JPH0734368B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to improvement of a non-aqueous electrolyte secondary battery, particularly to improvement of a positive electrode active material, and aims to improve cycle characteristics of the battery.

2. Description of the Related Art Non-aqueous electrolyte secondary batteries using lithium or a lithium compound as a negative electrode are expected to have high energy density at high voltage, and many studies have been conducted.

In particular, MnO ₂ and TiS ₂ have been well studied as a positive electrode active material for these batteries. Recently, Taclay et al. Reported that LiMn ₂ O ₄ could be used as a positive electrode active material (Material Research Bulletin 1983 Vol. 18, pp. 461-472). LiMn ₂ O ₄
Is a cubic crystal structure having a spinel structure, and when used as a positive electrode active material for a battery, the discharge voltage of the battery becomes a high voltage of about 4 V and is considered to be promising as a positive electrode active material.

However, this positive electrode active material had a problem in cycle characteristics, that is, the discharge capacity was remarkably reduced when charging and discharging were repeated.

With LiMn ₂ O ₄ positive electrode active material, when it was charged to 4.5 V and discharged to 2 V, it was around 4 V and 2.8 V as shown in Fig. 2.
It has a two-step discharge curve near the bolt. The horizontal axis shows the composition of the positive electrode active material at this time. Charge and discharge are performed by the inflow and outflow of Li into the positive electrode active material (report by Otsuki et al.
Proceedings of the 29th Battery Symposium, page 135). When the composition of the positive electrode active material is represented by Li _X Mn ₂ O ₄ , charging and discharging occur due to changes in the value of X.

Until now, paying attention to the second-stage discharge near 2.8 V, limiting the charging voltage to 3.8 V and discharging up to 2 V, that is, a good cycle by charging / discharging in which X changes from about 1 to 1.85. The characteristics are obtained.

However, this cannot achieve a high energy density. In order to achieve high energy density, the first-stage discharge that charges up to 4.5V and discharges up to 3V, that is, charge until X becomes 1 or less, preferably 0.7 or less, until X becomes 1 or 1.85. It is more advantageous to discharge until.
However, when the first-stage charging / discharging portion that charges until X becomes 0.7 or less is used, the cycle characteristics are poor and the discharge capacity is reduced to half in about 50 cycles. Further, when X is charged to exceed 0.7, charging is insufficient and it is difficult to obtain sufficient discharge capacity.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention aims to improve the cycle characteristics of a non-aqueous electrolyte secondary battery using LiMn ₂ O ₄ as a positive electrode active material, and to improve the positive electrode active material.

Means for Solving the Problems A nonaqueous electrolyte secondary battery using a lithium or lithium compound as a negative electrode and a nonaqueous electrolyte containing a lithium salt, wherein the positive electrode has the general formula Li _X M _Y Mn _(2-Y) O It is represented by ₄ , and M in the formula
Is a positive electrode active material in which at least one of Co, Cr, and Fe, X in the formula is 0.85 ≦ X ≦ 1.15, and Y in the formula is 0.02 ≦ Y ≦ 0.3, and the positive electrode active material is charged. The composition of the positive electrode active material in the charged state with more lithium removed is Li
_The feature is that _X M _Y Mn _(2-Y) O ₄ (X ≦ 0.7).

Action LiMn ₂ O ₄ has a cubic crystal structure with a spinel structure. Li is extracted from the crystal by charging and LiMn ₂ O ₄ is discharged by discharging.
Enters the crystal. When LiMn ₂ O ₄ after repeating the charge and discharge cycles was examined by X-ray diffraction, it was found that the crystallinity was lowered.

Furthermore, when the value of X was changed as Li _X Mn ₂ O ₄ and the active material was chemically synthesized to examine the characteristics, it was found that the discharge capacity and the cycle characteristics changed depending on the value of X. This indicates that the crystal stability of the active material itself is involved in the cycle characteristics.

Therefore, as a result of examining an active material in which Mn in Li _X Mn ₂ O ₄ was partially substituted with Co, Cr, or Fe, the crystal lattice constant was smaller than that of Li _X Mn ₂ O ₄ . When these materials were used to examine the characteristics of the secondary battery as a positive electrode active material, it was found that the positive electrode material for a secondary battery has good cycle characteristics and thus a large discharge capacity after cycling.

The reason for this is that when Mn in L _X iMn ₂ O ₄ is replaced with Co, Fe or Cr, the lattice constant of the spinel structure becomes smaller, which increases the crystal stability and improves the cycle characteristics.

Examples Examples will be described below.

The <Example> Mn of LiMn ₂ O ₄ as the active material was replaced by Co, LiMn ₂ O ₄ and Li
A solid solution of CoO ₂ was investigated.

Preparation of LiMn ₂ O ₄ After mixing 3 mol of Li ₂ CO ₃ and 4 mol of Mn ₃ O ₄ well, the mixture was heated in the air at 900 ° C. for 10 hours to obtain LiMn ₂ O _4.
made n ₂ O ₄ .

