JP2002270247A - Nonaqueous secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flat-shaped nonaqueous secondary cell with a thickness of less than 12 mm, a high energy capacity of not less than 30 Wh, and a volume energy density of 180 Wh/l, which has high capacity, and excellent cycle life and safety. SOLUTION: For the nonaqueous secondary cell, the positive electrode contains a mixture of lithium manganese double oxide expressed by the compositional formula; Lix Mn2-y MAy O4+z and lithium nickel double oxide expressed by the compositional formula; Lia Nib MBc O2 , as a positive electrode activator, and the negative electrode contains a mixture of graphitized mesocarbon micro beads, and double-structured graphite particle formed by covering the surface of the particle of graphite group of which, the face distance (d002) of (002) face, measured by X-ray wide angle diffraction method, is 0.34 nm or less, by an amorphous carbon layer with the face distance of 0.34 nm or more, as a negative electrode activator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous secondary battery, and more particularly to a non-aqueous secondary battery for a power storage system having excellent cycle life and safety.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of effective use of energy for resource saving and conservation of the global environment, a home-use decentralized power storage system and a vehicle for electric power storage for midnight power storage and solar power generation have been developed. Power storage systems are attracting attention. For example, Japanese Patent Application Laid-Open No. 6-86463 proposes a total system that combines electricity supplied from a power plant, gas cogeneration, a fuel cell, a storage battery, and the like, as a system capable of supplying energy to energy consumers under optimal conditions. there. Rechargeable batteries used in such a power storage system, energy capacity is different from the small secondary battery for the following mobile devices 10 Wh, is needed a large size large capacity. For this reason, in the above power storage system, usually, a plurality of secondary batteries are connected in series, and a voltage of 50
It is used as an assembled battery of about 400 V, and most of the systems use lead batteries.

On the other hand, in the field of small secondary batteries for portable equipment, nickel-metal hydride batteries, lithium secondary batteries, and the like have been rapidly developed in order to meet the conflicting needs of miniaturization and high capacity. Batteries having a volume energy density of l or more are commercially available. In particular, lithium ion batteries have the potential to achieve a volume energy density exceeding 350 Wh / l, and are more reliable in terms of safety and cycle characteristics than lithium secondary batteries that use metallic lithium for the negative electrode. Because of its excellence, its market is expanding exponentially. As a positive electrode active material of such a lithium ion battery, a material having an electromotive force of more than 4 V such as a lithium cobalt composite oxide, a lithium nickel composite oxide, and a lithium manganese composite oxide is used. Among these, lithium-cobalt composite oxides which are excellent in battery characteristics and easy to synthesize are currently used in the largest amount. However, the raw material, cobalt,
Since the recoverable reserves are small and expensive,
The use of a lithium nickel composite oxide as a substitute has been studied. Lithium nickel composite oxide has a layered rock salt structure like lithium cobalt composite oxide, and is a high capacity material exceeding 200 mAh / g. However, lithium nickel composite oxides are formed during charging
Due to the fact that Ni ⁴⁺ is chemically unstable, the structure of the lithium-nickel composite oxide in a high charge state in which lithium is largely extracted from the structure is unstable, etc.
Oxygen desorption start temperature from the crystal lattice is a problem that low. Also, Solid State Ionics, 69, No.3 / 4,265
(1994) reports that "the starting temperature of oxygen desorption of a charged lithium nickel composite oxide is lower than that of a conventional lithium cobalt oxide". For these reasons, batteries using lithium-nickel composite oxide alone as the positive electrode active material have problems in thermal stability in a high charge state, despite the fact that high capacity can be obtained. It has not been put to practical use until now because it cannot secure sufficient properties.

On the other hand, a lithium manganese composite oxide having a spinel type crystal structure is structurally different from a lithium cobalt composite oxide, a lithium nickel composite oxide or the like having a layered rock salt structure. Due to differences in the structure, the oxygen desorption start temperature in a high state of charge of the lithium-manganese composite oxide, compared to the lithium cobalt complex oxide and lithium-nickel composite oxide, high since, lithium-manganese composite oxide Is a highly safe cathode material.

However, a lithium secondary battery using a lithium manganese composite oxide as a positive electrode has a "capacity deterioration" in which the capacity gradually decreases as charging and discharging are repeated.
Since it is impossible to avoid this, its practical use has been difficult.

Japanese Patent Application Laid-Open Nos. 57-208079 and 63-24555 disclose negative electrode active materials for such small batteries.
Graphite has been proposed as a material that has excellent flexibility and does not cause lithium to precipitate in a dendritic manner during charge / discharge cycles. At present, graphite-based materials such as natural graphite, artificial graphite, graphite whose impurities have been reduced by acid treatment, mesocarbon microbeads, and graphitized carbon fibers have the property of forming intercalation compounds based on a unique layer structure. It has been put to practical use as an electrode material for secondary batteries utilizing this property. In addition, the use of materials with low crystallinity has been proposed. For example, JP-A-63-24555 proposes various carbon materials having a turbostratic structure and a preferred orientation obtained by thermally decomposing hydrocarbons in the gas phase in order to suppress the decomposition of the electrolytic solution. are doing.

However, these highly crystalline materials and low crystalline materials have both advantages and disadvantages.

When a highly crystalline carbon material such as graphite is used as a negative electrode material, the change in potential due to insertion and extraction of lithium is theoretically small, and the capacity available as a battery is increased. It is known. However, as the crystallinity of the carbon material increases, the charge / discharge efficiency, which is considered to be caused by the decomposition of the electrolytic solution, decreases, and the carbon material is destroyed by expansion / contraction of the crystal due to repeated charge / discharge. Leads to.

On the other hand, when a carbon material having low crystallinity is used as the negative electrode, there are not many problems related to charge and discharge, but the change in potential due to occlusion / release of lithium ions is large. In addition, the capacity that can be used as a battery decreases, and it becomes difficult to manufacture a high-capacity battery.

