Secondary battery

Abstract

To provide graphene oxide that is used as a material of a conductive auxiliary agent for forming an active material layer with high electron conductivity in a small quantity of the conductive auxiliary agent, and provide a positive electrode for a nonaqueous secondary battery using the graphene oxide as the conductive auxiliary agent.SOLUTION: Graphene oxide is used as a material of a conductive auxiliary agent for a positive electrode for a nonaqueous secondary battery and the weight ratio of oxygen to carbon is 0.405 or more in the graphene oxide.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to graphene oxide, a positive electrode for a non-aqueous secondary battery using the same, a method for manufacturing the same, a non-aqueous secondary battery, and an electronic device. and an electronic device.

Background Art

[0002] With the remarkable spread of portable electronic devices such as mobile phones, smartphones, e-books, and portable game machines in recent years, there has been an increasing demand for miniaturization and high capacity of secondary batteries, which are their driving power sources. As secondary batteries used in portable electronic devices, non-aqueous secondary batteries typified by lithium secondary batteries having advantages such as high energy density and large capacity are widely used. Among non-aqueous secondary batteries, lithium secondary batteries, which are widely used because of their high energy density, comprise a positive electrode containing an active material such as lithium cobalt oxide (LiCoO2) or lithium iron phosphate (LiFePO4), a negative electrode made of a carbon material such as graphite capable of intercalating and deintercalating lithium ions, and

[0003] a non-aqueous electrolyte solution in which an electrolyte composed of a lithium salt such as LiBF4 or LiPF6 is dissolved in an organic solvent such as ethylene carbonate or diethyl carbonate. Charge and discharge of a lithium secondary battery are performed by lithium ions in the secondary battery moving between the positive and negative electrodes through the non-aqueous electrolyte solution and lithium ions being inserted into and detached from the active materials of the positive and negative electrodes. A binder (also referred to as a binder) is mixed into the positive electrode or the negative electrode in order to bind the active material to the active material or the active material to the current collector. The binder is insulating PVDF (polyvinylidene fluoride). The non-aqueous electrolyte solution is composed of, for example, a non-aqueous electrolyte solution in which an electrolyte composed of a lithium salt such as LiBF4 or LiPF6 is dissolved in an organic solvent such as ethylene carbonate or diethyl carbonate. Charge and discharge of a lithium secondary battery are performed by lithium ions in the secondary battery moving between the positive and negative electrodes through the non-aqueous electrolyte solution and lithium ions being inserted into and detached from the active materials of the positive and negative electrodes. Charge and discharge of a lithium secondary battery are performed by lithium ions in the secondary battery moving between the positive and negative electrodes through the non-aqueous electrolyte solution and lithium ions being inserted into and detached from the active materials of the positive and negative electrodes. is carried out.

[0004] A binder (also referred to as a binder) is mixed into the positive electrode or the negative electrode in order to bind the active material to the active material or the active material to the current collector. The binder is insulating PVDF (polyvinylidene fluoride). Since polymer organic compounds such as etc. are common, the electron conductivity is extremely low. For this reason, the amount of active material When the ratio of the mixing amount of the binder is increased with respect to, the amount of the active material in the electrode relatively decreases, so that as a result, the discharge capacity of the secondary battery decreases.

[0005] Therefore, by mixing a conductive aid such as acetylene black (AB) or graphite (carbon) particles, the electron conductivity between the active materials or between the active material - current collector is improved. This enables the provision of a positive electrode active material with high electron conductivity (see Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, acetylene black used as a conductive aid is bulky particles with an average particle size of several tens of nm to several hundreds of nm, so it is difficult to have surface contact with the active material and is likely to form point contact. Therefore, the contact resistance between the active material and the conductive aid becomes high. On the other hand, when the amount of the conductive aid is increased to increase the contact points between the active material and the conductive aid, the ratio of the amount of the active material in the electrode decreases, and the discharge capacity of the battery decreases.

[0008] Also, when using graphite particles as a conductive aid, due to cost issues, it is common to use natural graphite. However, in that case, iron, lead, copper, etc. contained as impurities in the graphite particles react with the active material or the current collector, resulting in a decrease in the potential and capacity of the battery.

[0009] Furthermore, as the active material is micronized, the cohesive force between particles becomes stronger, making it difficult to mix it uniformly with the binder and conductive aid. For this reason, dense portions where the active material particles are aggregated and sparse portions where they are not aggregated are locally generated, and in the aggregated portions of the active material particles where the conductive aid is not mixed, the active material particles do not contribute to the formation of the discharge capacity of the battery. Therefore, in view of the above problems, in one aspect of the present invention, an object is to provide graphene, which is a raw material of a conductive aid for forming an active material layer having high electron conductivity with a small amount of conductive aid. Another object is to provide a positive electrode for a non-aqueous secondary battery including a positive electrode active material layer having a high filling amount and a high density with a small amount of conductive aid. Another object is to provide a non-aqueous secondary battery having a large capacity per electrode volume by using the positive electrode for a non-aqueous secondary battery.

Means for Solving the Problems

[0010] Graphene is a carbon material having a crystal structure in which the hexagonal skeleton formed by carbon extends in a plane. Graphene is obtained by extracting a single atomic plane of graphite crystal and has amazing characteristics in terms of electrical, mechanical or chemical properties. Therefore, applications in various fields such as high-mobility field-effect transistors, highly sensitive sensors, highly efficient solar cells, and transparent conductive films for the next generation are expected and attracting attention.

[0011]

[0012]

[0013] ​​​​​​​​​​​​​In this specification, graphene includes single-layer graphene or multi-layer graphene with 2 or more layers and 100 or less layers. Single-layer graphene refers to a sheet of a one-atom layer of carbon molecules having π bonds. In addition, graphene oxide refers to a compound obtained by oxidizing the above-mentioned graphene. When graphene is formed by reducing graphene oxide, not all of the oxygen contained in graphene oxide is desorbed, and a part of the oxygen remains in the graphene. When oxygen is contained in graphene, the proportion of oxygen is 2 atomic% or more and 20 atomic% or less of the whole, preferably 3 atomic% or more and 15 atomic% or less.

[0014] Here, when the graphene is multi-layer graphene, by having the graphene obtained by reducing graphene oxide, the interlayer distance of the graphene is 0.34 nm or more and 0.5 nm or less, preferably 0.38 nm or more and 0.42 nm or less, more preferably 0.39 nm or more and 0.41 nm or less. The interlayer distance of ordinary graphite is 0.34 nm, and the graphene used in the secondary battery according to one aspect of the present invention has a longer interlayer distance, so that the movement of carrier ions between the layers of multi-layer graphene becomes easy.

[0015] The positive electrode for a non-aqueous secondary battery according to one aspect of the present invention disperses graphene so as to overlap in the positive electrode active material layer and be in contact with a plurality of positive electrode active material particles. In other words, it can be said that a network for electron conduction by graphene is formed in the positive electrode active material layer. As a result, the bonding of a plurality of positive electrode active material particles is maintained, and as a result, a positive electrode active material layer having high electron conductivity can be formed.

[0016] ​​​​​​​​The positive electrode active material layer added with graphene as a conductive assistant can be manufactured by the following method. . First, after dispersing graphene in a dispersion medium (also referred to as a solvent), a positive electrode active material is added and kneaded to produce a mixture. A binder (also referred to as a binder) is added to this mixture and kneaded to produce a positive electrode paste. Finally, after applying the positive electrode paste to a positive electrode current collector, the dispersion medium is volatilized to produce a positive electrode active material layer added with graphene as a conductive assistant.

[0017] However, in order to form a network for electron conduction in the positive electrode active material layer using graphene as a conductive assistant, first, graphene must be uniformly dispersed in the dispersion medium. This is because the dispersibility in the dispersion medium directly depends on the dispersibility of graphene in the positive electrode active material layer. When the dispersibility of graphene is low, graphene aggregates and localizes within the positive electrode active material layer, preventing the formation of the network. Therefore, it can be said that the dispersibility of graphene used as a conductive assistant in the dispersion medium is an extremely important factor for enhancing the electron conductivity of the positive electrode active material layer. When the inventors of the present application confirmed the positive electrode active material layer prepared by putting graphene as a conductive assistant together with the active material and the binder into the dispersion medium, they found that the dispersibility was not sufficient, and as a result, a network for electron conduction could not be formed within the positive electrode active material layer. Furthermore, when reduced graphene oxide (hereinafter abbreviated as RGO (Reduced Graphene Oxide)), which is obtained by reducing graphene oxide, was used instead of graphene as a conductive assistant and put into the dispersion medium, the same result was obtained in the positive electrode active material layer. This is because the dispersibility in the dispersion medium directly depends on the dispersibility of graphene in the positive electrode active material layer. When the dispersibility of graphene is low, graphene aggregates and localizes within the positive electrode active material layer, preventing the formation of the network. Therefore, it can be said that the dispersibility of graphene used as a conductive assistant in the dispersion medium is an extremely important factor for enhancing the electron conductivity of the positive electrode active material layer. If the dispersibility of graphene is low, graphene aggregates and localizes within the positive electrode active material layer, preventing the formation of the network. Therefore, it can be said that the dispersibility of graphene used as a conductive assistant in the dispersion medium is an extremely important factor for enhancing the electron conductivity of the positive electrode active material layer. Therefore, it can be said that the dispersibility of graphene used as a conductive assistant in the dispersion medium is an extremely important factor for enhancing the electron conductivity of the positive electrode active material layer. Therefore, it can be said that the dispersibility of graphene used as a conductive assistant in the dispersion medium is an extremely important factor for enhancing the electron conductivity of the positive electrode active material layer.

[0018] Therefore, when the inventors of the present application confirmed the positive electrode active material layer prepared by putting graphene as a conductive assistant together with the active material and the binder into the dispersion medium, they found that the dispersibility was not sufficient, and as a result, a network for electron conduction could not be formed within the positive electrode active material layer. Furthermore, when reduced graphene oxide (hereinafter abbreviated as RGO (Reduced Graphene Oxide)), which is obtained by reducing graphene oxide, was used instead of graphene as a conductive assistant and put into the dispersion medium, the same result was obtained in the positive electrode active material layer. Furthermore, when reduced graphene oxide (hereinafter abbreviated as RGO (Reduced Graphene Oxide)), which is obtained by reducing graphene oxide, was used instead of graphene as a conductive assistant and put into the dispersion medium, the same result was obtained in the positive electrode active material layer. On the other hand, the inventors of the present application used graphene oxide (GO (Graphene Oxide)) as a conductive assistant. (hereinafter abbreviated as RGO (Reduced Graphene Oxide)) was put into the dispersion medium and the same result was obtained in the positive electrode active material layer prepared.

[0019] On the other hand, the inventors of the present application used graphene oxide (GO (Graphene Oxide)) as a conductive assistant. (also abbreviated as xide).) was put into a dispersion medium together with an active material and a binder to prepare a positive electrode paste After that, the dispersed graphene oxide was reduced by heat treatment to obtain graphene, and in the positive In the electrode active material layer, a network of electron conduction was formed within the active material layer, and it was found that excellent electron conduction performance was exhibited.

[0020] From the above, in the positive electrode active material layer in which graphene or RGO is dispersed as a raw material for a conductive aid, their dispersibility is low, whereas the graphene obtained by adding graphene oxide to form a positive electrode paste and then reducing it was found to have high dispersibility. The difference in dispersibility in the active material layer between such graphene or RGO and the graphene formed by reduction after the formation of the positive electrode paste using graphene oxide can be explained as follows in terms of the difference in dispersibility in the dispersion medium.

[0021] The difference in dispersibility in the active material layer between such graphene or RGO and the graphene formed by reduction after the formation of the positive electrode paste using graphene oxide can be explained as the difference in dispersibility in the dispersion medium as follows.

[0022] In Fig. 1(A), the structural formula of typical NMP (N-methylpyrrolidone, also called 1-methyl-2- pyrrolidone, N-methyl-2-pyrrolidone, etc.) as a dispersion medium is shown. NMP10 0 is a compound having a 5-membered ring structure and is one of the polar solvents. As shown in Fig. 1(A), the oxygen in NMP is electrically polarized with the oxygen on the minus (-) side and the carbon double-bonded to the oxygen on the plus (+) side. Graphene, RGO or graphene oxide is added to such a polar diluent solvent.

[0023] Graphene is, as described above, a carbon crystal structure with a hexagonal skeleton extended in a planar shape, and substantially no functional groups are contained in the structure. Also, RGO has had its original functional groups removed. ​​​​​The structure was reduced by heat treatment, and the proportion of functional groups in the structure was low at about 10 wt%. Therefore, the surface of graphene or RGO101 is non-polar, as shown in Figure 1(B). Therefore, the dispersion medium NMP100 and graphene or RGO1 The interaction with RGO101 is extremely small, and the interaction between graphene and RGO101 is rather small. This is thought to cause the graphene or RGO101 to aggregate (see Figure 1(C)).

[0024] On the other hand, the graphene oxide 102 has an epoxy group, a carbonyl group, a carboxyl group, a hydroxyl group, and a hydroxyl group. Graphene oxide 102 is a polar material that has functional groups such as silyl groups. Since the graphene oxides are negatively charged, they do not easily aggregate with each other in polar solvents. On the other hand, the interaction with the polar solvent NMP100 is large (see Figure 2(A)). As shown in FIG. 2B, the functional group such as an epoxy group of the graphene oxide 102 has a polar Because of the interaction with the solvent, the aggregation of graphene oxide particles is inhibited, resulting in the dispersion of It is considered that the graphene oxide 102 is uniformly dispersed in the graphene oxide 102 (see FIG. 2B).

[0025] From the above, it is believed that graphene can be used as a conductive additive to provide high electronic conductivity in the positive electrode active material layer. In order to construct a network having the above structure, the positive electrode paste is dispersed in the dispersion medium during preparation. It is very effective to use graphene oxide, which has high thermal conductivity. The dispersibility of a material depends on the amount of functional groups that contain oxygen, such as epoxy groups (in other words, the amount of oxygen that is dispersed). It is thought to depend on the degree of oxidation of laphene.

[0026] Therefore, one aspect of the present invention is to use the same as the above-mentioned as a raw material for a conductive assistant for a positive electrode for a non-aqueous secondary battery. The graphene oxide has a weight ratio of oxygen to carbon of 0.405 or more. It's graphene.

[0027] Here, the weight ratio of oxygen to carbon is an index showing the degree of oxidation, and is the weight ratio of the graphene oxide structure. The weight ratio of carbon and oxygen among the constituent elements is expressed as a ratio based on carbon. The weight of the elements that make up graphene oxide can be determined by, for example, X-ray photoelectron spectroscopy (XPS). This can be measured using a photoelectron spectroscopy (PES).

[0028] The weight ratio of oxygen to carbon in graphene oxide is 0.405 or more, which means that the polar Since graphene oxide has high dispersibility in solvents, epoxy groups, carbonyl groups, and carboxyl groups are easily dispersible. This means that the functional groups, such as carboxyl groups and hydroxyl groups, are sufficiently bonded to form a polar substance. Taste.

[0029] Therefore, graphene oxide having a weight ratio of oxygen to carbon of 0.405 or more is used as a positive electrode active material. The mixture is dispersed in a dispersion medium together with a binder and kneaded, then applied to the positive electrode current collector and heated. This has led to the development of a non-aqueous secondary battery containing graphene, which has high dispersibility and an electronic conductive network. A positive electrode for a battery can be formed.

[0030] The graphene oxide has a side length of 50 nm or more and 100 μm or less, preferably 800 nm or more. It is preferable that the thickness is at most 20 μm.

[0031] Another embodiment of the present invention is a conductive additive including a plurality of granular positive electrode active materials and a plurality of graphenes. and a binder. Larger than the average particle size of the material, graphene is dispersed in the positive electrode active material layer to such an extent that it makes surface contact with one or more other adjacent graphenes, and the graphene is a positive electrode for a non-aqueous secondary battery that makes surface contact so as to wrap a part of the surface of the granular positive electrode active material. As described above, since graphene oxide is a structure having a functional group containing oxygen, graphene oxides are uniformly dispersed in a polar solvent such as NMP without aggregating with each other. The dispersed graphene oxide is uniformly mixed with a plurality of granular positive electrode active materials. Therefore, due to the volatilization of the dispersion medium and the reduction treatment of the graphene oxide, the graphene formed from the graphene oxide is dispersed in the positive electrode active material layer to such an extent that it makes surface contact with other graphenes. Graphene is sheet-shaped and makes electrical connection by partial surface contact with each other. Therefore, when each graphene is regarded as one aggregate, it is considered that an electron conduction network is formed.

