KR20140085337A - Lithium secondary battery - Google Patents

Abstract

The present invention provides a lithium secondary battery with excellent stability under extremely-high temperatures. Between a positive electrode including a positive pole lead and a negative electrode including a negative pole lead, a separator is placed. The positive pole lead and the negative pole lead are overlapped to protrude in the same direction and are wound in a vortex shape to form a planar wound electrode. Nonaqueous electrolyte is sealed in a battery case which has a hollow pillar shape and a thickness equal to or greater than 40 mm. The separator includes a porous layer (I) mainly made of thermoplastic resin and a porous layer (II) mainly made of filler having a heat-resisting temperature equal to or higher than 150°C. The thickness of the porous layer (II) is equal to or smaller than 8 μm. In the planar wound electrode, a cross section from which the positive electrode and the negative electrode protrude and two lateral surfaces which face each other and are wider than other surfaces are fixed by a tape containing a resin which is not melted at the temperature which is equal to or smaller than a shutdown temperature.

Description

LITHIUM SECONDARY BATTERY [0002]

The present invention relates to a lithium secondary battery excellent in safety.

2. Description of the Related Art Recently, with the development of portable electronic devices such as cellular phones and notebook computers, and the practical use of electric vehicles, higher performance and higher stability of secondary batteries and capacitors used as these power sources are further demanded. Particularly, lithium secondary batteries are attracting attention as high-energy-density batteries, and various improvements have been made as suitable power sources for the above-mentioned devices.

Particularly, the lithium secondary battery used in smart phones and tablets, which have remarkable performance evolutions, has a larger screen size than that of a mobile phone and a larger battery size, thereby realizing a high capacity. Such a lithium secondary battery is formed by laminating a positive electrode and a negative electrode having a lead body with a separator interposed in a closed space composed of a battery can made of aluminum or an alloy thereof and a lid disposed at an opening end of the battery can A wound electrode body (wound electrode body), and a non-aqueous electrolyte.

In the lithium secondary battery, improvement in reliability and safety has also been demanded in response to the demand for higher capacity. For example, in Patent Document 1, in order to improve the durability against impact such as dropping in a lithium secondary battery and reliability in repetition of charging and discharging, a specific portion of the wound and rolled electrode body is fixed with a tape Technology is disclosed.

With regard to the safety of the lithium secondary battery, there have been proposed various techniques for avoiding the problem that the separator contracts and the positive electrode and the negative electrode come into direct contact with each other due to an excessively high temperature of the battery, for example.

For example, in Patent Document 2, an insulating member having a heat resistance higher than that of the separator is disposed at a portion of the battery can which is in contact with the battery can due to a rise in the temperature of the battery can, in order to suppress shrinkage of the separator Technology is disclosed. Patent Document 3 discloses a technique for integrally joining portions of the separators constituting the wound electrode body which protrude from the respective electrodes of the wound electrode body.

Patent Document 4 discloses a separator comprising a first separator layer containing a thermoplastic resin or the like for securing a shutdown function and a second separator layer containing a heat resistant filler so as to have a high heat resistance and to suppress heat shrinkage of the entire separator And a separator is constituted by a second separator layer.

Japanese Patent Application Laid-Open No. 2007-172975 Japanese Patent Application Laid-Open No. 2000-251866 Japanese Patent Application Laid-Open No. 2004-327362 International Publication No. 2007/066768

For example, in the case of the separator described in Patent Document 4, the safety and reliability of the lithium secondary battery can be satisfactorily increased.

However, lithium secondary batteries are required to have a higher capacity than the conventional ones. For example, if the separator is made thinner and the positive electrode and the negative electrode are thickened to increase the capacity of the active material of the positive electrode introduced into the battery, The heat resistance of the separator becomes insufficient, and the safety at an excessive high temperature may be lowered. Such a decrease in safety is worried as the size of the battery case becomes larger.

For this reason, even if the capacity of the lithium secondary battery is increased by the above-described method, it is required to develop a technique capable of ensuring good safety.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a lithium secondary battery excellent in safety at an extremely high temperature.

A lithium secondary battery according to the present invention which can achieve the above object is characterized in that a positive electrode having a positive electrode lead body and a negative electrode having a negative electrode lead body are interposed with a separator interposed therebetween so that the positive electrode lead body and the negative electrode lead body protrude in the same direction And a non-aqueous electrolyte solution is sealed in a hollow cylindrical battery case, characterized in that the separator comprises a porous layer (I) made mainly of a thermoplastic resin, And a porous layer (II) containing as a main component a filler having a heat-resistant temperature of not lower than 150 ° C .; the thickness of the porous layer (II) is 8 μm or less; And two side surfaces opposite to each other and wider than the other side are provided on both sides of the end surface on which the negative electrode lead body protrudes, It is fixed with a tape having a base material (基材) containing a resin that does not melt at a temperature below the operating temperature, and is characterized in that at least the width of the battery case 40㎜.

In the present specification, " heat-resistant temperature of 150 DEG C or higher " means that no deformation such as softening is observed at 150 DEG C or more.

According to the present invention, it is possible to provide a lithium secondary battery excellent in safety at an extremely high temperature.

1 is a perspective view schematically showing an example of a flat-shaped wound electrode body related to a lithium secondary battery of the present invention.
2 is a perspective view schematically showing another example of a flat-shaped wound electrode body related to the lithium secondary battery of the present invention.
3 is a perspective view schematically showing another example of a flat-shaped wound electrode body related to the lithium secondary battery of the present invention.
4 is a perspective view schematically showing an example of a lithium secondary battery of the present invention.
5 is a partial vertical cross-sectional view schematically showing an example of a lithium secondary battery of the present invention.

In the lithium secondary battery of the present invention, a porous layer (I) comprising a thermoplastic resin as a main component and a porous layer (II) containing a filler having a heat-resistant temperature of 150 ° C or higher as a main component are laminated on a separator interposed between a positive electrode and a negative electrode Separators are used.

When the lithium secondary battery reaches the melting point or more of the thermoplastic resin which is the main component of the porous layer (I), the porous layer (I) related to the separator is a porous layer The associated thermoplastic resin melts and blocks the pores of the separator, thereby causing shutdown which suppresses the progress of the electrochemical reaction.

The porous layer (II) related to the separator has a function of preventing a short circuit due to direct contact between the positive electrode and the negative electrode even when the internal temperature of the lithium secondary battery rises. By the filler having a heat- And the function is secured. That is, when the battery is heated to a high temperature, even if the porous layer (I) is shrunk, a short circuit due to direct contact of the positive electrode, which may occur when the separator is thermally shrunk by the porous layer (II) . In addition, since the porous layer (II) having excellent heat resistance functions as a skeleton of the separator, the heat shrinkage of the porous layer (I), that is, the heat shrinkage itself of the whole separator can be suppressed.

Further, in the separator according to the present invention, for example, in order to increase the capacity of the lithium secondary battery, the thickness of the porous layer (II) is made as thin as 8 mu m or less to suppress the increase in the thickness of the whole separator. Compared to a separator made of a polyolefin microporous membrane used in a battery, excellent heat resistance can be secured.

The positive electrode having the positive electrode lead body and the negative electrode having the negative electrode lead body overlap each other with the separator interposed therebetween so that the positive electrode lead body and the negative electrode lead body protrude in the same direction, (Analysis) of the internal heat distribution when the lithium ion secondary battery is held at a high temperature state, it has been found that regions which become higher in temperature are distributed around the positive electrode lead body and the negative electrode lead body.

In the case of using a separator in which the porous layer (II) responsible for heat resistance is thinned, in a portion disposed in the vicinity of the lead body of the positive electrode, which becomes particularly high temperature, The suppressing action becomes insufficient and it is found that there is a possibility that the positive electrode and the negative electrode are brought into contact with each other.

As described above, there is a demand for enlargement of the lithium secondary battery. Particularly, when the width of the battery case is 40 mm or more, as compared with a battery having a smaller battery case width, In this case, however, even if the heat shrinkage ratio of the separator is the same, the area of the region where shrinkage occurs, that is, the shrinkage amount increases, so that the problem of the contact between the positive electrode and the negative electrode becomes more likely to occur.