Preparation of LiCoO ₂ After thoroughly mixing 2 mol of CoCO ₃ with 1 mol of Li ₂ CO ₃ , the mixture was similarly heated in the atmosphere at 900 ° C. for 10 hours to prepare LiCoO ₂ .

Preparation of LiMn ₂ O ₄ with solid solution of LiCoO ₂ LiMn ₂ O ₄ was mixed well at a ratio of 45 mol to 10 mol of LiCoO ₂ , and then the mixture was heated at 900 ° C. for 40 hours in the atmosphere.

Batteries production 2 parts by weight of acetylene black as a conductive agent and 1 part by weight of polytetrafluoroethylene resin as a binder are added to 7 parts by weight of LiMn ₂ O ₄ in which LiCoO ₂ is dissolved as a positive electrode active material. The mixture was mixed to obtain a positive electrode mixture. 0.1 gram of this positive electrode mixture was press-molded to a diameter of 17.5 mm at 1 ton / cm ² to obtain a positive electrode.
A cross-sectional view of the manufactured battery is shown in FIG. Molded positive electrode 1
Was placed in a case 2, and a porous polypropylene film as a separator 3 was placed on the positive electrode 1. As a negative electrode, a lithium plate 4 having a diameter of 17.5 mm and a thickness of 0.3 mm was pressure-bonded to a sealing plate 5 to which a polypropylene gasket 6 was attached. As the non-aqueous electrolyte, a mixture of propylene carbonate and dimethoxyethane in a volume ratio of 1: 1 in which 1 mol / l lithium perchlorate was dissolved was used and added to the separator and the negative electrode. After that, the battery was sealed. This battery is designated as A.

Similarly, let B be a battery using LiMn ₂ O ₄ as a positive electrode active material as a conventional example. Further, as a conventional example, a battery using LiCoO ₂ as a positive electrode active material is designated as C. 2m of these batteries
The battery was charged to 4.5 V with a constant current of A, discharged to 3 V and repeatedly charged and discharged.

Under this condition, X, which represents the composition of Li in the positive electrode active material in FIG. 2, was charged to 0.3, which was 0.7 or less, and was discharged until X became 1.

FIG. 1 is a plot of the discharge capacity of each of these batteries in each cycle. From this, it is understood that the LiMn ₂ O ₄ positive electrode of the present invention in which LiCoO ₂ is solid-dissolved does not deteriorate much even if the charge and discharge cycle under the above conditions is repeated. Further, FIG. 4 shows a discharge curve of each battery in the 10th cycle, which is a typical discharge characteristic and is still less deteriorated. From this, the LiCoO _{2 of the} present invention
It can be seen that LiMn ₂ O ₄ with solid solution of is discharged at the same potential as LiMn ₂ O ₄ , and is different from LiCoO ₂ . When LiMn ₂ O _{4 in} which LiCoO ₂ of the present example was solid-solved was examined by X-ray diffraction, the diffraction pattern was the same as that of LiMn ₂ O ₄ .

However, the position of the peak is shifted to a higher angle side than LiMn ₂ O ₄ , and the lattice constant obtained from each diffraction peak is LiMn ₂ O _4.
It was 8.21Å, which was smaller than 8.24Å of ₂ O ₄ . Although the action is estimated from the results, it is considered that the reduction of the lattice constant stabilizes the crystal and improves the cycle characteristics even under the charge and discharge under the above conditions.

Generally, spinel has a composition of AB ₂ O ₄ like LiMn ₂ O ₄ . Where A is a metal element surrounded by an oxygen tetrahedron, B
Is a metal element surrounded by an octahedron of oxygen. But,
LiCoO ₂ does not have this composition. Therefore, it is considered that the solid solution described in this example has the following composition.

10LiCoO ₂ + 45LiMn ₂ O ₄ = Li ₅₅ Co ₁₀ Mn ₉₀ O _200, that is, Li _1.1 Co _0.2 Mn _1.8 O ₄ , which is the total of Co and Mn.
It is considered that 2.0 minutes is surrounded by an octahedron of oxygen, 1.0 minutes of Li enters the same position as a normal spinel, and the remaining 0.1 minutes enters into an empty oxygen tetrahedron in the spinel. Thus, the LiMn ₂ O ₄ of the present invention in which LiCoO ₂ is solid-soluted has a composition different from that of ordinary spinel.

In <Embodiment 2> This embodiment, by changing the ratio of LiCoO ₂ and LiMn ₂ O _4, make LiMn ₂ O ₄ was dissolved various LiCoO _2, was examined characteristics as a positive electrode active material.

In the same manner as described in Example 1, the battery was heated and manufactured, and a battery was experimentally manufactured and its characteristics were examined. As an index showing the cycle characteristics of the positive electrode active material, the discharge capacity from the 10th cycle to the 50th cycle
It was decided to use the value obtained by subtracting the discharge capacity at the cycle and dividing it by the discharge capacity at the 10th cycle. That is, it is the cycle deterioration rate, and the smaller this value, the better. FIG. 5 is a plot of the cycle characteristics of the active material against the ratio of LiCoO ₂ and LiMn ₂ O ₄ when forming a solid solution. The cycle characteristics improved as the LiCoO ₂ content increased. However, the degree of improvement slowed down from the ratio of LiCoO ₂ to LiMn ₂ O ₄ of around 10:45. Furthermore, when the ratio of LiCoO ₂ increased to 50:25, the cycle characteristics rather deteriorate.

