JPH0824043B2 - Manufacturing method of non-aqueous electrolyte secondary battery and its positive electrode active material - 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 electrolyte secondary batteries that use lithium or a lithium alloy as a negative electrode have hitherto been known as Ti, V, Cr,
Layered or tunnel oxides such as Mo and chalcogen compounds are known. 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. For this reason,
Since the crystal lattice of the compound itself simply expands and contracts and the crystal structure is not significantly destroyed, it is suitable as a positive electrode active material for secondary batteries.

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.

MnO ₂ has a rutile type crystal structure and has the above-mentioned tunnel structure. As the battery discharges, lithium ions enter and move into this tunnel, causing a so-called insertion reaction. In this discharge process, the crystal lattice of MnO ₂ expands, but the crystal structure itself is not destroyed. Therefore, the lithium ions that have penetrated into MnO ₂ during the discharge process can easily move within MnO ₂ . Nevertheless, due to charging,
It is difficult to extract lithium ions from MnO ₂ . This is a decrease in electron conductivity of 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, the separation of MnO ₂ particles and conductive agent particles makes it more difficult to release lithium ions during the charging process because Li _X MnO ₂ generated during the discharging process is close to an insulator. Therefore, when MnO ₂ is used in a secondary battery, the charging / discharging capacity is significantly reduced by the charging / discharging cycle and the life is short, so that MnO ₂ is not suitable for a positive electrode active material for a secondary battery.

In order to prevent the above capacity decrease of MnO ₂ during charge / discharge cycles, Li is added to MnO ₂ in advance and heated, and the degree of expansion and contraction of the crystal lattice during charge / discharge is smaller than that of MnO _2. It has been proposed to use LiMn ₂ O ₄ having a positive-type crystal structure as the positive electrode active material, and in particular, LiMn ₂ O ₄ obtained by heating at a low temperature is preferable from the viewpoint of discharge capacity. (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. Alternatively, 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 .

However, when LiMn ₂ O ₄ obtained by such a manufacturing method is used as a positive electrode active material, a battery using lithium or a lithium alloy as a negative electrode is assembled, and a charge / discharge cycle is repeated, lithium is obtained. There was a problem that the 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, MnO ₂ is transferred to β-type structure at such temperature, or Mn ₂ O ₃ is converted into Mn ₂ O ₃ which is significantly inactive in the reaction with Li. 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 charge 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
Electrochemically inactive Li ₂ MnO ₃ deposited with i was formed, while Li ₂ CO ₃ particles and MnO ₂ particles were not in contact MnO ₂
MnO ₂ still remains on the particle surface. That is, Li
_In the reaction of ₂ CO ₃ and MnO _2, a mixture of Li ₂ MnO ₃ and MnO ₂ on the same particle is easily generated. Li ₂ MnO ₃ and MnO ₂ are slightly eluted by a trace amount of water contained in the electrolyte, and thus reach the lithium or lithium alloy negative electrode, and as a result, lithium manganese oxide is formed on the negative electrode surface. Corrosion of the lithium negative electrode shortens the cycle life. Furthermore, MnO _2, as described above, since the volume reduction in the charge-discharge cycle is large, and Li ₂ CO ₃
Even when LiMn ₂ O ₄ obtained by the reaction of MnO ₂ is used, the charge and discharge capacity is still decreased. On the same particle like this
To avoid the formation of LiMn ₂ O ₄ that LiMn ₂ O ₄ and MnO ₂ are mixed, as disclosed in Example 1 of British patent publication GB2196785A, the Li / Mn atomic ratio, LiMn ₂ O ₄ The value given by the composition of i.e.
_{2 It} is necessary to mix CO ₃ and MnO ₂ . The reason for this is not clear, but by adding Li ₂ CO ₃ in excess compared to MnO ₂ , diffusion of Li into MnO ₂ during heating is carried out from the entire surface of the MnO ₂ particles, and LiMn ₂ O ₄ It is thought that the formation of However, it is disadvantageous to use an extra reagent from the viewpoint of material preparation cost, and it is most desirable to prepare the material at or near the amount of the reagent according to the composition formula of the material.