Fig. 1 is a perspective view schematically showing an example of a flat-shaped wound electrode body related to the lithium secondary battery of the present invention. The wound electrode body 30 shown in Fig. 1 has an end face 302 on which the positive electrode lead body 51 and the negative electrode lead body 52 protrude and two side faces 301 and 301 opposite to each other and wider than other faces (The side surface on the front surface side and the side surface on the rear surface side in the figure) are fixed with the tape 60. [

As shown in Fig. 1, in the lithium secondary battery of the present invention, the cross-section where the positive electrode lead body and the negative electrode lead body protrude from the flat-rolled electrode body and the two side faces opposite to each other, , And fastened with tape. The tape is made of a resin that does not melt at a temperature lower than the shutdown temperature of the lithium secondary battery.

In the flat-shaped wound electrode body, a separator is disposed so as to protrude from the positive electrode and the negative electrode in order to prevent contact between the positive electrode and the negative electrode in the end surface (upper and lower surfaces shown in Fig. 1). Since the positive electrode lead body and the negative electrode lead body exist, the cross section of the flat-rolled electrode body, in which heat shrinkage of the separator is likely to occur, and the two wider side faces are fixed by a tape having high heat resistance, It is possible to highly suppress the heat shrinkage of the separator in such a region even if the temperature in the battery excessively increases.

In the lithium secondary battery of the present invention, by employing the above-described configuration, even when the structure can be made to have a higher capacity as described above, high safety under high temperature can be ensured.

The shutdown temperature of the lithium secondary battery referred to in the present specification is a value measured by the method employed in the embodiment described later.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail, but these are only examples of embodiments of the present invention, and the present invention is not limited to these embodiments.

<Separator>

As described above, the separator according to the present invention has a porous layer (I) mainly composed of a thermoplastic resin and a porous layer (II) comprising a filler having a heat-resistant temperature of 150 ° C or higher as a main component.

As the thermoplastic resin to be the main component of the porous layer (I), a resin having a melting point, that is, a melting temperature measured using a differential scanning calorimeter (DSC) of 140 DEG C or less is preferable in accordance with JIS K 7121, , For example, polyethylene (PE). Examples of the form of the porous layer (I) include a sheet made of a microporous film commonly used as a separator for a lithium secondary battery, a sheet material obtained by applying a dispersion containing particles of PE to a base material such as a nonwoven fabric, . Further, a microporous membrane of a multi-layer (two-layer, three-layer, etc.) structure having a layer composed of PE and a layer composed of polypropylene (PP) may be used as the porous layer (I).

The total volume of the constituent components of the porous layer (I) (total volume excluding the void portion. The volume ratio of the thermoplastic resin as the main body in the porous layer (I) and the porous layer (II) related to the separator is the same hereinafter) is at least 50 vol% and not less than 70 vol% Is more preferable. Further, for example, when the porous layer (I) is formed of the microporous membrane of the PE, the volume content of the thermoplastic resin becomes 100 volume%.

The filler relating to the porous layer (II) is preferably a filler having a heat-resistant temperature of not less than 150 DEG C, which is stable to a non-aqueous electrolyte contained in the battery and is electrochemically stable, But it is preferably fine particles from the viewpoint of dispersion and the like, and inorganic oxide particles, more specifically, alumina, silica and boehmite are preferable. Since alumina, silica and boehmite have high oxidation resistance and can adjust the particle size and shape to a desired value, it is easy to control the porosity of the porous layer (II) with good precision. As the filler having a heat-resistant temperature of 150 ° C or higher, for example, the above-mentioned fillers may be used singly or two or more thereof may be used in combination.

The shape of the filler having a heat-resistant temperature of not less than 150 DEG C with respect to the porous layer (II) is not particularly limited and includes a substantially spherical shape (including a perfect spherical shape), a substantially ellipsoidal shape (including an ellipsoidal shape) Shape or the like can be used.

The average particle diameter of the filler having a heat-resistant temperature of 150 DEG C or more related to the porous layer (II) is preferably 0.3 mu m or more, more preferably 0.5 mu m or more because the permeability of the ion decreases when too small. If the filler having a heat-resistant temperature of 150 DEG C or higher is too large, the electrical characteristics tend to be deteriorated. Therefore, the average particle diameter is preferably 5 mu m or less, more preferably 2 mu m or less.

The average particle diameter of various particles (fillers having a heat-resistant temperature of 150 ° C or higher and a lithium-containing complex oxide, etc.) referred to in the present specification can be measured by a laser scattering particle size distribution meter (for example, -920 &quot; manufactured by Mitsubishi Chemical Corporation), the average particle diameter D _{50 %} measured by dispersing these particles in a medium which does not dissolve the particles.

Since the filler having a heat-resistant temperature of 150 ° C or higher is included as a main component in the porous layer (II), the total volume of the constituent components of the porous layer (II) . (Hereinafter the same shall apply to the total volume of the constituent components of the porous layer (II) and the porous layer (I)) is preferably 50 vol% or more and preferably 70 vol% or more, more preferably 80 vol% , More preferably 90 vol% or more. By setting the filler in the porous layer (II) to have a high content as described above, the heat shrinkage of the entire separator can be well suppressed even when the lithium secondary battery is heated to a high temperature, and a short circuit due to direct contact between the positive electrode and the negative electrode Can be suppressed more favorably.

As described later, since it is preferable to include an organic binder in the porous layer (II), the volume content of the filler having a heat-resistant temperature of 150 DEG C or higher in the entire volume of the constituent components of the porous layer (II) Preferably not more than 99.5% by volume.

It is preferable that an organic binder is contained in the porous layer (II) because the pellets having a heat resistance temperature of 150 DEG C or higher are bound together or the porous layer (II) and the porous layer (I) are integrated. Examples of the organic binder include ethylene-acrylic acid copolymer such as ethylene-vinyl acetate copolymer (EVA, 20 to 35 mol% of structural unit derived from vinyl acetate) and ethylene-ethyl acrylate copolymer, fluoric rubber, SBR, CMC , Hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), crosslinked acrylic resin, polyurethane, epoxy resin, A heat-resistant binder having a heat-resistant temperature of 150 DEG C or more is preferably used. As the organic binder, those illustrated above may be used singly or two or more of them may be used in combination.

Of the organic binders exemplified above, a highly flexible binder such as EVA, an ethylene-acrylic acid copolymer, a fluorine-based rubber, or SBR is preferable. Specific examples of such highly flexible organic binders include "EVA Flex Series (EVA)" of Mitsui DuPont Polychemical, EVA of Nippon Unicar Co., "EVA Flex-EEE series (ethylene-acrylic acid copolymer)" of Mitsui DuPont Polychemical Co., EIDE of Nippon Unicar Co., Ltd., "DaiL latex series (fluorine rubber)" of Daikin Industries, "TRD-2001 (SBR)" of JSR and "BM-400B (SBR)" of Nippon Zeon.

When the organic binder is used for the porous layer (II), it may be used in the form of an emulsion dissolved or dispersed in a solvent of a composition for forming a porous layer (II) described below.

The separator can be obtained by forming a composition (a liquid composition such as a slurry) for forming a porous layer (II) containing a filler or the like having a heat-resistant temperature of 150 ° C or higher in a sheet such as a microporous membrane for constituting the porous layer And then drying the solution at a predetermined temperature to form the porous layer (II).

The composition for forming the porous layer (II) contains a filler having a heat-resistant temperature of 150 ° C or higher, an organic binder as required, and the like, and these are dispersed in a solvent (including a dispersion medium; The organic binder may be dissolved in a solvent. The solvent used in the composition for forming the porous layer (II) is not particularly limited as long as it can uniformly disperse the filler having a heat-resistant temperature of 150 ° C or higher and can uniformly dissolve or disperse the organic binder. For example, Aromatic hydrocarbons, furans such as tetrahydrofuran, ketones such as methyl ethyl ketone and methyl isobutyl ketone, and the like, are suitably used. To these solvents, an alcohol (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added for the purpose of controlling the interfacial tension. In the case where the organic binder is water-soluble and used as an emulsion, water may be used as a solvent, and at this time, alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol or the like) Control.

The composition for forming the porous layer (II) preferably has a solid content of, for example, 10 to 80 mass% including a filler having a heat-resistant temperature of 150 캜 or higher and an organic binder.

In the separator, the porous layer (I) and the porous layer (II) need not be one layer each, and a plurality of layers may be contained in the separator. For example, the porous layer (I) may be disposed on both surfaces of the porous layer (II), or the porous layer (II) may be disposed on both surfaces of the porous layer (I). However, increasing the number of layers may increase the thickness of the separator to increase the internal resistance of the battery or lower the energy density. Therefore, it is not preferable to make the number of layers excessively large. In this case, (II) is preferably 5 layers or less, and particularly preferably 2 layers.

