JP3421877B2 - Non-aqueous electrolyte secondary battery - Google Patents

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 improvement of a positive electrode active material.

[0002]

2. Description of the Related Art In recent years, advances in electronic technology have led to advances in performance, miniaturization, and portability of electronic equipment, and the demand for higher energy density has also increased for secondary batteries used in these electronic equipment. ing. Secondary batteries that have been conventionally used in these electronic devices include nickel-cadmium batteries and lead batteries. However, these batteries have a low discharge potential, and cannot be said to sufficiently meet the above-mentioned demand for higher energy density.

On the other hand, recently, a lithium secondary battery using metallic lithium or a lithium alloy as a negative electrode active material and a lithium-containing compound as a positive electrode active material has attracted attention as a battery system satisfying these requirements, and has been actively researched. ing. However, in this lithium secondary battery, when metallic lithium is used for the negative electrode, lithium can grow into dendrite-like crystals from the negative electrode as the charge / discharge cycle progresses, and reach the positive electrode to induce an internal short circuit. In addition, when a lithium alloy is used for the negative electrode, there is a problem that the negative electrode becomes finer and the performance deteriorates when the charge / discharge cycle is repeated, and there are problems such as cycle life, safety, and quick charge performance. The points are being recognized. Therefore, this lithium secondary battery is only partially put into practical use as a coin type.

Therefore, in order to solve these problems,
A lithium ion secondary battery (non-aqueous electrolyte secondary battery) has been proposed in which a negative electrode active material is a substance capable of doping and dedoping lithium ions, such as a carbonaceous material, instead of metallic lithium or a lithium alloy. ing. Since this lithium ion secondary battery is a battery reaction in which lithium does not exist in a metallic state, there is no problem regarding cycle deterioration or safety due to crystal growth of lithium or the like. Then, by using a lithium-containing compound having a high redox potential for the positive electrode, the battery voltage becomes high and a high energy density is exhibited. In addition, the self-discharge is nickel
Compared with the cadmium battery, it has few advantages and is extremely excellent as a secondary battery. Therefore, 8m / mVT
It is a secondary battery, which has already been commercialized as a power supply for portable electronic devices such as R, CD players, laptop computers, and cellular telephones, and has great expectations in the future.

[0005]

By the way, the positive electrode used in the commercialized lithium ion secondary battery,
The materials for the negative electrode and the non-aqueous electrolyte are as follows. In other words, various carbonaceous materials that can be used as the negative electrode active material have been reported, but the ones actually used are carbonaceous materials with low crystallinity such as coke and glassy carbon that have been processed at a relatively low temperature. is there.

As a positive electrode active material, many composite oxides containing lithium have been reported, but only lithium cobalt oxide (LiCoO ₂ ) is used at the commercial level. Furthermore, as the non-aqueous solvent of the non-aqueous electrolytic solution, an organic solvent containing PC (propylene carbonate) as a main component, which is generally used in coin-type or cylindrical-type lithium primary batteries, is used.

However, with such a material structure, it is not possible to achieve a sufficiently high capacity, and further studies are being made. First, as the positive electrode active material, in addition to lithium / cobalt composite oxides, lithium / nickel composite oxides and lithium / manganese composite oxides have been proposed as lithium-containing compounds having a high redox potential. From the viewpoint of stable supply of raw materials, lithium-manganese oxides are promising.

However, two drawbacks have been clarified in the lithium-manganese composite oxide. One is that the cycle deterioration of the battery is large, and the other is that the battery capacity is relatively small. For this reason, improvement measures have been taken for these defects. For example, J. M. Ta
Rascon et al. Electrochem. So
c. , Vol 138, No. 10, P2859 (199
In 1), when LiMn ₂ O ₄ is used as the positive electrode active material, the cycle deterioration of the battery becomes large.
Ti, Ge, Ni, Zn, F as different metals in n ₂ O ₄
It has been reported that the addition of e improves the cycle characteristics of the battery. However, although addition of a different metal to LiMn ₂ O ₄ certainly improves cycle deterioration, this time it causes a disadvantage that the battery capacity becomes small, and it is not a sufficient countermeasure from the viewpoint of the performance of the entire battery. .

