JPH0821382B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to improvement of a positive electrode thereof.

2. Description of the Related Art Conventional positive electrode active materials for non-aqueous electrolysis secondary batteries using lithium or lithium alloys as negative electrodes have so far been classified as Ti, V, Cr, Mo.
There are known oxides and chalcogen compounds having a layered structure or a tunnel structure. In the compounds having these structures, lithium ions move in and out of the compound layer or tunnel as the battery is charged and discharged. Therefore, the crystal lattice of the compound itself simply expands and contracts, and the crystal structure is not significantly destroyed. Therefore, the compound is suitable for a positive electrode active material for a secondary battery.

By the way, MnO ₂ is applied to a non-aqueous electrolyte primary battery as a positive electrode active material having a high voltage and a large discharge capacity, that is, a high energy density, and is widely used as a power source for small electronic devices. However, MnO ₂ is not suitable for a positive electrode active material for a secondary battery because it has a rutile type crystal structure and has the above-mentioned tunnel structure, and the capacity is significantly reduced during charge / discharge cycles. This is because the decrease in electronic conductivity of the MnO ₂ particles themselves due to the discharge, a current collecting failure due to separation of the conductive material particles ₂ such as particles of carbon black MnO due to shrinkage of the MnO ₂ particles during charging. In particular, Mn
O ₂ particles and conductive agent particles are separated by Li _X M generated in the discharge process.
Since nO ₂ is close to an insulator, it becomes more difficult to release lithium ions from MnO ₂ particles during the charging process.

In order to prevent the capacity decrease of MnO _{2 in} the charge / discharge cycle as described above, Li is added to MnO ₂ in advance and heated, and the degree of expansion and contraction of the crystal lattice during the charge / discharge process is smaller than that of MnO ₂ . It has been proposed to use LiMn ₂ O ₄ having a spinel type crystal structure as a positive electrode active material, and in particular, from the viewpoint of discharge capacity, LiMn ₂ O ₄ obtained by heating at low temperature is said to be preferable. (UK publication GB2196785A). The manufacturing method of LiMn ₂ O ₄ at this low temperature is roughly as follows. Li ₂ CO ₃
And MnO ₂ are mixed and heated in a temperature range of 430 ° C. to 520 ° C., or a mixture of LiI and MnO ₂ is heated at 300 ° C. and then washed with an organic solvent to obtain LiMn ₂ O ₄ . Here, if the heating temperature is further increased, it becomes highly crystalline LiMn ₂ O ₄ , but since this highly crystalline LiMn ₂ O ₄ has a discharge capacity that is extremely small, it is not suitable as a positive electrode active material for batteries. Has been done.

However, using LiMn ₂ O ₄ obtained by such a manufacturing method at a low temperature up to about 500 ° C. as a positive electrode active material, a battery using lithium or a lithium alloy as a negative electrode is assembled and charged. When the discharge cycle was repeated, there was a problem that the lithium negative electrode was significantly corroded and the cycle life was short. This is for the following reason.

When Li ₂ CO ₃ and MnO ₂ are mixed and heated to obtain LiMn ₂ O ₄ , L
Since the melting point of i ₂ CO ₃ is 618 ° C., it is necessary to heat the Li ₂ CO ₃ to near this melting point so that Li ₂ CO ₃ can sufficiently react with MnO ₂ . However, at such temperatures, MnO ₂ is transformed into a β-type structure, or the reaction with Li is changed to Mn ₂ O _3, which is significantly inactive. β-type MnO ₂ has a tunnel structure in which Li can diffuse into MnO ₂ , but Li cannot be sufficiently incorporated into MnO ₂ . This can be seen from the fact that the discharge capacity of the non-aqueous electrolyte primary battery using β-type MnO ₂ as the positive electrode active material is extremely small. Therefore, Li ₂ CO ₃ and Mn
When preparing LiMn ₂ O ₄ from O ₂ , excess L on the surface of MnO ₂ particles
While i is is deposited electrochemically inactive Li ₂ MoO ₃ is formed, Li ₂ CO ₃ particles and MnO ₂ particles MnO ₂ particles on the surface which has not been in contact still remains as MnO _2. That is, Li ₂ C
In the reaction of O ₃ and MnO _2, a mixture of Li ₂ MnO ₃ and MnO ₂ on the same particle is easily generated. Since Li ₂ MnO ₃ and MnO ₂ are slightly eluted from the trace amount of water contained in the electrolyte, they reach the lithium or lithium alloy negative electrode, and as a result, lithium manganese oxide is formed on the negative electrode surface.
Since the lithium negative electrode is corroded, the cycle life is shortened.

