JP2008305720A - Negative electrode for nonaqueous secondary battery and nonaqueous secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain deterioration of conductivity in spite of progress of a charge and discharge cycle by sufficiently securing a conductive route of lithium vanadium oxide, other negative electrode active materials, and/or a conductive material in a negative electrode for a nonaqueous secondary battery using the lithium vanadium oxide and a nonaqueous secondary battery using the same negative electrode. <P>SOLUTION: In the negative electrode for a nonaqueous secondary battery having a first negative electrode active material made of the lithium vanadium oxide and a second negative electrode active material and/or conductive material made of a material different from the lithium vanadium oxide, the first negative electrode active material is spattered on the surface of the second negative electrode active material and/or the conductive material in advance, and such a first negative electrode active material is used for the negative electrode for a nonaqueous secondary battery and the nonaqueous secondary battery using the negative electrode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a nonaqueous secondary battery such as a lithium ion secondary battery and a negative electrode material thereof.

  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 material is made of lithium vanadium oxide. The lithium vanadium oxide is formed by mixing a lithium supply source such as lithium hydroxide and a vanadium supply source such as vanadium trioxide by a solid phase method and firing at 650 ° C. or higher. Then, the obtained lithium vanadium oxide is mixed with another negative electrode active material such as graphite or a conductive material, and the mixture is dispersed in a binder and coated on a metallic current collector, thereby providing a non-aqueous secondary. The negative electrode of the battery was obtained.

  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.

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

  In a conventional negative electrode for a non-aqueous secondary battery using lithium vanadium oxide, a binder is present or a void is formed at the interface between the lithium vanadium oxide and another negative electrode active material and / or conductive material. And since the interface resistance is high, it was a factor of the capacity | capacitance fall of a secondary battery. In addition, since each particle repeats expansion / contraction by repeating the charge / discharge cycle, there is a problem that a large void is formed at the interface, and the capacity of the non-aqueous secondary battery further decreases as the charge / discharge cycle progresses. It was.

  The present invention relates to a negative electrode for a non-aqueous secondary battery using lithium vanadium oxide, and charging / discharging by sufficiently securing a conductive path between the lithium vanadium oxide and another negative electrode active material and / or a conductive material. It aims at providing the non-aqueous secondary battery which has the negative electrode for non-aqueous secondary batteries which can suppress that electroconductivity falls even if a cycle progresses, and a high charging / discharging characteristic.

  In order to achieve the above object, the inventors of the present invention have conducted intensive studies, and as a result, when a lithium vanadium oxide and a negative electrode active material other than a conductive material or lithium vanadium oxide are simply mixed, the conductive path is It was considered that the crystal structure collapsed due to repeated charging and discharging, leading to further disappearance of the conductive path, and the characteristics were deteriorated, leading to the present invention.

  The negative electrode for a non-aqueous secondary battery of the present invention includes a first negative electrode active material made of lithium vanadium oxide, and a second negative electrode active material and / or a conductive material made of a material different from the lithium vanadium oxide. In the negative electrode for a non-aqueous secondary battery, the first negative electrode active material is preliminarily scattered on the surface of the second negative electrode active material and / or the conductive material. .

  Further, the negative electrode for a non-aqueous secondary battery according to the present invention includes a weight ratio of the first negative electrode active material and the second negative electrode active material, (weight of the second negative electrode active material) / (the first negative electrode active material). The weight of the negative electrode active material is 20/80 to 95/5.

  The negative electrode for a non-aqueous secondary battery according to the present invention includes a particle diameter ratio of the first negative electrode active material and the second negative electrode active material, (primary particles of the second negative electrode active material) / (first negative electrode). The primary particles) of the active material are 1 to 100. The primary particle described here is the size when the particle is directly observed with a scanning electron microscope.