Regarding the battery capacity, Japanese Patent Laid-Open No. 4-1
In Japanese Patent No. 47573, the lithium-manganese composite oxide is previously electrochemically or chemically doped with lithium to have a composition of Li _{1 + x} Mn ₂ O ₄ (where x> 0) as a positive electrode active material. Reported to be used as a substance. However, in this case, although the battery capacity is increased, the cycle deterioration is not so different from the conventional one, and the battery performance cannot be sufficiently improved only by this method.

Next, as the negative electrode active material, in addition to the above-mentioned low crystalline carbonaceous material obtained by firing at a relatively low temperature of 2000 ° C. or lower, a raw material which is easily crystallized is treated at a high temperature of around 3000 ° C. Graphite materials such as artificial graphite and natural graphite have also been proposed. Among them, the graphite material has much more stable physicochemical and electrochemical characteristics than the carbonaceous material obtained by processing at low temperature, and its high true density makes the filling property in the negative electrode mixture. Get higher Therefore, it is attracting attention as a negative electrode material that can increase the energy density of batteries.

However, the graphite material has a larger polarization during charging / discharging than the low crystalline carbonaceous material, and thus a battery using the graphite material as the negative electrode active material is not suitable for a battery using the low crystalline carbonaceous material as the negative electrode active material. In comparison, when the upper limit charging voltage of the battery is set to be the same, the positive electrode has a more noble potential. For this reason, the amount of lithium ions extracted per unit weight of the positive electrode active material is larger, and the stability of the crystal structure of the positive electrode active material shifts to a slightly lower direction. This has an adverse effect on battery characteristics such as cycle characteristics. Also, this effect tends to be more pronounced at higher charging voltages.

When a graphite material is used as the negative electrode active material, it is premised that ethylene carbonate (EC) is used as the high dielectric constant solvent mixed with the non-aqueous solvent. This is because propylene carbonate (PC), which is commonly used as a high dielectric constant solvent, is decomposed when coexisting with a graphite material and is unsuitable when a graphite material is used as the negative electrode active material. However, since EC is a solid at room temperature, it has a drawback that it has a low electrical conductivity at low temperatures and poor low-temperature characteristics.

As described above, various proposals have been made for the material constitution of the non-aqueous electrolyte secondary battery, but both have advantages and disadvantages, and both the battery capacity and the cycle characteristics of the battery are sufficient. The reality is that it cannot be improved. Therefore, the present invention has been proposed in view of such conventional circumstances, and an object thereof is to provide a non-aqueous electrolyte secondary battery having a high energy density and excellent cycle characteristics.

[0014]

[Means for Solving the Problems] In order to achieve the above-mentioned object, as a result of extensive studies by the present inventors, it was found that a lithium-manganese composite oxide is used as a positive electrode active material and its specific surface area is regulated. This has led to the finding that a non-aqueous electrolyte secondary battery having a high energy density and excellent cycle characteristics can be obtained.

The present invention has been proposed on the basis of such knowledge, and a positive electrode using a lithium-containing compound as a positive electrode active material and a carbonaceous material capable of doping / dedoping lithium as a negative electrode active material. In a non-aqueous electrolyte secondary battery having a negative electrode as a substance and a non-aqueous electrolyte, a lithium-containing compound as a positive electrode active material has a specific surface area of 0.05 to
It is characterized in that it is a powder of a lithium-manganese composite oxide of 5.0 m ² / g.

The carbonaceous material used as the negative electrode active material has a true specific gravity of 2.10 g / cm ³ or more, and is 00 according to the X-ray diffraction method.
Characterized by a graphite material alone or a graphite-mixed carbonaceous material mainly composed of this graphite material having a surface spacing of two surfaces of 0.335 to 0.34 nm and a bulk specific gravity of 0.3 g / cm ³ or more Is. Further, the non-aqueous solvent of the non-aqueous electrolytic solution is characterized by being a mixed solvent of ethylene carbonate and chain carbonic acid ester.

Furthermore, the mixing volume ratio of ethylene carbonate and chain carbonic acid ester (ethylene carbonate:
(Chain carbonic acid ester) is 3: 7 to 7: 3. The present invention provides a positive electrode using a lithium-containing compound as a positive electrode active material, a negative electrode using a carbonaceous material capable of doping and dedoping lithium as a negative electrode active material, and a non-aqueous electrolytic solution. It is applied to electrolyte secondary batteries.

