KR100971746B1 - Negative electrode for non-aqueous secondary battery, and non-aqueous electrolyte secondary battery including same - Google Patents

Abstract

The present invention relates to a nonaqueous secondary battery, and a nonaqueous secondary battery using the same, the nonaqueous secondary battery is a core material; And a negative electrode material previously scattered on the surface of the core material and including a first negative electrode active material including lithium vanadium oxide. The core material is selected from the group consisting of a second negative electrode active material different from the lithium vanadium oxide, a conductive material, and a mixture thereof.

The negative electrode for a non-aqueous secondary battery according to the present invention can sufficiently prevent the conductive degradation caused by the progress of the charge / discharge cycle by sufficiently securing a conductive path between lithium vanadium oxide and another negative electrode active material or conductive material.

Non-aqueous secondary battery, lithium vanadium oxide, negative electrode active material, conductive material, conductive path, cycle characteristics.

Description

Negative electrode for non-aqueous battery and non-aqueous battery using same TECHNICAL FIELD AND AND NON-AQUEOUS SECONDARY BATTERY, AND NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY INCLUDING SAME}

The present invention relates to a nonaqueous secondary battery and a nonaqueous secondary battery using the same. More specifically, in a nonaqueous secondary battery such as a lithium ion secondary battery, a nonaqueous secondary battery capable of suppressing a decrease in conductivity even when a charge and discharge cycle proceeds. The present invention relates to a negative electrode and a nonaqueous secondary battery having high charge and discharge characteristics.

The conventional non-aqueous secondary battery is formed by immersing a positive electrode and a negative electrode capable of occluding and releasing lithium ions in a non-aqueous electrolyte (see Japanese Patent Application Laid-Open No. 2003-68305, pages 3 to 11, and FIG. 10). At this time, lithium vanadium oxide is used as the negative electrode material, and the lithium vanadium oxide is formed by mixing at a solid state method with a lithium source such as lithium hydroxide and a vanadium source such as vanadium trioxide. The obtained lithium vanadium oxide was mixed with another negative electrode active material or conductive material such as graphite, and the mixture was dispersed in a binder and coated on a metallic current collector to prepare a negative electrode of a non-aqueous secondary battery.

At the time of charging the non-aqueous secondary battery, the negative electrode is negatively charged, and lithium ions occluded at the positive electrode are separated and occluded at the negative electrode. At the time of discharge of a non-aqueous secondary battery, lithium ions occluded in the negative electrode are detached and occluded in the positive electrode.

In the conventional negative electrode for non-aqueous batteries using lithium vanadium oxide, the interface resistance is high because of the presence of a binder or the formation of voids at the interface between the lithium vanadium oxide and other negative electrode active materials and / or conductive materials. It was a cause of the fall of the capacity of a secondary battery. In addition, since each particle repeats expansion / contraction as the charge and discharge cycle is repeated, a large void is formed by the interface, and as the charge and discharge cycle progresses, there is a problem that the capacity of the non-aqueous secondary battery is further reduced.

The present invention, in the negative electrode for a non-secondary battery using lithium vanadium oxide, by sufficiently securing the conductive path between the lithium vanadium oxide and the other negative electrode active material, and optionally the conductive material to suppress the decrease in conductivity even when the charge and discharge cycle proceeds An object of the present invention is to provide a negative electrode for a nonaqueous secondary battery and a nonaqueous secondary battery having high charge and discharge characteristics.

In order to achieve the above object, the inventors of the present invention have repeatedly studied, and when the lithium vanadium oxide and the negative electrode active material other than the conductive material or the lithium vanadium oxide are simply mixed, the conductive paths are insufficient, resulting in repeated charge and discharge. It has been found that the crystal structure collapses, and furthermore, that the properties associated with the disappearance of the conductive paths are deteriorated and the present invention is invented.

A negative electrode for a non-aqueous secondary battery according to an embodiment of the present invention, the core material; And a negative electrode material previously interspersed on the surface of the core material and including a first negative electrode active material including lithium vanadium oxide. The core material is selected from the group consisting of a second negative electrode active material different from the lithium vanadium oxide, a conductive material, and a mixture thereof.

The nonaqueous secondary battery negative electrode of the present invention is characterized in that the weight ratio (weight of the core material / weight of the first negative electrode active material) of the core material and the first negative electrode active material is 20/80 to 95/5.

The negative electrode for nonaqueous secondary battery of the present invention is characterized in that the particle size ratio (primary particle of the core material / primary particle of the first negative electrode active material) of the core material and the first negative electrode active material is 1 to 100. Here, the said primary particle is the magnitude | size when the particle is observed directly with a scanning electron microscope.