  In the negative electrode for a non-aqueous secondary battery of the present invention, the first negative electrode active material is a mixture of the second negative electrode active material and / or a precursor containing the first negative electrode active material in the conductive material. It is characterized by being interspersed by surface coating and firing in an inert gas atmosphere. In this configuration, the negative electrode active material other than lithium vanadium oxide is a material capable of removing and inserting lithium ions, such as graphite, hard carbon, and metal alloy, and the conductive material is highly conductive acetylene black, metal powder, etc. It is.

  The non-aqueous secondary battery of the present invention is characterized by comprising the above-configured negative electrode for non-aqueous secondary battery, a positive electrode, and an electrolyte.

  According to the present invention, the lithium vanadium oxide forming the negative electrode material for non-aqueous secondary batteries is preliminarily scattered on the surface of other negative electrode active materials and / or conductive materials, so that a high conductive path is secured in advance. In addition, even if expansion / contraction of the material in the negative electrode accompanying charging / discharging occurs, the conductivity between the materials does not disappear, so the charge / discharge characteristics of the non-aqueous secondary battery 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 a nonaqueous secondary battery according to an 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 sandwiching two layers of the front surface and the back surface of the positive electrode current collector 3b with a positive electrode mixture 3a containing a positive electrode active material. The negative electrode 4 is formed by sandwiching two layers of the front surface and the back surface of the negative electrode current collector 4b with a negative electrode mixture 4a containing a negative electrode active material. The cylindrical laminate 10 is housed in a hollow columnar case 2 and is immersed in an electrolyte (not shown). The 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.

As the positive electrode active material and the electrolyte, known materials are used as the positive electrode active material and the electrolyte of the non-aqueous secondary battery. For example, a lithium transition metal oxide such as lithium cobalt oxide is used for the positive electrode active material. As the electrolyte, a solvent such as ethylene carbonate or diethyl carbonate containing a solute composed of a lithium salt such as LiPF ₆ , Li ₂ SiF ₆ , Li ₂ TiF ₆ , or LiBF ₄ is used.

Anode 4 has that lithium vanadium oxide represented by Li _a V _b M _c O _d on the surface of the negative electrode active material or a conductive material other than the lithium vanadium oxide is scattered as an anode active material . Here, M is at least one or more elements selected from transition metals, alkali metals, and alkaline earth metals, and a, b, c, and d are arbitrary numerical values. Then, for example, 96% of the negative electrode active material, 2% of acetylene black, and 2% of the binder are mixed and applied onto the negative electrode current collector 3b made of copper, and pressed to 1.8 g / cm ^3. Is formed.

In this negative electrode active material, a precursor composed of a lithium compound, a vanadium compound, and a reducing agent is coated on the surface of a negative electrode material or a conductive material other than lithium vanadium oxide, and 1100 in an inert gas atmosphere such as a nitrogen atmosphere. It is formed by firing at 0 ° C. Specifically, for example, lithium carbonate (Li ₂ CO ₃ ) as a lithium compound, vanadium pentoxide (V ₂ O ₅ ) as a vanadium compound, a reducing agent and oxalic acid are mixed and reacted in an aqueous solution, and then evaporated. The solution obtained by drying is obtained by subjecting a carbon material to surface coating with a tumbling fluidized coating apparatus and baking.

In addition, when lithium carbonate, vanadium pentoxide, and oxalic acid are used, the organic acid salt can be easily obtained at a particularly low cost. As the lithium compound, lithium hydroxide, lithium oxalate, or the like may be used. As the reducing agent, an organic acid, a carbon material, hydrogen peroxide, or the like may be used.
In addition to nitrogen, the inert gas may be a mixed gas of nitrogen and hydrogen, or argon gas.
Further, as a method of interspersing lithium vanadium oxide, a mechanical processing method such as a mechanical milling method may be used.

  According to this production method, lithium vanadium oxide can easily form a negative electrode material other than lithium vanadium oxide or a negative electrode material that can easily secure a conduction path with a conductive material. Therefore, a negative electrode containing lithium vanadium oxide with good conductivity can be obtained.

  FIG. 2 is an image observed by a scanning electron microscope, FIG. 2 (a) is an image of graphite particles used in the examples of the present invention, and FIG. 2 (b) is a graphitic particle surface coated with a precursor. FIG. 2C is an image of a fired graphite particle whose surface is coated with a precursor, and FIG. 2D is an enlarged image of FIG. 2C.

