JP4895625B2 - Lithium secondary battery - Google Patents

Description

The present invention relates to a lithium secondary battery, and in particular, in a lithium secondary battery using a positive electrode active material having a large electrical resistance, such as lithium iron phosphate having an olivine structure represented by LiFePO ₄ , charging with a large current. It is characterized in that the discharge cycle characteristics are improved.

  In recent years, secondary batteries have been used as power sources for electronic devices. Especially, as a new secondary battery with high output and high energy density, non-aqueous electrolyte is used and lithium ions are moved between the positive and negative electrodes. Rechargeable lithium secondary batteries have come to be used.

In such a lithium secondary battery, lithium cobaltate LiCoO ₂ is generally used as the positive electrode active material in the positive electrode, and carbon capable of occluding and releasing lithium metal, a lithium alloy, and lithium in the negative electrode active material in the negative electrode. Material is used.

However, Co used for the positive electrode active material LiCoO ₂ has a limited reserve and is a scarce resource, and thus has a problem of high production costs. In addition, in the case of a lithium secondary battery using LiCoO ₂ as a positive electrode active material, there is a problem that the thermal stability is greatly reduced at a high temperature that cannot be considered in a normal use state in a charged state.

Therefore, in recent years, the use of lithium-containing metal composite oxides such as lithium spinel manganate LiMn ₂ O ₄ and LiNiCoMnO ₂ as a positive electrode active material in place of LiCoO ₂ has been studied.

However, when LiMn ₂ O ₄ is used as the positive electrode active material, it is difficult to obtain a sufficient discharge capacity, and when the battery temperature increases, there are problems such as dissolution of Mn in this LiMn ₂ O _4. It was. Further, when LiNiCoMnO ₂ is used as the positive electrode active material, there is a problem similar to that when LiCoO ₂ is used.

For this reason, in recent years, lithium secondary batteries using lithium iron phosphate having an olivine structure represented by LiFePO _4, which is rich in resources and excellent in thermal stability, are used as a positive electrode active material. It has been proposed (for example, see Patent Documents 1 and 2).

However, lithium iron phosphate having an olivine type structure has a problem that the electrical resistance is higher than that of the above-described LiCoO ₂ , LiMn ₂ O ₄ , LiNiCoMnO _{2, and the} like, and the electrical resistance value at the positive electrode is increased.

In particular, in a lithium secondary battery in which an electrode body wound with a separator interposed between a long positive electrode and a long negative electrode is housed in a battery container together with a non-aqueous electrolyte, the above phosphorous is used. When a positive electrode active material with high electrical resistance such as lithium iron oxide is used, charging and discharging with a large current causes the current to concentrate in a place where the reaction is likely to occur inside the electrode body, resulting in a non-uniform reaction. When charging / discharging is repeated, there is a problem that the materials in the positive electrode and the negative electrode gradually deteriorate locally, the operating voltage decreases, and the battery capacity decreases.
JP 2000-509193 A JP 2002-110162 A

  An object of the present invention is to solve the above problems in a lithium secondary battery using a positive electrode active material having a large electric resistance such as lithium iron phosphate having an olivine type structure, In a lithium secondary battery in which an electrode body wound with a separator interposed between a long positive electrode and a long negative electrode is housed in a battery container together with a non-aqueous electrolyte, charging and discharging are performed with a large current. When it repeats, it makes it a subject to suppress the material in a positive electrode or a negative electrode gradually degrading locally, and to improve the charging / discharging cycling characteristics in a large current.

In the present invention, in order to solve the above-described problems, a long positive electrode having a positive electrode layer containing a positive electrode active material capable of inserting and extracting lithium, and a negative electrode active material capable of inserting and removing lithium A positive electrode current collector provided in the above positive electrode by accommodating a wound electrode body together with a non-aqueous electrolyte in a battery container with a separator interposed between a long negative electrode formed with a negative electrode layer containing the tab in connection to the lithium secondary battery was a negative electrode external terminal, olivine Rutotomoni provided in the longitudinal direction both end portions of at least the negative electrode a negative electrode current collector tabs above SL, a positive electrode active material in the positive electrode layer is represented by LiFePO ₄ It is characterized by being lithium iron phosphate having a mold structure.