From this, the ratio of LiCoO ₂ and LiMn ₂ O ₄ is from 2:49 to 30:35.
It is found that 5: 47.5 to 26:37 are particularly desirable.

In other words, in terms of the composition of solid solution, Li _1.01 Co _0.02 Mn _0.98 O ₄
From Li _1.15 Co _0.3 Mn _0.7 O ₄ is good, especially Li _1.025 Co _0.05 Mn
_0.98 O ₄ to Li _1.13 Co _0.26 Mn _0.74 O ₄ are preferred.

When the active material used in this example was examined by X-ray diffraction, LiCoO ₂
The solid solution with the ratio of LiMn ₂ O ₄ and LiMn ₂ O ₄ up to 30:35 shows the same diffraction pattern as LiMn ₂ O _4, and the lattice constant of the cubic crystal decreases as the proportion of LiCoO ₂ in solid solution increases. I understood. When the ratio is higher than this, other peaks appear in the diffraction pattern, and it is difficult to call it only cubic crystals.

It was reacted LiCoO ₂ and LiMn ₂ O ₄ for the production of LiMn ₂ O ₄ obtained by solid solution <Example 3> Example 1 In LiCoO _2. This way, LiC
The reactivity of oO ₂ and LiMn ₂ O ₄ was slow and took a long time. In this example, rather than producing LiCoO ₂ and LiMn ₂ O ₄ separately, a predetermined amount of Li ₂ CO ₃ and Mn ₃ O ₄ and CoCO ₃ were mixed well, and then 1
The mixture was heated and reacted for 0 hour.

To prepare a solid solution having the same composition as described in Example 1, 27.5 mol of Li ₂ CO ₃ , 30 mol of Mn ₃ O ₄ and 10 mol of CoCO ₃ were mixed, and then mixed at 900 ° C. for 10 minutes. Heated for hours. The same result was obtained even when the product was subjected to X-ray diffraction and a similar battery test.

Example 4 In Examples 1 and 2, LiMn ₂ O ₄ having a spinel type crystal structure was used.
It was found that the solid-state solution of LiCoO ₂ in the solution can improve the cycle characteristics of the battery while maintaining the crystal structure of LiMn ₂ O ₄ . At this time, it is considered that Co enters in a form in which Mn is substituted, and further Li is increased to 1 or more with respect to oxygen 4.

In Example 3, it was found that Li _X Co _Y Mn _(2-Y) O ₄ can be synthesized by mixing a predetermined amount of Li compound, Co compound and Mn compound and heating.

Therefore, with respect to Li _X Co _Y Mn _(2-Y) O ₄ , one having fixed X and varying the value of Y and one having fixed Y and varying the value of X were prepared.
The cycle characteristics of the positive electrode active material were investigated.

For X = 1.0, 1.01, 1.025, 1.05, 1.10, 1.15, 1.20, Y = 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.
Li ₂ CO ₃ , CoCO ₃ , and Mn ₃ O ₄ were weighed so as to be ₃ , 0.4, a solid solution was prepared in the same manner as in Example 3, and a battery was prototyped as in Example 1, and a cycle test was performed. .

As the cycle characteristics, the cycle deterioration rate was taken as in Example 2, and the cycle deterioration rates of the active materials corresponding to X and Y are shown in Table 1. From this, it was found that in order to improve the cycle characteristics of the positive electrode active material, it is effective to limit both values of the amount of Li of X and the amount of Co of Y of the produced active material. However, it was also found that if Li and Co were too much, the effect would be lost.

The results of Examples 1 to 4 are summarized as Li _X Co _Y Mn.
_{When the} amount of Co, which is Y of _(2-Y) O ₄ , is 0.02 or more and 0.3 or less, Li
When the amount of X is 1 or more and 1.15 or less, a non-aqueous electrolyte secondary battery having good cycle characteristics and thus having a large discharge capacity after cycling can be obtained.

Example 5 Next, the case where _{X of} Li _X Co _Y Mn _(2-Y) O ₄ was smaller than 1 was examined.

Production method of LiMn ₂ O ₄ The same procedure as in Example 1 was performed.

Preparation of Li _X Mn ₂ O ₄ Li ₂ CO ₃ and Mn ₃ O ₄ were mixed well at a predetermined Li atom content of X moles and Mn atom content of 2 moles, and then the mixture was heated to 90
It was made by heating at 0 ° C for 10 hours.

Here, X = 0.95, 0.90, 0.85, and 0.80 were prepared and used as the positive electrode active material.

Preparation of Li _X Co _Y Mn _(2-Y) O _{4 Using} Li ₂ CO ₃ , Mn ₃ O ₄ and CoCO ₃ , Li atom content is X mole, Co atom content is Y mole, and Mn atom content is 2-Y. After mixing well at a molar ratio, the mixture was made by heating in air at 900 ° C. for 10 hours. Y = 0 for each of X = 0.95, 0.90, 0.85, 0.80.
The materials of 01, 0.02, 0.05, 0.1, 0.2, 0.3 and 0.4 were prepared as positive electrode active materials.