In the present invention, in such a non-aqueous electrolyte secondary battery, a lithium-manganese composite oxide is used as a positive electrode active material, and its specific surface area is regulated to obtain a high energy density and cycle characteristics. We will obtain an excellent secondary battery. That is, conventionally, lithium
A problem in using the manganese composite oxide as the positive electrode active material is cycle deterioration of the battery.

As a result of a detailed investigation by the present inventors regarding this cycle deterioration, in the battery using the lithium-manganese composite oxide as the positive electrode active material, the positive electrode active material after the charge / discharge cycle was compared with that before the charge / discharge cycle. It was confirmed that the miniaturization had progressed considerably, and it was considered that the miniaturization of this positive electrode active material was the cause of cycle deterioration. The mechanism of miniaturization of the positive electrode active material is considered as follows.

That is, the cubic lattice which constitutes the crystal structure of the lithium-manganese composite oxide contracts during charging when lithium is dedoped from the lithium-manganese composite oxide which is the positive electrode active material. On the other hand, during discharge in which lithium is doped into the positive electrode active material, the cubic crystal lattice of the lithium-manganese composite oxide expands. It is presumed that the volume change due to the contraction and expansion of the positive electrode active material due to the doping and dedoping of lithium gives stress to the positive electrode active material itself and promotes miniaturization. If the positive electrode active material is miniaturized, the contact property with, for example, a conductive agent deteriorates, resulting in cycle deterioration of the battery.

Therefore, in the present invention, in order to suppress the refinement of the lithium-manganese composite oxide which causes the cycle deterioration of the battery, the specific surface area of the lithium-manganese composite oxide is 0.05 to 5.0 m. The limit is ² / g. First, in order to suppress the refinement of the lithium-manganese composite oxide, its specific surface area is 5.0.
It needs to be m ² / g or less. In the lithium-manganese composite oxide, when the specific surface area exceeds 5 m ² / g, the particle size becomes small, and miniaturization tends to proceed with charging and discharging. As a result, the cycle is greatly reduced.

On the other hand, the lower limit of the specific surface area of the lithium-manganese composite oxide is 0.05 m ² / g. This is because when the specific surface area of the positive electrode active material is less than 0.05 m ² / g, although miniaturization of the positive electrode active material is suppressed, the particle size becomes too large and the heavy load characteristics deteriorate, resulting in battery capacity. This is because the inconvenience of becoming smaller occurs. Thus, considering the miniaturization and utilization efficiency of the active material,
The specific surface area of lithium manganese oxide is 0.05 to 5.
It should be 0 m ² / g.

Various composition ratios can be selected as the lithium-manganese oxide. For example, manganese 1
Lithium per atom including 0.5 atom, in addition to the spinel-type LiMn ₂ O ₄ produced by high temperature firing, LiMn ₂ O ₄ or the like which is generated by low-temperature firing disclosed in JP-A-63-274059 Is mentioned. Also, J. Electrochem. Soc. , Vol1
40, No. 12, P3396 (1993), L containing 1 atom of lithium per atom of manganese.
It may be iMnO ₂ . Furthermore, JP-A-2-376
The composition may be Li _x MnO _y disclosed in Japanese Patent Laid-Open No. 65 or a composition of Li _{1 + x} Mn ₂ O ₄ (where x> 0) by doping lithium into this.

These lithium-manganese oxides include, for example, lithium, manganese hydroxides, oxides, carbonates,
Starting from nitrates, etc., in an oxygen-existing atmosphere, 600-
It is produced by firing in a temperature range of 1000 ° C. and crushing. The starting materials are mixed at a mixing ratio according to the composition of the target product, and examples of the mixing method include a dry mixing method of directly mixing solid starting materials and a wet mixing method of mediated by an aqueous solution. It is not particularly limited.

On the other hand, the negative electrode active material used in the present invention is a carbonaceous material which can be doped with lithium ions and dedoped with a charge / discharge reaction. As a carbonaceous material, physicochemical and electrochemical properties are stable,
A graphite material is suitable because of its high true density. The graphite material has a true specific gravity of 2.10 g / cm ³ or more, and more preferably 2.18 in order to obtain a higher negative electrode mixture filling property.
It is preferably g / cm ³ or more. In order to have such a true specific gravity in the graphite material, it is necessary that the spacing between the 002 planes determined by X-ray diffractometry is 0.335 to 0.34 nm, and more preferably 0.335 nm.
Is about 0.337 nm. The crystallite thickness in the C-axis direction is preferably 16.0 nm or more, and is 24.0n.
It is more preferably m or more. Further, the bulk specific gravity needs to be 0.3 g / cm ³ or more. Then, in the graphite material particle shape, when the thickness of the thinnest portion is T, the length of the longest portion is L, and the length (depth) in the direction perpendicular to L is W, (L /
It is desirable that the average value x _{ave of} the values obtained by (T) × (W / T), that is, the average shape parameter x _ave be x _ave ≦ 125.

