JP5525419B2 - Negative electrode material for lithium ion secondary battery and method for producing the same - Google Patents

Description

  The present invention relates to a negative electrode material for a lithium ion secondary battery and a method for producing the same.

  2. Description of the Related Art In recent years, lithium ion secondary batteries have been frequently used as drive sources for various electronic devices in addition to electric vehicles and hybrid vehicles. The lithium ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte, and lithium ions in the electrolyte play a role of electrical conduction.

The operation of the lithium ion secondary battery during discharging and charging is as follows.
First, at the time of discharge, lithium molecules occluded in the negative electrode are ionized, and the generated lithium ions reach the positive electrode through the electrolyte. The lithium ions that have reached the positive electrode release electrons to become a lithium compound and are occluded by the positive electrode. On the other hand, at the time of charging, the lithium compound stored in the positive electrode is ionized, and the generated lithium ion reaches the negative electrode through the electrolyte. The lithium ions that have reached the negative electrode receive electrons and become lithium molecules, which are occluded by the negative electrode.

  Thus, as a negative electrode material of a lithium ion secondary battery, it is calculated | required that it is a material which can occlude / release lithium ion, and a carbonaceous material is usually used. Among these, highly crystalline graphite is preferably used. When graphite is used as the negative electrode material, a low negative electrode potential is obtained, and a high average voltage (potential difference between the positive electrode potential and the negative electrode potential) is obtained.

  By the way, as an evaluation index of battery performance, an energy density representing an energy storage amount per unit weight is used. The energy density is calculated by dividing the product of the average voltage and the capacity by the weight, and the higher the energy density, the better the battery. Therefore, to increase the energy density, it is essential to increase the average voltage and increase the capacity.

  Therefore, in addition to graphite, for example, a carbon-based material obtained by heat-treating an aromatic organic polymer compound in a reducing gas (see Patent Document 1) or xylene resin is heated and polymerized in an inert atmosphere. The obtained carbon-based material (see Patent Document 2) and the carbon-based material (see Patent Document 3) obtained by heat-treating a raw material mainly composed of pitch have been studied as negative electrode materials. All of these carbon-based materials are low crystalline carbon-based materials that have been heat-treated at a relatively low temperature. By using these as the negative electrode, a lithium ion secondary battery having a capacity larger than that of graphite can be obtained.

Japanese Patent No. 3363959 JP 2008-66259 A JP 2000-251885 A

  However, low-crystalline carbon-based materials such as Patent Documents 1 to 3 have a characteristic that the negative electrode potential increases as the discharge depth increases. FIG. 1 shows the battery capacity and negative electrode potential when a low crystalline polyparaphenylene fired product obtained by firing polyparaphenylene at a relatively low temperature (300 to 1000 ° C.) and graphite are used as the negative electrode. It is a figure which shows the relationship. As shown in FIG. 1, graphite has a smaller capacity than the calcined polyparaphenylene, but stably exhibits a low negative electrode potential regardless of the depth of discharge. In contrast, the calcined polyparaphenylene has a larger capacity than graphite, but the negative electrode potential increases as the depth of discharge increases.

When the negative electrode potential becomes high, the following problems occur.
FIG. 2 is a diagram showing the relationship between the negative electrode potential and the positive electrode potential when the fired polyparaphenylene and graphite are used as the negative electrode, respectively. The positive electrode potential in FIG. 2 is a positive electrode potential when LiNiCoMnO ₂ is used as the positive electrode. Here, the average voltage of the battery is determined by the potential difference between the positive electrode potential and the negative electrode potential, and the higher this potential difference, the higher the average voltage. As shown in FIG. 2, when the polyparaphenylene fired product is used as the negative electrode, the negative electrode potential increases as the depth of discharge increases, so the potential difference from the positive electrode potential is indicated by the oblique lines in FIG. 2 rather than graphite. It gets smaller by the minute. That is, when a polyparaphenylene fired product is used as a negative electrode, there arises a problem that a high average voltage cannot be obtained.

The above problems are caused by the following factors.
A low crystalline carbon-based material and a highly crystalline carbon-based material have different discharge potentials from which lithium ions are released during discharge. For this reason, the result of investigating the amount of lithium ions desorbed per unit voltage by differentiating the capacity with the potential is shown in FIG. FIG. 3 is a diagram showing the relationship between the negative electrode potential of the fired polyparaphenylene and graphite, and the desorption amount dQ / dV of lithium ions per unit voltage. As shown in FIG. 3, lithium ions are desorbed at around 0.2 V in graphite, whereas lithium ions are desorbed from around 0.2 V in the fired polyparaphenylene, especially around 1 V. Many lithium ions are desorbed. Thus, when a polyparaphenylene baked product is used as a negative electrode, the high average voltage cannot be obtained because the discharge potential of the occluded lithium ions is high.

  Therefore, a negative electrode material for a lithium ion secondary battery having a high energy density and high energy density is developed by reducing the discharge potential of the low crystalline carbon-based material to lower the negative electrode potential. It is desirable.

  This invention is made | formed in view of the above, The objective is to provide the negative electrode material for lithium ion secondary batteries which has a high average voltage and a large capacity | capacitance, and has a high energy density, and its manufacturing method. .

In order to achieve the above object, a negative electrode material for a lithium ion secondary battery according to the present invention includes conductive carbon and a carbon active material that covers the conductive carbon and absorbs and releases lithium ions. material, the conductive crystallinity than carbon has a low, a fired product of the burned material or xylene resin polyparaphenylene, the conductive carbon is vapor grown carbon fiber, the conductive carbon Content is 1-3 mass% with respect to the whole negative electrode material, It is characterized by the above-mentioned.

