JPH07211320A - Positive mix and battery using the same - Google Patents

Abstract

PURPOSE:To increase active material filling density per positive mix volume and energy density per battery volume. CONSTITUTION:A positive mix contains a positive active material, a conductive material, and an ion-conductive polymer solid electrolyte. The conductive material is made of carbon fibers with a diameter of 0.08-10mum and aspect ratio of 10 or more. A battery uses this positive mix.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte battery, particularly a lithium solid electrolyte battery and its positive electrode mixture.

[0002]

2. Description of the Related Art As solid electrolyte batteries and lithium solid electrolyte batteries, there are primary batteries and secondary batteries using a chalcogen compound as a positive electrode active material and metallic lithium, a carbonaceous material or the like as a negative electrode. Such a battery is constructed by mixing positive electrode active material particles, carbon particles such as acetylene black as a conductive agent, and a binder for each particle and an ion conductive polymer solid electrolyte material as an ion conductive material. To form a paste, which is applied to a metal substrate and cured into a sheet shape by curing the ion conductive polymer solid electrolyte material as a positive electrode, and a negative electrode via a separator made of the ion conductive solid electrolyte. A battery was obtained by filling the periphery of a metal substrate with a metal lithium sheet or a mixture made of a carbonaceous material bonded or coated with the mixture and filling the peripheral portion with a sealing agent. As the conductive agent used at that time, graphite and the like other than acetylene black are used.

[0003]

However, acetylene black has a chain structure suitable for electrical conductivity and is excellent in electrical conductivity, but has a large specific surface area and too large liquid-absorbing property, and therefore acetylene black is contained in the positive electrode mixture. Absorb a large amount of ion conductive polymer solid electrolyte material. Therefore, since the ion conductive polymer solid electrolyte also serves as a binder for the positive electrode active material and the conductive agent, it is difficult to exert its binding property by being absorbed, and the excess amount is required to exert the binding property. Since the ion conductive polymer solid electrolyte must be added, the packing density of the active material per volume of the positive electrode mixture becomes low. On the other hand, since graphite has a small liquid absorption property, the liquid absorption amount of the ion conductive polymer solid electrolyte is small, and its binding property is easily exhibited, and the active material packing density per positive electrode mixture volume is improved, but the structure is Since it is granular and exists in a dispersed state in the positive electrode mixture, it is difficult to obtain a structure in which a conductive agent necessary for conduction is chained, and the conductivity in the positive electrode mixture is not good. Therefore, in order to improve the utilization rate of the positive electrode active material in discharging, it is necessary to add an excessive amount of graphite, and the packing density of the active material per volume of the positive electrode mixture becomes low. Further, in the case of a secondary battery, further repeated charging and discharging causes expansion and contraction of the electrodes, resulting in poor current collection, and sufficient charge / discharge cycle characteristics cannot be obtained.

The present invention relates to a positive electrode mixture for a solid electrolyte battery, and by using carbon fibers as a conductive agent, the liquid absorption amount of an ion conductive polymer solid electrolyte by the conductive agent without lowering the conductivity of the positive electrode mixture. It is intended to reduce the energy density per battery volume by decreasing the active material packing density per positive electrode mixture volume. Furthermore, in the case of a secondary battery, it is intended to improve charge / discharge cycle characteristics.

[0005]

The positive electrode mixture of the present invention contains a positive electrode active material, a conductive agent and an ion conductive polymer solid electrolyte, and the conductive agent has a diameter of 0.08 to
It is characterized in that it is a carbon fiber of 10 μm and an aspect ratio of 10 or more.

The amount of carbon fiber added is 100% by weight based on the total weight of the positive electrode active material and the carbon fiber.
The effect is exhibited at 0.5 to 20% by weight. If the added amount is less than 0.5% by weight, the amount of the conductive agent is insufficient and the conductivity in the positive electrode mixture is insufficient. If the added amount is more than 20% by weight, the active material packing density per volume of the positive electrode mixture is lowered. Further, the diameter of the carbon fiber is 0.08 to 10 μm.
Is preferred. If it is less than 0.08 μm, the diameter is small and the strength of the carbon fiber is lowered, and the carbon fiber is broken during the mixing of the positive electrode mixture. On the other hand, when it exceeds 10 μm, the number of carbon fibers of the positive electrode mixture is reduced, the chance of contact between the positive electrode active material and the carbon fibers is reduced, and the conductivity is lowered.

Further, the effect is exhibited when the aspect ratio is 10 or more. When it is less than 10, the same phenomenon as in the case where graphite is added as a conductive agent occurs, and the conductivity in the positive electrode mixture is lowered as described above.

The orientation of the carbon fibers in the positive electrode mixture does not matter.

The positive electrode active material in the present invention is MnO ₂ or the like as a primary battery, and LiCoO ₂ or L as a secondary battery.
_{iV 3 O 8, LiMn 2 O} 4, V 2 O 5, LiNiO 2
Etc., but is not limited to these.

