JPH05283075A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To improve the cycle characteristic by providing a positive electrode, in which the specified compound oxide is used as active material, and a negative electrode made of lithium metal or the like and the nonaqueous electrolyte. CONSTITUTION:The compound oxide usually expressed with a formula LixM1-yAyO2 is used as active material of a positive electrode 3. In the formula, M means transition metal, A means the metal having a diameter smaller than that of M and arranged with 6 cations, and x<=1.0, 0.1<=y<=0.4. A negative electrode 1 is made of lithium metal, lithium alloy or carbon material, which can store and discharge lithium. In this battery provided with the positive electrode 3, the negative electrode 1 and the nonaqueous electrolyte, oxygen ion is easy to be absorbed by the crystal structure to facilitate the insertion and separation of lithium ion, and the distortion and the breakdown of the crystal structure with the repeat of charge and discharge is restricted to improve the cycle characteristic.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a positive electrode using a composite oxide of lithium and a transition metal as an active material, and a negative electrode made of a lithium metal, a lithium alloy, or a carbon material capable of inserting and extracting lithium. Relating to a battery with a non-aqueous electrolyte,
In particular, it relates to improvement of the positive electrode.

[0002]

2. Description of the Related Art Lithium metal or a lithium alloy is used as a negative electrode, and manganese dioxide is used as a positive electrode.
A lithium battery using a non-aqueous electrolyte as an electrolyte is a battery that has a high operating voltage, has little self-discharge, and is excellent in storage stability, and particularly as a battery that can be reliably used for a long period of 5 to 10 years. It has been widely put to practical use as a memory backup power source for various small electronic devices. These lithium batteries are mainly used as primary batteries, and their life ends when they are used once.

On the other hand, in recent years, the demand for rechargeable lithium secondary batteries has increased, and research has become active. As a lithium secondary battery satisfying such requirements, lithium metal, lithium alloy, or an intercalation compound capable of absorbing and releasing lithium ions is used for the negative electrode, and lithium and transition metal such as LiCoO ₂ having a layered structure for the positive electrode. A non-aqueous electrolyte secondary battery has been proposed in which a non-aqueous electrolyte solution is used as an electrolyte solution using a composite oxide of

However, LiCoO ₂ which is a positive electrode active material
The crystal structure such as is gradually distorted as lithium is repeatedly inserted into and desorbed from the layered lattice by charge and discharge, and is eventually destroyed, resulting in loss of the ability as an electrode.

[0005]

The present invention has been made in view of the above problems, and by using a positive electrode active material in which distortion of the crystal structure due to charge and discharge is suppressed, excellent cycle characteristics are obtained. It is an object to provide a non-aqueous electrolyte secondary battery.

[0006]

As a positive electrode active material, a compound represented by the general formula: Li _X M _1-Y A _Y O ₂ (where M is a transition metal, A has an ionic radius smaller than that of the transition metal M, and Metals whose cations are 6-coordinated, X ≦ 1.0, 0.1 ≦ Y ≦ 0.4)
The composite oxide represented by, that is, one in which a part of the transition metal M is substituted with a metal having an ionic radius smaller than that of the transition metal M and whose cation is 6-coordinated is used.

[0007]

The crystal of LiCoO ₂ as an example of the complex oxide represented by the general formula LiMO ₂ (where M is a transition metal) has a cobalt ion 7 at the center, as shown in FIG.
It has a structure in which octahedra having oxygen ions 8 at the top of the octahedron are connected, and lithium ions 9 enter between the layers of the connected octahedron to form an intercalation compound. The lithium ions 9 that have entered between the layers are desorbed by charging and reinserted into the layers by discharging, and the cycle is repeated.

At this time, the wider the space between layers is, the easier the insertion and desorption of lithium ions can be. However, the space between layers is greatly affected by the oxygen ions forming the octahedron. Also,
Oxygen ions largely depend on the ionic radius of the transition metal cation in the center of the octahedron, and the smaller the radius of the transition metal cation, the greater the degree of freedom of the oxygen atom, which facilitates insertion and desorption of lithium ions. Become.

Therefore, the composite oxide LiMO ₂ (however, M
Is a transition metal), a part of the transition M is replaced with a metal having an ionic radius smaller than M and the cation of which is 6-coordinated, and as shown in FIG. The degree of freedom of oxygen ions in the area is increased, and the oxygen ions are easily absorbed into the octahedron, so that the interlayer is widened, insertion / desorption of lithium ions, movement in the layer progress smoothly, and repeated charging and discharging can be performed. It is possible to suppress distortion and breakage of the accompanying crystal structure.