The thicker porous layer (II) in the separator improves the heat resistance of the separator, but if it is excessively thick, the entire separator becomes thick, which is disadvantageous for the purpose of, for example, increasing the capacity of the lithium secondary battery. Therefore, when the thickness of the porous layer (II) (in the case where the separator has a plurality of porous layers (II)), The same shall apply hereinafter) is 8 탆 or less, more preferably 6 탆 or less. However, if the porous layer (II) is too thin, the effect of improving the heat resistance of the separator due to the formation of the porous layer (II) may be reduced. Therefore, the thickness of the porous layer (II) is preferably 0.5 占 퐉 or more, more preferably 2 占 퐉 or more.

The thickness of the porous layer (I) in the separator (when the separator has a plurality of porous layers (I), the total thickness thereof). The same shall apply hereinafter) is preferably 5 占 퐉 or more, and more preferably 10 占 퐉 or more from the viewpoint of more effectively exhibiting the action (in particular, the shutdown action) by use of the porous layer (I). However, if the porous layer (I) is too thick, the thickness of the porous layer (II) may be limited as described above, and the effect of suppressing the increase in the thickness of the entire separator may be reduced. The heat shrinking force is increased, and the action of suppressing the heat shrinkage of the whole separator may be reduced. Therefore, the thickness of the porous layer (I) is preferably 20 占 퐉 or less, more preferably 16 占 퐉 or less.

The total thickness of the separator is preferably 28 占 퐉 or less and more preferably 21 占 퐉 or less from the viewpoint of securing the effect of restricting the thickness of the porous layer (II) as described above. However, if the separator is too thin, the strength may be insufficient. Therefore, the total thickness of the separator is preferably 10 mu m or more.

The porosity of the whole separator is preferably 30% or more in a dried state in order to ensure a sufficient liquid permeability of the nonaqueous electrolytic solution and good ion permeability. On the other hand, from the viewpoint of ensuring the strength of the separator and prevention of the internal short circuit, the porosity of the separator is preferably 70% or less in a dry state. The porosity P (%) of the separator can be calculated from the thickness of the separator, the mass per unit area, and the density of the constituent components by calculating the total for each component i using the following formula (1).

P = {1- (m / t) / (? _{I i} ? _I )} 100 (1)

Here, In the above formula, a _i: ratio of component i when the total mass of a 1, ρ _i: density (g / ㎤) of component i, m: mass of per unit area of the separator unit (g / ㎠), t is the thickness (cm) of the separator.

Further, in the above equation (1), for m a mass (g / ㎠) per unit surface area of the porous layer (Ⅰ) and, and a t a thickness (㎝) of the porous layer (Ⅰ), a _i a porous layer (%) Of the porous layer (I) can be obtained by using the ratio of the component i when the total mass of the porous layer (I) is taken as 1. The porosity of the porous layer (I) obtained by this method is preferably 30 to 70%.

In the above equation (1), for m a mass (g / ㎠) per unit surface area of the porous layer (Ⅱ) and, and a t a thickness (㎝) of the porous layer (Ⅱ), a _i a porous layer (%) Of the porous layer (II) can be obtained by using the ratio of the component i when the total mass of the porous layer (II) is 1, by using the above formula (1). The porosity of the porous layer (II) obtained by this method is preferably 20 to 60%.

As the separator, it is preferable that the mechanical strength is high, and for example, the penetration strength is preferably 3N or more. For example, when SiO _x having a large change in volume accompanying charge and discharge is used for the negative electrode active material (to be described later in detail), repeated charging and discharging causes mechanical damage to the separator facing to the negative electrode Respectively. When the penetration strength of the separator is 3N or more, good mechanical strength is secured, and the mechanical damage to the separator can be mitigated. By setting the separator as described above, the striking intensity can be set to the above value.

The sting intensity can be measured by the following method. A separator was fixed on a plate with a hole of 2 inches in diameter so that there was no wrinkle or warpage and a semicircular metal pin having a tip diameter of 1.0 mm was dropped to a measurement sample at a rate of 120 mm / , And the force at the time of puncturing the separator is measured five times. Then, an average value is obtained for three measurements excluding the maximum value and the minimum value among the five measured values, and this is taken as the stamper strength of the separator.

<Positive Electrode>

As the positive electrode relating to the lithium secondary battery of the present invention, for example, a positive electrode material mixture layer containing a positive electrode active material, a binder, a conductive auxiliary agent, and the like may be used in one side or both sides of the current collector.

&Lt; Positive electrode active material &

As the positive electrode active material related to the lithium secondary battery of the present invention, for example, a lithium-containing complex oxide containing lithium (Li) and a transition metal is used.

Specific examples of the lithium-containing complex oxide containing Li and a transition metal include lithium cobalt oxides such as LiCoO ₂ ; Lithium manganese oxides such as LiMnO ₂ and Li ₂ MnO ₃ ; Lithium nickel oxide such as LiNiO ₂ ; _{LiMn 2 O 4, Li 4/} 3 Ti 5/3 O 4 , such as a spinel (spinel) lithium-containing complex oxide of the structure; A lithium-containing complex oxide having an olivine structure such as LiFePO ₄ ; An oxide in which the oxide is substituted with various elements in a basic composition; And the like.

Further, the positive electrode active material is a lithium-containing complex oxide in which at least a part of the lithium-containing complex oxide containing lithium and a transition metal contains Ni as a transition metal, and the total moles of Ni in the entire positive electrode active material The ratio is preferably not less than 0.05 and not more than 1.0.

The lithium-containing complex oxide containing Ni as a transition metal contains at least Ni as a transition metal element constituting the composite oxide, and is at least one element selected from the group consisting of Co, Mn, titanium (Ti), chromium (Cr) For example, boron (B), phosphorus (P), boron (B) or the like may be contained as other constituent elements such as copper (Cu), silver (Ag), thallium (Ta), niobium (Nb), zirconium And elements other than transition metal elements such as zinc (Zn), aluminum (Al), calcium (Ca), strontium (Sr), barium (Ba), germanium (Ge), tin (Sn), and magnesium .

The lithium-containing complex oxide containing Ni as the transition metal is advantageous for increasing the capacity of the lithium secondary battery because the capacity at about 3 to 4.4 V (relative to Li) is larger than that of other lithium-containing complex oxides such as LiCoO ₂ . Therefore, from the viewpoint of increasing the capacity of the lithium secondary battery, it is preferable that the ratio of the total moles of Ni to the total amount of Li in the whole positive electrode active material is 0.05 or more.

On the other hand, however, the lithium-containing complex oxide containing Ni as a transition metal has a high reactivity with the non-aqueous electrolyte. Therefore, when a lithium secondary battery using a lithium-containing complex oxide containing Ni as a transition metal as a positive electrode active material is placed under an excessively high temperature in a charged state, etc., there is a possibility that thermal runaway, . Particularly, in a lithium secondary battery using a lithium-containing composite oxide containing Ni as a transition metal as a positive electrode active material, it is desired to further increase the capacity of the battery by using an end-of-charge voltage higher than that of a battery using LiCoO ₂ However, in a state where the battery is charged with a higher voltage, the risk of thermal runaway or the like is further increased. In the lithium secondary battery of the present invention, in addition to the use of the separator having the porous layer (I) and the porous layer (II), since a specific portion of the wound electrode body is fixed with a specific tape, It is possible to secure high safety.

The lithium secondary battery of the present invention can be applied to a use after being subjected to a constant current-constant voltage charging with the termination voltage of about 4.2 V, for example, as in the case of a conventional lithium secondary battery using LiCoO ₂ as a positive electrode active material , And when a lithium-containing complex oxide containing Ni as a transition metal is used for the positive electrode active material, it is more preferable to apply it to applications in which the constant-current-constant voltage charging exceeding 4.30 V is carried out after the end voltage is further increased And even when placed in an excessively high temperature environment in a charged state under such conditions, the safety is good.

The lithium-containing complex oxide containing Ni as a transition metal has high thermal stability and stability in a high potential state and can further enhance the safety and various battery characteristics of the lithium secondary battery. Therefore, the lithium-containing complex oxide represented by the following general formula (2) It is preferable to use a lithium-containing complex oxide.

