JPH02139860A - Non-aqueous electrolyte secondary battery and manufacture of positive electrode active substance therefor - Google Patents

Abstract

PURPOSE:To provide a highly reliable non-aqueous electrolyte secondary battery which has lesser decrease in the capacity at charge/discharge cycles by using LiMn2O4 having a specific grating constant as positive electrode active substance. CONSTITUTION:Li oxide, Li hydroxide or Li.Mn oxide, and gamma-type MnO2 are mixed together by a certain atomic ratio, with water added thereto if necessary followed by kneading, and the result is heated at a certain temp. to produce LiMn2O4 having a crystal grating constant (a) of no more than 8.22Angstrom , and this product is used to positive electrode active substance. If therein Li ions are allowed to come in and go out of the grating with charging/discharging, the degree of expansion and contraction is lesser because of small grating constant. Therefore, segregation of electroconductive material particles such as carbon black from LiMn2O4 particles is small under the charge/discharge process, and current collection within electrode plate is kept good, so that this is free from drop of the charge/discharge capacity with repetition of the charge/discharge. Therein also inclusions of Li2MnO3 or MnO2 are less, and corrosion of Li neg. electrode is inhibited, so that the cycle life will also be prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and particularly to improvements in its positive electrode.

Conventional technology As for the positive electrode active materials of non-aqueous electrolyte secondary batteries using lithium or lithium alloy as the negative electrode, Ti, V,
Oxides and chalcogen compounds having layered or tunnel structures such as Or and Mo are known. In compounds having these structures, lithium ions move in and out of the layer or tunnel of the compound 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, making it suitable as a positive electrode active material for secondary batteries.

By the way, MnO2 is applied to non-aqueous electrolyte secondary batteries as a positive electrode active material having high voltage, large discharge capacity, that is, high energy density, and is widely used including /J's type power supplies for electronic devices. .

MnO2 has a rutile 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 MnO2 expands, but the crystal structure itself is not destroyed. Therefore, the lithium ions that entered MnO2 during the discharge process
2 can be easily moved around. in spite of,
During charging, it is difficult to extract lithium ions from MnO2. This is due to a decrease in the electronic conductivity of the MnO□ particles themselves due to discharge, and a current collection failure due to separation of the MnO2 particles and conductive agent particles such as carbon black due to shrinkage of the MnO2 particles during charging. In particular, the separation of MnO□ particles and conductive agent particles is achieved by
Since nO2 is close to an insulator, it becomes more difficult to release lithium ions during the charging process.

Therefore, when MnO□ is used in a secondary battery, the charge/discharge capacity decreases significantly during charge/discharge cycles and the life is short, so MnO2 is not suitable as a positive electrode active material for a secondary battery.

In order to prevent the capacity reduction during the charge/discharge cycle of MnO2 as described above, Li is added to MnO2 in advance and heated, so that the degree of expansion and contraction of the crystal lattice during the charge/discharge process becomes Mn0.
LiM with a spinel crystal structure that is smaller than z
It has been proposed to use n2O4 as the active material of the positive electrode, and in particular, LiMn2O4 obtained by heating at a low temperature is said to be preferable from the viewpoint of high capacity (British Publication No. GB2196785A). .

The method for producing LiMn,.04 at this low temperature is generally as follows6. Mix Li2GO, and MnO, and heat at 430℃~
LiMn2O4 is obtained by heating in a temperature range of 620°C or by heating a mixture of Li and MnO2 at 300°C and washing with an organic solvent.

Problems to be Solved by the Invention However, LiMn2O4 obtained by such a production method
When assembling a battery using lithium as the positive electrode active material and lithium or lithium alloy as the negative electrode and repeating the charging/discharging cycle several times, there was a problem that the lithium negative electrode was severely corroded and the cycle life was short. .This is due to the following reason.