Battery Production and Charge / Discharge Test The same procedure as in Example 1 was performed.

Even under this condition, X showing the composition of Li in the positive electrode active material shown in FIG.
Means that it was charged to 0.7 or less to 0.3, and X was discharged to 1.

Figure 6 shows the discharge capacity of these batteries in the first cycle as Li
It is a plot of _X Mn ₂ O ₄ against X. From this, it can be seen that the discharge capacity increases as X decreases.

As an index representing the cycle characteristics of the positive electrode active material, a value obtained by subtracting the discharge capacity at the 50th cycle from the discharge capacity at the 10th cycle and dividing it by the discharge capacity at the 10th cycle was used. That is, it is the cycle deterioration rate, and the smaller this value, the better. Figure 7 shows the _X of Li _X Mn ₂ O ₄ .
Is a plot of the deterioration rate due to this cycle. The smaller X is, the higher the deterioration rate is.

Therefore, using Li _X Co _Y Mn _(2-Y) O _{4 in} which a part of Mn of Li _X Mn ₂ O ₄ is replaced with Co as the positive electrode active material, a battery is constructed in the same manner as described above. Then, a charge / discharge test was performed.

Table 2 shows the discharge capacity (unit: mAH) at the 50th cycle of Li _X Co _Y Mn _(2-Y) O ₄ for each X and Y. Also,
Table 3 shows the cycle deterioration rate of each active material.

FIG. 8 shows discharge curves at the 50th cycle of Battery D using Li _0.9 Co _0.1 Mn _0.9 O ₄ which is an example of the present invention and Battery B using LiMn ₂ O ₄ which is a conventional example. It was It can be seen that the battery of this example is excellent.

From the above, the cycle characteristics are improved when _{Y of} Li _X Co _Y Mn _(2-Y) O ₄ is 0.02 or more and 0.3 or less, and when X is less than 1 and 0.85 or more, Li _X Mn ₂ O ₄ The discharge capacity is larger than that of.

When the Li _X Co _Y Mn _(2-Y) O ₄ of the present invention was examined by X-ray diffraction, the diffraction pattern was the same as that of LiMn ₂ O ₄ . However, the lattice constant position determined from the diffraction peak is shifted to the higher angle side compared to LiMn ₂ O ₄ of the peak, compared to 8.24Å of LiMn ₂ O _4, the example Li _0.9 Co _0.1 Mn _0.9 O ₄ It was as small as 8.21Å. It is considered that the crystal becomes stable and the cycle characteristics are improved due to the smaller lattice constant.

From Example 5, represented by the formula Li _X Co _Y Mn _(2-Y) O ₄ , 0.85 ≦ X ≦ 1, 0.02 ≦
By using a material with Y ≦ 0.3 as the positive electrode active material, the capacity of the non-aqueous electrolyte secondary battery can be increased and the cycle characteristics can be improved.

Combining the above Examples 1 to 5, the formula Li _X Co _Y Mn _{(2-Y) 2} O
_{By using} a material represented by ₄ and having 0.85 ≦ X ≦ 1.15 and 0.02 ≦ Y ≦ 0.3 as the positive electrode active material, the capacity of the non-aqueous electrolyte secondary battery can be increased and the cycle characteristics can be improved.

Next, an active material in which Mn in LiMn ₂ O ₄ was partially replaced by Cr or Fe was examined. It was found that these discharge capacities decreased only in the first cycle, but became a positive electrode active material for a secondary battery with good cycle characteristics, and the discharge capacities also increased after the fifth cycle.

The reason for this is that if Mn in Li _X Mn ₂ O ₄ is replaced with Fe or Cr,
The lattice constant of the spinel structure becomes smaller as in the case of Co, but in this case as well, it is thought that this increased crystal stability and improved cycle characteristics. In addition, X of LiMn ₄ O in which a part of Mn at the stage of the synthesized active material is replaced with Fe or Cr
It has been found that the cycle characteristics are further improved as the size becomes larger.

<Example _{6> LiM Y Mn (2-} Y) O 4 (M = Cr, Fe) Preparation Li ₂ CO ₃ and Mn ₃ O ₄ of the Cr ₂ O ₃ or, Li atomic with Fe ₂ O ₃ 1 mole, Cr atom content or Fe atom content was Y mole, and Mn atom content was 2-Y mole, and the mixture was heated at 900 ° C. for 10 hours in the atmosphere. Cr or Fe with Y = 0.01, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4 was prepared as a positive electrode active material. The battery was manufactured and the charge / discharge test was performed in the same manner as in Example 1.

Even under this condition, X, which represents the composition of Li in the positive electrode active material in FIG. 2, was charged to 0.3, which was 0.7 or less, and was discharged until X was 1.

FIG. 9 shows a battery E using LiFe _0.2 Mn _1.8 O ₄ which is an example of the present invention and a battery B using LiMn ₂ O ₄ which is a conventional example.
The charge-discharge curve at the cycle is shown.

