JP2003197194A - Electrode material for nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode material for a lithium ion secondary battery with high capacity and high energy density having high voltage of 4.5 V or more vs. Li. <P>SOLUTION: This positive active material contains a spinel lithium manganese composite oxide represented by general formula (1), Li<SB>a</SB>(M<SB>x</SB>Mn<SB>2-x-y</SB>A<SB>y</SB>)O<SB>4</SB>(1) (In the formula, 0.4<x; 0<y; x+y<2; 0<a<1.2. M is selected from a group comprising Ni, Co, Fe, Cr, and Cu and contains at least one metal element containing at least Ni. A contains at least one metal element selected from Si and Ti. If A contains only Ti, a value of ratio y of A is 0.1<y.). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a positive electrode material for a lithium ion secondary battery and a secondary battery using the same,
In particular, the present invention relates to a secondary battery positive electrode material composed of a spinel-type lithium manganese composite oxide having a large discharge capacity and a secondary battery using the same.

[0002]

2. Description of the Related Art Lithium secondary batteries and lithium ion secondary batteries (hereinafter referred to as lithium ion secondary batteries)
Has a feature that it is small and has a large capacity, and is widely used as a power source for mobile phones, notebook computers, and the like. Currently, LiCoO ₂ is mainly used as a positive electrode active material for a lithium ion secondary battery, but the safety of the charged state is not always sufficient, and the cost of the Co raw material is high. The search for new positive electrode active materials is being actively pursued.

The use of LiNiO ₂ as a material having the same layered crystal structure as LiCoO ₂ has been studied, but LiNiO ₂ has a high capacity, but LiCoO ₂
It has a lower potential than that of, and has a problem in safety.

The use of LiMn ₂ O _{4 having} a spinel structure as another positive electrode active material has also been actively studied. However, LiMn ₂ O ₄ undergoes cycle-related deterioration and capacity decrease at high temperatures. This is due to the instability of trivalent Mn, and the average valence of Mn ions is trivalent and tetravalent.
It is considered that when the value varies between valences, a Jahn-Teller (yarn-Teller) strain is generated in the crystal, and the stability of the crystal structure is lowered, so that performance deterioration accompanying the cycle occurs.

From the above, the reliability of batteries has been improved so far.
In order to improve the property, trivalent Mn is placed with another element.
In other words, studies have been conducted to improve the structural stability. Tato
For example, Patent Document 1 discloses a secondary device including such a positive electrode active material.
Batteries are disclosed, and LiMn_TwoO_FourTrivalent included in
An active material in which Mn is replaced with another metal is disclosed. You
That is, the scope of the claims of Patent Document 1 includes the spinel structure.
Having a composition formula LiM _xMn_2-xO_Four(M is Al,
B, Cr, Co, Ni, Ti, Fe, Mg, Ba, Z
One or more selected from n, Ge and Nb, 0.01 ≦ x ≦
Two including a lithium manganese composite oxide represented by 1)
A secondary battery is described, and a detailed explanation of the invention of Patent Document 1 is given.
In the light column, LiMn_1.75Al_0.25O_FourThe positive electrode
An example of using it as an active material is specifically disclosed.

However, when the trivalent Mn is replaced by another element to reduce it as described above, the decrease in discharge capacity becomes a problem. LiMn ₂ O ₄ causes the following change in valence of Mn as it is charged and discharged.

Li ⁺ Mn ³⁺ Mn ⁴⁺ O ²⁻ ₄ → Li ⁺ + Mn ⁴⁺ ₂ O ²⁻ ₄ + e ^- As can be seen from this formula, LiMn ₂ O ₄ is trivalent Mn.
And tetravalent Mn are contained therein, and trivalent Mn among them changes to tetravalent to cause discharge. Therefore, if the trivalent Mn is replaced with another element, the discharge capacity is inevitably reduced. That is, even if an attempt is made to improve the structural stability of the positive electrode active material to improve the reliability of the battery, the discharge capacity is significantly reduced, and it is difficult to achieve both. In particular, it is very difficult to obtain a highly reliable positive electrode active material having a discharge capacity value of 130 mAh / g or more.

