JP5317407B2 - Non-aqueous secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous secondary battery containing lithium vanadium oxide in a negative electrode.

  A conventional non-aqueous secondary battery is disclosed in Patent Document 1. In this non-aqueous secondary battery, a positive electrode and a negative electrode capable of inserting and extracting lithium ions are immersed in a non-aqueous electrolyte. The negative electrode has a negative electrode active material made of lithium vanadium oxide. Since lithium vanadium oxide has poor conductivity, a negative electrode active material, a conductive material, and a binder are mixed and applied onto a current collector to form a negative electrode. As the conductive material, graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder, or the like is used.

  When the non-aqueous secondary battery is charged, the negative electrode is negatively charged, and lithium ions stored in the positive electrode are desorbed and stored in the negative electrode. At the time of discharging the non-aqueous secondary battery, lithium ions stored in the negative electrode are desorbed and stored in the positive electrode. By using lithium vanadium oxide having a large capacity per volume as the negative electrode active material, a non-aqueous secondary battery with high energy density can be obtained.

Japanese Patent Laid-Open No. 2003-68305 (page 3 to page 11, FIG. 10)

  Non-aqueous secondary batteries are widely used in portable electronic devices such as notebook personal computers and mobile phones, and it is desired that the operation time from full charge can be maintained long even when the power consumption of the electronic devices increases. For this reason, a non-aqueous secondary battery capable of obtaining a higher capacity is demanded.

  Further, in the non-aqueous secondary battery disclosed in Patent Document 1, when a carbon material is used as the negative electrode conductive material, the conductive material and lithium may react. As a result, there is a problem that the conductivity is reduced, and a problem that the irreversible capacity is increased due to an increase in contact resistance and the capacity of the nonaqueous secondary battery is reduced.

  In addition, when a metal capable of occluding lithium ions such as silicon is used as the negative electrode conductive material, the conductive material has a higher saturation potential than lithium vanadium oxide, so that the conductive material is more likely to occlude with lithium ions than lithium vanadium oxide. There is a case. Thereby, when the electrolyte solvent is co-inserted with the lithium ions in the conductive material, the conductive material is remarkably expanded and contracted by charge and discharge. For this reason, when a cycle is repeated, there exists a problem that a electrically conductive material will collapse and the capacity | capacitance of a non-aqueous secondary battery will fall.

  In view of the above problems, in the present invention, in a non-aqueous secondary battery using lithium vanadium oxide as a negative electrode active material, the optimum content is found according to the conductive material mixed with the negative electrode active material, and the capacity is increased. An object of the present invention is to provide a nonaqueous secondary battery.

  In order to achieve the above object, the present invention provides a nonaqueous secondary battery comprising a negative electrode formed by applying a negative electrode mixture comprising a negative electrode active material comprising a lithium vanadium oxide, a conductive material, and a binder onto a current collector. In the above, the conductive material has a saturation potential lower than that of lithium vanadium oxide when the lithium ion is occluded when charging / discharging with lithium as a counter electrode, and at the first occlusion and desorption of lithium ion. The reversible efficiency is 50% or more, the reversible capacity is 150 mAh / g or more, and the negative electrode mixture contains 15% by weight or more and 85% by weight or less of the conductive material.

  According to this configuration, charge / discharge characteristics are measured in a test cell in which lithium vanadium oxide is disposed on the positive electrode and metallic lithium is disposed on the negative electrode. The test cell has a saturation potential of, for example, about 0.20 V when the lithium cell is occluded or desorbed. In addition, charge / discharge characteristics are measured in a test cell in which a negative electrode conductive material is disposed on the positive electrode and metal lithium is disposed on the negative electrode. The test cell has a saturation potential lower than that of lithium vanadium oxide having an open potential of, for example, about 0.10 V at the time of insertion and extraction of lithium ions. Furthermore, at the time of the first occlusion and desorption of lithium ions by the latter test cell, the reversible efficiency is 50% or more and the reversible capacity is 150 mAh / g or more. The conductive material is contained in the negative electrode mixture of the negative electrode of the non-aqueous secondary battery in an amount of 15 wt% to 85 wt%.