In addition, the negative electrode for a non-aqueous secondary battery of the present invention is characterized in that the first negative electrode active material is mixed or surface-coated with a precursor containing the first negative electrode active material to the core material and fired in an inert gas atmosphere.

In the above configuration, the second negative electrode active material made of a material different from the lithium vanadium oxide, the metal material capable of alloying with lithium metal lithium; Transition metal oxides; Materials capable of doping and undoping lithium; Materials capable of forming compounds by reversibly reacting with lithium; It is preferably selected from the group consisting of materials capable of reversibly intercalating and deintercalating lithium ions and mixtures thereof.

In addition, the conductive material is preferably selected from the group consisting of highly conductive crystalline carbon material, amorphous carbon material, columnar carbon material, metal powder, metal fiber, and mixtures thereof.

In addition, the non-aqueous secondary battery according to another embodiment of the present invention is characterized by consisting of a negative electrode, a positive electrode, and an electrolyte for each of the above configuration.

According to the present invention, since the lithium vanadium oxide forming the negative electrode material for the non-aqueous secondary battery is previously scattered on at least one surface of another negative electrode active material and the conductive material, not only a high conductive path is secured but also the negative electrode accompanying charge and discharge Since the conductivity between the materials does not disappear even when the material is expanded / contracted, the charge and discharge characteristics of the non-aqueous secondary battery can be improved.

Embodiments of the present invention will now be described with reference to the drawings.

1 is a longitudinal sectional view showing a non-aqueous secondary battery according to one embodiment of the present invention.

Referring to Figure 1 in more detail, the non-aqueous secondary battery 1 is made of a spiral cylindrical lithium secondary battery. A center pin 6 is provided in the nonaqueous secondary battery 1, and a laminate 10 in which a separator 5 is inserted between the positive electrode 3 and the negative electrode 4 is a center pin. It is wound up multiplely in (6). Thereby, the laminated body 10 has comprised the cylindrical structure.

The positive electrode 3 is formed of two layers of the front and rear surfaces of the positive electrode current collector 3b by the positive electrode mixture 3a containing the positive electrode active material. The negative electrode 4 is formed of two layers on the front and rear surfaces of the negative electrode current collector 4b by the negative electrode mixture 4a containing the negative electrode active material. The cylindrical laminated body 10 is accommodated in the case 2 of the hollow park mold, and is immersed in electrolyte (not shown). The case 2 is connected to the positive electrode 3 and a positive terminal 7 having a lower end protruding therefrom.

Insulation plates 9b and 9a are provided above and below the laminate 10, respectively. The positive electrode current collector 3b penetrates through the insulating plate 9a 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 plate 13 having a convex shape in the direction of the insulating plate 9b is provided. Above the safety plate 13, a cap-shaped negative electrode terminal 8 having a convex shape in the opposite direction to the safety plate 13 is formed. The negative electrode current collector 4b penetrates through the insulating plate 9b and is connected to the negative electrode terminal 8 by the negative electrode lead 12. In addition, the edge surfaces of the safety plate 13 and the negative electrode terminal 8 are sealed by the gasket 14 and spaced apart from the positive electrode terminal 7.

As the positive electrode active material and the electrolyte, known materials can be 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 may be used as the cathode active material. As the electrolyte, one containing a solute made of a lithium salt such as LiPF ₆ , Li ₂ SiF ₆ , Li ₂ TiF ₆ , LiBF _{4 in} a solvent such as ethylene carbonate or diethyl carbonate can be used.

The negative electrode 4 has a first negative electrode active material of lithium vanadium oxide represented by Li _a V _b M _c O _d on the surface of a core material including a second negative electrode active material other than lithium vanadium oxide, a conductive material or a mixture thereof. It contains the dotted negative electrode material. Here, M is an element selected from the group consisting of transition metals, alkali metals, alkaline earth metals and combinations thereof, and a, b, c and d are arbitrary values.

The second negative electrode active material may include lithium metal, a metal material alloyable with lithium, a transition metal oxide, a material capable of doping and undoping lithium, a material capable of forming a compound by reversibly reacting with lithium, or lithium ions. Reversible intercalation / deintercalation materials and the like can be used.

Examples of the metal material alloyable with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn , Pb, Sb, Bi, and combinations thereof may be used. In addition, the transition metal oxide, a material capable of doping and undoping lithium, or a material capable of forming a compound by reversibly reacting with lithium may include vanadium oxide, Si, SiO _x (0 <x <2), Sn, SnO ₂ , tin alloy, tin oxide, and the like.