As described above, 3 contained in LiMn ₂ O ₄
An active material in which the valence Mn is replaced with another metal constitutes a lithium secondary battery having a so-called 4V-class electromotive force. As a technique in a direction different from this, for example, in Patent Document 2, LiMn is disclosed. Ni, Co, Fe, a part of Mn of ₂ O ₄
Studies have been made to substitute Cu, Cr or the like to increase the charge / discharge potential and increase the energy density.
These form a lithium secondary battery having a so-called 5V class electromotive force. Hereinafter, LiNi _0.5 Mn _{1 . 5} O ₄
Will be described as an example.

LiNi _0.5 Mn _1.5 O ₄ causes the following valence change of Ni with charge and discharge. Li ⁺ Ni ²⁺ _0.5 Mn ⁴⁺ _1.5 O ^2- ₄ → Li ⁺ + Ni ⁴⁺ _0.5 Mn ⁴⁺ _1.5 O ^2- ₄ +
e ^- As can be seen from this equation, LiNi _0.5 Mn _1.5 O
_In No. 4, electric discharge occurs when divalent Ni changes to tetravalent.
There is no change in the valence of Mn. Thus, by changing the metal involved in charge / discharge from Mn to Ni, Co, etc.,
It is possible to obtain a high electromotive force of 4.5 V or higher.

Further, Patent Document 3, crystalline _{LiMn 2-y-z} of the spinel structure charging and discharging at 4.5V or higher potential relative to Li metal Ni _y M z _{O 4} (where, M: Fe,
Co, Ti, V, Mg, Zn, Ga, Nb, Mo, Cu
At least one selected from the group consisting of 0.25 ≦ y
≦ 0.6, 0 ≦ z ≦ 0.1) are disclosed. In Patent Document 4, Mn of LiMn ₂ O ₄ is substituted with another transition metal, and further substituted with another element, a general formula Li _a Mn.
_2-y-i-j- k M y M1 i M2 j M3 k O 4 ( where, M1: 2-valent cation, M2: 3-valent cations, M3:
A 5V class positive electrode active material represented by a tetravalent cation, M: at least one transition metal element other than Mn, i ≧ 0, j ≧ 0, k ≧ 0, i + j> 0) is disclosed.

However, using such an active material
Is currently used LiCoO _TwoThe energy density
It is difficult under the present circumstances to significantly exceed. Also, above
The 5V class active material certainly produces an electromotive force of 4.5V or more.
However, there is a problem that the discharge capacity is reduced.

[0012]

[Patent Document 1] Japanese Patent Laid-Open No. 2001-176557

[Patent Document 2] Japanese Patent Laid-Open No. 9-147867

[Patent Document 3] Japanese Patent Laid-Open No. 2000-235857

[Patent Document 4] Japanese Patent Laid-Open No. 2002-063900

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of these circumstances, and an object thereof is to provide a positive electrode material having a high capacity and a high energy density which has never been obtained.

[0014]

According to the present invention for solving the above-mentioned problems, the following general formula (I) Li _a (M _x Mn _2-x-y A _y ) O ₄ (I) (wherein 0 <X, 0.4 <y, x + y <2, 0 <a <
1.2. M is Ni, Co, Fe, Cr and C
It contains one or more metal elements selected from the group consisting of u and containing at least Ni. A contains at least one metal element selected from Si and Ti. However, when A contains only Ti, the value of the ratio y of A is 0.1 <y. The present invention provides a positive electrode active material for a secondary battery, which comprises a spinel type lithium manganese composite oxide represented by the formula (1).

Further, according to the present invention, there is provided a positive electrode for a secondary battery, characterized in that the positive electrode active material for a secondary battery is bound by a binder.

Further, according to the present invention, there is provided a secondary battery comprising the above-mentioned positive electrode for secondary battery and a negative electrode arranged to face the positive electrode for secondary battery via a separator. .

