which is pressure-bonded to a current collector to form a negative electrode. As an example of the conductivity imparting agent, a conductive oxide powder or the like can be used in addition to the carbon material. As the binder, polyvinylidene fluoride or the like is used. As the current collector, a metal thin film mainly composed of Al, Cu or the like can be used.

  A non-aqueous electrolyte secondary battery according to the present invention comprises a negative electrode and a positive electrode laminated in a dry air or inert gas atmosphere via a separator, or after being rolled up, a battery can, for example, a positive electrode exterior It can be manufactured by being housed in a battery can made of a can and a negative electrode outer can, or by sealing with a flexible film made of a laminate of a synthetic resin and a metal foil.

  There are no restrictions on the battery shape, and it can take the form of a positive electrode and negative electrode facing each other with a separator in between, a wound type, a laminated type, etc., and the cell can also be a coin type, laminate pack, square cell, cylinder Type cells can be used. FIG. 3 shows a cross-sectional structure of a coin-type non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to examples.
<Examples 1-2 and Comparative Examples 1-18>
(Synthesis example of positive electrode active material f-1: Me = Fe)
The positive electrode active material was synthesized by the following procedure.
First, lithium carbonate ground and adjusted to an average particle size of 3 μm or less, and metal element content ratio (content ratio symbol) of Mn / Ni / Fe = 5/3/1 (molar ratio), similarly ground and adjusted to an average particle size of 5 μm or less The composite oxide having A) was weighed and mixed at a charge composition of [Li] / [Mn + Ni + Fe] = 1.13 / 0.9 (molar ratio), and then wet mixed in a wet ball mill using ethanol for 120 hours. The obtained mixed powder was vacuum-dried at 100 ° C. for 24 hours and then heated in air at 900 ° C. for 48 hours to perform primary firing. Subsequently, the primary fired powder was crushed and remixed, heated in oxygen at 700 ° C. for 72 hours, and then secondary fired to obtain a powdered positive electrode active material f-1.

The X-ray diffraction pattern of the obtained powdered positive electrode active material f-1 was measured using Cu Kα rays, and the results shown in FIG. 1 were obtained. As shown in FIG. 1, a diffraction pattern that can be roughly indexed in the space group R-3m was obtained. When the X-ray diffraction peak is broad overall and there is a small peak similar to Li ₂ MnO ₃ , there is a possibility that it will be indexed into a space group with slightly lower symmetry when examined in detail. Basically, it is considered that a layered lithium manganese composite oxide was obtained.

Further, when the composition of the obtained positive electrode active material f-1 was analyzed for a metal element by inductively coupled plasma emission spectrometry (sometimes referred to as IPC emission analysis), the content ratio of the metal element at the time of preparation Is Li / Mn / Ni / Fe = 1.13 / 0.5 / 0.3 / 0.1 (molar ratio), but the content ratio of the metal element of the obtained positive electrode active material f-1 is Li / Mn / Ni / It was estimated that Fe = 1.10 / 0.5 / 0.3 / 0.1 (molar ratio), and a positive electrode active material f-1 (Li [Mn _0.5 Ni _0.3 Fe _0.1 Li _0.1 ] O ₂ ) having a desired composition was obtained. . Table 1 summarizes the composition and the like of the obtained positive electrode active material f-1.

(Synthesis example of positive electrode active materials f-2 to f-4: Me = Fe)
The positive electrode active materials f-2 to f-4 are the same as the synthesis example of the positive electrode active material f-1 except that they are weighed and mixed with the charged composition of [Li] / [Mn + Ni + Fe] (molar ratio) shown in Table 1. Was prepared. Table 1 summarizes the compositions and the like of the obtained positive electrode active materials f-2 to f-4.

(Synthesis example of positive electrode active materials f-5 to f-10: Me = Fe)
Each composite oxide having a Mn / Ni / Fe content ratio (molar ratio) of content ratio symbols B to G shown in Table 1 was used, and lithium carbonate and each of the composite oxides shown in [Li] / Positive electrode active materials f-5 to f-10 were prepared in the same manner as in the synthesis example of the positive electrode active material f-1 except that each was weighed and mixed in a charged composition of [Mn + Ni + Fe] (molar ratio). Table 1 summarizes the compositions and the like of the obtained positive electrode active materials f-5 to f-10.