  According to FIG. 2B, it can be seen that the precursor containing lithium and vanadium is uniformly coated on the graphite particles. In addition, according to FIG. 2 (c), it can be seen that the lithium vanadium oxide particles are scattered on the surface of the graphite particles after firing, and it is easy to secure a conductive path between the graphite particles and the lithium vanadium oxide. I understand that. Thereby, the electrical conductivity fall accompanying charging / discharging reaction and the resistance rise inside a battery are suppressed, and the non-aqueous secondary battery of a highly efficient charging / discharging characteristic can be obtained.

  Next, examples of the present invention will be shown, and the embodiments of the present invention will be described in more detail.

Example 1
A predetermined amount of lithium carbonate (208 g), vanadium pentoxide (425 g) and oxalic acid (1218 g) was added to 5 L of ion-exchanged water and dissolved under conditions of 60 ° C. Using this solution as a precursor solution, the graphite particles were coated using a tumbling fluidized coating apparatus manufactured by Paulek. At this time, the graphite particles were processed using a material having an average particle size of about 10 μm so that the graphite particles and the lithium vanadium oxide were 90/10 by weight after firing. Moreover, after coating the lithium vanadium oxide precursor on the graphite material, the negative electrode material in which lithium vanadium oxide was scattered on the surface of the graphite material could be obtained by firing in a nitrogen atmosphere at 950 ° C. When the particles of the negative electrode material thus obtained were observed with a scanning electron microscope, the particle size ratio of primary particles of graphite particles / primary particles of lithium vanadium oxide was about 5. The obtained negative electrode material, acetylene black, and polyvinylidene fluoride (pvdf) were mixed at a weight ratio of 96: 2: 2, and N-methyl-2-pyrrolidone was added to prepare a slurry. The prepared slurry was applied to a copper foil, and after drying, the electrode density was 1.8 g / cm ³ to obtain a negative electrode. The positive electrode is lithium cobaltate, and the electrolyte is non-aqueous secondary using 1.4M LiPF ₆ dissolved in a solvent of ethyl carbonate (EC): diethyl carbonate (DEC) = 3: 7. A battery was produced.

(Example 2)
A negative electrode material was synthesized in the same manner as in Example 1 except that the weight ratio of graphite and lithium vanadium oxide was 75/25, and a nonaqueous secondary battery was produced.

(Example 3)
A negative electrode material was synthesized in the same manner as in Example 1 except that the weight ratio of graphite and lithium vanadium oxide was 50/50, and a non-aqueous secondary battery was produced.

Example 4
A negative electrode material was synthesized in the same manner as in Example 1 except that the weight ratio of graphite and lithium vanadium oxide was 25/75, and a nonaqueous secondary battery was produced.

(Example 5)
A negative electrode material was synthesized in the same manner as in Example 1 except that the weight ratio of graphite and lithium vanadium oxide was 10/90, and a nonaqueous secondary battery was produced.

(Example 6)
Example 1 except that the weight ratio of graphite and lithium vanadium oxide was 50/50, the firing temperature was 850 ° C., and the particle size ratio of primary particles of graphite particles / primary particles of lithium vanadium oxide was about 50. The negative electrode material was synthesized in the same manner as described above to produce a non-aqueous secondary battery.

(Example 7)
The weight ratio of graphite to lithium vanadium oxide was 50/50, and the particle size ratio of primary particles of graphite particles / primary particles of lithium vanadium oxide was set to about 10 by using a material having a particle size of graphite particles of 20 μm. A negative electrode material was synthesized in the same manner as in Example 1 except that a non-aqueous secondary battery was produced.

(Example 8)
Using graphite / lithium vanadium oxide weight ratio of 50/50, graphite particle size of 20 μm, and firing temperature of 850 ° C., graphite particle primary particles / lithium vanadium oxide primary particles A negative electrode material was synthesized in the same manner as in Example 1 except that the diameter ratio was about 70, and a nonaqueous secondary battery was produced.