Li _{1 + y} MO ₂ (2)

[In the general formula (2), -0.15? Y? 0.15, and M represents at least three or more element groups including Ni, Co and Mn, and among the elements constituting M, Ni, Co, B? 35, 5? C? 35 and 10? B + c? 70, respectively, when the ratio (mol%) of Mn is a, b and c, respectively.

The element group M in the general formula (2) representing the lithium-containing complex oxide may contain only Ni, Co, and Mn, and may contain elements other than Ni, Co, and Mn such as Ti, Cr, But may contain elements such as Fe, Cu, Zn, Al, Ge, Sn, Mg, Ag, Ta, Nb, B, P, Zr, Ca, However, in order to sufficiently obtain the above effect by containing Ni, Co, and Mn in the lithium-containing complex oxide, Ni, Co, and Mn The total proportion (mol%) of the other elements is preferably 15 mol% or less, more preferably 3 mol% or less.

The lithium-containing complex oxide having the above composition has a true density of 4.55 to 4.95 g / cm 3 and becomes a material having a high volume energy density. Incidentally, although the true density of the lithium-containing complex oxide containing Mn in a certain range largely varies depending on its composition, since the structure can be stabilized and the uniformity can be improved in the above narrow composition range, for example, LiCoO ₂ &lt; / RTI &gt; Further, the capacity per mass of the lithium-containing complex oxide can be increased, and a material excellent in reversibility can be obtained.

Further, in adjusting the molar ratio of the total amount of Ni to the total amount of Li in the positive electrode active material in the positive electrode active material to 0.05 or more and 1.0 or less, only the lithium-containing complex oxide containing Ni may be used as the transition metal, (Lithium cobalt oxide such as LiCoO ₂ described above; lithium manganese oxide such as LiMnO ₂ and Li ₂ MnO ₃ ; LiMn ₂ O ₄ , Li ₄ (Li ₂ O ₄₎ , etc.) as a transition metal together with a lithium- _{/ 3} Ti _5/3 O ₄ , a lithium-containing complex oxide having an olivine structure such as LiFePO _4, and an oxide in which the above-described oxide is used as a basic composition and substituted with various elements) do. In this case, one or two or more lithium-containing complex oxides containing Ni as a transition metal may be used in combination with one or more of other lithium-containing oxides.

The average particle diameter of the lithium-containing complex oxide used in the present invention is preferably 5 占 퐉 or more, more preferably 10 占 퐉 or more, further preferably 25 占 퐉 or less and further preferably 20 占 퐉 or less. These lithium-containing complex oxide particles may be secondary aggregates in which primary particles are aggregated, and the average particle diameter in this case means the average particle diameter of the secondary aggregate.

In addition, the lithium-containing complex oxide used in the present invention has a specific surface area by the BET method, for example, for securing the reactivity with lithium ions and suppressing a side reaction with the non-aqueous electrolyte. Is preferably 0.1 to 0.4 m &lt; 2 &gt; / g. The specific surface area of the lithium-containing complex oxide measured by the BET method can be measured using a specific surface area measurement apparatus ("Macsorb HM modele-1201" manufactured by Mountech Co.) by a nitrogen adsorption method.

The content ratio of the positive electrode active material in the positive electrode material mixture layer (the total content of all the positive electrode active materials) is preferably 60 to 95 mass%.

&Lt; Conductive auxiliary agent for positive electrode mixture layer >

The conductive auxiliary for the positive electrode material mixture layer related to the positive electrode of the lithium secondary battery of the present invention may be any one that is chemically stable in the lithium secondary battery. For example, graphite such as natural graphite (flake graphite and the like) and artificial graphite; Carbon black such as acetylene black, Ketjen black (trade name), channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as aluminum powder; Carbon fluoride; zinc oxide; Conductive whiskers composed of potassium titanate and the like; Conductive metal oxides such as titanium oxide; Organic conductive materials such as polyphenylene derivatives; These may be used singly or in combination of two or more kinds. Of these, graphite having high conductivity and carbon black having excellent liquid-absorbing properties are preferable. As the form of the conductive auxiliary agent, not only primary particles but also aggregates such as secondary aggregates and chain structures can be used. Such aggregates are easier to handle and improve productivity.

The content of the conductive auxiliary agent in the positive electrode material mixture layer is preferably 3 to 20% by mass.

&Lt; Binder of Positive Mixant Layer >

The binder of the positive electrode material mixture layer related to the positive electrode of the lithium secondary battery of the present invention can be used either as a thermoplastic resin or a thermosetting resin as long as it is chemically stable in the lithium secondary battery. More specifically, a vinylidene fluoride-based polymer (VDF-based polymer) in which a main component monomer is vinylidene fluoride (VDF) such as polyethylene, polypropylene, and polyvinylidene fluoride (PVDF) (TFE-VDF), tetrafluoroethylene-hexafluoroethylene (PTFE), polyhexafluoropropylene (PHFP), styrene butadiene rubber, tetrafluoroethylene- Tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotri Ethylene-chlorotrifluoroethylene copolymer (ECTFE), or ethylene-acrylic acid copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE) -Methacrylic acid copolymer, an ethylene-methyl acrylate copolymer, an ethylene-methyl methacrylate copolymer, and a Na ion crosslinked product of these copolymers. Of these, only one type may be used, Or may be used in combination.

Among these binders, P (TFE-VDF) and VDF-based polymers other than P (TFE-VDF) are preferably used in combination.

VDF polymer including PVDF is relatively widely used as a binder for a positive electrode mixture layer of a lithium secondary battery. However, in a positive electrode using a lithium-containing complex oxide containing Ni as a transition metal in a positive electrode active material, a VDF polymer is used for a binder A crosslinking reaction of the VDF polymer tends to occur, and the adhesion between the positive electrode material mixture layer and the current collector becomes excessively large. When such a positive electrode is used to form a wound electrode body together with a negative electrode or a separator, defects such as cracks are liable to occur particularly in the positive electrode material mixture layer on the inner peripheral side. However, when P (TFE-VDF) is used as a binder of the positive electrode material mixture layer together with the VDF-based polymer, adhesion between the positive electrode material mixture layer and the current collector can be appropriately suppressed by the action of P (TFE-VDF) The occurrence of defects in the positive electrode material mixture layer can be satisfactorily suppressed.

The content ratio of the binder in the positive electrode material mixture layer (the total content of all the binders when a plurality of kinds of binders are used, the same shall apply hereinafter with respect to the content of the binder in the positive electrode material mixture layer) The adhesion of the current collector becomes excessively high, and the above-described problems may easily occur. Therefore, the content is preferably 4% by mass or less, more preferably 3% by mass or less.

On the other hand, from the viewpoint of improving the capacity of the positive electrode, it is preferable to reduce the amount of the binder in the positive electrode material mixture layer to increase the content of the positive electrode active material. However, if the amount of the binder in the positive electrode material mixture layer is too small, , The shape (especially the shape on the outer peripheral side) of the wound electrode body using the positive electrode is deteriorated, and the productivity of the lithium secondary battery may be deteriorated. Therefore, the content of the binder in the positive electrode material mixture layer is preferably 1% by mass or more, and more preferably 1.4% by mass or more.

When P (TFE-VDF) and VDF-based polymer are used in combination as a binder of the positive-electrode mixture layer, the ratio of P (TFE-VDF) is set to 10% by mass or more when the total amount is 100% , More preferably not less than 20% by mass. Accordingly, even when the positive electrode material mixture layer containing the lithium-containing complex oxide containing Ni as the transition metal and the VDF-based polymer is used, the adhesion with the current collector can be appropriately suppressed.

However, if the amount of P (TFE-VDF) in the total of P (TFE-VDF) and VDF polymer is excessively large, the adhesion strength between the positive electrode material mixture layer and the current collector is decreased to increase battery resistance, Which may cause a decrease in load characteristics. Therefore, when the total amount of P (TFE-VDF) and VDF-based polymer in the positive electrode material mixture layer is 100 mass%, the ratio of P (TFE-VDF) is preferably 30 mass% or less.

&Lt; Positive Mixed Compound Layer, Current Collector, etc. &

The positive electrode is prepared by preparing a composition containing a positive electrode mixture in paste or slurry state in which the above-mentioned positive electrode active material, binder and conductive auxiliary agent are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) , And the binder may be dissolved in a solvent), and the resulting product is applied to one side or both sides of the current collector, followed by drying and then calendering if necessary. However, the method for producing the positive electrode is not limited to the above method, and may be produced by another manufacturing method.