[0032] As already described, since graphene oxide is a structure having a functional group containing oxygen, graphene oxides are uniformly dispersed in a polar solvent such as NMP without aggregating with each other. The dispersed graphene oxide is uniformly mixed with a plurality of granular positive electrode active materials. Therefore, due to the volatilization of the dispersion medium and the reduction treatment of the graphene oxide, the graphene formed from the graphene oxide is dispersed in the positive electrode active material layer to such an extent that it makes surface contact with other graphenes. Graphene is sheet-shaped and makes electrical connection by partial surface contact with each other. Therefore, when each graphene is regarded as one aggregate, it is considered that an electron conduction network is formed. The dispersed graphene oxide is uniformly mixed with a plurality of granular positive electrode active materials. Therefore, due to the volatilization of the dispersion medium and the reduction treatment of the graphene oxide, the graphene formed from the graphene oxide is dispersed in the positive electrode active material layer to such an extent that it makes surface contact with other graphenes. Graphene is sheet-shaped and makes electrical connection by partial surface contact with each other. Therefore, when each graphene is regarded as one aggregate, it is considered that an electron conduction network is formed. The dispersed graphene oxide is uniformly mixed with a plurality of granular positive electrode active materials. Therefore, due to the volatilization of the dispersion medium and the reduction treatment of the graphene oxide, the graphene formed from the graphene oxide is dispersed in the positive electrode active material layer to such an extent that it makes surface contact with other graphenes. Graphene is sheet-shaped and makes electrical connection by partial surface contact with each other. Therefore, when each graphene is regarded as one aggregate, it is considered that an electron conduction network is formed. The dispersed graphene oxide is uniformly mixed with a plurality of granular positive electrode active materials. Therefore, due to the volatilization of the dispersion medium and the reduction treatment of the graphene oxide, the graphene formed from the graphene oxide is dispersed in the positive electrode active material layer to such an extent that it makes surface contact with other graphenes. Graphene is sheet-shaped and makes electrical connection by partial surface contact with each other. Therefore, when each graphene is regarded as one aggregate, it is considered that an electron conduction network is formed. The dispersed graphene oxide is uniformly mixed with a plurality of granular positive electrode active materials. Therefore, due to the volatilization of the dispersion medium and the reduction treatment of the graphene oxide, the graphene formed from the graphene oxide is dispersed in the positive electrode active material layer to such an extent that it makes surface contact with other graphenes. Graphene is sheet-shaped and makes electrical connection by partial surface contact with each other. Therefore, when each graphene is regarded as one aggregate, it is considered that an electron conduction network is formed. The dispersed graphene oxide is uniformly mixed with a plurality of granular positive electrode active materials. Therefore, due to the volatilization of the dispersion medium and the reduction treatment of the graphene oxide, the graphene formed from the graphene oxide is dispersed in the positive electrode active material layer to such an extent that it makes surface contact with other graphenes. Graphene is sheet-shaped and makes electrical connection by partial surface contact with each other. Therefore, when each graphene is regarded as one aggregate, it is considered that an electron conduction network is formed. Also, since the connection between graphenes is surface contact, the contact resistance can be kept low, and a network with high electron conductivity is constructed. Also, since the connection between graphenes is surface contact, the contact resistance can be kept low, and a network with high electron conductivity is constructed.

[0033] On the other hand, each graphene is a sheet having a side length of 50 nm or more and 100 μm or less, preferably 800 nm or more and 20 μm or less, and is larger than the average particle size of the granular positive electrode active material. Therefore, a single sheet-shaped graphene can be connected to a plurality of granular positive electrode active materials. In particular, since graphene is sheet-shaped, it can make surface contact so as to cover the surface of the granular positive electrode active material. Therefore, the contact resistance between the granular positive electrode active material and graphene can be reduced without increasing the amount of the conductive assistant. On the other hand, each graphene is a sheet having a side length of 50 nm or more and 100 μm or less, preferably 800 nm or more and 20 μm or less, and is larger than the average particle size of the granular positive electrode active material. Therefore, a single sheet-shaped graphene can be connected to a plurality of granular positive electrode active materials. In particular, since graphene is sheet-shaped, it can make surface contact so as to cover the surface of the granular positive electrode active material. Therefore, the contact resistance between the granular positive electrode active material and graphene can be reduced without increasing the amount of the conductive assistant. On the other hand, each graphene is a sheet having a side length of 50 nm or more and 100 μm or less, preferably 800 nm or more and 20 μm or less, and is larger than the average particle size of the granular positive electrode active material. Therefore, a single sheet-shaped graphene can be connected to a plurality of granular positive electrode active materials. In particular, since graphene is sheet-shaped, it can make surface contact so as to cover the surface of the granular positive electrode active material. Therefore, the contact resistance between the granular positive electrode active material and graphene can be reduced without increasing the amount of the conductive assistant. On the other hand, each graphene is a sheet having a side length of 50 nm or more and 100 μm or less, preferably 800 nm or more and 20 μm or less, and is larger than the average particle size of the granular positive electrode active material. Therefore, a single sheet-shaped graphene can be connected to a plurality of granular positive electrode active materials. In particular, since graphene is sheet-shaped, it can make surface contact so as to cover the surface of the granular positive electrode active material. Therefore, the contact resistance between the granular positive electrode active material and graphene can be reduced without increasing the amount of the conductive assistant. On the other hand, each graphene is a sheet having a side length of 50 nm or more and 100 μm or less, preferably 800 nm or more and 20 μm or less, and is larger than the average particle size of the granular positive electrode active material. Therefore, a single sheet-shaped graphene can be connected to a plurality of granular positive electrode active materials. In particular, since graphene is sheet-shaped, it can make surface contact so as to cover the surface of the granular positive electrode active material. Therefore, the contact resistance between the granular positive electrode active material and graphene can be reduced without increasing the amount of the conductive assistant. On the other hand, each graphene is a sheet having a side length of 50 nm or more and 100 μm or less, preferably 800 nm or more and 20 μm or less, and is larger than the average particle size of the granular positive electrode active material. Therefore, a single sheet-shaped graphene can be connected to a plurality of granular positive electrode active materials. In particular, since graphene is sheet-shaped, it can make surface contact so as to cover the surface of the granular positive electrode active material. Therefore, the contact resistance between the granular positive electrode active material and graphene can be reduced without increasing the amount of the conductive assistant.

[0034] In addition, as the granular positive electrode active material, a material capable of inserting and extracting carrier ions such as lithium iron phosphate can be used.

[0035] Further, one aspect of the present invention has a positive electrode active material layer containing a plurality of granular positive electrode active materials, a conductive assistant containing a plurality of graphites, and a binder on a positive electrode current collector, and the bonding state of carbon contained in the positive electrode active material layer is such that the ratio of C = C bonds is 35% or more and the ratio of C - O bonds is 5% or more and 20% or less, which is a positive electrode for a non-aqueous secondary battery.

[0036] Further, one aspect of the present invention is to disperse graphene oxide having a weight ratio of oxygen to carbon of 0.405 or more in a dispersion medium, and add a positive electrode active material to the dispersion medium in which the graphene oxide is dispersed and knead to prepare a mixture, add a binder to the mixture and knead to prepare a positive electrode paste, apply the positive electrode paste to a positive electrode current collector, and after or simultaneously with volatilizing the dispersion medium contained in the applied positive electrode paste, reduce the graphene oxide to form a positive electrode active material layer containing graphene on the positive electrode current collector, which is a method for manufacturing a positive electrode for a non-aqueous secondary battery.

[0037] The above-mentioned graphene oxide and graphene preferably have a side length of 50 nm or more and 100 μm or less, more preferably 800 nm or more and 20 μm or less.

[0038] In the above manufacturing method, the positive electrode paste is dried in a reducing atmosphere or under reduced pressure. By doing so, the dispersion medium contained in the positive electrode paste can be volatilized and the graphene oxide contained in the positive electrode paste can be reduced.

[0039] Further, in the above manufacturing method, when adding a binder to the mixture and kneading, a dispersion medium is further added ​​​​​​By adding it, the viscosity of the positive electrode paste can be adjusted.

[0040] The positive electrode active material is added to a dispersion medium in which graphene oxide with an oxygen-to-carbon weight ratio of 0.405 or more is dispersed. By kneading this, a positive electrode active material layer with high dispersibility of graphene is formed. Graphene oxide may be contained at a ratio of at least 2 wt% (weight percent) with respect to the total weight of the positive electrode paste, which is a mixture of the positive electrode active material, the conductive assistant, and the binder. On the other hand, after applying the positive electrode paste to the current collector and reducing it, graphene may be contained at a ratio of at least 1 wt% with respect to the total weight of the positive electrode active material layer. This is because the weight of graphene is approximately halved due to the reduction of graphene oxide.

[0041] Specifically, at the stage of the positive electrode paste, it is preferable to add 2 wt% or more and 10 wt% or less of graphene oxide, 85 wt% or more and 93 wt% or less of the positive electrode active material, and 1 wt% or more and 5 wt% or less of the binder with respect to the total amount of the positive electrode paste. Also, at the stage of the positive electrode active material layer where the positive electrode paste is applied to the current collector and graphene oxide is reduced, it is preferable to add 1 wt% or more and 5 wt% or less of graphene, 90 wt% or more and 94 wt% or less of the positive electrode active material, and 1 wt% or more and 5 wt% or less of the binder with respect to the total amount of the positive electrode active material layer.

[0042] After applying the positive electrode paste to the positive electrode current collector, by drying it in a reducing atmosphere or under reduced pressure, oxygen contained in graphene oxide is desorbed to form a positive electrode active material layer containing graphene. Note that not all of the oxygen contained in graphene oxide is desorbed, and some oxygen may remain in graphene. ​​​​​​​​​​​​​

[0043] When graphene contains oxygen, the proportion of oxygen is 2 atomic% or more and 20 atomic% or less, preferably 3 atomic% or more and 15 atomic% or less of the whole. The lower the proportion of oxygen, the higher the conductivity of graphene can be enhanced, and as a result, a network with high electron conductivity can be formed. Also, the higher the proportion of oxygen, the more gaps serving as ion channels can be formed in graphene. omic% or less, preferably 3 atomic% or more and 15 atomic% or less. The lower the proportion of oxygen, the higher the conductivity of graphene can be enhanced, and as a result, a network with high electron conductivity can be formed. Also, the higher the proportion of oxygen, the more gaps serving as ion channels can be formed in graphene. omic% or less, preferably 3 atomic% or more and 15 atomic% or less. The lower the proportion of oxygen, the higher the conductivity of graphene can be enhanced, and as a result, a network with high electron conductivity can be formed. Also, the higher the proportion of oxygen, the more gaps serving as ion channels can be formed in graphene. By using the positive electrode, negative electrode, electrolyte, and separator manufactured as described above, a non-aqueous secondary battery can be manufactured. By using the positive electrode, negative electrode, electrolyte, and separator manufactured as described above, a non-aqueous secondary battery can be manufactured.

[0044] By using the positive electrode, negative electrode, electrolyte, and separator manufactured as described above, a non-aqueous secondary battery can be manufactured. By using the positive electrode, negative electrode, electrolyte, and separator manufactured as described above, a non-aqueous secondary battery can be manufactured.

Advantages of the Invention

[0045] It is possible to provide graphene oxide which is a raw material of a conductive auxiliary agent for forming an active material layer having high electron conductivity with a small amount of conductive auxiliary agent. It is possible to provide graphene oxide which is a raw material of a conductive auxiliary agent for forming an active material layer having high electron conductivity with a small amount of conductive auxiliary agent.

[0046] Also, by using the graphene oxide as a raw material of the conductive auxiliary agent, it is possible to provide a positive electrode for a non-aqueous secondary battery including a positive electrode active material layer having high electron conductivity with a small amount of conductive auxiliary agent. Also, by using the graphene oxide as a raw material of the conductive auxiliary agent, it is possible to provide a positive electrode for a non-aqueous secondary battery including a positive electrode active material layer having high electron conductivity with a small amount of conductive auxiliary agent. Also, it is possible to provide a positive electrode for a non-aqueous secondary battery including a positive electrode active material layer having a high filling amount and being highly densified with a small amount of conductive auxiliary agent. it is possible to provide a positive electrode for a non-aqueous secondary battery including a positive electrode active material layer having a high filling amount and being highly densified with a small amount of conductive auxiliary agent.

[0047] Also, by using the positive electrode for a non-aqueous secondary battery, it is possible to provide a non-aqueous secondary battery having a large capacity per electrode volume. Also, by using the positive electrode for a non-aqueous secondary battery, it is possible to provide a non-aqueous secondary battery having a large capacity per electrode volume.

Brief Description of the Drawings

[0048]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

[0049] Hereinafter, embodiments will be described with reference to the drawings. However, the embodiments can be implemented in many different ways, and it is easily understood by those skilled in the art that the form and details can be variously changed without departing from the spirit and its scope. Therefore, the present invention is not construed as being limited to the description of the following embodiments.

[0050] In each of the drawings described in this specification, the size, film thickness, or area of each component may be exaggerated for clarity. Therefore, it is not necessarily limited to that scale.

[0051] (Embodiment 1) In this embodiment, a positive electrode for a non-aqueous secondary battery according to one aspect of the present invention will be described with reference to FIGS. 3 and 1 9. A perspective view of the positive electrode is shown in FIG. 3(A), a plan view of the positive electrode active material layer is shown in FIG. 3(B), and longitudinal cross-sectional views of the positive electrode active material layer are shown in FIGS. 3(C) and 19.

[0052] FIG. 3(A) is a perspective view of the positive electrode 200. In FIG. 3(A), the positive electrode 200 is shown in a rectangular sheet shape, but the shape of the positive electrode 200 is not limited to this, and any shape can be appropriately selected. The positive electrode 200 is produced by applying a positive electrode paste onto the positive electrode current collector 201 and then drying it in a reducing atmosphere or under reduced pressure to form the positive electrode active material layer 202. In FIG. 3(A), the positive electrode active material layer 202 is formed only on one surface of the positive electrode current collector 201, but the positive electrode active material layer 202 may be formed on both surfaces of the positive electrode current collector 201. Further, the positive electrode active material layer 202 does not need to be formed on the entire surface of the positive electrode current collector 201, and non-coated regions such as a region for connecting to the positive electrode tab are appropriately provided.

[0053] The positive electrode current collector 201 may be made of stainless steel, gold, platinum, zinc, iron, copper, aluminum, titanium, etc. Metals and their alloys are highly conductive and can be alloyed with carrier ions such as lithium. Materials that are not available for use in the current laser include silicon, titanium, neodymium, scandium, molybdenum, and titanium alloys. Aluminum alloys containing elements such as ribium that improve heat resistance can be used. It may also be made of a metal element that reacts with silicon to form a silicide. Metal elements that react with Zn to form silicides include zirconium, titanium, hafnium, and um, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, The positive electrode current collector 201 may be in the form of a foil, a plate (sheet), a mesh, a punched metal, or the like. The positive electrode current collector 201 may be in a shape such as a barrel or an expanded metal. It is preferable to use a material having a thickness of 10 μm or more and 30 μm or less.

[0054] 3B and 3C are schematic diagrams showing the top surface and the vertical cross section, respectively, of the positive electrode active material layer 202. The positive electrode active material layer 202 is made of a granular positive electrode active material 203 and graphite as a conductive additive. The adhesive includes a phene 204 and a binding agent (also called a binder, not shown).

[0055] The positive electrode active material 203 is made by mixing raw material compounds in a predetermined ratio, sintering the mixture, and then sintering the mixture by a suitable method. A granular positive electrode made of secondary particles that have an average particle size and particle size distribution and are crushed, granulated, and classified. Therefore, in FIG. 3B and FIG. 3C, the positive electrode active material 203 is Although the formula is shown as a sphere, the shape is not limited to this.

[0056] The positive electrode active material 203 may be a material capable of inserting and extracting lithium ions. and can have, for example, an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure, such as a lithium-containing composite oxide. Examples include lithium-containing composite oxides having a spinel-type crystal structure.

[0057] Examples of the lithium-containing composite oxide having an olivine-type structure include composite oxides represented by the general formula LiMPO4 (M is , Fe(II), Mn(II), Co(II), Ni(II), or one or more thereof). Representative examples of the general formula LiMPO4 include LiFePO4, LiNi PO4, LiCoPO4, LiMnPO4, LiFe a Ni b PO4, LiFe a Co b PO4, LiFe a Mn b PO4, LiNi a Co b PO4, LiNi a Mn b PO4 ( a + b is 1 or less, 0 < a < 1, 0 < b < 1), LiFe c Ni d Co e PO4, LiFe c Ni d Mn e PO4, LiNi c Co d Mn e PO4 (c + d + e is 1 or less, 0 < c < 1, 0 < d < 1, 0 < e < 1), LiFe f Ni g Co h Mn i PO4 (f + g + h + i is 1 or less, 0 < f < 1, 0 < g < 1, 0 < h < 1, 0 < i < 1), etc.

[0058] In particular, LiFePO4 satisfies well the requirements for a cathode active material, such as safety, stability, high capacity density, high potential, and the presence of lithium ions that can be extracted during initial oxidation (charging). ​ Therefore, it is preferable.

[0059] Examples of the lithium-containing composite oxide having a layered rock salt-type crystal structure include, for example, lithium cobaltate (LiCoO2), LiNiO2, LiMnO2, Li2MnO3, LiNi 0. 8Co 0.2 O2 and other NiCo-based (general formula: LiNi x Co 1-x O2 (0 < x < 1) ), LiNi 0.5 Mn 0.5 O2 and other NiMn-based (general formula: LiNi x Mn 1-x O 2 (0 < x < 1)), LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 and other NiMnCo-based (also referred to as N MC). The general formula is LiNi x Mn y Co 1-x-y O2 (x > 0, y > 0, x + y < 1)). Further, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li2MnO3-LiMO2 (M = Co, Ni, Mn), etc. are also included.

[0060] In particular, LiCoO2 is preferable because it has advantages such as a large capacity, being more stable in the air compared to LiNiO2, and being thermally more stable compared to Li NiO2.

