JP4828690B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

【０１０８】
前記表１から明らかなように３Ｖカットの放電以降、さらに３Ｖから１Ｖに向う深い放電時の容量として１５〜３０ｍＡｈ／ｇを有する負極を備えた実施例１〜５の二次電池は、前記負極の容量が１５〜３０ｍＡｈ／ｇの範囲を外れる比較例１〜５の二次電池に比べて高温での充放電サイクルル特性が優れていることがわかる。
【０１０９】
なお、前述した実施例では図２に示す角型リチウムイオン二次電池について説明したが、本発明は前述した図１の円筒型リチウムイオン二次電池、図３および図４の薄型リチウムイオン二次電池に適用しても同様な優れた高温充放電サイクル特性を有する。
【０１１０】
【発明の効果】
以上詳述したように、本発明によれば負極を改良することによって高温充放電サイクル特性を向上した非水系電解液二次電池を提供することができる。
【図面の簡単な説明】
【図１】本発明に係る非水系電解液二次電池の一形態ある円筒型非水系電解液二次電池（円筒型リチウムイオン二次電池）を示す部分断面図。
【図２】本発明に係る非水系電解液二次電池の他の形態ある角型非水系電解液二次電池（角型リチウムイオン二次電池）を示す部分切欠斜視図。
【図３】本発明に係る非水系電解液二次電池のさらに他の形態ある薄型非水系電解液二次電池（薄型リチウムイオン二次電池）を示す斜視図。
【図４】図３のIV−IV線に沿う断面図。
【符号の説明】
１、２１…外装缶、
３，２３電極体、
４，２４，４８…負極、
５，２５，４５…セパレータ、
６，２６，４４…正極、
１２…封口板、
２８…蓋体、
４１…発電要素、
４３，４６…集電体、
５１…外装フィルム。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery having an improved negative electrode.
[0002]
[Prior art]
In recent years, with the reduction in size and weight of various electronic devices such as VTRs, mobile phones and personal computers, and cordless portable electronic devices, the demand for high energy density of these devices has increased, and metallic lithium has been used as the negative electrode active material. Non-aqueous electrolyte secondary batteries represented by such lithium secondary batteries have been proposed. However, in the lithium secondary battery using metallic lithium as the negative electrode active material, lithium dissolved in the electrolytic solution as lithium ions during discharge reacts with the nonaqueous solvent in the electrolytic solution and becomes partially inactive. For this reason, when charging and discharging are repeated, lithium is electrodeposited on the convex portion of the negative electrode surface and deposited in a dendritic shape (dendritic shape), and this dendritic lithium penetrates the separator and contacts the positive electrode, thereby causing an internal short circuit. There was a problem.
[0003]
For this reason, Japanese Patent Application Laid-Open No. 63-121260 discloses a lightweight secondary battery using carbon for the negative electrode. Thereafter, so-called lithium ion secondary batteries using various carbon materials such as coke, graphite, fired resin, pyrolytic vapor phase carbon, etc., have been proposed and put into practical use.
[0004]
As the lithium ion secondary battery, the positive electrode is LiCoO. ₂ , LiNiO ₂ , LiMn ₂ O _Four And the like using a carbon material for the negative electrode are known, and have various characteristics depending on the material of the carbon material. For example, as disclosed in JP-A-5-89879, a lithium ion secondary battery including carbon fibers having a lamellar structure in the cross-sectional direction of the fiber diameter as a negative electrode active material has excellent charge / discharge characteristics. Further, a lithium ion secondary battery containing graphite having a high degree of graphite as a negative electrode active material has high charging energy. Further, the lithium ion secondary battery has higher safety than a secondary battery using metallic lithium as a negative electrode, and is widely used as a power source for various portable terminals.
[0005]
As described above, coke, graphite, resin fired body, pyrolytic vapor phase carbon and the like are used as the active material of the negative electrode, but in the lithium ion secondary battery equipped with these negative electrodes, the required characteristics of the portable terminal, for example, thin , Weight reduction, high capacity, and high cycle maintenance ratio are not yet satisfied.
[0006]
[Problems to be solved by the invention]
The present invention seeks to provide a non-aqueous electrolyte secondary battery having improved high-temperature charge / discharge cycle characteristics by improving the negative electrode.
[0007]
[Means for Solving the Problems]
To achieve the above object, a non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode capable of inserting and extracting lithium, a negative electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte.
The positive electrode and the negative electrode have a structure in which a positive electrode material and a negative electrode material are applied to a current collector, respectively.
The negative electrode material contains a carbonaceous material including fibrous carbon materials (a) and (b) and a non-fibrous carbon material (c), and the fibrous carbon material (b) is mesophase low-temperature calcined carbon. ,And
The negative electrode has a discharge capacity of 15 to 30 mAh / g between a negative electrode potential of 1 V and 3 V.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the non-aqueous electrolyte secondary battery according to the present invention will be described in detail.
[0009]
This non-aqueous electrolyte secondary battery includes a positive electrode capable of inserting and extracting lithium, a negative electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte.
[0010]
Next, the negative electrode, the positive electrode, the separator, and the nonaqueous electrolytic solution will be described.
[0011]
1) Negative electrode
This negative electrode has a structure in which a negative electrode material is applied to a current collector.
[0012]
Examples of the current collector include a copper plate and a copper mesh material.
[0013]
The negative electrode material contains fibrous carbon materials (a) and (b), a non-fibrous carbon material (c), and a binder. This fibrous carbon material (b) is mesophase low-temperature calcined carbon.