Looking at the charging curve corresponding to discharging, it can be seen that a charging voltage of 4 volts or more is required. Further, the present invention was larger in both the charge electricity quantity and the discharge electricity quantity.

The discharge capacity of each of these batteries in each cycle is plotted in Figure 10. It can be seen that the cycle characteristics are improved in the case of the example.

As a result of chemical analysis of the positive electrode active material after completion of the 101st cycle of charging, X of the conventional example was 0.84,
The X of the present invention was 0.56. That is, it was found that the deterioration due to the cycle, which is remarkably observed in the conventional example, is because the positive electrode active material cannot be charged due to the collapse of the crystallinity or the like, that is, Li is less likely to escape from the active material.

The FIG. 11, the discharge capacity at the 50th cycle at the time of each Y of _{LiFe Y Mn (2-Y)} O 4 ( unit mAH) showed. In Figure 12,
The cycle deterioration rate of each active material is shown. It can be seen that the battery of the present invention is superior to the conventional example of Y = 0. From the above, it can be seen that when Y is 0.02 or more, the deterioration rate decreases depending on the cycle. When Y exceeds 0.3, the cycle deterioration rate increases. This is probably because strain occurs in the crystal. This reduced the discharge capacity as shown in FIG. From this, the value of Y is 0.02 or more
0.3 or less is preferable. Furthermore, using LiCr _Y Mn _(2-Y) O _{4 in} which part of Mn of LiMn ₂ O ₄ was replaced with Cr, a battery was constructed in the same manner as described above, and a charge / discharge test was conducted. Figure 13 shows LiCr _Y Mn
_The deterioration rate due to the cycle of the battery using each active material of Y of _(2-Y) O ₄ is shown. Even when LiCr _Y Mn _(2-Y) O ₄ is used as the active material, Y is 0.02 or more as in the case of using LiFe _Y Mn _(2-Y) O _4.
0.3 or less was good.

<Example 7> The relationship between the X value of Li _X M _Y Mn _(2-Y) O ₄ and the cycle characteristics in the produced active material stage was examined.

Preparation of Li _X M _Y Mn _(2-Y) O ₄ (M = Cr, Fe) Li ₂ CO ₃ and Mn ₃ O ₄ and Cr ₂ O ₃ or Fe ₂ O ₃ with Li atom content of X mole , Cr atom content or Fe atom content was Y mole, and Mn atom content was 2-Y mole, and the mixture was heated at 900 ° C. for 10 hours in the atmosphere. As Cr or Fe, Y = 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, and X = 1.0, 1.01, 1.025, 1.05, 1.10, 1.15, 1.20.

The battery configuration and test method were the same as in Example 1. As the cycle characteristics, the cycle deterioration rate was taken as in Example 6, and Table 4 shows the cycle deterioration rates of the active materials corresponding to X and Y when Fe is used as M.

From this, it was found that in order to improve the cycle characteristics of the positive electrode active material, it is effective to limit both the values of the amount of Li of X and the amount of Fe of Y of the produced active material. However, Li is also Fe
If the amount is too large, the cycle characteristics deteriorate as in the case of Example 1. Fe content of 0.02 to 0.3
I think that the amount should be 1 or more and 1.15 or less.

Similarly, when Cr was used as M, the same result as that of Fe was obtained, and the Cr amount was 0.02 or more and 0.3 or less, and the Li amount was 1 or more and 1.15 or less.

According to Examples 6 and 7 above, a lithium or lithium compound is used as a negative electrode, and a positive electrode in a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte containing a lithium salt is represented by the formula Li _X M _Y Mn _(2-Y) O ₄ . M is at least one of Cr and Fe, and uses a positive electrode active material satisfying 1 ≦ X ≦ 1.15 and 0.02 ≦ Y ≦ 0.3. The composition of the positive electrode active material of Li _X M _Y Mn _(2-Y) O ₄ (where X is
By satisfying ≦ 0.7), a lithium secondary battery having excellent cycle characteristics can be obtained.

Further, as in Example 5, Li _X M _Y Mn _(2-Y) O ₄ (M = F
e, Cr) where X is less than 1 was examined.

<Example 8> Method for producing Li _X M _Y Mn _(2-Y) O ₄ (M = Cr, Fe) Li ₂ CO ₃ , Mn ₃ O ₄ and Cr ₂ O ₃ or Li ₂ O ₃ was used. After mixing well in a ratio of X moles of atom content, Y moles of Cr atom content or Fe atom content, and 2-Y moles of Mn atom content, the mixture was heated at 900 ° C. in the atmosphere for 10 hours to prepare.

As Cr or Fe, Y = 0, 0.01, 0.02, 0.05, 0.1,
X = 0.95, 0.90, 0.85, 0.80 for 0.2, 0.3, 0.4 were prepared as positive electrode active materials. The battery was manufactured and the charge / discharge test was performed in the same manner as in Example 1.

Even under this condition, X indicating the composition of Li in the positive electrode active material in FIG. 2 was charged to 0.3, which is 0.7 or less, and discharged until X became 1. X at the end of charging is 0.7
Above, the discharge capacity is small and not practical.