(Synthesis example of positive electrode active material a-1: Me = Al)
The positive electrode active material a-1 was synthesized by the following procedure. First, lithium carbonate ground and adjusted to an average particle size of 3 μm or less, and metal element content ratio (content ratio) of Mn / Ni / Al = 5/3/1 (molar ratio), similarly ground and adjusted to an average particle size of 5 μm or less The composite oxide having the symbol A) was weighed and mixed at a charging composition of Li / [Mn + Ni + Al] = 1.11 / 0.9 (molar ratio), and then wet mixed in a wet ball mill using ethanol for 72 hours. The obtained mixed powder was vacuum-dried at 100 ° C. for 24 hours, and then heated in air at 750 ° C. for 48 hours to perform primary firing. Subsequently, the primary fired powder was crushed and remixed, heated in oxygen at 700 ° C. for 72 hours, and then secondary fired to obtain a powdered positive electrode active material a-1.

  When the X-ray diffraction pattern of the obtained powdered positive electrode active material a-1 was measured using Cu Kα rays, the same diffraction pattern as in FIG. 1 was obtained although the peak was slightly shifted to the high angle side. Obtained.

Further, the composition of the obtained positive electrode active material a-1 was analyzed in the same manner as in Example 1. As a result, the content ratio of the metal element at the time of preparation was Li / Mn / Ni / Al = 1.11 / 0.5 / 0.3 / Although the ratio was 0.1 (molar ratio), the metal element content ratio of the obtained positive electrode active material a-1 was estimated to be Li / Mn / Ni / Al = 1.10 / 0.5 / 0.3 / 0.1 (molar ratio). A positive electrode active material a-1 (Li [Mn _0.5 Ni _0.3 Al _0.1 Li _0.1 ] O ₂ ) having a target composition was obtained. Table 1 summarizes the composition and the like of the obtained positive electrode active material a-1.

(Synthesis example of positive electrode active materials a-2 to a-4: Me = Al)
The positive electrode materials a-2 to a-4 were prepared in the same manner as in the synthesis example of the positive electrode active material a-1 except that they were weighed and mixed with the charge composition of [Li] / [Mn + Ni + Al] (molar ratio) shown in Table 1. Prepared. Table 1 summarizes the compositions and the like of the obtained positive electrode active materials a-2 to a-4.

(Synthesis of positive electrode active materials a-5 to a-10: Me = Al)
Each composite oxide having a content ratio (molar ratio) of metal elements of Mn / Ni / Al with content ratio symbols B to G shown in Table 1 is used, and lithium carbonate and each of the composite oxides are shown in Table 1. Positive electrode materials a-5 to a-10 were prepared in the same manner as in the synthesis example of the positive electrode active material a-1, except that each was prepared and weighed and mixed in a charged composition of [Li] / [Mn + Ni + Al] (molar ratio). Table 1 summarizes the compositions and the like of the obtained positive electrode active materials a-5 to a-10.

(Preparation of positive electrode)
Positive electrode active materials f-1 to f-10 obtained in the above synthesis examples and any one of a-1 to a-10 positive electrode active materials, acetylene black (sometimes referred to as AB) and air as a conductivity-imparting material. Phase-grown carbon fiber (sometimes referred to as VGCF), polyvinylidene fluoride (sometimes referred to as PVDF) as a binder, positive electrode active material: AB: VGCF: PVDF = 87: 5: 2: 6 (mass) Ratio) was dispersed in N-methyl-2-pyrrolidone (sometimes referred to as NMP) to prepare a mixture coating solution. This coating solution was applied onto an Al metal foil current collector, and NMP was heated and evaporated to produce a positive electrode.

(Production of secondary battery)
A 2320 type coin cell was produced as follows. The battery positive electrode was used as a secondary battery positive electrode. A metal Li disk with a thickness of 1.4 mm is used as the negative electrode, a porous polypropylene film is used as the separator, the positive electrode and the negative electrode are placed opposite to each other with the separator interposed therebetween, placed in a coin cell, filled with the electrolyte, and sealed A battery was produced. As an electrolytic solution, LiPF ₆ is dissolved in a mixed solvent (volume ratio “30:70”) of ethylene carbonate (sometimes referred to as EC) and diethyl carbonate (sometimes referred to as DEC) to obtain a concentration of 1 M / L. What was done was used.

(Evaluation of charge / discharge characteristics)
The charge / discharge characteristics of the coin cell produced as described above were evaluated. The produced coin cell was charged to 4.6 V at a current value of 0.2 mA and discharged to 2.5 V at a current value of 0.2 mA in a temperature environment of 20 ° C., and the initial discharge dose was evaluated. The obtained results are shown in Table 1.

