JP6314563B2 - Positive electrode mixture layer - Google Patents

Description

  The present invention relates to a positive electrode mixture layer having good rapid charge capacity.

  With the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones in recent years, development of batteries that are used as power sources has been regarded as important. Also in the automobile industry and the like, development of high-power and high-capacity batteries for electric vehicles or hybrid vehicles is being promoted. Currently, lithium batteries are attracting attention among various batteries from the viewpoint of high energy density.

  Since lithium batteries currently on the market use an electrolyte solution containing a flammable organic solvent, a safety device for preventing a temperature rise at the time of a short circuit and a structure for preventing a short circuit are required. In contrast, a lithium battery in which the electrolyte is changed to a solid electrolyte layer to make the battery completely solid does not use a flammable organic solvent in the battery, so the safety device can be simplified, and manufacturing costs and productivity can be reduced. It is considered excellent.

  In the field of such lithium batteries, conventionally, attempts have been made to improve the performance of lithium batteries by paying attention to the materials contained in the positive electrode mixture layer. For example, Patent Document 1 discloses a secondary battery electrode mixture containing an ion conductive material containing a sulfur element and an alkali metal element and a conductive material.

JP 2012-160415 A

  According to Patent Document 1, it is reported that the performance of the secondary battery is improved by defining the weight ratio between the ion conductive material and the conductive material in the electrode mixture. On the other hand, when the weight ratio between the ion conductive material and the conductive material in the electrode mixture is defined, the results (trends) differ depending on the specific gravity of the ion conductive material and the conductive material. Similarly, the results (trends) differ depending on the ionic conductivity of the ionic conductive material and the electronic conductivity of the conductive material. Therefore, there is a problem that the rapid charge capacity cannot be sufficiently improved.

  This invention is made | formed in view of the said situation, and it aims at providing the positive electrode compound-material layer with favorable rapid charge capacity.

  As a result of various studies on the positive electrode mixture layer having a good rapid charge capacity, the present inventors have found that the ratio of the electron conductivity to the Li ion conductivity has a large effect on the rapid charge capacity. The present invention has been completed based on these findings.

  That is, in the present invention, a positive electrode active material that is an oxide having an Li element and a transition metal element, and a solid electrolyte material containing an Li element, a P element, and an S element, and with respect to Li ion conductivity Provided is a positive electrode mixture layer having a ratio of electron conductivity of 0.39 or less.

  According to the present invention, when the ratio of the electron conductivity to the Li ion conductivity is within a predetermined range, a positive electrode mixture layer having a good rapid charge capacity can be obtained.

  In this invention, there exists an effect that a positive mix layer with favorable rapid charge capacity can be provided.

It is a schematic sectional drawing for demonstrating the measuring method of Li ion conductivity. It is the graph which showed the quick charge capacity of Examples 1, 2 and Comparative Examples 1, 2.

  Hereinafter, the positive electrode mixture layer of the present invention will be described in detail.

  The positive electrode mixture layer of the present invention includes a positive electrode active material that is an oxide having a Li element and a transition metal element, and a solid electrolyte material containing a Li element, a P element, and an S element, and is capable of conducting Li ions. The ratio of the electron conductivity to the degree is 0.39 or less.

  According to the present invention, when the ratio of the electron conductivity to the Li ion conductivity is within a predetermined range, a positive electrode mixture layer having a good rapid charge capacity can be obtained.

  The ratio of the electronic conductivity to the Li ion conductivity is not conventionally known as a general parameter. The reason is considered that the method for measuring Li ion conductivity has not been established as a general method. Therefore, in the conventional positive electrode mixture layer, the knowledge that the ratio of the electron conductivity to the Li ion conductivity has a great influence on the rapid charge capacity has not been obtained. On the other hand, according to the present invention, by setting the ratio of the electron conductivity to the Li ion conductivity of the positive electrode mixture layer to be 0.39 or less, a positive electrode mixture layer having good rapid charge capacity can be obtained.

  The rapid charge capacity in the present invention, that is, the capacity at the time of rapid charge refers to a charge capacity at a rate of 0.5 C or more.

  In the present invention, the ratio of the electron conductivity to the Li ion conductivity may be 0.39 or less, preferably 0.2 or less, and particularly preferably 0.05 or less.

