JPH0737576A - Nonaqueous electrolyte secondary battery and manufacture of its positive pole active material - Google Patents

Abstract

PURPOSE:To provide a positive pole active material for a nonaqueous electrolyte secondary battery excellent in charge/discharge efficiency with high capacity by smoothly promoting intercalate/deintercalate reaction of lithium. CONSTITUTION:In a spherical and almost spherical or elliptical secondary particle 2, a plate-shaped monocrystal grain 1, having a stratified structure of regularly laminating a thin piece, is collected, and in almost or all the plate-shaped crystal grains for constituting a surface part of this secondary particle 2, a stratified structural surface of inercalating/deintercalating lithium is exposed toward the outside of this secondary particle 2.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery,
In particular, it relates to improvement of a lithium composite oxide which is an active material material for the positive electrode.

[0002]

2. Description of the Related Art In recent years, AV equipment and electronic equipment such as personal computers are rapidly becoming portable and cordless, and there is a demand for a secondary battery having a small size, a light weight and a high energy density as a power source for driving them. high. From this point of view, non-aqueous secondary batteries, especially lithium secondary batteries, are particularly expected as batteries having high voltage and high energy density.

A layered compound capable of intercalating and deintercalating lithium as a positive electrode active material satisfying the above demands, for example, US Pat. No. 4,302.
Li _(1-x) NiO ₂ (where 0 ≦ x <1) shown in Japanese Patent No. 518 or LiMM′O ₂ (where M: F e, Co shown in Japanese Patent Laid-Open No. 267053/1992). , N
i, M ': Ti, V, Cr, Mn) and other complex oxides mainly composed of lithium and a transition metal have been proposed.

These positive electrode active materials, such as the general formula Li
Lithium nickelate represented by NiO ₂ is manufactured as follows.

Raw material nickel hydroxide (Ni (OH) ₂ )
Is a mixture of nickel sulfate and sodium hydroxide having a predetermined concentration, and these are neutralized without stirring to obtain Ni (OH) ₂ agglomerates which precipitate at this time. This lump is dried, solidified, and then pulverized to obtain amorphous Ni (OH) ₂ particles having various particle shapes. Next, the Ni (OH) ₂ particles and lithium hydroxide (LiO
H) is mixed with a predetermined mixing ratio, and these are heat-treated in an oxygen atmosphere at 500 to 800 ° C. for a predetermined time to obtain LiNiO 2.
_{Get 2} Then, this LiNiO ₂ is pulverized so as to have a predetermined particle diameter to obtain amorphous LiNiO ₂ particles. The scanning electron micrograph is shown in FIG.

[0006]

However, the LiNiO ₂ particles obtained as described above have the following problems.

That is, nickel hydroxide (Ni (O
H) ₂ ) is a layered compound in which nickel ions and hydroxide ions are combined, and lithium nickelate (LiNiO ₂ ) is produced by the reaction of lithium of the lithium compound melted by heat into the interlayer portion of this layered structure. To be done.
FIGS. 5A and 5B show typical particle structures of nickel hydroxide (Ni (OH) ₂ ) used to produce the lithium nickel oxide (LiNiO ₂ ) up to now.

FIG. 5 (A) is a scanning electron microscopic photograph (hereinafter referred to as SEM) of the Ni (OH) ₂ particles at a magnification of 1000 times.
And (B) is a partially enlarged photograph of the particle surface.

As shown in FIGS. 5A and 5B, Ni (O)
H) ₂ grains do not grow until the single crystal grains have a plate-like and regularly laminated layered structure depending on the production conditions.
Single crystal grains with a very fine layered structure may nucleate in various directions. Then, due to the aggregation of these fine single crystal grains, amorphous secondary particles having various shapes were generated.

Further, in the Ni (OH) ₂ secondary particles,
Since the single crystal grains grow in various directions, the layer structure surface of the single crystal grain was rarely exposed to the outside of the secondary particles.