The present invention, as shown in formula (I), provides 3
Characterized by the point that it contains a transition metal M that can have both a valence number equal to or lower than the valence number and the valence number that is higher than that valence number, and that it contains Si or Ti that is lighter than Mn (element A). It is one.

In the present invention, the capacity of the battery is increased and the energy density is increased by substituting the spinel positive electrode material for elements. By substituting a part of Mn with at least one of Ni, Co, Fe, Cr, and Cu with respect to LiMn ₂ O ₄ , the high-voltage charge / discharge region resulting from the change in the valence of the substituting element, It will appear according to the substitution amount. To obtain a sufficiently high voltage charging / discharging region, L
In the case of iM _x Mn _2-x O ₄ , x> 0.4 is required. LiNi, one of the 5V class spinel
_In the case of _0.5 Mn _1.5 O ₄ , Mn is in a tetravalent state, and the valence change of the transition metal in the process of release and absorption of Li accompanying charge and discharge is not Mn but the valence change of Ni (2 The valence of Mn is kept at 4 depending on the change from valence to tetravalence. In the 5V-class spinel, Mn ³⁺ is ideally absent, and even if Mn is replaced with another element, the decrease in capacity due to cycling and the deterioration in reliability such as the deterioration of the crystal structure at high temperatures are unlikely to occur. Based on these points, the present invention
By replacing Mn, which does not directly contribute to charge and discharge, with a lighter weight metal, the discharge amount per weight is increased and the capacity is increased.

When the Mn element site of LiNi _0.5 Mn _1.5 O ₄ is replaced with an element having a small divalent or trivalent valence, the divalent Ni becomes trivalent and the remaining trivalent Mn is 4 The valence balance is maintained by becoming the valence. As a result, the amount of divalent Ni and the amount of trivalent Mn that contribute to charge and discharge are reduced, which causes a problem that the capacity is reduced. From this point of view, it is desirable that the substitution element is tetravalent.

The technique of substituting Mn of LiMn ₂ O ₄ with another element is also adopted in the above-mentioned 4V class active material, but these are intended to enhance the stability of the structure of the positive electrode active material. On the other hand, the present invention is different in that the purpose is to increase the capacity. As for the specific structure, in the 4V class, trivalent Mn involved in charge and discharge is replaced, whereas
In the present invention, the positive electrode active material contains a transition metal M capable of having both a valence of 3 or less and a valence higher than the valence, and the main metal involved in charging and discharging is M.
They are metals other than n, and are different in this respect. In the present invention, most of Mn is tetravalent due to the presence of the element M, and trivalent Mn involved in charge and discharge is scarcely contained.

As described above, in the present invention, the element M is introduced so that Mn basically does not participate in charge and discharge, and then Mn is replaced with a lighter weight metal to discharge per weight. We are aiming to increase the capacity and capacity.
A tetravalent and stable element that is lighter than Mn is S
There is i or Ti. That is, by replacing Mn with Si and Ti, high capacity can be realized while maintaining high reliability.

The effect of increasing the capacity by replacing Si and Ti is as follows.
The larger the amount of element substitution, the larger. Li _a (M _x
Mn _2−x−y A _y ) O ₄ has a particularly remarkable effect when y> 0.1, a capacity of 130 mAh / g or more is obtained, and reliability is high. In 5V class spinel, Si,
Since the capacity can be increased by substituting Ti and charging / discharging can be performed at a high voltage of 4.5 V or more with respect to Li metal, very excellent characteristics can be obtained in terms of energy density. Further, in the case of Ti substitution, it is newly found that the discharge potential can be increased, and these two effects can increase the energy density.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a compound represented by the general formula (I)
Among them, the element M contains Ni as an essential component, but Co, F
It may further include at least one selected from the group consisting of e, Cr and Cu. These are all 3
It is a transition metal that can have both a valence number equal to or lower than the valence number and a valence number higher than the valence number. A part of Mn of _{LiMn 2 O 4, Ni, Co} , Fe, Cr or _LiM was replaced by _{Cu x Mn 2-x O 4} (M is Ni, Co, Fe, C
At least one of r and Cu) is known as a 5V class manganese spinel type positive electrode active material. The reason why Ni is selected as an essential component as in the present invention is that the material price of Ni is low and the discharge capacity is large as an active material of the battery. Conventionally, 5V class manganese spinel containing Co, Fe, Cr or Cu has an advantage that the charging / discharging voltage of the battery is higher than the Ni containing 5V class manganese spinel, but has a problem that the discharge capacity value is small. was there. By including Ni as an essential element as described in the present invention, it is possible to improve the conventional low capacity characteristic of the battery using the 5V class manganese spinel containing Co, Fe, Cr or Cu. Furthermore, N
An electromotive force higher than that of the 5V class manganese spinel containing i alone can be obtained.