The G value obtained by laser Raman spectroscopy is also an important parameter for selecting a graphite material. That is, the laser Raman spectroscopy is a measurement method in which the information on the vibration of the crystal structure of the carbonaceous material is reflected with high sensitivity, and the G value obtained from the Raman spectrum observed by this laser Raman spectroscopy is microscopic. It is one of the effective indexes for evaluating structural defects. This G value is represented by the ratio of the area intensity of the Raman band derived from the complete graphite structure to the area intensity of the Raman band derived from the amorphous structure in the carbonaceous material. The G value of the graphite material used as the negative electrode active material is preferably 2.5 or more. 2.1 when G value is less than 2.5
In some cases, the true specific gravity of g / cm ² or more cannot be obtained.

Further, since the purpose of the present invention is to increase the energy density of the battery, it is desirable that the graphite material has a discharge capacity of 250 mAh or more per 1 g of the material as measured by the intermittent charge / discharge method. Two
It is more preferably 70 mAh or more. The graphite material as described above may be either natural graphite or artificial graphite obtained by carbonizing an organic material and subjecting it to high temperature treatment.

As a starting material for producing artificial graphite, organic materials such as coal and pitch are typical. As pitch, tars obtained by high-temperature thermal decomposition of coal tar, ethylene bottom oil, crude oil, etc., distillation of asphalt (vacuum distillation, atmospheric distillation, steam distillation), thermal polycondensation, extraction, chemical polycondensation, etc. Examples include those obtained by operation and those produced during carbonization of wood. Further, it is possible to use a high molecular compound such as polyvinyl chloride resin, polyvinyl acetate, polyvinyl butyrate, and 3,5-dimethylphenol resin as a starting material for pitch.

Coal, pitch, and polymer compounds, which are the starting materials, exist in a liquid state up to around 400 ° C. during carbonization, and when kept at that temperature, aromatic rings are condensed with each other,
It is polycyclic and is in a laminated orientation. After that, 500 ℃
At temperatures higher than the vicinity, a solid carbon precursor (semi-coke) is formed. Such a process is called a liquid-phase carbonization process, which is a typical formation process of graphitizable carbon.

As a starting material for artificial graphite, a fused polycyclic hydrocarbon compound such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, perylene, pentaphene and pentacene, and other derivatives (for example, carboxylic acid and carboxylic acid anhydride thereof) can be used. , Carboxylic acid imide, etc.) or a mixture, acenaphthylene, indole,
Fused heterocyclic compounds such as isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine and phenanthridine, and derivatives thereof may be used.

After carbonizing these organic materials at 300 to 700 ° C. in a stream of an inert gas such as nitrogen, 1
The temperature is raised to 900-1500 ° C at a rate of -100 ° C / min, and the temperature is maintained for 0-30 hours (calcination), and then 2
Artificial graphite is produced by heat treatment at 000 ° C or higher, preferably 2500 ° C or higher. The carbonization and calcination operations may be omitted in some cases.

Further, in this generation process, Japanese Patent Laid-Open No. 6-08
As disclosed in Japanese Patent No. 9721, when various volatile components generated during firing are efficiently removed,
It is possible to obtain a graphite material having a high lithium doping ability. Firing atmosphere conditions are important for efficient removal of volatile components. The firing atmosphere is preferably an inert gas atmosphere, and more preferably 0.1 cm ³ / min or more of an inert gas flow per 1 g of the raw material. Furthermore, when firing is performed while evacuation is performed, a graphite material having good characteristics is obtained, which is hardly affected by volatile components.

The above graphite material may be used alone as the negative electrode active material, but as shown in Japanese Patent Application No. 6-33434, the graphite material and the crystallinity are It is also possible to use a coexisting body of a low carbonaceous material (low crystalline carbonaceous material) as the negative electrode active material. here,
The proportion of low crystalline carbon in the carbon coexisting body is limited to 10 to 90% with respect to the total weight of the carbon coexisting body, and 20 to 80%.
Is more preferable.