In particular, in the composite oxide Li _X M _1-X A _Y O ₂ , it is promising to use M as Co, Ni, Fe and a mixed system thereof. Then, when M is Co,
As the replaceable metal A, Fe, Cr, Be, V, R
When e, Si, Ge, and M are Ni, the replaceable metal A is Co, Fe, Cr, Be, V, Re, Si,
When Ge and M are Mn, as the replaceable metal A,
Co, Ni, Fe, Cr, Be, V, Re, Si, G
When e and M are Fe, C is used as the replaceable metal A.
O, Cr, Be, V, Re, Si, Ge and the like can be mentioned respectively. In addition, the substitution amount of the metal M is preferably in the range of 10 to 40 mol%.

[0011]

【Example】

Example 1 Commercially available cobalt carbonate (CoCO ₃ ) powder, iron trioxide (Fe ₂ O ₃ ) powder, and lithium carbonate (Li ₂ C)
O ₃ ) powder to Co: Fe: Li = 0.9: 0.1: 1.0
And mixed in such a manner that it was heated to 900 ° C. for 10 hours in an air atmosphere. The obtained fired product was pulverized to 300 mesh or less, and this powder, graphite powder, and fluororesin powder were mixed at a weight ratio of 85: 10: 5 to obtain a positive electrode mixture. This was pressure-molded to have a pressure of 3 ton / cm ² , a diameter of 15 mm and a thickness of 0.8 mm, and vacuum dried at 250 ° C. for 2 hours to obtain a positive electrode pellet. As the negative electrode, a lithium foil having a thickness of 0.3 mm punched out to a diameter of 16 mm was used.

Next, a flat battery as shown in FIG. 1 was produced using the above positive electrode and negative electrode. Reference numeral 1 denotes a negative electrode, which is pressure-bonded to the inner bottom surface of the negative electrode can 2. Reference numeral 3 denotes a positive electrode, which is fixed to the inner bottom surface of the positive electrode can 4. 5 is a separator made of polypropylene, and 6 is a packing. The electrolyte used was 1. LiPF ₆ as a solute in propylene carbonate.
A solution of 0 mol / liter was used. The battery has a diameter of 20 mm and a height of 1.6 mm. This battery is designated as A.

Example 2 Cobalt carbonate (CoCO ₃ ) powder, iron trioxide (Fe ₂ O ₃ ) powder and lithium carbonate (Li ₂ CO ₃ ) powder were used as positive electrode active materials, and Co: Fe: Li =
A battery was produced in the same manner as in Example 1 except that the mixture was mixed so that the ratio was 0.7: 0.3: 1.0. This battery is designated as B.

[Example 3] Cobalt carbonate (CoCO ₃ ) powder, iron trioxide (Fe ₂ O ₃ ) powder and lithium carbonate (Li ₂ CO ₃ ) powder were used as positive electrode active materials, and Co: Fe: Li =
A battery was produced in the same manner as in Example 1 except that the mixture was mixed such that the ratio was 0.6: 0.4: 1.0. This battery is designated as C.

Example 4 Cobalt carbonate as a positive electrode active material
(COCO₃) Powder and vanadium pentoxide (V₂O _Five)powder
Powder and lithium carbonate (Li₂CO₃) Powder to Co: V: L
Other than mixing so that i = 0.7: 0.3: 1.0
A battery was manufactured in the same manner as in Example 1. This battery
Let be D.

Comparative Example 1 Cobalt carbonate (CoCO ₃ ) powder and magnesium hydroxide (Mg (O
H) ₂ ) powder and lithium carbonate (Li ₂ CO ₃ ) powder to C
A battery was produced in the same manner as in Example 1 except that the mixture was made such that o: Mg: Li = 0.9: 0.1: 1.0.
This battery is designated as E.

[Comparative Example 2] Carbon dioxide as a positive electrode active material
(COCO₃) Powder and lithium carbonate (Li₂CO ₃)powder
The powder is mixed so that Co: Li = 1.0: 1.0.
A battery was produced in the same manner as in Example 1 except for the above. This phone
Let the pond be F.

Charging current of 2 m using the above 6 types of batteries
A cycle test was conducted under the conditions of A, end-of-charge voltage 4.2V, discharge current 2mA, and end-of-discharge voltage 2.0V. The result is shown in FIG. From FIG. 4, batteries A, B, C, and D in which a part of Co in LiCoO ₂ is replaced with a metal having an ion radius smaller than that of Co have an ion radius larger than that of Co. It can be seen that the cycle characteristics are superior to the battery E substituted with metal or the battery F not substituted with metal. On the contrary, in the battery E substituted with Mg having an ionic radius larger than that of Co, the cycle characteristics are deteriorated as compared with the battery F in which nothing is substituted.

Further, it is effective that the substitution amount of metal is in the range of 10 to 30 mol%, and if it is increased more than this, the cycle characteristics are deteriorated as can be seen in comparison with the batteries A, B and C. Go

Example 5 Iron trioxide (Fe ₂ O ₃ ) powder, cobalt carbonate (CoCO ₃ ) powder and lithium carbonate (Li ₂ CO ₃ ) powder were used as the positive electrode active material, and Fe: Co: Li was used.
= 0.9: 0.1: 1.0 except for mixing
A battery was produced in the same manner as in Example 1. This battery is designated as G.