FIG. 14 shows a battery F using Li _0.9 Fe _0.2 Mn _1.8 O ₄ which is an example of the present invention and a battery G using Li _0.9 Cr _0.2 Mn _1.8 O ₄ and a comparative example with less Li and Fe and Cr. No. 5 of the battery H using Li _0.9 Mn ₂ O ₄ containing no hydrogen and the conventional battery B using LiMn ₂ O ₄
The charge-discharge curve at the 0th cycle is shown. Looking at the charging curve corresponding to discharging, it can be seen that a charging voltage of 4 volts or more is required. Further, the battery of the present invention had a larger amount of charge electricity and a larger amount of discharge electricity.

In FIG. 15, the discharge capacities of these F, H, and B batteries in each cycle are plotted. It can be seen that the cycle characteristics are improved when the active materials of the examples are used.

As a result of the chemical analysis of the positive electrode active material after the completion of the 101st cycle of charging, the X of A of the present invention was 0.58 although the X of the B of the conventional example was 0.84. It was found that the deterioration due to the cycle, which is conspicuously seen in the conventional example, is because the positive electrode active material cannot be charged due to the collapse of the crystallinity, that is, Li is less likely to escape than in the active material.

FIG. 16 shows the discharge capacity (unit: mAH) at the 50th cycle for each Y of Li _0.9 Fe _Y Mn _(2-Y) O ₄ . It can be seen that the battery of the present invention has a large discharge capacity and is superior to the conventional example of Y = 0.

As an index representing the cycle characteristics of the positive electrode active material, a value obtained by subtracting the discharge capacity at the 50th cycle from the discharge capacity at the 10th cycle and dividing it by the discharge capacity at the 10th cycle was used. That is, it is the cycle deterioration rate, and the smaller this value, the better.

FIG. 17 shows the cycle deterioration rate of each active material. It can be seen that the battery of the present invention is superior to the conventional example of Y = 0.

Similarly, the cycle deterioration rate of the active material of Li _0.9 Cr _Y Mn _(2-Y) O ₄ for each Y is shown in FIG.

By X-ray diffraction, Li _0.9 Fe _Y Mn _(2-Y) O ₄ and Li _0.9 Cr _Y Mn of this example
Examination of _(2-Y) O ₄ showed that the diffraction pattern was the same as LiMn ₂ O ₄ . However, the position of the peak lattice constant determined from the diffraction peak is shifted to the higher angle side compared to LiMn ₂ O _4, was smaller compared to LiMn ₂ O _4. It is considered that the crystal becomes stable and the cycle characteristics are improved due to the smaller lattice constant.

From the above, it can be seen that the cycle deterioration rate decreases when Y is 0.02 or more. If Y exceeds 0.3, the cycle deterioration rate increases. I think this is because strain occurs in the crystal. As a result, the discharge capacity was reduced as shown in FIG. Therefore, the value of Y is preferably 0.02 or more and 0.3 or less.

Next, as a positive electrode active material, X and Y of Li _X Fe _Y Mn _(2-Y) O ₄ were used.
Were synthesized, a battery was constructed in the same manner as described above, and a charge / discharge test was conducted. Table 5 shows Li _X Fe _Y Mn
The discharge capacities (unit: mAH) at the 50th cycle of _(2-Y) O ₄ for each of X and Y are shown. Further, Table 6 shows the cycle deterioration rate of each active material.

From the above, when _{Y of} Li _X Fe _Y Mn _(2-Y) O ₄ or Li _X Cr _Y Mn _(2-Y) O ₄ is 0.02 or more and 0.3 or less, cycle characteristics are improved, and X is less than 1 Is 0.85 or more, the conventional LiMn ₂ O ₄
The discharge capacity is also larger than that of Li _X Mn ₂ O ₄ of Comparative Example. further,
Li _X Cr _Y Mn _(2-Y) O ₄ was also investigated.

As a result, the same tendency as Li _X Fe _Y Mn _(2-Y) O ₄ was obtained, and when Y was 0.02 or more and 0.3 or less, cycle characteristics were improved,
In addition, when X is less than 1 and 0.85 or more, the conventional LiMn
Discharge capacity is large compared to the ₂ O ₄ of and Comparative Example Li _X Mn ₂ O _4.

Even if Fe is included in Table 5, the discharge capacity increases when X is less than 1 as compared to X = 1, as shown in FIG. 6, when X is 1 or less, the discharge capacity in the first cycle increases. And then Fe
This is considered to be the result of the improved cycle characteristics due to the inclusion of.

As above, charge up to 4.5V where X becomes 0.7 or less, and X becomes 1
The result of discharging until it became is shown. However, the present invention is not limited to discharging to X up to 1, and is also effective when charging X to 0.7 or less and discharging until X becomes 1 to 1.8. This is because the charge and discharge with X between 1 and 1.8 show good cycle characteristics even with the conventional composition,
This is because the positive electrode active material of this example also showed good cycle characteristics.