[0014]
The fibrous carbon material (a) functions as a main carbon material of the negative electrode material. Examples of the fibrous carbon material (a) include mesophase pitch-based carbon fiber, PAN-based carbon fiber, or a carbon material in the form of a fiber made of phenol resin or polyimide, and a fibrous vapor-grown carbon body. it can. In particular, mesophase pitch-based carbon fibers are preferable.
[0015]
The fibrous carbon material (a) preferably has an average fiber diameter of 8 to 18 μm, an average fiber length of 10 to 50 μm, and a true density of 2.24 g / cc or more. Such a fibrous carbon material (a) contributes to the improvement of charge / discharge cycle characteristics. In particular, when the average fiber length is less than 10 μm, the ratio indicating the fiber form is reduced to form a powder and the charge / discharge efficiency may be reduced. On the other hand, when the average fiber length exceeds 50 μm, the physical properties of the negative electrode provided with the negative electrode material containing the fibrous carbon material (a), for example, the adhesion between the current collector and the negative electrode material may be reduced.
[0016]
The fibrous carbon material (a) has a (101) diffraction peak P in the X-ray diffraction method by Cu-Kα. ₁₀₁ And (100) diffraction peak P ₁₀₀ Intensity ratio (P ₁₀₁ / P ₁₀₀ ) Is more preferably 1.2 to 1.9. The fibrous carbon material (a) has a surface spacing (d ₀₀₂ ) Is 0.3354 to 0.3370 nm (more preferably 0.3354 to 0.3359 nm), the crystallite size (La) in the a-axis direction is 60 nm or more, and the crystallite size (Lc in the c-axis direction) ) Is more preferably 40 nm or more.
[0017]
The fibrous carbon material (a) is formed by adding boron with an interval between graphite crystals (d ₀₀₂ ) Is expanded, that is, it is allowed to increase the degree of graphitization.
[0018]
The fibrous mesophase low-temperature calcined carbon (b) is calcined at a comparatively low temperature and contributes to an increase in negative electrode capacity and an improvement in charge / discharge cycle characteristics. The fibrous carbon (b) preferably has an average fiber diameter of 8 to 20 μm, an average fiber length of 8 to 20 μm, and a true density of 1.50 to 1.75 g / cc.
[0019]
As the non-fibrous carbon material (c), for example, scale Examples thereof include flake-shaped or spherical block-like graphite, and the like can be used alone or in the form of a mixture of two or more. The graphite preferably has an average particle size of 3 to 30 μm. If the average particle size of the graphite is less than 3 μm, the specific surface area and the oil absorption amount are increased, and the solid content ratio when the negative electrode material is applied to the current collector is decreased, and the irreversible capacity of the negative electrode may be increased. . On the other hand, when the average particle diameter of the graphite exceeds 30 μm, physical properties such as a decrease in the adhesion of the negative electrode material to the current collector and a reduction linear pressure required for press molding may increase.
[0020]
The blending ratio of the fibrous carbon materials (a) and (b) and the non-fibrous carbon material (c) is preferably 20 to 85% by weight for the former and 15 to 80% by weight for the latter. If the former compounding ratio exceeds 85% by weight, the amount of fibrous carbon material increases, and the negative electrode slurry can be prepared with a high solid content ratio, which is advantageous in terms of production, but the negative electrode material adheres to the current collector. It becomes difficult to increase the density of the material of the negative electrode due to the decrease in properties. On the other hand, if the latter exceeds 80% by weight, the amount of non-fibrous carbon material such as flake graphite increases, which is advantageous in increasing the electrode density, but the permeability of the non-aqueous electrolyte to the negative electrode is high. The charge / discharge cycle characteristics may be lowered.
[0021]
The fibrous carbon material (b) is desirably blended in an amount of 1 to 10% by weight, more preferably 2 to 9% by weight, based on the carbonaceous material. When the blending amount of the fibrous carbon material (b) is less than 1% by weight, it is difficult not only to increase the capacity but also to increase the electrode density. On the other hand, when the amount of the fibrous carbon material (b) exceeds 10% by weight, the charge / discharge cycle life may be shortened.
[0022]
The negative electrode includes a negative electrode material containing a carbonaceous material including the fibrous carbon materials (a) and (b) and the non-fibrous carbon material (c) described above, and a discharge capacity between a negative electrode potential of 1 V to 3 V. As 15 to 30 mAh / g. If the capacity | capacitance of the negative electrode on the said conditions deviates from the said range, the charge / discharge cycle characteristic at high temperature will fall. The capacity | capacitance of the negative electrode on the said more preferable conditions is 20-25 mAh / g.
[0023]
As the binder, a polymer material having solubility in an organic solvent typified by PVdF, a polymer material easily dispersed in water typified by CMC, SBR, or the like can be used. Is just an example and is not particularly restricted. However, in consideration of the future environment, a polymer material that is easily dispersed in water is preferable.
[0024]
The binder is preferably blended in an amount of 1.0 to 6.0% by weight with respect to the negative electrode material. When the blending amount of the binder is less than 1.0% by weight, it is preferable in terms of electrode performance such as an increase in capacity, but the adhesion of the negative electrode material to the current collector is reduced and the negative electrode is processed (particularly cutting). For example, when producing a group of electrodes by winding a strip with a separator interposed between the positive and negative electrodes, a minute defect is mixed in the electrode group, causing a short circuit between the positive and negative electrodes, etc. There is a risk of inviting. On the other hand, if the amount of the binder exceeds 6.0% by weight, the amount of the binder in the negative electrode may increase, leading to a decrease in capacity.
[0025]
2) Positive electrode
This positive electrode has a structure in which a positive electrode material is applied to a current collector.