Li 2Go and MnO□ are mixed and heated to form Li
When obtaining Mn2O4, the melting point of Li2Go is 618
℃, it is necessary to heat it to around this melting point in order to bring Li2GO into a state where it can sufficiently react with MnO2. However, at such temperatures, MnO2 transforms into a β-type structure or changes into Mn2O3, which is extremely inactive in reacting with Li. In β-type MnO2, Ll is M
Although it has a tunnel structure that allows diffusion into nO2, Li cannot be sufficiently incorporated into MnO2. this is,
This can be seen from the fact that the discharge capacity of non-aqueous electrolyte secondary batteries using β-type MnO□ as the positive electrode active material is extremely small. Therefore, from Li2Co3 and MnO2 to LiMn2
When O4 is prepared, excessive Li is deposited on the surface of MnO2 particles and becomes electrochemically inactive.On the other hand, on the surface of MnO□ particles where Li2CO3 particles and MnO2 particles were not in contact, MnO2 remains.
remains as. That is, 1. ri,, Co5 and MnO2
In the reaction, L i2 M n O5 and M
A mixture of nO2 is likely to be generated. Li2Mn0
, and MnO2 are slightly eluted by trace amounts of water contained in the electrolyte, and reach the lithium or lithium alloy negative electrode. As a result, lithium manganese oxide is formed on the negative electrode surface, causing corrosion of the lithium negative electrode. This shortens the cycle life. Furthermore, Mn
As described above, since O2 has a large capacity decrease during charge/discharge cycles, even if LiMn 2O obtained by the reaction of Li2Go and MnO2 is used, a decrease in charge/discharge capacity is still observed. Li on the same particle like this
In order to avoid the generation of LiMn2O4 in which 2Mn0 and MnO2 are mixed, British Publication Publication GB219678
As disclosed in Example 1 of 5A, the Li/Mn atomic ratio is set to a value given by the composition of LiMn2O4, that is, a ratio of 0.7, which is sufficiently larger than 0.6.
It is necessary to mix o5 and MnO□. The reason for this is not clear, but by adding Li2Go in excess compared to MnO2, the diffusion of Li into MnO2 during heating is suppressed.
LiMn2O4 must be applied from the entire O2 particle surface.
This is thought to facilitate the formation of However, from the viewpoint of the cost of material preparation, it is disadvantageous to use extra reagents, and it is most desirable to prepare the material with an amount of reagent that conforms to the compositional formula of the material or around it.

The present invention eliminates these conventional drawbacks.
LiMn2O contains less Li, MnO, and MnO2, and its capacity decreases less even after repeated charge/discharge cycles.
By using 4 as a positive electrode active material, a highly reliable non-aqueous electrolyte secondary battery can be provided, and furthermore, as shown in FIG.
The present invention also aims to provide a method for producing O4.

Means for Solving the Problems The nonaqueous electrolyte secondary battery of the present invention is characterized in that LiMn2O4 having a crystal lattice constant 4 of 8.22 Å or less is used as a positive electrode active material. Furthermore, in order to obtain this LiMn2O4, the manufacturing method of the present invention uses lithium oxide.

It is characterized by kneading lithium hydroxide or lithium manganese oxide, γ-type MnO2, and, if necessary, water and heating it, and further improving the characteristics,
It is characterized in that the produced LiMn 2 , O, is washed in an acidic solution phase with a pH of 4 or more.

Effect The LiMn crystal lattice constant a of the present invention is 8.22 Å or less.
When 2O4 is used as the positive electrode active material and lithium ions are moved in and out of the crystal lattice by charging and discharging, the crystal lattice constant written on the MuSTM card (rats-782) is 8.24762 LiMn,,O.

Compared to , the crystal lattice is contracted, that is, the unit cell is smaller, so the degree of expansion and contraction is small.

Therefore, during the charging and discharging process, the separation between conductive agent particles such as carbon black and LiMn2O4 particles is small, and current collection within the electrode plate is maintained well. However, the decrease in charge/discharge capacity is small.