The element M may contain other elements as a trace component. Alternatively, the element M may be Ni alone.

The composition ratio x of the element M is 0.4 <x <0.6.
Can be Particularly, when M is Ni alone, it is preferably within the above range. With such a range, high electromotive force and high capacity can be realized.

The positive electrode active material according to the present invention can be configured so that the average discharge voltage with respect to the lithium reference potential is 4.5 V or more. By doing so, a battery with a high operating voltage can be realized. With respect to the lithium reference potential,
For example, the potential of Ni is 4.7 V, Co is 5.1 V, and Cr is
Is 5.0 V, and by using these metals as components that contribute to charge and discharge, a positive electrode active material having an average discharge voltage of 4.5 V or more can be obtained.

In the general formula (I) of the present invention, A is S
The configuration may include i. In addition, A may include Ti.

The spinel type lithium manganese composite oxide in the present invention is specifically as follows (Ia) to (Ic).
The embodiment shown in FIG.

[0029] _{Li a (Ni x Mn 2-} x-y Si y) O 4 (Ia) ( wherein, 0.4 <x <0.6,0 <y , x + y <2,0
<A <1.2)

[0030] During _{Li a (Ni x Mn 2-} x-y Ti y) O 4 (Ib) ( wherein, 0.4 <x <0.6,0.1 <y , x + y <
2, 0 <a <1.2)

[0031] _{Li a (Ni x Mn 2-} x-y-z Si y Ti z) O 4 (Ic) ( wherein, 0.4 <x <0.6,0 <y , 0 <z, x + y
+ Z <2, 0 <a <1.2)

In the present invention, in the formula (I) or the formulas (Ia) to (Ic), a part of oxygen may be replaced with halogen such as F or Cl.

Next, a method for producing a positive electrode active material according to the present invention
Will be described. As a raw material for producing the positive electrode active material, Li
The raw material is Li_TwoCO_Three, LiOH, Li_TwoO, Li_Two
SO _FourCan be used, among which L
i_TwoCO_Three, LiOH, etc. are suitable. As Mn raw material
For electrolytic manganese dioxide (EMD) / Mn_TwoO_Three・ M
n_ThreeO_Four・ Various Mn oxides such as CMD, MnCO_Three,
MnSO_FourEtc. can be used. As a Ni raw material
Is NiO, Ni (OH)_Two, NiSO_Four, Ni (NO
_Three)_TwoEtc. can be used. TiO as a Ti raw material
_TwoEtc. are used, and SiO is used as the Si raw material._Two, SiO
Are typically used. Mn, Ni, Ti, Si
As a raw material, use a composite oxide containing these metal elements
You can also

These raw materials are weighed and mixed so that a desired metal composition ratio is obtained. The mixing is performed by crushing and mixing with a ball mill, a jet mill or the like. Mix powder from 600 ℃ to 9
The positive electrode active material is obtained by firing in air or oxygen at a temperature of 50 ° C. The firing temperature is preferably high in order to diffuse the respective elements, but if the firing temperature is too high, oxygen deficiency may occur, which may adversely affect the battery characteristics. From this, the firing temperature is 600 ° C
It is desirable that the temperature is from about 850 ° C.