[0026]
Examples of the current collector include an aluminum plate and an aluminum mesh material.
[0027]
The positive electrode material contains, for example, an active material and a binder. Examples of the active material include manganese dioxide, molybdenum disulfide, and LiCoO. ₂ , LiNiO ₂ , LiMn ₂ O _Four And the like chalcogen compounds. These chalcogen compounds can be used in a mixture of two or more. As the binder, for example, a thermoplastic resin such as a fluororesin, a polyolefin resin, a styrene resin, an acrylic resin, or a rubber resin such as fluororubber can be used. Specifically, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polyacrylonitrile, nitrile rubber, polybutadiene, butyl rubber, polystyrene, styrene-butadiene rubber, hydrogenated styrene-butadiene rubber, polysulfide rubber, nitrocellulose , Cyanoethyl cellulose, carboxymethyl cellulose and the like. Among these binders, an elastomer, a rubber cross-linked body, or a modified body having a polar group introduced is from the viewpoint of improving the adhesion between the current collector and the positive electrode material and improving the resistance increase effect during overcharge. Is preferred.
[0028]
The positive electrode material is allowed to further contain, as a conductive auxiliary material, acetylene black, graphite such as powdered expanded graphite, pulverized carbon fiber, pulverized graphitized carbon fiber, and the like.
[0029]
3) Separator
As this separator, for example, a polyethylene porous film or a polypropylene porous film having a thickness of 20 to 30 μm can be used.
[0030]
4) Non-aqueous electrolyte
This non-aqueous electrolyte is composed of, for example, lithium perchlorate (LiClO) in a non-aqueous solvent composed of at least one selected from ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and γ-butyrolactone. _Four ), Lithium hexafluorophosphate (LiPF) ₆ ), Lithium borofluoride (LiBF) _Four ), Lithium hexafluoroarsenide (LiAsF) ₆ And the like in which the composition is dissolved.
[0031]
The non-aqueous solvent is preferably used in a mixture of two to three types rather than being used alone because of viscosity, and the concentration of the electrolyte dissolved in the non-aqueous solvent is 0.5 to 1.5 mol. / L is preferable. In particular, the non-aqueous solvent preferably contains 10 to 80% by weight (more preferably 45 to 70% by weight) of γ-butyrolactone.
[0032]
Examples of the non-aqueous electrolyte secondary battery according to the present invention include a cylindrical type shown in FIG. 1 described below, a square type shown in FIG. 2, and a thin structure shown in FIGS.
[0033]
(1) Cylindrical non-aqueous electrolyte secondary battery
As shown in FIG. 1, a metal outer can 1 having a bottomed cylindrical shape also serves as a negative electrode terminal, for example, and a lower insulating plate 2 is disposed on the inner surface of the bottom. An electrode body 3 that is a power generation element is accommodated in the outer can 1. The electrode body 3 is produced by winding the negative electrode 4, the separator 5, and the positive electrode 6 in a spiral shape so that the separator 5 is located on the outermost periphery. A negative electrode lead tab 7 is provided on the lower end surface of the negative electrode 4, and the other end of the lead tab 7 is connected to the inner surface of the bottom of the outer can 1. An upper insulating plate 8 having a positive lead tab extraction hole in the vicinity of the center is disposed on the electrode body 3 in the outer can 1.
[0034]
A sealing member 9 having vague pores also serves as a positive electrode terminal, and is caulked and fixed to the upper end opening of the outer can 1 via an insulating gasket 10. The sealing member 9 includes a dish-shaped sealing plate 12 having a gas vent hole 11 opened in the vicinity of the center, and a valve membrane labcha 13 made of aluminum, for example, fixed to the sealing plate 12 so as to cover the gas vent hole 11; A ring-shaped PTC (Positive temperature Coefficient) 14 disposed on the periphery of the sealing plate 12 and a hat-shaped positive electrode terminal 16 having a plurality of vent holes 15 are formed. A positive electrode lead tab 17 is connected to the lower surface of the sealing plate 12, and the other end of the lead tab 17 is connected to the positive electrode 6 of the electrode 3 through a lead extraction hole of the upper insulating plate 8.
[0035]
(2) Square non-aqueous electrolyte secondary battery
An exterior can 21 made of a metal having a bottomed rectangular tube shape shown in FIG. 2, for example, aluminum, also serves as a positive electrode terminal, for example, and an insulating film 22 is disposed on the inner surface of the bottom. The electrode body 23 that is a power generation element is accommodated in the outer can 21. When the outer can is made of stainless steel or iron, it also serves as a negative electrode terminal. The electrode body 23 is manufactured by winding the negative electrode 24, the separator 25, and the positive electrode 26 in a spiral shape so that the positive electrode 26 is located on the outermost periphery, and then press-molding it into a flat shape. A spacer 27 made of, for example, synthetic resin having a lead extraction hole near the center is disposed on the electrode body 23 in the outer can 21.
[0036]
The metal lid 28 is airtightly joined to the upper end opening of the outer can 1 by, for example, laser welding. In the vicinity of the center of the lid body 28, an extraction hole 29 for the negative electrode terminal is opened. The negative electrode terminal 30 is hermetically sealed in the hole 29 of the lid 28 via an insulating material 31 made of glass or resin. A lead 32 is connected to the lower end surface of the negative electrode terminal 30, and the other end of the lead 32 is connected to the negative electrode 24 of the electrode body 23.