From Example 8, in a non-aqueous electrolyte secondary battery in which lithium or a lithium compound is used as a negative electrode and a non-aqueous electrolyte containing a lithium salt is used as a positive electrode, a positive electrode represented by the general formula Li _X Mn _(2-Y) O ₄ , Is at least one of Cr and Fe, and 0.85 ≦ X ≦ 1 and 0.02 ≦ Y ≦ 0.3
A non-aqueous electrolyte secondary battery having good cycle characteristics can be obtained by using the positive electrode active material of

When Examples 6 to 8 are summed up, lithium or a lithium compound is used as a negative electrode, and a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte containing a lithium salt is used as a positive electrode in the general formula Li _X M _Y Mn.
_(2-Y) O ₄ , M is at least one of Cr and Fe, and good cycle characteristics are obtained by using a positive electrode active material in which 0.85 ≦ X ≦ 1.5 and 0.02 ≦ Y ≦ 0.3. A non-aqueous electrolyte secondary battery can be obtained.

Furthermore, when Examples 1 to 8 are summed up, in a non-aqueous electrolyte secondary battery using lithium or a lithium compound as a negative electrode and a non-aqueous electrolyte containing a lithium salt, the positive electrode has the general formula Li _X M _Y Mn _{(2-Y )} O ₄ , M is at least one of Co, Cr and Fe, and 0.85 ≦ X ≦ 1.5, 0.02 ≦ Y ≦
By using the positive electrode active material of 0.3, a non-aqueous electrolyte secondary battery having good cycle characteristics can be obtained.

So far, examples have been shown in which the discharge is stopped up to 3 volts. However, with the active material of the present invention, the discharge is deepened and the second
The cycle characteristics were good even when the discharge up to 2 V as shown in the figure, that is, the second-stage discharge as well as the first-stage discharge was performed.

<Example 9> A similar battery was manufactured using the same active material as described in Examples 1 to 8.

Battery charge / discharge test Charge these batteries up to 4.5 V with a constant current of 2 mA, and
The charging and discharging to discharge to the voltage was repeated. Under this condition, X indicating the composition of Li in the positive electrode active material in FIG. 2 was charged to about 0.3 which is 0.7 or less, and discharged until X became 1.8. The active materials of the present invention shown in Examples 1 to 8 showed good characteristics even when discharged to 2 volts.

FIG. 19 shows the discharge curve (I-1) and the 50th cycle of the first cycle of Battery I using LiCo _0.2 Mn _1.8 O ₄ , which is an example of the present invention.
It is a discharge curve (I-50) at the cycle and a conventional example.
A discharge curve (B-1) at the first cycle and a discharge curve (B-50) at the 50th cycle of battery B using LiMn ₂ O ₄ are shown. This embodiment has less deterioration due to cycles. Comparing the discharge curves of the first cycle and the 50th cycle of the battery B, the discharge time of the second stage portion of 3 V or less and 2 V or more in discharge was slightly shortened and some deterioration occurred. However, the discharge time of the first stage portion of 4.5 V or less and 3 V or more becomes considerably short, and the deterioration is large. In the battery I of the present invention, the deterioration of the second part of the discharge curve is large. In the battery I of the present invention, the second part of the discharge curve is hardly deteriorated. Furthermore, it can be seen that the first stage also has little deterioration.

This result indicates that the deterioration due to the cycle, which is conspicuous in the conventional example, remarkably occurs in the first stage portion. Therefore, it can be understood that the reason why the active materials of the present invention shown in Examples 1 to 8 exhibit good characteristics even when discharged to 2 V is because the deterioration in the first step was small.

<Example 10> Using the same active materials as in Examples 1 to 8 and changing only the electrolyte, a battery was similarly prepared. Lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ and LiBF _{4 of} 1 mol / l each were used as solutes, and propylene carbonate or a mixed solvent of propylene carbonate and ethylene carbonate at a volume ratio of 1: 1 was used as a solvent. An electrolyte was prepared by combining a solute and a solvent.

The battery test is the same as in Example 1. The results are in Example 1.
To 8 and the active material of the present invention showed good cycle characteristics.

This result indicates that the active material of the present invention exhibits good properties regardless of the type of non-aqueous electrolyte containing a lithium salt.

Example 11 A battery was made in the same manner as in Examples 1 to 8 except that only the negative electrode was changed. Li-Al alloy, Li as negative electrode
WO ₂ intercalated with was used. Battery testing is
Same as Example 1 and Example 9. The results are in Example 1.
And almost the same as in Example 9, and the active material of the present invention showed good cycle characteristics.

<Example 12> Using the same active material as in Examples 1 to 8, a battery was made in the same manner. Charge and discharge were performed under the same conditions as in Example 1 except that the amount of electricity charged was changed. By changing the amount of charged electricity, the amount of _X represented by Li _X M _Y Mn _(2-Y) O ₄ changes at the end of charging. Therefore, the relationship between the quantity of electricity charged and the quantity of electricity discharged is expressed as
Then, the amount of discharge per 1 g of the active material was converted and examined. In FIG. 20, the relationship between the charge electricity quantity and the discharge electricity quantity at the first cycle of the battery using LiCoO _0.2 Mn _1.8 O ₄ which is an example of the present invention is plotted according to the above. From this, the composition of the positive electrode active material in the charged state is X.
However, it can be seen that the discharge capacity becomes sufficient at 0.7 or less.