Japanese Patent Application Laid-Open No. 4-368778 discloses that the formation of a double structure in which carbon particles having high crystallinity are coated with carbon having low crystallinity can prevent the carbon material from being damaged by repeated charge and discharge. ing. That is, when the double-structured carbon material prepared by this method is used as an active material, it is theoretically possible to prevent decomposition of the electrolytic solution and obtain a high-capacity electrode with excellent potential smoothness. it can. Also,
The carbon material also has the advantage of being inexpensive. However, a battery using the double-structured active material particles as a negative electrode material has a high capacity but is greatly deteriorated due to the passage of cycles. Further, since this material powder is very bulky, it is necessary to use a large amount (10% by weight or more) of the binder occupying the negative electrode constituting material in order to enhance the adhesiveness with the copper foil as the current collector. There is.

In the field of large batteries for power storage systems using these materials for the positive electrode, one of the leading options for high energy density batteries is the development of lithium ion batteries, such as the Lithium Battery Power Storage Technology Research Association (LIEBES). It has been promoted vigorously by.

The energy capacity of such a large-sized lithium ion battery is about 100 to 400 Wh, and the volume energy density is 200 to 400 Wh / l, which is equivalent to the level of a small secondary battery for portable equipment. Its size and shape are 50 ~
Typical examples are a flat prismatic shape such as a cylindrical shape having a length of about 70 mm x a length of about 250 to 450 mm, a rectangular shape having a thickness of about 35 to 50 mm, or an elliptical shape.

However, in these large lithium ion batteries, high energy density can be obtained, but since the battery design is an extension of the small battery for portable equipment, the diameter or thickness of the small battery for portable equipment is small. Three
It is formed in a battery shape such as a cylindrical shape or a square shape which is twice or more. In this case, heat is likely to be accumulated inside the battery due to Joule heat generated by the internal resistance of the battery during charging and discharging, or internal heat generated by the battery due to a change in entropy of the active material as lithium ions enter and exit. For this reason, the temperature difference between the temperature inside the battery and the temperature near the battery surface increases, and the internal resistance changes accordingly, so that the charge amount, the voltage and the like tend to vary. In addition, since a plurality of batteries of this type are used as assembled batteries, the heat storage easiness varies depending on the location of the batteries in the system, causing variations among the batteries, resulting in an accuracy of the entire assembled battery. Control becomes difficult. Furthermore, since the heat dissipation during high rate charge and discharge or the like is insufficient, the battery temperature rises, since it is placed in the undesirable condition for the battery, shortening of the life due to decomposition of the electrolytic solution, and further the battery heat In terms of runaway, it is said that reliability, especially safety, is sufficiently secured.
Hard to say.

[0014] In order to solve the above problems, WO99 / 60652
No., published 2000-251940, 2000-251941, 2000-260478
No. 2000-260477 include a flat non-aqueous secondary battery containing a non-aqueous electrolyte containing a positive electrode, a negative electrode, a separator and a lithium salt in a battery container, wherein the non-aqueous secondary battery A non-aqueous secondary battery having a flat shape with a thickness of less than 12 mm and an energy capacity of 30 Wh or more and a volume energy density of 180 Wh / l or more is disclosed. The technology described in these publications solves the problems related to reliability and safety caused by the above-mentioned heat storage and eliminates obstacles to practical use by making the battery a unique shape (flat shape). Trying to.

In general, large batteries such as batteries for power storage systems are required to have high safety and excellent cycle life of 1000 cycles or more. However, batteries using lithium-nickel composite oxide in the positive electrode material, since lack thermal stability at high charging, there is a problem of low safety. Although batteries using lithium manganese composite oxides have high safety, (1) it is difficult to achieve both high energy density (high charge / discharge capacity) and high cycle life, and (2) self-discharge. Therefore, there are two problems that the storage capacity is reduced.

First, in a battery using a lithium manganese composite oxide, the reason why high capacity cannot be realized is as follows.
It is conceivable that the reaction during the synthesis of the composite oxide is non-uniform, the influence of contaminating impurities, and the like. In addition, as a cause of capacity deterioration due to charge / discharge cycles, the average valence of Mn ions changes between trivalent and tetravalent as charge compensation due to the inflow and outflow of Li. Occurs during the process, Mn elutes from the lithium manganese composite oxide, and the eluted Mn
Is increased due to precipitation on the negative electrode active material or on the separator, furthermore, the influence of impurities, inactivation due to liberation of active material particles, and acid generated in the electrolytic solution by water-containing moisture. It is conceivable that the influence is caused, the electrolyte is deteriorated due to oxygen release from the lithium manganese composite oxide, and the like.

[0017] When the spinel single phase is formed, elution cause of Mn is trivalent Mn in spinel structure, the tetravalent and the electrolytic solution by some disproportionation into a divalent It is conceivable that the solution may be easily dissolved or may be eluted due to the relative shortage of Li ions. As a result, it is assumed that irreversible capacity generation and disorder of the atomic arrangement in the crystal are promoted by repeated charge and discharge, and that the eluted Mn ions precipitate on the negative electrode or the separator and hinder the movement of Li ions. Is done. In addition, the lithium manganese composite oxide distorts the Li ion by taking in and out of the Li ion, and the crystal is distorted by the Jahn-Teller effect, accompanied by expansion and contraction of several% of the unit cell length. Therefore, it is presumed that when the charge / discharge cycle is repeated, the particles do not function as an active material due to partial electrical isolation.

Further, it is considered that the release of oxygen from the lithium manganese composite oxide is facilitated along with the elution of Mn. When the amount of released oxygen increases, it is presumed that the decomposition of the electrolytic solution is accelerated, and that the deterioration of the electrolytic solution also causes deterioration of the charge / discharge cycle.