Therefore, in the LiNiO ₂ particles using the Ni (OH) ₂ particles as a starting material, the layer structure surface on which lithium intercalates and deintercalates is not exposed to the outside of the particles, so During the charging and discharging, the reaction of lithium intercalating and deintercalating with the positive electrode active material was not efficiently performed.

Therefore, when LiNiO ₂ or LiNiM nO ₂ which is a lithium composite oxide is used as the positive electrode active material, the amount of lithium intercalated between the layers of the active material is small and the capacity is low. There was a problem.

The present invention is intended to solve such a problem, in which the intercalation and deintercalation reactions of lithium in the complex oxide proceed smoothly, the capacity is high, and the charge / discharge efficiency is excellent. An electrolyte secondary battery and a positive electrode active material therefor are provided.

[0014]

In order to solve the above problems, in the non-aqueous electrolyte secondary battery of the present invention, the positive electrode active material is lithium nickel oxide represented by the general formula LiNiO ₂ or LiNi _{(1-x). )} Mn _x O ₂ (where 0 <x <0.3)
With lithium nickel manganate represented by, the single crystal grains are plate-like crystals having a layered structure in which flakes are regularly stacked, and the shape of the secondary particles in which the plate-like crystal grains are aggregated is spherical, Most or all of the plate-like crystal grains, which are substantially spherical or ellipsoidal and constitute the surface portion of the secondary particles, have their layered structure faces facing outward.

[0015]

In the non-aqueous electrolyte secondary battery of the present invention, the single crystal grains of LiNiO ₂ or LiNi _(1-x) Mn _x O ₂ (where 0 <x <0.3) as the positive electrode active material are It is a plate-like crystal that is regularly oriented and laminated.

The plate-like crystal grains have such a shape that when they are aggregated to form secondary particles, the shape of the secondary particles is spherical, almost spherical or ellipsoidal. The layered structure portions are assembled so as to be exposed toward the outside, that is, the surface of the secondary particles.

As described above, according to the present invention, the positive electrode active material particles have a plate-like structure in which the layered structure portions of the single crystal particles in which lithium is intercalated and deintercalated are regularly oriented and laminated. The layered structure portion is exposed and exists on the surface of the secondary particles in which single crystal grains are aggregated. Such a particle structure is extremely effective in promoting the reaction of intercalating and deintercalating lithium in the active material. Therefore, in a battery using this positive electrode active material, the reaction in which lithium intercalates and deintercalates smoothly at the positive electrode during charge / discharge of the battery, the charge / discharge efficiency of the active material increases, and the battery capacity increases. Can be made.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

(Example 1) The general formula Li was used as the positive electrode active material.
The case of using lithium nickelate represented by NiO ₂ will be described.

First, nickel hydroxide (N
i (OH) ₂ ) particles were prepared as follows. A predetermined amount of an aqueous solution of nickel sulfate having a concentration of about 1N and an aqueous solution of sodium hydroxide having a concentration of about 1N were put into a stirring tank, and these were stirred by rotating a stirring blade at a high speed. The solution was maintained under stirring at a pH of about 11 and a temperature of 40 ° C.

During this stirring, nickel hydroxide (Ni hydroxide) precipitated by the neutralization reaction of nickel sulfate and sodium hydroxide (Ni
The particle structure of (OH) ₂ ) is shown in FIGS. Figure 1
(A) is an SEM photograph of Ni (OH) ₂ particles at a magnification of 1000 times, and (B) is an enlarged photograph of a part of the surface.

As shown in FIGS. 1A and 1B, this N
The i (OH) ₂ particles are composed of single crystal grains composed of plate-like crystals in which a large number of thin flakes are laminated to form spherical, nearly spherical or ellipsoidal secondary particles. In most or all of the plate-like crystal grains forming the part, the surface facing the tank-like structure is exposed to the outside of the secondary particles.

Next, by changing the reaction aging time of nickel sulfate and sodium hydroxide, Ni (OH) 2
The particle size of ₂ is controlled, and the average particle size is 1, 2, 5 respectively.
, 10, 15, 20, 25 μm Ni (OH) ₂ particles were prepared.