The present invention also provides a nonaqueous secondary battery having a negative electrode formed by applying a negative electrode mixture comprising a negative electrode active material comprising a lithium vanadium oxide, a conductive material, and a binder onto a current collector. The negative electrode mixture is composed of a metal or a compound that has a volume resistivity of 5 × 10 ⁻⁴ Ω · cm or less and does not occlude lithium ions, and the negative electrode mixture contains 15% by weight or less of the conductive material.

  Further, the present invention is characterized in that the non-aqueous secondary battery having the above-described configuration is provided with an electrolyte containing 5 wt% or more and 50 wt% or less of propylene carbonate.

The present invention also provides a nonaqueous secondary battery having a negative electrode formed by applying a negative electrode mixture comprising a negative electrode active material comprising a lithium vanadium oxide, a conductive material, and a binder onto a current collector. When the lithium ion is charged / discharged, the open potential during occlusion of lithium ions has a lower saturation potential than lithium vanadium oxide, and the reversible efficiency during the first occlusion and desorption of lithium ions is 10%. Or a reversible capacity of 50 mAh / g or less, a specific surface area of 15 m ² / g or more, and the negative electrode mixture containing 10% by weight or more and 15% by weight or less of the conductive material. Here, the specific surface area is obtained by the BET method.

  According to this configuration, charge / discharge characteristics are measured in a test cell in which lithium vanadium oxide is disposed on the positive electrode and metallic lithium is disposed on the negative electrode. The test cell has a saturation potential of, for example, about 0.20 V when the lithium cell is occluded or desorbed. In addition, charge / discharge characteristics are measured in a test cell in which a negative electrode conductive material is disposed on the positive electrode and metal lithium is disposed on the negative electrode. The test cell has a saturation potential lower than that of lithium vanadium oxide having an open potential of, for example, about 0.10 V at the time of insertion and extraction of lithium ions. Furthermore, at the time of first occlusion and desorption of lithium ions, the reversible efficiency is 10% or less or the reversible capacity is 50 mAh / g or less. The negative electrode mixture of the negative electrode of the nonaqueous secondary battery contains 10% by weight to 15% by weight of a conductive material used in the latter test cell.

  According to the present invention, a conductive material having a lower saturation potential than that of lithium vanadium oxide, having a reversible efficiency of 50% or more at the time of first occlusion and desorption of lithium ions and a reversible capacity of 150 mAh / g or more is used. 15% by weight or more and 85% by weight or less, the irreversible capacity is small, the collapse of the conductive material can be avoided, and the capacity of the nonaqueous secondary battery can be increased and the cycle characteristics can be improved.

According to the present invention, since the negative electrode mixture contains a conductive material composed of a metal or a compound having a volume resistivity of 5 × 10 ⁻⁴ Ω · cm or less and does not occlude lithium ions, the conductive material has a small irreversible capacity. Thus, the capacity of the non-aqueous secondary battery can be increased and the cycle characteristics can be improved.

  Further, according to the present invention, since the non-aqueous secondary battery includes an electrolyte containing 5 wt% or more and 50 wt% or less of propylene carbonate, cycle characteristics can be further improved.

Also, according to the present invention, the open potential during occlusion of lithium ions has a lower saturation potential than lithium vanadium oxide, and the reversible efficiency during the first occlusion and desorption of lithium ions is 10% or less, or the reversible capacity is 50 mAh. / G or less, and a conductive material having a specific surface area of 15 m ² / g or more is contained in the negative electrode mixture in an amount of 10% by weight to 15% by weight. The capacity of the battery can be increased and the cycle characteristics can be improved.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view showing the nonaqueous secondary battery of the first embodiment. The non-aqueous secondary battery 1 is composed of a spiral cylindrical lithium secondary battery. The non-aqueous secondary battery 1 is provided with a center pin 6, and a laminate 10 in which a separator 5 is sandwiched between a positive electrode 3 and a negative electrode 4 is wound around the center pin 6 in a multiple manner. Thereby, the laminated body 10 has comprised the cylindrical structure.

  The positive electrode 3 is formed by mixing a positive electrode active material, a conductive material, and a binder, and a positive electrode mixture 3a sandwiching two layers of the front and back surfaces of the positive electrode current collector 3b. The negative electrode 4 is formed by sandwiching a negative electrode mixture 4a in which a negative electrode active material, a conductive material, and a binder are mixed, with two layers of the front surface and the back surface of the negative electrode current collector 4b interposed therebetween. The cylindrical laminate 10 is housed in a hollow cylindrical case 2 and is immersed in an electrolyte (not shown). A positive electrode 3 is connected by the case 2 and a positive electrode terminal 7 having a lower end protruding is formed.