[0019] The suppression of such Mn elution, reduction of lattice distortion,
It is important to improve the cycle characteristics of the lithium battery to realize such reduction of oxygen deficiency. Thus, Japanese Patent Application Laid-Open No. 2-270268 proposes improving the cycle characteristics by making the composition of Li sufficiently excessive with respect to the stoichiometric ratio. Further, it has been proposed to improve the cycle characteristics by replacing a part of the Mn element of the lithium manganese composite oxide with addition or doping of Co, Ni, Fe, Cr, Al or the like (Japanese Patent Application Laid-Open No. 4-141954). Gazette, JP-A-4-160758, JP-A-4-69076, JP-A-4-237970,
JP-A-4-282560 and JP-A-4-289662).
These Li excessive composition, methods such as addition of the metal element, the improvement of cycle characteristics, although effective, is accompanied with reduction of the charge and discharge capacity Conversely, satisfies both the high cycle life and high capacity I have not been able to.

Japanese Patent Application Laid-Open No. 10-112318 proposes to use a mixture of a lithium manganese composite oxide and a lithium nickel composite oxide as a positive electrode active material. According to this publication, the irreversible capacity in the initial charge / discharge is compensated, and a large charge / discharge capacity is obtained. Further, JP-A-7-235291 also, as the positive electrode active material, has proposed a technique of using a mixture of lithium-manganese composite oxide and the LiCo _0.5 Ni _0.5 O _2.

[0021] However, according to the inventor's research,
Simply using a mixture of a lithium manganese composite oxide and a lithium nickel composite oxide as the positive electrode active material still does not sufficiently improve the charge / discharge characteristics, cycle characteristics, and the like. It became clear that satisfactory results could not be obtained.

Regarding the shape of the battery, in the case of a large battery such as a rectangular or cylindrical battery that inherits the design concept of a conventional small battery, improvement in safety cannot be expected due to internal heat storage and the like.

[0023]

SUMMARY OF THE INVENTION Accordingly, the present invention provides
Providing a flat non-aqueous secondary battery with a large capacity of over Wh and a high volume energy density of over 180 Wh / l, a thickness of less than 12 mm, high capacity, and excellent cycle life and safety The purpose is to do.

[0024]

Means for Solving the Problems The present inventor has conducted research while paying attention to the current state of the art as described above, and as a result, has achieved the above object with a nonaqueous secondary battery having a specific configuration. succeeded in. That is, the present invention provides the following non-aqueous secondary battery. 1. A positive electrode, a negative electrode, a nonaqueous electrolyte containing a separator and a lithium salt contained in the battery container, a flat shape of less than 12mm thickness, nonaqueous energy capacity is in and volume energy density than 30Wh is 180 Wh / l or more In the secondary battery, the positive electrode has a composition formula of Li _x Mn _2-y MA _y O _{4 + z} (MA is Mg, A
l, Cr, Fe, at least one element selected from the group consisting of Co and Ni, and 1 <x ≦ 1.2, 0 <y ≦ 0.1, -0.
3 ≦ z ≦ 0.3) represented by lithium manganese composite oxide and the composition formula Li _a Ni _b MB _c O ₂ (MB is at least one element selected from the group consisting of Co, Al and Mn , And 1 ≦
a ≦ 1.1, 0.5 <b <1, 0 <c <0.5, b + c = 1) and a mixture comprising a lithium-nickel composite oxide represented by the following formula: (D002) is 0.34 nm or less.
A non-aqueous secondary battery comprising, as a negative electrode active material, a mixture of double-structured graphite particles coated with an amorphous carbon layer having a thickness exceeding 0.34 nm and graphitized mesocarbon microbeads. 2. Mixing weight ratio of the lithium-manganese composite oxide and lithium-nickel composite oxide in the positive electrode mixture,
Lithium-manganese composite oxide: lithium-nickel composite oxide = 95: 5 to 70: nonaqueous secondary battery according to claim 1 which is 30. 3. Item 3. The non-aqueous secondary battery according to Item 1 or 2, wherein the lithium manganese composite oxide and the lithium nickel composite oxide have a BET specific surface area of 1 m ² / g or less, respectively. 4. The above-mentioned item, wherein the weight mixing ratio between the double-structured graphite particles and the graphitized mesocarbon microbeads in the mixture for a negative electrode active material is double-structured graphite particles: graphitized mesocarbon microbeads = 95: 5 to 50:50. 2. The non-aqueous secondary battery according to 1. 5. Item 5. The non-aqueous secondary battery according to any one of Items 1 to 4, wherein the shape of the flat front and back surfaces is rectangular. 6. Item 1 wherein the plate thickness of the battery container is 0.2 to 1 mm.
5. The non-aqueous secondary battery according to any one of 5.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The non-aqueous secondary battery of the present invention has a flat shape with a thickness of less than 12 mm, an energy capacity of 30 Wh or more and a volume energy density of 180 Wh / l or more. Specific examples of the shape are described in WO99 / 60652,
-251940 JP, JP 2000-251941 JP, JP 2000-26047
No. 8, JP-A-2000-260477 and the like.

Hereinafter, the present invention will be described in more detail with reference to a non-aqueous secondary battery according to an embodiment of the present invention shown in the drawings.

FIG. 1 is a plan view and a side view of a flat rectangular (notebook) non-aqueous secondary battery for a power storage system according to an embodiment of the present invention, and FIG. 2 is a view showing FIG. FIG. 3 is a side view showing a configuration of an electrode laminate housed inside the battery.

As shown in FIGS. 1 and 2, the non-aqueous secondary battery according to the present embodiment includes a battery container including an upper lid 1 and a bottom container 2, and a plurality of positive electrodes 101a housed in the battery container. , A negative electrode 101 b, 101 c, and an electrode laminate including the separator 104. In the flat type non-aqueous secondary battery as in this embodiment, the positive electrode 101
a, (anode 101c disposed on both outer sides of the or laminate) anode 101b, for example, as shown in FIG. 2, but are stacked alternately arranged via a separator 104,
The non-aqueous secondary battery according to the present invention is not limited to such a specific arrangement, and the number of layers and the like can be variously changed according to required capacity and the like. The shape of the non-aqueous secondary battery shown in FIGS.
300 mm × 210 mm × 6 mm thick, for example, the positive electrode 101
A positive electrode material described below is used as a, and the negative electrodes 101b, 1
In the case of lithium secondary battery using the carbon material as 01c, it can be used in the energy storage system.