Example 6 Iron trioxide (Fe ₂ O ₃ ) powder, cobalt carbonate (CoCO ₃ ) powder and lithium carbonate (Li ₂ CO ₃ ) powder were used as the positive electrode active material, and Fe: Co: Li was used.
= 0.7: 0.3: 1.0 except for mixing
A battery was produced in the same manner as in Example 1. Let this battery be H.

[Example 7] Iron trioxide (Fe ₂ O ₃ ) powder, cobalt carbonate (CoCO ₃ ) powder and lithium carbonate (Li ₂ CO ₃ ) powder were used as the positive electrode active material, and Fe: Co: Li was used.
= 0.6: 0.4: 1.0 except for mixing
A battery was produced in the same manner as in Example 1. This battery is designated as I.

Example 8 Iron trioxide (Fe ₂ O ₃ ) powder, vanadium pentoxide (V ₂ O ₅ ) powder and lithium carbonate (Li ₂ CO ₃ ) powder were used as positive electrode active materials, and Fe: V: Li was used. =
A battery was produced in the same manner as in Example 1 except that the mixture was mixed so that the ratio was 0.9: 0.1: 1.0. This battery is J.

[Comparative Example 3] Iron trioxide (Fe ₂ O ₃ ) powder and magnesium hydroxide (Mg (O
H) ₂ ) powder and lithium carbonate (Li ₂ CO ₃ ) powder,
A battery was produced in the same manner as in Example 1 except that the mixing was performed such that e: Mg: Li = 0.9: 0.1: 1.0.
This battery is designated as K.

[Comparative Example 4] Iron trioxide (Fe ₂ O ₃ ) powder and lithium carbonate (Li ₂ CO ₃ ) powder were mixed as a positive electrode active material so that Fe: Li = 1.0: 1.0. A battery was produced in the same manner as in Example 1 except that the above was carried out. Let this battery be L.

Using the batteries G to L prepared in Examples 5 to 8 and Comparative Examples 9 and 10, the charging current was 2 mA and the final charging voltage was 4.
A cycle test was performed under the conditions of 2 V, discharge current 2 mA, and discharge end voltage 2.0 V. The result is shown in FIG. From FIG. 5, a battery G in which a part of Fe in LiFeO ₂ is replaced with a metal having an ionic radius smaller than that of Fe,
It can be seen that H, I, and J are superior in cycle characteristics to the battery K in which a metal having an ionic radius larger than that of Fe is substituted, or the battery L in which the ionic radius is not substituted, or the battery L in which no ionic radius is substituted.

[0027]

As described above, as the positive electrode active material, the general formula Li _X M _{1 -Y} A _Y O ₂ (where M is a transition metal, A has an ionic radius smaller than that of the transition metal M, and Metals whose cations are 6-coordinated, X ≦ 1.0, 0.1 ≦ Y ≦ 0.4)
By using the complex oxide represented by, oxygen ions in the crystal structure is easily absorbed in the octahedral direction,
Since the interlayer is widened, insertion and desorption of lithium ions can be facilitated, and movement between layers can be performed smoothly, so distortion and destruction of the crystal structure due to repeated charge and discharge can be suppressed, and excellent cycle characteristics have been improved. A non-aqueous electrolyte secondary battery can be provided, and its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a flat battery according to the present invention.

FIG. 2 is a conceptual diagram of diffusion of lithium ions in a Li _x M _1-Y A _Y crystal.

FIG. 3 is a conceptual diagram of diffusion of lithium ions in a Li _X MO ₂ crystal.

FIG. 4 is a cycle characteristic comparison diagram of the battery of the present invention and a comparative battery.

FIG. 5 is a cycle characteristic comparison diagram of the battery of the present invention and a comparative battery.

[Explanation of symbols]

 1 Negative electrode 2 Negative electrode can 3 Positive electrode 4 Positive electrode can 5 Separator 6 Insulating packing 7 Transition metal ion 8 Oxygen ion 9 Lithium ion 10 Metal ion with smaller ionic radius than transition metal

Claims (2)

[Claims] 1. The general formula Li _X M _1-Y A _Y O ₂ (where M is a transition metal, A is a metal having an ionic radius smaller than that of the transition metal M, and its cation is hexacoordinated, X ≦ 1.0,
0.1 ≦ Y ≦ 0.4) a positive electrode using a composite oxide as an active material, a lithium metal, a lithium alloy, or a negative electrode made of a carbon material capable of inserting and extracting lithium, and non-aqueous electrolysis And a non-aqueous electrolyte secondary battery. 2. The transition metal M is Co, Ni, Mn,
The non-aqueous electrolyte secondary battery according to claim 1, which is at least one selected from the group consisting of Fe and Fe.