JP2012033438A - Cathode for lithium ion secondary battery and lithium ion secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode for a lithium secondary battery which allows the achievement of a higher capacity, and to provide a lithium ion secondary battery using the same.SOLUTION: The cathode for a lithium secondary battery comprises: an anode active material of a complex oxide having an olivine structure expressed by the chemical formula of LiMPO(where 0<a≤1.2, 0.9≤x≤1.1, M is a transition metal including Fe or Mn), a conductive material and a binder. In the cathode, the content of the anode active material is between 91 and 93 wt.% inclusive; the specific surface area of the anode active material is 10-30 m/g; the conductive material contains fibrous carbon; the binder consists of a mixture of polyvinylidene fluoride and polyamide; the content of the binder in the cathode is between 3 and 6 wt.% inclusive; the content of the polyamide in the mixture of the polyvinylidene fluoride and the polyamide is between 38 and 70 wt.% inclusive; and the density of the cathode is between 1.9 and 2.2 g/cc inclusive.

Description

  The present invention relates to a positive electrode for a large-sized lithium secondary battery using a non-aqueous electrolyte and a method for producing the same, and more particularly to improvement of the positive electrode structure.

  In order to further improve the energy efficiency of automobiles, the development of plug-in hybrid automobiles (hereinafter abbreviated as PHEV) is required. Since the PHEV is used as a hybrid vehicle after running on energy charged by a household power source, the battery capacity is required as well as the 10-second output required for the hybrid vehicle as battery performance. As described above, in the battery characteristics required for PHEV, it is important to increase the output as well as increase the capacity. For this reason, since the lithium secondary battery for PHEV becomes a large sized large capacity battery, ensuring safety | security is important. In a large-capacity lithium secondary battery for in-vehicle use, an improvement in volume energy density and weight energy density is required in order to reduce the size and weight of the battery. In addition, since a large-scale, large-capacity lithium secondary battery stores a large amount of energy, a highly active and safe cathode active material is required.

In general, a positive electrode active material having an olivine structure composed of Fe or Mn as a transition metal (LiMPO ₄ , M is a transition metal containing Fe or Mn, hereinafter abbreviated as an olivine positive electrode material), oxygen and phosphorus in the crystal structure. The bond is strong and oxygen is not easily released from the crystal structure during overcharge, which is highly safe. However, it has been reported that the olivine positive electrode active material has low electronic conductivity and a low lithium ion diffusion coefficient into the positive electrode active material. In order to put the olivine positive electrode active material into practical use, the material has a high specific surface area to improve the diffusibility of lithium ions, and the carbon coating provides conductivity. Here, the carbon coating can contribute to the increase in specific surface area by imparting conductivity, suppressing crystal growth, and reducing the primary particle size to a submicron size.

The above olivine positive electrode active materials have the following problems in improving the volume energy density. For example, in the case of olivine Fe, the true density is 3.6 g / cc, which is higher than 5.1 g / cc of the layered LiNiMnCoO ₂ system, and the olivine positive electrode active material is a material that is difficult to increase in volume density. Further, the density is further reduced in the carbon-coated olivine positive electrode active material.

  Moreover, since an olivine positive electrode active material is comprised with a high specific surface area and a fine primary particle, it is a positive electrode active material with difficult electrode preparation as follows. In the case of a positive electrode active material composed of fine primary particles, the amount of binder required per specific surface area increases because active material particles having a high specific surface area are joined together. Decreases, and the volumetric energy density of the positive electrode decreases. For this reason, joining between the positive electrode members by a high binding binder is required. Further, since the surface of the olivine positive electrode active material is coated with carbon, the surface energy is high, and aggregation is likely to occur in the slurry used for electrode preparation. As described above, in order to increase the energy density of the positive electrode using the olivine positive electrode active material, it is desirable to use a binder that has high binding properties and does not cause aggregation in the slurry.

  Patent Document 1 discloses the following regarding increasing the content of the positive electrode active material. It is disclosed to improve the dispersion state of active material particles in the positive electrode forming coating liquid, prevent aggregation and precipitation of active material particles due to long-term storage, and increase the active material content. . Here, after mixing a large particle size positive electrode active material having an average particle size of 1-20 μm and a small particle size positive electrode active material having an average particle size of 5-100 nm, graphite such as natural graphite and artificial graphite, carbon black as a conductive material Coating liquid in which one kind or two or more kinds of conductive fibrous carbon are mixed in combination, and further, a fluorine resin, an aramid resin, or a polyamide is used as a binder, or two or more kinds are combined as necessary. And a positive electrode with an active material content of 80% or more, preferably 80-90%. Here, examples of the fibrous carbon include vapor grown fibrous carbon, single wall or multi-wall carbon nanotubes (hereinafter abbreviated as SWCNT and MWCNT). In Patent Document 1, a high content positive electrode is formed by mixing a small particle size and a large particle size positive electrode active material, which is different from the invention relating to a positive electrode composed of almost only submicron primary particles of an olivine positive electrode active material. That is, in Patent Document 1, the voids filled with the large particle size positive electrode active material are filled with the small particle size positive electrode active material to improve the positive electrode active material content.