In the present invention, the negative electrode material is composed of conductive carbon and a carbon active material that covers the conductive carbon and can occlude and release lithium ions. In addition, the carbon active material had a crystallinity lower than that of conductive carbon, and the content of conductive carbon was 1 to 3 % by mass with respect to the whole negative electrode material. Here, the “crystallinity” in the present invention means the ratio of the crystallized portion to the entire material when the carbon-based material is partially crystallized.
As a result, at the interface between the carbon active material and the conductive carbon, the crystal structure of the low crystalline carbon active material changes under the influence of the high crystalline conductive carbon and becomes highly crystalline like graphite. . As a result, lithium ions easily enter and exit between the crystal layers formed by high crystallization. As a result, the discharge potential is lowered, the negative electrode potential is lowered, and a high average voltage can be obtained. Therefore, according to the present invention, it is possible to provide a negative electrode material for a lithium ion secondary battery that has a high average voltage and a large capacity and has a high energy density.

In the present invention, the carbon active material is composed of a fired product of polyparaphenylene or a fired product of xylene resin, and the conductive carbon is composed of vapor grown carbon fiber.
According to the present invention, a fired product of polyparaphenylene or xylene resin, which is a carbon-based material having low crystallinity, and vapor-grown carbon fiber, which is a carbon-based material having very high crystallinity, are used. Thus, the above effect can be further enhanced. That is, at the interface between the fired product and the vapor-grown carbon fiber, the crystal structure of the fired product is greatly influenced by the vapor-grown carbon fiber and is highly crystallized like graphite. As a result, lithium ions easily enter and exit between crystal layers formed by high crystallization, and as a result, the discharge potential is greatly reduced, the negative electrode potential is greatly reduced, and a higher average voltage can be obtained. Therefore, according to the present invention, it is possible to provide a negative electrode material for a lithium ion secondary battery that has a higher average voltage and a larger capacity and has a higher energy density.

  The manufacturing method according to the present invention is a method for manufacturing a negative electrode material for a lithium ion secondary battery according to the above invention, wherein the conductive carbon is added to a raw material of the carbon active material, and the conductive carbon A step of synthesizing a precursor resin of the carbon active material in the presence, and a step of obtaining the carbon active material covering the conductive carbon by firing the precursor resin. .

In this invention, by passing through a step of synthesizing a precursor resin of a carbon active material in the presence of conductive carbon, and a step of obtaining a carbon active material covering the conductive carbon by firing the precursor resin, A negative electrode material for a lithium ion secondary battery according to the above invention was produced.
According to the present invention, by synthesizing a carbon active material precursor resin in the presence of conductive carbon, the conductive carbon is coated with the carbon active material precursor resin. And the carbon active material which coat | covers electroconductive carbon is reliably obtained by baking in this state. Therefore, according to the present invention, a negative electrode material for a lithium ion secondary battery that has both a higher average voltage and a large capacity and a high energy density can be obtained with certainty.

  The manufacturing method according to the present invention is a method for manufacturing a negative electrode material for a lithium ion secondary battery according to the above invention, wherein the step of mixing the precursor resin of the carbon active material and the conductive carbon, And calcining the mixture obtained in the step to obtain the carbon active material covering the conductive carbon.

In this invention, by passing through the process of mixing the precursor resin of carbon active material and conductive carbon, and the process of obtaining the carbon active material which coat | covers conductive carbon by baking the obtained mixture. A negative electrode material for a lithium ion secondary battery according to the above invention was manufactured.
According to the present invention, by mixing the carbon active material precursor resin and the conductive carbon, the conductive carbon is covered with the carbon active material precursor resin. And the carbon active material which coat | covers electroconductive carbon is reliably obtained by baking in this state. Therefore, according to the present invention, a negative electrode material for a lithium ion secondary battery that has both a higher average voltage and a large capacity and a high energy density can be obtained with certainty.

  The manufacturing method according to the present invention is a method for manufacturing a negative electrode material for a lithium ion secondary battery according to the above-described invention, wherein the carbon active material is obtained by firing the precursor resin of the carbon active material. And the step of obtaining the carbon active material covering the conductive carbon by adding the conductive carbon to the carbon active material, and pulverizing and mixing the conductive carbon.

In this invention, the step of obtaining a carbon active material by baking a precursor resin of the carbon active material, and adding the conductive carbon to the obtained carbon active material, pulverizing and mixing, thereby covering the conductive carbon The negative electrode material for a lithium ion secondary battery according to the above-described invention was manufactured through a step of obtaining a carbon active material.
According to the present invention, by adding conductive carbon to the carbon active material, and pulverizing and mixing the conductive carbon, the conductive carbon can be coated with the carbon active material. The material is reliably obtained. Therefore, according to the present invention, a negative electrode material for a lithium ion secondary battery that has both a higher average voltage and a large capacity and a high energy density can be obtained with certainty.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode material for lithium ion secondary batteries which has a high average voltage and a big capacity | capacitance and has a high energy density, and its manufacturing method can be provided.