After washing the obtained nickel hydroxide particles with water, alkali ions remaining in the particles were removed by decantation.

Then, nickel hydroxide (Ni (OH) ₂ ) particles having respective average particle diameters and lithium hydroxide (Li
OH) was mixed in a predetermined mixing ratio, and these were heat-treated in an oxygen atmosphere at 750 ° C. for 20 hours to obtain lithium nickelate (LiNiO ₂ ) particles of the present invention. LiN of the present invention
The structure of iO ₂ particles is shown in FIGS. 2 and 3. Figure 2 shows Li
FIG. 3 is an enlarged model view of the surface state of NiO ₂ particles, and FIG. 3 is a SEM photograph at a magnification of 10,000 times. As shown in FIG. 2 and FIG. 3, the LiNiO ₂ particles of the present invention have a structure that takes advantage of the shape of the raw material Ni (OH) ₂ particles, and the single crystal grains 1 composed of plate-like crystals in which flakes are laminated are The secondary particles 2 are spherical, nearly spherical or ellipsoidal aggregates.

In most or all of the plate-like crystal grains 1 constituting the surface portion of the secondary particle 2, the layered structure portion which is the reaction surface for intercalating and deintercalating lithium is the secondary particle. It is exposed to the outside.

Then, LiNi having an average particle diameter of 1, 2, 5, 10, 15, 20, 25 μm obtained in this way
A test electrode was prepared using O ₂ and the capacity of LiNiO ₂ was measured.

The test electrode 3 contains lithium nickel oxide (LiNiO ₂ ) and acetylene black, graphite and a fluororesin binder in a weight ratio of 100: 4: 4: 7.
Was mixed, and a predetermined organic solvent was added thereto to form a paste, and the paste was applied to both surfaces of the aluminum foil.

As shown in FIG. 6, the test electrode 3 is arranged in a glass container 6 together with a counter electrode 4 and a reference electrode 5 made of lithium.
A simple cell was constructed by using an electrolytic solution which was housed inside and in which lithium perchlorate was dissolved in an equal volume mixed solvent of propylene carbonate and ethylene carbonate at a ratio of 1 mol / l.

A charge / discharge test was conducted using this simple cell. In the charge / discharge test, the current density for the test electrode was set to 0.5 mA / cm ² , and a constant current was applied to the reference electrode for 4.
It was charged to 3V and discharged to 3.0V.

Further, as nickel hydroxide (Ni (OH) ₂ ) particles, nickel sulfate and sodium hydroxide are neutralized without stirring, and Ni (OH) which precipitates at this time is precipitated.
_The powder obtained by drying, solidifying, and crushing the agglomerates of No. ₂ was heat-treated with lithium hydroxide (LiOH) under the same conditions as in the present invention, and the amorphous LiNiO ₂ as shown in FIG. 4 was used. Particles were prepared and the particles were made into conventional LiNiO ₂
It was made into particles. Then, using this LiNiO ₂ particle, a simple cell similar to that of the present invention was constructed except for the above, and the same charge / discharge test as above was carried out for 50 cells. The results are shown in FIG.

[0032] In LiNiO ₂ particles of the present invention over conventional LiNiO ₂ particles as shown in FIG. 7, lithium intercalated lamellar structure portion of the de-intercalating crystals exposed on the surface of the particles Therefore, the intercalation and deintercalation reactions of lithium proceeded smoothly, and the charge / discharge capacity of the active material increased. Particularly in the case of the LiNiO ₂ particles of the present invention having an average particle diameter of 2 to 20 μm, the average is 15
It showed a high capacity value of 0 mAh / g or more. In FIG. 7, the upper and lower widths show variations in capacity.

Example 2 As the positive electrode active material, the general formula Li was used.
The case of using lithium nickel manganate represented by Ni _0.8 Mn _0.2 O ₂ will be described.