  The position of the negative electrode current collecting tab is not necessarily strictly limited to both ends in the longitudinal direction, and may be positioned on the winding start side and the winding end side of the electrode body. However, when the positive electrode and the negative electrode are wound with a separator interposed, the positive electrode active material cannot be present in the positive electrode portion where the negative electrode current collecting tab faces. This is because when the positive electrode active material is present in the positive electrode portion facing the negative electrode current collecting tab, lithium separated from the positive electrode active material during charging is inserted into the negative electrode active material in the vicinity of the negative electrode current collecting tab. This is because lithium that has not been inserted into the negative electrode active material precipitates on the negative electrode, causing an internal short circuit and a decrease in capacity. Therefore, a technique for surely positioning the negative electrode current collecting tab on the opposite surface where the positive electrode active material is not applied is required in addition to a decrease in capacity due to a decrease in the application portion of the positive electrode active material. For the above reasons, the negative electrode current collecting tab is preferably provided at a portion not facing the positive electrode, that is, at both ends in the longitudinal direction.

Here, as the positive electrode active material in the positive electrode layer, for example, lithium iron phosphate having an olivine structure represented by LiFePO ₄ is used. In addition, the surface of lithium iron phosphate is coated with carbon, or at least one element selected from B, F, Mg, Al, Ti, Cr, V, Fe, Cu, Zn, Nb, Zr, and Sn. For example, lithium iron phosphate can be used. Furthermore, the present invention is not limited to the case where lithium iron phosphate is used as the positive electrode active material, and is effective for the positive electrode in which the electric resistance value of the positive electrode layer is in the above range.

Further, when a positive electrode active material having a large electric resistance such as lithium iron phosphate having an olivine structure represented by LiFePO ₄ is used, the electric resistance value in the positive electrode layer is adjusted to a range of 3000Ω / cm to 50000Ω / cm. In doing so, a conductive agent is contained in the positive electrode layer, and it is preferable to use fibrous carbon as the conductive agent. This is because, when acetylene black or ketjen black is used as a conductive agent, it is necessary to add a large amount of these conductive agents in order to adjust the electrical resistance value in the positive electrode layer to the above range. Is difficult to form by coating, and the ratio of the positive electrode active material in the positive electrode layer decreases, so that a sufficient battery capacity cannot be obtained. In contrast, when fibrous carbon is used as the conductive agent, the electrical resistance value in the positive electrode layer can be reduced with a small amount compared to acetylene black or ketjen black, and the positive electrode layer can be easily formed by coating. In addition, the ratio of the positive electrode active material in the positive electrode layer is also prevented from decreasing, and a sufficient battery capacity can be obtained. In addition, as said fibrous carbon, favorable electronic conductivity is obtained, for example, when the average fiber diameter is in the range of 50 nm to 300 nm and the fiber length is in the range of 5 μm to 100 μm.

  Here, when adding fibrous carbon to the positive electrode layer as a conductive agent, if the amount of fibrous carbon added is small, the electrical resistance value in the positive electrode layer cannot be sufficiently reduced, while the amount added is large. If the amount is too large, it becomes difficult to form the positive electrode layer by coating, and the ratio of the positive electrode active material in the positive electrode layer decreases, so that a sufficient battery capacity cannot be obtained. For this reason, it is preferable to make the quantity of the fibrous carbon added in a positive electrode layer into the range of 6 wt%-20 wt%.

  In addition, if the thickness of the positive electrode layer becomes too thick, the diffusion of lithium ions in the positive electrode layer becomes slow and the reaction becomes non-uniform. Therefore, the thickness of the positive electrode layer is preferably 100 μm or less.