With the composition of the positive electrode active material in this charged state, a sufficient discharge capacity was obtained when X was 0.7 or less, which was the same result including the conventional example.

Effects of the Invention Summarizing the results described in Examples 1 to 12 above,
In a non-aqueous electrolyte secondary battery using lithium or a lithium compound as a negative electrode and a non-aqueous electrolyte containing a lithium salt, the positive electrode is represented by the general formula Li _X M _Y Mn _(2-Y) O ₄ , and M is C
at least one of o, Cr and Fe, and 0.85 ≦
Using a positive electrode active material in which X ≦ 1.15 and 0.02 ≦ Y ≦ 0.3, the composition of the positive electrode active material in a charged state in which lithium is removed from the positive electrode active material by charging is Li _X M _Y Mn _(2-Y) O ₄ (However, X ≦ 0.
By adopting 7), it is possible to realize a non-aqueous electrolyte secondary battery that has good cycle characteristics and can obtain a sufficient discharge capacity even after the cycle has passed, and its industrial significance is great.

[Brief description of drawings]

Fig. 1 is a cycle characteristic diagram of the battery, Fig. 2 is a general discharge curve diagram when the battery using LiMn ₂ O ₄ is charged to 4.5 V and discharged to 2 V, and Fig. 3 is used for the test. Longitudinal sectional view of the battery, Fig. 4 is the discharge characteristic diagram of the battery, and Fig. 5 is LiCo
A characteristic diagram showing cycle deterioration rate with respect to the ratio of O ₂ and LiMn ₂ O ₄ , FIG. 6 is a discharge capacity characteristic diagram of Li _X Mn ₂ O ₄ at the first cycle with respect to X, and FIG. 7 is Li _X Mn ₂ O _{4 is} a characteristic diagram of cycle deterioration rate with respect to X, and FIG. 8 is an example of the present invention Li _0.9 Co _0.1
A discharge curve diagram at the 50th cycle of Battery D using Mn _0.9 O ₄ and Battery B using LiMn ₂ O ₄ which is a conventional example, and FIG. 9 shows LiFe _0.2 Mn _1.8 O ₄ which is an example of the present invention. Fig. 10 is a discharge curve diagram at the 100th cycle of the battery E using the battery and the conventional battery B using the LiMn ₂ O ₄ , Fig. 10 is a discharge capacity characteristic diagram at each cycle of the battery, and Fig. 11 is this 50th at each Y of the invention LiFe _Y Mn _(2-Y) O ₄
FIG. 12 is a discharge capacity characteristic graph at the cycle, and FIG. 12 is a cycle deterioration rate characteristic graph at each Y of LiFe _Y Mn _(2-Y) O ₄ , which is the active material of the present invention.
FIG. 13 is a graph showing deterioration rate characteristics according to cycles of a battery using each Y active material of LiCr _Y Mn _(2-Y) O ₄ which is the active material of the present invention.
The figure shows a battery F using Li _0.9 Fe _0.2 Mn _1.8 O ₄ as an example of the present invention and Li _0.9 Cr _0.2 Mn _1.8 O ₄
Battery G using Li., A comparative example, battery H using Li _0.9 Mn ₂ O ₄ containing less Li and containing no Fe or Cr, and a conventional example LiMn ₂ O ₄
FIG. 15 is a comparison diagram of charging and discharging curves of the battery B in the 50th cycle using FIG. 15, FIG. 15 is discharge in each cycle of the battery, and FIG. 16 is Li _0.9 Fe _Y Mn _(2-Y) O ₄ of the present invention. Fig. 17 is a cycle deterioration rate characteristic diagram for each Y of Fig. 17, Fig. 17 is a cycle deterioration rate characteristic diagram of Li _0.9 Fe _Y Mn _(2-Y) O ₄ for each Y, and Fig. 18 is Li _0.9 Cr _Y Mn _(2-Y) O ₄
Fig. 19 is a time cycle deterioration rate characteristic diagram of each Y, Fig. 19 is a charge / discharge curve diagram of the battery I of the present invention and the battery B of the conventional example at the first cycle and the 50th cycle, and Fig. 20 is a graph showing the activity at the time of charging. It is a relationship diagram of a composition of a substance and discharge capacity. A: battery of one embodiment of the present invention, B: conventional example, C, D, E,
F, G, H, I ... Batteries of different embodiments of the present invention, 1 ... Positive electrode, 2 ... Case, 3 ... Separator, 4 ... Lithium plate, 5 ... Sealing plate, 6 ... Gasket.

Claims (1)

[Claims] 1. A negative electrode comprising lithium or a lithium compound, a non-aqueous electrolyte containing a lithium salt, and a general formula Li _X M _Y Mn _(2-Y) O ₄ , wherein M is Co, Cr, At least one of Fe, and X in the formula is 0.85 ≦ X ≦ 1.15, and Y in the formula
Is used as a positive electrode, and X in the formula is X ≦ 0.7 in a charged state, a non-aqueous electrolyte secondary battery.