JP3049973B2 - Non-aqueous electrolyte secondary battery - 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 battery using a lithium composite oxide as a positive electrode active material.

[0002]

2. Description of the Related Art In recent years, portable and cordless electronic devices have been rapidly advancing, and small and lightweight power sources for driving these devices have high energy densities, and have excellent charge / discharge cycle characteristics and long life. There is a high demand for secondary batteries. In this regard, non-aqueous electrolyte secondary batteries, particularly lithium secondary batteries, are expected to have high voltage and high energy density.

[0003] For a lithium secondary battery satisfying the above demands,
In recent years, active research has been conducted to develop positive electrode active materials.
Have been. For example, for nickel compounds, Li_yNi
_2-yO _Two(JP-A-2-40861) and Li_1-xNi
O_Two(U.S. Pat. No. 4,302,518)
There are proposals and more in the context of other transition metal compounds
Development cases have been reported.

[0004]

The lithium nickel compound Li _1-x NiO ₂ (where 0 ≦ x <1) has a high potential of 4 V or more with respect to lithium. -It is possible to produce a non-aqueous electrolyte secondary battery having a high energy density.

[0005] However, according to the conventional techniques, a high discharge capacity of 100 mA / g or more can be obtained as an initial charge / discharge characteristic, but the discharge capacity decreases remarkably with an increase in the number of charge / discharge cycles. However, it has a problem that the charge-discharge cycle characteristics are inferior and short because it decreases to about 65% of the initial capacity.

[0006]

The present invention SUMMARY OF] In order to solve the above problems, the general formula Li _x M _y NiO ₂ (provided that
M is at least one of Na and K), and the values of x and y in the formula are 0 <x + y ≦ 1.0 and 0 <y
A positive electrode containing an active material satisfying the condition of ≦ 0.3 is used.

It has been found that a non-aqueous electrolyte secondary battery having high voltage and high energy density and excellent charge / discharge cycle characteristics can be produced by using this positive electrode active material. is there.

[0008]

LiNiO ₂ belongs to the trigonal R-3m space group. When represented by the hexagonal system, LiNiO ₂ is a layered structure in which the planes composed of oxygen, nickel, and lithium atoms are regularly stacked in the c-axis direction. Forming the structure. In other words, nickel and oxygen form a NiO ₂ layer by a covalent bond, and LiNi is sandwiched between the NiO ₂ layers by a weak van der Waals force.
It is said to form O ₂ . Therefore LiNi
Lithium in O ₂ can be extracted or inserted electrochemically or chemically, and its reaction is reversible, so that it can be used as an electrode active material.

However, LiNiO ₂ is electrochemically oxidized by charging, and most of Li _1-x NiO ₂ (x is almost equal to ₁₎ generated when most of lithium is extracted at a high potential, or all of lithium is extracted. Ni extracted
O ₂ is chemically unstable, cannot maintain the layered structure described above, and loses the reversibility of the reaction. This is LiN
This is considered to be one of the causes of capacity deterioration due to the charge / discharge cycle of the iO ₂ positive electrode.

[0010] In the present invention, the general formula Li _x M _y NiO ₂ (where, M is Na, at least one of K) represented by, and replaced by sodium and or potassium portions of lithium LiNiO ₂ The problem is solved by applying a material having a structure to a positive electrode active material.

The action of this substance is presumed as follows.
The size of the chemical diffusion coefficients shown lithium, sodium, the speed of movement of the potassium in the Li _x M _y NiO ₂ during lithium extraction and insertion of lithium>sodium> decreases in the order of potassium. Stoklosa et al. (Solid
State Ionics, 18 & 19 (1986) 9
According to 74), the chemical diffusion coefficient of sodium is about one-tenth smaller than that of lithium. From this, L
i _x M _y NiO ₂ (where, M is Na, at least 1 of the K
Sodium and potassium remain in the substance and maintain the layered structure of the substance even when the lithium contained in it is charged and lithium is almost extracted. It is considered to be sustained.

