JPH0878007A - Lithium secondary battery - Google Patents

Abstract

PURPOSE: To provide a lithium secondary battery with high energy density, allowable to deep charge/discharge, and with long life by constituting a positive electrode active material with a specified composite oxide. CONSTITUTION: A positive electrode active material is made of a composite oxide (example: Li1.03 Ni0.89 Mn0.10 Al0.01 O2 ) having layer structure represented by a formula of Lia Nib Mc <1> Md <2> O2 (M<1> is Mn, Fe, Ti, V, Cr, or Cu, and M<2> is at least one of Al, In, and Sn.). For example, the active material is mixed with acetylene black and polytetrafluoroethylene powder, the mixture is molded to form a positive electrode 1, the positive electrode 1 is pressed into a positive can 4 with a positive current collector 6, and a negative electrode (example: lithium foil) 2 is pressed in a negative can 5 through a negative current collector 7, then an electrolyte (example: LiPF6 -EC/DEC solution) and a separator 3 are combined to obtain a lithium secondary 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
oO ₂ has the disadvantages of low cobalt, high cost, and low capacity. Further, LiNiO ₂ using nickel, which is resource-stable, has a larger capacity than LiCoO ₂ , but has a large capacity deterioration with cycles, and it is difficult to perform stable synthesis on a mass production scale as compared with LiCoO _2. Therefore, 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-63-121565,
JP-A-63-299056, JP-A-1-120765,
In JP-A-2-40861 and JP-A-5-325966, L
Although the composite oxide represented by iNi _x Co _1-x O ₂ to be used for the positive electrode have been proposed, there is a problem that the initial capacity decreases compared with LiNiO _2.

Further, JP-A-62-256371, JP-A-5-101827, JP-A-5-198301, and JP-A-5-301827.
-283076, JP-A-5-299092, JP-A-6-
96768 and the like describe a part of Ni in LiNiO ₂ as Co,
Substitution with various transition metals such as V, Cr, Fe, Cu, Mg, Ti, and Mn has been proposed, but improvement in cycle characteristics is insufficient.

On the other hand, in JP-A-4-253162, LiC is used.
part Pb of Co oO _2, Bi, it is proposed to replace in B, also the general formula in Kokoku 4-24831 A _x M _y
The transition metal element M such as Ni of N _z O ₂ contains Al, In, Sn.
Substitution with at least one element N of the above is proposed. Further, in JP-A-5-54889, the general formula Li
_{In x} M _y L _z O ₂ , a transition metal element M such as Ni is added to non-metal elements and metalloid elements of Group IIIB, IVB and VB of the periodic table, alkaline earth metal elements and Zn, Cu, Ti and the like. Substitution with one or more elements L selected from metal elements 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.

[0008]

The present invention has been made in view of the above problems, and its object is to:
It is to provide a long-life lithium secondary battery having a high energy density.

As a result of extensive studies on the above problems, Li
In NiO ₂ , when a part of Ni is replaced with an element such as Al, In, Sn, Mn, Fe, Ti, V, Cr, C
It has been found that the addition of u makes it much easier. The reason cannot be determined, but Mn, Fe, Ti,
V, Cr, and Cu are likely to have the same LiMO ₂ type layered structure as Ni, and are added by adding Mn, Fe, Ti, V, Cr, and Cu without inhibiting growth in the C-axis direction. Further, in LiCoO ₂ , elements such as Al, In and Sn can be easily replaced with Mn, Fe, Ti, V, Cr and Cu to form a layered structure. Therefore, LiNi
Ni in O ₂ can be uniformly replaced without inhibiting growth in the C-axis direction by adding elements such as Al, In and Sn at the same time as Mn, Fe, Ti, V, Cr and Cu. It is thought that it was possible.

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

It is known that 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 Al and In, lithium exists in a fixed form. This part is L
It plays a pillar role for the i-layer, and suppresses repulsion between oxygen layers in a charged state and suppresses changes in crystal structure. As a result of further study, these elements Al and In show that Mn, Fe, Ti,
It was found that due to the presence of V, Cr and Cu, they were uniformly present in the crystal and exhibited their effects. 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 repulsion between oxygen layers in a charged state and suppresses a change in crystal structure. Further investigation revealed that the Sn element was Mn, Fe, Ti, V, and C.
It was found that the presence of r and Cu uniformly existed in the crystal 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.