JP 2009-146788 A

  The objective of this invention is providing the positive electrode for lithium secondary batteries which achieves high capacity | capacitance, and a lithium ion secondary battery using the same.

  The outline of the present invention is as follows.

(1) It has an olivine structure represented by the chemical formula Li _a M _x PO ₄ (0 <a ≦ 1.2, 0.9 ≦ x ≦ 1.1, where M is a transition metal containing either Fe or Mn). In a positive electrode for a non-aqueous lithium ion secondary battery including at least a positive electrode active material of a composite oxide, a conductive material, and a binder, the content of the positive electrode active material in the positive electrode is 91% to 93% by weight, The specific surface area of the positive electrode active material is 10-30 m ² / g, the conductive material contains fibrous carbon, the binder is a mixture of polyvinylidene fluoride and polyamide, and the content in the positive electrode Is 3% to 6% by weight, the weight percentage of polyamide in the mixture of polyvinylidene fluoride and polyamide is 38% to 70%, and the density of the positive electrode is 1.9 g / cc to 2. 2g / cc or less Non-aqueous lithium ion secondary battery positive electrode characterized by and.

  (2) A non-aqueous lithium ion secondary characterized by using a positive electrode material in which the content of fibrous carbon in the total conductive material used for the positive electrode according to (1) is 20% or more and 60% or less by weight. Battery positive electrode.

  (3) In the lithium ion secondary battery using the positive electrode for a non-aqueous lithium ion secondary battery according to (1) (2), the energy density is 100 Wh / Kg or more and 150 Wh / Kg or less. Water-based lithium ion secondary battery.

  (4) In a laminate type lithium ion secondary battery using the positive electrode for a non-aqueous lithium ion secondary battery described in (1) and (2), after performing a cycle test 50 times with a charge / discharge rate of 3C A laminate-type lithium ion secondary battery, wherein the swelling of the battery is 10% or less of the initial thickness.

  (5) A battery module comprising a plurality of non-aqueous lithium ion secondary batteries according to (3) and / or a laminate type lithium ion secondary battery according to (4) electrically connected.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium secondary battery suitable for the apparatus application which needs high capacity | capacitance and high safety | security, such as a plug-in hybrid vehicle or an electric vehicle, can be provided.

The relationship between the high binding binder weight percentage in the binder used with a high volume energy density positive electrode and discharge capacity is shown. It is a notch sectional view of the cylindrical lithium secondary battery of the present invention.

  As a result of intensive studies to solve the above problems, the present inventors have studied the positive electrode active material, the conductive material, and the binder material and the composition of the positive electrode constituting the positive electrode, thereby including the positive electrode active material in the positive electrode. It has been found that the rate is improved, the density of the positive electrode is improved, and the energy density per unit volume is improved.

That is, the present invention relates to an olivine represented by the chemical formula Li _a M _x PO ₄ (0 <a ≦ 1.2, 0.9 ≦ x ≦ 1.1, where M is a transition metal containing either Fe or Mn). In a positive electrode composed of a composite oxide positive electrode active material having a structure, a conductive material and a binder, a positive electrode active material having a specific surface area in the range of 10 to 30 m ² / g, a conductive material in which carbon black and fibrous carbon are mixed. A positive electrode is formed using a binder in which the weight percentage of the fibrous carbon accounts for 30 to 60% of the conductive material, polyvinylidene fluoride (hereinafter abbreviated as PVDF), and the weight percentage of polyamide in the mixture of the polyamide is 38 to 70, It discovered that the said subject could be solved by setting it as a lithium secondary battery using this positive electrode.

  Further, according to the present invention, in the positive electrode, the content of the positive electrode active material is 91 to 93 by weight percentage, the content of the conductive material is 5 or less by weight, and the positive electrode density is 1.9 g / cc to 2.2 g / wt. It has been found that the above problem can be solved by forming a positive electrode so as to be cc or less and using this positive electrode as a lithium secondary battery.

  In order to increase the capacity of the battery, it is necessary to increase the thickness of the positive electrode, to increase the content of the positive electrode active material in the positive electrode, and to increase the density of the positive electrode. In order to achieve this, a binder with a high binding property is required, and a polyamide known to have a binding property several times that of PVDF is desirable. Polyamide has heat resistance, and this characteristic is advantageous for forming a high heat-resistant electrode as follows.

