JPH08315819A - Secondary battery - Google Patents

Abstract

PURPOSE: To provide a lithium secondary battery with high energy density and excellent rate characteristics by replacing part of nickel atoms in a positive electrode active material with B, Al, In, and Sn, and adding Co, Mn, and Fe. CONSTITUTION: A positive electrode active material of a lithium secondary battery is formed with a compound oxide having layer structure represented by Lia Nib M<1> c M<2> d M<3> c O2 . M<1> is at least one element selected from Co, Mn, and Fe. M<2> is at least one element selected from B, Al, In, and Sn. M<3> is at least one element selected from Mg and Zn. A positive electrode 1 using this positive electrode active material is pressed against a positive can 4 through a positive electrode current collector 6. A lithium foil of a negative electrode is pressed against a negative can 5 through a negative electrode current collector 7. The positive electrode can 4 is fit to the negative electrode can 5 through a separator 3 to assemble a coin type lithium battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to a positive electrode active material thereof.

[0002]

2. Description of the Related Art In recent years, an active material having an operating voltage of about 4 V for high energy density, a battery using a carbon material for a negative electrode for a long life, and the like have been attracting attention. Even when a carbon material is used for the negative electrode to prolong the life, it is difficult to obtain a high energy density battery unless the positive electrode has a high operating voltage. Therefore, LiCoO ₂ or LiNi
Such as O _2, such as a compound or LiMn ₂ O ₄ having a layered structure represented by LiMO _2, a compound having a spinel structure represented by LiM ₂ O ₄ have been proposed and already partially commercialized.

[0003]

However, LiC
As for oO ₂ , cobalt is a scarce resource, and the price is high, and the capacity is small and insufficient. Also, LiNiO ₂ using nickel, which is resource-stable, has a larger capacity than LiCoO ₂ , but has a large capacity deterioration due to the cycle, and it is difficult to perform stable synthesis on a mass production scale as compared with LiCoO _2. There was a problem in putting it to practical use.

In order to solve these problems, LiNi
Research and development for substituting a part of Ni in O ₂ to form a composite are also actively conducted. For example, JP-A-62-264560,
JP-A-63-114063, JP-A-63-21156
5, JP-A-63-299056, JP-A-1-120
765, JP-A-2-40861, and JP-A-5-325.
No. 966 proposes using a composite oxide represented by LiNi _x Co _{1 -x} O ₂ as a positive electrode.
The initial capacity is lower than that of O ₂ .

Further, JP-A-62-256371, JP-A-5-101827, JP-A-5-198301, JP-A-5-283076, JP-A-5-299092,
Japanese Unexamined Patent Publication No. 6-96768 discloses that in NiNiO ₂ , a part of Ni is Co, V, Cr, Fe, Cu, Mg, Ti, Mn.
It has been proposed to substitute various transition metals such as
Insufficient improvement in cycle characteristics.

On the other hand, in JP-A-4-253162, Li
It has been proposed to replace a part of Co of CoO ₂ with Pb, Bi, B, and in Japanese Examined Patent Publication No. 4-24831, the general formula A _x
The transition metal element M such as Ni of M _y N _z O ₂ contains Al, In,
Substitution with at least one element N in Sn has been proposed. In yet JP 5-54889, the formula _{Li x M y L z O 2} , the transition metal element M such as Ni,
Non-metal elements and metalloid elements of Group IIIB, IVB and VB of the Periodic Table, alkaline earth metal elements and Zn, Cu,
Substitution with one or more elements L selected from metal elements such as Ti has been proposed.

However, in LiCoO ₂ , it was easy to replace a part of Co with the element L, whereas it is difficult to synthesize an active material in which a part of Ni of LiNiO ₂ is replaced with the element L. It was found that L was not incorporated into the structure and remained as an impurity in the active material, which adversely affects the battery performance such as a decrease in charge / discharge efficiency and an increase in self-discharge. Although the reason cannot be determined, in the case of LiNiO ₂ , it is more difficult to form a layered structure than in LiCoO ₂ , and the element L hinders the growth in the C-axis direction at the crystal growth stage, the substitution of the element L is difficult to occur, and it remains as an impurity. Conceivable.