It is a figure which shows the relationship between the capacity | capacitance at the time of using a polyparaphenylene baked material and graphite for a negative electrode, and a negative electrode electric potential. It is a figure which shows the relationship between the negative electrode potential at the time of using a polyparaphenylene baked material and graphite for a negative electrode, and a positive electrode potential. It is a figure which shows the relationship between the negative electrode electric potential at the time of using a polyparaphenylene baked material and graphite for a negative electrode, and the desorption amount dQ / dV of lithium ion per unit voltage. It is a surface enlarged image of the interface part of VGCF and a polyparaphenylene baked product. It is a figure which shows typically the crystal structure of VGCF and polyparaphenylene baking products shown in FIG. 4, (A) is a schematic diagram of the crystal structure of VGCF of the area | region away from the interface part, (B) is an interface. It is a schematic diagram of the crystal structure of VGCF and a polyparaphenylene baked product in a part, (C) is a schematic diagram of the crystal structure of the polyparaphenylene baked product of the area | region away from the interface part. It is a flowchart of the manufacturing method 1 which concerns on one Embodiment of this invention. It is a flowchart of the manufacturing method 2 which concerns on one Embodiment of this invention. It is a flowchart of the manufacturing method 3 which concerns on one Embodiment of this invention. It is a figure which shows the relationship between the negative electrode electric potential in Examples 1-2, the reference examples 1-3, and the comparative example 1, and the desorption amount dQ / dV of lithium ion per unit voltage. It is a figure which shows the relationship between the capacity | capacitance and negative electrode potential in Reference Examples 1 and 3 and Comparative Examples 1-2. It is a figure which shows the relationship between content of VGCF and the capacity | capacitance in Examples 1-2 , Reference Examples 1-3, and Comparative Examples 1-2. It is a figure which shows the relationship between the negative electrode electric potential in Examples 6-7 , the reference examples 4-6, and the comparative example 3, and the desorption amount dQ / dV of lithium ion per unit voltage. It is a figure which shows the relationship between the capacity | capacitance and negative electrode potential in the reference examples 4 and 6 and the comparative examples 2 and 3. FIG.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

<Negative electrode material>
A negative electrode material for a lithium ion secondary battery according to an embodiment of the present invention includes conductive carbon and a carbon active material.

  Conductive carbon is contained in the negative electrode material in a state of being covered with a carbon active material described later. Conductive carbon is a carbon material with high crystallinity and has a higher crystallinity than a carbon active material described later. Examples of the shape of the conductive carbon include a fibrous one and a spherical one, and a fibrous one is preferably used. Specific examples of conductive carbon include vapor-grown carbon fibers, which are highly crystalline carbon fibers synthesized by a conventionally known vapor phase method. For example, “VGCF” manufactured by Showa Denko KK is preferably used. . In addition, electroconductive carbon may be used individually by 1 type, and may use several types together.

  Conductive carbon is contained in a proportion of 1 to 20% by mass with respect to the whole negative electrode material. When the conductive carbon content is less than 1% by mass, the discharge potential and the negative electrode potential cannot be sufficiently lowered, and a high average voltage cannot be obtained. On the other hand, when the content of the conductive carbon exceeds 20% by mass, the discharge potential and the negative electrode potential can be sufficiently reduced, but the capacity is reduced to the same level as that of the conductive carbon. A more preferable conductive carbon content is 5 to 20% by mass.

  The carbon active material is a carbon-based material capable of occluding and releasing lithium ions, and is a low-crystalline carbon-based material having a crystallinity lower than that of the conductive carbon described above. This carbon active material is contained in the negative electrode material in a state of covering the conductive carbon described above. Here, the “covered state” includes not only a state where the entire surface of the conductive carbon is covered with the carbon active material but also a state where a part of the surface of the conductive carbon is covered with the carbon active material. .

  As the carbon active material, a fired product of a thermosetting non-graphitizable resin that is difficult to become highly crystalline graphite is preferably used. Specifically, a fired product of polyparaphenylene or a fired product of xylene resin is preferable. Used. The fired product of these resins is a carbon material that is not highly crystallized and has low crystallinity unlike graphite.

The crystal structure of the carbon active material covering the conductive carbon will be described with reference to FIGS.
FIG. 4 is an enlarged image of the surface of the interface portion between the conductive carbon VGCF and the polyparaphenylene fired product which is a carbon active material covering the VGCF. FIG. 5 is a diagram schematically showing the crystal structure of the fired product of VGCF and polyparaphenylene shown in FIG. 4. FIG. 5 (A) is away from the portion (A) of FIG. 4, that is, the interface portion. It is a schematic diagram of the crystal structure of the VGCF in the region, (B) is a schematic diagram of the crystal structure of the VGCF and the polyparaphenylene fired product in the part (B) of FIG. 4, that is, the interface part, (C) FIG. 5 is a schematic diagram of the crystal structure of the fired polyparaphenylene product in the part (C) of FIG.

  As shown in FIGS. 4 and 5A, in the VGCF in the region away from the interface portion, the crystal orientation in the vertical direction in these figures is recognized, and the crystals are regularly oriented in layers. For this reason, it has a structure in which lithium ions easily enter and exit these crystal layers and easily absorb and release lithium ions.

  On the other hand, as shown in FIG. 4 and FIG. 5 (C), in the polyparaphenylene fired product in a region away from the interface portion, no crystal orientation is observed, and the crystal layer is present irregularly. For this reason, it has a structure in which lithium ions do not easily enter and exit between crystal layers, and lithium ions are difficult to occlude and release.

  On the other hand, as shown in FIG. 4 and FIG. 5 (B), in the polyparaphenylene fired product at the interface portion, the orientation of the crystal is recognized under the influence of VGCF, and the crystal is regularly oriented in a layered manner. ing. In other words, the crystal structure of the polyparaphenylene fired product at the interface portion is a structure in which lithium ions can easily enter and exit, and lithium ions can be easily stored and released, like VGCF. Thereby, in the carbon active material which coat | covers electroconductive carbon, a discharge potential and a negative electrode potential can be reduced, and a high average voltage is obtained.

  In addition, the negative electrode material for a lithium ion secondary battery according to the present embodiment may contain other components in addition to the conductive carbon and the carbon active material within a range where the effects of the present embodiment are exhibited. .

<Manufacturing method>
Although it does not specifically limit as a manufacturing method of the negative electrode material for lithium ion secondary batteries which concerns on this embodiment, Preferably, the following manufacturing methods 1-3 are employ | adopted. Hereinafter, production methods 1 to 3 will be described.

