JPH0367464A - Manufacture of organic electrolyte lithium secondary battery and composite oxide of lithium and manganese - Google Patents

Abstract

PURPOSE:To obtain excellent cycle reversibility by setting the ratio between the Li atom and Mn atom of a composite oxide of Li and Mn used as the active material of a positive electrode within a specific range. CONSTITUTION:An organic electrolyte Li secondary battery has a positive electrode using an active material made of a composite oxide of Li and Mn obtained by baking a mixture of Mn oxide (MnO2, Mn2O3 or Mn3O4) and LiNO3 in the air. The ratio between the Li atom and Mn atom of this active material must be 0.30:0.70-0.35:0.65. When the Mn oxide of the raw material is MnO2 in particular, the baking temperature is preferably 430-470 deg.C. When the Mn oxide is Mn2O3, the baking temperature is preferably 450-530 deg.C. When the Mn oxide is Mn3O4, the baking temperature is preferably 450-500 deg.C. An Li secondary battery with excellent cycle reversibility and high energy density can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an organic electrolyte lithium secondary battery having a high energy density using lithium as a negative electrode active material, and particularly to improvements in its positive electrode active material.

BACKGROUND OF THE INVENTION Primary lithium batteries using MnO2 as a positive electrode have already been put into practical use. In the case of lithium batteries, the presence of water has a negative effect on battery performance, so conventionally Mn02 is heat-treated at a temperature of 250°C to 400°C to remove attached water and bound water, and then used as a positive electrode for lithium batteries. It was used as

The crystal structure of MnO2 is described in Japanese Patent Publication No. 49-25571.
γ-β type heat-treated at a temperature of 250°C to 350°C as disclosed in US Pat. No. 4,13
3,856, 350°C.
It is considered to be the β type heat treated at a temperature of ~430°C.

However, in subsequent studies, MnO2 heat-treated at 400°C in air is also said to be γ-β type MnO2. However, it has been found that when MnO2 having these crystal structures is used as a lithium secondary battery, the capacity decreases with cycles due to the collapse of the crystal structure during charging and discharging.

Therefore, from the viewpoint of positive electrode active materials for lithium secondary batteries that require cycle reversibility, manganese oxide, including improvements to MnO2, has been actively developed, and several proposals have been made. One such attempt was to use manganese dioxide, which has a spinel-type structure, as a positive electrode active material.
8-220362 in combination with a solid electrolyte, or LiMn20. There are positive electrodes mainly composed of .

In addition, λ type M n having a structure similar to a spinel type
02 is also disclosed in JP-A-55-100224 and JP-A-63-187569.

However, a complete spinel type discharges in two stages, each with a small capacity and significant cycle deterioration. Also, those with a λ type or an intermediate structure between λ type and spinel type,
Although the capacity is large, cycle deterioration is large. Then, MnO
Attempts are also being made to improve the crystal structure by doping 2 with Li to improve cycle reversibility. For example, JP-A-62-108455, JP-A-62-10
M n O2 doped with Li as in Publication No. 8457
JP-A-61-16473, JP-A-62-126556, JP-A-62-1606
57, in which MnO2 is immersed in an aqueous solution of Li salt to dope Li, and JP-A-63-148550, in which Li-doped
These include those using nO2. Sarabanko (Yo, special 51
Hco M n 02 as in Publication No. 1986-290058
Pre-added LiMnO2, special SM 1986
There is also a method using MnO2 containing MnO2, i2Mno3, etc., as disclosed in Japanese Patent No. 114064.

In addition, lithium secondary batteries are similar (although there are some)
An attempt was made to dope Li (Japanese Unexamined Patent Publication No. 57-49164), in which Li (
For example, there is a method that mixes Li OH, Li NO:] and then heat-treats the mixture.

Furthermore, MnO2 is mixed with 30-40mo 1% of LiOH and heat treated to dope Li, MnO
About 30 mo1% of LiNO3 was mixed with No. 2, and the mixture was heat-treated at 400° C. to be doped with Li.