Nickel hydroxide (Ni (OH)) as a raw material
₂ ) was produced in the same manner as in Example 1 and had an average particle size of 1,
Nickel hydroxide particles of 2, 5, 10, 15, 20, 25 μm were obtained. Then, nickel hydroxide (Ni (OH) ₂ ) particles having respective average particle diameters are added to lithium hydroxide (Li
OH) and manganese carbonate (MnCO ₃ ) are mixed in a predetermined mixing ratio, and these are heat-treated in an oxygen atmosphere at 750 ° C. for 20 hours to obtain lithium nickel manganese oxide (Li) of the present invention.
Ni _0.8 Mn _0.2 O ₂ ) particles were obtained.

Further, as nickel hydroxide (Ni (OH) ₂ ) particles, nickel sulfate and sodium hydroxide are neutralized without stirring, and Ni (O ₂ ) precipitates at this time.
H) ₂ agglomerates were dried and solidified, and then ground powder was used, which was heat treated with lithium hydroxide (LiOH) and manganese carbonate (MnCO ₃ ) under the same conditions as in the present invention to give an amorphous form. Of LiNi _0.8 Mn _0.2 O ₂ particles
Manufactured, and used as conventional LiNi _0.8 Mn _0.2 O ₂ particles.

Then, according to the present invention and the conventional LiNi _0.8 Mn
_{Using 0.2} O ₂ particles, 50 test electrodes and 50 simple cells similar to those in Example 1 were configured, and the same charge and discharge test as in Example 1 was conducted. The result is shown in FIG.

As shown in FIG. 8, conventional LiNi _0.8 M
LiNi _0.8 Mn _0.2 O _{2 of the} present invention for n _0.2 O ₂ particles
In the particles, since the layered structure part of the crystal in which lithium intercalates and deintercalates is exposed on the surface of the particles, the lithium intercalation and deintercalation reactions proceed smoothly, and the charge / discharge capacity of the active material is increased. It got bigger. Particularly, the LiN of the present invention having an average particle size of 2 to 20 μm
The i _0.8 Mn _0.2 O ₂ particles showed a high capacity value.

Next, the optimum range of x of lithium nickel manganate represented by the general formula LiNi _(1-x) Mn _x O ₂ is evaluated for the charge-discharge cycle life characteristics of the cylindrical battery using this positive electrode active material. Examined by that.

LiNi of the present invention having an average particle size of 10 μm
_(1-x) Mn _x O ₂ particles (however, x is 0, 0.1, 0.
2, 0.3, 0.4) and acetylene black, graphite and a fluororesin binder in a weight ratio of 100: 4:
After mixing 4: 7 and adding a predetermined organic solvent to form a paste, the positive electrode mixture was applied to both sides of an aluminum foil, dried and rolled to produce a positive electrode plate.

For the negative electrode plate, a carbon material obtained by firing coke at a high temperature of about 2700 ° C. or higher and a fluororesin binder are mixed at a weight ratio of 100: 10, and the mixture is suspended in an aqueous carboxymethylcellulose solution to form a paste. The paste was applied to both sides of a copper foil, dried, and then rolled.

FIG. 9 is a vertical sectional view of a cylindrical battery constructed by using these positive and negative electrode plates. The battery was constructed by attaching a lead to each of the strip-shaped positive and negative electrode plates, spirally winding the whole through a polypropylene separator, and storing it in a battery case. As the electrolytic solution, a solution prepared by dissolving lithium perchlorate in an equal volume mixed solvent of propylene carbonate and ethylene carbonate at a ratio of 1 mol / l was injected into a predetermined amount, and the sealed one was used as a test battery. .

In FIG. 9, 7 is a battery case formed by processing a stainless steel plate resistant to organic electrolyte, 8 is a sealing plate provided with a safety valve, and 9 is an insulating packing.

The positive electrode plate 10 and the negative electrode plate 11 are spirally wound via the separator 12 and housed in the case 7. The positive electrode lead 13 is pulled out from the positive electrode plate 10 and connected to the sealing plate 8, and the negative electrode plate 11
The negative electrode lead 14 is drawn out from the above and is connected to the bottom of the battery case 7.