The positive electrode current collector 105a of each positive electrode 101a is:
Each of the negative electrodes 101 is electrically connected to the positive electrode terminal 3.
The negative electrode current collectors 105b of b and 101c are electrically connected to the negative electrode terminal 4. The positive terminal 3 and the negative terminal 4 are
It is attached in a state insulated from the battery container, that is, the upper lid 1.

The top cover 1 and the bottom container 2 are welded by melting the top cover over the entire circumference at a point A shown in the enlarged view of FIG. The upper lid 1 is provided with a liquid injection port 5 for an electrolytic solution. After the electrolytic solution is injected, the liquid is sealed using a sealing film 6 made of, for example, an aluminum-modified polypropylene laminated film. Final sealing step is at least
It is preferable to perform it after one charging operation. The pressure in the battery container after the final sealing step with the sealing film 6 is preferably lower than the atmospheric pressure, and is 8.66 × 10 ⁴ Pa (650 Torr).
It is more preferably the following, 7.33 × 10 ⁴ Pa (550 Tor
r) It is particularly preferred that The pressure in the battery container is determined in comprehensive consideration of the separator to be used, the type of electrolytic solution, the material and thickness of the battery container, the shape of the battery, and the like. When the internal pressure is equal to or higher than the atmospheric pressure, the battery tends to be larger than the designed thickness, or the thickness of the battery tends to vary greatly, so that the internal resistance and capacity of the battery tend to vary.

As the positive electrode active material used for the positive electrode 101a, Li _x Mn _2-y MA _y O _{4 + z} (MA is at least one kind selected from the group consisting of Mg, Al, Cr, Fe, Co and Ni) an element, and 1 <x ≦ 1.2,0 <y ≦ 0.1, -0.3 ≦ z ≦ 0.3 at a) lithium manganese composite oxide represented by (hereinafter be referred to as "composition formula (1) composite oxide" And the composition formula Li _a Ni _b
MB _c O ₂ (MB is at least one element selected from the group consisting of Co, Al, and Mn, and 1 ≦ a ≦ 1.1, 0.5 <b <
1, 0 <c <0.5, b + c = 1) by using a mixture consisting of a lithium nickel composite oxide (hereinafter sometimes referred to as “composition formula (2) composite oxide”) In addition, it was found that the amount of Mn ions eluted in the electrolytic solution was remarkably reduced, deterioration of the electrolytic solution, discoloration and generation of acid were suppressed, and Mn deposited on the negative electrode was reduced.

In a conventional non-aqueous battery, Mn added to the electrolyte
The reason elution large ions, to produce hydrogen ions by the reaction between the positive electrode / negative electrode and the residual moisture and a solute of the electrolyte, which is considered to Mn is eluted reacts with a portion of the lithium-manganese composite oxide. In particular, LiPF as electrolyte
_{When 6} and LiBF ₄ are used, the elution of Mn ions is large. In the present invention, the dissolution of Mn ions is remarkably reduced, and remarkable improvements in the charge / discharge characteristics, cycle characteristics, safety, and the like of the battery are achieved, but the reason has not yet been elucidated sufficiently.

In the present invention, as a main component of the positive electrode active material, a lithium manganese composite oxide having a specific composition (composition formula)
By using (1) composite oxide), Mn disproportionation is less likely to occur even if the battery is repeatedly charged and discharged, as compared to the case of using a spinel single-phase lithium manganese composite oxide. The amount of Mn ions eluted can be reduced, and the desorption of oxygen can be reduced. As a result, since it is possible to effectively suppress structural deterioration of the lithium manganese composite oxide (composition formula (1) composite oxide), the decomposition of the electrolytic solution, it is possible to improve the cycle characteristics.

In the composition formula (1), Li _x Mn _2-y MA _y O _{4 + z} , the Li ratio is in the range of 1 <x ≦ 1.2. When x is 1 or less, the cycle characteristics are not sufficiently improved, whereas 1.
If it exceeds 2, the capacity of the active material is greatly reduced. M
The A ratio is in the range of 0 <y ≦ 0.1. When y exceeds 0.1, the capacity of the active material is greatly reduced. Mn in the composition formula (1)
Improves cycle characteristics as an element MA that replaces
Examples include Mg, Al, Cr, Fe, Co and Ni, of which Al and Cr are more preferred.

[0035] In the present invention, as the positive electrode active material, the composition formula (1) lithium-manganese composite oxide and the composition formula represented by (2) Li _a Ni _b MB particular lithium nickel composite oxide represented by _c O ₂ Further improvement of the cycle characteristics can be achieved by using the compound in combination. Although the reason for the improvement of the cycle characteristics has not been elucidated yet, by blending the lithium-nickel composite oxide having the specific composition represented by the composition formula (2), the elution of Mn ions and the desorption of oxygen are further improved. It is considered to be suppressed. Further, the capacity of the lithium nickel composite oxide of the specific composition represented by the composition formula (2) is
Since the capacity is larger than the capacity of the lithium manganese composite oxide, higher capacity can be achieved.

In the composition formula (2) Li _a Ni _b MB _c O ₂ , the Li ratio is in the range of 1 ≦ a ≦ 1.1 so as not to decrease the capacity. Ni ratio is in the range 0.5 <b <1 in. When b is less than 0.5, the capacity becomes too small, whereas when b is 1, the cycle characteristics of the active material are significantly reduced. As the element MB to replace Ni in the composition formula (2), at least one selected from the group consisting of Co, Al and Mn is used from the viewpoint of cycle characteristics and safety. Substitution element ratio is in the range of 0 <c <0.5. When c is 0 (i.e., when not replacing Ni), the contrast cycle characteristics of the active material is not improved, if it is 0.5 or more, the capacity is too small.