[0010]

In the positive electrode mixture of the present invention, by using the above-mentioned carbon fiber as the conductive agent in the positive electrode mixture, the amount of the ion conductive polymer solid electrolyte material absorbed by the conductive agent can be reduced. Therefore, the packing density of the active material per volume of the positive electrode mixture is improved, and if the diameter of the carbon fiber is 0.08 μm or more, there is no crushing of the carbon fiber when the positive electrode mixture is mixed,
If it is m or less, the number of carbon fibers will not be insufficient and the conductivity of the positive electrode mixture will not be lowered. If the carbon fiber has an aspect ratio of 10 or more, since the structure is fibrous, it is easy to obtain a chained structure of carbon fibers necessary for conductivity in the positive electrode mixture, and the battery is added at an amount of 0.5 to 20% by weight. As a result, the utilization rate of the positive electrode active material in discharge can be improved, and the energy density per battery volume can be further increased. Further, in the case of a secondary battery, since the carbon fiber has flexibility, expansion and contraction of the electrode due to charge and discharge can be absorbed and current collection failure can be suppressed, so that charge and discharge cycle characteristics can be improved.

[0011]

EXAMPLES Examples of the present invention will be described below. (Example 1) A description will be given of one prepared by using three kinds of carbon fibers having aspect ratios of 20, 100 and 500 as the conductive agent in the positive electrode mixture. The average fiber diameters of the carbon fibers used are all 0.15 μm.

MnO ₂ , 1 as a positive electrode active material for primary batteries
100 g of the above carbon fiber as a conductive agent is mixed with 00 g, and an ion conductive polymer solid electrolyte material 5 is further used as a binder.
0 g and 0.025 g of azobisisobutyronitrile as a reaction initiator were mixed to obtain a positive electrode mixture paste. The ion conductive polymer solid electrolyte material is obtained by dissolving a mixture of ethylene oxide monoacrylate, diacrylate and triacrylate in LiClO ₄ in propylene carbonate.

Next, the above positive electrode mixture paste is cast on a stainless steel substrate, and the paste is cast at 100 ° C. in an inert gas atmosphere.
The mixture was left to stand for a period of time to be cured to obtain a sheet-shaped positive electrode mixture on a stainless steel substrate. The thickness of the obtained positive electrode mixture was about 100 μm.

Next, azobisisobutyronitrile 0.05
What was dissolved in 100 g of the above ion conductive polymer solid electrolyte material was cast on the above positive electrode mixture and cured in the same manner as above, and an ion conductive polymer solid electrolyte film was formed as a separator on the above positive electrode mixture. Formed. The thickness of the obtained coating was 20 μm.

A composite sheet consisting of the stainless steel substrate, the positive electrode mixture and the ion conductive polymer solid electrolyte coating obtained as described above is cut into a size of 1 cm × 1 cm, and the ion conductive polymer of this composite sheet is cut out. Metal lithium having a thickness of 100 μm was attached as a negative electrode on the solid electrolyte coating, and the structure shown in FIG. 1, namely, the stainless steel substrate 1, the positive electrode mixture 2, the ion conductive polymer solid electrolyte coating 3, and the negative electrode 4 were used.
A battery composed of the stainless steel substrate 5 and

A load of 1 kg / cm ² was applied to the obtained battery, and in that state, a discharge test was conducted at a constant current of 0.1 mA / cm ² at 20 ° C. and a discharge end voltage of 2.0V.

As a comparative example, a battery using a positive electrode mixture containing a conventional acetylene black as a conductive agent was also manufactured by the same method as described above. However, the amount of the ion conductive polymer solid electrolyte was 65
g and azobisisobutyronitrile were the same as above except that 0.033 g was required.

As described above, the energy density per battery volume was compared from the packing density of the active material per positive electrode mixture volume and the discharge characteristics of the four types of batteries having different conductive agents.

Table 1 shows the positive electrode active material utilization rate in the discharge test, the active material packing density per positive electrode mixture volume, and the energy density per battery volume.

[0020]

[Table 1]

As shown in Table 1, the conventional battery using acetylene black as the conductive agent has a higher utilization ratio than the battery of the present invention using the carbon fiber having an aspect ratio of 20. The packing density is considerably inferior to the three types of batteries of the present invention using carbon fiber. As a result, it can be seen that the energy density is inferior to the three types of batteries of the present invention.

Example 2 LiCoO ₂ as a positive electrode active material for a secondary battery, 100 g of the above carbon fiber 1 as a conductive agent
0 g was mixed, 50 g of an ion conductive polymer solid electrolyte material was further mixed as a binder, and 0.025 g of azobisisobutyronitrile was mixed as a reaction initiator to obtain a positive electrode mixture paste. The ion conductive polymer solid electrolyte material is a mixture of ethylene oxide monoacrylate, diacrylate, and triacrylate, which is mixed with ethylene carbonate and diethyl carbonate in LiPF ₆
It is the one obtained by dissolving in.

Next, the above positive electrode material mixture paste was cast on an aluminum substrate and allowed to stand in an inert gas atmosphere at 100 ° C. for 1 hour to be cured to obtain a sheet-shaped positive electrode material mixture. The thickness of the obtained positive electrode mixture was about 100 μm.