  Examples of the method for measuring the Li ion conductivity of the positive electrode mixture layer include the following methods. First, as shown in FIG. 1, the positive electrode mixture layer 1 is sandwiched between the solid electrolyte layer 2 having no electron conductivity, and further sandwiched between the positive electrode 3 and the negative electrode 4, whereby the positive electrode 3 / solid electrolyte layer 2 / positive electrode. The composition layer 1 / solid electrolyte layer 2 / negative electrode 4 is used. Next, only Li ions are allowed to flow through the positive electrode mixture layer 1 by flowing Li ions from the positive electrode 3 to the negative electrode 4. It is possible to measure the resistance value at this time and calculate the Li ion conductivity from the resistance value.

  As a method for measuring the electron conductivity of the positive electrode mixture layer, for example, only electrons are allowed to flow through the positive electrode mixture layer, the resistance value at this time is measured, and the electron conductivity can be calculated from the resistance value. is there.

1. Positive electrode active material The positive electrode active material in the present invention is an oxide having a Li element and a transition metal element. When the positive electrode mixture layer obtained by the present invention is used in, for example, an all-solid lithium secondary battery, lithium ion is used. Occlude / release.

The positive electrode active material is not particularly limited as long as it has an oxide containing an Li element and a transition metal element and is a material used as an electrode active material. Examples of the oxide include a general formula Li _x M _y O _z (M is a transition metal element, x = 0.02 to 2.2, y = 1 to 2, z = 1.4 to 4). The Li-containing transition metal oxide represented can be mentioned. In the above general formula, M is preferably at least one selected from the group consisting of Co, Mn, Ni, V and Fe, and preferably at least one selected from the group consisting of Co, Ni and Mn. More preferred. As such a Li-containing transition metal oxide, specifically, a rock salt layer type active material such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ or the like. And spinel active materials such as LiMn ₂ O ₄ and Li (Ni _0.5 Mn _1.5 ) O ₄ . Examples of the oxide active material other than the above general formula Li _x M _y O _z include, for example, the general formula Li _{1 + x} Mn _2−xy M _y O ₄ (M is Al, Mg, Co, Fe, Ni, and Zn). At least one selected from the group consisting of x and y are arbitrary real numbers), and is represented by a general formula Li _x TiO _y (where x and y are arbitrary real numbers). Lithium titanate, lithium metal phosphate represented by the general formula LiMPO ₄ (M is at least one selected from the group consisting of Fe, Mn, Co and Ni) may be used as the transition metal oxide.

  Examples of the shape of the positive electrode active material include a particle shape, and among them, a true spherical shape or an elliptical spherical shape is preferable. Further, when the positive electrode active material has a particle shape, the average particle diameter thereof is preferably within a range of 0.1 μm to 50 μm, for example, and particularly preferably within a range of 0.1 μm to 10 μm. It is preferably within a range of 0.1 μm to 5 μm. Moreover, although content of a positive electrode active material changes according to the composition of the target positive electrode compound material layer, it is 10 weight%-99 weight with respect to the total content of a positive electrode active material and a solid electrolyte material, for example. It is preferably in the range of wt%, more preferably in the range of 20 wt% to 90 wt%.

The positive electrode active material in the present invention may be coated with a coating layer. By forming the coating layer on the surface of the positive electrode active material, the reaction between the positive electrode active material and the solid electrolyte material can be suppressed, and an all solid lithium battery excellent in output characteristics can be obtained. The material used for the coating layer is not particularly limited as long as it has Li ion conductivity, does not flow in contact with the active material or the solid electrolyte material, and can maintain the shape of the coating layer. . For _example, a _{LiNbO 2, Li 3 PO 4,} Li 4 Ti 5 O 12 and the like. Moreover, as a coating method, the rolling fluidized coating method can be mentioned, for example.

2. Solid electrolyte material The solid electrolyte material in this invention contains Li element, P element, and S element. The solid electrolyte material in the present invention may contain only Li element, P element, and S element, and may further contain other elements. Examples of the other element include at least one of an O element and an I element. In particular, in the present invention, the sulfide solid electrolyte material is preferably a Li ₂ S—P ₂ S ₅ material. Also, the sulfide solid electrolyte _material, in addition to Li 2 _S-P 2 _{S 5} material preferably contains LiI and Li ₂ O.

  The solid electrolyte material used in the present invention may be crystalline, amorphous, or glass ceramic (crystallized glass). The amorphous solid electrolyte material can be obtained, for example, by performing an amorphization method on the raw material composition of the solid electrolyte material. Examples of the amorphization method include a mechanical milling method and a melt quenching method, and among them, the mechanical milling method is preferable. This is because processing at room temperature is possible, and the manufacturing process can be simplified. On the other hand, glass ceramics can be obtained, for example, by heat-treating an amorphous solid electrolyte material at a temperature higher than the crystallization temperature. That is, glass ceramics can be obtained by subjecting the raw material composition of the solid electrolyte material to an amorphization method and further heat treatment.