[Production Method 1]
FIG. 6 is a flowchart of the manufacturing method 1 according to the embodiment of the present invention.
As shown in FIG. 6, the manufacturing method 1 has step S11 and step S12. Moreover, when producing a negative electrode sheet, it has further step S13.

  In step S11, a thermosetting non-graphitizable resin corresponding to the precursor resin of the carbon active material is synthesized. Specifically, first, each synthetic raw material of thermosetting non-graphitic resin is blended in a predetermined molar ratio. Next, after the blend is mixed well, conductive carbon is added and mixed uniformly. At this time, conductive carbon is added so that it may become 1-20 mass% content with respect to the whole negative electrode material. In consideration of the carbonization yield of the thermosetting non-graphitic resin, the amount of conductive carbon added is such that the mass of the conductive carbon is 1 to 20% by mass relative to the mass after carbonization of the thermosetting graphitic resin. To calculate. That is, the mass ratio of the target conductive carbon (in the range of 0.01 to 0.2) and the carbonization yield of the thermosetting non-graphitic resin (for example, poly In the case of paraphenylene, the amount of conductive carbon added is calculated by multiplying the carbonization yield by about 0.85).

  Next, a thermosetting non-graphite resin is synthesized in the presence of conductive carbon. Specifically, the synthesis reaction of the thermosetting non-graphite resin is advanced in the presence of conductive carbon. Thereby, a thermosetting non-graphitizable resin corresponding to the precursor resin of the carbon active material is obtained. At this time, the thermosetting non-graphitic resin is formed in a state where the surface of the conductive carbon is coated.

In step S12, a negative electrode material composed of conductive carbon and a carbon active material that covers the conductive carbon and has a lower crystallinity than the conductive carbon by firing a thermosetting non-graphite resin. Get. Specifically, the carbon active material formed in a state where the surface of the conductive carbon is coated in step S11 is fired under a predetermined condition in an inert gas atmosphere. Thereby, a negative electrode material composed of conductive carbon and a carbon active material that covers the conductive carbon and has a lower crystallinity than the conductive carbon is obtained.
Note that the firing temperature is preferably 300 ° C. to 1000 ° C. because a low crystalline carbon material is easily obtained.

  In step S13, a negative electrode sheet is produced from the negative electrode material obtained in step S12. Specifically, first, a predetermined amount of a binder such as PVdF is added to and mixed with the negative electrode material obtained in step S12. Next, a predetermined amount of a diluent solvent such as NMP is added and kneaded with a homogenizer or the like to prepare a slurry. The prepared slurry is uniformly coated on a copper foil or the like as a current collector and dried to prepare a negative electrode sheet.

[Production Method 2]
FIG. 7 is a flowchart of the manufacturing method 2 according to the embodiment of the present invention.
As shown in FIG. 7, the manufacturing method 2 has step S21 and step S22. Moreover, when producing a negative electrode sheet, it has further step S23.

  In step S21, conductive carbon is added to a thermosetting non-graphitizable resin corresponding to the precursor resin of the carbon active material and mixed uniformly. At this time, conductive carbon is added so that it may become 1-20 mass% content with respect to the whole negative electrode material. The amount of conductive carbon added is calculated by the same calculation method as in manufacturing method 1 described above. A commercially available thing can be used as a thermosetting type non-graphite resin.

  In step S22, the mixture obtained in step S21 is fired under the same firing conditions as in manufacturing method 1 in an inert gas atmosphere. Thereby, a negative electrode material composed of conductive carbon and a carbon active material that covers the conductive carbon and has a lower crystallinity than the conductive carbon is obtained.

  In step S23, a negative electrode sheet is produced by performing the same process as in step S13 of manufacturing method 1 described above.

[Production Method 3]
FIG. 8 is a flowchart of the manufacturing method 3 according to an embodiment of the present invention.
As shown in FIG. 8, the manufacturing method 3 has step S31, step S32, and step S33. Moreover, when producing a negative electrode sheet, it has further step S34.

In step S31, a thermosetting non-graphite resin corresponding to the precursor resin of the carbon active material is synthesized. Specifically, first, each synthetic raw material of thermosetting non-graphitic resin is blended in a predetermined molar ratio. Next, after the mixture is mixed well, the synthesis reaction of the thermosetting non-graphitic resin proceeds. Thereby, a thermosetting non-graphitizable resin corresponding to the precursor resin of the carbon active material is obtained.
This step is not essential, and a commercially available thermosetting non-graphitic resin may be used instead of synthesizing the thermosetting non-graphitic resin.

  In step S32, a carbon active material is obtained by baking a thermosetting non-graphite resin. Specifically, the thermosetting non-graphitic resin obtained in step S31 is baked under the same baking conditions as in manufacturing method 1 in an inert gas atmosphere. Thereby, a carbon active material is obtained.

  In step S33, conductive carbon is added to the carbon active material obtained in step S32 to obtain a negative electrode material. Specifically, conductive carbon is added to the carbon active material obtained in step S32 so as to have a content of 1 to 20% by mass with respect to the entire negative electrode material. Next, ball milling is performed under predetermined ball mill conditions. Thereby, the negative electrode material comprised from a conductive carbon and the carbon active material which coat | covers a conductive carbon is obtained.

  In step S34, a negative electrode sheet is produced by performing the same process as in step S13 of manufacturing method 1 described above.

The negative electrode material for a lithium ion secondary battery according to this embodiment manufactured as described above is used for manufacturing a lithium ion secondary battery as follows, for example.
First, the negative electrode sheet produced as described above is alternately laminated via a separately produced positive electrode sheet and a separator to produce an electricity storage device. Subsequently, the produced electrical storage element and electrolyte solution are accommodated in a battery case. Finally, a lithium ion secondary battery is manufactured by connecting the positive electrode and the negative electrode to an external circuit.