The above crystal lattice constant a is 8.22 Å or less, and L
i2Mn0. LiMn2O4 with less mixture of MnO2 and MnO2
In order to obtain this, lithium oxide, etc., γ-type MnO2, and, if necessary, water are kneaded and heated. For example, LiOH
In the case of , the melting point of LiOH(7) becomes the ratio of Li2C06 to 44
At an extremely low temperature of 5° C.9, LiOH and MnO2 can easily react before MnO2 transforms into the β type, where lithium diffusion is difficult. Here, LiOH is dissolved by heating, and furthermore, a small amount of water contained in MnO□ is released from MnO2 during heating, and by melting LiOH, most of the surface of MnO□ particles are covered with LiOH. 9, LiOH and MnO
Reaction 2 proceeds uniformly.

Therefore, LiMn2O4 containing less Li2Mn05 and MnO2 is generated. Li2O and Li5Mn
Lithium manganese oxides such as 04 have a high melting point (Mn
Although they are difficult to react with O2, they dissolve in water, although their solubility is low, so by adding water when kneading with MnO□, the reaction with MnO2 can be carried out uniformly, and there is less mixing of Li2MnO3 and MnO. Li1An2
Even in the case of LiOH, which can obtain O4, MnO2
It is possible to carry out a more uniform reaction by adding water when kneading with.

Here, when MnO2 having a γ-type structure is used, r-type MnO2 has a large tunnel diameter for lithium diffusion, and when it reacts with a lithium compound, lithium can sufficiently diffuse into the inside of the MnO2 particles. is possible,
Excess Li is not deposited on the particle surface, and Li2Mn0. is difficult to form. Therefore, uniform LiMn2O4 is produced.

In the reaction between the lithium compound and MnO□ as described above,
Although it is not clear why LiMn2O4, which has a crystal lattice constant a of 8.24762 which is more contracted than the normal one, is produced, it is because the reaction between the lithium compound and MnO2 proceeds at a low temperature.
As mentioned above, during the reaction, LiMn is deposited on the particle surface.
This is thought to be because Li 2Mn05, which has a similar crystal structure to 2O, is likely to be 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 is Li2Mn0.

is generated, and when further heated at a temperature exceeding 610°C, L I M with a crystal lattice constant a larger than 8.22
n2O4 is produced.

Furthermore, by washing the generated LiMn2O4 in an acidic solution phase, 5. Li2Mn0. partially formed on the surface of LiMn2O4 particles. It is possible to remove unreacted residual lithium compounds such as LiOH and prevent corrosion of the lithium or lithium alloy negative electrode, thereby extending the cycle life of the battery. In this washing in the acidic solution phase, it is preferable that the pH of the solution phase is 4 or more. solution phase p
If H is less than 4, an exchange reaction between the atoms in the LiMn2O4 particles and H and O in the solution will occur, so even if a battery is constructed using the LiMn2O4 obtained in this way, the exchange reaction will cause LiMn,... H2O that has entered the 04 particles corrodes the lithium or lithium alloy negative electrode. Therefore, the cycle life of the battery is shortened.

Example Examples of the present invention will be described below.

Example 1 The L-engineered Mn2O4 of the present invention was produced as follows.

LiOH, H2O12,066f and γ type M n O2s
After mixing o, o o o y with ball mirte, H2
O2Oyll was added to form a paste, and the mixture was heated at 470°C for 6 hours. Furthermore, this product is ground and again H,,0
After adding 2 Om/ to form a paste, it was heated at 470°C. Powder X-ray diffraction of this compound was obtained as shown in Figure 1,
This compound can be easily identified as LiMn2O4, and no mixture of Li2MnO3 or MnO□ is observed. The lattice spacing of the X, W diffraction index (111) of LiMn 2O obtained in this way is 4.731 people! ], LiM
Since n, O, are cubic system, the crystal lattice constant a
is calculated as follows: a=d, 4V12 (1) (h, g is the surface index, d is the surface spacing of the surface index (hl)) 8.194 people.

This LiMn2O. A flat battery as shown in FIG. 3 was assembled using the above as a positive electrode active material, and a charge/discharge test was conducted. This will be explained below based on FIG.