Using these test batteries, a charge / discharge current of 10
0mA, charge end voltage 4.1V, charge end voltage 3.0V
The constant current discharge test under the above conditions was conducted up to 50 cycles at room temperature.

The results are shown in FIG. As shown in FIG. 10, in the range of the substitution atom number x of Mn in LiNi _(1-x) Mn _x O ₂ in the range of 0.1 to 0.3, LiNiO of x = 0.
Cycle life can be improved compared to ₂ . However, when x becomes 0.4, the alloy phase effective for the intercalation / deintercalation reaction of lithium in the active material decreases, resulting in a decrease in the capacity of the active material and a decrease in cycle life characteristics. did.

Therefore, the LiNi _(1-x) Mn _{x of the} present invention is
The range of x of O ₂ is preferably 0 <x <0.3.

The positive electrode active material particles represented by the general formulas LiNiO ₂ and LiNi _(1-x) Mn _x O ₂ (where 0 <x <0.3) of the present invention are shown in FIGS. 7 and 8. As described above, the variation in capacity indicated by the vertical width was smaller than that of the conventional positive electrode active material particles.

This is because in the conventional positive electrode active material particles, the orientation of the layered structure of the single crystal grains is non-uniform, the particle shape is also indefinite, and it is difficult to control the particle diameter. In the active material particles, the orientation of the layered structure of single crystal grains is uniform,
It is considered that this is because it is easy to control the particle shape and particle diameter.

In this embodiment, lithium hydroxide was used as the lithium compound, but the same effect can be obtained with any one of lithium nitrate, lithium carbonate and lithium oxide.

The same effect can be obtained if the manganese compound is manganese nitrate or manganese oxide in addition to manganese carbonate.

[0051]

As described above, in the non-aqueous electrolyte secondary battery of the present invention, the positive electrode active material is lithium nickel oxide represented by the general formula LiNiO ₂ or LiNi _(1-x) Mn _x O ₂ (however, 0 <x <0.3) lithium nickel manganate, the single crystal grains of which are plate-like crystals having a layered structure, and the shape of secondary particles in which a large number of these plate-like crystal grains are aggregated is , Spherical, almost spherical or ellipsoidal shape, and most or all of the plate-like crystal grains constituting the surface portion of the secondary particles, the layered structure surface in which lithium intercalates and deintercalates is the secondary particle Facing out of.

Therefore, in the positive electrode active material particles, the intercalation and deintercalation reactions of lithium proceed extremely smoothly, and the charge / discharge capacity of the positive electrode active material can be increased.

[Brief description of drawings]

FIG. 1A is an electron micrograph showing the particle structure of nickel hydroxide used in the present invention, and FIG.

FIG. 2 is an enlarged model diagram showing a typical surface state of lithium nickelate particles of the present invention.

FIG. 3 is an electron micrograph showing the particle structure of the lithium nickelate.

FIG. 4 is an electron micrograph showing the particle structure of conventional lithium nickel oxide.

FIG. 5 (A) Electron micrograph showing the particle structure of conventional nickel hydroxide (B) Enlarged photograph of the same part

FIG. 6 is a sectional view of a simple cell used in the present invention.

FIG. 7 is a graph showing the relationship between the average particle size and the capacity of the present invention and conventional lithium nickel oxide particles.

FIG. 8 is a graph showing the relationship between the average particle size and capacity of the present invention and conventional lithium nickel manganese oxide particles.

FIG. 9 is a sectional view of a cylindrical battery used in the present invention.

FIG. 10: LiN nickel manganate LiN of the present invention
i _(1-x) Mn _x O ₂ Graph showing the relationship between the number x of atoms of substitution of manganese in the particles and the charge-discharge cycle life characteristics

[Explanation of symbols]

 1 Single Crystal Grain 2 Secondary Particle 3 Test Electrode 4 Counter Electrode 5 Reference Electrode 6 Glass Container 7 Battery Case 8 Sealing Plate 9 Insulating Packing 10 Positive Electrode Plate 11 Negative Electrode Plate 12 Separator 13 Positive Electrode Lead 14 Negative Lead

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeo Kobayashi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (12)