  The content of the solid electrolyte material in the positive electrode mixture layer is preferably, for example, in the range of 5% by volume to 50% by volume when the total volume of the positive electrode mixture layer is 100% by volume, especially 27 volumes. % To 29% by volume, and particularly preferably 28.5% to 28.8% by volume.

Examples of the shape of the solid electrolyte material include a particle shape. Further, when the solid electrolyte material is in particulate form, average particle diameter _{(D 50)} thereof, for example, is preferably in the range of 0.01Myuemu～40myuemu, be in the range of 0.1μm~20μm More preferred. The Li ion conductivity of the solid electrolyte material at 25 ° C. is, for example, preferably 1 × 10 ⁻⁴ S / cm or more, and more preferably 1 × 10 ⁻³ S / cm or more.

3. Others The positive electrode mixture layer of the present invention may have a conductive additive and a binder.

  The conductive auxiliary agent is not particularly limited as long as it has predetermined conductivity, and examples thereof include carbon materials such as carbon particles and carbon fibers. Examples of the carbon particles include furnace black (FB), acetylene black (AB), ketjen black (KB), carbon nanotube (CNF), activated carbon, graphite, etc. Among them, KB is preferably used. it can. The particle diameter (primary diameter) of the carbon particles is, for example, preferably in the range of 1 nm to 10 μm, and more preferably in the range of 3 nm to 50 μm. In addition, the said average particle diameter can be calculated | required by the method similar to the solid electrolyte material and electrode active material which were mentioned above. Moreover, the said carbon fiber is a fibrous carbon substance, for example, VGCF (vapor-grown carbon fiber) can be used suitably.

  When the positive electrode mixture layer of the present invention contains a conductive additive, the content of the conductive additive is, for example, 10% by volume or less when the total volume of the positive electrode mixture layer is 100% by volume. Among these, 1.5 volume or less is preferable, and 0.8 volume% or less is particularly preferable.

  Examples of the binder include butylene rubber (BP), polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR), and the like.

4). Positive electrode mixture layer The positive electrode mixture layer in the present invention includes at least the positive electrode active material and the solid electrolyte material described above. Moreover, you may have a conductive support agent and a binder as needed.

  The thickness of the positive electrode mixture layer varies depending on the intended configuration of the all-solid lithium battery, but is preferably in the range of 0.1 μm to 1000 μm, for example.

5. All-solid lithium battery In this invention, the all-solid-state lithium battery characterized by having the positive mix layer mentioned above can be provided. Hereinafter, each configuration of the all solid lithium battery will be described.

(1) Positive electrode mixture layer The positive electrode mixture layer is the same as the contents described in the sections of “1. Positive electrode active material” to “4. .

(2) Negative electrode mixture layer The negative electrode mixture layer is composed of a negative electrode mixture. The negative electrode mixture layer usually includes a negative electrode active material and a solid electrolyte material, and may further include a conductive additive and a binder. The solid electrolyte material, the conductive additive, and the binder are the same as those described in the above sections “2. Solid electrolyte material” and “3.

  Examples of the negative electrode active material include a metal active material and a carbon active material. Examples of the metal active material include Li alloy, In, Al, Si, and Sn. On the other hand, examples of the carbon active material include graphite such as mesocarbon microbeads (MCMB) and highly oriented graphite (HOPG), and amorphous carbon such as hard carbon and soft carbon. Note that SiC or the like can also be used as the negative electrode active material.

  The thickness of the negative electrode mixture layer varies depending on the intended configuration of the all-solid lithium battery, but is preferably in the range of 0.1 μm to 1000 μm, for example.

(3) Solid electrolyte layer The solid electrolyte layer is a layer formed between the positive electrode mixture layer and the negative electrode mixture layer, and is a layer containing at least a solid electrolyte material. The solid electrolyte material is not particularly limited, and examples thereof include materials similar to those described in the above section “2. Solid electrolyte material”.

  The content of the solid electrolyte material in the solid electrolyte layer is, for example, preferably in the range of 10% by weight to 100% by weight, and more preferably in the range of 50% by weight to 100% by weight. The solid electrolyte layer may contain a binder. The binder is the same as the contents described in the above section “3. Others”, so the description thereof is omitted here.