  Insulating plates 9b and 9a are provided above and below the laminate 10, respectively. The positive electrode current collector 3 b passes through the insulating plate 9 a and is connected to the positive electrode terminal 7 by the positive electrode lead 11. On the insulating plate 9b on the opening side of the case 2, a safety valve 13 having a convex shape in the direction of the insulating plate 9b is provided. A cap-like negative electrode terminal 8 having a convex shape in the opposite direction to the safety valve 13 is formed above the safety valve 13. The negative electrode current collector 4 b passes through the insulating plate 9 b and is connected to the negative electrode terminal 8 by the negative electrode lead 12. Further, the edge surfaces of the safety valve 13 and the negative electrode terminal 8 are sealed by the gasket 14 and are separated from the positive electrode terminal 7.

For example, a lithium transition metal oxide such as lithium cobalt oxide is used as the positive electrode active material. For example, an electrolyte containing a solute composed of a lithium salt such as LiPF ₆ , Li ₂ SiF ₆ , Li ₂ TiF ₆ , or LiBF _{4 in} a solvent such as ethylene carbonate or diethyl carbonate is used.

The negative electrode active material is made of lithium vanadium oxide. This lithium vanadium oxide is represented by the general formula of LiaVbMcOd. Here, a, b, c, and d are arbitrary numerical values, and M is at least one element selected from transition metals, alkali metals, and alkaline earth metals. As a manufacturing method, for example, a method in which M is added using LiOH and V ₂ O ₃ as raw materials and baked at a predetermined temperature (dry method), or Li ₂ CO ₃ , V ₂ O ₅ , M and an organic acid are mixed. And a method (wet method) of firing the organic acid salt obtained at a predetermined temperature. In addition, since the raw material used is comparatively cheap, the wet method is more preferable in industrialization.

The conductive material of the negative electrode 4 has a saturation potential lower than that of lithium vanadium oxide when the lithium ion is occluded when charging / discharging with lithium as a counter electrode, and during the first occlusion and desorption of lithium ion. The material has a reversible efficiency of 50% or more and a reversible capacity of 150 mAh / g or more. The negative electrode mixture 4a of the negative electrode 4 contains 15% by weight to 85% by weight of the conductive material.

  FIG. 2 shows the results of measuring the lithium reference open potential in a test cell in which metallic lithium is arranged on the negative electrode and electrodes made of various materials are arranged on the positive electrode. The vertical axis represents the open circuit potential (unit: V), and the horizontal axis represents the charge amount (unit:%). In the figure, A is lithium vanadium oxide, B is graphite (graphite), C is aluminum, and D is carbon black.

  According to the figure, graphite B and carbon black D have a lower saturation potential than lithium vanadium oxide A which is a negative electrode active material. Aluminum C has a higher saturation potential than lithium vanadium oxide A.

  Further, graphite B has a reversible efficiency of 50% or more and a reversible capacity of 150 mAh / g or more at the time of first occlusion and desorption of lithium ions. Carbon black D does not have a reversible efficiency of 50% or more and a reversible capacity of 150 mAh / g or more at the first occlusion and desorption of lithium ions. Therefore, a conductive material made of graphite or the like may be contained in the negative electrode mixture 4a in an amount of 15% by weight to 85% by weight.

  In the nonaqueous secondary battery 1, lithium ions released from the positive electrode 3 by the first charge are occluded in the negative electrode 4. At the time of discharging, the reversible amount is released from the negative electrode 4 and returns to the positive electrode 3 and is observed as the battery capacity. For this reason, the capacity | capacitance fall of the non-aqueous secondary battery 1 can be suppressed by making the reversible efficiency of the electrically conductive material contained in the negative electrode 4 high 50% or more.

  Further, by setting the reversible capacity per weight of the conductive material to 150 mAh / g or more, it is possible to secure a large amount of negative electrode material that can be accommodated in a battery having a constant volume. Thereby, the capacity | capacitance of the non-aqueous secondary battery 1 can be increased. In addition, since the conductive material has a lower saturation potential than lithium vanadium oxide, the occlusion reaction with lithium ions is suppressed. Thereby, collapse of the conductive material due to expansion / contraction during charging / discharging can be prevented.