The specific surface area of the obtained lithium metal composite oxide is, for example, 3 m ² / g or less, preferably 1 m ²
/ G or less. This is because the larger the specific surface area, the more binder is required, which is disadvantageous in terms of the capacity density of the positive electrode.

In producing the positive electrode for a secondary battery, the obtained positive electrode active material is mixed with a conductivity-imparting agent and formed on a current collector with a binder. As an example of the conductivity-imparting agent, a carbon material, a metal substance such as Al, a powder of a conductive oxide, or the like can be used. Polybucca vinylidene or the like is used as the binder. A metal thin film mainly composed of Al or the like is used as the current collector.

The amount of the conductivity imparting agent added is, for example, 1 to 10.
The amount of the binder to be added can be 1 to 1
It can be about 0% by weight. The larger the weight ratio of the active material, the larger the capacity around the weight. If the ratio of the conductivity-imparting agent to the binder is too small, the conductivity cannot be maintained and the problem of electrode peeling occurs.

The secondary battery according to the present invention has a structure as shown in FIG. 1, for example. Positive electrode active material layer 1 on positive electrode current collector 3
Are formed to form the positive electrode. In addition, the negative electrode current collector 4
The negative electrode active material layer 2 is formed on the upper surface to form a negative electrode.
The positive electrode and the negative electrode are arranged to face each other with the porous separator 5 immersed in the electrolytic solution in between. The positive electrode outer can 6 that houses the positive electrode and the negative electrode outer can 7 that houses the negative electrode are joined together via an insulating packing portion 8.

By applying a voltage 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, and a charged state is established. Further, 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, resulting in discharge, contrary to charging.

Electrolyte solution used in the secondary battery according to the present invention
As, propylene carbonate (PC), ethylene
Carbonate (EC), butylene carbonate (B
C), vinyl carbonate (VC), etc.
Salts, dimethyl carbonate (DMC), diethyl carbonate
Carbonate (DEC), ethyl methyl carbonate (E
MC), dipropyl carbonate (DPC), etc.
Carbonates, methyl formate, methyl acetate, propionic acid
Aliphatic carboxylic acid esters such as ethyl, γ-butyryl
Γ-Lactones such as kutone, 1,2-ethoxyethane
(DEE), ethoxymethoxyethane (EME) chains
Ethers, tetrahydrofuran, 2-methyltetra
Cyclic ethers such as hydrofuran, dimethyl sulfoxy
De, 1,3-dioxolane, formamide, acetami
De, dimethylformamide, dioxolane, acetonite
Ryl, propyl nitrile, nitromethane, ethyl monog
Lime, phosphate triester, trimethoxymethane, di
Oxolane derivative, sulfolane, methylsulfolane,
1,3-dimethyl-2-imidazolidinone, 3-methyl
-2-Oxazolidinone, propylene carbonate derivative
Body, tetrahydrofuran derivative, ethyl ether, 1,
3-propane sultone, anisole, N-methylpyrroli
Aprotic such as don and fluorinated carboxylic acid ester
Use one or a mixture of two or more organic solvents.
Dissolve the lithium salt that is soluble in the organic solvent. Richiu
Examples of the murine salt include LiPF₆, LiAsF₆, Li
AlCl_Four, LiClO_Four, LiBF_Four, LiSb
F₆, LiCF_ThreeSO_Three, LiC_FourF₉CO _Three, LiC
(CF_ThreeSO_Two)_Two, LiN (CF_ThreeSO_Two)_Two, Li
N (C_TwoF₅SO_Two)_Two, LiB₁₀Cl₁₀, Lower fat
Aliphatic carboxylic acid lithium carboxylate, chloroborane lithiate
Um, lithium tetraphenylborate, LiBr, LiI,
Examples include LiSCN, LiCl, and imides. Well
A polymer electrolyte may be used instead of the electrolytic solution.