Further, in the mixture used as the positive electrode active material in the present invention, the mixing ratio (weight% ratio) of lithium manganese composite oxide (1) and lithium nickel composite oxide (2)
It is (1) :( 2) = 95: 5 to 70: is preferably 30. When the content of lithium nickel composite oxide is less than 5%, the effect of improving capacity and improving cycle characteristics is small, whereas
%, The safety of the battery may not be ensured due to the thermal instability of the lithium nickel composite oxide.

The average particle size of the positive electrode active material is the same as that of a conventional active material, and is usually about 1 to 60 μm, preferably 5 to 4 μm.
It is about 0 μm, more preferably about 10 to 30 μm. In addition, in this specification, "average particle size" means the center particle size in the volume particle size distribution obtained by a dry laser diffraction measurement method.

The specific surface area of the positive electrode active material, a lithium-manganese composite oxide is usually less than 1 m ² / g, more preferably about 0.2~0.7m ² / g. The lithium nickel composite oxide is usually less than 1 m ² / g, more preferably 0.2~0.7m
It is about ² / g. In this specification, the term "specific surface area" indicates the value measured by BET method using nitrogen gas.

The negative electrode active material used for the negative electrodes 101b and 101c is a double-structure graphite particle (hereinafter, referred to as a “first component” for simplicity) in which the surface of a core made of graphite particles is coated with amorphous carbon. ) And graphitized mesocarbon microbeads (hereinafter sometimes referred to as “second component” for simplicity).

In the present invention, the use of double-structure graphite particles as the first component of the negative electrode active material improves the battery capacity and reduces the charge / discharge efficiency, which is presumed to be due to decomposition of the electrolyte. It is substantially suppressed, and the destruction of the graphite structure is also prevented.

Graphite particles, which are the core of the double-structured graphite particles, have a (002) plane spacing (d002) of 0.3 by X-ray wide-angle diffraction.
It is less than 4 nm, more preferably about 0.3354 to 0.3380 nm, further preferably about 0.3354 to 0.3360 nm. If this value exceeds 0.34 nm, the crystallinity of the core portion becomes low, so that the potential change accompanying the release of lithium ions becomes large, and the effective capacity usable as a battery becomes low.
The plane spacing of the amorphous carbon layer covering the graphite-based particle core was determined by X-ray wide-angle diffraction method to be (002) plane spacing (d002) of 0.3.
It is 4 nm or more, more preferably about 0.34 to 0.38 nm, and still more preferably about 0.34 to 0.36 nm. When this value in the coating layer is less than 0.34 nm, the crystallinity is too high, and the charging / discharging efficiency, which is presumed to be due to decomposition of the electrolytic solution, is reduced. The expansion / contraction of the spacing increases the risk of breaking the carbon material. On the other hand, the (002) plane of the surface separation (d002)
If it exceeds 0.38 nm, lithium ions will not easily move, and the capacity available as a battery will decrease. In addition,
The method for producing such double-structured graphite particles is not particularly limited, but is described, for example, in WO97 / 18160.

The graphitized mesocarbon microbeads used as the second component of the negative electrode active material have a smaller capacity than the double component graphite particles as the first component, but have a small specific surface area. Can be manufactured. The graphitized mesocarbon microbeads are X
Line spacing (d002) of (002) plane by line wide angle diffraction method is 0.34nm
Less than, more preferably about 0.3354～0.3380Nm, more preferably about 0.3354～0.3360Nm. The method for producing such graphitized mesocarbon microbeads is not particularly limited, but is described in, for example, JP-A-9-151382.

Further, the mixture constituting the negative electrode active material in the present invention has a mixing ratio of the double-structure graphite particles as the first component and the graphitized mesocarbon microbeads as the second component.
It is essential that (weight% ratio) the first component: the second component = 95: 5 to 50:50. If the second component in the mixture is less than 5% by weight, it is necessary to use a large amount of binder in order to obtain good adhesion to the current collector Cu foil. Decrease capacity. On the other hand, when the second component exceeds 50% by weight, the capacity of the graphitized mesocarbon microbeads is lower than that of the double-structured graphite particles, so that the battery capacity is also reduced.

When a negative electrode is manufactured using a mixture of the first and second components, a polyvinylidene fluoride (PVDF) -based material is used as a binder. As the binder, modified P with -COOH group introduced into PVDF structure
VDF is more preferred.

The structure of the separator 104 is not particularly limited, but a single-layer or multi-layer separator can be used, and at least one sheet is preferably made of a nonwoven fabric. In this case, cycle characteristics are improved. . Also, the material of the separator 104 is not particularly limited, and examples thereof include polyolefin such as polyethylene and polypropylene, polyamide, kraft paper, glass, and cellulosic materials. Is determined as appropriate.

The power of the non-aqueous secondary battery used in this embodiment is
For the decomposition, publicly known electrolyte materials such as lithium salts are used.
Non-aqueous electrolytes dissolved in known solvents
You. The electrolyte depends on the type of cathode material, anode material,
Such as comprehensively taking into account the conditions of use of such pressure, according to the conventional method
Can be determined appropriately. More specifically, LiP
F ₆, LiBF_Four, LiClO_FourSuch as lithium salt
Boneto, ethylene carbonate, diethyl carbonate Ne
Dimethyl carbonate, methyl ethyl carbonate
G, dimethoxyethane, γ-butyrolactone, methyl acetate
Or one or more organic compounds such as methyl and methyl formate
An example is a solution dissolved in a solvent. The concentration of the electrolyte material
Is not particularly limited, but generally 0.5 to 2mo
It is about l / l. The electrolyte, of course, contains moisture.
As low as possible, specifically 100p water content
Those below pm are preferred. In addition, used in this specification
The term "non-aqueous electrolyte" refers to non-aqueous electrolytes and
It encompasses concepts that include organic electrolytes, and
The concept also includes a solid or solid electrolyte.