The weight ratio of LiMn2O4, carbon black as a conductive agent, and tetrafluoroethylene resin powder as a binder was 7.
They were mixed in a ratio of 10 to 20. This mixture 60q was molded and crimped into a battery case 2 to which a positive electrode current collector 1 made of titanium extracted band metal was spot welded to form a positive electrode 3. The diameter of the positive electrode plate is 14.3 mm. A lithium sheet with a thickness of 0.36 mm was used as the negative electrode 4, and a negative electrode current collector 6 made of stainless steel mesh was pressure-bonded to a sealing plate 6 spot-welded. The electrolytic solution used was a mixture of propylene carbonate and dimethoxyethane in equal volumes and LiCdO4 dissolved therein at a ratio of 1 mol/l. Moreover, a polypropylene nonwoven fabric was used for the separator 7. Further, the outer peripheries of the battery case 2 and the sealing plate 6 were sealed with a gasket 8. The battery of the present invention constructed in this way is referred to as A.

Next, as a comparative example, LiMn 2 O 4 was produced using Li 2 G O 5 and MnO 2 as raw materials. Li2Go510
．． 624f and γ-type MnO260,00Of were mixed in a ball mill and then heated at 470° C. for 6 hours. Powder X-ray diffraction of this compound was obtained as shown in Figure 2, and this compound was
In addition to LiMn2O4, Li2MnO3 and MnO2 are mixed. A flat battery described above was constructed in the same manner using LiMn 2 O 4 thus obtained as a positive electrode active material. The battery of this comparative example is designated as B.

The battery of the present invention configured as described above and the battery B of the comparative example
, a constant current of 0.8 mA, a lower discharge limit voltage of 2. O.V.
A charging/discharging test was conducted under the conditions of a charging upper limit of 7H pressure of 3.8V.

FIG. 4 is a diagram plotting the discharge capacities of Battery A of the present invention and Battery B of Comparative Example at each charge/discharge cycle. From FIG. 4, it can be seen that in the battery B of the comparative example, compared to the battery of the present invention,
It can be seen that the discharge capacity in each cycle is small, and the degree of decrease in discharge capacity in each charge/discharge cycle is also large. this is,
In the LiMn2O4 used in Comparative Example Battery B, Li2Mn0. This is because the discharge capacity decreases due to the presence of MnO7, which reduces the discharge capacity to a large extent during charge/discharge cycles. Furthermore, in battery B of the comparative example, the cycle life is short at about 130 cycles because Li2Mn0. , MnO2
This is because the small amount of water contained in the electrolyte dissolves out and corrodes the lithium negative electrode. Compared to the characteristics of Comparative Example Battery B as described above, the battery of the present invention has the following characteristics: discharge capacity and degree of capacity decrease in each cycle.

It can be seen that both cycle lives are excellent.

Example 2 In the process of obtaining LiMn2O4 of the present invention in Example 1, MnO2 of various crystal forms were used, but the groove bottom of the flat battery and the charging/discharging test conditions were the same.

(Left below) Table 1 shows the results of LiMn using various crystal forms of MnO2.
Discharge capacity at the 1st cycle when 2O4 was prepared, and LiMn 2O4 prepared using γ-type MnO2
The capacity ratio is shown when the discharge capacity of 100 is taken as 100. From Table 1, it can be seen that LiMn 2 O 4 produced using α-type or β-type MnO 2 having low reaction activity with Li has a small discharge capacity. The reason why LiMn2O4 produced by iR using δ-type MnO2 has a small discharge capacity is considered to be that δ-type MnO2 easily transforms into β-type MnO2 with low activity upon heating. From the above, it is possible to react LiM compound and MnO2 to create LiM
It can be seen that when obtaining n2O4, the γ type crystal form of MnO□ is particularly excellent.

Example 3 In the process of obtaining LiMn2O4 of the present invention in Example 1, Li
Except for changing the mixing ratio of OH-H2O and MnO2, the configuration of the flat battery and the charging/discharging conditions were the same.

Figure 6 shows the Li/Mn atomic ratio (LiOH-H2O and Mn
FIG. 3 is a graph plotting the discharge capacity of the product at the 10th cycle (mixing ratio of O□) and the cycle deterioration rate of the battery versus the Li/Mn atomic ratio. Also, each Li/M
The results of X-ray diffraction analysis of the product in n atomic ratio are also shown.