[0037]
The upper insulating paper 33 is covered on the entire outer surface of the lid 28. The lower insulating paper 35 having the slits 34 is disposed on the bottom surface of the outer can 21. A folded PTC element (Positive Temperature Coefficient) 36 has one surface interposed between the bottom surface of the outer can 21 and the lower insulating paper 35, and the other surface passing through the slit 34 and the insulating paper. 35 is extended to the outside. The outer tube 37 is disposed so as to extend from the side surface of the outer can 21 to the periphery of the upper and lower insulating papers 33 and 35, and the upper insulating paper 33 and the lower insulating paper 35 are fixed to the outer can 21. is doing. With such an arrangement of the outer tube 37, the other surface of the PTC element 36 extended to the outside is bent toward the bottom surface of the lower insulating paper 35.
[0038]
(3) Thin non-aqueous electrolyte secondary battery
As shown in FIG. 3 and FIG. 4, the power generation element 41 includes, for example, a positive electrode 44 in which a positive electrode active material layer 42 that is a positive electrode material containing an active material and a binder is supported on both surfaces of a current collector 43, a separator 45, and an active material. A negative electrode active material layer 46, which is a negative electrode material containing a substance and a binder, is formed by winding a negative electrode 48 supported on both surfaces of a current collector 47 and a separator 45 in a spiral shape, and forming a flat and rectangular shape. External lead terminals 49 and 50 connected to the positive electrode 44 and the negative electrode 48 extend from the same side surface of the power generation element 41 to the outside.
[0039]
As shown in FIG. 3, the power generation element 41 has, for example, a side surface in which the external lead terminals 49 and 50 of the power generation element 41 are extended in a cup 52 of a two-fold cup-type exterior film 51. It is wrapped so as to be located on the opposite side. As shown in FIG. 4, the exterior film 51 has a structure in which a sealant film 53 located on the inner surface side, an aluminum or aluminum alloy foil 54 and a rigid organic resin film 55 are laminated in this order. Three side portions corresponding to the two long side surfaces and one short side surface of the power generation element 1 excluding the bent portion in the exterior film 51 are heat-sealed between the sealant films 53 and extended in a horizontal direction. Portions 56a, 56b, and 56c are formed, and the power generating element 41 is sealed by these seal portions 56a, 56b, and 56c. External terminals 49 and 50 connected to the positive electrode 44 and the negative electrode 48 of the power generation element 41 are extended to the outside through a seal portion 56b on the opposite side to the bent portion. A nonaqueous electrolytic solution is impregnated and contained in the power generation element 41 and the exterior film 51 sealed by the seal portions 56a, 56b, and 56c.
[0040]
In the thin non-aqueous electrolyte secondary battery, the exterior film is not limited to the cup type but may be a pillow type or a pouch type.
[0041]
As described above, the non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode capable of inserting and extracting lithium, a negative electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte, and the positive electrode and the negative electrode Has a structure in which a positive electrode material and a negative electrode material are respectively applied to a current collector, and the negative electrode material includes a carbonaceous material including a fibrous carbon material (a), (b) and a non-fibrous carbon material (c). And the fibrous carbon material (b) is mesophase low-temperature calcined carbon, and the negative electrode has a discharge capacity of 15 to 30 mAh / g between a negative electrode potential of 1 V and 3 V.
[0042]
As such a carbonaceous material, it has a structure in which a negative electrode material containing fibrous mesophase low-temperature calcined carbon (b) together with fibrous carbon material (a) and non-fibrous carbon material (c) is applied to a current collector, and By providing an improved negative electrode having a discharge capacity of 15 to 30 mAh / g between the negative electrode potential 1 V and 3 V (that is, having a predetermined capacity even in the overdischarge region), charging at a high temperature (for example, 35 to 60 ° C.) A non-aqueous electrolytic secondary battery with improved discharge cycle characteristics can be obtained. In other words, because the negative electrode has a predetermined capacity in the overdischarge region, even if it is left in a high temperature environment for a long time after discharge, the capacity of the secondary battery is not lost, and the initial charge / discharge characteristics are exhibited by subsequent charging. it can.
[0043]
In particular, the fibrous carbon material (a) has an average fiber diameter of 8 to 18 μm, an average fiber length of 10 to 50 μm, a true density of 2.24 g / cc or more (more preferably in addition to these characteristics, X-ray diffraction by Cu-Kα) (101) diffraction peak P ₁₀₁ And (100) diffraction peak P ₁₀₀ Intensity ratio (P ₁₀₁ / P ₁₀₀ ) Is more preferably 1.2 to 1.9. The fibrous carbon material (a) has a surface spacing (d ₀₀₂ ) Is 0.3354 to 0.3370 nm, the crystallite size (La) in the a-axis direction is 60 nm or more, and the crystallite size (Lc) in the c-axis direction is 40 nm or more) A non-aqueous electrolytic secondary battery having an improved charge / discharge cycle life at a higher temperature can be obtained.
[0044]
Moreover, it is fired at a comparatively low temperature as the fibrous carbon material (b). The fibrous carbon has an average fiber diameter of 8 to 20 μm, an average fiber length of 8 to 20 μm, and a true density of 1.50 to 1.75 g / cc, thereby improving the charge / discharge cycle life at a higher temperature. A non-aqueous electrolytic secondary battery can be obtained.
[0045]
Further, as the non-fibrous carbon material scale By using flake-like or spherical block-like graphite (preferably graphite having an average particle diameter of 3 to 30 μm), it is possible to obtain a non-aqueous electrolytic secondary battery with improved charge / discharge cycle life at a higher temperature.