Further, a part of Ni of LiNiO ₂ is replaced with the element L.
Although the active material substituted with is improved in cycle characteristics,
The resistance of the active material itself was increased, and there was a problem in rate characteristics. Although the reason cannot be determined, it is considered that in the active material obtained by substituting a part of Ni of LiNiO ₂ with the element L, ion substitution is suppressed by the substituting element, the resistance of the active material itself is increased, and the rate characteristic is deteriorated.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a long-life lithium secondary battery having a large energy density and excellent rate characteristics.

[0010]

As a result of diligent study on the above problems, in NiNiO ₂ , a part of Ni was
When substituting with an element such as Al, In, Sn, Co, M
It has been found that the addition of n and Fe makes it very easy. The reason cannot be determined, but Co, Mn, Fe
Is likely to have the same LiMO ₂ type layered structure as Ni, and C
By adding o, Mn, and Fe, substitution is performed without inhibiting growth in the C-axis direction. As a result, both elements B, Al, In, Sn, etc. and Co, Mn, Fe can be easily replaced in LiNiO ₂ to form a layered structure. Therefore, Ni in LiNiO ₂ could be replaced uniformly without inhibiting growth in the C-axis direction by adding elements such as B, Al, In and Sn at the same time as Co, Mn and Fe. It is considered to be a thing.

Further, a part of Ni in LiNiO _{2 is}
The reason why the substitution with the elements such as Al, In, and Sn is selected is shown below.

It is known that B, Al and In have trivalence and Sn has tetravalence, but such elements do not contribute to the battery reaction.

In the portion substituted with the trivalent elements B, Al and In, lithium exists in a fixed form. This portion plays a pillar role of the Li layer, and suppresses repulsion between oxygen layers in a charged state and suppresses a change in crystal structure. Further examination revealed that these elements B, Al, and In were Co and M.
It was found that the presence of n and Fe uniformly existed in the crystal and exhibited its effect. As a result, the lithium remaining between the oxygen layers is evenly dispersed, enhancing its effect.

Further, since the portion substituted with the tetravalent element Sn is strongly bound to oxygen, it suppresses the repulsion between the oxygen layers in the charged state and suppresses the change of the crystal structure. As a result of further study, it was found that the Sn element was uniformly present in the crystal due to the presence of Co, Mn, and Fe, and exhibited its effect. As a result, the repulsion is suppressed between the oxygen layers as a whole, which enhances the effect.

Therefore, the active material of the present invention can be charged and discharged deeper than the conventional LiNiO ₂ by the above effects, so that the capacity is increased, and it is considered that the capacity decrease after the lapse of cycles is small.

Further, LiN which has been substituted as described above
The reason why the resistance of the active material itself is reduced and the rate characteristics are improved by substituting a part of Ni of iO ₂ with Mg and Zn is considered as follows. Co, M
By substituting elements such as B, Al, In, and Sn in the presence of n and Fe, a Li element that does not move in the crystal structure contributes to crystal stability during charging, but Li that is not involved in this charge / discharge is B , Al, In, Sn, etc., are strongly bound to each other, and the lithium inhibits the diffusion of lithium in the crystal, resulting in an increase in the resistance of the active material itself and a deterioration in the rate characteristic. By adding Mg or Zn to such a crystal, the bond between the substitutional element such as B, Al, In and Sn and lithium is relaxed. As a result, it is considered that the diffusion of lithium between the layers was promoted, the resistance of the active material itself was reduced, and the rate characteristics were improved.

[0017]

Function: In the presence of Co, Mn and Fe in LiNiO ₂ ,
The reason why the capacity is increased and the cycle characteristics are improved by substituting with elements such as B, Al, In and Sn, and the rate characteristics are improved by substituting with Mg and Zn is considered as follows.

Generally, when LiNiO ₂ is charged at a deep depth, the crystal structure changes, and further the crystal structure collapses. By removing Li in the layered structure,
Repulsion between the oxygen layers occurs and changes to a more stable crystal structure, or the crystal cannot collapse due to the inability to withstand the repulsion.

