JP3047693B2 - Non-aqueous electrolyte secondary battery and method for producing positive electrode active material thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In recent years, electronic devices such as AV devices and personal computers have been rapidly becoming hot and cordless, and there has been a demand for a small, lightweight secondary battery having a high energy density as a power supply for driving these devices. high. From such a viewpoint, non-aqueous secondary batteries, particularly lithium secondary batteries, are expected to have high voltage and high energy density.

A layered compound capable of intercalating and deintercalating lithium as a positive electrode active material satisfying the above demand, for example, US Pat.
Li _(1-x) NiO ₂ (0 ≦ x <1) described in the specification of US Pat. No. 518,518, and LiMM′O ₂ (M: Fe, Co , N
(i, M ': Ti, V, Cr, Mn), and composite oxides mainly composed of lithium and a transition metal have been proposed.

[0004] These positive electrode active materials, for example, the general formula Li
Lithium nickelate represented by NiO ₂ is produced as follows.

Nickel hydroxide (Ni (OH) ₂ ) as a raw material
Mixes a predetermined concentration of nickel sulfate and sodium hydroxide, and performs a neutralization reaction without stirring to obtain a mass of Ni (OH) ₂ which precipitates at this time. The mass is dried and solidified, and then pulverized to obtain amorphous Ni (OH) ₂ particles having various particle shapes. Then, the Ni (OH) ₂ particles and lithium hydroxide (LiO
H) at a predetermined mixing ratio, and heat-treat them at 500 to 800 ° C. for a predetermined time in an oxygen atmosphere to obtain LiNiO 2.
_{Get two} . Then, the LiNiO ₂ is pulverized to a predetermined particle size to obtain amorphous LiNiO ₂ particles. FIG. 4 shows a scanning electron microscope photograph.

[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 bonded, and lithium nickelate (LiNiO ₂ ) is generated by a reaction in which lithium of a lithium compound melted by heat enters into an interlayer portion of the layered structure. Is done.
FIGS. 5A and 5B show a typical particle structure of nickel hydroxide (Ni (OH) ₂ ) used for producing lithium nickel oxide (LiNiO ₂ ).

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

As shown in FIGS. 5A and 5B, Ni (O
H) Due to the manufacturing conditions, the ₂ grains do not grow until the single crystal grains have a plate-like and regularly laminated layered structure.
Single crystal grains having a very fine layered structure may grow nuclei in various directions. And, by the aggregation of these fine single crystal grains, amorphous secondary particles having various shapes have been generated.

[0010] In the Ni (OH) ₂ secondary particles,
Since the single crystal grains grow in various directions, the layer structure surface of the single crystal grains was rarely exposed toward 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 is intercalated and deintercalated is not exposed to the outside of the particles, so that the battery During the charging and discharging of, the reaction of intercalating and deintercalating lithium in the positive electrode active material was not efficiently performed.

Therefore, when the above-mentioned LiNiO ₂ or LiNiMnO ₂ which is a lithium composite oxide is used for the positive electrode active material, the amount of lithium intercalated between the layers of the active material is small and the capacity is low. The problem had arisen.

The present invention has been made to solve the above-mentioned problems, and a non-aqueous solution having a high capacity and excellent charge / discharge efficiency in which a lithium intercalate / deintercalate reaction in a composite oxide proceeds smoothly. It is intended to provide an electrolyte secondary battery and a positive electrode active material therefor.

[0014]

In order to solve the above-mentioned problems, a nonaqueous electrolyte secondary battery of the present invention uses a lithium nickelate or LiNi _(1-x) represented by the general formula LiNiO ₂ as a positive electrode active material. ₎ Mn _x O ₂ (however, 0 <x <0.3)
In the lithium nickel manganate represented by, the single crystal grains are plate crystals having a layered structure in which flakes are regularly stacked, and the shape of the secondary particles in which a large number of the plate crystal grains are aggregated is spherical, In addition to being substantially spherical or ellipsoidal, most or all of the plate-like crystal grains constituting the surface portion of the secondary particles have their layered structure faces outward.