[0046]
Furthermore, the positive electrode accompanying increasing the capacity | capacitance of the said negative electrode by using what contains 10-80 weight% (more preferably 45-70 weight%) of (gamma) -butyrolactone as a nonaqueous solvent of the said nonaqueous electrolyte solution. Thus, a non-aqueous electrolyte secondary battery can be obtained in which high temperature charge / discharge cycle characteristics can be improved and balanced performance can be obtained.
[0047]
【Example】
Hereinafter, preferred embodiments of the present invention will be described in detail.
[0048]
"Production of fibrous carbon material (a)"
A mesophase pitch was spun and infusible, carbonized at 680 ° C. in an argon atmosphere, pulverized appropriately, and then graphitized at 3000 ° C. in a nitrogen atmosphere to obtain a fibrous carbon material.
[0049]
The obtained fibrous carbon material has a c-axis direction crystallite (Lc) size of 60 nm, an average fiber diameter of 8.5 μm, an average fiber length of 18.5 μm, a true density of 2.26 g / cc, and a surface spacing (d ₀₀₂ ) (101) Diffraction peak P in X-ray diffraction method with 0.3359 nm, Cu-Kα ₁₀₁ And (100) diffraction peak P ₁₀₀ Intensity ratio (P ₁₀₁ / P ₁₀₀ ) Was 1.45.
[0050]
“Fabrication of fibrous mesophase low-temperature calcined carbon material (b)”
Several types of fibrous mesophase low-temperature calcined carbon materials having an average fiber diameter of 17 μm and a true density of 1.50 to 1.80 g / cc were prepared by changing the graphitization temperature.
[0051]
"Production of graphite"
Natural graphite was unwound into a spherical shape to obtain predetermined graphite. This graphite has an average particle size of 8.5 μm and a specific surface area of 6.7 m. ² / G, surface separation (d ₀₀₂ ) 0.3358 nm.
[0052]
Example 1
<Production of negative electrode>
First, the fibrous mesophase low-temperature calcined carbon material (b) having 50 parts by weight of the fibrous carbon material (a) and a true density of 1.55 g / cc is added to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight. 2 parts by weight and 48 parts by weight of the spherical graphite (c) were added, followed by shear dispersion. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and uniform mixing and stirring were performed to prepare a negative electrode coating slurry.
[0053]
Next, 103 g / m each of the coating slurry was applied to both sides of a 15 μm thick copper foil (current collector) by a knife edge coater. ² It was applied to become and dried. The density of the negative electrode material on the copper foil at this time was 1.23 g / cc. Thereafter, pressing and slitting were performed to produce a strip-shaped negative electrode having a thickness of 149 μm (negative electrode material density: 1.5 g / cc) and a width of 43.25 mm.
[0054]
About the obtained negative electrode, the discharge capacity between negative electrode potentials 1V-3V was measured with the following methods.
[0055]
The amount of active material (amount of negative electrode material) is calculated by subtracting the weight of the current collector from the total weight of a sample cut out to a size of 2 × 2 cm from the produced negative electrode. A glass filter is interposed between the sample and the counter electrode lithium metal, metal lithium is used as a reference electrode, and these are incorporated in a glass container with a three electrode terminal. In this glass container, LiBF was added to a mixed solvent of γ-butyrolactone and ethylene carbonate (mixing volume ratio 2: 1). _Four After injecting an electrolytic solution having a composition in which 1.5 mol / L is dissolved, the glass cell is assembled by evacuating to degas. The work so far is performed in a glove box in a dry argon atmosphere.
[0056]
The assembled glass cell is connected to a charger / discharger and placed in a thermostatic chamber in a 25 ° C. atmosphere. The charger / discharger monitors a voltage current when a current is passed between the sample and the counter electrode and a voltage between the counter electrode and the sample. As charging conditions, 320 mAh per 1 g of active material is set to 1 C, and 1 C current is determined according to the weight of the sample active material.
[0057]
The 1st to 3rd cycles were charged and discharged under the conditions of 0.3C × 10mV × 8h charge and 0.3C × 3.0V cutoff, and the 4th cycle was charged with 0.3C × 10mV × 8h. Charging / discharging is performed under the condition of 0.1 C × 1.0 V cutoff. Here, charging means that a current flows in a direction in which Li ions intercalate in the negative electrode sample.
[0058]
Then, in the fourth cycle, a value obtained by subtracting the discharge amount up to 3V from the discharge amount up to 1V is calculated as the discharge capacity (mAh / g) between 1V and 3V.
[0059]
From such tests and calculations, the discharge capacity between the negative electrode potential of 1 V and 3 V was 15 mAh / g.
[0060]
<Preparation of positive electrode>
First, 41.7 parts by weight of a 12% strength by weight polyvinylidene fluoride resin (PVdF) in N-methylpyrrolidone solution was added to LiCoO as an active material. ₂ 100 parts by weight of powder and 5 parts by weight of graphite powder (trade name, manufactured by Lonza Corporation; KS4) as a conductive filler were mixed and kneaded. Subsequently, 15 parts by weight of N-methylpyrrolidone was further added to the mixture, and the solid matter was dispersed using a bead mill to prepare a positive electrode coating slurry.
[0061]
Next, the positive electrode coating slurry was applied to both sides of a 15 μm thick Al foil (current collector) at 255 g / m. ² After coating and drying, a positive electrode having a thickness of 167 μm and a width of 42.00 mm was produced by pressing and slitting.
[0062]
<Assembly of secondary battery>
Next, lead tabs were respectively joined to the positive and negative electrode current collectors, and a flat electrode body was produced by winding up and spiraling through two polyethylene porous membranes using an automatic winding machine. . A voltage of 100 V was applied to the obtained electrode body from a DC power source for 5 seconds, and those that flowed 10 μV or more were judged as defective and excluded.