Further, it is preferable that the thickness of the positive electrode material mixture layer after calendering is 15 to 200 占 퐉 per one surface of the current collector. Further, after the calendering treatment, the density of the positive electrode material mixture layer is preferably 3.2 g / cm 3 or more, more preferably 3.6 g / cm 3 or more. By forming the positive electrode having such a high-density positive electrode material mixture layer, the capacity of the lithium secondary battery can be further improved. However, if the density of the positive electrode material mixture layer is excessively large, the porosity of the positive electrode material mixture layer after the calendering treatment is preferably 4.2 g / cm 3 or less since the porosity becomes small and the permeability of the nonaqueous electrolyte solution may be lowered. The calendering can be performed by, for example, line pressure of about 1 to 30 kN / cm, and by such a treatment, the positive electrode material mixture layer having the above density can be obtained.

In this specification, the density of the positive electrode material mixture layer is a value measured by the following method. The electrode is cut to a predetermined area, the mass is measured using an electronic balance of a minimum scale of 0.1 mg, and the mass of the current collector is subtracted to calculate the mass of the positive mixture layer. On the other hand, the total thickness of the electrode is measured at 10 points in a micrometer having a minimum scale of 1 占 퐉, and the volume of the positive electrode mixture layer is calculated from the average value and the area obtained by subtracting the thickness of the collector from these measured values. Then, the density of the positive electrode material mixture layer is calculated by dividing the mass of the positive electrode material mixture layer by the volume.

As the collector of the positive electrode, the same materials as those conventionally used for the positive electrode of a lithium secondary battery can be used. For example, an aluminum foil having a thickness of 10 to 30 m is preferable.

In the positive electrode according to the present invention, a lead body (positive electrode lead body) for electrically connecting the other member of the lithium secondary battery and the positive electrode is attached. The positive electrode lead body can be made of, for example, a metal foil (plate) made of nickel or the like, and is usually provided with an exposed portion in which a positive electrode mixture layer is not formed on a part of the positive electrode current collector, The above-mentioned foil is welded by welding or the like.

The thickness of the positive electrode lead body is preferably 40 to 200 mu m. It is preferable that the width of the positive electrode lead body is 4 to 8 mm.

<Negative electrode>

As the negative electrode relating to the lithium secondary battery of the present invention, for example, a negative electrode mixture layer containing a negative electrode active material, a binder and further, if necessary, a conductive auxiliary agent, may be used on one surface or both surfaces of the current collector.

Examples of the negative electrode active material include graphite carbon materials (natural graphite such as flake graphite; Artificial graphite obtained by graphitizing graphitized carbon such as pyrolytic carbon, mesophase carbon microbeads (MCMB) and carbon fiber at 2800 占 폚 or higher; Etc.), pyrolytic carbon materials, cokes, glass carbon materials, fired bodies of organic high molecular compounds, mesocarbon microbeads, carbon fibers, activated carbon, metal alloys (Si, Sn, etc.) , And one or more of these can be used.

Among the above-mentioned negative electrode active materials, in particular, in order to increase the capacity of the lithium secondary battery, a material containing Si and O as constituent elements (however, the atomic ratio x of O to Si is 0.5? X? 1.5, It is preferable to use this material as &quot; SiO _x &quot;).

SiO _x may contain a microcrystalline or amorphous phase of Si. In this case, the atomic ratio of Si and O is a ratio of Si to microcrystalline or amorphous Si. That is, SiO _x includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and the amorphous SiO ₂ and Si dispersed therein are combined to form the above circle It suffices that the self-flux x satisfies 0.5? X? 1.5. For example, in the case of a material in which Si is dispersed in an amorphous SiO ₂ matrix and a molar ratio of SiO ₂ to Si is 1: 1, x = 1, and hence the structural formula is expressed by SiO 2. In the case of the material having such a structure, for example, in the X-ray diffraction analysis, a peak due to the presence of Si (microcrystalline Si) may not be observed in some cases, but when the observation is made with a transmission electron microscope, have.

The SiO _x is preferably a complex compounded with a carbon material. For example, it is preferable that the surface of SiO _x is coated with a carbon material. Since SiO _x has low conductivity, when it is used as a negative electrode active material, mixing and dispersion of SiO _x and a conductive material in the negative electrode are improved by using a conductive material (conductive auxiliary agent) from the viewpoint of ensuring good battery characteristics , It is necessary to form an excellent challenge network. A composite in which SiO _x is complexed with a carbon material can form a conductive network in the negative electrode better than, for example, a material obtained by mixing only a conductive material such as SiO _x with a carbon material.

When the negative electrode using a composite of the SiO _x and the carbon material, the ratio of the SiO _x and the carbon material, from the viewpoint of satisfactorily exert the effect of the composite with the carbon material, SiO _x: relative to 100 parts by mass of carbon material Is preferably 5 parts by mass or more, more preferably 10 parts by mass or more. Further, in the composite, the SiO _x and the ratio of the carbon material composite is too large, in a consecutive to the degradation of the SiO _x content in the negative electrode material mixture layer, since it is concerned be small, the effect of high capacity, SiO _x: 100 parts by weight , The carbon material is preferably 50 parts by mass or less, more preferably 40 parts by mass or less.

When SiO _x (preferably a composite of SiO _x and a carbon material) is used for the negative electrode active material, a graphitic carbon material is also preferably used in combination. SiO _x has a higher capacity than a carbon material commonly used as a negative electrode active material of a lithium secondary battery and has a large amount of change in volume accompanied by charging and discharging of the battery. Therefore, a negative electrode having a negative electrode mixture layer having a high content of SiO _x is used In the lithium secondary battery, there is a risk that the negative electrode (negative electrode mixture layer) is largely changed in volume and deteriorated by repetition of charging and discharging, and the capacity is lowered (that is, the charge-discharge cycle characteristic is lowered). The graphitizable carbon material is generally used as a negative electrode active material of a lithium secondary battery and has a relatively large capacity, while the amount of volume change accompanying charging and discharging of the battery is smaller than that of SiO _x . Therefore, by using SiO _x and the graphite carbon material together with the negative electrode active material, it is possible to suppress the decrease in the charge-discharge cycle characteristics of the battery as much as possible while suppressing the decrease in the capacity improvement effect of the battery with reduction in the amount of SiO _x used It is possible to obtain a lithium secondary battery having a higher capacity and excellent charge / discharge cycle characteristics.

Examples of the graphite carbon material used as the negative electrode active material together with the above SiO _x include natural graphite such as flake graphite; Artificial graphite having graphitized carbon such as pyrolytic carbon, mesophase carbon microbeads (MCMB), and carbon fiber at 2800 ° C or higher; And the like.

In the case of using the composite of SiO _x and the carbon material and the graphite carbon material together with the negative electrode active material, from the viewpoint of satisfactorily securing the effect of increasing the capacity by using SiO _x , the total amount of SiO _x and the carbon material Is preferably 0.01 mass% or more, more preferably 1 mass% or more, and further preferably 3 mass% or more. From the viewpoint of better avoiding the problem caused by the volume change of SiO _x accompanying charge and discharge, the content ratio of the composite of SiO _x and the carbon material in the total negative electrode active material is preferably 20 mass% or less, more preferably 15 By mass or less.

The content of the negative electrode active material in the negative electrode material mixture layer (the total content of the total negative electrode active material) is preferably 80 to 99% by mass.

&Lt; Binder of negative electrode mixture layer >

Examples of the binder used in the negative electrode mixture layer include polysaccharides such as starch, polyvinyl alcohol, polyacrylic acid, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose and diacetylcellulose and their modified products; Thermoplastic resins such as polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide and polyamide, and their modified products; Polyimide; Rubber-like elastic polymers such as ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), butadiene rubber, polybutadiene, fluorine rubber and polyethylene oxide; And the like, and one or more of these may be used.

The content of the binder in the negative electrode material mixture layer is preferably 1 to 20% by mass.

<Conducting preparation of negative electrode mixture layer>

A conductive material may be further added to the negative electrode material mixture layer as a conductive auxiliary agent. Such a conductive material is not particularly limited as long as it does not cause chemical change in the lithium secondary battery, and examples thereof include carbon black (thermal black, furnace black, channel black, ketjen black, acetylene black and the like) One or more materials such as a powder (copper, nickel, aluminum, silver, etc.), a metal fiber, and a polyphenylene derivative (described in Japanese Patent Application Laid-Open No. 59-20971) Of these, carbon black is preferably used, and ketjen black or acetylene black is more preferable.