As a result of re-examining the technical contents shown in the above-mentioned known examples, all of the active materials of lithium secondary batteries in which MnO2 is doped with Li are the conventional γ-β type 1vin O2.
Improved cycle reversibility was observed compared to this is,
This is thought to be due to the effect of reinforcing the crystal structure by doping with Ll. However, none of them were sufficient. For example, in the case of Li-doped α-type or δ-type MnO2, the active material utilization rate is extremely poor, and α-type or δ-type MnO2 originally contains different types of cations in the crystal lattice. Deterioration of the negative electrode was observed, which was thought to be due to the elution of these cations. Furthermore, although some improvement in reversibility can be seen by doping M n 02 by immersing it in an aqueous solution of Li salt, the effect is small. This is considered to be because the amount of Li doped with this method is extremely small.

Next, although it is a technology related to lithium-secondary batteries, M n
For example, a Li compound of about the amount of bound water in 02
We applied a method of mixing OH and LiN0:+ and then heat-treating them to a lithium secondary battery. However, although it was certainly effective in improving the utilization rate as a primary battery, the effect on cycle reversibility was small. This is thought to be due to the fact that the addition of the Li compound in the amount of bound water is insufficient as a doping amount. Then, LiMn was added to MnO2.
Those to which O2 is added in advance, M containing Li2MnO3
I also tried using n02, but LiMnO2, L
Although the reversibility improves depending on the content of i2MnO3, since LiMnO2°L i 2M n 03 is a bulky material, there is a drawback that the volumetric efficiency of the capacity decreases due to its addition. Conventionally, MnO2 crystals have a tunnel in the C-axis direction, and L into this tunnel is caused by charging and discharging.
The entry and release of l takes place. That is, if the intrusion and release of Li are performed stably, excellent reversibility will be exhibited. In conventional γ-β type MnO2, the crystal structure is gradually destroyed by repeated charging and discharging cycles (intrusion and release of Li), and it is said that the capacity decreases with the cycles. The intrusion of Li is considered to be a kind of electrochemical Li doping, but as far as we look at the difference in cycle reversibility (reinforcement effect of crystal structure), it is not electrochemical doping.
It is thought that the coordination form of Li in MnOz is different from that in which Li is doped by chemical and thermal treatment in advance.

In addition, by some chemical and thermal treatment in advance, M n 0
2 doped with Li has excellent cycle reversibility, and basically MnO2 doped with Li through chemical and thermal treatment is promising as a positive electrode active material for lithium secondary batteries. it is conceivable that. In particular, among those reported so far, the most suitable cathode active material for lithium secondary batteries from the viewpoint of cycle reversibility and active material utilization rate is LiOH at 30mM relative to MnO2.
One was to mix about 1% o to 40mol and dope with Li, and the other was to mix MnO2 with LiNO3 and heat treat it at 400°C.

For example, by mixing 30mo1% of LiN0+ with CMD,
It has been reported that when fired at 00°C, an active material with high utilization rate as well as cycle reversibility can be obtained.

Including these methods, doping with Li generally lowers the density of the active material, resulting in a slightly lower volumetric efficiency, but it also improves the active material utilization rate per MnO2 and improves cycle reversibility. , can be an excellent positive electrode active material for lithium secondary batteries. However, subsequent studies revealed that these active materials have major drawbacks. It uses electrolytic manganese dioxide (E
(MD), and in the process of manufacturing a positive electrode, for example, if water is used as a medium to make a paste, the pH of the paste becomes extremely high, and the current collector material used in the positive electrode corrodes. . This is considered to be because alkali (considered to be Li OH) was liberated from the active material. In particular, when a material that is extremely weak against alkali, such as aluminum, is used as a current collector, severe corrosion accompanied by hydrogen generation occurs, and the material cannot even be used as an electrode plate. When titanium or stainless steel copper, which are thought to be relatively resistant to alkali, were used as the current collector material, it was possible to make the electrode plates, but it was found that the battery performance was significantly affected, such as a decrease in capacity. This means that - degree of liberated alkali is
This is probably because they are involved in some way. However, when a positive electrode manufacturing method that does not involve water (for example, a method in which a powdered conductive agent and a binder are dry mixed and press-molded), there was almost no effect on battery performance. In other words, this active material cannot be used unless water is involved in the positive electrode manufacturing process. However, there are limits to the shape and dimensions of the electrode plates that can be produced by dry process, and they are not sufficient from the viewpoint of versatility.