  The negative electrode active material used for the negative electrode is not particularly limited. For example, it is alloyed with a carbon material such as natural graphite, artificial graphite, non-graphitizable carbon, or coke, or Li such as Si or Sn. In addition, in order to obtain a high battery voltage in a wide area, graphite is mainly used as a negative electrode active material. Is preferred.

  Further, in the case where the negative electrode current collecting tab is provided at least at both ends in the longitudinal direction of the negative electrode, if the length of the negative electrode becomes too long, the non-uniformity of the reaction in the length direction becomes large. The length is preferably 100 cm or less.

  In addition, the positive electrode current collecting tab is preferably provided in the center portion rather than the longitudinal end portion of the positive electrode, and if the length between the positive electrode current collecting tabs is too long, the reaction in the length direction is highly uneven. Become. When the length of the positive electrode in the longitudinal direction is within 200 cm, it is preferable to have at least one positive electrode current collecting tab required when the positive electrode length / 100 cm is exceeded. Further, when there is one positive current collecting tab, it is preferably provided at the center in the longitudinal direction of the positive electrode. .

  Examples of the non-aqueous solvent used in the non-aqueous electrolyte include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, A mixture of one or more chain carbonates such as ethylpropyl carbonate can be used.

  Examples of the solute used in the non-aqueous electrolyte include lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and lithium-bis (oxalato). Lithium compounds such as borates can be used.

  In the lithium secondary battery according to the present invention, the negative electrode current collecting tabs in the long negative electrode in which the negative electrode layer containing the negative electrode active material capable of inserting and removing lithium is provided at both ends in the longitudinal direction of the negative electrode. In the case of a long positive electrode having a positive electrode layer containing a positive electrode active material capable of inserting and desorbing lithium, the negative electrode even when the electric resistance value of the positive electrode layer is in the range of 3000Ω / cm to 50000Ω / cm Charging / discharging is performed through the negative electrode current collecting tabs provided in FIG.

  As a result, in the lithium secondary battery according to the present invention, even when charging and discharging are repeatedly performed with a large current, local deterioration of the material in the positive electrode and the negative electrode is suppressed, and the operating voltage is lowered. The capacity is prevented from decreasing, and the charge / discharge cycle characteristics at a large current are improved.

  Next, the lithium secondary battery according to the embodiment of the present invention will be described in detail. In the lithium secondary battery according to this embodiment, even when charging and discharging are repeated with a large current, the operating voltage is high. It will be clarified by a comparative example that the decrease is suppressed and the charge / discharge cycle characteristics at a large current are improved. In addition, the lithium secondary battery in this invention is not limited to what was shown in the following Example, It can implement by changing suitably in the range which does not change the summary.

Example 1
In Example 1, when producing a positive electrode, lithium iron phosphate LiFePO ₄ having an olivine structure was used as a positive electrode active material.

Here, in producing LiFePO ₄ as the positive electrode active material, iron phosphate octahydrate Fe ₃ (PO ₄ ) ₂ .8H ₂ O and lithium phosphate Li ₃ (PO ₄ ) ₃ were mixed at a ratio of 1: 1. This mixture and a stainless steel ball having a diameter of 1 cm are put into a stainless steel pot having a diameter of 10 cm and mixed for 12 hours under the conditions of a revolution radius of 30 cm, a revolution speed of 150 rpm, and a rotational speed of 150 rpm. It was. Thereafter, this mixture was baked in an electric furnace in a non-oxidizing atmosphere at a temperature of 600 ° C. for 10 hours to obtain the above LiFePO ₄ powder.

Then, N-methyl-2 in which LiFePO ₄ powder as the positive electrode active material, fibrous carbon (fiber diameter: 150 nm, fiber length: 5 to 20 μm) as a conductive agent, and polyvinylidene fluoride as a binder are dissolved. The pyrrolidone solution was adjusted so that the weight ratio of the positive electrode active material, the conductive agent and the binder was 87: 10: 3, and these were kneaded to prepare a positive electrode slurry.