At this time, the low crystalline carbonaceous material coexisting with the graphite material is limited to one having a discharge capacity of 80% or more of that of the graphite material as the discharge capacity for the first cycle measured by the intermittent charge / discharge method. It Particularly, from the viewpoint of cycle characteristics, it is desirable that the low crystalline carbonaceous material has a capacity performance of 90% or more of that of the graphite material. Furthermore, the low crystalline carbonaceous material has a discharge capacity of 1st cycle measured by the intermittent charging / discharging method of 1.
Most preferably, the ratio of the discharge capacity up to 0.3V to the discharge capacity up to 5V is 0.5 or more.

In the non-aqueous electrolyte secondary battery of the present invention, a non-aqueous electrolyte solution in which an electrolyte is dissolved in a non-aqueous solvent is used as the electrolyte solution. When a graphite material is used for the negative electrode active material, it is premised that a solvent containing EC, which is not decomposed by the graphite material, as one of the main components is used as the non-aqueous solvent. It is advisable to mix a plurality of components in addition to EC with the solvent containing EC as a main constituent. It suppresses the decomposition of the solvent during the charging process, improves the conductivity to improve the current characteristics, further lowers the freezing point of the electrolyte to improve the low temperature characteristics, and also reduces the reactivity with lithium metal. This is for the purpose of improving safety.

As a component to be mixed with EC, a chain ester is suitable because it has a high withstand voltage, and carbonic acid, carboxylic acid,
Ester such as phosphoric acid, especially chain carbonic acid ester is preferable. Specifically, asymmetric chain carbonic acid esters such as MEC (methyl ethyl carbonate) and MPC (methyl propyl carbonate) are suitable. Further, good results can be obtained by adding a mixed solvent such as a mixed system of MEC and DMC (dimethyl carbonate) or a mixed system of MEC and DEC (diethyl carbonate) containing an asymmetric chain ester carbonate. Further, a solvent composed of a symmetrical chain ester carbonate such as a mixed system of DMC and DEC also shows relatively good characteristics.

Mixing ratio of EC and solvent other than EC (EC:
The solvent other than EC) is preferably 7: 3 to 3: 7 in volume ratio. When the solvent other than EC is composed of plural kinds of solvents, MEC-DMC mixed solvent, MEC-D
In the EC mixed solvent, it is preferable that the volume ratio of MEC: (DMC or DEC) is 2: 8 to 9: 1. Also,
In the DMC-DEC mixed solvent, it is preferable that the volume ratio of DMC: DEC is 1: 9 to 9: 1.

LiPF 6 as the electrolyte₆Is preferred
However, if it is used for this type of battery, use any
It can be used. For example LiClO_Four, LiAsF₆, L
iPF ₆, LiBF_Four, LiB (C₆H_Five)_Four, LiC
l, LiBr, LiSO₃CH ₃, LiSO₃CF₃,
LiN (SO₂CF₃)₂, LiC (SO₂CF₃)₃
Etc.

In a battery, the positive electrode made of the positive electrode active material, the negative electrode made of the negative electrode active material and the non-aqueous electrolyte are housed in, for example, an iron battery can, and the battery can and the battery lid are caulked and hermetically sealed. Consists of The positive electrode and the negative electrode are connected to a battery lid and a battery can by a lead member, respectively, and are energized from the outside through the battery lid or the battery can and the lead member. Note that such a battery may be provided with a current cutoff mechanism that cuts off the current in the battery system in response to an increase in the internal pressure of the battery when an abnormality such as overcharging occurs, thereby improving safety.

[0040]

[Function] A positive electrode using a lithium-manganese composite oxide as a positive electrode active material, a negative electrode using a carbonaceous material capable of doping / dedoping lithium as a negative electrode active material, and a non-aqueous electrolyte solution. In the non-aqueous electrolyte secondary battery, the specific surface area of the lithium-manganese composite oxide, which is the positive electrode active material, is 0.
When it is regulated within the range of 05 to 5.0 m ² / g, the cycle characteristics are improved, the energy density is high and the cycle characteristics are excellent. This is considered to be due to the following reasons.