[0015]

[Action] In a non-aqueous electrolyte secondary battery of the present invention is a positive electrode active material LiNiO ₂ or _{LiNi (1-x) Mn x} O 2 ( however, 0 <x <0.3) of the single crystal grains, It is a plate-like crystal that is stacked with regular orientation.

The plate-like crystal grains are formed so that when they are aggregated to form secondary particles, the shape of the secondary particles is spherical, almost spherical or ellipsoidal. The layered structure parts are assembled so as to be exposed to the outside, that is, toward 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 layered portions of single crystal particles in which lithium is intercalated and deintercalated are regularly oriented and laminated. The layered structure portion is exposed on the surface of the secondary particles in which the single crystal grains are aggregated. Such a particle structure is extremely effective in promoting a reaction of intercalating and deintercalating lithium into the active material. For this reason, in the battery using this positive electrode active material, the reaction in which lithium intercalates and deintercalates in the positive electrode during charging and discharging of the battery proceeds smoothly, the charge and discharge efficiency of the active material increases, and the battery capacity increases. Can be done.

[0018]

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

Example 1 As a positive electrode active material, a general formula Li was used.
The case where lithium nickel oxide represented by NiO ₂ is used will be described.

First, nickel hydroxide (N
i (OH) ₂ ) particles were prepared as follows. Predetermined amounts of an aqueous solution of about 1N nickel sulfate and an aqueous solution of about 1N sodium hydroxide were charged into a stirring tank, and these were stirred by rotating a stirring blade at a high speed. The solution was kept at a temperature of 40 ° C. while stirring, maintaining the pH at about 11.

At the time of this stirring, nickel hydroxide (Ni) precipitated by a neutralization reaction between nickel sulfate and sodium hydroxide.
The particle structure of (OH) ₂ ) is shown in FIGS. FIG.
(A) is an SEM photograph of Ni (OH) ₂ particles at a magnification of 1000, and (B) is an enlarged photograph of a partial surface thereof.

As shown in FIGS. 1A and 1B, this N
The i (OH) ₂ particles are formed by collecting single crystal grains composed of plate-like crystals in which a large number of flakes are stacked to form spherical, substantially spherical or ellipsoidal secondary particles, and the surface of the secondary particles Most or all of the plate-like crystal grains constituting the portion have a surface on which the tank-like structure can be exposed, which is exposed toward the outside of the secondary particles.

Next, by changing the reaction aging time between nickel sulfate and sodium hydroxide, Ni (OH)
_The average particle diameter is controlled to 1, 2, 5
, 10, 15, 20, and 25 μm Ni (OH) ₂ particles were produced.

After washing the obtained nickel hydroxide particles with water, decantation was performed to remove alkali ions remaining on the particles.

Then, nickel hydroxide (Ni (OH) ₂ ) particles having respective average particle diameters and lithium hydroxide (Li)
OH) at a predetermined mixing ratio, and heat-treated at 750 ° C. for 20 hours in an oxygen atmosphere to obtain lithium nickelate (LiNiO ₂ ) particles of the present invention. LiN of the present invention
The structure of the iO ₂ particles is shown in FIGS. FIG. 2 shows Li
FIG. 3 is an enlarged model diagram of the surface state of the NiO ₂ particles, and FIG. 3 is a SEM photograph at a magnification of 10,000 times. As shown in FIGS. 2 and 3, the LiNiO ₂ particles of the present invention have a structure utilizing the shape of Ni (OH) ₂ particles as a raw material, and a single crystal grain 1 composed of a plate-like crystal in which flakes are laminated is used. , Spherical, substantially spherical or elliptical secondary particles 2.

Almost or all of the plate-like crystal grains 1 constituting the surface portion of the secondary particles 2 have a layered structure portion, which is a reaction surface where lithium intercalates and deintercalates, of secondary particles. It is exposed to the outside.

Next, the thus obtained LiNi particles having an average particle diameter of 1, 2, 5, 10, 15, 20, 25 μm are obtained.
A test electrode was prepared using O _2, and the capacity of LiNiO ₂ was measured.