In order to produce LiMn ₂ O _{4 in} which Li ₂ MnO ₃ and MnO ₂ do not coexist as described above, the heating temperature may be raised to 800 ° C to 900 ° C. However, in this case, the charge / discharge capacity becomes extremely small, and it is not suitable as a positive electrode active material for batteries.

The present invention eliminates such conventional drawbacks, there is no mixture of Li ₂ MnO ₃ and MnO ₂ , and there is no corrosion of lithium or lithium negative electrode, so that the charge / discharge cycle life is extended and the discharge capacity is further increased. An object of the present invention is to provide a highly reliable non-aqueous electrolyte secondary battery by using a large LiMn ₂ O ₄ derivative as a positive electrode active material.

Means for Solving the Problems The non-aqueous electrolyte secondary battery of the present invention is a LiMn ₂ O ₄ derivative represented by the following formula in the positive electrode active material, and the elements A and B are LiMn ₂ O ₄ LiM in the crystal, respectively. It is characterized by using a derivative in which Mn sites are substituted with Li and Mn atoms.

(Li _1-Y・ A _Y ) _X・ (Mn _1-Z・ B _Z ) ₂・ O ₄ where A is an element selected from Na, K, Cu, Ag, Zn B is V, Cr, Element selected from Fe, Co, Ni 1.1 ≧ X ≧ 0.9 0.2 ≧ Y ≧ 0.0 0.2 ≧ Z ≧ 0.0 (Y and Z do not become 0.0 at the same time when X = 1.0) Action LiMn ₂ O ₄ is cubic Since it is a system, and Li is located at the center of a tetrahedron composed of four 0s, to escape from this tetrahedron and diffuse to the next frontal body, pass through a triangle ring of three 0s. It requires significant activation energy. In particular, LiMn ₂ O obtained by heating at high temperature
_{In 4} , the tendency is remarkable, and even if an attempt is made to insert more lithium ions in the discharging process, new lithium ions do not enter because Li, which is already located in the tetrahedron, is difficult to move. That is, the discharge capacity is reduced.

The present invention, by adjusting the amount of Li LiMn ₂ O _4, to facilitate the diffusion of Li in in the LiMn ₂ O ₄ increases the empty tetrahedral. Further, a strained spinel is produced by substituting a part of Li or a part of Mn with another element, and distorts the tetrahedron of 0 to facilitate the diffusion of Li. Therefore, such a LiMn ₂ O ₄ derivative has a sufficiently large discharge capacity even if it is obtained by heating at a high temperature. Then, since the LiMn ₂ O ₄ derivative in which Li ₂ MnO ₃ or MnO ₂ is not mixed can be obtained by heating at a high temperature to produce, a non-aqueous electrolyte secondary battery having a long charge / discharge cycle life can be configured.

Examples Hereinafter, examples of the present invention will be described.

Example 1 As an example of the present invention, Li _1.1 Mn ₂ O ₄ was produced as follows.

After mixing 13.21 g of Li ₂ CO _{3 and} 50.000 g of Mn ₃ O ₄ with a ball mill, the mixture was heated in an air atmosphere at 850 ° C. for 6 hours. further,
The product was ground and heated again at 850 ° C. for 18 hours to give a powder.