As the electrolyte, LiBF ₄ , LiP
_{F 6, LiClO 4, LiAsF 6} , LiSbF 6, L
iCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) N, LiC ₄ F
₉ SO ₃ , Li (CF ₃ SO ₂ ) ₃ C, Li (C ₂ F ₅
SO _{2) 2} N and the like can be used alone or in combination. The electrolyte concentration is, for example, 0.5 mol / l to 1.
It can be 5 mol / l. If the concentration is too high, the density and viscosity may increase, and if the concentration is too low, the electric conductivity may decrease.

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

The negative electrode active material is formed on the current collector by the conductivity-imparting agent and the binder. As an example of the conductivity imparting agent, a powder of a conductive oxide can be used in addition to the carbon material. Polybucca vinylidene or the like is used as the binder. A metal thin film mainly composed of Al, Cu or the like is used as the current collector.

The prepared positive electrode and negative electrode are opposed to each other by a separator without electrical contact. As the separator, a microporous film made of polyethylene, polypropylene or the like can be used.

The positive electrode and the negative electrode opposed to each other with the separator interposed therebetween are formed in a cylindrical shape or a laminated structure. These are housed in a battery case and immersed in an electrolytic solution so that both the positive electrode active material and the negative electrode active material come into contact with the electrolytic solution. Electrode terminals that maintain electrical contact with the positive electrode and the negative electrode are connected to each other, the electrode terminals are connected to the outside of the electrode case, and the battery case is sealed to complete the secondary battery.

The present invention has no limitation on the shape of the battery, and the positive electrode and the negative electrode facing each other with the separator interposed therebetween can be formed into a wound type, a laminated type, or the like.
Laminate packs, square cells, and cylindrical cells can be used.

[0047]

[Example] Example 1 The following samples were prepared as positive electrode active materials and evaluated.
It was LiNi_0.5Mn_1.5O_Four(Sample 1) LiNi_0.5Mn_1.45Ti_0.05O_Four(sample
2) LiNi_0.5Mn_1.4Ti_0.1O_Four(Sample 3) LiNi_0.5Mn_1.35Ti_0.15O_Four(sample
4) LiNi_0.5Mn_1.3Ti_0.2O_Four(Sample 5) LiNi_0.5Mn_1.2Ti_0.3O_Four(Sample 6) LiNi_0.5Mn_1.3Si_0.2O_Four(Sample 7) LiNi_0.5Mn_1.1Si_0.4O_Four(Sample 8) LiNi_0.5Mn_1.1Ti_0.3Si_0.1O
_Four(Sample 9) LiNi_0.5Mn_1.35Ti_0.05Si_0.1O
_Four(Sample 10) LiNi_0.5Mn_1.5O_Four(Sample 11) LiNi_0.4Co_0.2Mn_1.4O_Four(Sample 12) LiNi_0.4Co_0.2Ti_0.15Mn_1.25O
_Four(Sample 13) LiNi_0.3Co_0.4Mn_1.3O_Four(Sample 14) LiNi_0.3Co_0.4Ti_0.15Mn_1.15O
_Four(Sample 15) LiNi_0.4Fe_0.2Mn_1.4O_Four(Sample 16) LiNi_0.4Fe_0.2Ti_0.15Mn_1.25O
_Four(Sample 17) LiNi_0.4Cr_0.2Mn_1.4O_Four(Sample 18) LiNi_0.4Cr_0.2Si_0.05Mn_1.35O
_Four(Sample 19) LiNi_0.45Cu_0.05Mn_1.5O_Four(Sample 2
0) LiNi_0.45Cr_0.05Si_0.05Mn
_1.45O_Four(Sample 21)

[0048] (Production of Positive Electrode Active Material) Sample 1 to Sample 10,
For the metal raw materials other than Li of Samples 12 to 21, a complex acid was used.
Compound was used. Only sample 11 is MnO_Two, For NiO
To a metal composition ratio of_TwoCO
_ThreeWas pulverized and mixed as a Li raw material. Powder after mixing raw materials
Was baked at 750 ° C. for 8 hours. Sample 1 to Sample 10, Sample
Crystal structures 12 to 21 are almost single-phase spinel structures
Was confirmed. In sample 11, is it NiO
Heterogeneous phase was slightly detected.