As described above, since the olivine positive electrode material has low electron conductivity and high electrode resistance, the electrode generates heat when high rate discharge is performed. For this reason, the polyamide whose crystallization temperature used by this invention exceeds 300 degreeC is desirable. Further, as described above, the olivine positive electrode material is almost composed of submicron primary particles, and the surface thereof is covered with carbon. For this reason, it is easy to adsorb | suck a water | moisture content with a positive electrode active material and a positive electrode. Vacuum heat treatment at 100 ° C. or higher is necessary to remove moisture adsorbed in the electrode manufacturing process. Here, PVDF has a melting point of 134 ° C. or higher, and an electrode using only PVDF as a binder can hardly be heated to 130 ° C. or higher because moisture is almost completely removed from the positive electrode. On the other hand, the melting point of polyamide is 187 ° C., and moisture can be completely removed by heat treatment at 140 ° C. When a positive electrode that cannot remove moisture is used in a lithium secondary battery, HF is generated by the reaction of LiPF ₆ in the electrolyte and moisture, leading to expansion of the battery exterior. For the above reasons, the positive electrode configuration of the invention described above has been reached.

  As described above, polyamide has promising properties for forming a positive electrode, but the flexibility of the electrode may decrease. For this reason, the composition which does not enter a micro crack in electrode processing and can maintain discharge characteristics becomes important.

  As described above, the present invention defines the positive electrode structure of the olivine positive electrode material for the purpose of obtaining a high-safety large-capacity lithium secondary battery.

  Next, constituent members of the lithium secondary battery will be described in detail.

[Positive electrode material for lithium secondary batteries]
The positive electrode for a lithium secondary battery of the present invention is composed of an olivine positive electrode material having the following characteristics. That is, the specific surface area of the olivine positive electrode material is 10-30 m < ² > / g. Here, when the specific surface area is less than 10 m ² / g, the electrode resistance increases because the reaction area between the positive electrode material and lithium ions is small, and when the specific surface area exceeds 30 m ² / g, the positive electrode density is improved. Conductive network formation in the positive electrode cannot be achieved simultaneously. In particular, in the case of the olivine positive electrode material, since the electron conductivity is low, if a conductive network cannot be formed, the resistance becomes high and a desired discharge capacity cannot be obtained. The composition of the olivine positive electrode material is represented by the chemical formula Li _a M _x PO ₄ (0 <a ≦ 1.2, 0.9 ≦ x ≦ 1.1, where M is a transition metal containing either Fe or Mn). It is a complex oxide having an olivine structure.

  Next, the binder of the positive electrode for lithium secondary batteries of the present invention has the following characteristics. That is, the weight percentage of polyamide in the mixture of PVDF and polyamide in the binder is 38-70. In general, PVDF and polyamide are incompatible, but there are cases where two types of polymers form a co-continuous structure in which they are continuous phases by a mixing method. Therefore, in the present invention, PVDF and polyamide are heated and mixed in the above composition range and in the range of 140 to 190 ° C. and used for the positive electrode. If the weight percentage of the polyamide in the PVDF and polyamide mixture is 38-70, a high binder content is obtained because the polyamide, which is a heat-resistant binder, is high in the positive electrode, and the content of the olivine positive electrode material is high. An improvement in discharge capacity was observed in the positive electrode having a weight percentage of 91 to 93 and an electrode density of 1.9 g / cc to 2.2 g / cc. Moreover, since this positive electrode was excellent in heat resistance, it was possible to perform a vacuum heat treatment at 150 ° C. for 2 hours. As a result of measuring moisture in the electrode by the Karl Fischer method described later, it was 120 ppm or less. On the other hand, when the polyamide weight percentage was less than 38, the binding property was insufficient, and the discharge capacity was reduced in the positive electrode having the above specifications. The condition for removing water was 120 ° C., and the water content by the Karl Fischer method was 240 ppm.

  The specific surface area evaluation method and the Karl Fischer method for measuring the water content of the positive electrode will be described below as physical property evaluation methods for the olivine positive electrode material.

The method for evaluating the specific surface area of the positive electrode material is shown below. The sample cell is previously dried at 120 ° C., filled in a sample cell, and dried in nitrogen gas at 300 ° C. for 30 minutes. Next, the sample cell is attached to the measurement unit, and the specific surface area is calculated by the BET method after counting signals at the time of desorption with the He / N ₂ mixed gas.