[0015]

Function: LiNiO ₂ is mixed with Mn, Fe, Ti, V, Cr,
The reason why the capacity and the cycle characteristics are improved by substituting with an element such as Al, In, Sn in the presence of Cu 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, a part of Ni in LiNiO _{2 is} mixed with Al, in the presence of Mn, Fe, Ti, V, Cr and Cu.
By substituting with an element such as In or Sn, it is possible to form a non-moving portion of Li in the layered structure and suppress the repulsive force between oxygen, so that it is possible to prevent the change or 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.

[0018]

EXAMPLES Examples of the present invention will be described below.

[0019] In the preparation of (Example 1) lithium composite oxide having a layered structure, LiOH · H ₂ 0, Ni
_{2 CO 3, MnO 2, Al} (NO 3) using the _{3 · 9H 2 O, Li:} Ni: Mn: Al molar ratio of 1.03: 0.
Weigh and mix so as to be 89: 0.10: 0.01,
It was baked 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 manufactured 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 sheet having a thickness of 0.8 mm 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.

[0022] (Example _{2) Al (NO 3) 3} · 9H 2 O
In (NO ₃ ) ₃ · xH ₂ O is used in place of Li:
The molar ratio of Ni: Mn: In is 1.03: 0.89: 0.
A battery was produced in the same manner as in Example 1 except that the weight was adjusted to 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 A2.

Example 3 SnO was used instead of B ₂ O ₃ , and the molar ratio of Li: Ni: Mn: Sn was 1.03:
A battery was made in the same manner as in Example 1 except that the weight was adjusted to 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 A3.

(Example 4) Instead of MnO ₂ , Fe (N
O ₃₎ using the _{3 · 9H 2 O, Li:} Ni: Fe: Al molar ratio of 1.03: 0.89: 0.10: except that weighed so that 0.01 Example 1 A battery was prepared in the same manner as in. 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 5) Instead of MnO ₂ , Cr (N
O ₃₎ using the _{3 · 9H 2 O, Li:} Ni: Fe: Al molar ratio of 1.03: 0.89: 0.10: except that weighed so that 0.01 Example 1 A battery was prepared in the same manner as in. 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 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.

[0027] (Comparative Example _{2) LiOH · H 2 0,} NiCO
₃ , MnO ₂ is used, and the molar ratio of Li: Ni: Co is 1.
A battery was produced in the same manner as in Example 1 except that the weight was adjusted to 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.

[0028] (Comparative Example _{3) LiOH · H 2 0,} NiCO
_3, Al (NO ₃₎ using the _{3 · 9H 2 O, Li:} Ni:
A battery was made in the same manner as in Example 1 except that the weight ratio was adjusted to 1.03: 0.90: 0.10. From the X-ray diffraction pattern of the obtained positive electrode active material, it was confirmed that the layered crystal of LiNiO ₂ grew poorly and was a mixture of compounds that could not be sufficiently specified. Furthermore, when a chemical analysis of the obtained positive electrode active material was performed,
It is inferred that divalent Ni remained, and Ni was not sufficiently oxidized. This battery is designated as B3.

Batteries A1, A2 thus produced
A charge / discharge cycle test was performed using A3, B1, B2 and B3. The test conditions were a charge current of 3 mA, a charge end voltage of 4.2 V, a discharge current of 3 mA, and a discharge end voltage of 3.0 V.

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

[0031]

[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 and discharge capacity was larger than that of 3, and the decrease after 10 cycles was small.

In the examples, Li _a Ni _b M ¹ _c M
² _d O ₂ M ¹ is Mn, Fe, Cr, M ² is B, Pb,
Although Ge is mentioned, the same effect can be obtained by using Ti and M in M ¹ .
For V, Cu, M ² , P, Ga, Tl, Bi, Sb, Si
Was also confirmed.

In this way, Ni of LiNiO ₂ is added to M
Only by substituting under the coexistence of n, Fe, Ti, V, Cr, Cu and Al, In, Sn, the capacity increase and 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 and the shape of the battery 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.

[0036]

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.
Consisting of a composite oxide having a layered structure represented by O ₂ .
M ¹ is Mn, Fe, Ti, V, Cr, Cu, and M ²
Is a lithium secondary battery containing at least one element selected from Al, In and Sn.