  Next, this positive electrode slurry is applied to both surfaces of a positive electrode current collector made of aluminum foil, dried, and rolled with a rolling roller. As shown in FIG. 1, positive electrode layers 1b are formed on both surfaces of the positive electrode current collector 1a. After that, the positive electrode current collecting tab 1c was attached to the central portion of the positive electrode current collector 1a on which the positive electrode layer 1b was not formed to produce a long positive electrode 1. The length of the positive electrode 1 was 70 cm, and the thickness of the positive electrode layer 1b on one side was 68 μm.

  Here, in measuring the electrical resistance value A [Ω / cm] of the positive electrode layer 1b in the positive electrode 1 as described above, as shown in FIG. 2, a pair of terminals t1 and t2 are placed on the surface of the positive electrode layer 1b at a required interval. The electrical resistance X [Ω] between the pair of terminals t1 and t2 was measured with a resistance measuring instrument (MCP-T600 manufactured by Mitsubishi Chemical Corporation). In this case, as shown in FIG. 2, the current flows through the positive electrode layer 1b and the positive electrode current collector 1a whose electric resistance is significantly lower than that of the positive electrode layer 1b. Therefore, the electric resistance value A [Ω / cm] of the positive electrode layer 1b is The electric resistance X [Ω] and the thickness d [cm] of the positive electrode layer 1b on one side were calculated by the following formula. In addition, since the electrical resistance of the positive electrode current collector 1a was significantly lower than that of the positive electrode layer 1b as described above, it was negligible.

  A [Ω / cm] = X [Ω] ÷ d [cm] / 2

As a result, the electrical resistance value A of the positive electrode layer 1b using LiFePO ₄ as the positive electrode active material was 9300 Ω / cm.

  In preparing the negative electrode, the negative electrode active material graphite, the binder styrene butadiene rubber, and the thickener carboxymethyl cellulose dissolved in the aqueous solution, the negative electrode active material, the binder and the thickener. The weight ratio was adjusted to 98: 1: 1, and these were kneaded to prepare a negative electrode slurry.

  Next, this negative electrode slurry is applied to both sides of a negative electrode current collector made of copper foil, dried, and rolled with a rolling roller. As shown in FIG. 3, a negative electrode layer 2b is formed on both sides of the negative electrode current collector 2a. After forming the negative electrode current collector tab 2c, the negative electrode current collector tab 2c was attached to both ends of the negative electrode current collector 2a on which the negative electrode layer 2b was not formed to produce a long negative electrode 2. The length of the negative electrode 2 was 77 cm, and the thickness of the negative electrode layer 2b on one side was 48 μm.

  Then, a polyethylene separator 3 was sandwiched between the negative electrode 2 and the positive electrode 1, and these were wound up to produce an electrode body 10. In this case, the negative electrode current collecting tab 2c is positioned at the winding start portion and the winding end portion of the electrode body 10.

As the non-aqueous electrolyte, a non-aqueous electrolyte in which LiPF ₆ is dissolved in a mixed solvent in which ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1: 1 so as to have a concentration of 1 mol / liter. Was used.

  Then, as shown in FIG. 4, the electrode body 10 wound up as described above is inserted into the battery can 21 of the battery container 20, and the two negative electrode current collecting tabs 2 c in the negative electrode 2 are overlapped to overlap the negative electrode exterior. While welding to the bottom part of the battery can 21 used as the terminal, the positive electrode current collecting tab 1c in the positive electrode 1 was ultrasonically welded to the sealing body 22 used as the positive electrode external terminal, vacuum-treated at 110 ° C. for 2 hours, In the atmosphere, the non-aqueous electrolyte is poured into the battery can 20 and caulked with the insulating packing 23 sandwiched between the battery can 21 and the sealing body 22, and a cylindrical 18650 size having a capacity of about 1 Ah. A lithium secondary battery was produced.