The present invention eliminates such conventional drawbacks, using less Li ₂ MnO ₃ or MnO ₂ mixed, LiMn ₂ O ₄ with a small capacity reduction even after repeated charge and discharge cycles is used for the positive electrode active material. And a highly reliable non-aqueous electrolyte secondary battery, and a method for producing LiMn ₂ O ₄ , which exhibits excellent characteristics as a positive electrode active material for non-aqueous electrolyte secondary batteries. And

Means for Solving the Problems The non-aqueous electrolyte secondary battery of the present invention is characterized by using LiMn ₂ O ₄ having a crystal lattice constant a of 8.22 Å or less for the positive electrode active material. Furthermore, in order to obtain this LiMn ₂ O ₄ , the production method of the present invention uses lithium oxide, lithium hydroxide, or lithium manganese oxide, γ-type MnO ₂ and, if necessary, water. It is characterized by kneading and heating, and further, in order to improve the characteristics, the produced LiMn ₂ O ₄ is washed in an acidic solution phase of PH ₄ or more.

Action When LiMn ₂ O ₄ having a crystal lattice constant a of 8.22Å or less of the present invention is used as a positive electrode active material and lithium ions are allowed to enter and leave the crystal lattice by charge / discharge, an ASTM card (35-78
2) LiMn ₂ O ₄ having a crystal lattice constant a of 8.24762Å
Compared with, the crystal lattice is contracted, that is, the unit cell is smaller, so the degree of expansion and contraction is small. Therefore, the separation of the conductive agent particles such as carbon black and the LiMn ₂ O ₄ particles during the charging / discharging process is small, and the current collection in the electrode plate is maintained well, and the charging / discharging cycle is repeated. However, the decrease in charge / discharge capacity is small.

The above crystal lattice constant a is 8.22Å or less, and LiMn
_In order to obtain LiMn ₂ O _{4 in} which ₂ O ₄ and MnO ₂ are less mixed, lithium oxide and the like, γ-type MnO ₂ and, if necessary, water are kneaded and heated. For example, in the case of LiOH, the melting point of LiOH is remarkably low as 445 ° C. compared with Li ₂ CO _3, before the MnO ₂ is transferred to the hard β-type lithium diffusion, LiOH and MnO ₂ be readily react You can Here, LiOH is dissolved by heating, and further, when a small amount of water contained in MnO ₂ is heated, Mn
By being released from O ₂ and dissolving LiOH, the MnO ₂ particles are covered with most of the surface by LiOH, and the reaction between LiOH and MnO ₂ proceeds uniformly. Therefore, Li ₂ M
LiMn ₂ O ₄ containing less n ₂ O ₄ and MnO ₂ is produced. Li ₂ O and L
Lithium-manganese oxides such as i ₃ MnO ₄ have a high melting point and Mn
O ₂ and hardly react, but they by adding water during kneading with MnO ₂ to dissolve in water things solubility is small, it is possible to perform uniform reaction with MnO _2, Li ₂ MnO
It is possible to obtain LiMn ₂ O _{4 in} which ₃ and MnO ₂ are less mixed. Li
Even in the case of OH, it is possible to carry out a more uniform reaction by adding water during kneading with MnO ₂ .

Here, when MnO ₂ having a γ-type structure is used for MnO ₂ ,
γ-type MnO ₂ has a large tunnel diameter for lithium diffusion,
When reacted with a lithium compound, lithium can diffuse sufficiently to the inside of the MnO ₂ particles, and an excessive amount of lithium is present on the surface of the particles.
Li is not deposited and LiMnO ₃ is hard to be formed. Therefore, LiMn ₂ O ₄ is uniformly formed.

It is not clear why the reaction between the lithium compound and MnO ₂ produces LiMn ₂ O ₄ having a crystal lattice constant a which is smaller than the usual 8.24762 Å, but the reaction between the lithium compound and MnO ₂ is not clear.
In order to proceed the reaction with O ₂ at low temperature, as described above,
During the reaction, Li ₂ Mn with a crystal structure similar to that of LiMn ₂ O ₃ was formed on the particle surface.
It is considered that O ₃ is easily formed and this effect remains even if heating is continued. In fact, when the above reaction is carried out at 430 ° C. or lower, the reaction product produces LiMn ₂ O ₄ , and when heated at a temperature higher than 510 ° C., LiMn ₂ O ₄ having a crystal lattice constant a larger than 8.22 Å is produced. To do.