That is, in the non-aqueous electrolyte secondary battery using the lithium-manganese composite oxide as the positive electrode active material, the lithium-manganese composite oxide crystallizes during charging when lithium is dedoped from the lithium-manganese composite oxide. The cubic lattice that constitutes the structure contracts. On the other hand, during discharge in which lithium is doped into the positive electrode active material, the cubic crystal lattice of the lithium-manganese composite oxide expands. It is presumed that the volume change due to the contraction and expansion of the positive electrode active material due to the doping and dedoping of lithium gives stress to the positive electrode active material itself and promotes miniaturization. If the positive electrode active material is miniaturized, the contact property with, for example, a conductive agent deteriorates, resulting in cycle deterioration of the battery.

In such a non-aqueous electrolyte secondary battery,
Specific surface area of lithium-manganese composite oxide is 0.05m
^When the ratio is set to ² / g or more, it is possible to prevent the lithium-manganese composite oxide from becoming finer due to charge / discharge. Therefore, the lithium-manganese composite oxide is always in contact with the conductive agent in a good state, and excellent cycle characteristics can be obtained.

On the other hand, the lower limit of the specific surface area of the lithium-manganese composite oxide is set to 0.05 m ² / g, because when the specific surface area is less than 0.05 m ² / g, the positive electrode active material becomes fine. Although suppressed, the particle size becomes too large, so that the load characteristics deteriorate and the battery capacity decreases, which is a disadvantage.

[0044]

EXAMPLES Specific examples of the present invention will be described below based on experimental results. Example 1 The configuration of the non-aqueous electrolyte secondary battery prepared in this example is shown in FIG. This non-aqueous electrolyte secondary battery was manufactured as follows.

First, a lithium-manganese composite oxide as a positive electrode active material was produced as follows. A mixture of 1 mol of manganese dioxide and 0.25 mol of lithium carbonate was calcined in air at a temperature of 850 ° C. for 5 hours to give a massive Li powder.
Mn ₂ O ₄ was produced. And this massive LiMn ₂
O ₄ was pulverized and classified by a ball mill to obtain powdery LiMn ₂ O ₄ having a specific surface area of 0.05 m ² / g. The specific surface area of LiMn ₂ O ₄ was measured by using a cantasorb manufactured by Kantachrome Co., Ltd. based on the BET one-point method.

Powdered LiM produced as described above
86 wt% of n ₂ O ₄ and 1 graphite as a conductive material
0% by weight, polyvinylidene fluoride as a binder 4% by weight
Were mixed to prepare a positive electrode mixture, which was dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode mixture slurry. Then, the positive electrode mixture slurry was uniformly applied to both surfaces of a strip-shaped aluminum foil having a thickness of 20 μm, dried, and compression-molded with a roller press machine to fabricate a strip-shaped positive electrode 2.

Next, an artificial graphite material as a negative electrode active material was produced as follows. Oil pitch temperature 1200 ℃
After being calcined in, a heat treatment was performed at a temperature of 3000 ° C. in an inert gas atmosphere to generate an artificial graphite material, and the artificial graphite material was pulverized into a powder. As a result of powder X-ray diffraction measurement of this graphite material, the spacing of (002) planes was 0.337.
nm, the crystallite thickness in the C-axis direction was 30 nm. The G value measured by the laser Raman method was 13.6, and the true specific gravity measured by the pycnometer method was 2.20. The average particle size measured by laser diffraction particle size distribution measurement was 33 μm, the bulk specific gravity was 1.18, and the average shape parameter x _ave was 3.6.

90% by weight of the powdery graphite material powder thus produced and 10% by weight of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture, and N-methyl-2 as a solvent was mixed. -Dispersed in pyrrolidone to form a negative electrode mixture slurry. Then, this negative electrode mixture slurry was formed to a thickness of 1
A strip-shaped negative electrode 1 was prepared by uniformly coating both sides of a strip-shaped copper foil having a thickness of 0 μm, followed by drying and compression molding with a roller press.

The prepared strip-shaped negative electrode 1 and strip-shaped positive electrode 2 are used as a separator 3 made of a microporous polyolefin film.
A negative electrode 1, a separator 3, a positive electrode 2, and a separator 3 were laminated in this order and then wound many times, and the winding end portion of the outermost periphery was fixed with an adhesive tape to produce a spiral electrode body.
Then, this spiral electrode body was housed in a nickel-plated iron battery can 5, and insulating plates 4 were arranged on both upper and lower surfaces of the spiral electrode body. Then, the aluminum positive electrode lead 13 is led out from the positive electrode current collector 11 and welded to the protrusion of the safety valve device 8 that is electrically connected to the battery lid 7, and the nickel negative electrode lead 12 is connected to the negative electrode current collector. It was led out from No. 10 and welded to the bottom of the battery can 5.