Next, a second embodiment will be described. This embodiment is configured similarly to the first embodiment, and the configuration of the negative electrode 4 is different. The conductive material of the negative electrode 4 of the present embodiment is made of a metal or compound that has a volume resistivity of 5 × 10 ⁻⁴ Ω · cm or less and does not occlude lithium ions. The negative electrode mixture 4a contains 15% by weight or less of this conductive material. Further, the electrolyte contains 5% by weight or more and 50% by weight or less of propylene carbonate. Other parts are the same as those in the first embodiment.

As a conductive material, or a metal such as stainless steel having a volume resistivity of Ni of 6.84 × 10 ^-6 Ω · cm, the ^{1.67 × 10 -6 Ω · cm Cu} , 73 × 10 -6 Ω · cm, TiN, VC, compounds such as VN: can be used (volume resistivity ^{21.7 × 10 -6 Ω · cm~200 ×} 10 -6 Ω · cm) and the like.

  According to this embodiment, since a conductive material and lithium do not react, it is possible to prevent a decrease in conductivity. Moreover, the increase in the irreversible capacity due to the reaction between the conductive material and lithium can be prevented, the capacity of the nonaqueous secondary battery 1 can be increased, and the cycle characteristics can be improved.

  Furthermore, since the conductive material does not occlude lithium ions, it is possible to prevent the conductive material from collapsing due to expansion and contraction during charge and discharge by co-inserting an electrolyte solvent. In particular, since the propylene carbonate in which the electrolyte is easily co-inserted is contained in an amount of 5% by weight or more and 50% by weight or less, the conductive material can be more reliably prevented from collapsing.

Next, a third embodiment will be described. This embodiment is configured similarly to the first embodiment, and the configuration of the negative electrode 4 is different. The conductive material of the negative electrode 4 of the present embodiment has a saturation potential lower than that of lithium vanadium oxide when the lithium ion is occluded, and the reversible efficiency during the first occlusion and desorption of lithium ions is 10% or less or It is made of a material having a reversible capacity of 50 mAh / g or less and a specific surface area of 15 m ² / g or more. The negative electrode mixture 4a contains 10% by weight or more and 15% by weight or less of this conductive material. Here, the specific surface area is obtained by the BET method. Other parts are the same as those in the first embodiment.

In FIG. 2 described above, acetylene black D has a lower saturation potential than lithium vanadium oxide. Moreover, the reversible capacity at the time of occlusion and desorption of lithium ions for the first time is 50 mAh / g or less, and the specific surface area is 15 m ² / g. Therefore, carbon black such as acetylene black can be used as the conductive material. Ketjen black, which is a highly conductive carbon black, has a non-surface area of 1270 m ² / g, a reversible capacity of 50 mAh / g or less at the time of first occlusion and desorption of lithium ions, and a reversal efficiency of 10% or less. is there. Therefore, ketjen black may be used as the conductive material.

  According to the present embodiment, the reversible efficiency or reversible capacity of the conductive material of the negative electrode 4 is low, but since the content of the conductive material contained in the negative electrode mixture 4a is 15% by weight or less, the reaction between the conductive material and lithium is performed. Can be suppressed. Thereby, while preventing a fall of electroconductivity, an irreversible capacity | capacitance can be made small by suppressing the increase in contact resistance, and the capacity | capacitance of the non-aqueous secondary battery 1 can be increased. Furthermore, since the content of the conductive material contained in the negative electrode mixture 4a is 10% by weight or more, it is possible to further prevent the decrease in conductivity. This can improve cycle characteristics.

  In addition, since the conductive material has a lower saturation potential than lithium vanadium oxide, the occlusion reaction with lithium ions is suppressed. Thereby, collapse of the conductive material due to expansion / contraction during charging / discharging can be prevented.

  In each of the above-described embodiments, the mixing ratio to the negative electrode 4 is defined for each conductive material having different characteristics, and the negative electrode 4 is described as including a kind of conductive material. However, the present invention is not limited to this. Needless to say, a plurality of kinds of conductive materials may be used at the same time, for example, the conductive material of the first embodiment and the conductive material of the second embodiment are mixed in the negative electrode 4 at the same time.