[0063]
Next, the electrode body determined as a non-defective product was inserted into an aluminum outer can having a bottomed rectangular cylindrical shape having a thickness of 4.8 mm, a width of 30 mm, and a height of 47 mm, and after the nonaqueous electrolyte was injected, The above-described prismatic lithium ion secondary battery shown in FIG. 2 was assembled by airtightly bonding an aluminum lid to the opening of the can. The non-aqueous electrolyte is LiBF in a mixed solvent of γ-butyrolactone and ethylene carbonate (mixing volume ratio 2: 1). _Four Is dissolved in 1.5 mol / L.
[0064]
(Example 2)
A square lithium ion secondary battery having the same structure as that of Example 1 was assembled except that a negative electrode manufactured by the method described below was used. In addition, after preparation of the electrode body which has a positive / negative electrode and a separator, the quality determination same as Example 1 was performed, and only the electrode body determined as a non-defective product was used.
[0065]
<Production of negative electrode>
First, the fibrous mesophase low-temperature calcined carbon material (b) having 50 parts by weight of the fibrous carbon material (a) and a true density of 1.70 g / cc is added to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight. 2 parts by weight and 48 parts by weight of the spherical graphite (c) were added, followed by shear dispersion. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and uniform mixing and stirring were performed to prepare a negative electrode coating slurry.
[0066]
Next, 103 g / m each of the coating slurry was applied to both sides of a 15 μm thick copper foil (current collector) by a knife edge coater. ² It was applied to become and dried. The density of the negative electrode material on the copper foil at this time was 1.23 g / cc. Thereafter, pressing and slitting were performed to produce a strip-shaped negative electrode having a thickness of 149 μm (negative electrode material density: 1.5 g / cc) and a width of 43.25 mm.
[0067]
The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was 16 mAh / g by the same tests and calculations as in Example 1.
[0068]
(Example 3)
A square lithium ion secondary battery having the same structure as that of Example 1 was assembled except that a negative electrode manufactured by the method described below was used. In addition, after preparation of the electrode body which has a positive / negative electrode and a separator, the quality determination same as Example 1 was performed, and only the electrode body determined as a non-defective product was used.
[0069]
<Production of negative electrode>
First, the fibrous mesophase low-temperature calcined carbon material (b) having 50 parts by weight of the fibrous carbon material (a) and a true density of 1.60 g / cc is added to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight. ) 4 parts by weight and 46 parts by weight of the spherical graphite (c) were added, followed by shear dispersion. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and uniform mixing and stirring were performed to prepare a negative electrode coating slurry.
[0070]
Next, 103 g / m each of the coating slurry was applied to both sides of a 15 μm thick copper foil (current collector) by a knife edge coater. ² It was applied to become and dried. The density of the negative electrode material on the copper foil at this time was 1.23 g / cc. Thereafter, pressing and slitting were performed to produce a strip-shaped negative electrode having a thickness of 149 μm (negative electrode material density: 1.5 g / cc) and a width of 43.25 mm.
[0071]
The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was 20 mAh / g by the same tests and calculations as in Example 1.
[0072]
Example 4
A square lithium ion secondary battery having the same structure as that of Example 1 was assembled except that a negative electrode manufactured by the method described below was used. In addition, after preparation of the electrode body which has a positive / negative electrode and a separator, the quality determination same as Example 1 was performed, and only the electrode body determined as a non-defective product was used.
[0073]
<Production of negative electrode>
First, the fibrous mesophase low-temperature calcined carbon material (b) having 50 parts by weight of the fibrous carbon material (a) and a true density of 1.55 g / cc is added to 177 parts by weight of a viscous aqueous solution of 0.68% by weight of carboxymethyl cellulose. ) 4 parts by weight and 46 parts by weight of the spherical graphite (c) were added, followed by shear dispersion. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and uniform mixing and stirring were performed to prepare a negative electrode coating slurry.
[0074]
Next, 103 g / m each of the coating slurry was applied to both sides of a 15 μm thick copper foil (current collector) by a knife edge coater. ² It was applied to become and dried. The density of the negative electrode material on the copper foil at this time was 1.23 g / cc. Thereafter, pressing and slitting were performed to produce a strip-shaped negative electrode having a thickness of 149 μm (negative electrode material density: 1.5 g / cc) and a width of 43.25 mm.
[0075]
The discharge capacity between the potential of the obtained negative electrode 1 V to 3 V was determined by the same tests and calculations as in Example 1. 2 It was 5 mAh / g.
[0076]
(Example 5)
A square lithium ion secondary battery having the same structure as that of Example 1 was assembled except that a negative electrode manufactured by the method described below was used. In addition, after preparation of the electrode body which has a positive / negative electrode and a separator, the quality determination same as Example 1 was performed, and only the electrode body determined as a non-defective product was used.
[0077]
<Production of negative electrode>
First, the fibrous mesophase low-temperature calcined carbon material (b) having 50 parts by weight of the fibrous carbon material (a) and a true density of 1.70 g / cc is added to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight. ) 9 parts by weight and 41 parts by weight of the spherical graphite (c) were added, followed by shear dispersion. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and uniform mixing and stirring were performed to prepare a negative electrode coating slurry.
[0078]
Next, 103 g / m each of the coating slurry was applied to both sides of a 15 μm thick copper foil (current collector) by a knife edge coater. ² It was applied to become and dried. The density of the negative electrode material on the copper foil at this time was 1.23 g / cc. Thereafter, pressing and slitting were performed to produce a strip-shaped negative electrode having a thickness of 149 μm (negative electrode material density: 1.5 g / cc) and a width of 43.25 mm.