On the other hand, chemically synthesized manganese dioxide (CMI) is an EMD
However, active materials prepared in the same way did not release alkali at all even in the presence of water. This is because CMD has a larger surface area (porous) than EMD, and CMD
In this case, the reaction with LiOH has proceeded completely, and in EMD, LiO
This is thought to be because the reaction with H or LiNO3 is incomplete. In addition, when 30 mo1% of LiNO3 is added to EMD and fired at 400°C, the active material utilization rate is improved compared to when LiOH is used, and the release of alkali when water is involved is lower than when using LiOH. It was a little lower than that. However, since it is not perfect, problems remain, and it is not sufficient from the viewpoint of versatility. However, an active material obtained by doping EMD with Li using LiN0:+ has a better active material utilization rate than one using LiOH, and can be said to be the most excellent active material for lithium secondary batteries at present.

Problems to be Solved by the Invention An object of the present invention is to provide a lithium secondary battery that has a discharge capacity that is always stable as the cycle progresses and has a high energy density. The object of the present invention is to improve the positive electrode active material. Manganese oxide has not only excellent cycle reversibility, but also excellent active material utilization rate and volumetric efficiency, and is also widely used in the manufacturing process of positive electrodes. The purpose of the present invention is to provide an active material with excellent properties.

Means for Solving the Problems The present invention provides MnO2゜Mn2 as manganese oxide.
Composite oxidation of lithium and manganese obtained by mixing 031 or M n 304 with lithium nitrate and LiNO3, and firing in air, preferably at a temperature range of 430°C or higher and 530°C or lower. It uses a substance as an active material. However, the ratio of lithium atoms to manganese atoms (Li:Mn) in this composite oxide is 0.
．． The necessary condition is 30:0.70 to 0.35:0.65. In particular, the raw material manganese oxide is MnO
2, the firing temperature is 430°C or higher, 470°C
It is preferable that the manganese oxide is Mn2O
3, the firing temperature is 450°C or higher, 530°C
It is preferable that it is below. Furthermore, manganese oxide is M
n 304, the firing temperature is preferably 450°C or higher and 5oo°C or lower. Furthermore, since neither Li nor Mn is lost during firing, the composite oxide (Mn) can be prepared by mixing the raw materials manganese oxide and LiNO3. Furthermore, water is used as a medium when mixing manganese oxide and LiNO3 before firing,
It is preferable that lithium nitrate be dissolved in water in advance and then fired at the above predetermined temperature.

By using the above-described positive electrode active material and manufacturing method of the present invention, it is possible to achieve better cycle reversibility, active material utilization rate, and volumetric efficiency than any of the conventional technologies, and also excellent versatility in the positive electrode manufacturing process. Becomes the positive electrode.

For example, compared to LiNO3, which is conventionally considered the best positive electrode active material for lithium secondary batteries, processed into EMD at 30 mo1% and heat-treated at 400°C, the cycle reversibility is almost the same, but the active material utilization rate is In addition, the volumetric efficiency is at least 10% higher, no alkali is liberated even when water is involved, and the versatility is extremely excellent. That is, by using the positive electrode active material of the present invention, it is possible to provide a high energy density lithium secondary battery that has excellent manufacturing versatility and always has a stable discharge capacity as the cycle progresses.

Function Conventionally, Li was used as a raw material for doping MnO2 with Li.
When using OH and LiNO3, differences were observed in the active material utilization rate, volumetric efficiency, and free state of alkali when water was involved, so we compared their crystal forms using X-ray diffraction. I tried it. FIG. 1 compares the X-ray diffraction patterns of EMD prepared by mixing 30 mo1% of each of LiOH and LiNO3, kneading with water, and then heating in air at 400° C. for 5 hours. As is clear from this comparison diagram, the one using LiNO3 (Fig. 1A) has a 2θ of around 21.8 and 20
= 53.1 using LiOH (Figure 1B)
A peak that is not present can be seen. Although the details are not clear, there are clearly different crystal phases.
At least it can be said that they are made of different materials. This is also different from the X-ray diffraction pattern of spinel type LiMn20* and the conventional γ-β type M n O2. In other words, since LiOH is a different material,
It is considered that the characteristics are improved compared to when it is used as a doping source for i. However, the active material of the present invention can further improve the active material utilization rate and suppress the release of alkali compared to the conventional one, but this is due to the fact that LiN0:+ and EMD
This is because the chemical and thermal doping of Li that occurs between the two is extremely complete. However, the difference was not noticeable in X-ray diffraction. In particular, when LiNO3 and EMD are mixed and fired, No.
However, under the conditions of the present invention, the generation of NO during firing was much more intense than under the conventional conditions.