[0061] Examples of the lithium-containing composite oxide having a spinel-type crystal structure include, for example, LiMn2O 4, Li 1+x Mn 2-x O4, Li(MnAl)2O4, LiMn 1.5 Ni 0.5 O 4, etc.

[0062] Lithium-containing composite oxides having a spinel crystal structure containing manganese such as LiMn2O4 When a small amount of lithium nickelate (LiNiO2, LiNi 1-x MO2 (M = Co, A l, etc.)) is mixed, there are advantages such as suppressing the elution of manganese and suppressing the decomposition of the electrolytic solution, which is preferable. It is preferable.

[0063] Also, as the positive electrode active material, a composite oxide represented by the general formula Li (2-j) MSiO4 (M is one or more of Fe(II), Mn (II), Co(II), Ni(II), 0 ≦ j ≦ 2) can be used. Representative examples of the general formula Li MSiO4 include Li (2-j) MSiO4. Representative examples include Li (2-j ) FeSiO4, Li (2-j) NiSiO4, Li (2-j) CoSiO4, Li (2 -j) MnSiO4, Li (2-j) Fe k Ni l SiO4, Li (2-j) Fe k Co l SiO4, Li (2-j) Fe k Mn l SiO4, Li (2-j) Ni k Co l SiO 4, Li (2-j) Ni k Mn l SiO4 (k + l is 1 or less, 0 < k < 1, 0 < l < 1) , Li (2-j) Fe m Ni n Co q SiO4, Li (2-j) Fe m Ni n Mn q Si O4, Li (2-j) Ni m Con Mn q SiO4 (where m + n + q is 1 or less, 0 < m < 1, 0 < n < 1, 0 < q < 1), Li (2-j) Fe r Ni s Co t Mn u SiO4 (r + s + t + u is 1 or less, 0 < r < 1, 0 < s < 1, 0 < t < 1, 0 < u < 1), etc. can be mentioned 。

[0064] Also, as the positive electrode active material, A x M2(XO4)3 (A = Li, Na, Mg, M = Fe, M n, Ti, V, Nb, Al, X = S, P, Mo, W, As, Si) represented by the general formula can be used. Examples of the NASICON-type compound include Fe2(MnO4) 3, Fe2(SO4)3, Li3Fe2(PO4)3, etc. Also, as the positive electrode active material compounds represented by the general formula of Li2MPO4F, Li2MP2O7, Li5MO4 (M = Fe, Mn), perovskite-type fluorides such as NaF3, FeF3, metal chalcogenides (sulfides, selenides, tellurides) such as TiS2, M oS2, lithium-containing composite oxides having an inverse spinel-type crystal structure such as LiMVO4, vanadium oxide-based (V2O 5, V6O 13 8, LiV3O8, etc.), manganese oxide-based, organic sulfur-based, etc. materials can be used. 5, V6O 13 When the carrier ion is an alkali metal ion, alkaline earth metal ion, beryllium ion, or magnesium ion other than lithium ion, in the above-mentioned

[0065] lithium compounds and lithium-containing composite oxides, instead of lithium, an alkali metal ion, alkaline earth metal ion, beryllium ion, or magnesium ion can be used. ion, alkaline earth metal ion, beryllium ion, or magnesium ion can be used. Metals (such as sodium and potassium), alkaline earth metals (such as calcium, strontium, barium, etc.), beryllium, or magnesium may also be used. Lithium, barium, etc.), beryllium, or magnesium may be used.

[0066] In addition, the graphene 204 added to the positive electrode active material layer 202 as a conductive aid is formed by subjecting graphene oxide having a weight ratio of oxygen to carbon of 0.405 or more to a reduction treatment. Is formed by performing a reduction treatment on graphene oxide having a weight ratio of oxygen to carbon of 0.405 or more. Is formed.

[0067] Graphene oxide having a weight ratio of oxygen to carbon of 0.405 or more can be produced using an oxidation method called the Hummers method. Can be produced using an oxidation method called the Hummers method.

[0068] In the Hummers method, a sulfuric acid solution of potassium permanganate, hydrogen peroxide water, etc. is added to graphite powder to cause an oxidation reaction to produce a dispersion containing graphite oxide. Graphite oxide Is produced by adding a sulfuric acid solution of potassium permanganate, hydrogen peroxide water, etc. to graphite powder to cause an oxidation reaction to produce a dispersion containing graphite oxide. Graphite oxide Is formed by the oxidation of the carbon in graphite, and functional groups such as epoxy groups, carbonyl groups, carboxyl groups, Hydroxyl groups, etc. are bonded. Therefore, the interlayer distance of a plurality of graphene layers becomes longer than that of graphite, and it becomes easier to form thin flakes by separating the layers. Next, by applying ultrasonic vibration to the dispersion containing graphite oxide, the graphite oxide with a long interlayer distance is Cleaved to separate the graphene oxide, and a dispersion containing graphene oxide can be produced. Then, by removing the solvent from the dispersion containing graphene oxide, powdery Graphene oxide can be obtained. Cleaved to separate the graphene oxide, and a dispersion containing graphene oxide can be produced. And by removing the solvent from the dispersion containing graphene oxide, powdery Graphene oxide can be obtained.

[0069] Here, graphene oxide having a weight ratio of oxygen to carbon of 0.405 or more can be formed by appropriately adjusting the amount of an oxidizing agent such as potassium permanganate. That is, the amount of An oxidizing agent such as potassium permanganate can be adjusted as appropriate to form. That is, the amount of By increasing the amount of the oxidizing agent with respect to the graphite powder, the degree of oxidation of graphene (weight ratio of oxygen to carbon) can be increased. Therefore, the amount of the oxidizing agent with respect to the graphite powder as a raw material may be determined according to the amount of graphene oxide to be produced.

[0070] Note that the production of graphene oxide is not limited to the Hummers method using a sulfuric acid solution of potassium permanganate. For example, the Hummers method using nitric acid, potassium chlorate, sodium nitrate, etc., or a method for producing graphene oxide other than the Hummers method may be appropriately used.

[0071] In addition, the thinning of the graphite oxide may be performed by adding ultrasonic vibration, irradiating microwave, radio wave, or thermal plasma, or applying physical stress.

[0072] The produced graphene oxide has epoxy groups, carbonyl groups, carboxyl groups, hydroxyl groups, etc. In a polar solvent typified by NMP, oxygen in the functional group is negatively charged, so while interacting with NMP, different graphene oxides repel each other and are difficult to aggregate. Therefore, in a polar solvent, graphene oxide is likely to be uniformly dispersed.

[0073] In addition, the length of one side of the graphene oxide (also referred to as the flake size) is 50 nm or more and 100 μm or less, preferably 800 nm or more and 20 μm or less. In particular, when the flake size is smaller than the average particle size of the granular positive electrode active material 203, it becomes difficult to make surface contact with a plurality of positive electrode active materials 203, and it also becomes difficult to connect graphene to each other. Therefore, it becomes difficult to improve the electron conductivity of the positive electrode active material layer 202.

[0074] ​​​​​​​​​​​ As shown in the top view of the positive electrode active material layer 202 shown in FIG. 3(B), a plurality of granular positive electrode active materials 203 are covered by a plurality of graphenes 204. A single sheet-like graphene 20 4 is connected to a plurality of granular positive electrode active materials 203. In particular, since the graphene 204 is sheet-like it can make surface contact so as to wrap a part of the surface of the granular positive electrode active material 203. Unlike granular conductive aids such as acetylene black that make point contact with the positive electrode active material, the graphene 2 04 enables surface contact with low contact resistance, so without increasing the amount of the conductive aid it is possible to improve the electron conductivity between the granular positive electrode active material 203 and the graphene 204 .

[0075] Also, the plurality of graphenes 204 are in surface contact with each other. This is because graphene oxide with extremely high dispersibility in a polar solvent is used for the formation of the graphene 204. By volatilizing and removing the solvent from the dispersion medium containing uniformly dispersed graphene oxide and reducing the graphene oxide to graphene, the graphene 204 remaining in the positive electrode active material layer 202 partially overlaps each other and is dispersed to the extent of making surface contact with each other, thereby forming a path for electron conduction. In the top view of the positive electrode active material layer 202 shown in FIG. 3(B), the graphene 204 does not necessarily overlap with other graphene only on the surface of the positive electrode active material layer 202. A part of the graphene 2 04 is formed to be three-dimensionally arranged such as penetrating into the positive electrode active material layer 202. Also, since the graphene 204 is an extremely thin film (sheet) composed of a single layer of carbon molecules or a stack thereof

[0076] it traces the surface of each individual granular positive electrode active material 203 In the top view of the positive electrode active material layer 202 shown in FIG. 3(B), the graphene 204 does not necessarily overlap with other graphene only on the surface of the positive electrode active material layer 202. A part of the graphene 2 04 is formed to be three-dimensionally arranged such as penetrating into the positive electrode active material layer 202. Also, since the graphene 204 is an extremely thin film (sheet) composed of a single layer of carbon molecules or a stack thereof it traces the surface of each individual granular positive electrode active material 203 it is formed so as to trace the surface of each individual granular positive electrode active material 203. Since the graphene 204 is an extremely thin film (sheet) composed of a single layer of carbon molecules or a stack thereof It covers and contacts a part of the surface, and the part that is not in contact with the positive electrode active material 203 is bent between a plurality of granular positive electrode active materials 203, forming wrinkles or being stretched and in a taut state. It exhibits a state of being bent, wrinkled, or stretched between the granular positive electrode active materials 203. It is.

[0077] In the longitudinal section of the positive electrode active material layer 202, as shown in FIG. 3(C), sheet-like graphene 204 is dispersed approximately uniformly inside the positive electrode active material layer 202. In FIG. 3(C), graphene 204 is schematically represented by a thick line, but actually it is a thin film having a single layer or multiple layers of carbon molecules. Similar to the description of the upper surface of the positive electrode active material layer 202, a plurality of graphenes 204 are formed so as to wrap or cover a plurality of granular positive electrode active materials 203, and thus are in surface contact with each other. Also, the graphenes 204 are in surface contact with each other, forming an electron conduction network by a plurality of graphenes 204. A schematic diagram obtained by further enlarging FIG. 3(C) is FIG. 19. Graphene 204 covers the surface of a plurality of granular positive electrode active materials 203 as if sticking thereto, and the graphenes also contact each other to form a network. Since they are formed so as to wrap or cover a plurality of granular positive electrode active materials 203, they are in surface contact with each other. Also, the graphenes 204 are in surface contact with each other, forming an electron conduction network by a plurality of graphenes 204. A schematic diagram obtained by further enlarging FIG. 3(C) is FIG. 19. Graphene 204 covers the surface of a plurality of granular positive electrode active materials 203 as if sticking thereto, and the graphenes also contact each other to form a network. each other to form a network. forming a network.

[0078] As shown in FIGS. 3(B), 3(C) and 19, a plurality of sheet-like graphenes 204 are three-dimensionally dispersed inside the positive electrode active material layer 202, and by their surface contact with each other, a three-dimensional electron conductive network is formed. Also, each graphene 204 covers a plurality of granular positive electrode active materials 203 and is in surface contact with them. Therefore, the bonding between the positive electrode active materials 203 is maintained. From the above, graphene oxide having a weight ratio of oxygen to carbon of 0.405 or more is used as a raw material, and graphene reduced after the formation of the paste is obtained. By using [substance name] as a conductive aid, a positive electrode active material layer 202 having high electron conductivity can be formed. This can be achieved.

[0079] Also, in order to increase the contact points between the positive electrode active material 203 and the graphene 204, the addition of a conductive aid does not necessarily require an increase in the amount, so the ratio of the positive electrode active material 203 in the positive electrode active material layer 202 of the positive electrode active material 203 can be increased. As a result, the discharge capacity of the secondary battery can be increased.

[0080] The average particle diameter of the primary particles of the granular positive electrode active material 203 is 500 nm or less, preferably 50 nm It is advisable to use those with a size of 50 nm or more and 500 nm or less. For the purpose of surface contact with a plurality of the granular positive electrode active materials 203 the graphene 204 preferably has a side length of 50 nm or more and 100 μm or less, preferably 800 nm or more and 20 μm or less.

[0081] In addition, as the binder contained in the positive electrode active material layer 202, typical polyvinylidene fluoride (PVDF), polyimide, polytetrafluoroethylene, polyvinyl chloride ide, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile -butadiene rubber, fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethy lene, nitrocellulose, etc. can be used.

[0082] The positive electrode active material layer 202 shown above contains the positive electrode active material 203, graphene 2 04 as a conductive aid, and a binder. With respect to the total amount of the positive electrode active material layer 202, the positive electrode active material 203 is 9 0 wt% or more and 94 wt% or less, graphene is 1 wt% or more and 5 wt% or less, and the binder is 1 wt % or more and 5 wt% or less, preferably.

[0083] As shown in this embodiment, graphene 204 having an average particle size larger than that of the granular positive electrode active material 203 is in the positive electrode active material layer 202 and is in surface contact with one or more other adjacent graphenes 204 to each other and is dispersed to such an extent as to be in surface contact with a part of the surface of the granular positive electrode active material 203, so that a positive electrode for a non-aqueous secondary battery including a positive electrode active material layer having a high filling amount and a high density can be provided with a small amount of a conductive assistant.

[0084] This embodiment can be implemented in appropriate combination with other embodiments.

[0085] (Embodiment 2) Next, a method for manufacturing a positive electrode 200 including a positive electrode active material layer will be described with reference to FIG. 4 by preparing a positive electrode paste using the above-described positive electrode active material, conductive assistant, binder, and dispersion medium, and applying the positive electrode paste onto the positive electrode current collector 201 and drying it in a reducing atmosphere or under reduced pressure.

[0086] First, NMP is prepared as a dispersion medium (step S11), and graphene oxide having a weight ratio of oxygen to carbon of 0.405 or more as described in Embodiment 1 is dispersed in NMP (step S12). When the amount of graphene oxide is less than 2 wt% with respect to the total amount of the positive electrode paste, the conductivity decreases when the positive electrode active material layer 202 is formed. When the amount of graphene oxide exceeds 10 wt%, the viscosity of the positive electrode paste becomes high, although it depends on the particle size of the positive electrode active material. Further, during the drying process after applying the positive electrode paste to the positive electrode current collector 201, convection occurs in the positive electrode paste due to heating, and the light and thin graphene oxide moves and aggregates, so that the positive electrode active material layer 202 cracks or the positive electrode active material layer 202 peels off from the positive electrode current collector 201.​​​​​​​​​​​​​ There is a risk. Therefore, the amount of graphene oxide is preferably 2 wt% to 10 wt% based on the total weight of the positive electrode paste (positive electrode active material, conductive aid, and binder). Note that graphene oxide is reduced by a subsequent heat treatment step to become graphene and its weight is approximately halved. Therefore, the weight ratio in the positive electrode active material layer 202 is 1 wt% to 5 wt%.

[0087] Next, lithium iron phosphate is added as the positive electrode active material (step S13). The average particle diameter of the primary particles of lithium iron phosphate is preferably 50 nm or more and 500 nm or less. The amount of lithium iron phosphate added is preferably 85 wt% or more based on the total amount of the positive electrode paste. For example, it may be 85 wt% or more and 93 wt% or less.

[0088] Note that carbohydrates such as glucose may be mixed during the firing of lithium iron phosphate to coat the particles of lithium iron phosphate with carbon. This treatment increases the conductivity.

[0089] Next, these mixtures are kneaded (kneaded in a high-viscosity state) to break up the aggregation of graphene oxide and lithium iron phosphate. In addition, since graphene oxide has functional groups, in a polar solvent, the oxygen in the functional groups is negatively charged, so different graphene oxides are less likely to aggregate with each other. In addition, graphene oxide has a strong interaction with lithium iron phosphate. Therefore, graphene oxide can be more uniformly dispersed in lithium iron phosphate.

[0090] Next, PVDF is added as a binder to these mixtures (step S14). The amount of PVD F can be set according to the amounts of graphene oxide and lithium iron phosphate, and the positive electrode paste For the slurry, it may be added in an amount of 1 wt% or more and 5 wt% or less. The graphene oxide is in a state of being uniformly dispersed so as to be in surface contact with a plurality of positive electrode active material particles, and by adding a binder it is possible to bind the positive electrode active material and the graphene oxide while maintaining the dispersed state. In addition, depending on the ratio of lithium iron phosphate and graphene oxide, it may not be necessary to add a binder, but when a binder is added, the strength of the positive electrode can be improved.

[0091] Next, NMP is added to these mixtures until a predetermined viscosity is reached (step S15), and by kneading a positive electrode paste can be produced (step S16). In the above steps, by producing a positive electrode paste, a positive electrode paste with a uniform kneaded state of graphene oxide, a positive electrode active material, and a binder can be produced.

[0092] Next, the positive electrode paste is applied onto the positive electrode current collector 201 (step S17).

[0093] Next, the positive electrode paste applied onto the positive electrode current collector 201 is dried (step S18). The drying process is performed by heating at 60°C to 170°C for 1 minute to 10 hours to evaporate NMP. Note that the atmosphere is not particularly limited.

[0094] Next, the positive electrode paste is dried in a reducing atmosphere or under reduced pressure (step S19). By setting it to a reducing atmosphere or under reduced pressure and heating at a temperature of 130°C to 200°C for 10 hours to 30 hours, NMP and water remaining in the positive electrode paste are evaporated, and oxygen contained in the graphene oxide is desorbed. Thereby, the graphene oxide can be made into graphene. Note that Not all of the oxygen contained in the graphene oxide is desorbed, and some oxygen may remain in the graphene. This is also acceptable.