The non-aqueous secondary battery constructed as described above has a large capacity and a high energy density, so that it can be used for home power storage systems (nighttime power storage, cogeneration,
Solar power generation), a power storage system such as an electric vehicle, and the like. In such a power storage system, the energy capacity is preferably at least 30 Wh, more preferably at least 50 Wh, and the energy density is preferably at least 180 Wh / l, more preferably at least 200 Wh / l.
If the energy capacity is less than 30 Wh or the volume energy density is less than 180 Wh / l, since the capacity is small, it is necessary to increase the number of series-parallel batteries to obtain a sufficient system capacity, It is not preferable for a power storage system because a compact design is difficult.

The nonaqueous secondary battery of the present embodiment has the flat shape, its thickness is less than 12 mm, more preferably 10mm
Is less than. It is practical to set the lower limit of the thickness to 2 mm or more in consideration of the filling rate of the electrode, the battery size (the smaller the thickness, the larger the area to obtain the same capacity). When the thickness of the battery is more than 12 mm, it is difficult to sufficiently radiate the heat inside the battery to the outside, and the temperature difference between the inside of the battery and the vicinity of the battery surface increases, resulting in a difference in internal resistance. In addition, there is a large problem that variations in the amount of charge and the voltage in the battery become large.
The specific thickness of the battery is appropriately determined according to the battery capacity, the energy density, and the like. However, it is preferable to design the battery to have a maximum thickness at which expected heat radiation characteristics can be obtained.

Further, the non-aqueous secondary battery of the present embodiment can have various shapes such as a flat, front and back surface having a rectangular shape, a circular shape, and an oval shape. When the shape is a square, it is generally a rectangle, but may be a polygon such as a triangle or a hexagon depending on the application. Further, it may be a cylindrical shape such as a thin cylinder. When the shape is cylindrical, the thickness of the cylinder is the thickness referred to here. Further, from the viewpoint of ease of manufacture, as shown in FIG. 1, a “note-type” shape in which the flat front and back surfaces of the battery are rectangular is preferable.

The material used for the upper lid 1 and the bottom container 2 serving as the battery container is appropriately selected depending on the use and shape of the battery.
There is no particular limitation, and iron, stainless steel, aluminum and the like are general and practical. Also, the thickness of the battery container itself is appropriately determined depending on the use and shape of the battery or the material of the battery case, and is not particularly limited. In order to ensure the strength required for battery production, the thickness of the part with a total surface area of 80% or more of the battery (the thickness of the largest area that composes the battery container) should be 0.2mm or more. More preferably, it is more preferably 0.3 mm or more. Further, the thickness of the part at the same time, preferably at 1mm or less, and more preferably to 0.7mm or less.
When the thickness exceeds 1 mm, although the force for pressing down the electrode surface increases, the internal volume of the battery decreases, and it is not desirable because sufficient capacity cannot be obtained and the weight increases. .

[0052]

As described above, the thickness of the non-aqueous secondary battery is
By designing to less than mm, for example, even at the time of high rate charging and discharging of a battery having a large capacity of 30 Wh or more and a high energy density of 180 Wh / l or more, the rise in battery temperature is small,
Shows excellent heat dissipation characteristics. Therefore, heat storage of the battery due to internal heat generation is reduced, and as a result, thermal runaway of the battery can be suppressed, and a non-aqueous secondary battery excellent in reliability and safety can be obtained.

[0053]

The present invention will be described more specifically below with reference to examples of the present invention. The present invention is not limited by the description of these examples.

Example 1 (1) First, Li as a lithium-manganese composite oxide
_1.1 Mn _1.8 Al _0.1 O ₄ and LiNi _1.8 Co _0.2 O ₂ as lithium nickel composite oxide and acetylene black as a conductive material were dry-mixed, and the resulting mixture was dissolved polyvinylidene fluoride (PVDF) as a binder Slurry-1 was prepared by uniformly dispersing in N-methyl-2-pyrrolidone (NMP). Next, the slurry-1 was applied to both sides of an aluminum foil serving as a current collector, dried, and pressed to obtain a positive electrode.

The solid content ratio (weight ratio) in the positive electrode was calculated as follows: lithium lithium manganate: lithium lithium nickelate: acetylene black: PVDF = 0.92 (100-α): 0.92α: 3: 5
When expressed as above, seven types of positive electrodes of α = 0, 5, 10, 20, 30, 40, and 50 were prepared.

[0056] Figure 3- (a) is an explanatory view of a positive electrode. In this embodiment, the coating area of the positive electrode 101a (W1 × W2) is 262.
5 is a × 192mm ^2. In addition, the short side of the electrode, the electrode is is provided collecting part 106a which is not coated, it is punched with a diameter of 3mm in the center.

[0057] (2) On the other hand, the double structure graphite particles (trade name "OPCG-K", manufactured by Osaka Gas Chemicals; of graphite particle core (002)
Surface spacing (d002) = less than 0.34 nm, surface spacing (d002) of coating layer (d002) = 0.34 nm or more), graphitized mesocarbon microbeads (MCMB, manufactured by Osaka Gas Chemicals, product number “25-28”) ”; (0
02) Plane spacing (d002) = less than 0.34 nm) and acetylene black as a conductive material were dry-mixed, and then uniformly dispersed in NMP in which PVDF as a binder was dissolved.
2 was prepared. Then, the slurry -2 was applied to both sides of a copper foil as a current collector, dried and pressed to obtain a negative electrode.

The solid content ratio (weight ratio) in the negative electrode was expressed as double structure graphite particles: graphitized mesocarbon microbeads: acetylene black: PVDF = 0.92 (100-β): 0.92β: 2: 6. Then, eight types of negative electrodes having β = 0, 5, 10, 20, 30, 40, 50, and 100 were produced.