  Next, examples of the present invention will be described. Table 1 shows a 2032 type test cell in which a conductive material sample of the negative electrode 4 used for investigating the performance of the non-aqueous secondary battery 1 of the first embodiment is arranged on the positive electrode and metallic lithium is arranged on the negative electrode. The result of measuring the discharge characteristics is shown.

  Sample number B1 is a conductive material of the negative electrode 4 of Example 1, and is made of graphite. Sample number B2 is a conductive material of the negative electrode 4 of Example 2 described later, and is made of carbon black that has been heat-treated at 1000 ° C. Sample numbers B11 to B13 are conductive materials of the negative electrode 4 of the comparative example, and are made of graphite nanofibers, carbon black heat-treated at 1500 ° C., and aluminum, respectively.

In addition, graphite consists of the powder obtained by heat-processing the pitch which is a distillation residue of tar at 2800-3000 degreeC. Graphite nanofibers consist of fine carbon fibers that are graphitized by spray decomposition of organic matter in the gas phase. Li _1.1 V _0.9 O ₂ is used as a negative electrode active material made of lithium vanadium oxide.

Li _1.1 V _0.9 O _2, which is a negative electrode active material, has a saturation potential of an open potential of 0.2 V during occlusion of lithium ions. Sample No. B1, which is the conductive material of Example 1, has a saturation potential of 0.1 V, which is lower than Li _1.1 V _0.9 O _2, when the open potential during occlusion of lithium ions. Sample numbers B11 and B12 of the comparative example also have a saturation potential of 0.1 V, which is lower than Li _1.1 V _0.9 O _2, when the open potential at the time of occlusion of lithium ions. Sample No. B13 of the comparative example has a saturation potential of 0.4 V, in which the open potential during occlusion of lithium ions is higher than Li _1.1 V _0.9 O ₂ .

  The charge / discharge of the test cell using these samples was performed, and the reversible capacity of sample number B1 at the time of first occlusion and desorption of lithium ions was 330 mAh / g. The reversible capacities of sample numbers B11, B12, and B13 are 330 mAh / g, 50 mAh / g, and 700 mAh / g, respectively.

  Further, the reversible efficiency of sample number B1 at the time of the first occlusion and desorption of lithium ions is 92%. The reversible efficiencies of sample numbers B11, B12, and B13 are 40%, 40%, and 70%, respectively.

3 and 4 show that each sample shown in Table 1 is used as a conductive material for the negative electrode 4 of the 18650-type non-aqueous secondary battery 1, and the 18650-type non-aqueous secondary battery 1 is manufactured. The results of measuring the battery capacity and the battery capacity retention rate after 100 cycles using the content of the conductive material contained as a parameter are shown. The vertical axis represents the battery capacity (unit: mAh) and the retention rate (unit:%), and the horizontal axis represents the content of the conductive material (unit:% by weight). Here, LiCoO ₂ was used as the active material of the positive electrode 3, LiPF ₆ was used as the electrolyte, and a mixed solvent of ethylene carbonate: diethyl carbonate = 3: 7 was used as the solvent.

  According to FIG. 3, sample number B1 has a high battery capacity of 2000 mAh or more and a high retention rate of 90% or more when the content of the conductive material is in the range of 15 wt% to 85 wt%. In contrast, sample numbers B11 and B12 have a battery capacity lower than 2000 mAh when the conductive material content is in the range of 20 wt% to 85 wt%. Sample No. B13 has a retention rate lower than 90% when the content of the conductive material is in the range of 15 wt% to 85 wt%.

  In Table 1 above, the sample number B2 is a conductive material of the negative electrode 4 of Example 2, and is made of carbon black that has been heat-treated at 1000 ° C. The reversible capacity of sample number B2 at the time of the first occlusion and desorption of lithium ions is 160 mAh / g. In addition, the reversible efficiency of sample number B2 at the time of the first occlusion and desorption of lithium ions is 55%.

In FIG. 3, the sample number B2 has a high battery capacity of 2000 mAh or more and a high retention rate of 90% or more when the content of the conductive material is in the range of 15 wt% to 85 wt%. .