<Negative electrode mixture layer, current collector, etc.>

The negative electrode is prepared by preparing a composition containing a negative electrode active material mixture in a paste state or a slurry state in which the above-described negative electrode active material and binder, and further, a conductive auxiliary agent to be used, if necessary, are dispersed in a solvent such as NMP or water The binder may be dissolved in a solvent), which is then coated on one side or both sides of the current collector, dried, and then subjected to calendering if necessary. However, the manufacturing method of the negative electrode is not limited to the above method, and may be manufactured by another manufacturing method. The thickness of the negative electrode material mixture layer is preferably 10 to 100 占 퐉, for example, per one surface of the current collector.

As the collector of the negative electrode, a copper foil, a nickel foil, a punching metal, a net, an expanded metal, or the like can be used, but a copper foil is usually used. In order to obtain a battery having a high energy density, the negative electrode current collector preferably has an upper limit of 30 mu m in thickness when the entire negative electrode is thinned, and a lower limit of 5 mu m in order to secure mechanical strength Do.

Further, a lead body (negative electrode lead body) for electrically connecting the other member of the lithium secondary battery and the positive electrode is attached to the negative electrode according to the present invention. The negative electrode lead body can be made of, for example, a metallic foil (plate) made of nickel or the like. Normally, an exposed portion in which a negative electrode mixture layer is not formed is provided on a part of the negative electrode current collector, For example, by welding or the like.

The thickness of the negative electrode lead body is preferably 40 to 200 mu m. It is preferable that the width of the negative electrode lead body is 4 to 8 占 퐉.

&Lt; Flat-shaped wound electrode body &

The flat wound electrode body related to the lithium secondary battery of the present invention is formed by overlapping the positive electrode and the negative electrode with the separator interposed therebetween so as to have a flat cross-section while being wound in a spiral shape. 1, the flat wound electrode body according to the present invention is configured such that the positive electrode lead body 51 and the negative electrode lead body 52 protrude from the same direction, that is, from the same cross-sectional side, as shown in Fig.

The end face 302 of the flat-shaped wound electrode body 30 on which the positive electrode lead body 51 and the negative electrode lead body 52 are protruded and the two side faces 301, 301 are fixed by a tape 60.

The tape 60 is provided with a resin which does not melt at a temperature lower than the shutdown temperature of the lithium secondary battery, that is, a resin containing a resin having a melting point higher than the shutdown temperature or not having a melting point (not melting) And a pressure-sensitive adhesive layer is formed on one surface. With such a tape, even if the internal temperature of the lithium secondary battery exceeds the shutdown temperature, at least until the melting point of the constituent resin of the substrate related to the tape (when the constituent resin has a melting point) The heat shrinkage of the separator in the vicinity of the end face where the positive electrode lead body and the negative electrode lead body protrude can be satisfactorily suppressed and a highly reliable lithium secondary battery can be constructed.

As the base material of the tape according to the present invention, it is possible to use a base material such as PP, polyphenylene sulfide (PPS), polyester (polyethylene terephthalate, polybutylene terephthalate), polyamide (nylon 66, etc.) (Film), woven fabric, non-woven fabric and the like made of a constituent resin.

The pressure sensitive adhesive constituting the pressure sensitive adhesive layer of the tape may be the same as the pressure sensitive adhesive (acrylic pressure sensitive adhesive, rubber pressure sensitive adhesive, silicone pressure sensitive adhesive, etc.) conventionally used for the pressure sensitive adhesive tape used in the lithium secondary battery.

2 and 3 are perspective views schematically showing another example of a flat-shaped wound electrode body related to the lithium secondary battery of the present invention. In the flat-rolled electrode body related to the present invention, the number of the fixing points on the tape and the fixing position may be appropriately determined depending on the arrangement of the positive electrode lead body and the negative electrode lead body. As shown in Fig. 1, for example, there may be one fixing position in the tape, and two positions or three or more positions as shown in Fig. 2 and Fig. 3 may be used. However, if the number of fixing points on the tape is excessively increased, the productivity of the flat-rolled electrode body, and furthermore, the productivity of the lithium secondary battery may be impaired, so that it is more preferable that the number of fixing points in the tape is 1 to 2 Do.

In the case where the number of fixing points on the tape is one, it is preferable that the fixing position is set to be a side view (more wide side) of the flat-rolled electrode body from the viewpoint of suppressing the heat shrinkage of the separator more preferably, , It is preferable that the distance from the central portion of the flat-rolled electrode body to the position where it is 40% in the width direction is set to 100% when the length in the width direction of the flat-rolled electrode body is 100%.

The width A (mm) of the tape (the length of A in Fig. 1, the width of each tape when the tape is fixed at a plurality of points, the same shall apply hereinafter) Mm) is preferably 0.05 or more, and more preferably 0.10 or more. By using a tape having a width that satisfies the relationship with the width W of the battery case, the heat shrinkage of the separator can be suppressed more favorably.

The upper limit of the ratio (A / W) of the width A of the tape to the width W of the battery case is not particularly limited, but is about 0.5 in consideration of productivity and the like. Further, when there are a plurality of fixing points on the tape, the achievable width A can be appropriately selected within a range in which the value of A / W satisfies the above lower limit value.

In the flat-rolled electrode body, it is preferable that the porous layer (II) of the separator is disposed so as to face at least the positive electrode. Since oxidation of the separator by the positive electrode can be suppressed more favorably by forming the porous layer (II) containing a filler having a heat-resistant temperature of 150 ° C or more as a main component and having a more excellent oxidation resistance with the positive electrode, The storage characteristics and the charge / discharge cycle characteristics may be enhanced. As described later, an additive such as vinylene carbonate or cyclohexylbenzene may be added to the non-aqueous electrolyte relating to the lithium secondary battery. However, these additives may be formed by forming a film on the positive electrode side and clogging the pores of the separator Which may cause deterioration of battery characteristics. Therefore, by confronting the relatively porous porous layer (II) on the positive electrode, the effect of suppressing clogging of pores can be expected.

On the other hand, when one surface of the separator is the porous layer (I), it is preferable that the porous layer (I) faces the negative electrode. Thus, for example, when the porous layer The molten thermoplastic resin can be prevented from being absorbed into the compounded layer of the electrode and can be effectively used for the occlusion of the separator.

<Non-aqueous electrolyte>

As the non-aqueous electrolyte relating to the lithium secondary battery of the present invention, for example, a solution in which a lithium salt is dissolved in an organic solvent can be used.

The lithium salt used for the non-aqueous electrolyte is not particularly limited as long as it dissociates in the solvent to form lithium ions and it is difficult to cause side reactions such as decomposition in a voltage range used as a battery. For example, _{LiClO 4, LiPF 6, LiBF 4} , LiAsF 6, inorganic lithium salts such as _{LiSbF 6, LiCF 3 SO 3,} LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3) 2, LiN (CF 3 SO _{2) 2, LiC (CF 3} SO 2) 3, LiC n F 2n + 1 SO 3 (n≥2), LiN (RfOSO 2) 2 [wherein Rf is a fluoroalkyl group] can be used, and organic lithium salts such as have.

The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / l, and more preferably 0.9 to 1.25 mol / l.

The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt described above and does not cause side reactions such as decomposition in the voltage range used as the battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate; Chain esters such as methyl propionate; cyclic esters such as? -butyrolactone; Chain ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; Cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; Nitriles such as acetonitrile, propionitrile and methoxypropionitrile; Sulfurous acid esters such as ethylene glycol sulfite; These may be used in combination of two or more. In addition, in order to obtain a battery having better characteristics, it is preferable to use a combination such as a mixed solvent of ethylene carbonate and a chain carbonate, in which a high conductivity can be obtained.

It is preferable that the non-aqueous electrolyte used for the lithium secondary battery contains vinylene carbonate (VC). In the lithium secondary battery using the non-aqueous electrolyte containing VC, a film derived from VC is formed on the surface of the negative electrode, and deterioration of the non-aqueous electrolyte due to the reaction of the negative electrode with the non- Therefore, the charge / discharge cycle characteristics can be improved.

The content of VC in the non-aqueous electrolyte used for the lithium secondary battery is preferably 1% by mass or more, and more preferably 1.5% by mass or more. However, if the amount of VC in the non-aqueous electrolyte is excessively large, excessive gas may be generated at the time of film formation, which may cause expansion of the battery case. Therefore, the content of VC in the non-aqueous electrolyte used for the lithium secondary battery is preferably 10 mass% or less, more preferably 5 mass% or less.

