JP2000138077A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a battery characteristic, especially, a charge/discharge cycle characteristic, a storage characteristic, and safety, by adding a sulfur simple substance whose grain size is less than a specific value or sulfate to a positive electrode, or by solving the sulfur simple substance whose grain size is less than a specific value or sulfate in electrolyte. SOLUTION: A sulfur simple substance whose grain size is not more than 50 μm or sulfate is contained in a battery. When the sulfur simple substance is contained in a positive electrode, or is solved in electrolyte, considering a reaction with the electrolyte, the grain size of the sulfur is preferably not more than 50 μm, and is desirable not to have absorbing water or structural water or to get dehydrate treatment. Manganese sulfate mixed into the positive electrode or solved in electrolyte, considering a reaction with the electrolyte, the grain size is preferably not more than 50 μm, and is desirable not to have absorbing water or structure water or to get dehydrate treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to lithium which has improved charge / discharge characteristics, particularly cycle life at high temperatures, capacity storage characteristics and self-discharge characteristics, and has excellent safety. Related to secondary batteries.

[0002]

_2. Description of the Related Art As lithium ion secondary batteries, those using LiCoO ₂ for the positive electrode and graphite or amorphous carbon for the negative electrode are known. When this material system is used, for example, as disclosed in JP-A-55-136131, when LiCoO ₂ and LiNiO ₂ are used as positive electrodes and metallic Li is used as a negative electrode, the battery voltage is about 3.9.
~ 4.5V, theoretical energy density is 1100W
Expression of a high energy density of h / kg is expected. However, experimentally, the energy that can be used for charging and discharging is much smaller than the theoretical energy density. Therefore, it is needless to say that the available energy at a practical level is still smaller.

[0003] The reason for this is that, for example, the positive electrode active material is LiCo.
In the case of O ₂ , when Li ions are released from LiCoO ₂ by charging, Co, which was originally trivalent, is partially tetravalent in a form to compensate for a change in charge due to the release of Li, and the tetravalent state is obtained. It is considered that the host structure of LiCoO ₂ changes due to the instability of Co, and as a result, the characteristics deteriorate. Journal of El
electrochemical Society Vo
l. 139, no. 8, pp2091-2097
In (JN Reimers, JR Dahn), a phase diagram of a host-structured crystal system is created from the relationship between the amount of released Li ions, the change in potential, and the relationship between lattice constants, and hexagonal / monoclinic. It reports the phase transition of the system. In addition, some similar reports have already been seen at the Electrochemical Society Conference and the Battery Discussion Meeting.

In order to solve the above problem, Japanese Patent Publication No. 4-24831 discloses, for example, substituting a part of Co of LiCoO ₂ with another metal. Also, Ma
terminal Research Bulletin
Vol. 27, pp327-337 or Soli
d State Ionics Vol. 53-56,
In pp681-687, evaluation of LiCoO ₂ having a spinel structure, which is a three-dimensional host structure instead of a two-dimensional layered structure, is performed by firing at a low temperature.

However, there is a limit in reducing the self-discharge and improving the cycle characteristics by any of the methods.

[0006] Co, which is a raw material of LiCoO ₂ , is also regarded as a problem in terms of resources, and is naturally very disadvantageous in terms of cost. The reasons for this are that the abundance of Co in the continental crust is inherently small, that there is not much ore extraction for Co, and that it is often extracted as a by-product of other ore resources. Anxiety and the like. (New Metal Data Book Metal Review, Industrial Rare Metal No. 105, pp76-81
Therefore, when it is anticipated that lithium ion secondary batteries will be applied to various fields in the future, the resource problem of Co is important.

On the other hand, LiNiO _{2, which} is expected as an alternative material to LiCoO ₂ , also has a large irreversible capacity, it is difficult to synthesize a material having high quality, that is, a material exhibiting characteristics suitable for a positive electrode material, and has to deal with troublesome handling such as consideration for humidity. That there are concerns about environmental impact,
There are still many challenges for practical use, such as the fact that the cost advantage over LiCoO ₂ is not so large in the final product stage. Lithium manganate is one of the positive electrode materials that attracts attention from such a situation. This material system was already reported in the 1950's as a subject for studying magnetic behavior (Journal of A).
American Chemical Society
Vol. 78, pp 3255-3260), but in 1983 Material Res.
ear Bulletin Vol. 18, pp
461-472. M. Since Thackeray et al. Reported that Li ions could be electrochemically transferred in and out, they have been studied as cathode materials for lithium secondary batteries (for example, Journal of Ele).
crochemical Society Vol.
136, no. 11, pp3169-3174 or the Journal of Electrochemi
calSociety Vol. 138, no. 1
0, pp 2859-2864). This lithium manganate has a spinel structure represented by the chemical formula LiMn ₂ O ₄ and functions as a 4V-class positive electrode material between compositions with λ-MnO ₂ . Lithium manganate with spinel structure is LiC
Since it has a three-dimensional host structure different from the layered structure such as that of oO _{2 and the} like, most of the theoretical capacity can be used, and excellent cycle characteristics are expected.

However, in practice, a lithium secondary battery using lithium manganate as a positive electrode is inevitably subjected to a capacity deterioration in which the capacity gradually decreases due to repeated charging and discharging, which is a serious problem for its practical use. Was left.