  According to the conductive materials (B1, B2) of Examples 1 and 2, the reversible capacity at the time of the first occlusion and desorption of lithium ions is 150 mAh / g or more, and the reversible efficiency is 50% or more. High battery capacity and cycle characteristics can be obtained when the amount is in the range of 15 wt% to 85 wt%. Further, when the content of the conductive material contained in the negative electrode mixture 4a is 30% by weight to 70% by weight, higher battery capacity and cycle characteristics can be obtained.

  On the other hand, since the reversible efficiency of the conductive material of sample number B11 of the comparative example is lower than 50%, a high battery capacity cannot be obtained when the content is in the range of 15% by weight to 85% by weight. Since the conductive material of sample number B12 has a reversible capacity lower than 150 mAh / g and a reversible efficiency lower than 50%, a high battery capacity cannot be obtained. Since the conductive material of sample number B13 has a higher saturation potential than that of the lithium ion oxide, the cycle characteristics deteriorate.

  Table 2 shows the material characteristics of the conductive material of the negative electrode 4 used for examining the performance of the nonaqueous secondary battery 1 of the second embodiment.

  Sample number C1 is a conductive material of the negative electrode 4 of Example 3, and is made of nickel. Sample number C2 is a conductive material of the negative electrode 4 of Example 4 described later, and is made of stainless steel. Sample number C3 is a conductive material of the negative electrode 4 of Example 5 to be described later, and is made of VN (vanadium nitride). Sample number C11 is a conductive material of the negative electrode 4 of the comparative example, and is made of BN (boron nitride).

Sample No. C1, which is the conductive material of the negative electrode 4 of Example 3, has a specific surface area of 5 m ² / g and a volume resistivity of 6.8 × 10 ⁻⁶ Ω · cm. Sample No. C11 of the comparative example has a specific surface area of 5 m ² / g and a volume resistivity of 1900 × 10 ⁻⁶ Ω · cm.

FIG. 5 shows a conductive material contained in the negative electrode mixture by producing the 18650 type non-aqueous secondary battery 1 using each sample shown in Table 2 as the conductive material of the negative electrode 4 of the 18650 type non-aqueous secondary battery 1. The battery capacity and the retention rate of the battery capacity after 100 cycles were measured using the material content as a parameter. The vertical axis represents the battery capacity (unit: mAh) and the retention rate (unit:%), and the horizontal axis represents the content of the conductive material (unit:% by weight). Here, LiCoO ₂ was used as the active material of the positive electrode 3, LiPF ₆ was used as the electrolyte, and a mixed solvent of ethylene carbonate: diethyl carbonate = 3: 7 was used as the solvent.

  According to the figure, the sample number C1 has a high battery capacity of 2000 mAh or more and a high retention rate of 90% or more when the content of the conductive material is 15% by weight or less. On the other hand, in the sample number C11, the retention rate is lower than 90% when the content of the conductive material is in the range of 10% by weight to 15% by weight.

In Table 2 above, the sample number C2 is the conductive material of the negative electrode 4 of Example 4, and is made of stainless steel having Ni of 20% by weight, Cr of 25% by weight, and Fe of 55% by weight. Sample No. C2 has a specific surface area of 5 m ² / g and a volume resistivity of 73 × 10 ⁻⁶ Ω · cm. In FIG. 5, Sample No. C2 has a high battery capacity of 2000 mAh or more and a high retention rate of 90% or more when the content of the conductive material is in the range of 15% by weight or less.

In Table 2 described above, the sample number C3 is a conductive material of the negative electrode 4 of Example 5, and is made of VN. Sample No. C3 has a specific surface area of 5 m ² / g and a volume resistivity of 200 × 10 ⁻⁶ Ω · cm. In FIG. 5, Sample No. C3 has a high battery capacity of 2000 mAh or more and a high retention rate of 90% or more when the content of the conductive material is 15% by weight or less.

According to the conductive materials (C1 to C3) of Examples 3 to 5, since the volume resistivity is 200 × 10 ⁻⁶ Ω · cm or less, the battery capacity is high when the content of the conductive material is 15% by weight or less. Cycle characteristics can be obtained. On the other hand, since the volume resistivity of the conductive material of sample number C11 of the comparative example is higher than 200 × 10 ⁻⁶ Ω · cm, it is not possible to obtain a high retention rate within a range of 15% by weight or less. .