Originally, the decomposition temperature of LiNO3 is 600°C, and LiNO3 cannot be decomposed at the firing temperature of the present invention.

Therefore, it is expected that a decomposition reaction of LiNO3 using M n O2 as a catalyst occurs concurrently, but it is thought that this decomposition reaction occurs more easily under the conditions of the present invention (higher temperature than conventional ones). . Furthermore, N03. generated during this decomposition process. N 2 O 2 and the like act as strong oxidizing agents, and it is thought that at least the surface of M n O 2 is in an extremely active state. Presumably, these factors work effectively to completely dope Li, resulting in a material that does not cause alkali release, and also contributes to improving the utilization rate of the active material.

Conventionally, Mn2O3 or Mn, which is a reduced form of MnO,
304 could not be used as an active material due to its low activity and extremely low capacity, but when it is fired with LiNO3 under the conditions of the present invention, it has a capacity.
Although its capacitance characteristics are slightly inferior to those of MnO2, it now has sufficient performance. Further, products using these materials as raw materials also generated a significant amount of NoX during the firing process under the conditions of the present invention.

In other words, in this case as well, the catalytic reaction of LiNO3 occurs simultaneously, and more conveniently, the oxidizing power of NOl improves the activity of these manganese oxides themselves (
It is thought that Mn203 or MrzO< was oxidized to a state extremely close to Mn02).

As mentioned above, this is just one method of doping Li, but
The technology of the present invention using LiNOs is extremely interesting.

Example Examples of the present invention will be shown below.

Example 1 An active material comprising a complex oxide of Li and manganese of the present invention was prepared as follows. First, LiNO3 is dissolved in a predetermined amount of water to create something close to a saturated aqueous solution of LiNO3. A predetermined amount of manganese oxide powder is added thereto, thoroughly stirred and mixed, and a portion of the water is evaporated to form a mud-like mass, which is then fired at a predetermined temperature for 4 to 5 hours using an electric furnace. After firing, white powder, which is thought to be unreacted substances, may be seen on the powder surface; in this case, it is best to add water, knead, and fire again. Even after firing twice in this way, the battery characteristics were not affected at all. The same product could also be prepared by mixing manganese oxide and LiNO3 in powder form in advance and then adding water and kneading. However, when the mixture of powders was directly fired without using water, the reaction did not occur uniformly, resulting in large variations in performance. Therefore, it is preferable to involve water in the mixing.

Next, as an active material for comparative study, one using LiOH as a Li doping source was also prepared. The preparation method in this case was almost the same as above, and the one in which water was used for mixing and baking was superior with less variation.

Example 2 Using EMD as manganese oxide, using the method of Example 1, Li:Mn=0.3:0.7 (corresponding to Li content of 30 mo1%), and the firing temperature was set to 400°C. A comparative study was conducted between the conventional active material in which the above-mentioned active material was used, and the active material of the present invention having the same composition but at a firing temperature of 440°C. For reference, we also prepared an active material with the same composition prepared at 400°C using LiOH as a doping source and EMD at 400°C.
A γ-β type M n O2 heat-treated was also prepared.

First, a button-type battery as shown in Figure 2 was assembled using the above four active materials, and its characteristics were compared. In Figure 2, the positive electrode 1 contains carbon powder as a conductive material (5% by weight based on the active material) and tetrafluoroethylene resin powder as a binder (7% by weight based on the active material). It is a mixture that is press-molded onto a titanium net 2 fixed to the inside of the positive electrode case by spot welding. That is, this is a dry method that does not involve water in the positive electrode manufacturing process. Also,
The amount of active material was 100μ in both cases.