[0095] Through the above steps, a positive electrode 200 including a positive electrode active material layer 202 in which graphene 204 is uniformly dispersed in the positive electrode active material can be manufactured. Note that after the drying step, a pressing step may be performed on the positive electrode 200. This is also acceptable.

[0096] As described in this embodiment, by adding a positive electrode active material to a dispersion medium in which graphene oxide with an oxygen weight ratio to carbon of 0.405 or more is dispersed and kneading, graphene oxide can be uniformly dispersed in the positive electrode active material. By adding a binder in a state where the graphene oxide is dispersed in contact with a plurality of positive electrode active material particles, the binder can be uniformly dispersed without inhibiting the contact between the graphene oxide and the plurality of positive electrode active material particles. Using the positive electrode paste produced in this way, a positive electrode including a positive electrode active material layer with a high filling amount and high density of the positive electrode active material can be manufactured. Further, by using this positive electrode to manufacture a battery, a non-aqueous secondary battery with high capacity can be manufactured. Furthermore, since the binder can maintain the state in which the sheet-like graphene is in contact with a plurality of positive electrode active materials, peeling between the positive electrode active material and the graphene can be suppressed, and a non-aqueous secondary battery with good cycle characteristics can be manufactured.

[0097] This embodiment can be implemented in appropriate combination with other embodiments.

[0098] (Embodiment 3) In this embodiment, regarding the structure of the non-aqueous secondary battery and its manufacturing method, with reference to FIGS. 5 and 6 ​​​​​​​​​​This will be described with reference to the drawings.

[0099] FIG. 5(A) is an external view of a coin-type (single-layer flat-type) non-aqueous secondary battery, and FIG. 5(B) is its cross-sectional view.

[0100] The coin-type secondary battery 300 includes a positive electrode can 301 that also serves as a positive electrode terminal and a negative electrode can 302 that also serves as a negative electrode terminal, which are insulated and sealed with a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact therewith. Further, the negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact therewith. Between the positive electrode active material layer 306 and the negative electrode active material layer 309, there are a separator 310 and an electrolyte (not shown). The positive electrode 304 can use the positive electrode 200 shown in Embodiment 1 and Embodiment 2.

[0101] The negative electrode 307 is formed by forming a negative electrode active material layer 309 on the negative electrode current collector 308 by a CVD method, a sputtering method, or a coating method.

[0102] For the negative electrode current collector 308, metals such as aluminum, copper, nickel, and titanium, and highly conductive materials such as aluminum-nickel alloys and aluminum-copper alloys can be used. The negative electrode current collector 308 can appropriately use shapes such as foil, plate (sheet), net, punching metal, and expanded metal. The negative electrode current collector 308 preferably has a thickness of 10 μm

[0103] or more and 30 μm or less. As the negative electrode active material, lithium dissolution / precipitation or lithium ion insertion / desorption is possible.

[0104]

[0104] As the negative electrode active material, materials capable of lithium dissolution / precipitation or lithium ion insertion / desorption are used. Materials can be used, for example, lithium metal, carbon-based materials, alloy-based materials, etc. are mentioned.

[0105] Lithium metal has a low redox potential (-3.045 V vs. standard hydrogen electrode) and a large specific capacity per weight and volume (3860 mAh / g and 2062 mAh / cm 3 ) respectively, so it is preferable.

[0106] Examples of carbon-based materials include graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black, etc.

[0107] Examples of graphite include artificial graphite such as mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch -based artificial graphite, etc., and natural graphite such as spheroidized natural graphite.

[0108] Graphite shows a potential as low as that of lithium metal (0.1 - 0.3 V vs. Li / Li ) when lithium ions are inserted into graphite (when forming a lithium-graphite intercalation compound). + Due to this, lithium-ion batteries can exhibit a high operating voltage. Furthermore, graphite has advantages such as a relatively high capacity per unit volume, small volume expansion, low cost, and high safety compared to lithium metal, so it is preferable.

[0109] As the negative electrode active material, alloy-based materials capable of performing charge and discharge reactions through alloying and dealloying reactions with lithium metal can also be used. For example, materials containing at least one of Al, Si, Ge, Sn, Pb, Sb, Bi, Ag, Zn, Cd, In, Ga, etc. are mentioned. These elements have a large capacity relative to carbon. In particular, silicon has a theoretical capacity of 4200 m Ah / g, which is significantly higher. Therefore, it is preferable to use silicon as the negative electrode active material. As alloy-based materials using such elements, for example, SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni 3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, La Sn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. can be mentioned.

[0110] In addition, as the negative electrode active material, oxides such as titanium dioxide (TiO2), lithium titanate (Li4T i5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5) , tungsten oxide (WO2), molybdenum oxide (MoO2), etc. can be used.

[0111] In addition, as the negative electrode active material, Li3N-type structured Li 3-x M x N (M = Co, Ni, Cu), which is a complex nitride of lithium and transition metals, can be used. For example, Li 2.6 Co 0.4 N3 exhibits a large charge-discharge capacity (900 mAh / g) and is preferable.

[0112] When using a complex nitride of lithium and transition metals, since lithium ions are contained in the negative electrode active material, it can be preferably combined with materials such as V2O5 and Cr3O8 that do not contain lithium ions as the positive electrode active material. Even when using a material containing lithium ions as the positive electrode active material, by previously desorbing lithium ions, a complex nitride of lithium and transition metals can be used. It is possible.

[0113] In addition, a material in which a conversion reaction occurs can also be used as the negative electrode active material. For example , transition metal oxides such as cobalt oxide (CoO), nickel oxide (NiO), iron oxide (FeO), etc., which do not undergo an alloying reaction with lithium may be used as the negative electrode active material. As materials in which a conversion reaction occurs, further, oxides such as Fe2O3, CuO, Cu2O, RuO2, Cr2O 3, etc., sulfides such as CoS , NiS, CuS, etc., nitrides such as Zn3N2, Cu3N, G 0.89 e3N4, etc., phosphides such as NiP2, FeP2, CoP3, etc., and fluorides such as FeF3, BiF3 also occur. Since the potential of the above fluorides is high, they may be used as the positive electrode active material .

[0114] When forming the negative electrode active material layer 309 using a coating method, a conductive assistant and a binder are added to the negative electrode active material to prepare a negative electrode paste, which is then coated on the negative electrode current collector 308 and dried.

[0115] In addition, when forming the negative electrode active material layer 309 using silicon as the negative electrode active material, it is preferable to form graphene on the surface of the negative electrode active material layer 309. Since silicon has a large volume change accompanying the absorption and release of carrier ions in the charge-discharge cycle, the adhesion between the negative electrode current collector 308 and the negative electrode active material layer 309 decreases, and the battery characteristics deteriorate due to charge-discharge . Therefore, by forming graphene on the surface of the negative electrode active material layer 309 containing silicon , even if the volume of silicon changes in the charge-discharge cycle, a decrease in the adhesion between the negative electrode current collector 308 and the negative electrode active material layer 309 can be suppressed, and deterioration of the battery characteristics is reduced , which is preferable.

[0116] The graphene formed on the surface of the negative electrode active material layer 309 can be formed by reducing graphene oxide in the same manner as the method for producing the positive electrode. The graphene oxide can be the graphene oxide described in Embodiment 1.

[0117] A method for forming graphene oxide on the negative electrode active material layer 309 by electrophoresis will be described with reference to FIG. 6(A).

[0118] FIG. 6(A) is a cross-sectional view for explaining electrophoresis. In a container 401, there is a dispersion liquid in which graphene oxide is dispersed in the dispersion medium described in Embodiment 1 (hereinafter referred to as graphene oxide dispersion liquid 402). Further, an object to be formed 403 is provided in the graphene oxide dispersion liquid 402 and used as an anode. Also, a conductor 404 serving as a cathode is provided in the graphene oxide dispersion liquid 402. The object to be formed 403 is the negative electrode current collector 308 and the negative electrode active material layer 309 formed thereon. The conductor 404 may be a material having conductivity, for example, a metal material or an alloy material.

[0119] By applying an appropriate voltage between the anode and the cathode, a layer of graphene oxide is formed on the surface of the object to be formed 403, that is, on the surface of the negative electrode active material layer 309. This is because graphene oxide is negatively charged in a polar solvent as described above, and when a voltage is applied, the negatively charged graphene oxide is attracted to the anode and adheres to the object to be formed 403. The negative charge of graphene oxide is due to the detachment of hydrogen ions from substituents such as hydroxyl groups and carboxyl groups possessed by graphene oxide, and when the object and the substituent are bonded, it becomes neutral. ​​​​​​​​​​​​​​It is converted. Note that the applied voltage does not have to be constant. Also, the amount of charge flowing between the anode and the cathode By measuring, the thickness of the graphene oxide layer attached to the object can be estimated.

[0120] The voltage applied between the anode and the cathode is preferably in the range of 0.5 V to 2.0 V. More preferably It is 0.8 V to 1.5 V. For example, when the voltage applied between the anode and the cathode is 1 V An oxide film that may be formed by the principle of anodization is less likely to be formed between the object to be formed and the graphene oxide layer.

[0121] When the required thickness of graphene oxide is obtained, the object to be formed 403 is pulled out from the graphene oxide dispersion liquid 40 2 and dried.

[0122] In the electrodeposition of graphene oxide by electrophoresis, it is rare for graphene oxide to be further laminated on the part already covered with graphene oxide. This is because the conductivity of graphene oxide is sufficiently low. On the other hand, on the part that is not yet covered with graphene oxide, graphene oxide is preferentially laminated. For this reason, the thickness of the graphene oxide formed on the surface of the object to be formed 403 becomes a practically uniform thickness.

[0123] The time for performing electrophoresis (the time for applying voltage) may be longer than the time required for the surface of the object to be formed 403 to be covered with graphene oxide. For example, it may be 0.5 minutes or more and 30 minutes or less, preferably 5 minutes or more and 20 minutes or less.

[0124] When using the electrophoresis method, ionized graphene oxide can be electrically moved to the active material. Therefore, even if the surface of the negative electrode active material layer 309 has irregularities, it is possible to uniformly provide graphene oxide. ​​​​​

[0125] Next, a reduction treatment is performed to desorb a part of oxygen from the formed graphene oxide. As the reduction treatment, the reduction treatment by heating or the like described in Embodiment 1 using graphene may be performed, but here, an electrochemical reduction treatment (hereinafter referred to as electrochemical reduction) will be described. The electrochemical reduction of graphene oxide is a reduction using electrical energy, which is different from the reduction by heat treatment. As shown in FIG. 6(B), a negative electrode having graphene oxide provided on the negative electrode active material layer 309 is used as a conductor 407 to form a closed circuit, and a potential at which the reduction reaction of the graphene oxide occurs, or a potential at which the graphene oxide is reduced, is supplied to the conductor 407 to reduce the graphene oxide to graphene. In this specification, the potential at which the reduction reaction of graphene oxide occurs, or the potential at which the graphene oxide is reduced, is referred to as the reduction potential. The reduction method of graphene oxide will be specifically described with reference to FIG. 6(B). The container 405 is filled with the electrolyte 406, and a conductor 407 having graphene oxide and a counter electrode 408 are inserted therein and immersed. Next, the conductor 407 having graphene oxide is used as a working electrode, and at least the counter electrode 408 and the electrolyte 406 are used to form an electrochemical cell (open circuit). The reduction potential of graphene oxide is supplied to the potential of the conductor 407 (working electrode) to reduce the graphene oxide to graphene. The reduction potential to be supplied is the reduction potential with reference to the counter electrode 408, or the reduction potential with reference to the reference electrode provided in the electrochemical cell. For example, when the counter electrode 408 and the reference electrode are made of lithium metal, the reduction potential to be supplied is the lithium metal

[0126] Unlike the reduction by heat treatment, the electrochemical reduction of graphene oxide is a reduction using electrical energy. As shown in FIG. 6(B), a negative electrode having graphene oxide provided on the negative electrode active material layer 309 is used as a conductor 407 to form a closed circuit, and a potential at which the reduction reaction of the graphene oxide occurs, or a potential at which the graphene oxide is reduced, is supplied to the conductor 407 to reduce the graphene oxide to graphene. In this specification, the potential at which the reduction reaction of graphene oxide occurs, or the potential at which the graphene oxide is reduced, is referred to as the reduction potential. Unlike the reduction by heat treatment, the electrochemical reduction of graphene oxide is a reduction using electrical energy. As shown in FIG. 6(B), a negative electrode having graphene oxide provided on the negative electrode active material layer 309 is used as a conductor 407 to form a closed circuit, and a potential at which the reduction reaction of the graphene oxide occurs, or a potential at which the graphene oxide is reduced, is supplied to the conductor 407 to reduce the graphene oxide to graphene. In this specification, the potential at which the reduction reaction of graphene oxide occurs, or the potential at which the graphene oxide is reduced, is referred to as the reduction potential. Unlike the reduction by heat treatment, the electrochemical reduction of graphene oxide is a reduction using electrical energy. As shown in FIG. 6(B), a negative electrode having graphene oxide provided on the negative electrode active material layer 309 is used as a conductor 407 to form a closed circuit, and a potential at which the reduction reaction of the graphene oxide occurs, or a potential at which the graphene oxide is reduced, is supplied to the conductor 407 to reduce the graphene oxide to graphene. In this specification, the potential at which the reduction reaction of graphene oxide occurs, or the potential at which the graphene oxide is reduced, is referred to as the reduction potential. Unlike the reduction by heat treatment, the electrochemical reduction of graphene oxide is a reduction using electrical energy. As shown in FIG. 6(B), a negative electrode having graphene oxide provided on the negative electrode active material layer 309 is used as a conductor 407 to form a closed circuit, and a potential at which the reduction reaction of the graphene oxide occurs, or a potential at which the graphene oxide is reduced, is supplied to the conductor 407 to reduce the graphene oxide to graphene. In this specification, the potential at which the reduction reaction of graphene oxide occurs, or the potential at which the graphene oxide is reduced, is referred to as the reduction potential. Unlike the reduction by heat treatment, the electrochemical reduction of graphene oxide is a reduction using electrical energy. As shown in FIG. 6(B), a negative electrode having graphene oxide provided on the negative electrode active material layer 309 is used as a conductor 407 to form a closed circuit, and a potential at which the reduction reaction of the graphene oxide occurs, or a potential at which the graphene oxide is reduced, is supplied to the conductor 407 to reduce the graphene oxide to graphene. In this specification, the potential at which the reduction reaction of graphene oxide occurs, or the potential at which the graphene oxide is reduced, is referred to as the reduction potential. Unlike the reduction by heat treatment, the electrochemical reduction of graphene oxide is a reduction using electrical energy. As shown in FIG. 6(B), a negative electrode having graphene oxide provided on the negative electrode active material layer 309 is used as a conductor 407 to form a closed circuit, and a potential at which the reduction reaction of the graphene oxide occurs, or a potential at which the graphene oxide is reduced, is supplied to the conductor 407 to reduce the graphene oxide to graphene. In this specification, the potential at which the reduction reaction of graphene oxide occurs, or the potential at which the graphene oxide is reduced, is referred to as the reduction potential.