Example 9
In Example 9, lithium vanadium oxide was interspersed on the surface of conductive graphite of about 2 μm serving as a conductive material, not graphite serving as a negative electrode active material. A predetermined amount of lithium carbonate (208 g), vanadium pentoxide (425 g) and oxalic acid (1218 g) was added to 5 L of ion-exchanged water and dissolved under conditions of 60 ° C. Using this solution as a precursor solution, the conductive graphite particles were coated using a tumbling fluidized coating apparatus manufactured by Paulek. After firing, the conductive graphite particles and the lithium vanadium oxide were treated so as to have a weight ratio of 50/50. In addition, after coating a conductive graphite material with a lithium vanadium oxide precursor, a negative electrode material in which lithium vanadium oxide is scattered on the surface of the conductive graphite material can be obtained by firing in a nitrogen atmosphere at 950 ° C. did it. The obtained negative electrode material and pvdf were mixed at a weight ratio of 96: 4, and N-methyl-2-pyrrolidone was added to prepare a slurry. The prepared slurry was applied to a copper foil, and after drying, the electrode density was 1.8 g / cm ³ to obtain a negative electrode. The positive electrode is lithium cobaltate, and the electrolyte is non-aqueous secondary using 1.4M LiPF ₆ dissolved in a solvent of ethyl carbonate (EC): diethyl carbonate (DEC) = 3: 7. A battery was produced.
The weight ratio of lithium vanadium oxide was 50/50. The synthesis was performed at a firing temperature of 850 ° C., and the particle size ratio of conductive graphite / lithium vanadium oxide was about 1.

Subsequently, the manufacturing methods of Comparative Examples 1 to 4 will be described.
(Comparative Example 1)
A solution to which 208 g of lithium carbonate, 425 g of vanadium pentoxide and 1218 g of oxalic acid were added was dried with a stationary dryer at 130 ° C., and then fired at 950 ° C. in a nitrogen atmosphere. The obtained lithium vanadium oxide and graphite particles having a primary particle diameter of 10 μm are mixed so as to have a weight ratio of 10/90 to obtain a negative electrode material, and the negative electrode material, acetylene black, and pvdf are in a weight ratio of 96: 2: 2. And N-methyl-2-pyrrolidone was added to prepare a slurry. At this time, the particle size ratio of primary particles of graphite particles / primary particles of lithium vanadium oxide was about 5.
Moreover, the produced slurry was apply | coated to copper foil, and after drying, the electrode density was set to 1.8 g / cm < ³ > and it was set as the negative electrode. The positive electrode is lithium cobaltate, and the electrolyte is non-aqueous secondary using 1.4M LiPF ₆ dissolved in a solvent of ethyl carbonate (EC): diethyl carbonate (DEC) = 3: 7. A battery was produced.

(Comparative Example 2)
A non-aqueous secondary battery was fabricated by synthesizing a negative electrode material in the same manner as in Comparative Example 1 except that the lithium vanadium oxide and graphite were 50/50 by weight.
(Comparative Example 3)
A non-aqueous secondary battery was produced by synthesizing a negative electrode material in the same manner as in Comparative Example 1 except that the firing temperature was 1100 ° C.
(Comparative Example 4)
A non-aqueous secondary battery was produced by synthesizing a negative electrode material in the same manner as in Comparative Example 1 except that the firing temperature was 1100 ° C. and the weight ratio of the obtained lithium vanadium oxide and graphite was 90/10.

Next, the evaluation results of the lithium secondary battery thus obtained will be described.
Table 1 shows the evaluation results of Examples 1 to 9 and Comparative Examples 1 to 4.