The test electrode 3 is composed of lithium nickelate (LiNiO ₂ ), acetylene black, graphite and a fluororesin binder in a weight ratio of 100: 4: 4: 7.
And a predetermined organic solvent was added to the mixture to form a paste, and then this paste was applied to both surfaces of an aluminum foil to produce a paste.

As shown in FIG. 6, the test electrode 3 is connected to a glass container 6 together with a counter electrode 4 made of lithium and a reference electrode 5.
And a simple cell was constructed using an electrolytic solution 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.

Then, a charge / discharge test was performed using this simple cell. In the charge / discharge test, the current density for the test electrode was 0.5 mA / cm ² , and the current density for the reference electrode was 4.
The test was performed by charging to 3 V and discharging to 3.0 V.

In addition, nickel sulfate (Na (OH) ₂ ) particles are subjected to a neutralization reaction without stirring with nickel sulfate (Ni (OH) ₂ ) particles.
Dried ₂ lumps, solidified and ground using a powder obtained, which lithium hydroxide (LiOH) with the present invention and amorphous as shown in FIG. 4 was heat-treated at the same conditions LiNiO ₂ Particles were prepared, which were converted to conventional LiNiO ₂
Particles. A simple cell similar to that of the present invention was constructed using the LiNiO ₂ particles except for the above, and the same charge / discharge test as above was performed for each of 50 cells. These 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 μm.
It showed a high capacity value of 0 mAh / g or more. In FIG. 7, the upper and lower widths indicate variations in capacitance.

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

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

As nickel hydroxide (Ni (OH) ₂ ) particles, nickel sulfate and sodium hydroxide are subjected to a neutralization reaction without stirring, and Ni (O) precipitates at this time.
H) The lump of ₂ was dried and solidified, and then a powder obtained by crushing the solid was used. The powder was heat-treated together with lithium hydroxide (LiOH) and manganese carbonate (MnCO ₃ ) under the same conditions as in the present invention to obtain an amorphous form. LiNi _0.8 Mn _0.2 O ₂ particles
And used as conventional LiNi _0.8 Mn _0.2 O ₂ particles.

The present invention and the conventional LiNi _0.8 Mn
Using 50 test electrodes and 50 simple cells similar to those in Example 1 using _0.2 O ₂ particles, the same charge / discharge test as in Example 1 was performed. The result is shown in FIG.

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

[0038] Then, the optimum range of the general formula _{LiNi (1-x) Mn x} O 2 in represented by Nikkeruma manganese acid lithium x, evaluating the charge-discharge cycle life characteristics of the cylindrical battery using the cathode active material Considered by:

LiNi of the present invention having an average particle size of 10 μm
_{(1-x) Mn x O} 2 particles (although, 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:
The mixture was mixed at 4: 7, and a predetermined organic solvent was added to the mixture to form a paste. The positive electrode mixture was applied to both sides of an aluminum foil, dried, and then rolled to prepare a positive electrode plate.

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

FIG. 9 is a longitudinal sectional view of a cylindrical battery constituted by using these positive and negative electrode plates. The battery was configured such that leads were attached to strip-shaped positive and negative plates, and the whole was spirally wound via a polypropylene separator, and housed in a battery case. As the electrolyte, a solution prepared by dissolving lithium perchlorate at a ratio of 1 mol / l in an equal volume mixed solvent of propylene carbonate and ethylene carbonate, injecting a predetermined amount of the solution, and sealing the resultant was used as a test battery. .

In FIG. 9, reference numeral 7 denotes a battery case formed by processing a stainless steel plate having resistance to an organic electrolytic solution, 8 denotes a sealing plate provided with a safety valve, and 9 denotes an insulating packing.

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

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

FIG. 10 shows the result. As shown in FIG. 10, when the number x of substituted atoms of Mn in LiNi _(1-x) Mn _x O _{2 is} in the range of 0.1 to 0.3, Li = 0 (x = 0)
_The cycle life can be improved as compared with ₂ . However, when x becomes 0.4, the alloy phase effective for the lithium intercalation and deintercalation reactions in the active material decreases, so that the capacity of the active material decreases and the cycle life characteristics deteriorate. did.