Further, it is preferable that the non-aqueous electrolyte used in the lithium secondary battery contains a halogen-substituted cyclic carbonate. Particularly, in the case of a lithium secondary battery using SiO _x as a negative electrode active material, even if a new surface is formed due to the breakage of SiO _x particles or the like due to charging and discharging, a coating derived from a halogen- It is possible to suppress deterioration of charge-discharge cycle characteristics of the battery due to the formation of such a new surface.

As the cyclic carbonate substituted with a halogen element, 4-fluoro-1,3-dioxolan-2-one (FEC) is particularly preferable.

The content of the halogen-substituted cyclic carbonate in the non-aqueous electrolyte used in the lithium secondary battery is preferably 1% by mass or more, more preferably 1.5% by mass or more, Is more preferable. However, if the amount of the halogen-substituted cyclic carbonate in the non-aqueous electrolyte is excessively large, the activity of SiO _x may be deteriorated particularly when SiO _x is used as the negative electrode active material. Therefore, the content of the halogen-substituted cyclic carbonate in the non-aqueous electrolyte used for the lithium secondary battery is preferably 5% by mass or less, more preferably 3% by mass or less.

It is preferable that the non-aqueous electrolyte used for the lithium secondary battery contains a phosphonoacetate type compound represented by the following general formula (3).

[Chemical Formula 1]

In the general formula (3), R ¹ to R ³ each independently represent an alkyl group, an alkenyl group or an alkynyl group having 1 to 12 carbon atoms which may be substituted with a halogen atom, and n represents an integer of 0 to 6.

As the phosphonoacetate type compound represented by the following general formula (3), 2-propynyl 2- (diethoxyphosphoryl) acetate and ethyldiethylphosphonoacetate are preferable.

The content of the phosphonoacetate compound represented by the general formula (1) in the nonaqueous electrolyte used in the lithium secondary battery is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, further preferably 30% Or less, more preferably 5.0 mass% or less.

The non-aqueous electrolyte used in the lithium battery includes, for example, anhydrous acid, sulfonic acid ester, dinitrile, and the like for the purpose of improving the charge-discharge cycle characteristics of a battery, improving safety such as suppression of high temperature expansion, (Including derivatives thereof) such as 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, t-butylbenzene and succinonitrile You can.

<Battery Case>

Fig. 4 is a perspective view schematically showing the appearance of an example of the lithium secondary battery of the present invention, and Fig. 5 is a partial longitudinal sectional view of the lithium secondary battery shown in Fig. The lithium secondary battery 1 shown in Figs. 4 and 5 has a columnar battery case 10. The battery case 10 is hollow and has a flattened spiral wound electrode body 30, And a nonaqueous electrolytic solution (not shown).

The battery case 10 is composed of an outer can 11 and a lid 20. The outer can 11 has a shape of a cylindrical shape with a bottom, The body 20 is covered and integrated with the lid body 20 by welding. The outer can 11 and the cover 20 are made of, for example, an aluminum alloy.

A terminal 21 made of stainless steel or the like protrudes from the lid body 20 and an insulating packing 22 made of PP or the like is interposed between the terminal 21 and the lid body 20. A lead plate 25 made of stainless steel or the like is attached to the terminal 21 via an insulator 24. The terminal 21 is connected to the negative electrode in the battery case 10. In this case the terminal 21 functions as a negative terminal and the external can 11 and the cover 20 are connected to the positive terminal . However, depending on the material of the battery case 10, the terminal 21 is connected to the positive electrode in the battery case 10 to function as a positive electrode terminal, and the external can 11 and the lid body 20 function as negative terminal Sometimes it works. In addition, a non-aqueous electrolyte injection port is provided in the lid body 20, and after the non-aqueous electrolyte is injected into the battery case 10, the lid body 20 is sealed with the sealing member 23.

The flattened wound electrode body 30 accommodated in the battery case 10 is constituted by a positive electrode 31, a negative electrode 32 and a separator 33. The outer case 11 And an insulator 40 made of a PE sheet or the like is disposed at the bottom. In the lithium secondary battery 1, the external can 11 and the lid body 20 function as positive electrode terminals by directly welding the positive electrode lead body 51 of the positive electrode 31 to the lid body 20, The negative electrode lead body 52 of the negative electrode lead 32 is welded to the lead plate 25 and the negative electrode lead body 52 and the terminal 21 are made conductive through the lead plate 25, Terminal.

The side surface portion of the battery case 10, that is, the side surface portion of the external can 11, faces two mutually opposed surfaces, and two wider light beams (widths wider than the other surfaces ) Surfaces 111 and 111, respectively. When the pressure in the battery case 10 is larger than the threshold value on at least one of the light-absorbing surfaces 111 and 111 (the light-absorbing surface 111 on the front surface in Fig. 4) (Not shown).

However, in Fig. 5, the collectors used in the production of the positive electrode 31 and the negative electrode 32 are not shown, and the respective layers of the separator are not separately shown in order to avoid the redundancy. In addition, the portion on the inner circumferential side of the flat-shaped wound electrode body is not a section.

Further, the battery case according to the present invention has a width (length in the transverse direction in Fig. 5) of 40 mm or more, but its upper limit value is usually about 70 mm.

The lithium secondary battery of the present invention can be used for the same purpose as various applications to which a conventionally known lithium secondary battery is applied.

[Example]

Hereinafter, the present invention will be described in detail based on examples. However, the following examples are not intended to limit the present invention.

Example 1

&Lt; Preparation of positive electrode &

And a lithium-containing composite oxide as Li _{1 .02} Ni _{0 .6} Co and _{0 .2 Mn 0 .2 O 2,} LiCoO 2, weighing a mass ratio of 20: 80, 30 min mixing using a Henschel mixer (Henschel mixer) To obtain a mixture. 20 parts by mass of a solution obtained by dissolving 100 parts by mass of the obtained mixture (positive electrode active material) and PVDF and P (TFE-VDF) as binders in NMP and 20 parts by mass of carbon having an average fiber length of 100 nm and an average fiber diameter of 10 nm 1.04 parts by weight of the fibers and 1.04 parts by weight of graphite were kneaded by using a biaxial kneader and NMP was further added to adjust the viscosity to prepare a positive electrode material mixture containing paste. The amount of the NMP solution of PVDF and P (TFE-VDF) is preferably such that the amount of dissolved PVDF and P (TFE-VDF) is such that the mixture of the lithium-containing complex oxide A and LiCoO _{2 and} the mixture of PVDF and P -VDF) and the conductive additive (that is, the total amount of the positive electrode material mixture layer) of 2.34% by mass and 0.26% by mass, respectively. That is, in the positive electrode, the total amount of the binder in the positive electrode material mixture layer is 2.6% by mass, and the ratio of P (TFE-VDF) in 100% by mass of P (TFE-VDF) and PVDF is 10% by mass.

The positive electrode material mixture-containing paste was intermittently applied to both sides of an aluminum foil (positive electrode collector) having a thickness of 15 탆 while adjusting its thickness, dried and calendered to form a positive electrode material mixture layer thickness So as to have a width of 54.5 mm, thereby preparing a positive electrode. A nickel foil lead body having a thickness of 80 mu m and a width of 6 mm was welded to the exposed portion of the aluminum foil of this positive electrode.

<Fabrication of negative electrode>

(The amount of the carbon material in the composite is 10 mass% or less, hereinafter referred to as &quot; SiO / carbon material composite &quot;) having an average particle diameter of 8 占 퐉 and a surface of SiO having an average particle diameter of 8 占 퐉 is coated with a carbon material 98 parts by mass of an anode active material obtained by mixing graphite having a particle size of 16 占 퐉 in an amount such that the amount of the SiO / carbon material composite is 5% by mass, a CMC aqueous solution having a concentration of 1% by mass adjusted to have a viscosity of 1,500 to 5,000 mPa 占 퐏, 100 parts by mass of SBR and 1.0 part by mass of SBR were mixed with ion-exchanged water having a specific resistance of 2.0 x 10 &lt; ⁵ &gt; OMEGA cm or more as a solvent to prepare a paste containing a negative electrode material mixture in an aqueous system.