On the other hand, the electrolytic solution was prepared by dissolving the supporting electrolyte LiPF ₆ at a concentration of 1 mol / liter in an organic solvent in which ethylene carbonate and methyl ethyl carbonate were mixed at a volume ratio of 5: 5. Then, after injecting the electrolytic solution into the battery can 5 in which the spiral electrode body is incorporated as described above, the battery can 5 is caulked through the insulating sealing gasket 6 whose surface is coated with asphalt to cut off the current. The safety valve device 8 having a mechanism, the PTC element 9 and the battery lid 7 are fixed, and the outer diameter is 18 mm and the height is 65 m.
m cylindrical battery was created. Examples 2 to 5 By controlling the pulverization and classification steps when producing the positive electrode active material, LiMn ₂ O ₄ powder having a specific surface area shown in Table 1 was produced, and this was used as the positive electrode active material. A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1. Comparative Example 1 and Comparative Example 2 By controlling the pulverization and classification steps when producing the positive electrode active material, the specific surface area is 0.05 to 5.0 m as shown in Table 1.
^A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that LiMn ₂ O ₄ powder deviated from ² / g was used as the positive electrode active material.

Regarding the non-aqueous electrolyte secondary battery produced as described above, the charging voltage was 4.20 V and the charging current was 100.
After charging at 0 mA and charging time 2.5 hours,
A charging / discharging cycle is repeated such that discharging is performed under the conditions of a discharge current of 1500 mAh and an end voltage of 2.75 V, and a discharge capacity of the first cycle of discharge (initial capacity) and a discharge of the 300th cycle relative to the discharge capacity of the second cycle of charge / discharge. The capacity ratio (capacity maintenance rate) was determined.

The results are shown in Table 1 together with the specific surface area of the LiMn ₂ O ₄ powder.

[0053]

[Table 1]

As can be seen from Table 1, the specific surface area is 0.0
5 to 5.0 m²/ G of LiMn ₂O_FourPowder as positive electrode
The batteries of Examples 1 to 5 used as materials had an initial capacity of
The amount is 1000mAh or more, and the capacity retention rate is 85% or more.
The deviation is high. On the other hand, LiMn
₂O_FourSpecific surface area of powder is 0.05m²Ratio smaller than / g
The battery of Comparative Example 1 had a low initial capacity of 890 mAh,
Mn₂O_FourThe specific surface area of the powder is 5.0m²Ratio exceeding / g
The battery of Comparative Example 2 has a low capacity retention ratio of 72.0%.
ing. The battery of Comparative Example 2 has a low capacity retention rate.
Has a specific surface area of 5.0 m²/ M exceeding Lig
n₂O_FourThe powder has a small particle size, and as a result,
It is thought that this is due to the progress of miniaturization. On the other hand, Comparative Example 1
The initial capacity of these batteries is low due to the specific surface area
Is 0.05m²/ Mg less than g₂O_FourPowder is grain
Very small diameter, resulting in poor utilization efficiency as an active material
This is because the heavy load characteristics are inferior.

From the above, in the non-aqueous electrolyte secondary battery, using LiMn ₂ O ₄ as the positive electrode active material and setting the specific surface area of this to 0.05 to 5.0 m ² / g means that the initial capacity is It was found that it is effective in obtaining a battery having a high energy density and excellent cycle characteristics, suppressing cycle deterioration without lowering the temperature. Examination of Negative Electrode Active Material Next, in the case of using a lithium-manganese composite oxide having a specific surface area regulated within a predetermined range as a positive electrode active material, an appropriate type of negative electrode active material and composition of an electrolytic solution were examined.

As the negative electrode active material, instead of the graphite material,
A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 using a mixed carbon material obtained by mixing 50% by weight of a graphite material and 50% by weight of a pitch crystalline coke which is a low crystalline carbon material or pitch coke alone. Experimental example 1, experimental example 2). Then, the initial capacity and the capacity retention rate were examined in the same manner as described above. The results are shown in Table 2.