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

The positive electrode active material particles of the present invention represented by the general formulas LiNiO ₂ and LiNi _(1-x) Mn _x O ₂ (where 0 <x <0.3) are shown in FIGS. 7 and 8. As described above, the variation in the 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 single crystal grains is non-uniform, the particle shape is irregular, and the control of the particle diameter is difficult. In the active material particles, the orientation of the layer structure of single crystal grains is uniform,
It is considered that the control of particle shape and particle diameter is easy.

In the present embodiment, lithium hydroxide was used as the lithium compound. However, the same effect can be obtained if any of lithium nitrate, lithium carbonate and lithium oxide is used.

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

[0051]

As it is evident from the foregoing description, the non-aqueous electrolyte secondary battery of the present invention, lithium nickelate or LiNi represented a positive electrode active material by formula _{LiNiO 2 (1-x) Mn} x O 2 ( where 0 <x <0.3), and the single crystal grains thereof are plate-like crystals having a layered structure. In addition to being spherical, almost spherical or ellipsoidal, most or all of the plate-like crystal grains constituting the surface of the secondary particles have lithium-intercalated and de-intercalated layered structure surfaces with secondary particles. Facing outside.

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 the drawings]

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 the 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 a conventional lithium nickelate.

FIG. 5A is an electron micrograph showing the particle structure of a conventional nickel hydroxide, and FIG.

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

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

FIG. 8 is a diagram showing the relationship between the average particle diameter and the capacity of the present invention and conventional lithium nickel manganate particles.

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

FIG. 10 shows lithium nickel manganate LiN of the present invention.
i _(1-x) diagram illustrating the relationship between the Mn _x O substituted atoms of manganese ₂ grains element x and the charge-discharge cycle life characteristics

[Explanation of symbols]

 DESCRIPTION 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 electrode lead

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeo Kobayashi 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-6-267539 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01M 4/02 H01M 4/04 H01M 4/36-4/62 H01M 10/40

Claims (6)

(57) [Claims] 1. A active material formula _{LiNi (1-x) Mn x} O 2
(However, nickel man represented by 0 <x <0.3)
A lithium cancer acids that fine monocrystal grains are a number set to spherical, a positive electrode forming a substantially spherical or ellipsoidal secondary particles, lithium, lithium alloys and lithium intercalation, deintercalation A non-aqueous electrolyte secondary battery comprising a negative electrode using any of the carbon materials that can be used and a non-aqueous electrolyte. 2. The secondary particles have an average particle diameter of 2 to 20 μm.
The non-aqueous electrolyte secondary battery according to claim 1, wherein 3. A positive electrode, intercalated with lithium, a lithium alloy and lithium.
Carbon material that can be deintercalated
The negative electrode used comprises a non-aqueous electrolyte, and the positive electrode has an active material represented by a general formulaLiNi _(1-x) Mn _x O
_Two (However, 0 <x <0.3)Nickel represented byMa
NganLithium oxide, the single crystal grains of which are plate-like having a layered structure, and the shape of secondary particles in which a large number of the plate-like crystal grains are aggregated is spherical
Shape, almost spherical or ellipsoidal shape,
At least most of the plate-like grains that make up the surface
Non-aqueous electrolyte secondary battery with the layered structure surface facing outward. 4. The secondary particles have an average particle size of 2 to 20 μm.
The non-aqueous electrolyte secondary battery according to claim 3, wherein 5. The method of claim 1 wherein the nickel salt aqueous solution and the alkali aqueous solution
Plate-like single crystal grains of nickel hydroxide precipitated by neutralization reaction
Into a spherical, nearly spherical or ellipsoidal shape
A step of forming particles, secondary particles of the nickel hydroxide, and a group consisting of manganese carbonate, manganese nitrate, and manganese oxide
A manganese compound selected from
, Lithium nitrate, lithium carbonate and lithium oxide
Any lithium compound selected from the group consisting of
Heat treatment under oxygen atmosphere to obtain lithium nickelate
Preparation of the positive electrode active material of the nonaqueous electrolyte secondary battery comprising a degree
Law. 6. The manganese compound is manganese carbonate,
The lithium compound according to claim 5, wherein the lithium compound is lithium hydroxide.
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.