The prepared positive electrode active material was mixed with carbon as a conductivity-imparting agent and dispersed in N-methylpyrrolidone in which poly (Fuccavinylidene) (PVDF) was dissolved to obtain a slurry. The weight ratio of the positive electrode active material, the conductivity-imparting agent, and the binder was 88/6/6. The slurry was applied on the Al current collector. Then, it was dried in vacuum for 12 hours to obtain an electrode material. The electrode material was cut into a circle having a diameter of 12 mm. Then, pressure molding was performed at 3 t / cm ² . A Li metal disk was used as the negative electrode.

A PP film is used for the separator,
The positive electrode and the negative electrode were placed opposite to each other, placed in a coin cell, filled with an electrolytic solution, and sealed. The electrolytic solution is solvent EC (ethylene carbonate) / DEC (diethyl carbonate) =
Electrolyte LiPF ₆ was added in an amount of 1 mol / 3/7 (vol-%).
1 The dissolved product was used.

Evaluation of battery characteristics of samples 1 to 11
Charges to 4.9V at a charge rate of 0.1C,
It was discharged to 3V at a rate of 0.1C. Sample 12
From sample 21 to sample 21 at a charging rate of 0.1C up to 5.1V.
And then discharge to 3V at a rate of 0.1C.
It was The measurement results of capacity and average operating voltage are shown in Table 1 below.
Show. It is confirmed that the capacity increased with both Ti substitution and Si substitution.
It has been certified. In Figure 2, LiNi_0.5Mn_1.3Ti_0.2
O_Four(Sample 5), LiNi_0.5Mn_1.5O _Four(sample
1), LiNi_0.5Mn_1.5O_FourRelease of (Sample 11)
An electric curve is shown. In the Ti substitution, the capacity increases
The slope where the potential of the discharge plateau near 4.7V increases
The direction was seen. This is due to the presence of Ti
This is probably because the discharge potential increased due to a change in state.
It Ti substitution has two effects: high capacity and high voltage.
Found that higher energy density can be obtained
It was In Samples 1 and 11, Mn and Ni were used as raw materials for Mn.
Sample 1 using a composite oxide of Ni and Ni is more than Sample 11
Also had a large capacity, especially the 5V discharge region increased. this is
Sample 1 has more Mn, Ni, and Ni in the spinel than Sample 11.
Li or the like diffuses uniformly, and a highly crystalline active material is obtained.
It is thought to be a tame.

[0052]

[Table 1]

Example 2 Using the positive electrode obtained in Example 1, cycle characteristics were evaluated. The positive electrode is an active material, LiNi _0.5 Mn _1.5 O
₄ (Sample 1), LiNi _0.5 Mn _1.4 Ti _0.1 O
₄ (Sample 3), LiNi _0.5 Mn _1.35 Ti _0.1
5 O ₄ (Sample 4), LiNi _0.5 Mn _1.3 Ti
_0.2 O ₄ (Sample 5), LiNi _0.5 Mn _1.3 Si
_A positive electrode material was produced in the same manner as in Example 1 using _0.2 O ₄ (Sample 7). For the negative electrode, graphite was used as an active material, carbon as a conductivity-imparting agent was mixed, and N-
Methylpyrrolidone to Polyfukka vinylidene (PVDF)
Was dispersed in a melted solution to form a slurry. The weight ratio of the negative electrode active material, the conductivity-imparting agent, and the binder was 90/1/9. The slurry was applied on the Cu current collector. Then, it was dried in vacuum for 12 hours to obtain an electrode material. The electrode material was cut into a circle having a diameter of 13 mm. After that, 1.5t / c
It was pressure molded at m ² .