  The method for measuring the water content of the positive electrode is shown below. A measurement sample is put in a heating furnace at 150 ° C. in which nitrogen gas is flowed and held for 1 minute. Then, the flowd nitrogen gas is introduced into a measurement cell of a Karl Fischer moisture meter, and moisture is measured. Here, the integrated value up to the titration end point is taken as the moisture content.

[Manufacturing method of olivine cathode material]
Finely pulverized iron oxalate dihydrate, ammonium dihydrogen phosphate and lithium carbonate are mixed at a molar ratio of 2: 2: 1.0 and calcined in a nitrogen atmosphere at 300 ° C. Thus, a precursor was obtained. Thereafter, the precursor and polyvinyl alcohol are mixed and heat-treated for 8 hours in a nitrogen atmosphere at 700 ° C., whereby an olivine positive electrode material can be obtained.

[Production method of lithium ion secondary battery]
The lithium ion secondary battery of the present invention may be any of a cylindrical type, a laminated type, a coin type, a card type, and the like, and is not particularly limited. As an example, a method for manufacturing a laminated type lithium ion secondary battery will be described below. .

(1) Method for Producing Positive Electrode A conductive material such as acetylene black and fibrous carbon is added to and mixed with the olivine positive electrode material produced as described above. The olivine positive electrode material used in the present invention has a high specific surface area and a high liquid absorption property of an organic solvent used for electrode preparation. For this reason, N-methyl-2-pyrrolidinone (hereinafter abbreviated as NMP), which is an organic solvent, is mixed with the positive electrode active material in advance to absorb NMP in the positive electrode active material, and then the conductive material is dispersed in the positive electrode active material. Let Thereafter, a binder dissolved in a solvent such as NMP is added to the mixture and kneaded to obtain a positive electrode slurry. Here, a mixed binder obtained by heating and mixing PVDF and polyamide in the range of 140 to 190 ° C. is used as the binder. Next, after apply | coating this slurry on aluminum metal foil, it dries and produces a positive electrode plate.

(2) Method for Fabricating Negative Electrode A conductive material such as acetylene black and carbon fiber is added to and mixed with an amorphous carbon material that is a negative electrode active material. To this, PVDF or a rubber binder (SBR or the like) dissolved in NMP is added as a binder and then kneaded to obtain a negative electrode slurry. Next, after apply | coating this slurry on copper foil, it dries and produces a positive electrode plate.

(3) Battery Formation Method The positive electrode and the negative electrode plate are dried after the slurry is applied to both surfaces of the electrode. Further, it is densified by rolling and cut into a desired shape to produce an electrode. Next, lead pieces for passing a current through these electrodes are formed. A porous insulating material separator is sandwiched between the positive electrode and the negative electrode, wound, and then inserted into a battery can molded of stainless steel or aluminum. Next, after connecting the lead piece and the battery can, a non-aqueous electrolyte is injected, and finally the battery can is sealed to obtain a lithium ion secondary battery.

  In the laminate type battery, the positive electrode and the negative electrode were cut to a width of 83 mm and a height of 115 mm. At that time, the tab (current collector in the uncoated portion where the positive electrode and the negative electrode active material were not applied) to be joined to the current terminal was left 15 mm wide and 4 mm high. An aluminum current terminal was joined to the positive tab portion, and a nickel current terminal was joined to the negative tab portion. The separator was cut several millimeters larger than the electrode. After laminating them, the electrolyte solution was injected, and then an aluminum laminate sheet in which both sides of the aluminum foil were covered with polypropylene or the like was used as an exterior material, which was thermally welded and sealed.

  The laminate type battery was initialized by repeating charge / discharge three times at a rate of 0.3C, and then subjected to a cycle test at a charge / discharge rate of 2C to evaluate the subsequent expansion of the thickness of the laminate type battery. The rate of change obtained by dividing the initial thickness by the thickness after the cycle was defined as “laminate cell thickness expansion coefficient”.

(4) Modularization of a battery As a form using the said lithium ion secondary battery, the lithium ion battery module which connected the some battery in series is mentioned. The battery module using the lithium ion secondary battery of the present invention can be increased in capacity.

(Example)
EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but these examples do not limit the scope of the present invention.

[Example 1]
<Production of olivine cathode material>
Iron oxalate dihydrate, ammonium dihydrogen phosphate, and lithium carbonate, which were finely pulverized for 3 hours in a ball mill, were mixed at a molar ratio of 2: 2: 1.0. The precursor was obtained by calcination in an atmosphere. Thereafter, the precursor and polyvinyl alcohol were mixed and heat-treated for 8 hours in a nitrogen atmosphere at 700 ° C. to obtain an olivine positive electrode material (1) as a carbon-coated LiFePO ₄ positive electrode material. Here, the amount of carbon covered was 4 wt%.