According to this embodiment, the following effects are produced.
In the present embodiment, the negative electrode material is composed of conductive carbon and a carbon active material that covers the conductive carbon and can occlude and release lithium ions. In addition, the carbon active material had a lower crystallinity than that of conductive carbon, and the content of conductive carbon was 1 to 20% by mass with respect to the entire negative electrode material.
As a result, the crystal structure of the low crystalline carbon active material changes under the influence of the high crystalline conductive carbon at the interface between the carbon active material and the conductive carbon, and the crystal structure becomes highly crystalline like graphite. To do. As a result, lithium ions easily enter and exit between the crystal layers formed by high crystallization. As a result, the discharge potential is lowered, the negative electrode potential is lowered, and a high average voltage can be obtained. Therefore, according to this embodiment, it is possible to provide a negative electrode material for a lithium ion secondary battery that has both a high average voltage and a large capacity and has a high energy density.

  Further, by using a fired product of polyparaphenylene or xylene resin, which is a carbon material having low crystallinity, and vapor-grown carbon fiber, which is a carbon material having very high crystallinity, The effect is further enhanced. That is, at the interface between the fired product and the vapor-grown carbon fiber, the crystal structure of the fired product is greatly influenced by the vapor-grown carbon fiber and is highly crystallized like graphite. As a result, lithium ions easily enter and exit between crystal layers formed by high crystallization, and as a result, the discharge potential is greatly reduced, the negative electrode potential is greatly reduced, and a higher average voltage can be obtained.

Moreover, in the manufacturing method 1, it passes through the process of synthesize | combining the precursor resin of carbon active material in presence of electroconductive carbon, and the process of baking a precursor resin and obtaining the carbon active material which coat | covers electroconductive carbon. Thus, the negative electrode material for a lithium ion secondary battery according to this embodiment was produced.
According to the manufacturing method 1, by synthesizing a carbon active material precursor resin in the presence of conductive carbon, the conductive carbon is covered with the carbon active material precursor resin. And the carbon active material which coat | covers electroconductive carbon is reliably obtained by baking in this state. Therefore, according to this production method 1, a negative electrode material for a lithium ion secondary battery having a higher average voltage and a large capacity and having a high energy density can be obtained with certainty.

Moreover, in the manufacturing method 2, the process of mixing the precursor resin of carbon active material and conductive carbon, and the process of obtaining the carbon active material which coat | covers conductive carbon by baking the obtained mixture, By passing, the negative electrode material for lithium ion secondary batteries which concerns on this embodiment was manufactured.
According to this production method 2, by mixing the carbon active material precursor resin and the conductive carbon, the conductive carbon is coated with the carbon active material precursor resin. And the carbon active material which coat | covers electroconductive carbon is reliably obtained by baking in this state. Therefore, according to the present invention, a negative electrode material for a lithium ion secondary battery that has both a higher average voltage and a large capacity and a high energy density can be obtained with certainty.

In addition, in the production method 3, the carbon active material precursor resin is baked to obtain the carbon active material, and conductive carbon is added to the obtained carbon active material and pulverized and mixed. The negative electrode material for lithium ion secondary batteries according to the present embodiment was manufactured through a step of obtaining a carbon active material that coats.
According to this production method 3, by adding conductive carbon to the carbon active material, pulverizing and mixing, the conductive carbon can be covered with the carbon active material, and the conductive carbon is coated. A carbon active material is obtained reliably. Therefore, according to this production method 3, a negative electrode material for a lithium ion secondary battery having a higher energy density and a higher energy density can be obtained with certainty.

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications and improvements within the scope that can achieve the object of the present invention are included in the present invention.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

<Example 1>
First, benzene, anhydrous aluminum chloride and anhydrous copper chloride were mixed at a molar ratio of 4: 1: 1 as a precursor resin synthesis raw material for a carbon active material. After mixing, “VGCF” manufactured by Showa Denko KK as conductive carbon was added so as to have a content of 1% by mass with respect to the whole negative electrode material, and mixed uniformly.

  After uniformly mixing, the synthesis reaction by Kovacic method was allowed to proceed in the presence of VGCF. As a result, polyparaphenylene, a thermosetting non-graphite resin, corresponding to the precursor resin of the carbon active material was obtained. The obtained polyparaphenylene was formed in the state which coat | covered the surface of VGCF.

Next, the polyparaphenylene formed in a state where VGCF was coated was fired in an inert gas atmosphere according to the following conditions. As a result, a negative electrode material composed of VGCF and a fired polyparaphenylene corresponding to a carbon active material covering VGCF was obtained.
[Baking conditions]
Temperature increase rate: 10 ° C / min Firing temperature: 640 ° C
Retention time: 6 hours

Finally, a negative electrode sheet was prepared from the negative electrode material obtained above. Specifically, a negative electrode sheet was produced according to the following procedure.
First, PVdF was added and mixed as a binder to the negative electrode material obtained above. The addition amount was 10 by PVdF with respect to the negative electrode material 90 by mass ratio. Next, NMP was added as a diluent solvent and kneaded with a homogenizer to prepare a slurry. The prepared slurry was uniformly applied onto a copper foil as a current collector and dried to prepare a negative electrode sheet.

<Example 2>
A negative electrode sheet was prepared after obtaining a negative electrode material in the same manner as in Example 1 except that the content of VGCF in Example 1 was changed and added so as to be 3% by mass with respect to the entire negative electrode material.