評価項目として、１サイクル目の容量を１００とした場合の、２００サイクル後の容量維持率（％）を採用した。ここでは、容量維持率（％）は、８０％以上であれば良好といえる。
実施例１〜９では、黒鉛の重量割合、粒子径比を変更させた場合でも、２００サイクル後の容量維持率が８０％以上であることが確認できる。
一方、比較例１〜４では、２００サイクル後の容量維持率は、比較例１で３４％、比較例２で２７％、比較例３で２１％、比較例４で２３％であり、単純に混合しただけでは、黒鉛とリチウムバナジウム酸化物とが、単独で存在するに過ぎず、接触抵抗が増加し容量維持率が低下したものと推察される。

As an evaluation item, the capacity retention rate (%) after 200 cycles when the capacity at the first cycle was set to 100 was adopted. Here, it can be said that the capacity retention rate (%) is good if it is 80% or more.
In Examples 1 to 9, it can be confirmed that the capacity retention after 200 cycles is 80% or more even when the weight ratio of graphite and the particle diameter ratio are changed.
On the other hand, in Comparative Examples 1 to 4, the capacity retention rate after 200 cycles was 34% in Comparative Example 1, 27% in Comparative Example 2, 21% in Comparative Example 3, and 23% in Comparative Example 4, and simply It is presumed that graphite and lithium vanadium oxide existed alone by mixing, and that the contact resistance increased and the capacity retention rate decreased.

Thus, according to the present invention, since the lithium vanadium oxide forming the negative electrode material for non-aqueous secondary batteries is preliminarily scattered on the surface of other negative electrode active materials and / or conductive materials, In addition to securing a conductive path, even if the material in the negative electrode expands or contracts due to charge / discharge, the conductivity between the materials does not disappear, improving the charge / discharge characteristics of the non-aqueous secondary battery It can be made.
In addition, since the size of the lithium vanadium oxide particles can be reduced, the lithium vanadium oxide particles can be prevented from collapsing even when expansion / contraction of the lithium vanadium oxide particles due to charge / discharge occurs. The charge / discharge characteristics of the water secondary battery can be further improved.

As mentioned above, although embodiment of this invention was described referring an Example, this invention is not limited to these Examples.
For example, the lithium secondary battery using the negative electrode active material of the present embodiment is not limited to a spiral cylindrical lithium secondary battery, but also in a coin-type lithium secondary battery or a square lithium secondary battery. The same effect can be obtained as long as it has characteristics.
The composition of the negative electrode active material of the present embodiment, the type of Me element contained therein, the material, shape, manufacturing process, manufacturing conditions of each component, the configuration of the lithium secondary battery, etc. have the features of the present invention. As long as it is within the scope of the present invention.

It is a longitudinal cross-sectional view which shows the non-aqueous secondary battery of this embodiment. (A) is an image of graphite particles used in the examples of the present invention, (b) is an image of a graphite particle surface coated with a precursor, and (c) is a calcined graphite particle surface-coated with a precursor. (D) is an enlarged image of (c).

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 (5)

In a negative electrode for a non-aqueous secondary battery, comprising: a first negative electrode active material made of lithium vanadium oxide; and a second negative electrode active material and / or a conductive material made of a material different from the lithium vanadium oxide.
The negative electrode for a non-aqueous secondary battery, wherein the first negative electrode active material is preliminarily scattered on the surface of the second negative electrode active material and / or the conductive material.   The weight ratio between the first negative electrode active material and the second negative electrode active material, (weight of the second negative electrode active material) / (weight of the first negative electrode active material) is 20/80 to 95 / The non-aqueous secondary battery negative electrode according to claim 1, wherein the negative electrode is 5.   The particle diameter ratio between the first negative electrode active material and the second negative electrode active material, (primary particles of the second negative electrode active material) / (primary particles of the first negative electrode active material) is 1 to 100 A negative electrode for a non-aqueous secondary battery according to claim 1 or claim 2   The first negative electrode active material is obtained by mixing or surface-coating a precursor containing the first negative electrode active material with the second negative electrode active material and / or the conductive material, and firing in an inert gas atmosphere. 4. The negative electrode for a non-aqueous secondary battery according to claim 1, wherein the negative electrode is dotted with   A non-aqueous secondary battery using the negative electrode for a lithium secondary battery according to claim 1.

Images