<Specific surface area measurement method>
The olivine positive electrode material (1) was previously dried at 120 ° C., filled in a sample cell, and dried in nitrogen gas at 300 ° C. for 30 minutes. Next, the sample cell was attached to the measurement unit, and the specific surface area was calculated by the BET method after counting signals at the time of desorption with the He / N ₂ mixed gas. As a result, the specific surface area of the secondary particles was 30 m ² / g.

<Method of measuring moisture in positive electrode>
A measurement sample is put in a heating furnace at 150 ° C. in which nitrogen gas is flowed and held for 1 minute. Then, the flowd nitrogen gas is introduced into a measurement cell of a Karl Fischer moisture meter, and moisture is measured. Here, the integrated value up to the titration end point is taken as the moisture content.

<Production method of mixed binder>
Weighed 8 wt% PVDF dissolved in NMP and 5 wt% polyamide solution dissolved in NMP so that the solids weight of the polyamide would be 52 wt% of the total binder solids weight. While this mixture was heated at 160 ° C., the mixture was stirred at 10,000 revolutions using a high speed mixer to obtain a mixing binder.

<Preparation of positive electrode>
Using the olivine positive electrode material (1), a positive electrode plate was prepared by the following procedure. A solution prepared by dissolving the above mixed binder in NMP as a solvent in advance, an olivine cathode material (1), acetylene black as a carbon-based conductive material having an average particle diameter of 35 nm, and vapor-grown fibrous carbon (diameter: 150 nm, fiber length: 10 −20 μm) was mixed to prepare a positive electrode mixture slurry. At this time, the two kinds of conductive materials are equal in weight ratio, and the olivine positive electrode material (1), the carbon-based conductive material, and the binder are expressed in weight percentage ratios, and are mixed in a ratio of 91: 4: 5, respectively. did. This slurry is uniformly applied onto an aluminum sheet having a thickness of 20 μm, dried at 100 ° C., and pressed with a press at about 1.5 ton / cm ² to form a coating film with a thickness of about 60 μm. A positive electrode plate 7 of 2.1 g / cm ³ was obtained. Next, in order to remove moisture from the electrode, vacuum heat treatment was performed at 140 ° C. for 2 hours.

<Evaluation of positive electrode>
The positive electrode plate 7 was punched into φ15, and the counter electrode and the reference electrode were made of metallic lithium to produce a test battery. At this time, a mixed solvent of ethyl carbonate and dimethyl carbonate using 1.0 mol of LiPF ₆ as an electrolyte was used as the electrolytic solution.

This test battery was initialized by repeating charging and discharging at 0.3 C to an upper limit voltage of 3.6 V and a lower limit voltage of 2.0 V three times. Further, after performing constant current and constant voltage charging at an upper limit voltage of 3.6 V for 5 hours at an equivalent of 0.3 C, a constant current discharge was performed up to a lower limit voltage of 2.0 V at an equivalent of 0.3 C to obtain the discharge capacity. . Next, in order to calculate the volumetric energy density of the electrode, the discharge capacity is divided by the mixture weight of the electrode (the total weight of the olivine positive electrode material, conductive material and binder), and then the electrode density 2.1 g / cm ³ and the positive electrode The product of the active material content of 91% by weight was taken as the volume energy density (mAh / cc). This value represents the energy per unit volume and serves as an index for increasing the battery charge. As a result of the electrode evaluation in Example 1, Table 1 shows the specific surface area, electrode density, positive electrode active material content, binder content, polyamide content in the mixed binder, and electrode volume energy density of the olivine Fe positive electrode material.

<Evaluation of water content of positive electrode>
Table 1 shows the results obtained by measuring the Φ15 electrode by the water content evaluation method described above. As a result of the measurement, it was 115 ppm in Example 1.

<Battery expansion evaluation with laminate type battery>
In the laminate type battery, the positive electrode and the negative electrode were cut to a width of 83 mm and a height of 115 mm. At that time, the tab (current collector in the uncoated portion where the positive electrode and the negative electrode active material were not applied) to be joined to the current terminal was left 15 mm wide and 4 mm high. An aluminum current terminal was joined to the positive tab portion, and a nickel current terminal was joined to the negative tab portion. The separator was cut several millimeters larger than the electrode. After laminating them, the electrolyte solution was injected, and then an aluminum laminate sheet in which both sides of the aluminum foil were covered with polypropylene or the like was used as an exterior material, which was thermally welded and sealed.