  FIG. 6 shows the battery capacity of the test cell of the 463048 type non-aqueous secondary battery and the change in thickness when left at 80 ° C. for 24 hours. The vertical axis represents the battery capacity (unit: mAh) and the thickness after standing (unit:%), and the horizontal axis represents the content (unit: weight%) of PC (propylene carbonate) in the electrolyte.

  The electrolyte is a solution A in which LiPF6 is dissolved at a volume molar concentration of 1.0 mol / L in a solute obtained by mixing EC (ethylene carbonate) and DEC (diethyl carbonate) in a ratio of 3: 7, and a solute composed of PC is 1. Solution B in which LiPF6 is dissolved at a volume molar concentration of 0 mol / L is mixed. That is, the PC content is expressed as B solution weight / (A solution weight + B solution weight).

  In the figure, sample number C4 is a conductive material of the negative electrode 4 of Example 6, and is made of Ni powder. Sample number C12 is a conductive material of the negative electrode 4 of the comparative example, and is made of ketjen black. According to the figure, in all cases, a high battery capacity is maintained when the PC content is in the range of 5 wt% to 50 wt%, and the thickness change after being left at 80 ° C. is small. In addition, since PC has high surface tension, when 70 wt% of PC was included in the electrolyte, none of the separators penetrated and charging / discharging was not performed.

  FIG. 7 shows the retention rate of the battery capacity after 100 cycles of this non-aqueous secondary battery. The vertical axis represents the retention rate (unit:%), and the horizontal axis represents the PC content (unit:% by weight) in the electrolyte. According to the figure, the sample number C4 has a high retention rate of 90% or more when the content of PC in the electrolyte is in the range of 5% by weight to 50% by weight. In contrast, sample number C12 has a retention rate lower than 90% when the content of PC in the electrolyte is in the range of 5 wt% to 50 wt%. That is, by using Ni that does not occlude / desorb lithium ions as a conductive material, co-insertion of PC is prevented and cycle characteristics are improved.

  Table 3 shows a specific surface area of the sample of the conductive material of the negative electrode 4 used for examining the performance of the nonaqueous secondary battery 1 of the third embodiment, and 2032 in which this sample is arranged on the positive electrode and metallic lithium is arranged on the negative electrode. The result of having measured the charging / discharging characteristic in the test cell of the type nonaqueous secondary battery is shown.

  Sample number D1 is a conductive material of the negative electrode 4 of Example 7, and is made of carbon black heat-treated at 1500 ° C. Sample number D2 is a conductive material of the negative electrode 4 of Example 8 to be described later, and is made of ketjen black. Sample number D11 is a conductive material of the negative electrode 4 of the comparative example, and is made of carbon powder.

Sample number D1, which is the conductive material of negative electrode 4 of Example 7, has a specific surface area of 15 m ² / g, and sample number D11 has a specific surface area of 3 m ² / g. The charge / discharge of the test cell using these samples was performed, and the reversible capacity of sample number D1 at the time of the first occlusion and desorption of lithium ions was 50 mAh / g. The reversible capacity of sample number D11 is 50 mAh / g. Moreover, the reversible efficiency of the sample number D1 at the time of the first occlusion and desorption of lithium ions is 40%. The reversible efficiency of sample number D11 is 40%.

FIG. 8 shows a sample 18650 type non-aqueous secondary battery 1 using each sample shown in Table 3 as a conductive material of the negative electrode 4 of the 18650 type non-aqueous secondary battery 1, and is included in the negative electrode mixture 4a. The results of measuring the battery capacity and the battery capacity retention rate after 100 cycles using the content of the conductive material as a parameter are shown. The vertical axis represents the battery capacity (unit: mAh) and the retention rate (unit:%), and the horizontal axis represents the content of the conductive material (unit:% by weight). Here, LiCoO ₂ was used as the active material of the positive electrode 3, LiPF ₆ was used as the electrolyte, and a mixed solvent of ethylene carbonate: diethyl carbonate = 3: 7 was used as the solvent.

  According to the figure, sample number D1 has a high battery capacity of 2000 mAh or more and a high retention rate of 90% or more when the content of the conductive material is in the range of 10 wt% to 15 wt%. On the other hand, in the sample number D11, the retention rate is lower than 90% when the content of the conductive material is in the range of 10% by weight to 15% by weight.