As is apparent from the results in Table 1, when the metal element Me serving as a trivalent cation is Fe, Li / Mn / Ni / Fe of the positive electrode active material f-1 of Example 1 = 1.1 / 0.5 / 0.3 / 0.1 It can be seen that the content ratio (molar ratio) of the metal element is the highest. Similarly, when the metal element Me serving as a trivalent cation is Al, the positive electrode of Example 2 having the same metal element content ratio (molar ratio) of Li / Mn / Ni / Al = 1.1 / 0.5 / 0.3 / 0.1 The active material a-1 has the highest capacity.
The positive electrode active materials of Comparative Examples 1 to 18 had problems such as the occurrence of a different phase of Ni oxide and high resistance, and the positive electrode active materials f-1 and a-1 of Examples 1 and 2 were used for the positive electrode. Compared with the non-aqueous secondary battery, the secondary battery using the positive electrode active material of these comparative examples as the positive electrode clearly had a low initial discharge capacity.

  In addition, the metal element content ratio of the positive electrode active material when the total content ratio (mol%) of the Mn, Ni, and Me metal elements of the positive electrode active material of the examples and comparative examples is set to 100% is illustrated. Then, it becomes like FIG.

<Examples 3-4, Comparative Examples 19-36>
(Preparation of positive electrode)
Any positive electrode active material synthesized in Examples 1-2 and Comparative Examples 1-18, acetylene black (AB) and vapor-grown carbon fiber (VGCF) as a conductivity imparting material, PVDF as a binder, Cathode active material: AB: VGCF: PVDF = 87: 5: 2: 6 (mass ratio) was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare each mixture coating solution. Each of the mixture coating liquids is applied onto an Al metal foil current collector, NMP is heated and evaporated, and then a mixture portion (collector) composed of the positive electrode active material, the conductivity-imparting material and the binder is passed through a roll press. The positive electrode of the secondary battery was manufactured at a density of 2.85 g / cm ³ excluding the electric body. The density of the mixture was determined by cutting the prepared positive electrode into a predetermined size, measuring its weight and dimensions, and subtracting the weight and thickness of the Al metal foil to obtain the volume and weight of the mixture. The density was determined from the volume and weight values of the agent.

(Preparation of negative electrode)
Amorphous carbon is used as the negative electrode active material. Amorphous carbon: AB: PVDF = 92: 3: 5 (mass ratio) is dispersed in NMP to prepare a coating solution. It was applied to an electric body, and NMP was evaporated by heating to obtain a negative electrode.

(Production of battery)
The above positive electrode and negative electrode were wound through a separator to produce an 18650 cylindrical battery. As the electrolytic solution, a mixed solution (volume ratio 50:50) of ethylene carbonate (EC) and diethyl carbonate (DEC) in which 1M LiPF ₆ was dissolved was used. After sealing the cylindrical battery, it was charged to 4.5 V at a charge rate of 0.2 C, and then discharged to 2.5 V at a discharge rate of 0.5 C to produce a battery.

(Evaluation of recovery capacity ratio by high temperature storage test)
A high temperature storage test was conducted using the 18650 cylindrical battery produced as described above. Specifically, the following series of operations were performed. Each cylindrical battery was charged to 4.5 V at a charge rate of 0.1 C at room temperature, and then discharged to 2.5 V at a discharge rate of 0.2 C. The discharge capacity at this time was _defined as a pre-storage capacity D _p .
Subsequently, the battery was charged to 4.5 V at a charging rate of 0.1 C, and the charged battery was stored in a thermostat at 50 ° C. for 1 week. After taking out from the thermostat, discharge to 2.5V at a discharge rate of 0.2C at room temperature, and again charge to 4.5V at a 0.1C charge rate and discharge to 2.5V at a 0.2C discharge rate. The discharge capacity at the time of the last discharge was taken as the post-storage capacity D _f , and the recovery capacity ratio D _r was obtained by the following formula (4). The obtained results are shown in Table 2.
D _r = (D _p / D _f ) × 100 (4)

  As is apparent from the results in Table 2, the cylindrical battery using the positive electrode active material f-1 and the positive electrode active material a-1 of Example 3 and Example 4 shows very excellent storage characteristics.

<Examples 5 to 25>
(Preparation of positive electrode, negative electrode and battery)
A positive electrode was produced in the same manner as in Example 3 or 4 except that the density of the mixture in the positive electrode was changed as shown in Table 3 by changing the linear pressure of the roll press, and the same as in Example 3 or 4 above. Thus, a negative electrode and a battery were produced.