  The laminate type battery was initialized by repeating charge / discharge three times at a rate of 0.3 C, then subjected to a cycle test at a charge and discharge rate of 2 C, and the results of evaluating the subsequent expansion of the thickness of the laminate type battery are shown in Table 1. Shown in As a result, in Example 1, the laminate cell thickness expansion coefficient was 3%.

<Cylindrical battery evaluation>
In order to produce a cylindrical battery, the positive electrode plate 7 using the olivine positive electrode material (1) was cut to a coating width of 5.4 cm and a coating length of 60 cm, and an aluminum foil lead piece was welded to take out the current. A positive electrode plate was produced.

  Next, in order to produce a cylindrical battery in combination with the positive electrode plate, a negative electrode plate was produced. A negative electrode mixture slurry was prepared by dissolving and mixing the graphite carbon material of the negative electrode active material in NMP of the binder. At this time, the dry weight ratio of the graphite carbon material and the binder was set to 92: 8. This slurry was uniformly applied to a 10 μm rolled copper foil. Then, it was compressed and shaped by a roll press machine, cut to a coating width of 5.6 cm and a coating length of 64 cm, and a copper foil lead piece was welded to prepare a negative electrode plate.

A cylindrical battery schematically shown in FIG. 2 was produced by the following procedure using the positive electrode plate and the negative electrode plate produced as described above. First, a separator 9 was placed between the positive electrode plate 7 and the negative electrode plate 8 so that they were not in direct contact with each other, and wound to produce an electrode group. At this time, the positive electrode plate lead piece 13 and the negative electrode plate lead piece 11 were positioned on the opposite end surfaces of the electrode group. Further, the arrangement of the positive electrode plate 7 and the negative electrode plate 8 prevents the positive electrode mixture application portion from protruding from the negative electrode mixture application portion. The separator 9 used here was a microporous polypropylene film having a thickness of 25 μm and a width of 5.8 cm. Next, the electrode group was inserted into a battery can 10 made of SUS, the negative electrode plate lead piece 11 was welded to the bottom of the can, and the positive electrode lead piece 13 was welded to the sealing lid portion 12 also serving as a positive electrode current terminal. In a battery can 10 in which this electrode group is arranged, 1.0 mol / liter LiPF ₆ was dissolved in a mixed solvent of 1: 2 by volume ratio of nonaqueous electrolyte (ethylene carbonate (EC) and dimethyl carbonate (DMC)). After that, the sealing lid portion 12 to which the packing 15 was attached was caulked and sealed to the battery can 10 to obtain a cylindrical battery having a diameter of 18 mm and a length of 65 mm. Here, the sealing lid portion 12 has a cleavage valve that cleaves when the pressure in the battery rises to release the pressure inside the battery, and an insulating plate 14 is disposed between the sealing lid portion 12 and the electrode group.

  This small cylindrical battery was initialized by repeating charging and discharging at 0.3 C up to an upper limit voltage of 3.6 V and a lower limit voltage of 2.0 V three times. Further, charge and discharge were performed up to an upper limit voltage of 3.6 V and a lower limit voltage of 2.0 V at 0.3 C, and the battery discharge capacity was measured. The battery capacity was 1.3 Ah.

  As described above, the cylindrical battery using the positive electrode plate 7 was able to output the battery at a high output.

  Next, 10 batteries were connected in series to obtain a battery module with high output.

[Example 2]
In <Method for producing mixed binder> in Example 1, the polyamide was weighed so that the solid content weight of the polyamide was 38% by weight of the total binder solid content weight. The binder mixing method, electrode preparation method, and battery evaluation method were performed in the same manner as in Example 1. As a result of evaluating the electrode volume energy density, it was 267 mAh / cc. These results are shown in Example 2 of Table 1.

Example 3
In <Method for producing mixed binder> in Example 1, the polyamide was weighed so that the solid content weight of the polyamide was 70% by weight of the total binder solid content weight. The binder mixing method, electrode preparation method, and battery evaluation method were performed in the same manner as in Example 1. As a result of evaluating the electrode volume energy density, it was 267 mAh / cc. These results are shown in Example 3 of Table 1.

[Comparative Example 1]
In Example 1, an electrode was produced using only a PVDF binder. Here, it is the same as that of Example 1 except that the vacuum heat treatment was performed at 120 ° C. for 2 hours by the vacuum heat treatment of the electrode manufacturing method. The battery evaluation method was performed in the same manner as in Example 1. As a result of evaluating the electrode volume energy density, it was 222 mAh / cc. As a result of observing the electrode, peeling was observed. Moreover, as a result of evaluating the positive electrode containing water content similarly to Example 1, it was 300 ppm. Furthermore, as a result of evaluating the laminate cell thickness expansion rate in the same manner as in Example 1, it expanded at 13%. These results are shown in Comparative Example 1 of Table 1.