On the other hand, by substituting a part of Ni in LiNiO _{2 with} an element such as B, Al, In and Sn in the presence of Co, Mn and Fe, Li does not move in the layered structure. Since it is possible to suppress the repulsive force between oxygen and the formation of the portion, it is possible to prevent the change and collapse of the crystal structure. Therefore, as compared with the conventional LiNiO ₂ , it seems that even if deep charge / discharge is performed, excellent cycle stability is exhibited.

Here, lithium that is not associated with charge / discharge, which is associated with elements such as B, Al, In, and Sn, inhibits diffusion of lithium in the crystal, and as a result, the resistance of the active material itself increases, resulting in rate characteristics. Is believed to have deteriorated. By adding Mg or Zn to such a crystal, B, A
The bond between the substitutional element such as l, In and Sn and lithium is relaxed. As a result, diffusion of lithium between layers is promoted,
It is considered that the resistance of the active material itself was reduced and the rate characteristics were improved.

EXAMPLES Examples of the present invention will be described below.

[0021] In the preparation of (Example 1) lithium composite oxide having a layered structure, LiOH · H ₂ 0, Ni
₂ CO ₃ , CoCO ₃ , B ₂ O ₃ , MgO, L
The molar ratio of i: Ni: Co: B: Mg is 1.03: 0.8.
Weighed to be 8: 0.10: 0.01: 0.01,
The mixture was mixed and calcined in oxygen at 750 ° C. for 20 hours. After firing, the product was cooled in dry air and ground in a dry atmosphere to obtain a positive electrode active material.

From the X-ray diffraction pattern of the obtained positive electrode active material, it was found that crystals were obtained in a single phase.

Using this active material, a coin-type lithium secondary battery was prototyped as follows. The active material was mixed with acetylene black and polytetrafluoroethylene powder at a weight ratio of 85: 10: 5, toluene was added, and the mixture was sufficiently kneaded. This was formed into a 0.8 mm thick sheet by a roller press. Next, this was punched into a circle having a diameter of 16 mm and heat-treated at 200 ° C. for 15 hours under reduced pressure to obtain a positive electrode 1.
The positive electrode 1 was used by pressure bonding to a positive electrode can 4 having a positive electrode current collector 6. The negative electrode 2 is made of a lithium foil having a thickness of 0.3 mm and a diameter of 15 mm.
punched into a circular shape of mm, and the negative electrode can 5 via the negative electrode current collector 7.
It was used by pressure bonding to. An electrolytic solution in which 1 mol / l of LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 was used, and a polypropylene microporous film was used as the separator 3. The positive electrode, the negative electrode,
Diameter 20mm and thickness 1.6 using electrolyte and separator
mm coin type lithium battery was prepared. This battery is A
Set to 1.

Example 2 Instead of B ₂ O ₃ , Al (N
O ₃₎ using the _{3 · 9H 2 O, Li:} Ni: Co: Al:
The molar ratio of Mg is 1.03: 0.88: 0.10: 0.0.
A battery was produced in the same manner as in Example 1 except that the weight was adjusted to 1: 0.01. From the X-ray diffraction pattern of the obtained positive electrode active material, it was found that crystals were obtained in a single phase. This battery is designated as A2.

Example 3 Instead of B ₂ O ₃ , In (N
O _{3) 3} · xH with _{2 O, Li: Ni: Co} : In:
The molar ratio of Mg is 1.03: 0.88: 0.10: 0.0.
A battery was produced in the same manner as in Example 1 except that the weight was adjusted to 1: 0.01. From the X-ray diffraction pattern of the obtained positive electrode active material, it was found that crystals were obtained in a single phase. This battery is designated as A3.

Example 4 SnO was used instead of B ₂ O ₃ , and the molar ratio of Li: Ni: Co: Sn: Mg was 1.0.
A battery was made in the same manner as in Example 1 except that the weight was adjusted to 3: 0.88: 0.10: 0.01: 0.01. From the X-ray diffraction pattern of the obtained positive electrode active material, it was found that crystals were obtained in a single phase. This battery is designated as A4.