The ionic radii of lithium, sodium and potassium are larger in the order of lithium <sodium <potassium. As a result, sodium ions and potassium ions, which are larger than lithium, are located between the NiO ₂ layers of the layered structure and spread between the layers, thereby promoting the diffusion of lithium ions and facilitating the extraction and insertion of lithium ions accompanying charge and discharge. It is also possible that.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. In the examples, for the convenience of the test, a cylindrical battery was prepared as a battery and evaluated.

[0014] The chemical formula Li _x M _y NiO ₂ (however, M is N
a, K) at least one of x and y in the formula
A method for synthesizing an active material satisfying the conditions of 0 <x + y ≦ 1.0 and 0 <y ≦ 0.3 will be described.

Among the synthetic materials, any one of Ni (OH) ₂ , NiCO ₃ and NiO is used for the nickel compound, and LiNO ₃ ,
Any one of Li ₂ CO ₃ , Li ₂ O and LiOH is used, and NaNO ₃ , N
a ₂ CO ₃ , Na ₂ O, or NaOH, and KNO ₃ , K ₂ CO ₃ , K ₂
Using either O or KOH, it has been confirmed that synthesis is possible using any combination of these synthetic materials. Therefore, the synthetic material described here is shown only for the sake of convenience only when Ni (OH) ₂ , LiNO ₃ , NaNO ₃ , and KNO ₃ are used.

In the synthesis, predetermined amounts of a lithium compound, a nickel compound, a sodium compound, and a potassium compound were mixed, put into a combustion boat, and fired in an electric furnace. The firing is performed in an oxygen atmosphere at a primary firing temperature of 600 ° C. for 12 hours.
The heating was performed at a secondary firing temperature of 750 ° C. for 12 hours. The composition of the product was determined by chemical analysis and then pulverized to prepare an electrode plate.

An outline of a method and a configuration of a test cylindrical battery is shown below. The positive electrode mixture is a mixture of an active material, acetylene black, graphite, and a fluorine-based resin binder in a weight ratio of 100: 4: 4: 7, respectively. It was applied to both sides of the foil, dried and rolled to prepare a positive electrode plate.

On the other hand, the negative electrode plate is made of a carbon material obtained by firing coke and a fluororesin binder at a ratio of 100: 10.
, And kneaded with an aqueous solution of carboxymethyl cellulose to form a paste, applied to both surfaces of a copper foil, and dried and rolled to prepare a paste. The electrolytic solution was prepared by dissolving lithium perchlorate as a supporting electrolyte at a ratio of 1 mol / l in a mixed solvent of propylene carbonate and ethylene carbonate in an equal volume.

Leads are attached to the positive and negative strip plates,
The whole was spirally wound around a polypropylene separator. After storing this in a stainless steel battery case, a predetermined amount of electrolyte was injected, and a sealing plate and other components were attached to form a battery. FIG. 1 shows a longitudinal sectional view of the cylindrical battery thus produced. Here, the positive electrode lead 5 is connected to the sealing plate 2, and the negative electrode lead 6 is the battery case 1.
The packing of 3 has a function of keeping the airtightness and insulating the sealing plate serving as the positive electrode terminal from the battery case forming the negative electrode terminal. The insulating ring of 7
This prevents the positive and negative plates from contacting the battery case and sealing plate inside the battery and causing a short circuit.

[0020] Figure 2 is a chemical formula Li _x M _y NiO ₂ (provided that
M is at least one of Na and K), the values of x and y in the formula are 0 <x + y ≦ 1.0, and the difference between the values of y (y = 0,
0.1, 0.2, 0.3, 0.4, 0.5) charge / discharge test (charge / discharge current 100 mA constant current, voltage 3.0 to 3.0)
The difference in the initial discharge capacity at 4.5 V) is shown.