And a polypropylene separator 3. The metal lithium negative electrode 5 and the electrolytic solution 6 (1 mol of LiAsF6 dissolved in a mixed solvent of propylene carbonate and ethylene carbonate) were sealed together with a polypropylene gasket 7, which was crimped onto the sealing plate 4, and the diameter was 20 m1. height 1, 6
It was made into a battery of mm. In addition, this battery was prototyped for the purpose of comparing the characteristics of the positive electrode, and the capacity of the negative electrode was filled to about 4 times the capacity of the positive electrode, so that the charging and discharging characteristics would not be affected by the lack of the negative electrode. ing. The charge/discharge test is 2
For constant current charging and discharging of mA, the final charge voltage is 3.8V, and the final discharge voltage is 2. I set it as Ov. FIG. 3 shows the discharge capacity-cycle characteristics of a battery to which the above four types of active materials are applied. In FIG. 3, curve 8 is the characteristic of γ-β type M n 02. Its initial capacity is higher than the others, but its capacity degradation with cycling is the greatest. Next, curve 9 is 30mo
It was fired at 400° C. using LiOH equivalent to 1% as a doping source, and has excellent cycle reversibility but low capacity. However, in this case, M contained in the active material
When calculated from the amount of n O2, the utilization rate is higher than that of γ-β type M n 02 alone.

Next, curve 10 shows the conventional LiNO equivalent to 30mo1%.
Curve 11 is the characteristic of the active material fired at 400℃ using 3.
using 30 mo1% LiN0+ according to the present invention, 44
These are the characteristics of the active material fired at 0°C. All of them had excellent cycle reversibility, and the capacity was also larger than curve 9, but between curve IO and curve 11, curve 11 was superior in both capacity and cycle reversibility.

As mentioned earlier, this seems to be an effect due to the difference in the degree of completion of Li doping. Furthermore, in this battery, the weight of the active materials is unified, but as a result of comparing the bulk density of each active material, it was found that the γ-β type M n 02 was 100%
In this case, one using LiOH as a doping source and one using LiOH as a doping source
The conventional active material using NO3 was about 80,
The value of the present invention was about 85. This indicates that the active material of the present invention has a more dense structure because the degree of completion of Li doping is high. Therefore, assuming that electrode plates of the same dimensions are made and considered from the viewpoint of volumetric efficiency, the active material of the present invention is even more superior.

Example 3 Next, regarding the active material to be fired by adding LiNO3, Li
The content of is fixed at 30mo1% and the firing temperature is set to 350
The temperature was varied in 20°C increments between 550°C and 550°C. Incidentally, conventional active materials have a firing temperature of 400°C. Next, 1 of each of these active materials
The same button-type battery as in Example 2 was constructed using 0.00 mm each, and a charge/discharge test was conducted under the same conditions as in Example 2. FIG. 4 shows the capacity-cycle characteristics at each firing temperature. Looking at this, if the firing temperature is 390℃ or less (
Curve 12: 350°C 9 Curve 13: 370°C.

It can be seen that curve 14 (390°C) has insufficient cycle reversibility. It is presumed that this is because the intended crystal structure was not formed because the Li doping was incomplete.

In addition, at 410°C or higher, both have excellent cycle reversibility, but at 490°C or higher (curve 19: 490°C 1 curve 20: 510°C 2 curve 21: 530°C.

Curve 22: It can be seen that the capacity decreases overall when the temperature reaches 550°C. This seems to be due to a decrease in the activity of the active material itself. Also, 410℃ (curve 1
5) and 430°C to 470°C (curves 16 to 470°C), an increase in capacity and improved cycle reversibility is seen in the latter. This is because there is a large change in the degree of NoX generation between 410°C and 430°C.
This means that some change occurs in the active material itself between 10°C and 430°C. Therefore, we investigated the temperature range that is thought to provide large capacity and excellent cycle reversibility by further varying the firing temperature. Figure 5 shows the firing temperatures of 420°C (curve 23) and 430°C (curve 2).
4), 440°C (curve 25), 450°C (curve 26),
460°C (curve 27), 470°C (curve 28), and 4
This figure compares the capacity-cycle characteristics of active materials prepared at 80° C. (curve 29) when similar battery tests were conducted. As a result, the firing temperature was 430°C to 470°C.
It was found that the capacity increased at 440°C to 460°C. Furthermore, as a result of investigating whether the bulk density of the active material changes depending on the firing temperature, it was found that those fired at 430° C. or higher have a higher density. Therefore, from the viewpoint of volumetric efficiency, the active material of the present invention can be said to be more preferable.