[0079]
The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was 30 mAh / g by the same tests and calculations as in Example 1.
[0084]
(Comparative Example 1)
A square lithium ion secondary battery having the same structure as that of Example 1 was assembled except that a negative electrode manufactured by the method described below was used. In addition, after preparation of the electrode body which has a positive / negative electrode and a separator, the quality determination same as Example 1 was performed, and only the electrode body determined as a non-defective product was used.
[0085]
<Production of negative electrode>
First, 50 parts by weight of the fibrous carbon material (a) and 50 parts by weight of the spherical graphite (c) were added to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight, followed by shear dispersion. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and uniform mixing and stirring were performed to prepare a negative electrode coating slurry.
[0086]
Next, 103 g / m each of the coating slurry was applied to both sides of a 15 μm thick copper foil (current collector) by a knife edge coater. ² It was applied to become and dried. The density of the negative electrode material on the copper foil at this time was 1.23 g / cc. Thereafter, pressing and slitting were performed to produce a strip-shaped negative electrode having a thickness of 149 μm (negative electrode material density: 1.5 g / cc) and a width of 43.25 mm.
[0087]
The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was 7 mAh / g by the same tests and calculations as in Example 1.
[0088]
(Comparative Example 2)
A square lithium ion secondary battery having the same structure as that of Example 1 was assembled except that a negative electrode manufactured by the method described below was used. In addition, after preparation of the electrode body which has a positive / negative electrode and a separator, the quality determination same as Example 1 was performed, and only the electrode body determined as a non-defective product was used.
[0089]
<Production of negative electrode>
First, the fibrous mesophase low-temperature calcined carbon material (b) having 50 parts by weight of the fibrous carbon material (a) and a true density of 1.63 g / cc is added to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight. ) 1 part by weight and 49 parts by weight of the spherical graphite (c) were added, followed by shear dispersion. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and uniform mixing and stirring were performed to prepare a negative electrode coating slurry.
[0090]
Next, 103 g / m each of the coating slurry was applied to both sides of a 15 μm thick copper foil (current collector) by a knife edge coater. ² It was applied to become and dried. The density of the negative electrode material on the copper foil at this time was 1.23 g / cc. Thereafter, pressing and slitting were performed to produce a strip-shaped negative electrode having a thickness of 149 μm (negative electrode material density: 1.5 g / cc) and a width of 43.25 mm.
[0091]
The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was 10 mAh / g by the same tests and calculations as in Example 1.
[0092]
(Comparative Example 3)
A square lithium ion secondary battery having the same structure as that of Example 1 was assembled except that a negative electrode manufactured by the method described below was used. In addition, after preparation of the electrode body which has a positive / negative electrode and a separator, the quality determination same as Example 1 was performed, and only the electrode body determined as a non-defective product was used.
[0093]
<Production of negative electrode>
First, the fibrous mesophase low-temperature calcined carbon material (b) having 50 parts by weight of the fibrous carbon material (a) and a true density of 1.55 g / cc is added to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight. ) 7 parts by weight and 43 parts by weight of the spherical graphite (c) were added, followed by shear dispersion. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and uniform mixing and stirring were performed to prepare a negative electrode coating slurry.
[0094]
Next, 103 g / m each of the coating slurry was applied to both sides of a 15 μm thick copper foil (current collector) by a knife edge coater. ² It was applied to become and dried. The density of the negative electrode material on the copper foil at this time was 1.23 g / cc. Thereafter, pressing and slitting were performed to produce a strip-shaped negative electrode having a thickness of 149 μm (negative electrode material density: 1.5 g / cc) and a width of 43.25 mm.
[0095]
The discharge capacity between the potential 1V and 3V of the obtained negative electrode was 40 mAh / g by the same test and calculation as in Example 1.
[0096]
(Comparative Example 4)
A square lithium ion secondary battery having the same structure as that of Example 1 was assembled except that a negative electrode manufactured by the method described below was used. In addition, after preparation of the electrode body which has a positive / negative electrode and a separator, the quality determination same as Example 1 was performed, and only the electrode body determined as a non-defective product was used.
[0097]
<Production of negative electrode>
First, the fibrous mesophase low-temperature calcined carbon material (b) having 50 parts by weight of the fibrous carbon material (a) and a true density of 1.70 g / cc is added to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight. ) 12 parts by weight and 38 parts by weight of the spherical graphite (c) were added, followed by shear dispersion. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and uniform mixing and stirring were performed to prepare a negative electrode coating slurry.
[0098]
Next, 103 g / m each of the coating slurry was applied to both sides of a 15 μm thick copper foil (current collector) by a knife edge coater. ² It was applied to become and dried. The density of the negative electrode material on the copper foil at this time was 1.23 g / cc. Thereafter, pressing and slitting were performed to produce a strip-shaped negative electrode having a thickness of 149 μm (negative electrode material density: 1.5 g / cc) and a width of 43.25 mm.
[0099]
The discharge capacity between the potential 1V and 3V of the obtained negative electrode was 40 mAh / g by the same test and calculation as in Example 1.
[0100]
(Comparative Example 5)
A square lithium ion secondary battery having the same structure as that of Example 1 was assembled except that a negative electrode manufactured by the method described below was used. In addition, after preparation of the electrode body which has a positive / negative electrode and a separator, the quality determination same as Example 1 was performed, and only the electrode body determined as a non-defective product was used.