The negative electrode material mixture-containing paste was intermittently applied to both surfaces of a copper foil (negative electrode collector) having a thickness of 8 占 퐉 while adjusting the thickness, dried and calendered to obtain a thickness of the negative electrode material mixture layer And cut to a width of 55.5 mm to prepare a negative electrode. A nickel foil lead body having a thickness of 80 mu m and a width of 6 mm was welded to the exposed portion of the copper foil of this negative electrode.

<Fabrication of Separator>

5 kg of ion-exchanged water and 0.5 kg of a dispersant (aqueous polycarboxylic acid ammonium salt, solid concentration 40% by mass) were added to 5 kg of boehmite secondary aggregate having an average particle diameter of 3 m, The mixture was subjected to a decolorization treatment with a ball mill for 10 hours to prepare a dispersion liquid. A portion of the dispersion after the treatment was vacuum-dried at 120 캜 and observed by a scanning electron microscope (SEM). As a result, the boehmite had a substantially plate shape. The average particle diameter of the treated boehmite was 1 mu m.

To 500 g of the above dispersion was added 0.5 g of xanthan gum as a thickening agent and 17 g of resin binder dispersion (modified polybutyl acrylate, solid content 45% by mass) as a binder, and 3 g of 3 And the mixture was stirred for a time to prepare a homogeneous slurry (slurry for forming the porous layer (II), solid content ratio of 50 mass%).

Porous microporous separator made of PE for lithium secondary battery [Porous layer (I): corona discharge treatment (discharging amount: 40 W · cm) was formed on one side of a thickness of 12 탆, porosity of 40%, average pore diameter (0.08 탆, melting point of PE: 135 캜) The slurry for forming the porous layer (II) was coated on the treated surface by a micro gravure coater and dried to form a porous layer (II) having a thickness of 2 m to obtain a laminate type separator . The mass per unit area of the porous layer (II) in this separator was 5.5 g / m 2, the volume content of boehmite was 95 vol%, and the porosity was 45%.

<Assembly of Battery>

The positive electrode and negative electrode thus obtained were rolled up in a spiral shape while interposing the porous layer (II) of the separator so as to face the positive electrode, thereby producing a wound electrode body. As shown in Fig. 2, the central position of the positive electrode lead body and the negative electrode lead body, and the position of 10 mm from the negative electrode lead body were set to 6 mm in width and 30 mm in length Of tape. A tape (30 占 퐉 thick) made of a film made of PP (melting point 165 占 폚) was used for the tape.

The above-mentioned flat-wound wound electrode body was placed in an aluminum alloy outer can having a thickness of 5.1 mm, a width of 51 mm, and a height of 61 mm. As a non-aqueous electrolyte, LiPF ₆ was dissolved in a solvent in which ethylene carbonate, ethylmethyl carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1: 1 so as to have a concentration of 1.1 mol / l. A solution obtained by adding VC to an amount of 1.0% by mass and further adding 1.0% by mass of 2-propynyl 2- (diethoxyphosphoryl) acetate was prepared, and this was added to the aluminum alloy outer can . After the injection of the nonaqueous electrolyte solution, the outer can was sealed, and a lithium secondary battery having the structure shown in Fig. 5 was produced from the appearance shown in Fig. The ratio (A / W) of the width A of the tape used for fixing the flat electrode winding body to the width W of the battery case in this lithium secondary battery is 0.117.

Example 2

A lithium secondary battery was produced in the same manner as in Example 1 except that the tape was fixed at the position where the tape was wound between the positive electrode lead body and the negative electrode lead body as shown in Fig.

Example 3

A lithium secondary battery was produced in the same manner as in Example 1 except that the size of the battery can was 5.6 mm in thickness, 56 mm in width, and 64 mm in height. The ratio (A / W) of the width A of the tape used for fixing the flat electrode winding body to the width W of the battery case in this lithium secondary battery is 0.107.

Example 4

A lithium secondary battery was produced in the same manner as in Example 2 except that the tape width A used for fixing the flat wound electrode body was changed to 8 mm. The ratio (A / W) of the width A of the tape used for fixing the flat electrode winding body to the width W of the battery case in this lithium secondary battery is 0.156.

Comparative Example 1

A lithium secondary battery was produced in the same manner as in Example 1 except that the flat wound electrode body was not fixed with tape.

Comparative Example 2

A lithium secondary battery was produced in the same manner as in Example 1 except that the porous layer (II) was not provided in the separator.

Reference example

A separator was produced in the same manner as in Example 1 except that the thickness of the porous layer (II) was changed to 10 탆. A lithium secondary battery was produced in the same manner as in Comparative Example 1 except that the separator was used.

With respect to each of the lithium secondary batteries of Examples 1 to 4 and Comparative Example 2, when the battery was placed in an oven and heated to 150 占 폚 at a rate of 5 占 폚 / min, the internal resistance of the battery rose to 5 times or more as compared with room temperature The temperature was measured, and this temperature was set as the shutdown temperature. As a result, the shutdown temperature of these batteries was all 140 ° C.

Further, each of the lithium secondary batteries of Examples 1 to 4, Comparative Examples 1 and 2, and Reference Example (batteries different from those in which the shutdown temperature was measured) was subjected to a heating test at 150 캜 by the following method. Constant current-constant voltage charging (total charging time (constant current charging time)) in which each battery is first charged after initial charging and discharging until it reaches 4.4 V at a constant current of 1 C at room temperature (25 캜) and then charged at a constant voltage of 4.4 V : 2.5 hours). Each battery after being charged was placed in a thermostatic chamber, heated from 30 ° C to 150 ° C at a rate of 1 ° C per minute and heated, and then held at 150 ° C for 30 minutes. Then, each battery was taken out from the thermostatic chamber and then decomposed to confirm visually the degree of heat shrinkage of the separator in the flat-rolled electrode body, and evaluated according to the following criteria. The lithium secondary battery in which the evaluation based on the following criteria is "⊚" and "◯" can be said that the safety is good.

Heat shrinkage of the separator is hardly recognized:?,

The separator is slightly thermally shrunk, but the contact between the positive electrode and the negative electrode is not enough:

The separator is thermally shrunk enough to cause contact between the positive electrode and the negative electrode:?,

The separator is thermally shrunk enough to cause contact between the positive electrode and the negative electrode.

Table 1 shows the above evaluation results.

As shown in Table 1, in the lithium secondary battery of Reference Example using the separator having a comparatively thick porous layer (II), the positive electrode and the negative electrode were in contact with each other in the heating test at 150 ° C without fixing the flat- , The heat shrinkage of the separator does not occur. However, the battery of Comparative Example 1 using the separator in which the porous layer (II) is made thin is not as good as the battery of Comparative Example 2 using the separator not forming the porous layer (II) The separator is thermally shrunk, and there is a fear that the positive electrode and the negative electrode are in contact with each other.

On the other hand, in the lithium secondary batteries of Examples 1 to 4 having a flat-shaped wound electrode body in which a suitable portion was fixed with an appropriate tape, although the same separator as the battery of Comparative Example 1 was used, So that the heat shrinkage of the separator is suppressed well, thereby providing high safety. Particularly, the lithium secondary batteries of Examples 1 to 3, in which the ratio (A / W) of the width A of the tape to the width W of the battery case was set to a more appropriate value than the lithium secondary battery of Example 4, The heat shrinkage is highly suppressed, and thus excellent safety can be secured.

1: lithium secondary battery 10: battery case
11: External can
111: Battery case (exterior can)
12: flushing groove 20: cover body
30: Flat-shaped wound electrode body 51: Positive electrode lead body
52: negative electrode lead body 60: tape

Claims (3)

A flat wound electrode body comprising a positive electrode having a positive electrode lead body and a negative electrode having a negative electrode lead body interposed between the positive electrode lead body and the negative electrode lead body so as to protrude in the same direction, And a nonaqueous electrolytic solution enclosed in a hollow cylindrical battery case,
Wherein the separator has a porous layer (I) composed mainly of a thermoplastic resin and a porous layer (II) containing a filler having a heat-resistant temperature of 150 ° C or higher as a main component and the porous layer (II) Or less,
Wherein the flat wound electrode body has a cross section in which the positive electrode lead body and the negative electrode lead body protrude and two side faces opposite to each other and wider than the other face, Which is fixed by a tape,
Wherein the battery case has a width of 40 mm or more. The method according to claim 1,
Wherein the ratio (A / W) of the width (A) (mm) of the tape to the width (W) (mm) of the battery case is 0.05 or more. 3. The method according to claim 1 or 2,
And the thickness of the separator is 28 占 퐉 or less.

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