Furthermore, by washing the formed LiMn ₂ O ₄ in an acidic solution phase, it is possible to remove lithium compounds such as Li ₂ MnO ₃ partially formed on the surface of the LiMn ₂ O ₄ particles and unreacted residual LiOH. Therefore, the lithium or lithium alloy negative electrode is prevented from corroding, so that the cycle life of the battery is extended. For the washing in the acidic solution phase, the pH of the solution phase is preferably 4 or more. When the pH of the solution phase is less than 4, an exchange reaction between Li ⁺ in the LiMn ₂ O ₄ particles and H ₃ O ^{+ in} the solution occurs, so a battery is prepared using LiMn ₂ O ₄ thus obtained. Even if you configure
H ₂ O contained in the LiMn ₂ O ₄ particles by the exchange reaction corrodes the lithium or lithium alloy negative electrode. Therefore, the cycle life of the battery is shortened.

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

Example 1 LiMn ₂ O ₄ of the present invention was produced as follows.

After mixing LiOH ・ H ₂ O 12.066g and γ-type MnO ₂ 50.000g in a ball mill, add H ₂ O 20ml to make a paste and 470 ℃
Heated for 5 hours. Furthermore, this product is crushed and again
After adding 20 ml of H ₂ O to form a paste, the mixture was heated at 470 ° C. The powder X-ray diffraction of this compound was obtained as in FIG.
This compound can be easily identified as LiMn ₂ O ₄ , and Li ₂ Mn
O ₃ and MnO ₂ are not mixed. Li obtained in this way
Since the lattice spacing of the X-ray diffraction index (111) of Mn ₂ O ₄ is 4.731Å and LiMn ₂ O ₄ is a cubic system, the lattice constant a of the crystal is calculated by the following equation. (H, k, l is the surface index, d is the surface spacing of the surface index (hkl)) 8.194Å
Is calculated.

Using this LiMn ₂ O ₄ as a positive electrode active material, a flat battery as shown in FIG. 3 was assembled and a charge / discharge test was conducted. Hereinafter, description will be given with reference to FIG.

LiMn ₂ O ₄ , carbon black which is a conductive agent, and tetraboride ethylene resin powder which is a binder in a weight ratio of 70:20
Mixed at a ratio of 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. For the electrolyte, a mixture of propylene carbonate and dimethoxyethane in an equal volume ratio was added to the electrolyte at a ratio of 1 mol / Li.
It was prepared by dissolving the ClO _4. A polypropylene nonwoven fabric was used for the separator 7. The outer peripheral portions of the battery case 2 and the sealing plate 6 were sealed with a gasket 8. The battery of the present invention thus constructed is designated as A.

Next, as a comparative example, LiMn ₂ O using Li ₂ CO ₃ and MnO ₂ as raw materials
₄ was produced. 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 powder X-ray diffraction of this compound is obtained as shown in FIG. 2, and this compound contains Li ₂ MnO ₃ and MnO ₂ in addition to LiMn ₂ O ₄ .
The LiMn ₂ O ₄ thus obtained was used as the positive electrode active material, and the flat battery described above was similarly constructed. The battery of this comparative example is designated as B.

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

FIG. 4 is a diagram in which the discharge capacities of the battery A of the present invention and the battery B of the comparative example are plotted in each charge / discharge cycle. It can be seen from FIG. 4 that the battery B of the comparative example has a smaller discharge capacity in each cycle and a greater degree of decrease in the discharge capacity in the charge / discharge cycle than the battery A of the present invention. This is because the LiMn ₂ O ₄ used in the battery B of the comparative example contains electrochemically inactive Li ₂ MnO ₃ and thus has a small discharge capacity, and the discharge capacity decreases in the charge / discharge cycle. This is because large MnO ₂ is mixed. Furthermore, the battery B of the comparative example has a short cycle life of about 130 cycles because the mixed Li ₂ MnO ₃ and MnO ₂ are eluted by a small amount of water contained in the electrolytic solution and corrode the lithium negative electrode. is there. As compared with the characteristics of the battery B of the comparative example as described above, it is understood that the battery A of the present invention is excellent in discharge capacity, degree of capacity decrease in each cycle, and cycle life.

Example 2 In the process of obtaining LiMn ₂ O ₄ of the present invention in Example 1, the configuration and charge / discharge test conditions of the flat battery were the same, except that MnO ₂ of various crystal forms was used.