Therefore, various methods have been studied to improve the cycle characteristics of an organic electrolyte secondary battery using lithium manganate for the positive electrode. For example, characteristics improvement by improving reactivity at the time of synthesis (Japanese Patent Application Laid-Open Nos. 3-67664, 3-119656, and 3-12)
7453, JP-A-7-245106, JP-A-7-73883, etc.), and characteristic improvement by controlling the particle size (JP-A-4-198080, JP-A-5-28307, JP-A-6-295724, JP-A-7-97216, etc.), and characteristic improvement by removing impurities (JP-A-5-21063)
However, none of them has achieved satisfactory improvement in cycle characteristics.

Apart from the above, Japanese Patent Application Laid-Open No. 2-270268 discloses an attempt to improve the cycle characteristics by sufficiently increasing the composition ratio of Li with respect to the stoichiometric ratio. The synthesis of a similar excess Li-containing composite oxide is disclosed in Japanese Patent Application Laid-Open Nos.
No. 47573, JP-A-5-205744, JP-A-7-282798 and the like. The improvement of the cycle characteristics by this method can be clearly confirmed experimentally.

Further, the same effect as the Li excess composition is aimed at.
Mn spinel material LiMn_TwoO_FourAnd this
Li-Mn composite oxide Li richer than the material_TwoM
n_TwoO _Four, LiMnO_Two, Li_TwoMnO_ThreeEtc. mixed and positive
The technique used as a pole active material is also disclosed in Japanese Patent Laid-Open No. 6-338320.
And Japanese Unexamined Patent Publication No. 7-262988.
I have. However, excessive addition of Li or another L
Cycle characteristics when mixed with i-rich compounds
Of charging / discharging capacity and charging / discharging energy
High energy density and long cycle life.
There was a problem that could not be set up. In contrast,
In Japanese Unexamined Patent Publication No. Hei 6-275276, high energy density,
High-rate charge / discharge characteristics (current during charge / discharge
Aiming at improvement of the reaction and completeness of the reaction,
Attempts to increase the product have been made,
Achieving a lifetime is difficult.

On the other hand, studies have been made to improve characteristics by adding another element to a ternary compound of Li-Mn-O. For example, addition, doping of Co, Ni, Fe, Cr, Al or the like (Japanese Unexamined Patent Publication No. Hei 4-14195)
No. 4, JP-A-4-160758, JP-A-4-160758
160976, JP-A-4-237970,
JP-A-4-282560, JP-A-4-28966
No. 2, JP-A-5-28991, JP-A-7-1
No. 4572). The addition of these metal elements is accompanied by a reduction in charge / discharge capacity, and further measures are required to satisfy the total performance.

In the study of the addition of other elements, the addition of boron is expected to improve other characteristics, such as cycle characteristics and self-discharge characteristics, with almost no decrease in charge / discharge capacity.
For example, JP-A-2-253560, JP-A-3-29
No. 7058 and Japanese Unexamined Patent Publication No. Hei 9-115515 disclose that fact. In each case, manganese dioxide or lithium-manganese composite oxide is mixed with a boron compound (for example, boric acid) in a solid phase or immersed in an aqueous solution of a boron compound, and then heat-treated to synthesize a lithium-manganese-boron composite oxide. ing. Since the composite particles of the boron compound and the manganese oxide have reduced surface activity, it was expected that the reaction with the electrolytic solution would be suppressed and the storage characteristics of the capacity would be improved.

However, the mere addition of boron caused grain growth and a decrease in tap density, and did not directly lead to an increase in capacity as a battery. In addition, depending on the synthesis conditions, the capacity may be reduced in the effective potential range when combined with the carbon anode, or the reaction with the electrolytic solution may be insufficiently suppressed, which is not necessarily effective in improving the storage characteristics. Was not.

As described above, various approaches have been tried to improve the cycle characteristics of lithium manganate.
At present, the cycle characteristics are comparable to those of the mainstream Co-based alloys, and particularly, the degradation mechanism is promoted in a high-temperature use environment. Therefore, further improvements are required to realize the cycle characteristics in a high-temperature use. In particular, considering the future expansion of application fields such as notebook computers and electric vehicles, it can be said that securing the cycle characteristics at high temperatures is becoming increasingly important.

[0016]

As described above, as described above, lithium manganate LiMn ₂ O ₄ is a complex oxide which is expected to be a substitute for LiCoO ₂ , which is currently the mainstream cathode active material. When LiMn ₂ O ₄ synthesized by the method is used, there are the following problems.

The first problem is capacity deterioration accompanying a charge / discharge cycle. The cause is that the average valence of Mn ions changes between trivalent and tetravalent as charge compensation accompanying the inflow and outflow of Li, thereby causing Jahn-Teller distortion in the crystal, and Mn from lithium manganate. Or an increase in impedance due to the elution of Mn. In order to solve this problem, improvement of the synthesis method, addition of other transition metal elements, Li excess composition, and the like have been studied.However, in order to simultaneously satisfy both high discharge capacity and high cycle life. Not reached.

The second problem is a decrease in storage capacity due to self-discharge. This is considered to be mainly due to insufficient stability of lithium manganate with respect to the electrolytic solution. Attempts have been made to reduce the active sites on the surface of the lithium manganate particles by forming composite particles with the B compound, but the effect has not been obtained sufficiently to be practically used.

In particular, when used in a high-temperature environment, the deterioration of both the first problem and the second problem is promoted, which is a major obstacle to the expansion of applications.