[0127] The reduction method of graphene oxide will be specifically described with reference to FIG. 6(B). The container 405 is filled with the electrolyte 406, and a conductor 407 having graphene oxide and a counter electrode 408 are inserted therein and immersed. Next, the conductor 407 having graphene oxide is used as a working electrode, and at least the counter electrode 408 and the electrolyte 406 are used to form an electrochemical cell (open circuit). The reduction potential of graphene oxide is supplied to the potential of the conductor 407 (working electrode) to reduce the graphene oxide to graphene. The reduction potential to be supplied is the reduction potential with reference to the counter electrode 408, or the reduction potential with reference to the reference electrode provided in the electrochemical cell. For example, when the counter electrode 408 and the reference electrode are made of lithium metal, the reduction potential to be supplied is the lithium metal The reduction method of graphene oxide will be specifically described with reference to FIG. 6(B). The container 405 is filled with the electrolyte 406, and a conductor 407 having graphene oxide and a counter electrode 408 are inserted therein and immersed. Next, the conductor 407 having graphene oxide is used as a working electrode, and at least the counter electrode 408 and the electrolyte 406 are used to form an electrochemical cell (open circuit). The reduction potential of graphene oxide is supplied to the potential of the conductor 407 (working electrode) to reduce the graphene oxide to graphene. The reduction potential to be supplied is the reduction potential with reference to the counter electrode 408, or the reduction potential with reference to the reference electrode provided in the electrochemical cell. For example, when the counter electrode 408 and the reference electrode are made of lithium metal, the reduction potential to be supplied is the lithium metal The reduction method of graphene oxide will be specifically described with reference to FIG. 6(B). The container 405 is filled with the electrolyte 406, and a conductor 407 having graphene oxide and a counter electrode 408 are inserted therein and immersed. Next, the conductor 407 having graphene oxide is used as a working electrode, and at least the counter electrode 408 and the electrolyte 406 are used to form an electrochemical cell (open circuit). The reduction potential of graphene oxide is supplied to the potential of the conductor 407 (working electrode) to reduce the graphene oxide to graphene. The reduction potential to be supplied is the reduction potential with reference to the counter electrode 408, or the reduction potential with reference to the reference electrode provided in the electrochemical cell. For example, when the counter electrode 408 and the reference electrode are made of lithium metal, the reduction potential to be supplied is the lithium metal The reduction method of graphene oxide will be specifically described with reference to FIG. 6(B). The container 405 is filled with the electrolyte 406, and a conductor 407 having graphene oxide and a counter electrode 408 are inserted therein and immersed. Next, the conductor 407 having graphene oxide is used as a working electrode, and at least the counter electrode 408 and the electrolyte 406 are used to form an electrochemical cell (open circuit). The reduction potential of graphene oxide is supplied to the potential of the conductor 407 (working electrode) to reduce the graphene oxide to graphene. The reduction potential to be supplied is the reduction potential with reference to the counter electrode 408, or the reduction potential with reference to the reference electrode provided in the electrochemical cell. For example, when the counter electrode 408 and the reference electrode are made of lithium metal, the reduction potential to be supplied is the lithium metal The reduction method of graphene oxide will be specifically described with reference to FIG. 6(B). The container 405 is filled with the electrolyte 406, and a conductor 407 having graphene oxide and a counter electrode 408 are inserted therein and immersed. Next, the conductor 407 having graphene oxide is used as a working electrode, and at least the counter electrode 408 and the electrolyte 406 are used to form an electrochemical cell (open circuit). The reduction potential of graphene oxide is supplied to the potential of the conductor 407 (working electrode) to reduce the graphene oxide to graphene. The reduction potential to be supplied is the reduction potential with reference to the counter electrode 408, or the reduction potential with reference to the reference electrode provided in the electrochemical cell. For example, when the counter electrode 408 and the reference electrode are made of lithium metal, the reduction potential to be supplied is the lithium metal The reduction method of graphene oxide will be specifically described with reference to FIG. 6(B). The container 405 is filled with the electrolyte 406, and a conductor 407 having graphene oxide and a counter electrode 408 are inserted therein and immersed. Next, the conductor 407 having graphene oxide is used as a working electrode, and at least the counter electrode 408 and the electrolyte 406 are used to form an electrochemical cell (open circuit). The reduction potential of graphene oxide is supplied to the potential of the conductor 407 (working electrode) to reduce the graphene oxide to graphene. The reduction potential to be supplied is the reduction potential with reference to the counter electrode 408, or the reduction potential with reference to the reference electrode provided in the electrochemical cell. For example, when the counter electrode 408 and the reference electrode are made of lithium metal, the reduction potential to be supplied is the lithium metal The reduction method of graphene oxide will be specifically described with reference to FIG. 6(B). The container 405 is filled with the electrolyte 406, and a conductor 407 having graphene oxide and a counter electrode 408 are inserted therein and immersed. Next, the conductor 407 having graphene oxide is used as a working electrode, and at least the counter electrode 408 and the electrolyte 406 are used to form an electrochemical cell (open circuit). The reduction potential of graphene oxide is supplied to the potential of the conductor 407 (working electrode) to reduce the graphene oxide to graphene. The reduction potential to be supplied is the reduction potential with reference to the counter electrode 408, or the reduction potential with reference to the reference electrode provided in the electrochemical cell. For example, when the counter electrode 408 and the reference electrode are made of lithium metal, the reduction potential to be supplied is the lithium metal For example, when the counter electrode 408 and the reference electrode are made of lithium metal, the reduction potential to be supplied is the lithium metal​ The reduction potential (vs. Li / Li + ) based on the redox potential of the genus. By this step , in the electrochemical cell (closed circuit), a reduction current flows when graphene oxide is reduced. Therefore , to confirm the reduction of graphene oxide, it is only necessary to continuously confirm the reduction current . The state where the reduction current falls below a certain value (the peak corresponding to the reduction current disappears) can be regarded as the state where graphene oxide is reduced (the reduction reaction has ended).

[0128] In addition, when controlling the potential of the conductor 407, not only should it be fixed below the reduction potential of graphene oxide , but it may also be swept including the reduction potential of graphene oxide, and furthermore, the sweeping may be periodically repeated like cyclic voltammetry. Also, there is no limitation on the sweeping speed of the potential of the conductor 4 07. When performing the sweeping of the potential of the conductor 407 , it may be swept from the high potential side to the low potential side, or it may be swept from the low potential side to the high potential side.

[0129] The reduction potential of graphene oxide varies slightly depending on its composition (such as the presence or absence of functional groups) and the method of potential control (such as the sweeping speed), but it is about 2.0V (vs. Li / L i i + ). Specifically, it is sufficient to control the potential of the conductor 407 within the range of 1.6V or more and 2.4V or less (vs. Li / Li + ).

[0130] Through the above steps, graphene can be formed on the conductor 407. When performing electrochemical reduction treatment, compared with the graphene formed by heat treatment, the ratio of carbon-carbon double bonds with sp bonds increases, so graphene with high conductivity can be used as the negative electrode active 2 two layer bonds increases, so graphene with high conductivity can be used as the negative electrode active material​​ It can be formed on the material layer 309 .

[0131] After graphene was formed over the conductor 407, the negative electrode active material layer 309 was The lithium may be pre-doped by sputtering. Alternatively, a lithium layer may be formed on the surface of the negative electrode active material layer 309 by a coating method. By providing a lithium foil on the surface of the negative electrode active material layer 309, lithium can be predoped in the negative electrode active material layer 309. It can be grouped.

[0132] The separator 310 may be made of cellulose (paper), or perforated polypropylene, poly An insulator such as ethylene may be used.

[0133] The electrolyte solution uses a material having carrier ions as an electrolyte. Representative examples of electrolytes include LiClO4, LiAsF6, LiBF4, LiPF6, Li(C2F5SO2)2 There are lithium salts such as N.

[0134] In addition, the carrier ion is an alkali metal ion other than the lithium ion, an alkaline earth metal ion, etc. In the case of lithium ions, beryllium ions, or magnesium ions, the above-mentioned lithium ions are used as the electrolyte. In lithium salts, alkali metals (e.g., sodium, potassium, etc.) are used instead of lithium. ), alkaline earth metals (e.g., calcium, strontium, barium, etc.), beryllium Alternatively, zinc or magnesium may be used.

[0135] As the solvent for the electrolyte, a material capable of transporting carrier ions is used. The solvent is preferably an aprotic organic solvent. Representative examples of the aprotic organic solvent include , ethylene carbonate (EC), propylene carbonate, dimethyl carbonate, di ethyl carbonate (DEC), γ-butyrolactone, acetonitrile, dimethoxyetha ne, tetrahydrofuran, etc. are available, and one or more of these can be used. Also , by using a polymer material that is gelled as a solvent for the electrolyte, the safety against leakage and the like is enhanced. Also, the non-aqueous secondary battery can be made thinner and lighter. Representative examples of the gelled polymer materials include silicone gel, acrylic gel, acrylonitrile gel, polyethy lene oxide, polypropylene oxide, fluorine-based polymers, etc. Also, as a solvent for the electrolyte, one or more ionic liquids (room temperature molten salts) that are flame retardant and hardly volatile are used, so even if the internal temperature of the secondary battery rises due to internal short circuit, overcharging, etc., rupture or ignition of the secondary battery can be prevented.

[0136] Also, instead of the electrolyte, a solid electrolyte having an inorganic material such as a sulfide-based or oxide-based material, or a solid electrolyte having a polymer material such as a P EO (polyethylene oxide)-based material can be used. When using a solid electrolyte, the installation of a separator and a spacer becomes unnecessary. Also, since the entire battery can be solidified, the risk of leakage disappears and the safety is dramatically improved.

[0137] The positive electrode can 301 and the negative electrode can 302 are made of metals such as nickel, aluminum, and titanium, alloys of the metal, alloys of the metal and other metals (for example, stainless steel, etc.), laminates of the metal, laminates of the metal and the aforementioned alloys (for example, stainless steel / aluminum, etc.), laminates of the metal and other metals, which have corrosion resistance against liquids such as electrolytes during charge and discharge of the secondary battery. Layers (such as nickel / iron / nickel, etc.) can be used. The positive electrode can 301 is the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307 respectively.

[0138] These negative electrode 307, positive electrode 304, and separator 310 are impregnated with an electrolyte, as shown in FIG. 5(B) As shown, with the positive electrode can 301 facing downwards, the positive electrode 304, separator 310, negative electrode 307, and negative electrode Can 302 are laminated in this order, and the positive electrode can 301 and the negative electrode can 302 are crimped via a gasket 303 To manufacture a coin-shaped secondary battery 300.

[0139] Next, an example of a laminated secondary battery will be described with reference to FIG. 7.

[0140] The laminated secondary battery 500 shown in FIG. 7 includes a positive electrode current collector 501 and a positive electrode active material layer 50 2, a positive electrode 503, a negative electrode current collector 504 and a negative electrode active material layer 505, a negative electrode 50 6, a separator 507, an electrolytic solution 508, and an exterior body 509. A separator 507 is installed between the positive electrode 503 and the negative electrode 506 provided in the exterior body 509. Also The interior of the exterior body 509 is filled with the electrolytic solution 508. In the laminated secondary battery 500 shown in FIG. 7, the positive electrode current collector 501 and the negative electrode current collector

[0141] 504 also serve as terminals for obtaining electrical contact with the outside. Therefore, a part of the positive electrode current collector 5 01 and the negative electrode current collector 504 are arranged so as to be exposed to the outside from the exterior body 509

[0142] In the laminated secondary battery 500, the exterior body 509 is, for example, a film made of a material such as polyethylene, poly propylene, polycarbonate, ionomer, polyamide, etc., and on the film, an A metal thin film with excellent flexibility such as aluminum, stainless steel, copper, nickel, etc. is provided, and further on the metal thin film, an insulating synthetic resin film such as a polyamide resin or a polyester resin is provided as the outer surface of the exterior body, and a three-layer laminate film can be used. By adopting such a three-layer structure, the permeation of electrolytic solution and gas is blocked, insulation is ensured, and at the same time, it has resistance to electrolytic solution. A resin film is provided on the metal thin film as the outer surface of the exterior body, and a three-layer laminate film can be used. Next, an example of a cylindrical secondary battery will be described with reference to FIG. 8. As shown in FIG. 8(A), the cylindrical secondary battery 600 has a positive electrode cap (battery lid) 601 on the upper surface and a battery can (outer can) 602 on the side surface and the bottom surface. These positive electrode cap and battery can (outer can) 602 are insulated by a gasket (insulating packing) 610. FIG. 8(B) is a diagram schematically showing a cross section of the cylindrical secondary battery. Inside the hollow cylindrical battery can 602, a battery element is provided in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 interposed therebetween. Although not shown, the battery element is wound around a center pin. One end of the battery can 602 is closed and the other end is open. For the battery can 602, metals such as nickel, aluminum, titanium, alloys of the metal, alloys of the metal and other metals (for example, stainless steel, etc.), laminates of the metal, laminates of the metal and the aforementioned alloys (for example, stainless steel / aluminum, etc.), laminates of the metal and other metals (for example, nickel / iron / nickel, etc.) that have corrosion resistance against liquids such as electrolytic solution during charging and discharging of the secondary battery can be used. Inside the battery can 602, the positive electrode, the negative electrode, and the separator Next, an example of a cylindrical secondary battery will be described with reference to FIG. 8. As shown in FIG. 8(A), the cylindrical secondary battery 600 has a positive electrode cap (battery lid) 601 on the upper surface and a battery can (outer can) 602 on the side surface and the bottom surface. These positive electrode cap and battery can (outer can) 602 are insulated by a gasket (insulating packing) 610.

[0143] Next, an example of a cylindrical secondary battery will be described with reference to FIG. 8. As shown in FIG. 8(A), the cylindrical secondary battery 600 has a positive electrode cap (battery lid) 601 on the upper surface and a battery can (outer can) 602 on the side surface and the bottom surface. These positive electrode cap and battery can (outer can) 602 are insulated by a gasket (insulating packing) 610. 00 has a positive electrode cap (battery lid) 601 on the upper surface and a battery can (outer can) 602 on the side surface and the bottom surface as shown in FIG. 8(A). These positive electrode cap and battery can (outer can) 602 are insulated by a gasket (insulating packing) 610. 02 and the positive electrode cap are insulated by a gasket (insulating packing) 610.

[0144] FIG. 8(B) is a diagram schematically showing a cross section of the cylindrical secondary battery. Inside the hollow cylindrical battery can 602, a battery element is provided in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 interposed therebetween. Although not shown, the battery element is wound around a center pin. One end of the battery can 602 is closed and the other end is open. For the battery can 602, metals such as nickel, aluminum, titanium, alloys of the metal, alloys of the metal and other metals (for example, stainless steel, etc.), laminates of the metal, laminates of the metal and the aforementioned alloys (for example, stainless steel / aluminum, etc.), laminates of the metal and other metals (for example, nickel / iron / nickel, etc.) that have corrosion resistance against liquids such as electrolytic solution during charging and discharging of the secondary battery can be used. Inside the battery can 602, the positive electrode, the negative electrode, and the separator 602, a battery element is provided in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 interposed therebetween. Although not shown, the battery element is wound around a center pin. The battery can 602 has one end closed and the other end open. For the battery can 602, metals such as nickel, aluminum, titanium, alloys of the metal, alloys of the metal and other metals (for example, stainless steel, etc.), laminates of the metal, laminates of the metal and the aforementioned alloys (for example, stainless steel / aluminum, etc.), laminates of the metal and other metals (for example, nickel / iron / nickel, etc.) that have corrosion resistance against liquids such as electrolytic solution during charging and discharging of the secondary battery can be used. For the battery can 602, metals such as nickel, aluminum, titanium, alloys of the metal, alloys of the metal and other metals (for example, stainless steel, etc.), laminates of the metal, laminates of the metal and the aforementioned alloys (for example, stainless steel / aluminum, etc.), laminates of the metal and other metals (for example, nickel / iron / nickel, etc.) that have corrosion resistance against liquids such as electrolytic solution during charging and discharging of the secondary battery can be used. For the battery can 602, metals such as nickel, aluminum, titanium, alloys of the metal, alloys of the metal and other metals (for example, stainless steel, etc.), laminates of the metal, laminates of the metal and the aforementioned alloys (for example, stainless steel / aluminum, etc.), laminates of the metal and other metals (for example, nickel / iron / nickel, etc.) that have corrosion resistance against liquids such as electrolytic solution during charging and discharging of the secondary battery can be used. For the battery can 602, metals such as nickel, aluminum, titanium, alloys of the metal, alloys of the metal and other metals (for example, stainless steel, etc.), laminates of the metal, laminates of the metal and the aforementioned alloys (for example, stainless steel / aluminum, etc.), laminates of the metal and other metals (for example, nickel / iron / nickel, etc.) that have corrosion resistance against liquids such as electrolytic solution during charging and discharging of the secondary battery can be used. For the battery can 602, metals such as nickel, aluminum, titanium, alloys of the metal, alloys of the metal and other metals (for example, stainless steel, etc.), laminates of the metal, laminates of the metal and the aforementioned alloys (for example, stainless steel / aluminum, etc.), laminates of the metal and other metals (for example, nickel / iron / nickel, etc.) that have corrosion resistance against liquids such as electrolytic solution during charging and discharging of the secondary battery can be used. The wound battery element is sandwiched between a pair of opposing insulating plates 608 and 609. . Further, a non-aqueous electrolyte (not shown) is injected into the interior of the battery can 602 in which the battery element is provided. As the non-aqueous electrolyte, the same one as that used in coin-type or laminate-type non-aqueous secondary batteries can be used.

[0145] The positive electrode 604 and the negative electrode 606 may be manufactured in the same manner as the positive electrode and the negative electrode of the coin-type non-aqueous secondary battery described above. However, since the positive electrode and the negative electrode used in a cylindrical non-aqueous secondary battery are wound, they are different in that active materials are formed on both sides of the current collector. A positive electrode terminal (positive current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative current collector lead) 607 is connected to the negative electrode 606. . Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to the safety valve mechanism 612, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602, respectively. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a PTC element (Positive Temperature Coefficient) 611. The safety valve mechanism 612 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery rises beyond a predetermined threshold. The PTC element 611 is a thermal sensing resistor element whose resistance increases when the temperature rises. By increasing the resistance, the current amount is limited to prevent abnormal heat generation. As the PTC element, barium titanate (BaTiO3)-based semiconductor ceramics or the like can be used.

[0146] In this embodiment, as the secondary battery, coin-type, laminate-type, and cylindrical non-aqueous Although a secondary battery has been shown, various shaped non-aqueous secondary batteries such as other sealed non-aqueous secondary batteries and square non-aqueous secondary batteries can be used. In addition, a structure in which a plurality of positive electrodes, negative electrodes, and separators are stacked or a structure in which the positive electrode, negative electrode, and separator are wound may be used.

[0147] The positive electrodes of the secondary batteries 300, 500, and 600 shown in this embodiment use the positive electrode according to one aspect of the present invention. Therefore, the discharge capacities of the secondary batteries 300, 500, and 600 can be increased.

[0148] This embodiment can be implemented in appropriate combination with other embodiments.

[0149] (Embodiment 4) The non-aqueous secondary battery according to one aspect of the present invention can be used as a power source for various electric devices driven by electric power.