  Although the thickness of a solid electrolyte layer is not specifically limited, For example, it is preferable to exist in the range of 0.1 micrometer-1000 micrometers, and it is more preferable to exist in the range of 0.1 micrometer-300 micrometers.

(4) Other configurations The all-solid lithium battery includes at least the positive electrode mixture layer, the negative electrode mixture layer, and the solid electrolyte layer described above. Further, usually, it has a positive electrode current collector for collecting current of the positive electrode mixture layer and a negative electrode current collector for collecting current of the negative electrode mixture layer. Examples of the material for the positive electrode current collector include SUS, Ni, Cr, Au, Pt, Al, Fe, Ti, and Zn. On the other hand, examples of the material for the negative electrode current collector include SUS, Cu, Ni, Fe, Ti, Co, and Zn. The thickness, shape, and the like of the positive electrode current collector and the negative electrode current collector are preferably appropriately selected according to the use of the battery. Moreover, the battery case of a general battery can be used for the battery case used for this invention. Examples of the battery case include a SUS battery case.

(5) All-solid-state lithium battery The all-solid-state lithium battery may be a primary battery or a secondary battery, and among these, a secondary battery is preferable. This is because it can be repeatedly charged and discharged and is useful, for example, as a vehicle-mounted battery. Examples of the shape of the all solid lithium battery include a coin type, a laminate type, a cylindrical type, and a square type.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described in more detail with reference to examples.

[Example 1]
(Preparation of positive electrode active material)
LiNbO ₃ was coated on a positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) having an average particle diameter of 4 μm in an atmospheric environment by using a rolling fluid coating apparatus (manufactured by POWREC). Thereafter, firing was performed in an atmospheric environment.

(Preparation of positive electrode mixture layer)
In a polypropylene container, a 5 wt% butyl butyrate solution of butyl butyrate and a pre-vinylidene fluoride binder (manufactured by Kureha), and the positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) obtained above. And an average particle size of 6 μm, 70% by volume) and Li ₂ S—P ₂ S ₅ series glass ceramics (28.8% by volume of the whole positive electrode mixture layer) containing LiI as a solid electrolyte material, and ultrasonic dispersion The mixture was stirred for 30 seconds with an apparatus (UH-50 manufactured by SMT). Next, the container was shaken with a shaker (manufactured by Shibata Kagaku Co., Ltd., TTM-1) for 3 minutes, and further stirred with an ultrasonic dispersion device for 30 seconds. Then, it coated on carbon coating Al foil (Showa Denko SDX) by the blade method using the applicator. The coated electrode was naturally dried and then dried on a hot plate at 100 ° C. for 30 minutes. This obtained the positive mix layer. Further, the ratio of electron conductivity to Li ion conductivity (electron conductivity / Li ion conductivity) was 0.013.

In addition, Li ion conductivity of the positive electrode mixture layer was measured by the following method. First, as shown in FIG. Thereafter, only Li ions were allowed to flow through the positive electrode mixture layer 1, the resistance value at this time was measured, and the Li ion conductivity was calculated from the resistance value. Specifically, a resistance value was measured from a voltage change when swept at 1 mA / cm ² in a thermostatic bath at 25 ° C., and Li ion conductivity was calculated from the resistance value. Further, regarding the electron conductivity of the positive electrode mixture layer, only electrons were passed through the positive electrode mixture layer, the resistance value at this time was measured, and the electron conductivity was calculated from the resistance value. Specifically, a resistance value was measured from a voltage change when swept at 1 mA / cm ² in a constant temperature bath at 25 ° C., and electron conductivity was calculated from the resistance value.

(Preparation of negative electrode mixture layer)
In a container made of polypropylene, butyl butyrate, a 5 wt% butyl butyrate solution of pre-vinylidene fluoride binder (manufactured by Kureha), natural graphite-based carbon (Mitsubishi Chemical, average particle size 10 μm) as a negative electrode active material, and solid electrolyte material And Li ₂ S—P ₂ S ₅ glass ceramics containing LiI were added, and the mixture was stirred for 30 seconds with an ultrasonic dispersion device (SMH UH-50). Next, the container was shaken for 30 minutes with a shaker (manufactured by Shibata Kagaku Co., Ltd., TTM-1). Then, it coated on Cu foil by the blade method using the applicator. The coated electrode was naturally dried and then dried on a hot plate at 100 ° C. for 30 minutes.