As described above, lithium manganate is expected to be used as a substitute for LiCoO ₂ , but there are problems to be improved when the battery is actually evaluated. Nevertheless, material systems that can be expected to satisfy the performance required of today's high-performance secondary batteries, such as high electromotive force, voltage flatness during discharge, cycle characteristics, and energy density, are limited. There is a need for a new spinel-structured lithium manganate that does not deteriorate in discharge capacity and has excellent cycle characteristics and storage characteristics.

Accordingly, the present invention has been made in view of such conventional problems, and a lithium-manganese composite oxide excellent in battery characteristics, particularly, charge-discharge cycle characteristics, storage characteristics, and safety has been developed. An object of the present invention is to provide a nonaqueous electrolyte dual battery used as a positive electrode active material.

[0022]

Means for Solving the Problems The present inventors have made various studies to achieve the above object, and as a result, completed the present invention.

According to the present invention, there is provided a non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide as a positive electrode, wherein the battery contains divalent Mn ions dissolved from a Mn salt. The present invention relates to a liquid secondary battery. In order to make the battery contain divalent Mn ions dissolved from the Mn salt, a divalent Mn salt is contained in the positive electrode, or a divalent Mn salt is contained in the electrolytic solution.
It can be carried out by dissolving the n salt.

The present invention also relates to a non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide for a positive electrode, wherein the battery contains sulfur or a sulfur compound. . In this case as well, sulfur or a sulfur compound can be contained in the battery by incorporating sulfur or a sulfur compound in the positive electrode or dissolving sulfur or the sulfur compound in the electrolytic solution.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, lithium manganate LiMn ₂ O ₄ is the currently mainstream cathode active material LiCoO _2.
Although it is a composite oxide that has attracted great promise as an alternative material to the above, it is difficult for conventional batteries using LiMn ₂ O ₄ to (1) achieve both high energy density (high charge and discharge capacity) and high cycle life. (2) There is a problem in two points, that is, a reduction in storage capacity due to self-discharge.

As the cause, technical problems in battery manufacturing and compatibility with the electrolyte have been pointed out. However, when focusing on the positive electrode material itself and the influence due to the positive electrode material, the following is considered. Can be

First, the reasons why high energy density cannot be realized include non-uniform reaction, phase separation, excessive imbalance in the composition ratio of Li and Mn, influence of impurities, insufficient tap density, and the like.

The heterogeneity of the reaction and the separation of the phases
Process depending on the process, but firing after dry mixing
In general, the mixing uniformity, starting material particle size and firing temperature
Is determined. That is, the reaction proceeds on the solid phase surface.
Therefore, mixing of the Li source and the Mn source is insufficient,
If the diameter is too coarse or the firing temperature is too high, Mn _Two
O_Three, Mn_ThreeO_Four, Li_TwoMnO_Three, LiMnO_Two, Li_TwoM
n_TwoO_Four, Li_TwoMn_FourO₉, Li_FourMn_FiveO₁₂Phase like
Generated, causing a drop in battery voltage and a drop in energy density.
Wake up.

The cause of capacity deterioration due to charge / discharge cycles is L
The average valence of Mn ions changes between trivalent and tetravalent as charge compensation as i enters and exits, and therefore Jahn-Tel
Ler distortion is generated in the crystal, and Mn is eluted from lithium manganate or the impedance is increased due to Mn elution. That is, as the cause of the capacity deterioration in which the charge / discharge capacity is reduced by repeating the charge / discharge cycle, the influence of impurities, the elution of Mn from lithium manganate, the precipitation of the eluted Mn on the negative electrode active material or the separator, and the Inactivation due to the release of the material particles, the influence of the acid generated by the contained water, and the deterioration of the electrolytic solution due to the release of oxygen from lithium manganate are considered.

Assuming that a single spinel phase is formed, the elution of Mn is caused by disproportionation of trivalent Mn in the spinel structure to tetravalent Mn and divalent Mn, so that Mn is dissolved in the electrolyte. It can be considered that Mn is easily dissolved in water, or it is eluted due to the relative shortage of Li ions, and the generation of irreversible capacity due to repeated charging and discharging and disorder of the atomic arrangement in the crystal Is promoted, and the eluted Mn ions precipitate on the negative electrode or the separator, and L
It appears to hinder i-ion migration. Lithium manganate distorts Li ions, cubic symmetry is distorted by the Jahn-Teller effect, and is accompanied by expansion and contraction of several% of the unit cell length. Therefore, by repeating the cycle, it is expected that some electrical contact failures occur and the released particles do not function as an electrode active material.

Further, it is considered that the release of oxygen from lithium manganate is facilitated along with the elution of Mn. Lithium manganate with many oxygen vacancies has a 3.3 V plateau capacity that increases with the passage of cycles, and as a result, the cycle characteristics also deteriorate. Further, it is presumed that a large amount of oxygen release affects the decomposition of the electrolytic solution, and the deterioration of the electrolytic solution may cause cycle deterioration.

Therefore, reduction of Mn elution, reduction of lattice distortion, reduction of oxygen deficiency, and the like are derived as countermeasures.

Next, the cause of the decrease in the storage capacity due to self-discharge is that if the phenomena of internal short-circuit such as insufficient alignment of the positive and negative electrodes due to the battery manufacturing process and mixing of metal scraps from the electrodes are excluded, the storage characteristics can be improved. It is considered that this is effective in improving the stability of lithium manganate with respect to the electrolytic solution, that is, suppressing elution of Mn, reaction with the electrolytic solution, release of oxygen, and the like.