Example 4 Next, the ratio of lithium atoms to manganese atoms (Li:Mn) in the composite oxide was studied. First, as a preliminary study, the mixing ratio of LiN0:+ and EMD,
As a result of investigating the relationship between the atomic ratios of Li and Mn in the composite oxide by chemical analysis of the composite oxide, it was confirmed that they agree with each other regardless of the firing temperature. The method for preparing the active material was as shown in Example 1, the firing temperature was fixed at 440°C, and the Li content was 10 mo1%, 15 mo1%, 20 mo1%.
1%, 25mo1%, 3Qmo1%.

35mo1%, 40mo1%, 45mo1%.

Nine types of active materials were prepared with a concentration of 50 mo1%.

Then, the same button type batteries as in the above example were constructed using 100 µm of each of these active materials, and a charge/discharge test was conducted under the same conditions as in the above example. FIG. 6 compares the capacity-cycle characteristics of active materials with different Li contents. As the Li content increases, the cycle reversibility improves (curve 30: 10mo 1%1 curve 3
1: 15mo 1%.

Curve 32: 20mo 1%2 Curve 33: 25mo 1
%) Especially when the Li content is 30 mo1% or more (curves 34 to 3
8) was excellent. However, the Li content is 45m
When o1% or more (curves 37 to 38), cycle reversibility was excellent, but the capacity tended to be low. this is,
The active material filling amount is 100μ in each case, and M in the active material is
This is because the amount of n 02 becomes relatively small. Furthermore, those having a Li content of 45 mo1% or more have the disadvantage that their bulk density is extremely low and their volumetric efficiency is extremely low. Therefore, from the relationship between cycle reversibility and capacity, the Li content should be 30mo1% or more, 4Qmo1% or less,
That is, the ratio of lithium atoms to manganese atoms (L i :
Mn) Mo 0.30: 0.70-0.40: 0.
60 is preferred.

Example 5 Regarding the Li content range of 30 mo1% to 40 mo1%, which showed favorable results in Example 4, the degree of alkali release when water was involved was investigated. Further, in this study, the firing temperature was set at 440°C. First, 1 g of active materials with different Li contents were placed in test tubes, 5 Qmf of water was added to each tube, and the tubes were thoroughly stirred and left for about 6 hours. Next, since the shield substance precipitated after being left to stand, the supernatant liquid was collected and the pH was examined. As a result, when the Li content was 35 mo1% or less, the pH was 7 to 8 in all cases, and it seems that almost no alkali was liberated. However, the Li content is 36mol
% or more, an increase in pH due to alkali liberation was observed, and when it reached 39 m o 1%, the pH exceeded 10.

Next, an aluminum foil was immersed in each of the above supernatant liquids, and the effects thereof were observed. As a result, Li with a pH of 10 or more
In those with a content of 39 mo1% and 40 mo1%,
Significant gas generation was observed. In addition, the Li content is 36~
In the case of 38 mo1%, the pH was higher than 8, and gas generation was still observed, albeit mildly. In addition, no gas generation was observed when the Li content was 35 mo1% or less.

It is unclear whether the release of alkali affects battery performance or not, and if a corrosion-resistant current collector is used, it may be possible to use it even with the release of alkali. Therefore, in this example, the dry method described above was used. Instead of using the positive electrode manufacturing method, the positive electrode mixture was made into a paste using an aqueous dispersion liquid of tetrafluoroethylene resin instead of the polytetrafluoroethylene resin powder used as a binder, and this was filled into a titanium net current collector material. We tried a wet manufacturing method in which the material was then dried and further rolled to produce a positive electrode. Then, a button type battery similar to that described above was constructed using the positive electrode thus produced, and a charge/discharge test was conducted.

As a result, in the active material whose pH was 10 or more in the above test, a significant decrease in the active material utilization rate (30% to 40% decrease in capacity) was observed compared to the positive electrode made by the dry method.
For those with a pH of 8 or more, a decrease in the utilization rate of the active material (5% to 10% decrease in capacity) was also observed. However, those with a Li content of 35 mo1% or less and a pH of 7 to 8 showed almost the same utilization rate as those made by the dry method. From the above, it seems that the liberation of alkali has a particularly negative effect on the active material utilization rate, and furthermore, when the Li content is 35 mo1%
It is presumed that the following substances cause almost no alkali release. Therefore, from the viewpoint of versatility in the positive electrode manufacturing method, the Li content should be 35 mo1% or less.