[Comparative Example 2]
In <Method for producing mixed binder> in Example 1, the polyamide was weighed so that the solid weight of the polyamide was 21% by weight of the total solid weight of the binder. The method for mixing the binder was the same as in Example 1. Here, it is the same as that of Example 1 except that the vacuum heat treatment was performed at 120 ° C. for 2 hours by the vacuum heat treatment of the electrode manufacturing method. The battery evaluation method was performed in the same manner as in Example 1. As a result of evaluating the electrode volume energy density, it was 231 mAh / cc. As a result of observing the electrode, peeling was observed. Further, the positive electrode-containing water content was evaluated in the same manner as in Example 1. As a result, it was 290 ppm. Furthermore, as a result of evaluating the laminate cell thickness expansion rate in the same manner as in Example 1, it expanded at 12%. These results are shown in Comparative Example 2 of Table 1.

[Comparative Example 3]
In Example 1, an electrode was produced using only a polyamide binder. Here, the electrode preparation method and the battery evaluation method were performed in the same manner as in Example 1, and the electrode volume energy density was evaluated. As a result, it was 225 mAh / cc. As a result of observing the electrodes, cracks were observed. These results are shown in Comparative Example 3 of Table 1.

  The polyamide binder weight percentage in the mixed binders of Examples 1, 2, 3 and Comparative Examples 1, 2, 3 is shown in FIG. Here, the vertical axis is normalized by the volume energy density of Example 1.

Example 4
In <Preparation of Positive Electrode> in Example 1, the olivine positive electrode material (1), the carbon-based conductive material, and the binder were mixed in a weight percentage ratio of 93: 3: 4, respectively. The electrode preparation method and the battery evaluation method were performed in the same manner as in Example 1. As a result of evaluating the electrode volume energy density, it was 290 mAh / cc. As a result of evaluating the water content of the positive electrode in the same manner as in Example 1, it was 117 ppm. Furthermore, as a result of evaluating the laminate cell thickness expansion rate in the same manner as in Example 1, it expanded at 3%. Moreover, it was 1.4 Ah as a result of producing a 18650 type battery similarly to Example 1, and measuring a battery capacity. These results are shown in Example 4 of Table 1.

[Comparative Example 5]
In <Preparation of positive electrode> in Example 1, the electrode density was 2.3 g / cc, and other electrode preparation methods and battery evaluation methods were performed in the same manner as in Example 1. As a result of evaluating the electrode volume energy density, 150 mAh / Cc. As a result of observing the electrode, peeling was observed. These results are shown in Comparative Example 5 of Table 1.

[Comparative Example 6]
In <Preparation of Positive Electrode> in Example 1, the olivine positive electrode material (1), the carbon-based conductive material and the binder were mixed in a weight percentage ratio of 94: 1: 5. The electrode preparation method and the battery evaluation method were performed in the same manner as in Example 1. As a result of evaluating the electrode volume energy density, it was 120 mAh / cc. Peeling was observed on the electrode. These results are shown in Comparative Example 6 of Table 1.

[Comparative Example 7]
In <Production of olivine positive electrode material> of Example 1, an olivine positive electrode material was produced under the same conditions except that the firing temperature was 680 ° C. for 20 hours. It was 40 m < ² > / g as a result of measuring a specific surface area. The electrode preparation method and the battery evaluation method were performed in the same manner as in Example 1. As a result of evaluating the electrode volume energy density, it was 120 mAh / cc. Since an olivine cathode material having a large specific surface area was used, peeling was observed on the electrode. Further, because of the high specific surface area positive electrode material, the electrode density increased only to 1.7 g / cc. These results are shown in Comparative Example 7 of Table 1.

Example 5
In <Production of olivine positive electrode material> in Example 1, the olivine positive electrode material was produced under the same conditions except that the firing temperature was 750 ° C. for 8 hours. It was 10 m < ² > / g as a result of measuring a specific surface area. The electrode preparation method and the battery evaluation method were performed in the same manner as in Example 1. As a result of evaluating the electrode volume energy density, it was 258 mAh / cc. These results are shown in Example 5 of Table 1.

[Comparative Example 8]
In <Production of olivine positive electrode material> of Example 1, an olivine positive electrode material was produced under the same conditions except that the firing temperature was 760 ° C. for 20 hours. It was 9 m < ² > / g as a result of measuring a specific surface area. The electrode preparation method and the battery evaluation method were performed in the same manner as in Example 1. As a result of evaluating the electrode volume energy density, it was 210 mAh / cc. In the case of the olivine positive electrode material, the reactivity is improved at a high specific surface area and a high discharge capacity is obtained. Therefore, the discharge capacity cannot be obtained with a positive electrode material having a low specific surface area. These results are shown in Comparative Example 8 of Table 1.