Table 1 shows the discharge capacities at the 10th cycle and the γ-type Mn when LiMn ₂ O ₄ was prepared using MnO ₂ having various crystal forms.
This is a description of the capacity ratio when the discharge capacity of LiMn ₂ O ₄ produced using O ₂ is 100. From Table 1, Li prepared by using α-type or β-type MnO ₂ which has low activity of reaction with Li
It can be seen that Mn ₂ O ₄ has a small discharge capacity. δ type MnO ₂
The low discharge capacity of LiMn ₂ O ₄ prepared by using is because δ-type MnO ₂ is easily activated by β-type with low activity.
It is thought that this is due to the transition to MnO ₂ . From the above, when LiMn ₂ O ₄ is obtained by reacting a lithium compound with MnO ₂ , MnO
_It can be seen that the crystal form of ₂ is particularly excellent in γ type.

Example 3 In the process of obtaining LiMn ₂ O ₄ of the present invention in Example 1, LiOH.H ₂ O
In addition to changing the mixing ratio of MnO ₂ and MnO ₂ ,
Charge and discharge conditions were the same.

Figure 5 plots the discharge capacity of the product at the 10th cycle against the Li / Mn atomic ratio (mixing ratio of LiOH.H ₂ O and MnO ₂ ), and the cycle deterioration rate of the battery against the Li / Mn atomic ratio. FIG. The results of X-ray diffraction analysis of the product at each Li / Mn atomic ratio are also shown. Here, the cycle deterioration rate was calculated by the following equation.

From FIG. 5, when the Li / Mn atomic ratio is less than 3/7, the discharge capacity is large, but the cycle deterioration rate is extremely poor.
This is because MnO ₂ having a large cycle deterioration rate is mixed. Furthermore, from FIG. 5, when the Li / Mn atomic ratio exceeds 4/6, the cycle deterioration rate is small and good, but the discharge capacity is remarkably reduced. From the above, the discharge capacity is large,
The region where the cycle deterioration rate is small is a region where MnO ₂ and Li ₂ MnO ₃ are not mixed, and the Li / Mn atomic ratio is 3/7 to 4/6.
Here, the value 4/6 (= 0.667) is the value for Li ₂ CO ₃ and MnO ₂ .
LiMn ₂ O ₄ having a Li / Mn atomic ratio of 0.7 and no mixture of Li ₂ MnO ₃ and MnO ₂ is observed (see British Patent Publication GB21967854A and Comparative Example in Example 1 of the present application specification). On the other hand, the Li / Mn atomic ratio was as small as 5%, and it was 3/7 (= 0.42).
The value 9) is 14% smaller than the Li / Mn atomic ratio = 0.5 given by the composition of LiMn ₂ O ₄ . That is, the LiMn ₂ O ₄ of the present invention
The use of the manufacturing method of 1 is characterized in that LiMn ₂ O ₄ can be manufactured at a low temperature and a lithium compound / MnO ₂ mixture ratio with a smaller Li / Mn atomic ratio than before.

Example 4 Except that the heating temperature was changed in the process of obtaining LiMn ₂ O ₄ of the present invention in Example 1, the configuration of the flat type battery and the charging / discharging test conditions were the same.

FIG. 6 is a diagram in which the crystal lattice constant a with respect to the heating temperature and the cycle deterioration rate with respect to the heating temperature in LiMn ₂ O ₄ obtained by changing the heating temperature are plotted.
Here, the crystal lattice constant a was calculated from the plane spacing of the X-ray diffraction index (111) using equation (1), and the cycle deterioration rate was calculated using equation (2).

From Fig. 6, the crystal lattice constant a with respect to the heating temperature increases rapidly when the heating temperature exceeds 510 ° C and reaches a constant value of 8.248Å
become. Correspondingly, the cycle deterioration rate also increases significantly. The reason for this is that LiMn ₂ O ₄ obtained at a heating temperature in excess of 510 ° C has a large degree of expansion and contraction of the crystal lattice during the charge / discharge process, and the current is collected by separation from carbon black particles, which are the conductive agent. Because of the defect, the cycle deterioration rate is large. It can be seen from FIG. 6 that the crystal lattice constant a must be 8.22Å or less in order for the cycle deterioration rate to be sufficiently small. On the other hand, in the region where the heating temperature is 430 ° C. or lower, the cycle deterioration rate increases even though the crystal lattice constant a is sufficiently smaller than 8.22Å. this is,
This is because in this temperature range, the reaction between LiOH.H ₂ O and MnO ₂ does not proceed rapidly, and Li ₂ MnO ₃ and MnO ₂ are mixed in addition to LiMn ₂ O ₄ .

As described above, the crystal lattice constant a is 8.22Å or less, and Li ₂ M
In order to obtain LiMn ₂ O _{4 in} which n ₂ O ₄ and MnO ₂ are not mixed, it is desirable to set the heating temperature between 430 ° C and 510 ° C.