Here, the cycle deterioration rate was calculated using the following formula.

Cycle deterioration rate = 10th cycle discharge capacity 10th cycle discharge capacity 1
Discharge capacity at 0th cycle X10 ×10o...
(2) From FIG. 6, when the Li/Mn atomic ratio is less than 377, although the discharge capacity is large, the cycle deterioration rate is extremely poor. This is because MnO□ has a high cycle deterioration rate.
This is because there is a mixture of Furthermore, from Fig. 6, Li/M
When the n atomic ratio exceeds 4/6, the cycle deterioration rate is small and good, but the discharge capacity is significantly reduced. From the above, the region where the discharge capacity is large and the cycle deterioration rate is small is the region where MnO2 and Li2MnO3 are not mixed, and the Li/Mn atomic ratio is 3/7 to 4/6. Here, the value 4/6 (=o, 667) is Li2C
o, and MnO□te have a Li/Mn atomic ratio of 0.7 and are Li
2Mn0, or LiMn where no mixture of MnO2 is recognized.
2O4 is produced (see British Publication No. GB2196785 and the comparative example in Example 1 in the specification of this application), whereas the Li/Mn atomic ratio is 5% smaller, and 3
The value of /7 (==0.429) is given by the composition of LiMn2O4, which is the Li/Mn atomic ratio of 20, 6 and 14.
%small. In other words, if the LiMn2O4 manufacturing method of the present invention is used, L can be produced with a lithium compound/MnO2 mixture ratio with a smaller Li/Mn atomic ratio than before, and at low temperatures.
It has the characteristic that iMn2O4 can be produced.

Example 4 A flat battery configuration was used, except that the heating temperature was changed in the process of obtaining LiMn2O4 of the present invention in Example 1.

The charge/discharge test conditions were the same.

Figure 6 shows LiMn2O obtained by changing the heating temperature.
4, the crystal lattice constant a with respect to the heating temperature, and
FIG. 3 is a diagram plotting cycle deterioration rate versus heating temperature. Here, the crystal lattice constant a is the X-ray diffraction index (111
) was calculated using equation (1), and the cycle deterioration rate was calculated using equation (2).

From FIG. 6, it can be seen that the crystal lattice constant a with respect to the heating temperature increases rapidly when the heating temperature exceeds 610°C, and has a constant value of 8.
It becomes 2488. Correspondingly, the cycle degradation rate also increases significantly. The reason for this is that in LiMn2O4 obtained at a heating temperature exceeding 610°C, the degree of expansion and contraction of the crystal lattice during the charging and discharging process is large, resulting in poor current collection due to separation from carbon black particles, which are the conductive agent. Therefore, the cycle deterioration rate is high. From Figure 6, in order for the cycle deterioration rate to be sufficiently small, the crystal lattice constant a must be 8.2.
It can be seen that the thickness must be 2 Å or less. On the other hand, in a region where the heating temperature is 430°C or lower, the crystal lattice constant a is 8.
Even though it is much smaller than 22 people, the cycle deterioration rate is increasing. This means that in this temperature range, Li
The reaction between OH-H2O and MnO2 does not proceed quickly, and Li
Mn2O. Besides, Li2Mn0, .

This is because MnO2 becomes mixed.

As mentioned above, when the crystal lattice constant a is 8.22 Å or less, L
i 2Mn0 , and LiMn2O with no mixture of MnO2
4, it is desirable to set the heating temperature between 430°C and 510'C.

Example 5 In the process of obtaining LiMn2O4 of the present invention in Example 1, lithium compounds were used as Li2O, LiOH, LiOH-H2
O.

Li3MnO4, Li2Mn0. , LiMnO2, and used alone or as a mixture, the configuration of the flat battery and the charging/discharging test conditions were the same.