[0057]

[Table 2]

As can be seen from Table 2, as compared with the battery of Experimental Example 2 in which pitch coke alone was used as the negative electrode active material,
Battery of Experimental Example 1 using a mixed carbon material of graphite material and pitch coke and Example 1 using the above-mentioned graphite material alone
Battery is superior in both initial capacity and capacity retention rate. From this, it was found that the graphite material alone or the mixed carbonaceous material containing the graphite material is more suitable as the negative electrode active material than the low crystalline carbonaceous material. Examination of Non-Aqueous Solvent for Electrolyte As a non-aqueous solvent for electrolyte, a mixture of ethylene carbonate and methyl ethyl carbonate shown in Table 3 is used instead of the mixed solvent of ethylene carbonate and methyl ethyl carbonate mixed at a volume ratio of 5: 5. Non-aqueous electrolyte secondary batteries were produced in the same manner as in Example 1 except that the mixed solvent mixed in the ratio was used (Experimental Examples 3 to 6). Then, the initial capacity and the capacity retention rate were examined in the same manner as described above. The results are shown in Table 3.

[0059]

[Table 3]

From Table 3, the batteries of Experimental Example 4 and Experimental Example 5 in which the mixing ratio of ethylene carbonate and methyl ethyl carbonate which is a chain carbonic acid ester was in the range of 3: 7 to 7: 3, maintained the initial capacity and capacity. Excellent for any of the rates. On the other hand, in the battery of Experimental Example 3 in which the ratio of ethylene carbonate and methyl ethyl carbonate was 2: 8, the capacity retention rate was relatively low although the initial capacity was not a problem. On the other hand, in the battery of Experimental Example 6 in which the ratio of ethylene carbonate and methyl ethyl carbonate was 8: 2, the capacity retention rate was excellent, but the initial capacity was smaller than the others.

From this, when a mixed solvent of ethylene carbonate and chain carbonic acid ester is used as the non-aqueous solvent of the electrolytic solution, the mixing ratio of ethylene carbonate and chain carbonic acid ester should be 3: 7 to 7: 3. It turns out to be suitable. The specific embodiment of the present invention has been described above by taking the cylindrical non-aqueous electrolyte secondary battery as an example. However, the shape of the battery is not limited to the cylindrical type and may be a square type, a flat type, a coin type, or a button type. It may be present, and the same effect can be obtained in any case.

[0062]

As is apparent from the above description, in the non-aqueous electrolyte secondary battery of the present invention, lithium-manganese composite oxide powder is used as the positive electrode active material, and its specific surface area is 0.05 to Since it is regulated within the range of 5.0 m ² / g, it can be said that a secondary battery having a high energy density and an excellent cycle life can be stably supplied at a low price, and its industrial and commercial value is extremely large.

[Brief description of drawings]

FIG. 1 is a schematic vertical cross-sectional view showing one structural example of a non-aqueous electrolyte secondary battery to which the present invention is applied.

[Explanation of symbols]

1 negative electrode 2 positive electrode 3 separator

Front page continuation (72) Inventor Atsushi Komaru 2-22-3 Shibuya, Shibuya-ku, Tokyo Sony Energy Tech Co., Ltd. (56) References JP-A-8-17471 (JP, A) JP-A-7 -235293 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/00-4/04 H01M 4/36-4/62 H01M 10/40

Claims (3)

(57) [Claims] 1. A positive electrode using a lithium-containing compound as a positive electrode active material, a negative electrode using a carbonaceous material capable of doping and dedoping lithium as a negative electrode active material, and a non-aqueous electrolyte. in aqueous electrolyte secondary battery, a lithium-containing compound comprising the above-described positive electrode active material has a specific surface area of the powder of the lithium-manganese composite oxide of 0.05~5.0m 2 / ^g, the above-mentioned negative electrode active material Carbonaceous materials have a true specific gravity of 2.10
g / cm ³ or more, the interplanar spacing of the 002 plane by the X-ray diffraction method is
0.335~0.34nm, the bulk specific gravity of 0.3g / cm ³
The above is the graphite material alone or mainly this graphite material
A non-aqueous electrolyte secondary battery characterized in that it is a graphite-mixed carbonaceous material . 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous solvent of the non-aqueous electrolyte is a mixed solvent of ethylene carbonate and chain ester carbonate. 3. A mixing volume ratio of the ethylene carbonate and the chain carbonate ester (ethylene carbonate: chain carbonate) is 3: 7 to 7: Non-water according to claim 2, characterized in that the 3 Electrolyte secondary battery.