Up to this point in the examples, studies have been conducted using MnO2 as a raw material for manganese oxide, but in this example, studies have also been attempted using Mn3O4 and Mn2O3 as manganese oxides. First, M n 304 and Mn2O3
A button type battery similar to that described above was constructed using the same as the active material, and a charge/discharge test was conducted. As a result, as shown in curve 39° and curve 40 in FIG. 7, the batteries had extremely low capacities. Next, in the same manner as in Example 1, L was adjusted so that the atomic ratio of Mn and Li was 0.7:0.3.
An active material was prepared by mixing iNO3 with M n 203 or M n 304 and firing the mixture at 470°C. Then, a button type battery similar to that described above was constructed using these active materials, and a charge/discharge test was conducted.

As a result, it has a capacity as shown in curve 41 (using Mn304) and curve 42 (using Mn203) in FIG. Compared to curve 43), its capacity is slightly lower.

However, when looking at the rate of decrease in capacity with cycling, that is, the cycle reversibility, it is actually superior to that using MnO□. Therefore, this active material is rather preferred in applications where a high degree of cycling reversibility is required rather than capacity.

Next, Mn20. For M n 304 as well, the optimum firing temperature, optimum Li content, and degree of alkali release were investigated in the same way as the examination of M n O2 in Examples 3 to 5. As a result, when Mn is 30°, the firing temperature is preferably 450°C or higher and 500°C or lower;
It was found that for n2O3, the temperature is preferably 450°C or higher and 530°C or lower. In addition, the optimum Li content is determined based on the active material utilization rate and the degree of alkali release in both cases.
The range of 30 mo1% or more and 35 mo1% or less, which is the same as nO2, was preferable.

As described above, it has been found that although the optimum firing temperature is different, the optimum Li content is the same for any of the above manganese oxides. That is, in the active material of the present invention which is a composite oxide of lithium and manganese oxide, the ratio of lithium atoms to manganese atoms in the composite oxide (Li:
Mn) is 0.30:0.70-0.35:0.65
It can be said that it is a necessary condition.

Effects of the Invention As described above, according to the present invention, a lithium secondary battery having excellent cycle reversibility and high energy density can be provided.

[Brief explanation of drawings]

Figures 1A and B are X-ray diffraction pattern diagrams for material comparison;
Figure 2 is a vertical cross-sectional view of the battery used in the embodiment of the present invention;
FIG. 4, FIG. 5, FIG. 6, and FIG. 7 are comparison diagrams of capacity-cycle characteristics showing the effects of the present invention. 1...Positive electrode, 2...Titanium net, 3
... Separator, 4... Sealing plate, 5.
... Lithium negative electrode, 6 ... Electrolyte, 7.
·····gasket.

Claims (5)

[Claims] (1) A positive electrode having a composite oxide of lithium and manganese obtained by firing a mixture of manganese oxide (MnO_2, Mn_2O_3 or Mn_3O_4) and lithium nitrate (LiNO_3) in air as an active material, The ratio of lithium atoms to manganese atoms in the oxide (Li:
An organic electrolyte lithium secondary battery characterized in that Mn) is 0.30:0.70 to 0.35:0.65. (2) The organic electrolyte lithium secondary battery according to claim 1, wherein the manganese oxide is electrolytic manganese dioxide and is fired together with lithium nitrate at a temperature of 430° C. or more and 470° C. or less. (3) The organic electrolyte lithium secondary battery according to claim 1, wherein the manganese oxide is Mn_2O_3 and is fired together with lithium nitrate at a temperature of 450°C or higher and 530°C or lower. (4) The organic electrolyte lithium secondary battery according to claim 1, wherein the manganese oxide is Mn3O_4 and is fired together with lithium nitrate at a temperature of 450°C or higher and 500°C or lower. (5) Use water as a medium when mixing lithium nitrate and manganese oxide, and after dissolving lithium nitrate in water in advance,
A method for producing a composite oxide of lithium and manganese, which comprises firing in air at a temperature of 30 to 530°C.