As a material capable of reversibly intercalating / deintercalating the lithium ions, any carbon-based negative electrode active material generally used in a lithium ion secondary battery may be used, and representative examples thereof include crystalline carbon. , Amorphous carbon or these can be used together. Examples of the crystalline carbon may include graphite such as amorphous, plate, flake, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon may include soft carbon (low temperature calcined carbon). Or hard carbon, mesophase pitch carbide, calcined coke, and the like.

As the conductive material, crystalline carbon material, amorphous carbon material, columnar carbon material, metal powder, metal fiber or a mixture thereof can be used. The crystalline carbon material may include natural graphite, artificial graphite, and the like, and the amorphous carbon material may include carbon black, acetylene black, ketjen black, and the like, and the columnar carbon material may include carbon fibers and carbon nanotubes. Examples of the metal include copper, nickel, aluminum, silver, and the like.

The negative electrode 4 may further include the conductive material, optionally, in addition to the negative electrode material. The conductive material is the same as described above.

Thus, for example, 96% of the negative electrode material, 2% of acetylene black, and 2% of the binder are mixed and coated on the negative electrode current collector 3b made of copper, and press-formed to form 1.8 g / cm ³ . .

In the first negative electrode active material, the precursor of the first negative electrode active material containing a lithium compound, a vanadium compound, and a reducing agent is subjected to surface coating on the surface of a second negative electrode active material or a conductive material other than lithium vanadium oxide as a core material. It forms by baking at 850-1200 degreeC in inert gas atmosphere, such as these. Specifically, for example, a solution obtained by mixing 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, reacting in an aqueous solution, and then evaporating to dryness. It is obtained by surface-coating a carbon material with an electrophoretic flow coating apparatus and baking it.

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

According to this manufacturing method, it is easy to form the negative electrode material which is easy to ensure the conductive path of the 1st negative electrode active material of lithium vanadium oxide, and the 2nd negative electrode active material or conductive material other than lithium vanadium oxide. Thus, a negative electrode containing lithium vanadium oxide having good conductivity can be obtained.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

(Example 1)

208 g of lithium carbonate, 425 g of vanadium pentoxide, and 1218 g of oxalic acid were added to 5 L of ion-exchanged water at a predetermined ratio and dissolved in 60 ° C conditioning. Using this solution as a precursor solution, coating was performed on graphite particles using an electrophoretic fluid coating device made by Powder Co., Ltd. The graphite particles at this time were treated with a material having an average particle size of about 10 μm, so that the graphite particles and lithium vanadium oxide were 90/10 in weight ratio after firing. Further, after coating the lithium vanadium oxide precursor on the graphite material, baking was performed at 950 ° C. in a nitrogen atmosphere, whereby a negative electrode material in which lithium vanadium oxide was dotted on the graphite material surface was obtained.

As a result of observing the particles with a scanning electron microscope, the negative electrode material thus obtained had a particle diameter ratio of the primary particles of graphite particles / primary particles of lithium vanadium oxide to about 5.

The resulting 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 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. A positive electrode was produced by using lithium cobalt acid and 1.4 M LiPF ₆ dissolved in a mixed solvent of ethyl carbonate (EC): diethyl carbonate (DEC) = 3: 7 (volume ratio) as an electrolyte. It was.

(Example 2)

A negative electrode material was synthesized in the same manner as in Example 1 except that the weight ratio of graphite to lithium vanadium oxide was 75/25, to prepare a non-aqueous secondary battery.

(Example 3)

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

(Example 4)

A negative electrode material was synthesized in the same manner as in Example 1 except that the weight ratio of graphite to lithium vanadium oxide was 25/75, to prepare a non-aqueous secondary battery.

(Example 5)

A negative electrode material was synthesized in the same manner as in Example 1 except that the weight ratio of graphite to lithium vanadium oxide was 10/90, to produce a non-aqueous secondary battery.

(Example 6)

The weight ratio of graphite and lithium vanadium oxide is 50/50, the temperature at the time of baking is 850 degreeC, and the particle diameter ratio of the primary particle of graphite particle / primary particle of lithium vanadium oxide is about 50, It is the same as Example 1 The negative electrode material was synthesize | combined by the method, and the nonaqueous secondary battery was produced.

(Example 7)

Except that the weight ratio of graphite to lithium vanadium oxide is 50/50 and the particle size ratio of the primary particles of lithium particles / lithium vanadium oxide is about 10 using a material having a particle size of 20 μm of graphite particles. The negative electrode material was synthesize | combined by the method similar to 1, and the nonaqueous secondary battery was produced.