Therefore, in the present invention, the inclusion of divalent Mn ions dissolved from the Mn salt in the battery increases the Mn concentration in the electrolytic solution and suppresses the elution of Mn from the active material.

Examples of the Mn salt used include divalent manganese salts such as manganese sulfate, manganese carbonate, manganese nitrate, and manganese acetate. Of these, manganese sulfate is preferred. With manganese sulfate, 2
This is because the effect of adding a valence Mn ion and the effect of adding a sulfur compound described later are obtained.

At this time, the Mn salt may be contained in the positive electrode or may be dissolved in the electrolytic solution. In any case, the effect can be obtained by including the Mn salt in the battery, and the amount of use can be appropriately selected depending on the Mn salt used. Mn concentration is preferably included so as to be 18 ppm or more. When manganese sulfate is used, [lithium-manganese composite oxide]: [manganese sulfate] = 100−
a: When expressed as a (% by weight), a content of 0.053 ≦ a is contained in the positive electrode, or 2
It can be dissolved and used so that the valence Mn concentration becomes 18 ppm or more.

When a divalent Mn salt such as manganese sulfate is contained in the positive electrode, divalent Mn ions dissolve in the electrolytic solution before trivalent or tetravalent Mn ions. Therefore,
LiMn ₂ O ₄ , LiMnO ₂ , Li ₂ used as an active material
It dissolves in the electrolytic solution before Mn in the lithium-manganese composite oxide mainly composed of Mn ₂ O ₄ . As a result, the Mn concentration in the electrolyte increases, and the elution of Mn from the active material is suppressed. In particular, when manganese sulfate is used, the active site at the positive electrode active material-electrolyte interface is reduced due to the catalytic poisoning effect of S on Mn due to SO ₄ ^2- minutes generated during the dissolution of Mn, and elution occurs at the same time. Activity of the Mn ions thus reduced. This suppresses decomposition reactions of the electrolyte at the cathode active material-electrolyte interface and various side reactions such as various reduction reactions involving Mn ions on the surface of the anode such as carbon materials, Li metal, and Li alloy. Can be.

Thus, a battery having excellent cycle characteristics and storage characteristics can be obtained. Further, since manganese sulfate does not need to react with the lithium-manganese composite oxide which is a positive electrode active material, an active material having high purity and high crystallinity can be used. Therefore, it is possible to keep the capacity loss only by the weight of the manganese sulfate powder added in a trace amount, and it is possible to suppress the capacity decrease as low as possible.

On the other hand, when manganese sulfate is dissolved in the electrolytic solution in advance, the same effect as described above can be obtained. Also, there is almost no reduction in battery capacity.

By including manganese sulfate in the positive electrode or dissolving manganese sulfate in the electrolytic solution, cycle characteristics and capacity storage characteristics can be improved. There are also advantages in terms of securing. If an abnormal situation occurs during battery use, such as overcharging, short-circuiting, or leaving the battery in a high-temperature environment, sulfur dioxide gas is generated inside the battery, and safety mechanisms such as disconnect devices can be quickly activated. it can.

The manganese sulfate to be mixed in the positive electrode or the manganese sulfate to be dissolved in the electrolytic solution is desirably a particle size of 50 μm or less in consideration of the reaction with the electrolytic solution, and has no adsorbed water or structured water, or Those subjected to heat dehydration treatment are preferred.

Further, when sulfur or a sulfur compound other than manganese sulfate is contained in the battery in the present invention,
The same catalytic poisoning effect on Mn as in the case of using manganese sulfate is observed.

Examples of the sulfur or sulfur compound to be used include a simple substance of sulfur; a sulfur-containing gas such as sulfur dioxide and hydrogen sulfide; and a sulfate such as manganese sulfate and lithium sulfate. Among them, simple sulfur, sulfur dioxide, hydrogen sulfide and manganese sulfate are preferred.

The sulfur alone can be contained in the positive electrode as a sulfur powder or can be used by dissolving it in the electrolytic solution. The sulfur-containing gas can be used by dissolving it in the electrolytic solution.
It may be merely contacted with the lithium-manganese composite oxide.

When sulfur alone is contained in the positive electrode or dissolved in the electrolytic solution, the particle size of the sulfur is desirably 50 μm or less in consideration of the reaction with the electrolytic solution. Those which do not have, or those which have been subjected to heat dehydration treatment are preferred. In addition, it is preferable that the sulfur-containing gas such as sulfur dioxide and hydrogen sulfide has a small impurity content.

The amount of the sulfur or the sulfur compound to be used can be appropriately selected depending on the type of the sulfur or the compound to be used. However, in order to obtain a clear effect, [lithium-manganese composite oxide]: [sulfur powder] = 100 -A: a
(Wt%), sulfur was mixed into the positive electrode at a mixing ratio of 0.011 ≦ a,
It is preferable to use an electrolytic solution in which 0.02 g or more of sulfur powder is dissolved per ml, or use an electrolytic solution in which 1 ml or more of a sulfur-containing gas is bubbled with respect to 100 ml of the electrolytic solution.

The lithium-manganese composite oxide used in the present invention is an oxide composed of lithium, manganese and oxygen, and lithium manganate having a spinel structure such as LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , and LiMnO ₂ And the like. Among these, lithium manganate having a spinel structure such as LiMn ₂ O ₄ is preferable, and the [Li] / [Mn] ratio may deviate from 0.5 as long as the spinel structure is obtained, and the [Li] / [Mn] ratio As for 0.5-
0.65, preferably 0.51 to 0.6, most preferably 0.53 to 0.58.