(Comparative Example 1)
In Comparative Example 1, in the production of the negative electrode 2 in Example 1 described above, the negative electrode current collector tab 2c was attached only to one end of the negative electrode current collector 2a, and the negative electrode current collector tab 2c was wound around the electrode body 10 described above. A lithium secondary battery of Comparative Example 1 was produced in the same manner as in Example 1 except that it was positioned at the end portion.

(Reference Example 1)
In Reference Example 1, Li _1.1 Mn _1.895 Al _0.005 O, which is a lithium manganate having a spinel structure with LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as a positive electrode active material in producing the positive electrode 1. N-methyl-2-pyrrolidone solution in which the positive electrode active material, the conductive carbon fiber, and the polyvinylidene fluoride binder are dissolved, using a mixture of ₄ and _{4 in} a weight ratio of 1: 1. And a positive electrode slurry in which the weight ratio of the positive electrode active material, the conductive agent, and the binder is adjusted to 94: 3: 3, the length is 67 cm, and the positive electrode layer 1b on one side has a thickness of 60 μm. 1 was produced. As for the positive electrode 1, as in the case of Example 1, the electrical resistance value A [Ω / cm] of the positive electrode layer 1b was measured. As a result, the electrical resistance value A of the positive electrode layer was 1800 Ω / cm. Met.

  Further, in the production of the negative electrode 2, the negative electrode current collector tab 2 c is attached only to one end of the negative electrode current collector 2 a, and the negative electrode current collector tab 2 c is wound around the electrode body 10, as in Comparative Example 1 above. It was located at the end.

  Except for these, the lithium secondary battery of Reference Example 1 was produced in the same manner as in Example 1 above. The lithium secondary battery of Reference Example 1 had a capacity of about 1.2 Ah.

  Next, the lithium secondary batteries of Example 1 and Comparative Example 1 were charged to 4.2 V with a constant current of 1 A, respectively, and then charged at a constant voltage of 4.2 V until the current reached 50 mA. The battery was discharged to 2.0 V at a constant current of 10 A, and this was regarded as one cycle, and 200 cycles of charging and discharging were repeated to obtain discharge curves at 1 cycle and 200 cycles. The results are shown in FIG. The amount of decrease in operating voltage during the cycle was determined and the results are shown in Table 1 below.

  In addition, for the lithium secondary battery of Reference Example 1 described above, after charging to 4.2 V with a constant current of 1 A, constant voltage charging of 4.2 V was performed until the current reached 50 mA, and then a constant current of 10 A. The battery was discharged to 2.5V, and this was regarded as one cycle, and 200 cycles of charge / discharge were repeated. The discharge curves at the 1st cycle and the 200th cycle were obtained. The results are shown in FIG. The amount of decrease was determined and the results are shown in Table 1 below.

  As a result, when comparing the lithium secondary batteries of Example 1 and Comparative Example 1 using the positive electrode layer 1b having a high electrical resistance value A of 9300 Ω / cm, the negative electrode current collecting tab 2c is In the lithium secondary battery of Example 1 provided at both ends of the negative electrode 2 so as to be positioned at the end of winding, one end of the negative electrode 2 is positioned so that the negative electrode current collecting tab 2 c is positioned only at the end of winding of the electrode body 10. Compared with the lithium secondary battery of Comparative Example 1 provided only in the part, the decrease in the operating voltage at the time of 200 cycles was greatly reduced.

  On the other hand, in the lithium secondary battery of Reference Example 1 using the positive electrode layer 1b having a low electric resistance A of 1800 Ω / cm, the negative electrode 2 is arranged so that the negative electrode current collecting tab 2c is positioned only at the end of winding of the electrode body 10. Even when it was provided only at one end, the decrease in operating voltage was small. Further, in Reference Example 1, even when the negative electrode current collecting tab 2c is provided at both ends of the negative electrode 2 so as to be positioned at the winding start portion and the winding end portion of the electrode body 10, the operating voltage decreases by one. When there is almost no change and the electrical resistance value A is low, even if the negative electrode current collecting tab 2c is provided at both ends of the negative electrode 2, a decrease in operating voltage when charging / discharging is repeated with a large current is suppressed. The effect was not obtained.