However, the value of x changes according to the charging / discharging process from the operating principle of the electrode. As can be seen from FIG.
The initial discharge capacity decreases with an increase in the value of. The difference between the case where M is sodium and the case where M is potassium is small. This phenomenon is considered to be a decrease in the discharge capacity due to a decrease in the amount of lithium involved in the reaction with an increase in the value of y. From this result, it can be seen that when y is 0.3 or more, the initial discharge capacity is remarkably reduced, and is not suitable as an electrode active material.

FIG. 3 is a chemical formula Li _x M _y NiO ₂ (provided that
M is at least one of Na and K), wherein the values of x and y in the formula are 0 <x + y ≦ 1.0, and the values of y are 0, 0.1, 0.
Charge / discharge test at 2, 0.3 (charge / discharge current 100 mA)
It shows a change in the discharge capacity up to the 50th cycle at a constant current and a voltage of 3.0 to 4.5 V).

As can be seen from FIG. 3, when y = 0, the capacity sharply decreases due to the charge / discharge cycle.
In the case of = 0.1, 0.2, 0.3, the decrease in the capacity due to the charge / discharge cycle is small, and the initial capacity is inferior to that in the case of y = 0, but is reversed during the cycle. This shows that the addition of sodium and potassium improves the charge / discharge cycle characteristics. The effect is greater when potassium is M than when sodium is M, and the one exhibiting the best characteristics is one in which potassium is added in a molar fraction of 0.1.

[0024] Figure 4 is the chemical formula Li _x M _y NiO ₂ (provided that
M is at least one of Na and K) wherein the values of x and y in the formula are 0 <x + y ≦ 1.0, the value of y is 0.1, and the ratio of sodium and potassium occupying this is changed. Charge / discharge test (charge / discharge current 100 mA constant current, voltage 3.0 to 3.0
4.5 V) shows the difference in the discharge capacity at the 50th cycle.

As can be seen from FIG. 4, as the mole fraction of potassium increases, the discharge capacity at the 50th cycle increases. Even when sodium and potassium are mixed, the effect of improving the cycle characteristics is observed, but rather, potassium alone is used. Is more effective.

Further, in these active materials, the discharge sustaining voltage is slightly higher than that of LiNiO ₂ , and a slight improvement in high-rate discharge characteristics is recognized, but details thereof are currently under study.

[0027]

As it is apparent from the foregoing description, according to the present invention as a positive electrode active material the chemical formula Li _x M _y NiO ₂ (where, M
Is at least one of Na and K), the values of x and y in the formula satisfy the conditions of 0 <x + y ≦ 1.0 and 0 <y ≦ 0.3, thereby providing excellent cycle characteristics. Thus, a non-aqueous electrolyte secondary battery can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a cylindrical battery according to an embodiment of the present invention.

In Figure 2 Li _x M _y NiO ₂ (where, M is Na, at least one K), illustrates the differences in initial discharge capacity due to the difference in the value of y

[3] Li _x M _y NiO ₂ (where, M is Na, at least one K), the diagram showing the difference in charge-discharge cycle characteristics due to the difference in the value of y

FIG. 4 is a diagram showing the difference in discharge capacity at the 50th charge / discharge cycle due to the difference in the ratio of K and Na to M in Li _x M _0.1 NiO ₂ (where M is at least one of Na and K).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulation packing 4 Electrode group 5 Positive electrode lead 6 Negative electrode lead 7 Insulation ring

Continuation of the front page (72) Inventor Shigeo Kobayashi 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-3-289049 (JP, A) JP-A-5-74451 (JP) U.S. Pat. No. 4,497,726 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/02-4/04 H01M 4/58 H01M 10/40

Claims (1)

(57) [Claims] 1. A general formula Li _x M _y NiO ₂ (where, M is N
a, K), wherein x in the formula
And y are 0 <x + y ≦ 1.0 and 0 <y ≦ 0.
Insert a positive electrode containing an active material that satisfies condition 3 and lithium.
A non-aqueous electrolyte secondary battery comprising a negative electrode containing a pourable and extractable carbon material as an active material, and a non-aqueous electrolyte.