Using this Li _1.1 Mn ₂ O ₄ as a positive electrode active material, a flat battery was assembled as shown in FIG. 2 and a charge / discharge test was conducted. Less than,
A description will be given based on FIG.

Li _1.1 Mn ₂ O ₄ , carbon black as a conductive agent, and tetrafluoroethylene resin powder as a binder in a weight ratio of 70:20
Mixed at a ratio of 10 to 10. 50 mg of this mixture was molded into a battery case 2 in which a positive electrode current collector 1 made of titanium expanded metal was spot-welded and pressure-bonded to obtain a positive electrode 3. The diameter of the positive electrode plate is 14.3 mm. A lithium sheet having a thickness of 0.35 mm was used as the negative electrode 4, and the negative electrode current collector 5 made of stainless mesh was spot-welded and pressure-bonded to the sealing plate 6. The electrolyte solution was a mixture of propylene carbonate and dimethoxyethane in equal volume ratio, and 1 mol / l Li
It was prepared by dissolving the ClO _4. A polypropylene nonwoven fabric was used for the separator 7. The battery of the present invention thus constructed is designated as A.

Next, as a comparative example, Li ₂ CO ₃ and Mn ₃ O ₄ have a Li / Mn atomic ratio of 1 /
2 except that the LiM was heated in the same manner as Li _1.1 Mn ₂ O ₄ above.
n ₂ O ₄ was prepared and a similar flat battery was constructed. This battery is designated as B.

Further, as a comparative example, LiMn using Li ₂ CO ₃ and MnO ₂ as raw materials
₂ O ₄ was prepared. Li ₂ CO _{3 (} 10.624 g) and γ-type MnO _{2 (} 50.000 g) were mixed in a ball mill and then heated at 470 ° C. for 5 hours. The LiMn ₂ O ₄ thus obtained was used as the positive electrode active material, and the flat battery described above was similarly constructed. This battery is designated as C.

The battery A of the present invention and the battery of the comparative example configured as described above
In B and C, a charge / discharge test was performed under the conditions of a constant current of 0.8 mA, a discharge lower limit voltage of 2.0 V, and a charge upper limit voltage of 3.8 V.

FIG. 1 is a diagram in which the discharge capacities of the battery A of the present invention and the batteries B and C of the comparative example in each charge / discharge cycle are plotted. From FIG. 1, it can be seen that the battery B of the comparative example has an extremely small discharge capacity of less than half that of the battery A of the present invention and is not suitable as a positive electrode active material of the battery. The reason for this is significantly higher crystallinity of LiMn ₂ O ₄ used in the battery B of Comparative Example, LiMn ₂
This is because it is difficult to diffuse Li in O ₄ . Further, as shown in FIG. 1, the battery C of the comparative example has the same discharge capacity as the battery A of the present invention, but the cycle life (the number of cycles when the discharge capacity becomes half of the initial capacity) is about. As short as 130 cycles. This is because Li ₂ MnO ₃ and MnO ₂ are mixed as impurities in LiMn ₂ O ₄ used for the battery C of the comparative example, and these are eluted by a trace amount of water in the electrolytic solution and corrode the lithium negative electrode. is there. From the above, it is understood that the battery A of the present invention is excellent in both discharge capacity and cycle life.

Example 2 The LiMn ₂ O ₄ derivative shown in Table 1 was prepared in the same manner as Li _1.1 Mn ₂ O ₄ was prepared as an example of the present invention in Example 1.
Here, the elements Na and K are as hydroxides, and the elements cu, Ag, and
Zn was used as an oxide in predetermined amounts in Li ₂ CO ₃ and Mn ₃ O, respectively.
Mix with ₄ and heat.

The configuration and charge / discharge test of the flat battery were performed in the same manner as in Example 1.