In Table 3 above, the sample number D2 is the conductive material of the negative electrode 4 of Example 8, and is made of a ketchen bra. The specific surface area of sample number D2 is 1270 m ² / g. The reversible capacity of sample number D2 at the time of the first insertion and extraction of lithium ions is 45 mAh / g. The reversible efficiency of sample number D2 at the time of the first occlusion and desorption of lithium ions is 8%.

  In FIG. 8, sample number D2 has a high battery capacity of 2000 mAh or more and a high retention rate of 90% or more when the content of the conductive material is in the range of 10 wt% to 15 wt%. .

According to the conductive materials (D1, D2) of Examples 7 and 8, the specific surface area is 15 m ² / g or more, the reversible capacity is 50 mAh / g or less at the time of first occlusion and desorption of lithium ions, or the reversibility efficiency is 10 % Or less, high battery capacity and cycle characteristics can be obtained when the content of the conductive material is in the range of 10 to 15% by weight.

On the other hand, since the specific surface area of the conductive material of Sample No. D11 of the comparative example is lower than 15 m ² / g, the cycle characteristics are degraded when the content is in the range of 10 wt% to 15 wt%.

  The present invention can be used for non-aqueous secondary batteries such as lithium ion secondary batteries.

The longitudinal cross-sectional view which shows the nonaqueous secondary battery of 1st Embodiment of this invention. The figure which shows the charge characteristic in the various electrically conductive material of the negative electrode of a non-aqueous secondary battery The figure which shows the relationship between content of the electrically conductive material of the negative electrode of the non-aqueous secondary battery of 1st Embodiment of this invention, battery capacity, and the retention of the battery capacity after 100 cycles. The figure which shows the relationship between the content of the comparative example of the electrically conductive material of the negative electrode of the non-aqueous secondary battery of 1st Embodiment of this invention, battery capacity, and the retention of the battery capacity after 100 cycles. The figure which shows the relationship between content of the electrically conductive material of the negative electrode of the non-aqueous secondary battery of 2nd Embodiment of this invention, battery capacity, and the retention of the battery capacity after 100 cycles. The figure which shows the relationship between content of PC of the electrolyte of the non-aqueous secondary battery of 2nd Embodiment of this invention, battery capacity, and thickness change. The figure which shows the relationship between PC content and the retention rate of the electrolyte of the nonaqueous secondary battery of 2nd Embodiment of this invention. The figure which shows the relationship between content of the electrically conductive material of the negative electrode of the nonaqueous secondary battery of 3rd Embodiment of this invention, battery capacity, and the retention of the battery capacity after 100 cycles.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nonaqueous secondary battery 2 Case 3 Positive electrode 4 Negative electrode 5 Separator 6 Center pin 7 Positive electrode terminal 8 Negative electrode terminal 10 Laminated body

Claims (2)

In a non-aqueous secondary battery comprising a negative electrode formed by applying a negative electrode mixture comprising a negative electrode active material comprising a lithium vanadium oxide, a conductive material and a binder onto a current collector,
The conductive material is formed of graphite made of powder obtained by heat treatment at 2800 to 3000 ° C. of pitch, which is a distillation residue of tar, or carbon black heat-treated at 1000 ° C. and charged with lithium as a counter electrode. When the discharge is performed, the open potential during occlusion of lithium ions has a lower saturation potential than lithium vanadium oxide, the reversible efficiency during the first occlusion and desorption of lithium ions is 50% or more, and the reversible capacity is 150 mAh. The non-aqueous secondary battery, wherein the negative electrode mixture contains 15% by weight or more and 85% by weight or less of the conductive material. In a non-aqueous secondary battery comprising a negative electrode formed by applying a negative electrode mixture comprising a negative electrode active material comprising a lithium vanadium oxide, a conductive material and a binder onto a current collector,
The conductive material is formed of carbon black or ketjen black that has been heat-treated at 1500 ° C., and has a higher open potential than that of lithium vanadium oxide when lithium ions are occluded when charging / discharging with lithium as a counter electrode. It has a low saturation potential, has a reversible efficiency at the time of first occlusion and desorption of lithium ions of 10% or less, a reversible capacity of 50 mAh / g or less, and a specific surface area of 15 m ² / g or more. A non-aqueous secondary battery, wherein the material contains 10% by weight to 15% by weight of the conductive material.

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