< Reference Example 1 >
A negative electrode sheet was prepared after obtaining a negative electrode material in the same manner as in Example 1 except that the content of VGCF in Example 1 was changed and added so as to be 5% by mass with respect to the whole negative electrode material.

< Reference Example 2 >
A negative electrode sheet was prepared after obtaining a negative electrode material in the same manner as in Example 1 except that the content of VGCF in Example 1 was changed and added so as to be 10% by mass with respect to the entire negative electrode material.

< Reference Example 3 >
A negative electrode material was obtained in the same manner as in Example 1 except that the content of VGCF in Example 1 was changed and added so as to be 20% by mass with respect to the entire negative electrode material.

<Example 6>
First, “Nicanol NP140” manufactured by Fudou Co., Ltd. was mixed with ethanol as a precursor resin material for a carbon active material. After mixing, “VGCF” manufactured by Showa Denko KK as conductive carbon was added so as to have a content of 1% by mass with respect to the whole negative electrode material, and mixed uniformly.

  After mixing uniformly, ethanol was dried in the presence of VGCF. Thereby, a xylene resin of a thermosetting non-graphite resin corresponding to a precursor resin of a carbon active material was obtained. The obtained xylene resin was formed in the state which coat | covered the surface of VGCF.

  Next, the xylene resin formed in a state where VGCF was coated was baked according to the same conditions as in Example 1 in an inert gas atmosphere. As a result, a negative electrode material composed of VGCF and a fired xylene resin corresponding to the carbon active material covering VGCF was obtained.

  Finally, a negative electrode sheet was prepared from the negative electrode material obtained above. Specifically, a negative electrode sheet was produced according to the same procedure as in Example 1.

<Example 7>
A negative electrode material was obtained in the same manner as in Example 6 except that the content of VGCF in Example 6 was changed and added so as to be 3% by mass with respect to the entire negative electrode material, and then a negative electrode sheet was produced.

< Reference Example 4 >
A negative electrode material was obtained in the same manner as in Example 6 except that the content of VGCF in Example 6 was changed and added so as to be 5% by mass with respect to the entire negative electrode material.

< Reference Example 5 >
A negative electrode material was obtained in the same manner as in Example 6 except that the content of VGCF in Example 6 was changed and added so as to be 10% by mass with respect to the whole negative electrode material.

< Reference Example 6 >
A negative electrode material was obtained in the same manner as in Example 6 except that the content of VGCF in Example 6 was changed and added so as to be 20% by mass with respect to the entire negative electrode material.

<Example 11>
First, benzene, anhydrous aluminum chloride and anhydrous copper chloride were mixed at a molar ratio of 4: 1: 1 as a precursor resin synthesis raw material for a carbon active material. After mixing well, the synthesis reaction by Kovacic method was allowed to proceed. As a result, polyparaphenylene, a thermosetting non-graphite resin, corresponding to the precursor resin of the carbon active material was obtained.

  The polyparaphenylene obtained above was fired under the same firing conditions as in Example 1 in an inert gas atmosphere. Thereby, a polyparaphenylene fired product corresponding to the carbon active material was obtained.

To the polyparaphenylene fired product obtained above, VGCF as conductive carbon was added so as to have a content of 1% by mass with respect to the whole negative electrode material. Subsequently, the ball mill process was implemented according to the following ball mill conditions. This obtained the negative electrode material comprised from VGCF and the polyparaphenylene baked material which coat | covers VGCF.
[Ball mill conditions]
Rotation speed: 200rpm
Processing time: 2 hours

  Finally, a negative electrode sheet was prepared from the negative electrode material obtained above. Specifically, a negative electrode sheet was produced according to the same procedure as in Example 1.

<Example 12>
A negative electrode material was obtained in the same manner as in Example 11 except that the content of VGCF in Example 11 was changed and added so as to be 3% by mass with respect to the entire negative electrode material, and then a negative electrode sheet was produced.

< Reference Example 7 >
A negative electrode material was obtained in the same manner as in Example 11 except that the content of VGCF in Example 11 was changed and added so as to be 5% by mass with respect to the whole negative electrode material, and then a negative electrode sheet was produced.

< Reference Example 8 >
A negative electrode material was obtained in the same manner as in Example 11 except that the content of VGCF in Example 11 was changed and added so as to be 10% by mass with respect to the entire negative electrode material.

< Reference Example 9 >
A negative electrode sheet was prepared after obtaining a negative electrode material in the same manner as in Example 11 except that the content of VGCF in Example 11 was changed and added so as to be 20% by mass with respect to the entire negative electrode material.

<Example 16>
First, as a precursor resin material of a carbon active material, “Nicanol NP140” manufactured by Fudou Co., Ltd. was fired under the same firing conditions as in Example 1 in an inert gas atmosphere. Thus, a fired xylene resin corresponding to the carbon active material was obtained.

  VGCF as conductive carbon was added to the fired xylene resin obtained above so as to have a content of 1% by mass with respect to the whole negative electrode material. Next, ball milling was performed under the same conditions as in Example 11. This obtained the negative electrode material comprised from VGCF and the xylene resin baking products which coat | cover VGCF.

  Finally, a negative electrode sheet was prepared from the negative electrode material obtained above. Specifically, a negative electrode sheet was produced according to the same procedure as in Example 1.

<Example 17>
A negative electrode material was obtained in the same manner as in Example 16 except that the content of VGCF in Example 16 was changed and added so as to be 3% by mass with respect to the entire negative electrode material, and then a negative electrode sheet was produced.

< Reference Example 10 >
A negative electrode material was obtained in the same manner as in Example 16 except that the content of VGCF in Example 16 was changed and added so as to be 5% by mass with respect to the entire negative electrode material, and then a negative electrode sheet was produced.