FIG. 3B is an explanatory diagram of the negative electrode. Negative electrode 1
The application area (W1 × W2) of 01b is 267 × 195 mm ² . In addition, a current collector 106b to which no electrode is applied is provided on the short side of the electrode, and a hole having a diameter of 3 mm is formed in the center thereof.

Further, the slurry-2 was applied only on one side by the same method as described above, thereby producing a single-sided electrode. The single-sided electrode is disposed outside in the electrode laminate of item (3) described later (101c in FIG. 2).

(3) As shown in FIG. 3, eight positive electrodes obtained in the above item (1) and nine negative electrodes obtained in the above item (2) are used.
(2 sheets on one side) and separator material A (rayon-based nonwoven fabric,
Basis weight 12.6 g / m ²⁾ and the separator material B (polyethylene microporous membrane; alternately laminated through a basis weight 13.3 g / m ²⁾ and the separator 104 of the combined, further outside for insulation between the battery container The separator material B was arranged further outside of the negative electrode 101c to produce an electrode laminate. The separator 10
4 shows that the separator material A is located on the positive electrode side and the separator material B
Is located on the negative electrode side.

(4) As shown in FIG. 4, SUS30 having a thickness of 0.5 mm
Diaphragm 4 made thin in the depth 5 mm, to create a bottom vessel 2, the upper cover 1 was also produced by SUS304 steel sheet having a thickness of 0.5 mm. Next, the positive electrode terminal 3 made of aluminum and the negative electrode terminal 4 made of copper (head diameter 6 mm, threaded portion at the tip M3) were attached to the upper lid 1.
The positive and negative terminals 3 and 4 were insulated from the upper lid 1 by a polypropylene gasket.

(5) The holes of the respective positive electrode current collectors 106a and the holes of the respective negative electrode current collectors 106b of the electrode laminate prepared in the above item (3) are inserted into the negative electrode terminal 4, respectively. After the connection, the connected electrode laminate was fixed with an insulating tape, and the corner A of FIG. 1 was laser-welded over the entire circumference. Next, the injection port 5 (diameter 6
mm) from the electrolyte (solvent obtained by mixing ethylene carbonate and diethyl carbonate in a 1: 2 weight ratio to a concentration of 1 mol / l
(a solution in which iPF ₆ was dissolved). Next, the injection port 5 was temporarily closed using a bolt for temporary fixing under atmospheric pressure.

(6) After charging this battery to 4.2V with a current of 5A, a constant current constant voltage charging of applying a constant voltage of 4.2V is performed for a total of 8 hours, and then discharging to 2.5V with a constant current of 5A. did.

(7) Next, after removing the temporary fixing bolts of the battery, under a reduced pressure of 4 × 10 ⁴ Pa (300 Torr), a 0.08 mm-thick aluminum foil-modified polypropylene laminated film punched into a diameter of 12 mm. Sealing film 6 consisting of
Temperature 250 to 350 ° C., a pressure 1 to 3 kg / cm ^2, by heat-sealing under the conditions of pressing time 5-10 seconds, the injection port 5 to a final sealing, height 300 mm × Thickness Width 210 mm × A 6 mm flat notebook battery was obtained.

[0066] (8) was charged to 4.2V these batteries in "5A of current, a constant current constant voltage charging applying a constant voltage of 4.2V total of 8 hours, followed by 2.5V at 5A constant current The charge / discharge cycle of discharging until 100 times was performed 100 times. Further, in order to evaluate the cycle characteristics, the capacity retention ratio was calculated from the discharge capacity at one cycle and 100 cycles. Table 1 shows the results
And Table 2.

Tables 1 and 2 show the safety evaluation tests using these flat notebook batteries in accordance with UL-164.
The results of the nail penetration test performed in accordance with 2 are also shown. The nail piercing test is a test for forcibly causing an internal short circuit by piercing a battery with a nail, and was performed using a 4 mm nail. Cells, was repeated three times the same charge and discharge in the same cycle test as above was charged, and subjected to a nail penetration test.

[0068]

[Table 1]

[0069]

[Table 2]

As is clear from the results shown in Table 1, when α = 0 when the lithium nickel composite oxide was not added to the positive electrode active material (when lithium manganese composite oxide was used alone), the cycle test was performed. Large capacity deterioration. In the nail penetration test, smoke was generated when a mixture of α = 40 and 50 having a high compounding ratio of lithium nickel composite oxide was used. Therefore, in consideration of the cycle characteristics and safety, the mixing range of the lithium nickel composite oxide to lithium manganese composite oxide, it is appropriate to 5 ≦ α ≦ 30.

[0071] From the results shown in Table 2, without the addition of graphitized mesocarbon microbeads as a negative electrode active material β
When = 0 (when the dual structure graphite particles are used alone), the capacity deterioration in the cycle test is large. In contrast,
When β = 100 (when the graphitized mesocarbon microbeads are used alone), the cycle characteristics are good, but the battery capacity is small. Therefore, in consideration of cycle characteristics and battery capacity, it is appropriate that the mixing range of the graphitized mesocarbon microbeads with respect to the double-structured graphite particles in the negative electrode active material is 5 ≦ β ≦ 50.

The composition formula (1) Li _x M used in Example 1 was used.
n _2-y MA _y O _{4 + z} , MA as Mg, Cr, Fe, Co or N
Even when another lithium manganese composite oxide containing i as a component is used, the same remarkable effect as described above is achieved.

Further, the composition formula similarly used in Example 1 was used.
(2) When using other lithium nickel composite oxides containing Al or Mn as the lithium nickel composite oxide MB represented by Li _a Ni _b MB _c O ₂ , The effect is achieved.