(Left below) Table 2 shows various lithium compounds or mixtures and γ-type M
Using nO2, the crystal lattice constant a is 8.22 Å or less,
L x M with less mixture of Li 2Mn05 and MnO2
It describes the conditions for producing n 2 O a,
Furthermore, the charge/discharge cycle life (the number of cycles when the discharge capacity becomes half of the initial capacity) of the battery using the produced LiMn 2 O 4 is described.

From Table 2, when the lithium compound is lithium oxide or lithium hydroxide, the mixing ratio of the lithium compound and MnO□ is 3/7 to 4/6 in Li/Mn atomic ratio, and the heating temperature range is 430°C to It can be seen that the temperature is 510°C. When the lithium compound contains lithium manganese oxide, the upper limit of the Li/Mn atomic ratio is 3.6/8.6, which is slightly lower than that of lithium oxide or hydroxide.
The lower limit of the heating temperature is approximately 460°C. The reason for this is that lithium manganese oxide is less likely to release 2Li than lithium oxide or hydroxide.

Furthermore, the cycle life of batteries fabricated using lithium manganese oxides is slightly shorter because lithium manganese oxides such as Li 2Mn05 remain to an extent that cannot be recognized by X-ray diffraction analysis. It is thought that this is because trace amounts of water contained in the electrolyte dissolve and corrode the lithium negative electrode.

In LiMn2O4 obtained under the conditions in Table 2, the full width at half maximum of the diffraction peak of the X-ray diffraction index (311) is:
Both are less than 1.1° in terms of FeKa radiation, and the LiMn disclosed in British Publication Publication GB2196785
It has higher crystallinity than 2O4 and is difficult to be eluted by moisture in the electrolyte, so the lithium negative electrode is less likely to be corroded, so it has the advantage of a longer charge-discharge cycle life.

Example 6 In the process of mixing the lithium compound and γ-type MnO2, LiMn2 was mixed in the same manner as in Example 1, except that water was added or not.
Production of O4, construction of a flat battery, and charge/discharge tests were conducted.

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

According to Table 3, no matter which lithium compound is used, γ-type M
When H2O is added during kneading with nO2, the discharge capacity increases by about 6 to 10% compared to when H2O is not added, especially for lithium manganese oxide.

It can be seen that this is remarkable in lithium oxide.

The reason for this is that due to the 1(2O) added during kneading, these lithium and manganese oxides are eluted and cover the MnO□ particles, although their solubility is small, so that LiMn2O4 is generated uniformly and electrochemically inactive Li,
This is because MnO is no longer mixed.

Example 7 Similar to Example 6, various lithium compounds and γ-type MnO
2 and H2O were kneaded and heated to obtain LiMn2O4.

The thus obtained LiMn2O430,0OOf was poured into 400ml of ion-exchanged water, stirred, and 4NH2S
o, the solution was added dropwise until the pH in the solution phase settled to about 5. Next, this acidic LiMn2O4 solution was filtered, and the LiMn2O4 was repeatedly washed with ion-exchanged water until the pH of the waste solution after washing became 6 to 7.

The structure of the battery and the charge/discharge test were conducted in the same manner as in Example 1.

- (blank below) Table 4 lists the discharge capacity of LiMn 2 O 4 obtained from each lithium compound at the 10th cycle before and after acid solution treatment. From this, L treated with acidic solution
iMn2O4 is LiMn,O before treatment.

The discharge capacity has increased compared to the previous model, and remains at a constant value of approximately 5.7 mAh. This is a combination of lithium compounds and MnO2
LiMn 2O4 obtained by heating contains a small amount of L x 2 M n that cannot be recognized by X-ray diffraction analysis.
Lithium compounds such as Os and LiOH remain,
This is because it is removed by acid treatment.

Although not listed in Table 4, LiMn2O4 treated with acidic solution has no residual Li2Mn0, so the cycle life of the battery is generally shorter than that of LiMn2O4 treated with acidic solution.
It had the effect of being elongated compared to iMn2O4.