Similarly, as long as lithium manganate has a spinel structure, the ratio of [Li + Mn] / [O] is 0.1.
It may be shifted from 75.

The particle diameter of the lithium-manganese composite oxide is expressed as a weight average particle diameter in consideration of the ease of preparation of the slurry suitable for preparing the positive electrode and the uniformity of the battery reaction.
Usually, it is 5 to 30 μm.

Such a lithium / manganese composite oxide can be produced as follows.

Manganese (Mn) raw material and lithium (L
i) As a raw material, first, as a Li raw material, for example, a lithium compound such as lithium carbonate, lithium oxide, lithium nitrate, and lithium hydroxide can be used. As a Mn raw material, for example, electrolytic manganese dioxide (EMD), Mn ₂ O ₃ , M
Various Mn such as n ₃ O ₄ and chemical manganese dioxide (CMD)
Manganese compounds such as oxides and manganese salts such as manganese carbonate and manganese oxalate can be used. But L
Easy to secure the composition ratio of i and Mn, energy density per unit volume due to difference in bulk density, easy to secure target particle size, easy to process and handle in industrial mass synthesis, In consideration of the occurrence, cost, etc., a combination of electrolytic manganese dioxide and lithium carbonate is preferable.

At this time, as a step before mixing the starting materials, it is preferable that the lithium material and the manganese material are pulverized, if necessary, so as to have an appropriate particle size.

The non-aqueous electrolyte secondary battery of the present invention uses the lithium-manganese composite oxide containing manganese sulfate, sulfur compound and the like as the positive electrode (dissolving divalent Mn ions and ionic compounds in the electrolyte). In this case, it does not need to be included).

On the other hand, as the negative electrode active material, a carbon material such as lithium, lithium alloy, graphite or amorphous carbon capable of inserting and extracting lithium is used.

The separator is not particularly limited.
Glass fibers, porous synthetic resin films and the like can be used. For example, a polypropylene or polyethylene porous film is suitable in terms of a thin film, large area, film strength and film resistance.

As the solvent for the non-aqueous electrolyte, those which are commonly used may be used, and examples thereof include carbonates, chlorinated hydrocarbons, ethers, ketones, and nitriles. Preferably, ethylene carbonate (EC), propylene carbonate (P
C), at least one of γ-butyrolactone (GBL) and the like, and diethyl carbonate (DE) as a low-viscosity solvent.
C), at least one selected from dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), esters and the like, and a mixture thereof is used. EC + DEC, P
C + DMC or PC + EMC is preferred.

As the supporting salt, LiClO ₄ , LiI, L
iPF ₆ , LiAlCl ₄ , LiBF ₄ , CF ₃ SO ₃ Li
For example, at least one type is used. In the present invention, the use of a supporting salt which easily generates an acid can suppress the acid in the electrolytic solution, and is particularly preferable when LiPF ₆ or LiBF ₄ is used, since the most effective effect can be obtained. The concentration of the supporting salt is, for example, 0.8 to 1.5M.

The structure of the battery is a prismatic, paper type,
Various shapes such as a laminated type, a cylindrical type, and a coin type can be adopted. In addition, components include a current collector, an insulating plate, and the like, but these are not particularly limited, and may be selected according to the above shape.

[0059]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

Example 1 In the synthesis of lithium manganate, lithium carbonate (Li ₂ CO ₃ ) and electrolytic manganese dioxide (EMD) were used as starting materials. Prior to the mixing of the starting materials, pulverization of Li ₂ CO ₃ and classification of EMD were performed in order to improve the reactivity and secure lithium manganate having a target particle size.

In the ordinary solid-phase reaction synthesis method, the particle size of lithium manganate is almost determined by the particle size of EMD before firing. That is, the synthesis of lithium manganate having the target particle size is ensured by classification of the EMD before firing at the target particle size. When lithium manganate is used as a positive electrode active material of a battery, an average particle diameter of 5 to 30 μm is preferable in consideration of ensuring uniformity of reaction, ease of slurry preparation, safety, and the like. Therefore, the particle size of EMD is set to 5 to 30 μm, which is the same as the target particle size of lithium manganate.

Li ₂ CO ₃ is pulverized to a D50 particle size of 1.4 μm, and [Li] / [Mn] = 1.05 /
And 2 were mixed. This is because it is considered that a particle size of 5 μm or less is desirable for ensuring a uniform reaction.

Next, this mixed powder was placed under an atmosphere of oxygen flow.
It was fired at 800 ° C. Fine particles having a particle diameter of 1 μm or less in the obtained lithium manganate particles were removed by an air classifier. At this time, the specific surface area of the obtained lithium manganate was about 0.9 m ² / g. Tap density is 2.17
g / cc, the true density is 4.09 g / cc, and the D50 particle size is 1.
The powder characteristics were 7.2 μm and the lattice constant was 8.236 °.

Example 2 Lithium manganate synthesized in Example 1 was used as a positive electrode active material, and manganese sulfate powder was mixed with PTFE as a conductivity-imparting agent and a binder.
The mixture was kneaded to prepare a positive electrode, and a 2320 coin cell having a metal Li counter electrode was prototyped. However, the manganese sulfate powder was subjected to vacuum drying at 100 ° C. for 12 hours as a pretreatment, and the mixing ratio of the positive electrode was adjusted to lithium manganate: conductivity imparting agent: PTFE: manganese sulfate = 76: 10: 10: 4
After being kneaded, a product rolled to a thickness of about 0.5 m was punched out to a diameter of 15 mm and used. The negative electrode is 1mm thick, φ
Using 17mm metal Li, the electrolyte is 1M LiClO
₄ A mixed solvent of propylene carbonate (PC) + dimethyl carbonate (DMC) = 50 + 50 (volume ratio)
A 25 μm thick polypropylene porous membrane was used as the separator.