Table 1 shows the discharge capacity and cycle life at the 10th cycle of the flat battery using each LiMn ₂ O ₄ derivative as the positive electrode active material. From Table 1, it can be seen that the LiMn ₂ O ₄ derivative of the present invention is excellent in both discharge capacity and cycle life.

In addition, when the LiMn ₂ O ₄ derivative of this example is represented by the following formula, which element is improved in both the (Li _1-Y · A _Y ) _X Mn ₂ O ₄ discharge capacity and the cycle life is Also in A, the range was approximately 1.1 ≦ X ≦ 0.9 0.2 ≧ Y ≧ 0.0 (Y is not 0 when X = 1.0).

Example 3 The LiMn ₂ O ₄ derivatives shown in Table 2 were prepared in the same manner as Li _1.1 Mn ₂ O ₄ was prepared as an example of the present invention in Example 1. Here, the elements V, Cr, Fe, C, and Ni were each mixed as a oxide in a predetermined amount with Li ₂ Co ₃ and Mn ₃ O ₄ and heated.

The configuration and charge / discharge test of the flat battery were performed in the same manner as in Example 1.

Table 2 shows the discharge capacity at 10th cycle and the cycle life of a flat battery using each LiMn ₂ O ₄ derivative as a positive electrode active material. From Table 2, it can be seen that the LiMn ₂ O ₄ derivative of the present invention exhibits excellent characteristics in both discharge capacity and cycle life.

When the LiMn ₂ O ₄ derivative of this example is represented by the following formula, it is determined by which element B that the characteristics are improved in both Li (Mn _1-Z · B _Z ) ₂ O ₄ discharge capacity and cycle life. In general, the range was 0.2 ≧ Z> 0.0.

As described above, in Examples 2 and 3, by substituting a part of Li or Mn in LiMn ₂ O ₄ with another element, LiMn ₂ O ₄ derivatives having excellent discharge capacity and cycle life can be obtained. The reason why the same specific range is achieved regardless of which element is used is that the Li of the present invention is used.
All of the Mn ₂ O ₄ derivatives are considered to be substitution elements and solid solutions (states in which the sites of Li and Mn metal elements in the LiMn ₂ O ₄ crystal structure are randomly replaced by the polymetallic elements added) and are outside this specific range. Then, it is considered that a double oxide is formed and the characteristics are deteriorated.

EFFECTS OF THE INVENTION As described above, according to the present invention, since a LiMn ₂ O ₄ derivative is used as a positive electrode active material, a highly reliable non-aqueous electrolytic secondary battery having excellent discharge capacity and cycle life is obtained. be able to.

[Brief description of drawings]

FIG. 1 is a diagram in which the discharge capacities in each cycle of the battery A of the present invention and the batteries B and C of the comparative example are plotted, and FIG. 2 is a sectional view of the flat type battery used in the examples and comparative examples of the present invention. Is. 1 ... Positive electrode current collector, 2 ... Battery case, 3 ... Positive electrode, 4
…… Negative electrode, 5 …… Negative electrode current collector, 6 …… Seal plate, 7 …… Separator, 8 …… Gasket.

Claims (1)

[Claims] 1. A battery comprising a positive electrode, a lithium ion conductive non-aqueous electrolyte, and a negative electrode containing lithium as an active material, wherein the positive electrode is a Li represented by the following composition formula.
It is a derivative of Mn ₂ O ₄ and the elements A and B are LiMn ₂ O ₄
A non-aqueous electrolyte secondary battery characterized in that a derivative substituting Li, Mn atoms at Li, Mn sites in a crystal is used as an active material. (Li _1-Y・ A _Y ) _X・ (Mn _1-Z・ B _Z ) ₂・ O ₄ where A is an element selected from Na, K, Cu, Ag, Zn B is V, Cr, Element selected from Fe, Co, Ni 1.1 ≧ X ≧ 0.9 0.2 ≧ Y ≧ 0.0 0.2 ≧ Z ≧ 0.0 (when X = 1.0, Y and Z do not become 0.0 at the same time)