Example 5 In the process of obtaining LiMn ₂ O ₄ of the present invention in Example 1, a lithium compound was added to Li ₂ O, LiOH, LiOH.H ₂ O, Li ₃ MnO ₄ , Li ₂ MnO ₃ , LiMn.
Except that at least one kind was selected from O _{2 and} used alone or as a mixture, the flat battery configuration and charge / discharge test conditions were the same.

Table 2 shows various lithium compounds or mixtures and γ type
Using MnO ₂ , the crystal lattice constant a is 8.22Å or less, and Li ₂ MnO
₃ describes the conditions for producing LiMn ₂ O ₄ with a small mixture of MnO ₂ and MnO ₂ , and the charge and discharge cycle life of the battery using the produced LiMn ₂ O ₄ (the discharge capacity is half of the initial capacity). The number of cycles) was described.

From Table 2, when the lithium compound is a lithium oxide or a lithium hydroxide, the mixing ratio of the lithium compound and MnO ₂ is 3/7 to 4/6 in terms of Li / Mn atomic ratio, and the heating temperature range is 430 ° C to
You can see that it is 510 ℃. When the lithium compound contains lithium-manganese oxide, the upper limit of Li / Mn atomic ratio is 3.5 / 6.5, which is slightly lower than that of lithium oxide or hydroxide, and the heating temperature has a lower limit of about 460 ° C. Get higher The reason for this is that lithium-manganese oxide is less likely to release Li than lithium oxide or hydroxide. Furthermore, the cycle life of the battery made using lithium manganese oxide is slightly shorter because the amount of lithium manganese oxide such as Li ₂ MnO ₃ that is not recognized by X-ray diffraction analysis remains. And
It is considered that this is because the trace amount of water contained in the electrolytic solution elutes and corrodes the lithium negative electrode.

In addition, in LiMn ₂ O ₄ obtained under the conditions of Table 2, the full width at half maximum of the diffraction peak of the X-ray diffraction index (311) was less than 1.1 ° in terms of FeKα line, and the publication was GB2196785.
The crystallinity is higher than that of LiMn ₂ O ₄ disclosed in A, it is difficult to elute with water in the electrolytic solution, and therefore, the lithium negative electrode is less corroded, which has the advantage of prolonging the charge / discharge cycle life.

Example 6 In the process of mixing a lithium compound and γ-type MnO ₂ , in the same manner as in Example 1, except that water was not added, LiMn ₂ O ₄ was produced, a flat battery configuration, and a charge / discharge test were performed. It was

In Table 3, the mixing ratio of the lithium compound and γ-type MnO ₂ is 1/2 in terms of Li / Mn atomic ratio, and the heating temperature is 470
° C.

From Table 3, no matter which lithium compound is used,
When H ₂ O is added during kneading with MnO ₂ , the discharge capacity is increased by about 5 to 10% compared to the case where it is not added, and it is particularly remarkable in lithium manganese oxide and lithium oxide. Recognize. The reason for this is that the H ₂ added during kneading
Although lithium has a low solubility due to O, these lithium manganese oxides elute and cover the MnO ₂ particles, so that LiMn ₂ O ₄ is uniformly generated and electrochemically inactive L
This is because i ₂ MnO ₃ is not mixed.

Example 7 Similar to Example 6, various lithium compounds and γ-type MnO ₂
And H ₂ O were kneaded and heated to obtain LiMn ₂ O ₄ . 30.000 g of LiMn ₂ O ₄ thus obtained was added to 400 ml of deionized water,
With stirring, 4NH ₂ SO ₄ solution was added dropwise until the pH in the solution phase settled to about 5. Then pass this acidic LiMn ₂ O ₄ solution,
LiMn ₂ O ₄ was repeatedly washed with ion-exchanged water until the pH of the waste liquid after washing became 6 to 7. The configuration of the battery and the charge / discharge test were performed in the same manner as in Example 1.

Table 4 shows the discharge capacities of LiMn ₂ O ₄ obtained from each lithium compound at the 10th cycle before and after the acidic solution treatment. From this, LiMn ₂ O treated with acidic solution
_4, the discharge capacity compared to LiMn ₂ O ₄ before processing is increasing,
It is a constant value of about 5.7mAh. This is because in LiMn ₂ O ₄ obtained by heating a lithium compound and MnO ₂ , a small amount of a lithium compound such as Li ₂ MnO ₂₃ and LiOH, which cannot be recognized by X-ray diffraction analysis, remains and This is because it is removed by the processing. Although not shown in Table 4, since the LiMn ₂ O ₄ was treated with an acid solution is not residual Li ₂ MnO _3, in general, LiMn ₂ O cycle life of the battery is not processed
_It had the effect of being longer than ₄ .