Comparative Example 1 A metal L was prepared in the same manner as in Example 2 except that lithium manganate synthesized in Example 1 was used as a positive electrode active material and manganese sulfate was not contained in the positive electrode mixture.
A prototype i-type 2320 coin cell was manufactured. The positive electrode was made of lithium manganate, a conductivity-imparting agent and PTFE 80:
A mixture kneaded at a weight ratio of 10:10 and rolled to a thickness of about 0.5 m was punched out to φ15 mm and used. The same negative electrode, electrolytic solution and separator as in Example 2 were used.

[Evaluation Test Example 1] Example 2 and Comparative Example 1
A charge / discharge cycle test was performed using the coin cell prototype manufactured in the above. The cycle was 0.5 mA / cm ^{2 for} both charging and discharging.
, And the charge / discharge voltage range is 3.0 to 4.5 V v
s Li. The evaluation temperature was set at 10 ° C. from 10 ° C. to 60 ° C.

Table 1 shows # 50 / # 1 (the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the 1st cycle) of the coin cells of Example 2 and Comparative Example 1 based on the cycle evaluation temperature. . The coin cell of Example 2 has a higher capacity remaining ratio even when the cycle temperature is increased.

[0068]

[Table 1] Example 3 Lithium manganate synthesized in Example 1 was used as a positive electrode active material, and P was used as a conductivity-imparting agent and a binder.
A positive electrode was prepared by mixing and kneading sulfur powder in addition to TFE to produce a 2320 coin cell having a metallic Li counter electrode. However, sulfur powder is used as a pretreatment at 12
It was used after vacuum drying for hours.

The mixing ratio of the positive electrode was as follows: kneading lithium manganate: conductivity imparting agent: PTFE: sulfur = 79: 10: 10: 1 and rolling to a thickness of about 0.5 m.
It was punched out to 15 mm. The negative electrode is 1mm thick, φ1
Using 7 mm metal Li, the electrolyte is 1 M LiClO4
Propylene carbonate (PC) + dimethyl carbonate (DMC) = 50 + 50 (volume ratio), and a 25 μm-thick polypropylene porous membrane was used as a separator.

[Comparative Evaluation Example 2] Example 3 and Comparative Example 1
A charge / discharge cycle test was performed using the coin cell prepared in the above. The cycle was 0.5 mA / cm ^{2 for} both charging and discharging.
, And the charge / discharge voltage range is 3.0 to 4.5 V v
s Li. The evaluation temperature was set at 10 ° C. from 10 ° C. to 60 ° C.

Table 2 shows # 50 / # 1 (the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the 1st cycle) of the coin cells of Example 3 and Comparative Example 1 based on the cycle evaluation temperature. . The coin cell of Example 3 has a higher capacity remaining ratio even when the cycle temperature is increased.

[0072]

[Table 2] [Example 4] Using lithium manganate synthesized in Example 1 as a positive electrode active material, a 2320 coin cell having a metal Li counter electrode was prototyped in the same manner as in Comparative Example 1. The positive electrode was made of lithium manganate, a conductivity-imparting agent, and PTFE at 80: 10: 1.
A mixture kneaded at a weight ratio of 0 and rolled to a thickness of about 0.5 mm was punched out to a diameter of 15 mm and used.

The electrolytic solution uses 1M LiPF ₆ as a supporting salt,
A solution obtained by dissolving manganese sulfate subjected to heat dehydration treatment in a solvent using propylene carbonate (PC) + diethyl carbonate (DEC) = 50 + 50 (volume ratio) was used. The Mn concentration at this time was 190 ppm. The same negative electrode and separator as in Example 2 were used.

Example 5 Using lithium manganate synthesized in Example 1 as a positive electrode active material, a 2320 coin cell having a metal Li counter electrode was prototyped in the same manner as in Comparative Example 1. The positive electrode is
Lithium manganate, conductivity imparting agent and PTFE
A mixture kneaded at a weight ratio of 0:10:10 and rolled to a thickness of about 0.5 mm was punched out to a diameter of 15 mm and used. The electrolyte used was 1 M LiPF ₆ as a supporting salt, and propylene carbonate (PC) + diethyl carbonate (DEC) = 5.
A solution prepared by dissolving a sulfur powder subjected to heat dehydration treatment in a solution using 0 + 50 (volume ratio) as a solvent was also used. At this time, the sulfur concentration was 560 ppm. The same negative electrode and separator as in Example 2 were used.

[Example 6] Using lithium manganate synthesized in Example 1 as a positive electrode active material, a 2320 coin cell having a metal Li counter electrode was prototyped in the same manner as in Comparative Example 1. The positive electrode is
Lithium manganate, conductivity imparting agent and PTFE
A mixture kneaded at a weight ratio of 0:10:10 and rolled to a thickness of about 0.5 mm was punched out to a diameter of 15 mm and used.