Next, azobisisobutyronitrile 0.05
What was dissolved in 100 g of the above ion conductive polymer solid electrolyte material was cast on the above positive electrode mixture and cured in the same manner as above, and an ion conductive polymer solid electrolyte film was formed as a separator on the above positive electrode mixture. Formed. The thickness of the obtained coating was 20 μm.

The composite sheet comprising the aluminum substrate, the positive electrode mixture and the ion conductive polymer solid electrolyte coating obtained as described above was cut into a size of 1 cm × 1 cm,
A negative electrode mixture made of a carbonaceous material having a thickness of 100 μm was attached on the ion conductive polymer solid electrolyte coating of this composite sheet to have the structure shown in FIG.
Then, a battery composed of the positive electrode mixture 7, the ion conductive polymer solid electrolyte coating 8, the negative electrode mixture 9 and the copper substrate 10 was prepared.

A load of 1 kg / cm ² was applied to the obtained battery, and a charge / discharge test was carried out at 20 ° C in that state. Charging is constant current constant voltage charging, the current density of constant current is 1m
A / cm ² , a final voltage of 4.2V, and constant voltage charging was performed at a voltage of 4.2V for 5 hours. The discharge was a constant current discharge, a current density was 1 mA / cm ² , and a discharge end voltage was 3.0 V, and a discharge test was conducted.

As a comparative example, a battery using a positive electrode mixture containing conventional acetylene black as a conductive agent was also manufactured by the same method as described above. However, the amount of the ion conductive polymer solid electrolyte was 65
g and azobisisobutyronitrile were the same as above except that 0.033 g was required.

As described above, comparison was made from the packing density of the active material per volume of the positive electrode mixture of four types of batteries having different conductive agents, and the initial discharge capacity and the capacity retention rate of the discharge capacity at the 100th cycle with respect to the initial discharge capacity. It was

Table 2 shows the initial discharge capacity in the charge / discharge test, the capacity retention ratio of the discharge capacity at the 100th cycle to the initial discharge capacity, and the active material packing density per positive electrode mixture volume. Here, the discharge capacity is converted into the capacity per 1 g of the positive electrode active material.

[0030]

[Table 2]

As shown in Table 2, the conventional battery using acetylene black as the conductive agent has the same initial discharge capacity as that of the battery of the present invention using the carbon fiber having the aspect ratio of 20, but the active material. The packing density is considerably inferior to the three types of batteries of the present invention using carbon fiber.
Also, the capacity retention rate after 100 cycles is 67%.
Fall to. On the other hand, in all the batteries using the positive electrode mixture containing carbon fiber as the conductive agent, the active material packing density per positive electrode mixture volume was significantly improved compared to the conventional example, and the charge / discharge cycle characteristics were also the discharge capacity after 100 cycles. The retention rate has also improved significantly.

[0032]

From the above, in the positive electrode mixture using carbon fibers as the conductive agent from Examples 1 and 2, it is possible to reduce the amount of the ion conductive polymer solid electrolyte material absorbed by the conductive agent. The positive electrode mixture can be produced without deteriorating the binding characteristics of the positive electrode active material and the conductive agent. Thereby, the packing density of the active material per volume of the positive electrode mixture can be improved. If the carbon fiber has an aspect ratio of 10 or more, since the structure is fibrous, it is easy to obtain a structure in which a conductive agent necessary for conductivity in the positive electrode mixture is chained, and a battery is added in an amount of 0.5 to 20% by weight. As a result, the utilization rate of the positive electrode active material in discharge can be improved, and the energy density per battery volume can be further increased. Further, in the case of a secondary battery, since the carbon fiber has flexibility, expansion and contraction of the electrode due to charge and discharge can be absorbed and current collection failure can be suppressed, so that charge and discharge cycle characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a battery using a positive electrode mixture of Example 1 of the present invention.

FIG. 2 is a sectional view of a battery using the positive electrode mixture of Example 2 of the present invention.

[Explanation of symbols]

 1 Stainless Steel Substrate 2 Positive Electrode Mixture 3 Ion Conductive Polymer Solid Electrolyte Coating 4 Negative Electrode 5 Stainless Steel Substrate 6 Aluminum Substrate 7 Positive Electrode Mixture 8 Ion Conductive Polymer Solid Electrolyte Coating 9 Negative Electrode Mixture 10 Copper Substrate

Claims (3)

[Claims] 1. A positive electrode mixture containing a positive electrode active material, a conductive agent, and an ion conductive polymer solid electrolyte, wherein the conductive agent comprises carbon fibers having a diameter of 0.08 to 10 μm and an aspect ratio of 10 or more. A positive electrode mixture characterized by: 2. The addition amount of the carbon fibers is 100% by weight based on the total weight of the positive electrode active material and the carbon fibers.
It is 0.5 to 20 weight%, The positive electrode mixture of Claim 1 characterized by the above-mentioned. 3. A battery comprising the positive electrode mixture according to claim 1 or 2.