  As a result, when the positive electrode layer 1b having a high electric resistance A is used as in the lithium secondary batteries of Example 1 and Comparative Example 1 described above, the negative electrode current collecting tab 2c is It was found that an excellent effect can be obtained when it is provided at both ends of the negative electrode 2 so as to be positioned at the end of winding.

  Next, for each of the lithium secondary batteries of Example 1, Comparative Example 1, and Reference Example 1, the battery temperature increased during the discharge of 10 A before and after the above charge / discharge cycle, respectively. The results are shown in Table 2 below.

  As a result, only the lithium secondary battery of Comparative Example 1 had an increase in battery temperature during discharge after the charge / discharge cycle. This is because, in the case of the lithium secondary battery of Comparative Example 1, non-uniform reaction occurs inside the electrode body 10, and when charging and discharging are repeated with a large current, the materials in the positive electrode 1 and the negative electrode 2 gradually become locally. This is probably because the battery resistance has increased due to deterioration.

  As a result, when the positive electrode layer 1b having a high electric resistance A is used as in the lithium secondary batteries of Example 1 and Comparative Example 1 described above, the negative electrode current collecting tab 2c is placed at the end of winding of the electrode body 10. However, as charging and discharging are repeated with a large current, the material in the positive electrode and the negative electrode is locally deteriorated due to non-uniform reaction, and the battery resistance increases. When it was provided at both ends of the negative electrode 2 so as to be positioned at the winding start portion and the winding end portion of 10, the reaction non-uniformity inside the electrode body was suppressed, and charging and discharging were repeated with a large current. Later, it was found that the operating voltage did not decrease and showed excellent characteristics.

(Example 2)
In Example 2, in preparation of positive electrode 1 in Example 1 above, LiFePO ₄ powder as a positive electrode active material, fibrous carbon (fiber diameter: 150 nm, fiber length: 5 to 20 μm) as a conductive agent, binding The positive electrode slurry was prepared so that the weight ratio of the positive electrode active material, the conductive agent and the binder was 82: 15: 3 with the N-methyl-2-pyrrolidone solution in which the polyvinylidene fluoride as the agent was dissolved. Otherwise, the lithium secondary battery of Example 2 was fabricated in the same manner as in Example 1 above. In addition, with respect to the positive electrode 1 manufactured as described above, the electrical resistance value A [Ω / cm] of the positive electrode layer 1b was measured in the same manner as in Example 1 above. The resistance value A was 4300 Ω / cm.

(Comparative Example 2)
In Comparative Example 2, in preparation of positive electrode 1 in Example 1 above, LiFePO ₄ powder as a positive electrode active material, fibrous carbon as a conductive agent (fiber diameter: 150 nm, fiber length: 5 to 20 μm), binding The positive electrode slurry was prepared by adjusting the weight ratio of the positive electrode active material, the conductive agent and the binder to 92: 5: 3 with the N-methyl-2-pyrrolidone solution in which the polyvinylidene fluoride as the agent was dissolved. Otherwise, a lithium secondary battery of Comparative Example 2 was produced in the same manner as in Example 1 above. In addition, with respect to the positive electrode 1 manufactured as described above, the electrical resistance value A [Ω / cm] of the positive electrode layer 1b was measured in the same manner as in Example 1 above. The resistance value A was 59800 Ω / cm.