[0150] Specific examples of electric devices using the non-aqueous secondary battery according to one aspect of the present invention include display devices such as televisions and monitors, lighting devices, desktop or notebook personal computers, word processors, image playback devices that play still images or moving images stored on recording media such as DVDs (Digital Versatile Discs), portable CD players, radios, tape recorders, headphone stereos, stereos, table clocks, wall clocks, cordless phone handsets, transceivers, portable radios, mobile phones, car phones, portable game machines, calculators, portable information terminals, electronic notebooks, e-books, electronic translators, voice input devices, video cameras, digital still cameras, toys, electric shavers, high-frequency heating devices such as microwave ovens, electric rice cookers Appliances, electric washing machines, vacuum cleaners, water heaters, fans, hair dryers, air conditioners, humidifiers Appliances, dehumidifiers and other air conditioning equipment, dishwashers, dish dryers, clothes dryers, futon dryers, electric Refrigerators, freezers, refrigerator-freezers, DNA storage freezers, flashlights, chain saws and other Power tools, smoke detectors, dialysis machines and other medical devices. Furthermore, induction lights, traffic lights , belt conveyors, elevators, escalators, industrial robots, power storage systems, power Smoothing and energy storage devices for smart grids and other industrial equipment. Also, non-aqueous Vehicles propelled by an electric motor using power from a secondary battery are also included in the scope of electrical equipment as things to be included. As the above-mentioned moving bodies, for example, electric vehicles (EVs), hybrid vehicles (HEVs) that combine an internal combustion engine and an electric motor , plug-in hybrid vehicles (PHEVs), tracked vehicles obtained by changing their tire wheels to endless tracks, motorized bicycles including electric assist bicycles , motorcycles, electric wheelchairs, golf carts, small or large ships, submarines, helicopters , airplanes, rockets, artificial satellites, space exploration vehicles and planetary exploration vehicles, spaceships, etc. can be mentioned. In addition, the above-mentioned electrical equipment can use a non-aqueous secondary battery according to one aspect of the present invention as a main power source for supplying almost all of the power consumption. Alternatively, the above-mentioned electrical equipment can use a non-aqueous secondary battery according to one aspect of the present invention as an uninterruptible power supply that can supply power to the electrical equipment when the supply of power from the above-mentioned main power source or commercial power source stops. Alternatively, the above-mentioned electrical equipment can use a non-aqueous secondary battery according to one aspect of the present invention as an auxiliary power source for supplying power to the electrical equipment in parallel with the supply of power from the above-mentioned main power source or commercial power source to the electrical equipment.

[0151] Note that the above-mentioned electrical equipment can use a non-aqueous secondary battery according to one aspect of the present invention as a main power source for supplying almost all of the power consumption. Or, when the supply of power from the above-mentioned main power source or commercial power source stops, the above-mentioned electrical equipment can use a non-aqueous secondary battery according to one aspect of the present invention as an uninterruptible power source that can supply power to the electrical equipment. Or, the above-mentioned electrical equipment can use a non-aqueous secondary battery according to one aspect of the present invention as an auxiliary power source for supplying power to the electrical equipment in parallel with the supply of power from the above-mentioned main power source or commercial power source to the electrical equipment. Note that the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as a main power source to cover almost all of the power consumption. Alternatively, the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as an uninterruptible power source that can supply power to the electrical equipment when the power supply from the above main power source or commercial power source stops. Alternatively, the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as an auxiliary power source for supplying power to the electrical equipment in parallel with the power supply from the above main power source or commercial power source to the electrical equipment. Note that the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as a main power source to cover almost all of the power consumption. Or, when the power supply from the above main power source or commercial power source stops, the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as an uninterruptible power source that can supply power to the electrical equipment. Or, the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as an auxiliary power source for supplying power to the electrical equipment in parallel with the power supply from the above main power source or commercial power source to the electrical equipment. Note that the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as a main power source to cover almost all of the power consumption. Or, when the power supply from the above main power source or commercial power source stops, the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as an uninterruptible power source that can supply power to the electrical equipment. Or, the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as an auxiliary power source for supplying power to the electrical equipment in parallel with the power supply from the above main power source or commercial power source to the electrical equipment. Note that the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as a main power source to cover almost all of the power consumption. Or, when the power supply from the above main power source or commercial power source stops, the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as an uninterruptible power source that can supply power to the electrical equipment. Or, the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as an auxiliary power source for supplying power to the electrical equipment in parallel with the power supply from the above main power source or commercial power source to the electrical equipment. Note that the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as a main power source to cover almost all of the power consumption. Or, when the power supply from the above main power source or commercial power source stops, the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as an uninterruptible power source that can supply power to the electrical equipment. Or, the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as an auxiliary power source for supplying power to the electrical equipment in parallel with the power supply from the above main power source or commercial power source to the electrical equipment. Note that the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as a main power source to cover almost all of the power consumption. Or, when the power supply from the above main power source or commercial power source stops, the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as an uninterruptible power source that can supply power to the electrical equipment. Or, the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as an auxiliary power source for supplying power to the electrical equipment in parallel with the power supply from the above main power source or commercial power source to the electrical equipment.

[0152] Fig. 9 shows the specific configuration of the above electrical equipment. In Fig. 9, the display device 700 is an example of an electrical equipment using a non-aqueous secondary battery 704 according to one aspect of the present invention. Specifically, the display device 700 corresponds to a display device for receiving TV broadcasts, and includes a housing 701, a display unit 702, a speaker unit 703, a non-aqueous secondary battery 704, etc. The non-aqueous secondary battery 704 according to one aspect of the present invention is provided inside the housing 701. The display device 700 can receive power supply from a commercial power source, or can also use the power stored in the non-aqueous secondary battery 704. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the non-aqueous secondary battery 704 according to one aspect of the present invention as an uninterruptible power supply, the display device 700 can be used. The display unit 702 can be provided with a light-emitting device having a light-emitting element such as a liquid crystal display device or an organic EL element in each pixel, an electrophoretic display device, a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), an FED (Field Emission Display), etc., and a semiconductor display device can be used. In addition, the display device includes all display devices for information display, such as for personal computers and for advertisement display, in addition to those for receiving TV broadcasts. In Fig. 9, the installed lighting device 710 is an example of an electrical equipment using a non-aqueous secondary battery 713 according to one aspect of the present invention. Specifically, the lighting device 710 includes a housing 711, a light source 712, a non-aqueous secondary battery 713, etc. In Fig. 9, the non-aqueous secondary battery 713 is located inside the housing 71 11.

[0153]

[0154]

[0155] ​ illustrates the case where it is provided inside the ceiling 714 where the light source 712 is installed However, the non-aqueous secondary battery 713 may be provided inside the housing 711. The lighting device 7 10 can receive power supply from a commercial power source, or can use the power stored in the non-aqueous secondary battery 713 Therefore, even when the power supply from the commercial power source cannot be received due to a power outage or the like, by using the non-aqueous secondary battery 713 according to one aspect of the present invention as an uninterruptible power supply the lighting device 710 can be used

[0156] In addition, in FIG. 9, an installed lighting device 710 provided on the ceiling 714 is illustrated. However, the non-aqueous secondary battery according to one aspect of the present invention can be used not only for the ceiling 714 but also for installed lighting devices provided on, for example, side walls 715, floors 716 , windows 717, etc., or can be used for tabletop lighting devices

[0157] In addition, as the light source 712, an artificial light source that artificially obtains light using power can be used . Specifically, incandescent bulbs, discharge lamps such as fluorescent lamps, and light-emitting elements such as LEDs and organic EL elements are cited as an example of the above artificial light source

[0158] In FIG. 9, an air conditioner having an indoor unit 720 and an outdoor unit 724 is an example of an electric device using the non-aqueous secondary battery 723 according to one aspect of the present invention. Specifically, the indoor unit 7 20 has a housing 721, an air outlet 722, a non-aqueous secondary battery 723, etc. In FIG. 9, the case where the non-aqueous secondary battery 723 is provided in the indoor unit 720 is illustrated. However, the non-aqueous secondary battery 723 may be provided in the outdoor unit 724. Alternatively, the indoor unit 720 and the outdoor unit 7 24 ​​Both 24 may be provided with a non-aqueous secondary battery 723. The air conditioner can also receive power supply from a commercial power source, or use the power stored in the non-aqueous secondary battery 723. In particular, when the non-aqueous secondary battery 7 23 is provided in both the indoor unit 720 and the outdoor unit 724, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the non-aqueous secondary battery 723 according to an aspect of the present invention as an uninterruptible power supply, the air conditioner can be used.

[0159] Note that in FIG. 9, a separate type air conditioner composed of an indoor unit and an outdoor unit is exemplified However, the non-aqueous secondary battery according to an aspect of the present invention can also be used for an integrated type air conditioner having the functions of the indoor unit and the outdoor unit in one housing.

[0160] In FIG. 9, the electric refrigerator 730 is an example of an electric device using the non-aqueous secondary battery 734 according to an aspect of the present invention. Specifically, the electric refrigerator 730 includes a housing 731, a refrigerator door 732, a freezer door 733, a non-aqueous secondary battery 734, and the like. In FIG. 9, the non-aqueous secondary battery 734 is provided inside the housing 731. The electric refrigerator 730 can receive power supply from a commercial power source, or use the power stored in the non-aqueous secondary battery 734. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the non-aqueous secondary battery 734 according to an aspect of the present invention as an uninterruptible power supply, the electric refrigerator 730 can be used.

[0161] Among the above-described electric devices, high-frequency heating devices such as microwave ovens, and electric appliances such as electric rice cookers The machine requires high power in a short time. Therefore, by using a non-aqueous secondary battery according to an aspect of the present invention as an auxiliary power source to supplement the power that cannot be covered by the commercial power supply, it is possible to prevent the breaker of the commercial power supply from tripping when the electric device is in use. Also, during the time when the electric device is not in use, particularly in the time period when the ratio of the actually used power amount to the total power amount that can be supplied by the commercial power supply source (referred to as the power usage rate) is low, by storing power in the non-aqueous secondary battery, it is possible to suppress the increase in the power usage rate outside the above time period. For example, in the case of an electric refrigerator 730, at night when the temperature is low and the opening and closing of the refrigerator door 732 and the freezer door 733 do not occur, power is stored in the non-aqueous secondary battery 734.

[0162] And during the day when the temperature rises and the opening and closing of the refrigerator door 732 and the freezer door 733 occur, by using the non-aqueous secondary battery 734 as an auxiliary power source, the power usage rate during the day can be kept low. This embodiment can be implemented in appropriate combination with other embodiments.

[0163]

[0164] (Embodiment 5) Next, a portable information terminal, which is an example of an electric device, will be described with reference to FIG. 10.

[0165] FIGS. 10(A) and 10(B) show a foldable tablet-type terminal 800. FIG. 10(A) shows the open state, and the tablet-type terminal 800 has a housing 801, a display unit 802a, a display unit 802b, a display mode changeover switch 803, a power switch 804, a power saving mode changeover switch 805, and an operation switch 807.

[0166] ​​​​​​​​​The display unit 802a can have a part as the touch panel area 808a, and data can be input by touching the displayed operation key 809. In the display unit 802a, as an example, a configuration in which half of the area has only a display function and the other half has a touch panel function is shown, but it is not limited to this configuration. It is also possible to have a configuration in which all of the area of the display unit 802a has a touch panel function. For example, the entire surface of the display unit 802a can be used to display keyboard buttons to serve as a touch panel, and the display unit 802b can be used as a display screen .

[0167] Also, in the display unit 802b, similar to the display unit 802a, a part of the display unit 802b can be set as the touch panel area 808b. Also, by touching the position where the keyboard display switching button 810 of the touch panel is displayed with a finger or a stylus, etc., keyboard buttons can be displayed on the display unit 80 2b.

[0168] Also, simultaneous touch input can be performed on the touch panel area 808a and the touch panel area 808b.

[0169] Also, the display mode switching switch 803 can select switching of the display orientation such as vertical display or horizontal display, switching between black and white display and color display, etc. The power saving mode switching switch 805 can optimize the display brightness according to the amount of external light detected by the optical sensor built into the tablet type terminal during use. The tablet type terminal can incorporate not only an optical sensor but also other detection devices such as sensors for detecting inclination such as a gyro and an acceleration sensor . .

[0170] ​​​​​​In addition, FIG. 10(A) shows an example where the display areas of the display unit 802b and the display unit 802a are the same, but it is not particularly limited thereto. The size of one may be different from that of the other, and the display quality may also be different. For example, one may be a display panel capable of performing a higher definition display than the other. FIG. 10(B) shows a closed state. The tablet terminal 800 includes a housing 801, a solar cell 811, a charge / discharge control circuit 850, a battery 851, and a DCDC converter 852. Note that FIG. 10(B) shows a configuration having a battery 851 and a DCDC

[0171] converter 852 as an example of the charge / discharge control circuit 850. The battery 851 has the non-aqueous secondary battery described in the above embodiment. Since the tablet terminal 800 is foldable in two, the housing 801 can be closed when not in use. Therefore, since the display units 802a and 802b can be protected, a tablet terminal 800 with excellent durability and reliability from the viewpoint of long-term use can be provided.

[0172]

[0173]

[0174] In addition, the tablet terminal shown in FIGS. 10(A) and 10(B) can also have functions such as displaying various information (still images, moving images, text images, etc.), displaying a calendar, date, or time on the display unit, a touch input function for touch input operations or editing of the information displayed on the display unit, and a function of controlling processing by various software (programs).

[0174]

[0174] Power is supplied to the touch panel and the surfaceIt can be supplied to the display unit, the video signal processing unit, etc. Note that the solar cell 811 can be provided on one side or both sides of the housing 801, and it is suitable because it can be configured to efficiently charge the battery 851. As the battery 851, using the non-aqueous secondary battery according to one aspect of the present invention has advantages such as miniaturization.

[0175] Also, the configuration and operation of the charge / discharge control circuit 850 shown in FIG. 10(B) will be described with reference to the block diagram in FIG. 10(C). FIG. 10(C) shows the solar cell 811, the battery 851, the DC-DC converter 852, the converter 853, the switches SW1 to SW3, and the display unit 80 2. The battery 851, the DC-DC converter 852, the converter 85 3, and the switches SW1 to SW3 correspond to the charge / discharge control circuit 850 shown in FIG. 10(B).

[0176] First, an example of the operation when power is generated by the solar cell 811 due to external light will be described. The power generated by the solar cell is stepped up or down by the DC-DC converter 852 to a voltage for charging the battery 851. When the power from the solar cell 811 is used for the operation of the display unit 802, the switch SW1 is turned on, and the converter 853 steps up or down the voltage to the voltage required for the display unit 802. When the display on the display unit 802 is not performed, SW1 can be turned off and SW2 can be turned on to charge the battery 851.

[0177] Note that the solar cell 811 is shown as an example of the power generation means, but it is not particularly limited, and other power generation means such as piezoelectric elements (piezoelectric elements) and thermoelectric conversion elements (Peltier elements) can be used for the battery ​​​​​​ It may be configured to charge the Terry 851. For example, power is transmitted and received wirelessly (non-contact) and charged using a contactless power transmission module or in combination with other charging means. This may also be done.

[0178] Moreover, if it is equipped with the non-aqueous secondary battery described in the above embodiment, it goes without saying that it is not particularly limited to the electric equipment shown in FIG. 10.

[0179] (Embodiment 6) Furthermore, an example of a moving body, which is an example of an electric device, will be described with reference to FIG. 11.

[0180] The non-aqueous secondary battery described in the previous embodiment can be used as a battery for control. The battery for control can be charged by external power supply by plug-in technology or non-contact power feeding. In the case where the moving body is an electric railway vehicle, it can be charged by power supply from an overhead wire or a conductive rail.

[0181] FIGS. 11(A) and (B) show an example of an electric vehicle. An electric vehicle 860 is equipped with a battery 861. The power of the battery 861 is adjusted by a control circuit 862 and supplied to a drive device 863. The control circuit 862 is controlled by a processing device 864 having a ROM, RAM, CPU, etc. (not shown).

[0182] The drive device 863 is configured by combining a DC motor or an AC motor alone, or a motor and an internal combustion engine. The processing device 864 receives the operation information (acceleration, deceleration, stop, etc.) of the driver of the electric vehicle 860 and information during running (information such as uphill and downhill, load information applied to the drive wheels Based on input information (such as), a control signal is output to the control circuit 862. The control circuit 862 adjusts the electrical energy supplied from the battery 861 according to the control signal of the processing device 864 to control the output of the driving device 863. When an AC motor is installed, although not shown, an inverter for converting DC to AC is also built in.

[0183] The battery 861 can be charged by external power supply using plug-in technology. For example, the battery 861 is charged from a commercial power supply through a power plug. The charging can be performed by converting it to a DC constant voltage having a certain voltage value through a conversion device such as an AC / DC converter. By mounting a non-aqueous secondary battery according to an aspect of the present invention as the battery 861, it is possible to contribute to increasing the capacity of the battery and the like, and to improve convenience. In addition, if the characteristics of the battery 861 are improved and the battery 861 itself can be made smaller and lighter, it can contribute to reducing the weight of the vehicle, and thus the fuel efficiency can be improved.

[0184] Of course, if the non-aqueous secondary battery according to an aspect of the present invention is provided, it is not particularly limited to the electronic devices shown above.

[0185] This embodiment can be implemented in appropriate combination with other embodiments.

Example

[0186] Hereinafter, the present invention will be specifically described using examples. In this example, the results of manufacturing the positive electrode by the method shown in Embodiment 2 will be described. Note that the present invention is not limited to the following examples only.