[Claims] 1. A positive electrode in which the active material is lithium nickelate represented by the general formula LiNiO ₂ , and a large number of fine crystal grains are aggregated to form spherical, almost spherical or ellipsoidal secondary particles. A non-aqueous electrolyte secondary battery comprising a negative electrode using any one of lithium, a lithium alloy, and a carbon material capable of intercalating and deintercalating lithium, and a non-aqueous electrolyte. 2. The average particle diameter of the secondary particles is 2 to 20 μm.
The non-aqueous electrolyte secondary battery according to claim 1. 3. A positive electrode, a negative electrode using any one of lithium, a lithium alloy, and a carbon material capable of intercalating and deintercalating lithium, and a non-aqueous electrolyte solution. The positive electrode contains an active material. Lithium nickel oxide represented by the general formula LiNiO ₂ , wherein the single crystal grains are plate-like having a layered structure, and the shape of the secondary particles in which a large number of the plate-like crystal grains are aggregated is spherical, almost spherical or A non-aqueous electrolyte secondary battery having an ellipsoidal shape and most of the plate-like crystal grains constituting at least the surface portion thereof have the layered structure surface facing outward. 4. The average particle size of the secondary particles is 2 to 20 μm.
The non-aqueous electrolyte secondary battery according to claim 3. 5. The active material is of the general formula LiNi _(1-x) Mn _x O ₂
(Provided that 0 <x <0.3), and a positive electrode in which a large number of fine single crystal grains thereof are aggregated to form spherical, nearly spherical or ellipsoidal secondary particles. A non-aqueous electrolyte secondary battery comprising a negative electrode using any one of lithium, a lithium alloy, and a carbon material capable of intercalating and deintercalating lithium, and a non-aqueous electrolyte. 6. The average particle diameter of the secondary particles is 2 to 20 μm.
The non-aqueous electrolyte secondary battery according to claim 5. 7. A positive electrode, a negative electrode using any one of lithium, a lithium alloy, and a carbon material capable of intercalating and deintercalating lithium, and a non-aqueous electrolyte solution. The positive electrode contains an active material. General formula LiNi _(1-x) Mn _x O
₂ (provided that 0 <x <0.3), and the single crystal grain is a plate-like having a layered structure, and the secondary particles are a collection of a large number of the plate-like crystal grains. The non-aqueous electrolyte secondary battery has a spherical shape, a substantially spherical shape, or an ellipsoidal shape, and most of the plate-like crystal grains forming at least the surface portion thereof have the layered structure surface facing outward. 8. The average particle diameter of the secondary particles is 2 to 20 μm.
The non-aqueous electrolyte secondary battery according to claim 7. 9. A step of forming secondary particles by aggregating plate-like single crystal particles of nickel hydroxide, which are precipitated by a neutralization reaction between a nickel salt aqueous solution and an alkaline aqueous solution, into a spherical shape, a substantially spherical shape or an ellipsoidal shape. A step of heat-treating the secondary particles of nickel hydroxide and any lithium compound selected from the group consisting of lithium hydroxide, lithium nitrate, lithium carbonate and lithium oxide in an oxygen atmosphere to obtain lithium nickelate And a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising: 10. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 9, wherein the lithium compound is lithium hydroxide. 11. A step of forming secondary particles by aggregating plate-like single crystal particles of nickel hydroxide, which are precipitated by a neutralization reaction of a nickel salt aqueous solution and an alkaline aqueous solution, into a spherical shape, a substantially spherical shape or an ellipsoidal shape. A secondary particle of nickel hydroxide, any one of manganese compounds selected from the group consisting of manganese carbonate, manganese nitrate and manganese oxide, selected from the group consisting of lithium hydroxide, lithium nitrate, lithium carbonate and lithium oxide To obtain lithium nickel oxide by heat-treating any of these lithium compounds in an oxygen atmosphere to produce a positive electrode active material for a non-aqueous electrolyte secondary battery. 12. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 11, wherein the manganese compound is manganese carbonate and the lithium compound is lithium hydroxide.