[0074] Further, the mixing ratio is 5 ≦ α ≦ 3 of the lithium nickel composite oxide to lithium manganese composite oxide
0, and the mixing ratio of the graphitized mesocarbon microbeads to the dual structure graphite particles is 5 ≦ β ≦ 50
, The same result as above can be obtained. EXAMPLE by two same manner as in Example 1, solid content in the positive electrode (weight _{ratio) Li 1.1 Mn 1.8 Al 0.1 O} 4: LiNi 1.8 Co 0.2 O 2:
Acetylene black: PVDF = 0.92 (100-α): 0.92α: 3:
When expressed as 5, the positive electrode was prepared with α = 20, and the solid content ratio (weight ratio) in the negative electrode was double structure graphite particles: graphitized mesocarbon microbeads: acetylene black: PVDF =
When expressed as 0.92 (100-β): 0.92β: 2: 6, a negative electrode was prepared with β = 30. Using these positive and negative electrodes, a separator, an electrolytic solution using the same materials as in Example 1, cell A (flat shape of the notebook, width 210 mm × height 300 mm ×
Comparative battery B (square, width 84 mm × height 150 mm × thickness 30 mm) and comparative battery C (cylindrical, diameter 60 mm) with different shapes
× height 135 mm).

Using these batteries, the cycle characteristics and the capacity retention were measured in the same manner as in Example 1, and the safety was evaluated by a nail penetration test. Table 3 shows the results
Shown in

[0076]

[Table 3]

As is clear from the results shown in Table 3, even if the constituent materials are exactly the same as those of the present invention, the comparative batteries B and C having different battery shapes are inferior in safety and cannot be put to practical use. . In contrast, laptop battery A according to the present invention,
It is clear that ignition does not occur in the nail penetration test and that the safety is extremely excellent.

In the second embodiment, when the lithium-manganese composite oxide and the lithium-nickel composite oxide are each substituted with another element,
Alternatively, the mixing ratio of the lithium nickel composite oxide to the lithium manganese composite oxide is in the range of 5 ≦ α ≦ 30, and the mixing ratio of the graphitized mesocarbon microbeads to the double structure graphite particles is 5 ≦ β ≦ 50. If within range also, the same results as the above can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view and a side view of a non-aqueous secondary battery for a power storage system according to an embodiment of the present invention.

FIG. 2 is a side view showing a configuration of an electrode laminate housed inside the battery shown in FIG.

FIG. 3 is an explanatory diagram of a positive electrode, a negative electrode, and a separator used in a nonaqueous secondary battery according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram of a top lid and a bottom container in the non-aqueous secondary battery according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Top cover 2 Bottom container 3 Positive electrode terminal 4 Negative terminal 5 Injection port 6 Sealing film 101a Positive electrode (both sides) 101b Negative electrode (both sides) 101c Negative electrode (one side) 104 Separator 105a Positive current collector 105b Negative current collector 106a Positive current collector 106b Negative electrode current collector

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Shizukuni Yada 4-1-2, Hirano-cho, Chuo-ku, Osaka City, Osaka Prefecture Inside Kansai New Technology Research Institute Co., Ltd. (72) Haruo Kikuta Hirano, Chuo-ku, Osaka City, Osaka Prefecture 1-Chome 1-2-2, Osaka Gas Co., Ltd. F-term (reference) 5H011 AA03 AA13 CC02 CC06 CC10 DD05 DD13 KK01 KK02 5H029 AJ03 AJ05 AJ12 AK03 AK18 AL07 AL08 AL19 AM03 AM04 AM05 AM07 AM16 BJ03 BJ12 DJ02 DJ03 DJ04 DJ05 HJ01 HJ02 HJ04 HJ07 HJ13 HJ19 5H050 AA07 AA08 AA16 BA17 CA08 CA09 CA29 CB08 CB09 CB29 EA10 EA24 FA12 FA20 GA22 HA01 HA02 HA04 HA07 HA13 HA19

Claims (6)

[Claims] A non-aqueous electrolyte containing a positive electrode, a negative electrode, a separator and a lithium salt is accommodated in a battery container and has a thickness of 12
mm, a non-aqueous secondary battery having an energy capacity of 30 Wh or more and a volume energy density of 180 Wh / l or more, wherein the positive electrode has a composition formula of Li _x Mn _2-y MA _y O _{4 + z} ( MA is Mg, Al, C
at least one selected from the group consisting of r, Fe, Co and Ni
A species of elements, and 1 <x ≦ 1.2,0 <y ≦ 0.1, -0.3 ≦ z
≤ 0.3) and a lithium manganese composite oxide represented by the composition formula Li _a Ni _b MB _c O ₂ (MB is at least one element selected from the group consisting of Co, Al and Mn, and 1 ≦ a ≦ 1.
A mixture comprising a lithium nickel composite oxide represented by 1, 0.5 <b <1, 0 <c <0.5, b + c = 1) is used as a positive electrode active material, and the negative electrode is obtained by X-ray wide-angle diffraction ( 002) Face spacing (d00
2) is 0.34 nm or less the surface of the graphite-based particles is 0.34 nm
A non-aqueous secondary battery characterized by using, as a negative electrode active material, a mixture of double-structured graphite particles covered with an amorphous carbon layer having a thickness exceeding 90% and graphitized mesocarbon microbeads. 2. The weight mixture ratio of the lithium manganese composite oxide and the lithium nickel composite oxide in the positive electrode mixture is lithium manganese composite oxide: lithium nickel composite oxide = 95: 5 to 70:30. nonaqueous secondary battery according to claim 1. 3. The non-aqueous secondary battery according to claim 1, wherein each of the lithium manganese composite oxide and the lithium nickel composite oxide has a BET specific surface area of 1 m ² / g or less. 4. The weight ratio of the double structure graphite particles to the graphitized mesocarbon microbeads in the mixture for a negative electrode active material is as follows: double structure graphite particles: graphitized mesocarbon microbeads = 95: 5 to 50: nonaqueous secondary battery according to claim 1 which is 50. 5. The non-aqueous secondary battery according to claim 1, wherein the flat front and back surfaces are rectangular. 6. The non-aqueous secondary battery according to claim 1, wherein the thickness of the battery container is 0.2 to 1 mm.