[0101]
<Production of negative electrode>
First, the fibrous mesophase low-temperature calcined carbon material (b) having 50 parts by weight of the fibrous carbon material (a) and a true density of 1.52 g / cc is added to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight. ) 13 parts by weight and 37 parts by weight of the spherical graphite (c) were added, followed by shear dispersion. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and uniform mixing and stirring were performed to prepare a negative electrode coating slurry.
[0102]
Next, 103 g / m each of the coating slurry was applied to both sides of a 15 μm thick copper foil (current collector) by a knife edge coater. ² It was applied to become and dried. The density of the negative electrode material on the copper foil at this time was 1.23 g / cc. Thereafter, pressing and slitting were performed to produce a strip-shaped negative electrode having a thickness of 149 μm (negative electrode material density: 1.5 g / cc) and a width of 43.25 mm.
[0103]
The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was 70 mAh / g by the same tests and calculations as in Example 1.
[0104]
The obtained secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 5 were initially charged at 25 ° C. with 700 mA, 4.2 V, 6 h, subjected to aging for 12 hours, and then subjected to aging at 700 ° C. at 25 ° C. The average capacity when discharged with a 3.0 V cutoff was measured.
[0105]
After the completion of the initial charge, each secondary battery is transferred to an atmosphere of 60 ° C., subjected to aging for 12 hours, and then charged at 700 mA, 4.2 V, 6 h, and at a cutoff of 700 mA, 3.0 V at the same temperature. The discharge capacity retention ratio (cycle characteristics) with respect to the initial discharge capacity when the discharge was repeated 100 times was measured.
[0106]
These results are shown in Table 1 below. Table 1 also shows the discharge capacity between the negative electrode potentials 1 V to 3 V incorporated in the secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 5.
[0107]
[Table 1]

[0108]
As is clear from Table 1, Examples 1 to 5 having a negative electrode having a capacity of 15 to 30 mAh / g as a capacity at the time of deep discharge further from 3 V to 1 V after 3 V cut discharge. 5 It can be seen that the secondary battery of the present invention is superior in charge / discharge cycle characteristics at high temperatures as compared with the secondary batteries of Comparative Examples 1 to 5 in which the capacity of the negative electrode is outside the range of 15 to 30 mAh / g.
[0109]
In the above-described embodiment, the prismatic lithium ion secondary battery shown in FIG. 2 has been described. However, the present invention relates to the cylindrical lithium ion secondary battery shown in FIG. 1 and the thin lithium ion secondary battery shown in FIGS. Even when applied to a battery, it has the same excellent high-temperature charge / discharge cycle characteristics.
[0110]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having improved high-temperature charge / discharge cycle characteristics by improving the negative electrode.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing a cylindrical non-aqueous electrolyte secondary battery (cylindrical lithium ion secondary battery) which is an embodiment of a non-aqueous electrolyte secondary battery according to the present invention.
FIG. 2 is a partially cutaway perspective view showing a prismatic nonaqueous electrolyte secondary battery (a prismatic lithium ion secondary battery) which is another form of the nonaqueous electrolyte secondary battery according to the present invention.
FIG. 3 is a perspective view showing a thin non-aqueous electrolyte secondary battery (thin lithium ion secondary battery) which is still another embodiment of the non-aqueous electrolyte secondary battery according to the present invention.
4 is a cross-sectional view taken along line IV-IV in FIG.
[Explanation of symbols]
1,21 ... Exterior can,
3,23 electrode bodies,
4, 24, 48 ... negative electrode,
5, 25, 45 ... separator,
6, 26, 44 ... positive electrode,
12 ... sealing plate,
28 ... the lid,
41 ... Power generation element,
43, 46 ... current collector,
51 ... Exterior film.

Claims (8)

Equipped with a positive electrode capable of inserting and extracting lithium, a negative electrode capable of inserting and extracting lithium, a separator and a non-aqueous electrolyte solution,
The positive electrode and the negative electrode have a structure in which a positive electrode material and a negative electrode material are applied to a current collector, respectively.
The negative electrode material contains a carbonaceous material including fibrous carbon materials (a) and (b) and a non-fibrous carbon material (c), and the fibrous carbon material (b) is mesophase low-temperature calcined carbon. And the said negative electrode has 15-30 mAh / g as discharge capacity between negative electrode potentials 1V-3V, The non-aqueous electrolyte secondary battery characterized by the above-mentioned.   The non-aqueous electrolyte secondary solution according to claim 1, wherein the fibrous carbon material (a) has an average fiber diameter of 8 to 18 µm, an average fiber length of 10 to 50 µm, and a true density of 2.24 g / cc or more. battery.   The fibrous carbon material (b) is mesophase low-temperature calcined carbon having an average fiber diameter of 8 to 20 µm, an average fiber length of 8 to 20 µm, and a true density of 1.50 to 1.75 g / cc. The non-aqueous electrolyte secondary battery described. The non-fiber-based carbon material (c) is a non-aqueous electrolyte secondary battery according to claim 1, characterized in that the graphite scales flake or spherical mass.   The non-aqueous electrolyte secondary battery according to claim 3, wherein the fibrous carbon material (b) is blended in an amount of 1 to 10% by weight with respect to the carbonaceous material.   The non-aqueous electrolyte secondary battery according to claim 3, wherein the fibrous carbon material (b) is blended in an amount of 2 to 9% by weight with respect to the carbonaceous material.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte contains γ-butyrolactone as a non-aqueous solvent.   The non-aqueous electrolyte secondary battery according to claim 7, wherein the γ-butyrolactone accounts for 45 to 70% by weight in the non-aqueous solvent.

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