A PP (polypropylene) film was used as a separator, and the positive electrode and the negative electrode were placed opposite to each other, placed in a coin cell, filled with an electrolytic solution, and sealed to prepare a battery. The electrolytic solution is a solvent EC (ethylene carbonate) /
DEC (diethyl carbonate) = 3/7 (vol-
%) In which the electrolyte LiPF ₆ was dissolved at 1 mol / l was used.

The battery characteristics were evaluated in a constant temperature bath at a temperature of 45 ° C.
It was charged up to 4.75 V at a charge rate of 1 C, and then constant voltage charging was performed at 4.75 V. The total charging time was 150 minutes. Next, discharge was performed up to 3 V at a rate of 1C. By repeating this, the capacity after 300 cycles was evaluated. The results are shown in Table 2.

It was confirmed that the capacity retention rate after cycling was increased by using the Ti-substituted and Si-substituted positive electrode active materials.

[0057]

[Table 2]

[0058]

As described above, according to the present invention, a positive electrode material having an unprecedentedly high capacity and high energy density is provided. Specifically, a positive electrode material for a lithium-ion secondary battery, which has a high capacity and a high energy density of 4.5 V or higher with respect to Li, is provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a secondary battery according to the present invention.

FIG. 2 is a discharge curve of a positive electrode using the positive electrode active material of the present invention.

[Explanation of symbols]

1 Positive electrode active material layer 2 Negative electrode active material layer 3 Positive electrode current collector 4 Negative electrode current collector 5 separator 6 Positive electrode can 7 Negative electrode exterior can 8 Insulation packing part

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4G048 AA04 AB06 AC06 AD06 AE05                 5H029 AJ03 AK03 AL02 AL06 AL07                       AL11 AL12 AL18 AM02 AM03                       AM04 AM05 AM07 BJ03 CJ02                       CJ08 DJ17 HJ02 HJ18                 5H050 AA08 BA17 CA09 CB02 CB07                       CB08 CB11 CB12 CB29 FA19                       GA02 GA10 HA02 HA18

Claims (10)

[Claims] 1. The following general formula (I) Li _a (M _x Mn _2−x−y A _y ) O ₄ (I) (wherein 0.4 <x, 0 <y, x + y <2, 0 < a <
1.2. M is Ni, Co, Fe, Cr and C
It contains one or more metal elements selected from the group consisting of u and containing at least Ni. A contains at least one metal element selected from Si and Ti. However, when A contains only Ti, the value of the ratio y of A is 0.1 <y. ) A positive electrode active material for a secondary battery, comprising a spinel type lithium manganese composite oxide represented by 2. The positive electrode active material for a secondary battery according to claim 1, wherein M in the general formula (I) is Ni. 3. The positive electrode active material for a secondary battery according to claim 1, wherein A is Si in the general formula (I). 4. The positive electrode active material for a secondary battery according to claim 1, wherein A is Ti in the general formula (I). 5. The positive electrode active material for a secondary battery according to claim 1, wherein A is S in the general formula (I).
A positive electrode active material for a secondary battery, which contains i and Ti. 6. The positive electrode active material for a secondary battery according to claim 1, wherein Li ₂ CO ₃ , LiOH and Li _{2 are used.}
A positive electrode active material for a secondary battery, which is obtained by firing a mixture of one Li raw material selected from O and Li ₂ SO ₄ and a raw material of a composite oxide of a metal other than Li. 7. The positive electrode active material for a secondary battery according to claim 1, wherein the value of the ratio x of M in the general formula (I) is 0.4 <x <0.6. A positive electrode active material for a secondary battery, which is characterized by being present. 8. The positive electrode active material for a secondary battery according to claim 1, wherein an average discharge voltage with respect to a lithium reference potential is 4.5 V or more. . 9. A positive electrode for a secondary battery, comprising the positive electrode active material for a secondary battery according to claim 1 bound by a binder. 10. A positive electrode for a secondary battery according to claim 9,
A secondary battery comprising a positive electrode for a secondary battery and a negative electrode arranged to face the secondary battery via a separator.