The electrolytic solution uses 1M LiPF ₆ as a supporting salt,
A mixture of propylene carbonate (PC) + diethyl carbonate (DEC) = 50 + 50 (volume ratio) as a solvent was prepared by bubbling sulfur dioxide gas. At this time, the amount of sulfur dioxide at the time of bubbling was 1.0 ml with respect to 10 ml of the electrolytic solution. The same negative electrode and separator as in Example 2 were used. At this time, the sulfur concentration in the electrolytic solution was 620 ppm.

Example 7 The lithium manganate synthesized in Example 1 was placed in a closed container, and 1.2 g of sulfur dioxide was sealed in 10 g of lithium manganate in the container, and the container was left as it was for 24 hours. . This operation was performed in dry air.

[Example 8] Lithium manganate synthesized in Example 1 was subjected to the treatment described in Example 7 to obtain a positive electrode active material.
We prototyped 20 coin cells. For the positive electrode, a material obtained by kneading lithium manganate, a conductivity-imparting agent and PTFE in a weight ratio of 80:10:10, and rolling it to a thickness of about 0.5 mm and punching it into φ15 mm was used.

The electrolytic solution uses 1M LiPF ₆ as a supporting salt,
Propylene carbonate (PC) + diethyl carbonate (DEC) = 50 + 50 (volume ratio) was used as a solvent. The same negative electrode and separator as in Example 2 were used.

[Comparative Evaluation Example 3] A charge / discharge cycle test was performed using the coin cells prototyped in Examples 4, 5, 6, 8 and Comparative Example 1. The cycle is 0.5 for both charge and discharge
mA / cm ² constant current, and the charge / discharge voltage range was 3.0 to
The test was performed at 4.5 V vs. Li. The evaluation temperature is 60 ° C
And

FIG. 1 shows the cycle characteristics of the coin cells of Examples 4, 5, 6, and 8 and Comparative Example 1. (The discharge capacity in the first cycle is defined as 100%, and the remaining capacity ratio in each cycle is shown.) Comparing the remaining capacity ratios up to 50 cycles, the order of Example 6, Example 8, Example 5, and Example 4 And the residual rate is high. This is because in Example 4, the sulfur component M
In addition to the catalytic poisoning effect on n, Mn from lithium manganate
This is probably because the effect of suppressing the amount of dissolution was added.

The coin cells fabricated in Examples 6 and 7 exhibited the same effect with other S-containing gases such as hydrogen sulfide.

[Example 9] Using the lithium manganate synthesized in Example 1 as a positive electrode active material, a 18650 cylindrical cell was produced as a trial.

First, lithium manganate and a conductivity-imparting agent were dry-mixed, and N was dissolved in PVDF as a binder.
-Disperse uniformly in methyl-2-pyrrolidone (NMP) to make a slurry. The slurry was applied on an aluminum metal foil having a thickness of 25 μm, and NMP was evaporated to obtain a positive electrode sheet. The solid content ratio in the positive electrode was lithium manganate: conductivity imparting agent: manganese sulfate: PVDF = 7
5: 10: 5: 10 (% by weight). On the other hand, the negative electrode sheet was prepared by mixing carbon: PVDF = 90: 10, dispersing it in NMP, and applying it on a copper foil having a thickness of 20 μm. The electrolytic solution used was 1 M LiPF ₆ as a supporting salt, and ethylene carbonate (EC) + diethyl carbonate (DEC) = 50 + 50 (volume ratio) as a solvent. The separator used was a 25 μm-thick polypropylene porous membrane.

Example 10 An 18650 cylindrical cell was fabricated using lithium manganate synthesized in Example 1 as a positive electrode active material.

First, lithium manganate and a conductivity-imparting agent are dry-mixed, and N is dissolved in PVDF as a binder.
-Disperse uniformly in methyl-2-pyrrolidone (NMP) to make a slurry. The slurry was applied on an aluminum metal foil having a thickness of 25 μm, and NMP was evaporated to obtain a positive electrode sheet. The solid content ratio in the positive electrode was lithium manganate: conductivity imparting agent: PVDF = 80: 10: 10
(% By weight). On the other hand, the negative electrode sheet is made of carbon: PV
The mixture was mixed at a ratio of DF = 90: 10, dispersed in NMP, and applied to a copper foil having a thickness of 20 μm.

The electrolytic solution uses 1M LiPF ₆ as a supporting salt,
A material obtained by heating and dehydrating a solution containing ethylene carbonate (EC) + diethyl carbonate (DEC) = 50 + 50 (volume ratio) as a solvent and dissolving manganese sulfate was used.

However, the Mn concentration b (Table 3) in the electrolyte was 5
Manganese sulfate was dissolved from 30 ppm to 3052 ppm. The separator used was a 25 μm-thick polypropylene porous membrane.

Comparative Example 2 Manganese sulfate was not dissolved in the electrolytic solution, and 1M LiPF ₆ was used as a supporting salt, and ethylene carbonate (EC) + diethyl carbonate (DEC) =
An 18650 cylindrical cell was produced in the same manner as in Example 9, except that the electrolyte used was 50 + 50 (volume ratio) as the solvent. At this time, the Mn concentration in the electrolytic solution was 0.1 ppm or less, which was below the detection limit of the device.

[Comparative Evaluation Example 4] Using the cylindrical cells produced in Examples 9, 10 and Comparative Example 2, 18650
A safety test of the cylindrical cell was performed. The safety evaluation items are an overcharge test and a short-circuit test. Overcharge test is 12V, 3
The short circuit test was performed under the condition of C and a forced short circuit was performed at 4.2 V in a fully charged state at room temperature. For details of other test conditions, refer to UL-
1642.