< Reference Example 11 >
A negative electrode material was obtained in the same manner as in Example 16 except that the content of VGCF in Example 16 was changed and added so as to be 10% by mass with respect to the entire negative electrode material, and then a negative electrode sheet was produced.

< Reference Example 12 >
A negative electrode material was obtained in the same manner as in Example 16 except that the content of VGCF in Example 16 was changed and added so as to be 20% by mass with respect to the whole negative electrode material, and then a negative electrode sheet was produced.

<Comparative Example 1>
First, benzene, anhydrous aluminum chloride and anhydrous copper chloride were mixed at a molar ratio of 4: 1: 1. After mixing well, the synthesis reaction by Kovacic method was allowed to proceed. As a result, polyparaphenylene, a thermosetting non-graphite resin, was obtained.

  The polyparaphenylene obtained above was fired under the same firing conditions as in Example 1 in an inert gas atmosphere. The resulting polyparaphenylene fired product was used as the negative electrode material of Comparative Example 1. In addition, a negative electrode sheet was produced according to the same procedure as in Example 1. The negative electrode material of Comparative Example 1 corresponds to a material having a VGCF content of 0%.

<Comparative example 2>
VGCF was used as the negative electrode material of Comparative Example 2. In addition, a negative electrode sheet was produced according to the same procedure as in Example 1. The negative electrode material of Comparative Example 2 corresponds to a material having a VGCF content of 100%.

<Comparative Example 3>
First, as a precursor resin material of a carbon active material, “Nicanol NP140” manufactured by Fudou Co., Ltd. was fired under the same firing conditions as in Example 1 in an inert gas atmosphere. The fired xylene resin corresponding to the carbon active material thus obtained was used as the negative electrode material of Comparative Example 3. In addition, a negative electrode sheet was produced according to the same procedure as in Example 1. The negative electrode material of Comparative Example 3 corresponds to a material having a VGCF content of 0%.

<Evaluation>
Lithium ion secondary batteries were produced using the negative electrode sheets produced in the examples , reference examples and comparative examples, and the battery performance was evaluated. Specifically, the production and evaluation of the secondary battery were performed according to the following procedure.

First, the negative electrode sheets produced in each example , reference example and comparative example were punched out to a diameter of 14 mmφ. The punched negative electrode sheet was pressed with a hand press machine, and this was used as the negative electrode.

Next, lithium metal was put into a coin-type case and pressed. As the electrolytic solution, 1 mol LiPF ₆ / ethylene carbonate EC: ethyl methyl carbonate EMC (3: 7 volume ratio) was used, and a separator immersed in this electrolytic solution was placed on lithium metal and a gasket was put.

  Next, the negative electrode after the press treatment was placed on the separator so as to face the lithium metal. Furthermore, after inserting a spacer and a washer, the case was covered with a lid and sealed with a caulking machine to produce a coin-type lithium ion secondary battery (hereinafter referred to as “coin cell”).

The produced coin cell was set in a charge / discharge device, and a charge / discharge test was performed according to the following conditions. In addition, the intercalation and the Dope reaction of lithium ions into carbon were set as charging, and the deintercalation and the Undope reaction were discharged.
[Charge / discharge test conditions]
Current value: 30 mA / g
Charge end potential: 0V, CCCV (constant current constant voltage) Charge CV (constant voltage) Charge time: 50 hours Discharge end potential: 2.8V, CC (constant current) discharge

<Evaluation results>
First, the evaluation results of Examples 1-2 and Reference Examples 1-3 in which a negative electrode material was produced by the production method 1 while using a polyparaphenylene fired product as the carbon active material will be described.
FIG. 9 is a graph showing the relationship between the negative electrode potential and the desorption amount dQ / dV of lithium ions per unit voltage in Examples 1-2, Reference Examples 1-3, and Comparative Example 1. As shown in FIG. 9, in Comparative Example 1 in which the fired polyparaphenylene itself was used for the negative electrode without adding VGCF, large peaks were observed around 0.2 V and 1 V, and around 0.2 V and 1 V. Lithium ions were desorbed and released. On the other hand, in Examples 1-2 and Reference Examples 1-3 in which the negative electrode material having a configuration in which a predetermined amount of VGCF is coated with the fired polyparaphenylene is used for the negative electrode, as the content of VGCF increases, The peak near 1 V observed in Comparative Example 1 was reduced and disappeared. Further, the peak near 0.2 V observed in Comparative Example 1 was shifted to the lower potential side as the content of VGCF increased.

From the results shown in FIG. 9, according to the negative electrode material containing 1 to 20% by mass of VGCF and covering this VGCF with a fired polyparaphenylene, the occluded lithium ions are desorbed and released at a lower potential. I found out that As a result, according to Examples 1-2 and Reference Examples 1-3 , it turned out that a discharge potential and a negative electrode potential can be reduced and a high average voltage is obtained. It is also found that by setting the content of VGCF to 5 to 20% by mass, the peak near 1V disappears completely, lithium ions can be desorbed and released at a lower potential, and a higher average voltage can be obtained. It was.

FIG. 10 is a diagram showing the relationship between the capacity and the negative electrode potential in Reference Examples 1 and 3 and Comparative Examples 1 and 2. As shown in FIG. 10, in Comparative Example 1 in which the fired polyparaphenylene itself without adding VGCF was used as the negative electrode, the negative electrode potential was high while the capacity was large, and in Comparative Example 2 in which VGCF was used as the negative electrode, It was confirmed that the capacity was small while the negative electrode potential was low. On the other hand, in Reference Examples 1 and 3 in which the negative electrode material having a configuration in which VGCF was coated with a fired polyparaphenylene was used for the negative electrode, the negative electrode potential was lower than that of Comparative Example 1. Further, when the content of VGCF was 20% by mass as in Reference Example 3, the capacity was reduced to almost the same as Comparative Example 2 in which VGCF was used for the negative electrode.