Figure 7 shows the cycle life of the battery and the water content in the lithium-manganese oxide obtained by the treatment with respect to the pH in the acidic solution phase in which LiMn2O4 is treated using Lion-H2O as the lithium compound. It is a plotted figure. Here, the reason why LiMn2O4 treated with an acidic solution is described as lithium manganese oxide is that LiMn2O4 treated in a low pH acidic solution phase is LiMn2O4.
This is because Li is released from within the n2O4 particles and cannot be expressed by a simple compositional formula.

From FIG. 7, it can be seen that when the pH in the acidic solution phase is less than 4, the cycle life of the battery is short. This is because, as is clear from FIG. 7, when the pH is less than 4, the amount of water in the lithium-manganese oxide obtained by the treatment increases rapidly, and this water corrodes the lithium negative electrode. From the above, the pH in the acidic solution phase in which LiMn2O4 is treated must be 4 or higher.

In addition, in FIG. 7, LiOH-H is used as the lithium compound.
Although the above description focused on LiMn2O4 using 2O, similar results were obtained for LiMn2O4 obtained using other lithium compounds. Furthermore, although H2SO4 was used as the acid in this example, other acids such as HC (
1. Similar effects can be obtained by using H2WO4, CH3CO0H, etc.

Effects of the Invention As described above, since the non-aqueous electrolyte secondary battery of the present invention uses LiMn2O4 with a crystal lattice constant a of 8.22 Å or less as the positive electrode active material, the nonaqueous electrolyte secondary battery of the present invention has a reliable battery with small capacity loss during charge/discharge cycles. A high-quality non-aqueous electrolyte secondary battery can be obtained. Furthermore, by the method for producing LiMn 2O4 of the present invention, Li2
Mn0. The LiMn2O. is obtained.

[Brief explanation of the drawing]

FIG. 1 shows L, which is a positive electrode active material in an embodiment of the present invention.
An X-ray diffraction diagram of iMn 2,04, Figure 2 is an X-ray diffraction diagram of LiMn 2O4 containing Li2MnO3 and MnO2, which are positive electrode active materials in a comparative example, and Figure 3 is an X-ray diffraction diagram of an example of the present invention and a comparative example. Cross-sectional view of the flat battery used, No. 4
The figure is a diagram plotting the discharge capacity at each cycle of the battery of the present invention and battery B of the comparative example.
A diagram plotting discharge capacity and cycle deterioration rate against Mn atomic ratio (lithium compound/MnO□ mixture ratio),
Figure 6 is a diagram plotting the crystal lattice constant a and cycle deterioration rate of LiMn2O4 produced against the heating temperature of the lithium compound/MnO2 mixture, and Figure 7 is a diagram plotting the cycle life of the battery and the lithium FIG. 3 is a diagram plotting the amount of water in manganese oxide. 1...Positive electrode current collector, 2...Battery case, 3...Positive electrode, 4...Negative electrode, 6...
...Negative electrode current collector, 6... Sealing plate, 7...
... Separator, 8... Gasket. Name of agent: Patent attorney Shigetaka Awano and one other person

Claims (4)

[Claims] (1) A positive electrode, a lithium ion conductive nonaqueous electrolyte,
A battery comprising a negative electrode made of lithium or a lithium alloy, the positive electrode having a crystal lattice constant a of 8.
．． A non-aqueous electrolyte secondary battery characterized by being made of LiMn_2O_4 with a thickness of 22 Å or less. (2) Li_2O, LiOH, LiOH-H_2O, L
i_3MnO_4Li_2MnO_3, LiMnO_2
at least one lithium compound selected from γ
By mixing type MnO_2 at a Li/Mn atomic ratio in the range of 3/7 to 4/6 and heating at a temperature between 430°C and 510°C, LiMn_2 according to claim 1 is obtained.
A method for producing a positive electrode active material characterized by obtaining O_4. (3) A method for producing a positive electrode active material, characterized in that in the process of producing the positive electrode active material according to claim 2, a lithium compound, γ-type MnO_2, and water are kneaded and heated. (4) The method for producing a positive electrode active material according to claim 2 or 3, characterized in that the produced LiMn_2O_4 is treated in an acidic solution phase having a pH of 4 or higher.