(Comparative Example 3)
In Comparative Example 3, acetylene black was used as the conductive agent in the production of the positive electrode 1 in Example 1 described above, LiFePO ₄ powder as the positive electrode active material, acetylene black as the conductive agent, and polyvinylidene fluoride as the binder. The dissolved N-methyl-2-pyrrolidone solution was used to adjust the positive electrode slurry so that the weight ratio of the positive electrode active material, the conductive agent and the binder was 92: 5: 3. In the same manner as in Example 1, a lithium secondary battery of Comparative Example 3 was produced. In addition, with respect to the positive electrode 1 manufactured as described above, the electrical resistance value A [Ω / cm] of the positive electrode layer 1b was measured in the same manner as in Example 1 above. The resistance value A was 123000 Ω / cm. When acetylene black is used as the conductive agent, adjusting the amount of acetylene black to 10 wt% makes it difficult to adjust the positive electrode slurry, and the positive electrode slurry can be appropriately applied to the positive electrode current collector 1a. It became difficult.

  Next, the lithium secondary batteries of Examples 1 and 2 and Comparative Example 2 were charged to 4.2 V with a constant current of 1 A, respectively, and then charged at a constant voltage of 4.2 V until the current reached 50 mA. Thereafter, the battery was discharged to 2.0 V at a constant current of 10 A to determine the operating voltage at the time of discharge, and the results are shown in Table 2 below.

  As a result, in the lithium secondary battery of Comparative Example 2 in which the electrical resistance value A of the positive electrode layer 1b was 50000 Ω / cm or more, the electron conductivity in the positive electrode 1 was poor and a sufficient operating voltage could not be obtained. .

  In addition, in the lithium secondary battery of each of the above embodiments, even when the number of the positive electrode current collecting tabs 1c in the positive electrode 1 is increased, charging / discharging is performed through each positive electrode current collecting tab 1c. There is a problem that the positive electrode layer 1b is not formed at the position of the positive electrode current collecting tab 1c, the amount of the positive electrode active material in the positive electrode 1 is reduced, and sufficient capacity cannot be obtained.

It is a schematic plan view of the elongate positive electrode produced in the lithium secondary battery which concerns on the Example of this invention. It is the schematic explanatory drawing which showed the state which measures the electrical resistance value of the positive electrode layer in said positive electrode. It is a schematic plan view of the elongate negative electrode produced in the lithium secondary battery which concerns on said Example. It is a schematic sectional drawing of the lithium secondary battery which concerns on said Example. It is the figure which showed the discharge curve in the 1st cycle time and 200th cycle time of the lithium secondary battery which concerns on Example 1 and Comparative Example 1. FIG. It is the figure which showed the discharge curve in the 1st cycle time of the lithium secondary battery which concerns on the reference example 1, and 200th cycle time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 1a Positive electrode collector 1b Positive electrode layer 1c Positive electrode current collection tab 2 Negative electrode 2a Negative electrode current collector 2b Negative electrode layer 2c Negative electrode current collection tab 3 Separator 10 Electrode body 20 Battery container 21 Battery can (negative electrode external terminal)
22 Sealing body (positive electrode external terminal)
23 Insulation packing

Claims (3)

A long positive electrode formed with a positive electrode layer containing a positive electrode active material capable of inserting and extracting lithium, and a long negative electrode formed with a negative electrode layer containing a negative electrode active material capable of inserting and removing lithium An electrode body wound with a separator interposed therebetween is accommodated in a battery container together with a non-aqueous electrolyte, and a positive electrode current collecting tab provided on the positive electrode is connected to a positive electrode external terminal and provided on the negative electrode. in the negative electrode current collector tab a lithium secondary battery was connected to the negative electrode external terminal was, Rutotomoni provided in the longitudinal direction both end portions of at least the negative electrode a negative electrode current collector tabs above SL, a positive electrode active material in the positive electrode layer in LiFePO ₄ A lithium secondary battery characterized by being lithium iron phosphate having an olivine-type structure represented. The lithium secondary battery according to claim 1, wherein the positive electrode layer contains a conductive agent made of fibrous carbon . In the lithium secondary battery as claimed in 請 Motomeko 2. Lithium secondary battery, characterized in that fibrous carbon is contained in the range of 6 wt% 20 wt% in the positive electrode layer.

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