(Example 8)

The particle size of the primary particles of the graphite particles / primary particles of lithium vanadium oxide using a material having a weight ratio of graphite and lithium vanadium oxide of 50/50 and using a material having a particle size of 20 µm and a firing temperature of 850 ° C A negative electrode material was synthesized in the same manner as in Example 1 except that the cost was about 70, to thereby fabricate a nonaqueous secondary battery.

(Example 9)

In Example 9, lithium vanadium oxide was interspersed on the surface of about 2 micrometers of conductive graphite which becomes a conductive material instead of graphite which becomes a negative electrode active material.

208 g of lithium carbonate, 425 g of vanadium pentoxide, and 1218 g of oxalic acid were added to 5 L of ion-exchanged water at a predetermined ratio, and dissolved by conditioning at 60 ° C. Using this solution as a precursor solution, the conductive graphite particles were coated using an electrophoretic fluid coating device manufactured by Powder Co., Ltd. After baking, the conductive graphite particles and the lithium vanadium oxide were treated so as to have a weight ratio of 50/50. Further, after coating the lithium vanadium oxide precursor on the conductive graphite material, baking was carried out at 950 ° C. in a nitrogen atmosphere, whereby a negative electrode material containing lithium vanadium oxide on the surface of the conductive graphite material was obtained. The resulting negative electrode material and polyvinylidene fluoride were mixed in a weight ratio of 96: 4, and N-methyl-2-pyrrolidone was added to prepare a slurry. 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 cathode electrode. As a positive electrode, a non-aqueous secondary battery was produced using lithium cobalt acid and 1.4 M LiPF ₆ dissolved in a mixed solvent of ethyl carbonate (EC): diethyl carbonate (DEC) = 3: 7 (volume ratio). . The weight ratio of lithium vanadium oxide was 50/50. It synthesize | combined at the baking temperature of 850 degreeC, and the particle diameter ratio of electroconductive graphite / lithium vanadium oxide was about one.

Then, the manufacturing method of Comparative Examples 1-4 is demonstrated.

(Comparative Example 1)

A solution containing 208 g of lithium carbonate, 425 g of vanadium pentoxide, and 1218 g of oxalic acid was dried in a stationary dryer at 130 ° C., and then calcined at 950 ° C. in a nitrogen atmosphere. The obtained lithium vanadium oxide and graphite particles having a primary particle diameter of 10 μm were mixed at a weight ratio of 10/90 to obtain a negative electrode material, and the negative electrode material, acetylene black, and polyvinylidene fluoride were mixed at a weight ratio of 96: 2: 2. After the addition of N-methyl-2-pyrrolidone to prepare a slurry. At this time, the particle diameter ratio of the primary particle of graphite particle / primary particle of lithium vanadium oxide was about five.

Moreover, the produced slurry was apply | coated to copper foil, and after drying, the negative electrode was produced with electrode density to 1.8 g / cm <3>. A cathode electrode was prepared by dissolving lithium cobalt acid and 1.4 M LiPF ₆ dissolved in a mixed solvent of ethyl carbonate (EC): diethyl carbonate (DEC) = 3: 7 (volume ratio) as an electrolyte. It was.

(Comparative Example 2)

A nonaqueous secondary battery was produced in the same manner as in Comparative Example 1 except that lithium vanadium oxide and graphite were 50/50 in weight ratio.

(Comparative Example 3)

A negative electrode material was synthesized in the same manner as in Comparative Example 1 except that a lithium vanadium oxide obtained at a firing temperature of 1100 ° C. was fabricated.

(Comparative Example 4)

A negative electrode material was synthesized in the same manner as in Comparative Example 1 except that the weight ratio of lithium vanadium oxide and graphite obtained at a calcination temperature of 1100 ° C. was 90/10 to produce a nonaqueous secondary battery.

Graphite particles in Example 1, the particles obtained as a result of coating the precursor on the surface of the graphite particles, and the resulting particles after firing the graphite particles surface-coated the precursor was observed by a scanning electron microscope. The results are shown in Figures 2a to 2d.

Figure 2a is a photograph of the graphite particles used in Example 1 of the present invention, Figure 2b is a photograph of the resulting particles after coating the precursor on the surface of the graphite particles, Figure 2c is a graphite particle surface-coated precursor After firing, it is a photograph of the resultant particles (magnification 1500 times), and FIG. 2D is a photograph of the resulting particles after firing the graphite particles coated with the precursor (magnification of 2000 times), which is 1.3 times larger than that of FIG. It is also.