In the overcharge test, in Comparative Example 2, slight vapor to smoke was generated, while in Example 10, no smoke and ignition occurred in all the cylindrical cells. In the short-circuit test, the cylindrical cells of the electrolytic solution having an Mn concentration of 9 ppm or less emitted slight vapor or smoke, whereas all the cylindrical cells having an Mn concentration of 18 ppm or more did not emit smoke or fire. The above results are considered to be due to the fact that sulfur dioxide gas was generated due to the temperature rise in the forced short circuit state, and the disconnect device became easier to operate.

From the results, it was found that the Mn concentration b in the electrolytic solution is desirably 18 ppm or more from the viewpoint of safety of overcharge and short circuit.

[0093]

[Table 3]

[0094]

As is clear from the above description, according to the present invention, the presence of a divalent Mn salt in a battery suppresses the elution of Mn from lithium manganese oxide as an active material. In addition, the presence of sulfur or a sulfur compound in the battery reduces the activity of Mn due to the catalytic poisoning effect of sulfur component on Mn, thereby suppressing the progress of side reactions. Therefore, in the nonaqueous electrolyte secondary battery of the present invention, the charge / discharge cycle, particularly the charge / discharge life at a high temperature, is greatly improved. In addition, when manganese sulfate is present in the battery, sulfur dioxide gas is generated at the time of overcharge and temperature rise,
Safety is improved.

Further, the non-aqueous electrolyte secondary battery of the present invention is inexpensive and does not require any special equipment in the battery manufacturing process. large.

[Brief description of the drawings]

FIG. 1 is a diagram showing discharge capacity and cycle characteristics of a coin cell of the present invention and a conventional coin cell.

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[Procedure amendment]

[Submission date] December 24, 1999 (1999.12.
24)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

According to the present invention, there is provided a non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide for a positive electrode, characterized in that the battery contains sulfur alone or a sulfate having a particle size of 50 μm or less. The present invention relates to a water electrolyte secondary battery.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0024

[Correction method] Change

[Correction contents]

The present invention also relates to a non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide for a positive electrode, wherein the battery contains a sulfur-containing gas. In addition, the present invention provides a lithium cathode
In a non-aqueous electrolyte secondary battery using a manganese composite oxide, the positive electrode must be made of lithium-manganese composite oxide with manganese sulfate added, or manganese sulfate dissolved in the electrolyte And a non-aqueous electrolyte secondary battery.

Continued on the front page F-term (reference)

Claims (15)

[Claims] 1. A non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide for a positive electrode, wherein the battery contains divalent Mn ions dissolved from a Mn salt in the battery. Next battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein a divalent Mn salt is contained in the positive electrode or a divalent Mn salt is dissolved in the electrolytic solution. 3. A non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide for a positive electrode, wherein the battery contains sulfur or a sulfur compound. 4. The non-aqueous electrolyte secondary battery according to claim 3, wherein sulfur or a sulfur compound is contained in the positive electrode, or sulfur or a sulfur compound is dissolved in the electrolyte. 5. The non-aqueous electrolyte secondary battery according to claim 4, wherein the sulfur or the sulfur compound is sulfur alone, a sulfur-containing gas or a sulfate. 6. The non-aqueous electrolyte secondary battery according to claim 5, wherein the sulfur-containing gas is sulfur dioxide or hydrogen sulfide. 7. A non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide for a positive electrode, wherein manganese sulfate is contained in the positive electrode or manganese sulfate is dissolved in the electrolyte. Characteristic non-aqueous electrolyte secondary battery. 8. A non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide for a positive electrode, wherein [lithium-manganese composite oxide]: [manganese sulfate] = 100-a: a
A non-aqueous electrolyte secondary battery characterized in that manganese sulfate is contained in the positive electrode at a mixing ratio of 0.053 ≦ a when expressed as (% by weight). 9. A non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide for a positive electrode, wherein a divalent M
A non-aqueous electrolyte secondary battery characterized by using an electrolyte in which manganese sulfate is dissolved such that n concentration is represented by b in a range of 18 ppm ≦ b. 10. A non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide for a positive electrode, wherein [lithium-manganese composite oxide]: [sulfur powder] = 100-a: a
A nonaqueous electrolyte secondary battery characterized in that sulfur is mixed in the positive electrode at a mixing ratio of 0.011 ≦ a when expressed as (% by weight). 11. A non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide for a positive electrode, the electrolyte comprising 10 ml of an electrolyte.
A non-aqueous electrolyte secondary battery using an electrolyte in which 0.02 g or more of sulfur powder is dissolved. 12. A non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide for a positive electrode, wherein the electrolyte
1. A non-aqueous electrolyte secondary battery characterized by using an electrolyte solution in which 1 ml or more of a sulfur-containing gas is bubbled with respect to 1. 13. A non-aqueous electrolyte secondary battery using a lithium / manganese composite oxide for a positive electrode, wherein the lithium / manganese composite oxide contacted with a sulfur-containing gas is used as a positive electrode active material. Water electrolyte secondary battery. 14. A non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide for a positive electrode, wherein 10 g of the lithium-manganese composite oxide is contacted with at least 1 ml of a sulfur-containing gas. Item 14. A non-aqueous electrolyte secondary battery according to Item 13. 15. The non-aqueous electrolyte secondary battery according to claim 13, wherein the sulfur-containing gas is sulfur dioxide or hydrogen sulfide.