Example 4 ZnO was used instead of MgO, and the molar ratio of Li: Ni: Co: B: Zn was 1.03:
A battery was produced in the same manner as in Example 1 except that the weight was adjusted to 0.88: 0.10: 0.01: 0.01. From the X-ray diffraction pattern of the obtained positive electrode active material,
It was found that the crystals were obtained in a single phase. This battery is designated as A5.

(Comparative Example 1) LiOH.H ₂ O, NiCO
_A battery was produced in the same manner as in Example 1 except that ₃ was used and weighed so that the molar ratio of Li: Ni was 1.03: 1.00. From the X-ray diffraction pattern of the obtained positive electrode active material, it was found that crystals were obtained in a single phase. This battery is designated as B1.

[0029] (Comparative Example _{2) LiOH · H 2 0,} NiCO
_A battery was prepared in the same manner as in Example 1 above, except that ₃ and CoCO ₃ were used and weighed so that the molar ratio of Li: Ni: Co was 1.03: 0.90: 0.10. From the X-ray diffraction pattern of the obtained positive electrode active material, it was found that crystals were obtained in a single phase. This battery is designated as B2.

[0030] (Comparative Example _{3) LiOH · H 2 0,} NiCO
₃ , B ₂ O _3, and the molar ratio of Li: Ni: B is 1.0.
A battery was produced in the same manner as in Example 1 except that the weight was adjusted to 3: 0.90: 0.10. From the X-ray diffraction pattern of the obtained positive electrode active material, it was confirmed that the layered crystal growth of LiNiO ₂ was poor and the mixture was a compound that could not be sufficiently specified. Furthermore, when the obtained positive electrode active material was chemically analyzed, it was inferred that divalent Ni remained and that sufficient oxidation of Ni did not occur. This battery is designated as B3.

[0031] (Comparative Example _{4) LiOH · H 2 0,} NiCO
₃ , CoCO ₃ and B ₂ O ₃ are used, and Li: Ni: CoB is used.
A battery was prepared in the same manner as in Example 1 except that the weight ratio was 1.03: 0.89: 0.10: 0.01. From the X-ray diffraction pattern of the obtained positive electrode active material, it was found that crystals were obtained in a single phase. This battery is designated as B4.

Batteries A1, A2 thus produced
A charge / discharge cycle test was performed using A3, A4, A5, B1, B2, B3 and B4. Test condition is charging current 3m
A, end-of-charge voltage 4.2V, discharge current 3mA, 10m
A, discharge end voltage was 3.0V.

Table 1 shows the results of the charge / discharge test of the batteries thus manufactured.

[0034]

[Table 1]

As can be seen from Table 1, Battery A according to the invention
1, A2, A3, A4, A5 are comparative batteries B1, B2, B
The initial charge / discharge capacity was large as compared with 3, and the decrease in capacity after 10 cycles was small. Furthermore, the battery A according to the invention
1, A2, A3, A4, A5, compared to the comparative battery B4,
It was found that the rate characteristic was improved.

In this way, Ni of LiNiO ₂ is converted into C
Only when O, Mn, and Fe are replaced with B, Al, In, and Sn in the coexistence, and further replaced with Mg or Zn, the rate characteristics can be improved and the cycle stability can be realized.

The present invention is not limited to the starting materials of the active material, the manufacturing method, the positive electrode, the negative electrode, the electrolyte, the separator, the shape of the battery, etc. described in the above embodiments. Further, it is also applicable to those using a carbon material for the negative electrode, those using a solid electrolyte instead of the electrolyte or separator, and the like.

[0038]

As described above, the present invention can provide a long-life lithium secondary battery having a large discharge capacity and excellent reversibility.

[Brief description of drawings]

FIG. 1 is a sectional view of a coin-type lithium secondary battery according to a first embodiment of the present invention.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode can 5 Negative electrode can 6 Positive electrode current collector 7 Negative electrode current collector 8 Insulation packing

Claims (1)

[Claims] 1. The positive electrode active material is Li _a Ni _b M ¹ _c M ² _d.
It is composed of a composite oxide having a layered structure represented by M ³ _e O ₂ , M ¹ is at least ^one element selected from Co, Mn and Fe, and M ² is at least B, Al and I.
A secondary battery comprising at least one element selected from n and Sn, and M ³ at least one element selected from Mg and Zn.