  As a result, as shown in Table 1, although good results were obtained in the respective examples, there were some items in which sufficient characteristics could not be obtained in the comparative examples.

Example 6
In <Preparation of Positive Electrode> in Example 1, acetylene black and vapor-grown fibrous carbon were used as the carbon-based conductive material. An electrode was prepared using MWCNT having an average diameter of 10 to 150 nm and an average length of 1 to 10 μm instead of the fibrous carbon. The battery evaluation method was performed in the same manner as in Example 1. As a result of evaluating the electrode volume energy density, it was 282 mAh / cc. The results are shown in Example 7 in Table 1.

Example 7
It was prepared olivine cathode material represented by the composition formula LiMn _0.8 Fe _0.2 PO ₄ below in place of the Example 1 <Preparation of olivine cathode material>.

Mixing 7.2 g NH ₄ H ₂ PO ₄ , 2.27 g LiOH.H ₂ O, 9 g MnC ₂ O ₄ .2H ₂ O, and 2.25 g FeC ₂ O ₄ .2H ₂ O Then, sucrose was added to 12% by mass, and zirconia grinding balls were put into a zirconia pot and mixed using a planetary ball mill. This mixed powder was put into an alumina crucible and calcined at 400 ° C. for 10 hours under an argon flow of 0.3 L / min.

The obtained calcined product was once crushed in an agate mortar, charged again into an alumina crucible, and subjected to main firing at 700 ° C. for 10 hours under an argon flow of 0.3 L / min. After the main firing, the obtained powder was crushed in an agate mortar, and the particle size was adjusted with a 40 μm mesh sieve to obtain a material represented by the composition formula LiMn _0.8 Fe _0.2 PO ₄ .

Next, the same positive electrode as Example 1 was produced. Since LiMn _0.8 Fe _0.2 PO ₄ has a lower true density than the LiFePO ₄ positive electrode material, the electrode density was 1.95 g / cc. Further, as a result of battery evaluation as in Example 1, the electrode volume energy density was 262 mAh / cc.

  ADVANTAGE OF THE INVENTION According to this invention, the highly safe large sized lithium secondary battery suitable for the apparatus application which needs high capacity | capacitance, such as an electric vehicle and a plug-in hybrid vehicle, can be provided.

7 Positive electrode plate 8 Negative electrode plate 9 Separator 10 Battery can 11 Negative electrode plate lead piece 12 Sealing lid 13 Positive electrode plate lead piece 14 Insulating plate 15 Packing

Claims (5)

Composite oxide having an olivine structure represented by the chemical formula Li _a M _x PO ₄ (0 <a ≦ 1.2, 0.9 ≦ x ≦ 1.1, where M is a transition metal containing either Fe or Mn) In the positive electrode for a non-aqueous lithium ion secondary battery comprising at least a positive electrode active material, a conductive material and a binder,
The positive electrode active material content in the positive electrode is 91% or more and 93% or less by weight percentage, the specific surface area of the positive electrode active material is 10-30 m ² / g, and
The conductive material contains fibrous carbon;
The binder is a mixture of polyvinylidene fluoride and polyamide, and the content in the positive electrode is 3% or more and 6% or less by weight percentage,
The weight percentage of polyamide in the mixture of polyvinylidene fluoride and polyamide is 38% or more and 70% or less,
A positive electrode for a non-aqueous lithium ion secondary battery, wherein the density of the positive electrode is 1.9 g / cc or more and 2.2 g / cc or less.   2. The positive electrode for a non-aqueous lithium ion secondary battery according to claim 1, wherein the content of fibrous carbon in the total conductive material of the positive electrode is 20% or more and 60% or less by weight percentage. Positive electrode for lithium ion secondary battery.   3. A lithium ion secondary battery using the positive electrode for a nonaqueous lithium ion secondary battery according to claim 1 or 2, wherein the energy density is 100 Wh / Kg or more and 150 Wh / Kg or less. Next battery.   3. A laminate-type lithium ion secondary battery using the positive electrode for a non-aqueous lithium ion secondary battery according to claim 1 or 2, wherein the battery swells after 50 cycles of a cycle test with a charge / discharge rate of 3C. Is a laminate type lithium ion secondary battery characterized by having a thickness of 10% or less of the initial thickness.   A battery module comprising a plurality of non-aqueous lithium ion secondary batteries according to claim 3 and / or a laminate type lithium ion secondary battery according to claim 4 electrically connected thereto.

Images