[0187] ​​​​​​​Graphene oxide (here, the weight ratio of oxygen to carbon (or oxidation degree, expressed as O / C) The cell was designed to have a positive electrode with a conductive additive made of 0.547% Cr. RGO (Reduced Graphene Oxide) or We compare the charge / discharge characteristics with those of a cell incorporating a positive electrode that has graphene as a conductive additive. In addition, we developed a cell that incorporates a positive electrode that uses conventional acetylene black (AB) as a conductive additive. The charge and discharge characteristics of the battery are also compared.

[0188] (Preparation of a positive electrode with a conductive additive made from graphene oxide) The positive electrode was fabricated using graphene oxide with an O / C ratio of 0.547. Lithium iron phosphate (LiFePO4) particles, binder (Polyvinylidene fluoride (PVDF) The positive electrode paste was made by mixing graphene oxide as a conductive additive. The positive electrode paste is applied to a current collector (aluminum), and then dried and reduced to produce a positive electrode. The mixing ratio of the positive electrode paste during production (LiFePO4:conductive additive (graphene oxide) The ratio of the polymer to the PVDF was 93:2:5 (unit: wt%).

[0189] (Preparation of positive electrode using RGO as conductive additive) In this specification, RGO (Reduced Graphene Oxide) is a This refers to graphene obtained by reducing graphene oxide, and the graphene has already been reduced by the time it is dispersed in the dispersion medium. Therefore, it is believed that functional groups such as epoxy groups have almost completely disappeared due to the reduction reaction. RGO is made by annealing the graphene oxide prepared by the method described in the first embodiment in a vacuum for 1 After this, the temperature is increased to 170°C and held for 10 hours. It was fabricated. It is considered that the functional groups such as epoxy groups on the surface of RGO are reduced to about 10 wt% (weight percent) or less by reduction. This RGO was mixed into NMP, and lithium iron phosphate and PVDF were added to prepare a positive electrode paste. The positive electrode paste coated on the current collector was heated to volatilize the dispersion medium to prepare a positive electrode having a positive electrode active material layer on the current collector. The mixing ratio (LiFePO4: conductive assistant (RGO): PVDF) of the positive electrode active material layer was 94:1 :5. (Fabrication of positive electrode using graphene as conductive assistant) Graphene manufactured by Graphene Supermarket was used. The specific surface area of the graphene is 600 m / g, the flake size is about 10 μm, the thickness is 1 nm or less, and O / C is 0.02. Similar to the above RGO, the number of functional groups that bind to graphene is extremely small compared to graphene oxide. This graphene was heated at 170 °C for 10

[0190] hours in the same manner as above to fabricate a positive electrode. Two types of positive electrodes were fabricated with the mixing ratio of the active material layer (LiFePO4: conductive assistant ( graphene): PVDF) being 94:1:5 and 90:5:5. (Fabrication of positive electrode using acetylene black as conductive assistant) 2 Powdered acetylene black (AB) manufactured by Denki Kagaku Kogyo Co., Ltd. was used. The specific surface area is 6 8 m / g and the average particle size is 35 nm. The mixing ratio (LiFePO4: conductive assistant (AB): PVDF) of the positive electrode active material layer was 80:15:5. (Measurement of electrode conductivity)

[0191] Graphene oxide, graphene with a mixing ratio of 1%, graphene with a mixing ratio of 5%, and acetylene blac k 8 m 2 / g, the average particle size is 35 nm. The mixing ratio (LiFePO4: conductive assistant (AB): PVDF) of the positive electrode active material layer was 80:15:5.

[0192] (Measurement of electrode conductivity) Graphene oxide, graphene with a mixing ratio of 1%, graphene with a mixing ratio of 5%, and acetylene blac The conductivity of the positive electrode active material layer using each rack was measured. As a result of the measurement, the results in Table 1 below were obtained. As a result.

[0193]

Table 1

[0194] The conductivity was the lowest at 1.3×10 -6 S / cm for the positive electrode active material layer containing the conductive aid using graphene oxide. In contrast, graphene and acetylene black had conductivity values two digits higher or more.

[0195] (Charge and discharge characteristics) Graphene reduced after applying the paste containing the above-mentioned graphene oxide to the current collector, and R GO, graphene, and acetylene black (AB) were used as conductive aids, respectively, to fabricate positive electrodes and incorporated them into half cells, and the charge and discharge characteristics of each cell were measured. For convenience, the cell using the conductive aid made from graphene oxide as a raw material according to the present invention is designated as Cell D, the cell using RGO is designated as Cell E, the cell using 1% graphene by mixing ratio is designated as Cell F, the cell using 5% graphene by mixing ratio is designated as Cell G, and the cell using AB is designated as Cell H. The charge rate was set to 0.2C (however, for the cell (Cell H) with the positive electrode using AB, it was 0.16C) and measured. Also, the discharge rate was set to 1C (however, for Cell H, it was 0.82C) and measured as such. As a result of the measurement, in Cell E using RGO as the conductive aid and Cell F using 1% graphene by mixing ratio as the conductive aid, no charge and discharge could be performed at all. On the other hand, in Cell G using 5% graphene by mixing ratio as the conductive aid and the conventional acetylene black as the conductive aid, the charge and discharge characteristics were measured. As a result of the measurement, in Cell E using RGO as the conductive aid and Cell F using 1% graphene by mixing ratio as the conductive aid, no charge and discharge could be performed at all.

[0196] As a result of the measurement, in Cell E using RGO as the conductive aid and Cell F using 1% graphene by mixing ratio as the conductive aid, no charge and discharge could be performed at all. On the contrary, in Cell G using 5% graphene by mixing ratio as the conductive aid and the conventional acetylene black

[0197] As for this, in Cell G using 5% graphene by mixing ratio as the conductive aid and the conventional acetylene black In cell H with acetylene black as the conductive aid, battery characteristics were confirmed. The charge-discharge characteristics are shown in Fig. 12 together with cell D using a conductive aid made from the graphene oxide according to the present invention as a raw material.

[0198] Fig. 12 is a drawing showing charge-discharge characteristics, with the discharge capacity (mAh / g) on the horizontal axis and the voltage (V) on the vertical axis. The thick line is the curve showing the charge-discharge characteristics of cell D having a positive electrode using a conductive aid made from graphene oxide as a raw material. In contrast, the thin line is the curve showing the charge-discharge characteristics of cell G with 5% graphene added as a conductive aid. Also, the dashed line is the curve showing the charge-discharge characteristics of cell H with acetylene black as the conductive aid.

[0199] In cell D, it was found that good charge-discharge characteristics were obtained from the discharge curve 901a and the charge curve 901b.

[0200] On the other hand, in cell G with graphene as the conductive aid, the charge-discharge plateau region was narrow in the discharge curve 902a and the charge curve 902b, and the discharge capacity was small.

[0201] Furthermore, in cell H with acetylene black as the conductive aid, no plateau discharge region was confirmed in the discharge curve 903a and the charge curve 9 03b, and the discharge capacity was small.

[0202] As described above, when using a positive electrode mixed with RGO or graphene having almost no functional groups as a conductive aid, a cell with good charge-discharge characteristics cannot be obtained. In contrast, in a positive electrode prepared by dispersing graphene oxide having functional groups bonded by an oxidation reaction in a dispersion medium, a cell showing good charge-discharge characteristics was obtained. From this, graphene oxide in the positive electrode paste ​​​​​In the positive electrode active material layer that was reduced to graphene after being dispersed, it is considered that a network with high electronic conductivity is formed by the graphene. On the other hand, in the positive electrode active material layer prepared by dispersing RGO or graphene that has almost no functional groups in the positive electrode paste, it is considered that a network with sufficient electronic conductivity is not formed. Therefore, it has been found that using graphene oxide having a functional group as a raw material for the conductive assistant is important for expressing high electronic conductivity of the positive electrode active material layer. It is considered that a network with high electronic conductivity is formed by the graphene. On the other hand, the positive electrode active material layer prepared by dispersing RGO or graphene that has almost no functional groups in the positive electrode paste is considered to have an insufficiently formed network of electronic conductivity. Therefore, using graphene oxide having a functional group as a raw material for the conductive assistant is important for expressing high electronic conductivity of the positive electrode active material layer.

Example

[0203] Next, an experiment was conducted to confirm the charge and discharge characteristics of the secondary battery due to differences in the oxidation degree of graphene oxide (the amount of oxygen-containing functional groups such as epoxy groups).

[0204] (Fabrication of positive electrode) First, in order to confirm the charge and discharge characteristics of the secondary battery due to differences in the oxidation degree of the graphene oxide used, three types of positive electrodes, sample A, sample B, and sample C, using graphene oxide with different oxidation degrees were fabricated.

[0205] In this example, in order to confirm the difference in the charge and discharge characteristics of the secondary battery due to the difference in the oxidation degree of graphene oxide, it was necessary to prepare graphene oxide with different oxidation degrees. For this reason, instead of using the graphite powder described in Embodiment 1, graphene having almost no functional groups was used as a raw material. By oxidizing graphene by changing the amount of the oxidizing agent with respect to a certain amount of graphene to obtain graphene oxide, graphene oxide with different oxidation degrees can be fabricated.

[0206] For Samples A, B, and C, graphene manufactured by Cheap tubes was used. . Graphene with an average thickness of 3 nm was used. For Samples A, B, and C , the weight of graphene was set to 0.25 g. For Sample A, 1.5 g of potassium permanganate (KMnO4) as an oxidizing agent was added to 46 ml of sulfuric acid, for Sample B, 0.5 g of the same oxidizing agent was added, and for Sample C, 0.2 g of the same oxidizing agent was added. The graphene was mixed and oxidized in the sulfuric acid. The oxidation treatment was carried out by stirring at room temperature for 2.5 hours. Then, pure water was added, heated, and stirred for 15 minutes, and hydrogen peroxide solution was further added to obtain a yellowish-brown suspension containing graphite oxide.

[0207] For the prepared graphite oxide for Sample A, graphite oxide for Sample B, and graphite oxide for Sample C, the degree of oxidation was measured by X-ray photoelectron spectroscopy (XPS). The measurement was carried out under the conditions of using monochromatic light Al (1486.6 eV) as the X-ray source, a measurement area of 100 μm in diameter, and a take-off angle of 45°. The measurement results are shown in Tables 2 and 3.

[0208]

Table 2

[0209]

Table 3

[0210] Table 2 shows the quantitative values (unit: atomic%) of each element of C, O, N, and S for Samples A, B, and C, respectively, and the weight ratio of oxygen to carbon (or degree of oxidation, denoted as O / C). The graphite oxide for Sample A using 1.5 g of the oxidizing agent has a higher oxygen weight than the other samples The O / C was 0.487. In contrast, for sample B using 0.5 g of the oxidizing agent, the graphene oxide had an O / C of 0.405, and for sample C using 0.2 g of the oxidizing agent, the graphene oxide had an O / C of 0.311. From the above, by adjusting the weight of the oxidizing agent used for the oxidation of graphene, graphene oxides with different degrees of oxidation could be prepared.

[0211] Table 3 shows the surface bonding states of the graphene oxides of the above samples A to C classified by their states. The higher the O / C, the lower the ratios of the C-C, C-H, and O=C-O bonds, while on the other hand, the ratio of C-O tends to be higher.

[0212] Next, using each of the graphene oxides prepared under the above conditions, the positive electrodes of sample A, sample B, and sample C were fabricated. The positive electrode was prepared by mixing each of the graphene oxides prepared under the above conditions as a conductive assistant with positive electrode active material (lithium iron phosphate (LiFePO4)) particles, a binder (polyvinylidene fluoride (PVDF), manufactured by Kureha Chemical Co., Ltd.), and then fabricating a positive electrode paste, applying the positive electrode paste to a current collector (aluminum), and drying and reducing it.

[0213] The method for preparing the lithium iron phosphate commonly used as the positive electrode active material of sample A, sample B, and sample C will be described. Lithium carbonate (Li2CO3), iron oxalate (FeC2 O4·2H2O), and ammonium dihydrogen phosphate (NH4H2PO4), which are raw materials, were weighed at a weight ratio of 1:2:2, and pulverized and mixed at 300 rpm for 2 hours using a wet ball mill (ball diameter 3 mm, using acetone as the solvent). After drying, it was calcined temporarily at 350 °C for 10 hours in a nitrogen atmosphere. ​

[0214] Next, wet ball milling (ball diameter 3 mm) was performed at 300 rpm for 2 hours for pulverization and mixing. Thereafter, it was fired at 600 °C for 10 hours in a nitrogen atmosphere.

[0215] Next, NMP (manufactured by Tokyo Chemical Industry Co., Ltd.), which is a polar solvent, was prepared as a dispersion medium, and graphene oxide was dispersed in the NMP. After that, lithium iron phosphate was added and kneaded. PVDF was added as a binder to the mixture of graphene oxide and lithium iron phosphate, and then NMP was further added as a dispersion medium and kneaded to prepare a positive electrode paste. After adding PVDF as a binder to the mixture of graphene oxide and lithium iron phosphate, NMP was further added as a dispersion medium and kneaded to prepare a positive electrode paste. The positive electrode paste prepared by the above method was applied onto an aluminum foil with a thickness of 20 μm serving as a current collector, dried at 80 °C for 40 minutes in an air atmosphere, and then dried at 170 °C for 10 hours in a reduced-pressure atmosphere to reduce graphene oxide in the positive electrode paste and form graphene. The mixing ratio of the positive electrode paste was prepared such that lithium iron phosphate:graphene oxide:PVDF = 93:2:5.

[0216] This mixing ratio becomes a positive electrode active material layer of lithium iron phosphate:graphene:PVDF = 94:1:5 by the reduction treatment of graphene oxide. However, such a change in the mixing ratio hardly affects the calculation of the discharge capacity of the secondary battery. In addition, in order to exclude the influence of the interfacial resistance between the current collector and the positive electrode active material layer, an anchor coat was applied to the surface of the current collector in any of Sample A, Sample B, and Sample C. Thereafter, it was dried at 80 °C for 40 minutes in an air atmosphere, and then dried at 170 °C for 10 hours in a reduced-pressure atmosphere to reduce graphene oxide in the positive electrode paste and form graphene. The mixing ratio of the positive electrode paste was prepared such that lithium iron phosphate:graphene oxide:PVDF = 93:2:5. This mixing ratio becomes a positive electrode active material layer of lithium iron phosphate:graphene:PVDF = 94:1:5 by the reduction treatment of graphene oxide. However, such a change in the mixing ratio hardly affects the calculation of the discharge capacity of the secondary battery. In addition, in order to exclude the influence of the interfacial resistance between the current collector and the positive electrode active material layer, an anchor coat was applied to the surface of the current collector in any of Sample A, Sample B, and Sample C. The mixing ratio of the positive electrode paste was prepared such that lithium iron phosphate:graphene oxide:PVDF = 93:2:5. This mixing ratio becomes a positive electrode active material layer of lithium iron phosphate:graphene:PVDF = 94:1:5 by the reduction treatment of graphene oxide. However, such a change in the mixing ratio hardly affects the calculation of the discharge capacity of the secondary battery. In addition, in order to exclude the influence of the interfacial resistance between the current collector and the positive electrode active material layer, an anchor coat was applied to the surface of the current collector in any of Sample A, Sample B, and Sample C. This mixing ratio becomes a positive electrode active material layer of lithium iron phosphate:graphene:PVDF = 94:1:5 by the reduction treatment of graphene oxide. However, such a change in the mixing ratio hardly affects the calculation of the discharge capacity of the secondary battery. In addition, in order to exclude the influence of the interfacial resistance between the current collector and the positive electrode active material layer, an anchor coat was applied to the surface of the current collector in any of Sample A, Sample B, and Sample C. This mixing ratio becomes a positive electrode active material layer of lithium iron phosphate:graphene:PVDF = 94:1:5 by the reduction treatment of graphene oxide. However, such a change in the mixing ratio hardly affects the calculation of the discharge capacity of the secondary battery. In addition, in order to exclude the influence of the interfacial resistance between the current collector and the positive electrode active material layer, an anchor coat was applied to the surface of the current collector in any of Sample A, Sample B, and Sample C. In order to exclude the influence of the interfacial resistance between the current collector and the positive electrode active material layer, an anchor coat was applied to the surface of the current collector in any of Sample A, Sample B, and Sample C. In order to exclude the influence of the interfacial resistance between the current collector and the positive electrode active material layer, an anchor coat was applied to the surface of the current collector in any of Sample A, Sample B, and Sample C.

[0217] As described above, positive electrodes using three types of graphene oxides with different oxidation degrees as raw materials for conductive aids were prepared as Sample A, Sample B, and Sample C. As described above, positive electrodes using three types of graphene oxides with different oxidation degrees as raw materials for conductive aids were prepared as Sample A, Sample B, and Sample C.

[0218] (Charge and Discharge Characteristics) The positive electrodes of Sample A, Sample B, and Sample C prepared as described above were incorporated into half-cells to form Cell A , Cell B, and Cell C, and the charge-discharge characteristics of each cell were measured. The characteristics were evaluated in the form of a CR2 032 type (diameter 20 mm, height 3.2 mm) coin-shaped cell. Also, for the negative electrode, a lithium foil was used, for the separator, a 25-μm-thick polypropylene (PP) film was used, and for the electrolyte, , a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 was used, in which lithium hexafluorophosphate (LiPF6) was dissolved at a concentration of 1 mol / L . Charging was performed by CCCV at 0.2C and an upper limit voltage of 4.3V. Discharging was performed by CC for all rates of 0.2C, 1C, 2C, 5C, and 10C, and the lower limit voltage was 2V.