(Evaluation of charge / discharge rate characteristics)
The rate characteristic at the time of charging / discharging of each cylindrical battery produced as mentioned above was evaluated. First, it was charged to 4.5 V at a charging rate of 0.1 C, and then discharged to 2.5 V at a discharging rate of 0.2 C, and the discharging capacity at that time was 0.2 C capacity. Subsequently, the battery was charged to 4.5 V at a charging rate of 0.1 C, and then discharged to 2.5 V at a discharging rate of 5 C, and the discharging capacity at that time was set to 5 C capacity. From these values, [5C capacity] / [0.2C capacity] (%) in each cylindrical battery was determined and shown in Table 3.

When the electrode mixture density is 2.41 g / cm ³ or less, or 3.11 g / cm ³ or more, the charge / discharge rate characteristics are drastically lowered, and the mixture density is preferably in the range of 2.55 to 3.05 g / cm ^3. I understand.

As described above, the metal element content ratio is [Mn]: [Ni]: [Fe] = 5: 3: 1 (molar ratio) and [Li] / [Mn + Ni + Me] = 1.22 (molar ratio). By using a positive electrode active material containing a lithium manganese composite oxide that satisfies the above condition, a high-capacity and inexpensive non-aqueous electrolyte secondary battery can be realized. Further, by setting the density of the positive electrode mixture at that time to 2.55 to 3.05 cm ³ , good rate characteristics can be obtained.

  In this example, [Mn, Ni, Me] composite oxide was used as a precursor, but a composite hydroxide was used as a precursor, or a liquid system method such as a sol-gel process or hydrothermal synthesis. It was confirmed that the positive electrode active material synthesized by the above has the same effect when the final composition is the same.

  The positive electrode active material of the present invention and the positive electrode for a secondary battery using the same are suitably used for the production of a non-aqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery according to the present invention can be preferably used in applications such as HEV and UPS.

2 is an X-ray diffraction pattern of a positive electrode active material synthesized in Example 1. FIG. It is a figure which shows the content rate of the metal element of the positive electrode active material synthesize | combined by the present Example and the comparative example. It is a figure which shows the cross-section of the nonaqueous electrolyte secondary battery of one Embodiment which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode mixture 2 Negative electrode mixture 3 Positive electrode collector 4 Negative electrode collector 5 Separator 6 Positive electrode outer can 7 Negative electrode outer can 8 Insulation packing

Claims (6)

The content ratio of the metal element (molar ratio) is represented by the following formula (1), and a non-aqueous electrolyte characterized in that it comprises a satisfying lithium manganese composite oxide represented by the following formula (2) Positive electrode active material for liquid secondary battery.
[Mn]: [Ni]: [Me] = 5: 3: 1 (molar ratio) (1)
[Li] / [Mn + Ni + Me] = 1.22 (molar ratio) (2)
(In the above formula, Me represents Fe or Al .) A lithium manganese based composite oxide in which the content ratio (molar ratio) of the metal element is represented by the following formula (1) and satisfies the condition represented by the following formula (2), the value of the following formula (1) and A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the value of the following formula (2) is in a range of ± 2.5% with respect to each value.
[Mn]: [Ni]: [Me] = 5: 3: 1 (molar ratio) (1)
[Li] / [Mn + Ni + Me] = 1.22 (molar ratio) (2)
(In the above formula, Me represents Fe or Al.) The lithium manganese-based composite oxide, the positive electrode active material for non-aqueous electrolyte secondary battery according to claim 2, wherein the lithium manganese-based composite oxide represented by the following following formula (3).
Li [Mn _0.5 Ni _0.3 Me _0.1 Li _0.1 ] O ₂ (3)
(In the above formula, Me represents Fe or Al .) In a non-aqueous electrolyte secondary battery comprising at least a negative electrode capable of inserting / extracting lithium and a positive electrode using a positive electrode active material disposed opposite to the negative electrode via a non-aqueous electrolyte, the positive electrode active A nonaqueous electrolyte secondary battery, wherein the substance is a positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3 . It is a positive electrode for secondary batteries using the positive electrode active material for non-aqueous-electrolyte secondary batteries in any one of Claims 1-3 , Comprising: The collector which comprises this positive electrode for secondary batteries is remove | excluded The positive electrode for a secondary battery, wherein the mixture has a density of 2.55 to 3.05 g / cm ³ . A non-aqueous electrolyte secondary battery using the positive electrode for a secondary battery according to claim 5 .

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