Moreover, FIG. 11 is a figure which shows the relationship between content of VGCF and capacity | capacitance in Examples 1-2 , Reference Examples 1-3, and Comparative Examples 1-2. As shown in FIG. 11, in Examples 1 to 2 and Reference Examples 1 to 3 in which a negative electrode material composed of VGCF coated with a fired polyparaphenylene was used for the negative electrode, the capacity increased as the content of VGCF increased. Had fallen.

  From the results of FIGS. 10 and 11, in the negative electrode material having a configuration in which VGCF is coated with the fired polyparaphenylene, by setting the content of VGCF to 1 to 20% by mass, the negative electrode potential can be lowered and a high average voltage is obtained. As a result, it was found that a lithium ion secondary battery having a large capacity and a high energy density was obtained.

In addition, about Example 11-12 and Reference Examples 7-9 which manufactured the negative electrode material with the manufacturing method 3 while using a polyparaphenylene baked material as a carbon active material, said Examples 1-2 and Reference Example 1 were mentioned. It was the same evaluation result as -3 .

Next, the evaluation results of Examples 6 to 7 and Reference Examples 4 to 6 in which the negative electrode material was manufactured by the manufacturing method 2 while using a fired xylene resin as the carbon active material will be described.
FIG. 12 is a graph showing the relationship between the negative electrode potential and the lithium ion desorption amount dQ / dV per unit voltage in Examples 6 to 7, Reference Examples 4 to 6 and Comparative Example 3. As shown in FIG. 12, in Comparative Example 3 in which the baked xylene resin itself was used as the negative electrode without adding VGCF, a large peak was observed near 1V, and lithium ions were desorbed and released near 1V. . On the other hand, in Examples 6 to 7 and Reference Examples 4 to 6 in which the negative electrode material having a configuration in which a predetermined amount of VGCF is coated with a fired xylene resin is used for the negative electrode, the content of VGCF increases as the content of VGCF increases. The peak near 1 V observed in Comparative Example 3 was reduced and disappeared, and the peak was shifted to the lower potential side.

From the results shown in FIG. 12, according to the negative electrode material containing 1 to 20% by mass of VGCF and covering this VGCF with a fired xylene resin, the occluded lithium ions are desorbed and released at a lower potential. I found out. As a result, according to Examples 6-7 and Reference Examples 4-6 , it turned out that a discharge potential and a negative electrode potential can be reduced and a high average voltage is obtained. In addition, by setting the content of VGCF to 5 to 20% by mass, and further to 10 to 20% by mass, the peak near 1V almost disappears, and lithium ions can be desorbed and released at a lower potential. It was also found that voltage could be obtained.

FIG. 13 is a diagram showing the relationship between the capacity and the negative electrode potential in Reference Examples 4 and 6 and Comparative Examples 2 and 3. As shown in FIG. 13, in Comparative Example 3 in which the baked xylene resin itself was used as the negative electrode without adding VGCF, the negative electrode potential was high but the capacity was large. In Comparative Example 2 in which VGCF was used as the negative electrode, the negative electrode It was confirmed that the capacitance was small while the potential was low. On the other hand, in Reference Examples 4 and 6 in which the negative electrode material formed by coating VGCF with a fired xylene resin was used for the negative electrode, the negative electrode potential increased as the content of VGCF increased compared to Comparative Example 3. It was falling. Further, when the content of VGCF was 20% by mass as in Reference Example 6, the capacity was reduced to almost the same as Comparative Example 2 in which VGCF was used for the negative electrode.

  From the result of FIG. 13, in the negative electrode material composed of VGCF coated with a fired xylene resin, by setting the content of VGCF to 1 to 20% by mass, the negative electrode potential can be lowered and a high average voltage can be obtained. It has been found that a lithium ion secondary battery having a large capacity and a high energy density can be obtained.

In addition, about Example 16-17 and Reference Examples 10-12 which used the xylene resin baked material as a carbon active material, and manufactured the negative electrode material with the manufacturing method 3, said Examples 6-7 and Reference Examples 4-6 It was the same evaluation result.

Claims (4)

A conductive carbon, and a carbon active material that covers the conductive carbon and absorbs and releases lithium ions,
The carbon active material, the conductive crystallinity than carbon has a low, a fired product of the burned material or xylene resin polyparaphenylene,
The conductive carbon is vapor grown carbon fiber,
Content of the said conductive carbon is 1-3 mass% with respect to the whole negative electrode material, The negative electrode material for lithium ion secondary batteries characterized by the above-mentioned. It is a manufacturing method of the negative electrode material for lithium ion secondary batteries of Claim 1 ,
Adding the conductive carbon to the raw material of the carbon active material, and synthesizing a precursor resin of the carbon active material in the presence of the conductive carbon;
And a step of obtaining the carbon active material covering the conductive carbon by firing the precursor resin. A method for producing a negative electrode material for a lithium ion secondary battery. It is a manufacturing method of the negative electrode material for lithium ion secondary batteries of Claim 1 ,
Mixing the precursor resin of the carbon active material and the conductive carbon;
And baking the mixture obtained in the step to obtain the carbon active material covering the conductive carbon. The method for producing a negative electrode material for a lithium ion secondary battery, comprising: It is a manufacturing method of the negative electrode material for lithium ion secondary batteries of Claim 1 ,
Firing the carbon active material precursor resin to obtain the carbon active material;
And a step of obtaining the carbon active material covering the conductive carbon by adding the conductive carbon to the carbon active material and pulverizing and mixing the negative electrode for a lithium ion secondary battery. Material manufacturing method.