Figure 7 shows L using LiOH · H ₂ O as the lithium compound.
FIG. 4 is a diagram in which the cycle life of the battery and the amount of water in the lithium-manganese oxide obtained by the treatment are plotted against the pH in the acidic solution phase in which iMn ₂ O ₄ is treated. Here, the reason why LiMn ₂ O ₄ after being treated with an acidic solution is described as lithium-manganese oxide is that it was treated in an acidic solution phase having a low pH.
This is because LiMn ₂ O ₄ has Li released from inside the LiMn ₂ O ₄ particles and cannot be represented by a simple composition formula.

From FIG. 7, it can be seen that the cycle life of the battery is short when the pH in the acidic solution phase is less than 4. This is because, as is clear from FIG. 7, when the pH is less than 4, the amount of water contained in the obtained titanium / manganese oxide increases rapidly, and this water corrodes the lithium negative electrode. From the above, the pH in the acidic solution phase for treating LiMn ₂ O ₄ must be 4 or more.

In addition, in FIG. 7, LiOH.H ₂ O is used as the lithium compound.
Although LiMn ₂ O ₄ using is described, similar results were obtained for LiMn ₂ O ₄ obtained using other lithium compounds. Further, although H ₂ SO ₄ was used as the acid in this example, the same effect can be obtained by using other acids such as HCl, H ₂ NO ₃ , CH ₃ COOH and the like.

EFFECTS OF THE INVENTION As described above, since the non-aqueous electrolyte secondary battery of the present invention uses LiMn ₂ O ₄ having a crystal lattice constant a of 8.22Å or less as the positive electrode active material, it has a small capacity decrease during charge / discharge cycles and is reliable. A non-aqueous electrolyte secondary battery having high properties is obtained. Further, by the process of the LiMn ₂ O ₄ of the present invention, to obtain a Li ₂ MnO ₃ and LiMn ₂ O ₄ there is little MnO _2, is suppressed corrosion of the lithium negative electrode, LiMn ₂ O cycle life of the battery is prolonged You get ₄ .

[Brief description of drawings]

FIG. 1 shows the positive electrode active material Li in one embodiment of the present invention.
An X-ray diffraction diagram of Mn ₂ O ₄ , FIG. 2 is an X-ray diffraction diagram of LiMn ₂ O ₄ mixed with Li ₂ MnO ₃ and MnO ₂ which are positive electrode active materials in a comparative example, and FIG. Sectional views of the flat type batteries used in Examples and Comparative Examples, FIG. 4 is a diagram in which the discharge capacity in each cycle of Battery A of the present invention and Battery B of Comparative Example is plotted, and FIG. 5 is Li / Mn atom. Fig. 6 is a graph plotting the discharge capacity and cycle deterioration rate against the ratio (lithium compound / MnO ₂ mixture ratio). Fig. 6 shows the crystal lattice constant a and cycle of the formed LiMn ₂ O ₄ versus the heating temperature of the lithium compound / MnO ₂ mixture. FIG. 7 is a diagram in which the deterioration rate is plotted, and FIG. 7 is a diagram in which the cycle life of the battery and the amount of water in the lithium-manganese oxide are plotted against the pH in the LiMn ₂ O ₄ treatment solution phase. 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 (4)

[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, the positive electrode having a crystal lattice constant a of 8.22.
Å A non-aqueous electrolyte secondary battery comprising the following LiMn ₂ O ₄ as an active material. 2. At least one lithium compound selected from the group consisting of Li ₂ O, LiOH, LaOH.H ₂ O, Li ₃ MnO ₄ , Li ₂ MnO ₃ and LiMnO ₂ and γ-type MnO ₂ . Li / Mn atomic ratio 3 / 7-4 /
LiMn ₂ O ₄ having a crystal lattice constant a of 8.22Å or less by mixing at a ratio of 6 and heating at a temperature of 430 ° C to 510 ° C.
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises: 3. The lithium compound and γ-type MnO ₄ are further kneaded with water and heated.
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the item. 4. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2 or 3, further comprising a step of treating the produced LiMn ₂ O ₄ in an acidic solution phase having a pH of 4 or more. Law.