(Preparation of solid electrolyte layer)
In a container made of polypropylene, heptane, a 5 wt% heptane solution of a butylene rubber-based binder, and Li ₂ S—P ₂ S ₅ glass ceramic containing LiI as a solid electrolyte material are placed, and an ultrasonic dispersion apparatus (SMT UH— 50) and stirred for 30 seconds. Next, the container was shaken for 30 minutes with a shaker (manufactured by Shibata Kagaku Co., Ltd., TTM-1). Then, it coated on Al foil by the blade method using the applicator. The coated electrode was naturally dried and then dried on a hot plate at 100 ° C. for 30 minutes.

(Production of evaluation battery)
A solid electrolyte layer was placed in a 1 cm ² mold and pressed at 1 ton / cm ² . Next, the positive electrode mixture layer was put on one side of the solid electrolyte layer and pressed at 1 ton / cm ² , and then the negative electrode mixture layer was put on the other side of the solid electrolyte layer and pressed at 6 ton / cm ² . . This produced the evaluation battery comprised from the positive mix layer / solid electrolyte layer / negative mix layer.

[Example 2]
In the production of the positive electrode mixture layer, as a solid electrolyte material, Li ₂ S—P ₂ S ₅ glass ceramics containing LiI and Li ₂ O (average particle diameter 0.8 μm, 28.5% by volume of the whole positive electrode mixture layer) ) And a vapor grown carbon fiber (0.8% by volume of the entire positive electrode composite material layer) was added as a conductive additive, and an evaluation battery was produced in the same manner as in Example 1. The ratio of the electron conductivity to the Li ion conductivity of the positive electrode mixture layer (electron conductivity / Li ion conductivity) was 0.0386.

[Comparative Example 1]
In the production of the positive electrode mixture layer, as a solid electrolyte material, Li ₂ S—P ₂ S ₅ glass ceramics containing LiI and Li ₂ O (average particle diameter 0.8 μm, 28.3 vol% of the whole positive electrode mixture layer) ) And a vapor growth carbon fiber (1.5% by volume of the whole positive electrode composite material layer) was added as a conductive additive, and an evaluation battery was produced in the same manner as in Example 1. The ratio of the electron conductivity to the Li ion conductivity of the positive electrode mixture layer (electron conductivity / Li ion conductivity) was 5.5.

[Comparative Example 2]
In the production of the positive electrode mixture layer, as a solid electrolyte material, Li ₂ S—P ₂ S ₅ glass ceramics containing LiI and Li ₂ O (average particle diameter 0.8 μm, 28.1% by volume of the whole positive electrode mixture layer) ) And a vapor growth carbon fiber (2.3% by volume of the whole positive electrode composite material layer) was added as a conductive additive, and an evaluation battery was produced in the same manner as in Example 1. The ratio of the electron conductivity to the Li ion conductivity of the positive electrode mixture layer (electron conductivity / Li ion conductivity) was 36.3.

[Comparative Example 3]
In the production of the positive electrode mixture layer, as a solid electrolyte material, Li ₂ S—P ₂ S ₅ glass ceramics containing LiI and Li ₂ O (average particle size 0.8 μm, 27.9% by volume of the whole positive electrode mixture layer) ) And a vapor growth carbon fiber (3% by volume of the whole positive electrode composite material layer) was added as a conductive additive, and an evaluation battery was produced in the same manner as in Example 1. The ratio of the electron conductivity to the Li ion conductivity of the positive electrode mixture layer (electron conductivity / Li ion conductivity) was 109.

[Evaluation 1]
(Evaluation of quick charge capacity)
In constant current-constant voltage charging, the SOC was charged at 6 C until the SOC reached 80% (4.18 V), and the charged capacity was measured to obtain a quick charge capacity. As a result of measuring the quick charge capacity, as shown in Table 1 and FIG. 1, the ratio of the electron conductivity to the Li ion conductivity of the positive electrode mixture layer (electron conductivity / Li ion conductivity) is 0.39 or less. In Examples 1 and 2, the rapid charge capacity was dramatically improved as compared with Comparative Examples 1 to 3.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode compound material layer 2 ... Solid electrolyte layer 3 ... Positive electrode 4 ... Negative electrode

Claims (1)

A positive electrode active material which is an oxide having a Li element and a transition metal element;
A solid electrolyte material containing Li element, P element, and S element,
The positive electrode active material is LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ,
It further has VGCF (vapor grown carbon fiber) as a conductive aid,
The ratio of the electronic conductivity with respect to Li ion conductivity is 0.39 or less, The positive mix layer characterized by the above-mentioned.

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