According to FIG. 2B, it turns out that the precursor containing lithium and vanadium is uniformly coated by the graphite particle. 2C shows that lithium vanadium oxide particles are interspersed on the surface of the graphite particles after firing, and it is understood that the electrical conduction path between the graphite particles and the lithium vanadium oxide is easily secured. Accordingly, it can be expected that a non-aqueous secondary battery having high efficiency charge and discharge characteristics can be obtained by suppressing a decrease in conductivity due to charge and discharge reactions and an increase in resistance inside the battery.

Next, the lithium secondary batteries obtained in Examples 1 to 9 and Comparative Examples 1 to 4 were evaluated. The results are shown in Table 1 below.

As the evaluation item, the capacity retention rate (%) after 200 cycles when the capacity of the first cycle was 100 was employed. Here, it can be said that the capacity retention rate (%) is good if it is 80% or more.

In Examples 1 to 9, even when the weight ratio and the particle diameter ratio of graphite were changed, it can be confirmed that the capacity retention ratio after 200 cycles was 80% or more. 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, 23% in Comparative Example 4, and simply It is presumed that only the graphite and lithium vanadium oxide are present alone in the mixture, and the contact resistance increases and the capacity retention rate is lowered.

As described above, according to the present invention, since the lithium vanadium oxide forming the negative electrode material for the non-aqueous secondary battery is previously scattered on the surface of another negative electrode active material and / or the conductive material, not only a high conductive path is secured, but also charge and discharge are accompanied. Even when the material is expanded / contracted in the negative electrode, the conductivity between the materials is not lost, and thus the charge / discharge characteristics of the non- rechargeable battery can be improved.

In addition, since the size of the lithium vanadium oxide particles can be reduced, even when expansion / contraction of the lithium vanadium oxide particles accompanying charging and discharging occurs, the collapse of the lithium vanadium oxide particles can be suppressed and the charge and discharge of the non-aqueous secondary battery The characteristic can be further improved.

Although the Example of this invention was described referring an Example above, 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 the spiral cylindrical lithium secondary battery, and the coin-type lithium secondary battery and the square lithium secondary battery are the same as long as they possess the features of the present invention. Effect is obtained.

Characteristics of the present invention with respect to the composition of the negative electrode active material of this embodiment, the type of metal (Me) element contained therein, the material, shape, manufacturing process, manufacturing conditions, shape of a lithium secondary battery, and the like of each structural member. As long as it owns, it is included in the scope of the present invention.

1 is a longitudinal sectional view showing a non-aqueous secondary battery according to one embodiment of the present invention.

Figure 2a is a photograph of the graphite particles used in Example 1 of the present invention, Figure 2b is a photograph when the precursor is coated on the surface of the graphite particles, Figure 2c is a photograph when the precursor is calcined surface coated graphite particles (1500 times magnification), and FIG. 2D is an enlarged view of 1.3 times the above-mentioned FIG. 2C.

[Description of main parts of drawing]

1 non-rechargeable secondary battery

2 cases

3 anode

4 cathode

5 separator

6 Center Pin

7 Positive terminal

8 Cathode terminal

9a, 9b insulation plate

10 laminate

Claims (7)

Core material; And A negative electrode material including a first negative electrode active material, which is interspersed on the surface of the core material in advance and comprises lithium vanadium oxide, Wherein the core material is selected from the group consisting of a second negative electrode active material, a conductive material, and a mixture thereof different from the lithium vanadium oxide. The method of claim 1, The weight ratio (weight of the core material / weight of the first negative electrode active material) of the core material and the first negative electrode active material is 20/80 to 95/5 negative electrode for a secondary battery. The method of claim 1, A negative electrode for a non-aqueous secondary battery having a particle diameter ratio (primary particle of the core material / primary particle of the first negative electrode active material) of the core material and the first negative electrode active material is 1 to 100. The method of claim 1, The first negative electrode active material is a negative electrode for a non-aqueous battery that is interspersed by mixing or surface coating a precursor containing the first negative electrode active material to the core material, and firing in an inert gas atmosphere. The method of claim 1, The second negative electrode active material is lithium metal; Metallic materials alloyable with lithium; Transition metal oxides; Materials capable of doping and undoping lithium; Materials capable of forming compounds by reversibly reacting with lithium; Materials capable of reversibly intercalating and deintercalating lithium ions; And a negative electrode for a non-aqueous battery that is selected from the group consisting of a mixture thereof. The method of claim 1, The conductive material may be selected from the group consisting of crystalline carbon material, amorphous carbon material, columnar carbon material, metal powder, metal fiber, and mixtures thereof. A nonaqueous secondary battery comprising the negative electrode for a lithium secondary battery according to any one of claims 1 to 6.

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