[0219] The measurement results of the charge-discharge characteristics of Cell A and Cell B are shown in Fig. 13. Fig. 13(A) shows the charge-discharge characteristics of Cell A having the positive electrode of Sample A using graphene formed from graphene oxide with an O / C of 0 .487 as a raw material. Also, Fig. 13(B) shows the charge-discharge characteristics of Cell B having the positive electrode of Sample B using graphene formed from graphene oxide with an O / C of 0.4 05 as a raw material. In each case, the horizontal axis represents the discharge capacity per unit weight of the active material (unit: mAh / g), and the vertical axis represents the voltage (unit: Volt).

[0220] As shown in Fig. 13(A), Cell A exhibited good battery characteristics.

[0221] Also, as shown in Fig. 13(B), Cell B also exhibited good battery characteristics.

[0222] On the other hand, a sample having graphene formed using graphene oxide with an O / C of 0.311​​ Regarding the positive electrode of material C, cell C using this did not operate at all as a battery.

[0223] As described above, in cells A and B incorporating a positive electrode containing a conductive assistant using graphene oxide with an O / C indicating an oxidation degree of 0.405 or more as a raw material, sufficient charge-discharge characteristics were obtained. On the other hand, in cell C incorporating a positive electrode containing a conductive assistant using graphene oxide with an O / C of 0.311 as a raw material, battery characteristics could not be obtained. From this, when using graphene oxide with an O / C of at least 0.405 or more, since it has sufficient functional groups having oxygen that binds to graphene oxide, it is considered that graphene oxide in the dispersion medium is uniformly dispersed. For this reason, the graphene formed by the reduction treatment of graphene oxide by heating the positive electrode paste is mixed with high dispersibility in the positive electrode active material, and since they are in face contact with each other, it is considered that battery characteristics can be obtained by forming a network with high electron conductivity. On the other hand, when using a positive electrode containing a conductive assistant using graphene oxide with an O / C of 0.311 or less as a raw material, the dispersibility of graphene oxide in the positive electrode paste is low. For this reason, the graphene formed by reduction is not sufficiently dispersed in the positive electrode active material or aggregates, so that a sufficient electron conduction network cannot be formed, and it is considered that battery characteristics could not be obtained.

[0224] On the other hand, when using a positive electrode containing a conductive assistant using graphene oxide with an O / C of 0.311 or less as a raw material, the dispersibility of graphene oxide in the positive electrode paste is low. For this reason, by reduction the formed graphene is not sufficiently dispersed in the positive electrode active material or aggregates, so that a sufficient electron conduction network cannot be formed, and it is considered that battery characteristics could not be obtained.

Example

[0225] In order to visually confirm that the dispersibility in the positive electrode active material is enhanced by using graphene oxide having a functional group, a positive electrode active material layer prepared using graphene oxide as a raw material of a conductive assistant Observation was carried out by SEM (Scanning Electron Microscope). For comparison, SEM observation was also carried out on the positive electrode active material layer using RGO as a conductive assistant and the positive electrode active material layer using graphene as a conductive assistant.

[0226] Figure 14(A) shows the SEM image of the surface of the positive electrode active material layer prepared using graphene oxide as the raw material of the conductive assistant. In the image, reduced graphene exists not only in the dark-colored parts but also overall. Graphene is observed to adhere in a mottled pattern. A partial enlargement of Figure 14(A) is shown in Figure 14(B). Multiple granular positive electrode active materials 1001 are observed. Most of the granular positive electrode active materials 1001 aggregate in units of several or dozens. In Figure 14(B), for example, as shown within the dashed circle, the dark-colored part is graphene 1002. Figure 15 is an SEM image obtained by further magnifying a part of Figure 14(B). It can be confirmed that graphene 1002 spreads so as to cover the aggregated multiple granular positive electrode active materials 1001. Since graphene 1002 is thin, it makes surface contact so as to wrap along the surface of the granular positive electrode active material. Moreover, the part of graphene 1002 that is not in contact with the positive electrode active material 1001 is stretched, bent, or forms wrinkles. Also, graphene 1002 exists not only on the surface but is also confirmed inside the active material layer.

[0227] Figures 16(A)(B), Figures 20(A)(B), Figure 21, and Figure 22 are SEM images obtained by observing the cross-section of the positive electrode active material layer prepared using graphene oxide as the raw material of the conductive assistant.

[0228] Lithium iron phosphate LiFePO4: Conductive assistant (graphene oxide): PVDF = 93:2:​​ The positive electrode active material layer prepared with a composition of 5 (unit: wt%) is shown in FIGS. 16(A), (B) and 21. The positive electrode active material layer in FIG. 16 was prepared using PVDF(1100) manufactured by Kureha. In FIG. 21, it was prepared using PVDF(9100) manufactured by Kureha. In FIG. 21, in order to easily observe graphene oxide, it was photographed with potential contrast.

[0229] In the SEM images of FIGS. 16(A) and 21, a plurality of granular positive electrode active materials are confirmed. Partially, aggregated positive electrode active materials can also be confirmed. Here, what appears as white filamentous or string-like is graphene. Note that in the case of graphene, few-layer graphene may not be observed in the SEM image. Also, even if the graphene is observed separately, there may be a case where it is connected by few-layer graphene that is not observed in the SEM image. Graphene can be confirmed in a filamentous or string-like form in the gaps (voids) between a plurality of positive electrode active materials, but it is also adhered to the surface of the positive electrode active material. Some of the graphene in the SEM image of FIG. 16(A) are highlighted and shown by thick lines in FIG. 16(B). In both FIG. 16(B) and FIG. 21, it can be seen that graphene 1 002 is three-dimensionally dispersed in the positive electrode active material so as to wrap the positive electrode active material 1001. Graphene 1002 is in surface contact with a plurality of granular positive electrode active materials 1001 and is also in surface contact with each other. Therefore, it is confirmed that inside the positive electrode active material layer, graphene are connected to each other and form an electron conduction network.

[0230] Prepared with a composition of lithium iron phosphate: graphene oxide: PVDF = 94:1:5 (unit: wt%) The fabricated positive electrode active material layer is shown in FIGS. 20(A) and (B). In the SEM images of FIGS. 20(A) and (B), a plurality of granular positive electrode active materials are confirmed. Partially, aggregated positive electrode active materials can also be confirmed. Similar to the cases of FIGS. 16(A) and (B) and FIG. 21, graphene can be confirmed in a filamentous or stringy form in the gaps (voids) between a plurality of positive electrode active materials, but it is also attached to the surface of the positive electrode active material. Some of the graphene in the SEM image of FIG. 20(A) are emphasized and shown with thick lines in FIG. 20(B). In FIG. 20 as well, it can be seen that the graphene 1002 is three-dimensionally dispersed in the positive electrode active material so as to wrap the positive electrode active material 1001.

[0231] The positive electrode active material layer prepared with a composition of lithium iron phosphate: graphene oxide: PVDF = 94.4: 0.6: 5 (unit: wt%) is shown in FIG. 22. In FIG. 22, some of the graphene in the SEM image are emphasized and shown with thick lines. Similar to the cases of FIGS. 16(A) and (B), FIGS. 20(A) and (B), and FIG. 21, it can be seen that the graphene 1002 is three-dimensionally dispersed in the positive electrode active material so as to wrap the positive electrode active material 1001. Also, the graphene 1002 is in surface contact with a plurality of granular positive electrode active materials 1001, and the graphene 1002 are in surface contact with each other. ) Even at a mixing ratio of 0.6 wt%, it was confirmed that the graphene are connected to each other inside the positive electrode active material layer, forming an electron conduction network.

[0232] Thus, it was confirmed that even when the type of PVDF is different or the blending of graphene oxide is different, the graphene oxide in the positive electrode active material layer is similarly three-dimensionally dispersed and an electron conduction network can be formed.

[0233] ​​​​​​​​Next, in Fig. 17, SEM observation of the surface of the positive electrode active material layer using RGO as a conductive assistant is shown. The results are shown. The darker-colored part slightly below the center shown in Fig. 17(A) is the part where RGO exists. An SEM image of this RGO observed at an enlarged scale is shown in Fig. 17(B). Although the granular positive electrode active material 1 003 and RGO 1004 are in contact, in Fig. 17(B), RGO is only seen near the center of the image and is not confirmed in other regions. That is, RGO had poor dispersibility and existed in an aggregated state on the surface of the positive electrode active material layer.

[0234] Next, in Fig. 18, SEM observation results of the surface of the positive electrode active material layer using graphene as a conductive assistant are shown. In Fig. 18(A), some darker-colored parts confirmed as dot-shaped are graphene. An enlarged view of a part of Fig. 18(A) is shown in Fig. 18(B). Some graphene 1006 is scattered among a plurality of positive electrode active materials 1005. Similar to RGO, it was also confirmed that graphene had poor dispersibility and existed in an aggregated state.

[0235] From the above results, when graphene oxide is used as a raw material for the conductive assistant, due to having functional groups, its dispersibility in polar solvents is high. As a result, it was found that the graphene formed by reduction exists with high dispersibility in the positive electrode active material layer. Therefore, it was confirmed that graphene can form an electron conduction network in the positive electrode active material layer, enabling the formation of a positive electrode having high electron conductivity.

Example

[0236] Next, regarding the positive electrode according to the present invention containing graphene reduced after applying a paste containing graphene oxide to a current collector, XPS analysis is performed to confirm the composition of the positive electrode active material layer after the production of the positive electrode. ​ Analysis was performed.

[0237] The analysis was performed on four different types of positive electrodes (positive electrode GN1, positive electrode GN2, positive electrode GN3, and positive electrode GN4) obtained by subjecting a positive electrode paste with a composition ratio of lithium iron phosphate: graphene oxide: PVDF = 93:2:5 to the following four different conditions of treatment. to the following four different conditions of treatment.

[0238] (Positive electrode GN1) Positive electrode GN1 is an electrode on which no reduction treatment has been performed on graphene oxide, and is an electrode that has been immersed in an electrolytic solution and then washed. The electrolytic solution immersed is a mixed solution in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 1:1, and in which lithium hexafluorophosphate (LiPF6) is dissolved at a concentration of 1 mol / liter. Further, the washing for removing lithium salts was performed using DEC. When producing positive electrode GN1, drying for volatilizing the dispersion medium is performed, but since it is a treatment at 80 °C for 40 minutes in an air atmosphere, graphene oxide is not reduced. to the following four different conditions of treatment. to the following four different conditions of treatment. to the following four different conditions of treatment. to the following four different conditions of treatment. to the following four different conditions of treatment. to the following four different conditions of treatment.

[0239] (Positive electrode GN2) Positive electrode GN2 is an electrode on which electrochemical reduction treatment has been performed on graphene oxide, and is washed with DEC in the same manner as positive electrode GN1. The electrochemical reduction treatment was performed by fabricating a coin cell using lithium as the counter electrode. The reduction of graphene oxide was performed by discharging at a rate of 1 C until a reduction potential of 2.0 V (vs. Li / Li to the following four different conditions of treatment. to the following four different conditions of treatment. Li + ) and then holding the potential at 2.0 V for 10 hours. to the following four different conditions of treatment.

[0240] (Positive electrode GN3) Positive electrode GN3 is an electrode that has undergone the same electrochemical reduction as positive electrode GN2, and then charged at 0.2 C up to 4.3 V. Charged by a current and held at a potential until the current value reaches 0.01C at 4.3V Thereafter, the positive electrode GN3 was taken out from the cell and washed with DEC after the charging.

[0241] (Positive electrode GN4) The positive electrode GN4 is an electrode obtained by thermally reducing graphene oxide. The thermal reduction treatment was performed under a reduced pressure atmosphere at 170°C for 10 hours. Thereafter, it was immersed in an electrolytic solution in the same manner as the above positive electrode and then washed.

[0242] (Analysis results by XPS) The results of XPS analysis of the positive electrode active material layers of the above positive electrodes GN1, GN2, GN3, and GN4 are shown in Tables 4 and 5 below.

[0243]

Table 4

[0244]

Table 5

[0245] Tables 4 and 5 show the bonding states of carbon contained in the positive electrode active material layers of the positive electrodes GN1, GN2, GN3, and GN4 respectively by analyzing the C1 S spectrum by waveform separation and showing them by state. Table 4 shows the ratio of the bonding states of carbon quantified by XPS analysis and Table 5 shows the ratio to all bonding states.

[0246] As shown in Tables 4 and 5, the C=C bond was not quantified in the non-reduced positive electrode GN1, whereas in the reduced positive electrodes GN2, GN3, and GN4 ​​​, 24.1 atomic% (40.5% with respect to all states) and 27.5 atomic c% (46.0%), 24.6 atomic% (41.4%) were found to be contained. On the other hand, in the non-reduced positive electrode GN1, while it contains a large amount of C-O bonds (17 .1 atomic%), in the reduced positive electrodes GN2, GN3, and GN4, it is less (8.4 atomic%, 8.8 atomic%, and 7.7 atomic % in order). The positive electrode active material layer of each analyzed electrode also contains a binder, but such a reduction treatment does not change the composition of the binder. Therefore, due to the reduction treatment, the functional groups bonded to graphene oxide decreased, so it is considered that while the C=C bond increased, the C-O bond decreased.

[0247] From the above, it was confirmed that by performing the reduction treatment after applying the positive electrode paste, the graphene oxide contained in the positive electrode paste was reduced.

[0248] In the positive electrode produced by such a reduction treatment, the bonding state of carbon contained in the positive electrode active material layer is such that the ratio of the C=C bond is 35% or more, and the ratio of the C-O bond is 5% or more and 20% or less, preferably the ratio of the C=C bond is 40% or more, and the ratio of the C-O bond is 10% or more and 15% or less.

[0249] By using such a positive electrode active material layer, a positive electrode for a non-aqueous secondary battery having high electron conductivity with a small amount of conductive assistant can be provided. Also, a positive electrode for a non-aqueous secondary battery with a high filling amount and high density can be provided with a small amount of conductive assistant.

[0250] ​The above XPS analysis was performed on the positive electrode active material layer including the binder. For comparison, the XPS analysis results before and after thermal reduction of graphene oxide alone in powder form are shown in Tables 6 and 7. Table 6 shows the weight ratio of the carbon bonding states of the graphene oxide in powder form, and Table 7 shows the ratio to the total bonding states. It can be seen that thermal reduction increases the C=C bond while decreasing the C-O bond.

Symbol Explanation

[0251]

Table 6

[0252]

Table 7

[0253] It can be seen that thermal reduction increases the C=C bond while decreasing the C-O bond.

Symbol Explanation

[0254] 100 NMP 101 Graphene or RGO 102 Graphene Oxide 200 Positive Electrode 201 Positive Electrode Current Collector 202 Positive Electrode Active Material Layer 203 Positive Electrode Active Material 204 Graphene 300 Secondary Battery 301 Positive Electrode Can 302 Negative Electrode Can 303 Gasket 304 Positive Electrode 305 Positive Electrode Current Collector 306 Positive Electrode Active Material Layer 307 Negative Electrode 308 Negative Electrode Current Collector 309 Negative Electrode Active Material Layer 310 Separator 401 Container 402 Graphene Oxide Dispersion 403 Formed Object 404 Conductor 405 Container 406 Electrolyte 407 Conductor 408 Counter electrode 500 Secondary battery 501 Positive current collector 502 Positive active material layer 503 Positive electrode 504 Negative current collector 505 Negative active material layer 506 Negative electrode 507 Separator 508 Electrolyte 509 Outer package 600 Secondary battery 601 Positive electrode cap 602 Battery can 603 Positive electrode terminal 604 Positive electrode 605 Separator 606 Negative electrode 607 Negative electrode terminal 608 Insulating plate 609 Insulating plate 610 Gasket (insulating packing) 611 PTC element 612 Safety valve mechanism 700 Display device 701 Housing 702 Display section 703 Speaker section 704 Non-aqueous secondary battery 710 Lighting device 711 Housing 712 Light source 713 Non-aqueous secondary battery 714 Ceiling 715 Side wall 716 Floor 717 Window 720 Indoor unit 721 Housing 722 Air outlet 723 Non-aqueous secondary battery 724 Outdoor unit 730 Electric refrigerator-freezer 731 Housing Door for the 732 Refrigerator Compartment Door for the 733 Freezer Compartment Non-aqueous Secondary Battery 800 Tablet Terminal 801 Housing 802 Display Unit 802a Display Unit 802b Display Unit 803 Display Mode Switching Switch 804 Power Switch 805 Power Saving Mode Switching Switch 807 Operation Switch 808a Region 808b Region 809 Operation Key 810 Keyboard Display Switching Button 811 Solar Cell 850 Charge and Discharge Control Circuit 851 Battery 852 DCDC Converter 853 Converter 860 Electric Vehicle 861 Battery 862 Control Circuit 863 Driving Device 864 Processing Device 901a Discharge Curve of Cell D 901b Charge Curve of Cell D 902a Discharge Curve of Cell G 902b Charge Curve of Cell G 903a Discharge Curve of Cell H 903b Charge Curve of Cell H 1001 Positive Electrode Active Material 1002 Graphene 1003 Positive Electrode Active Material 1004 RGO 1005 Positive Electrode Active Material 1006 Graphene

Claims

1. A secondary battery comprising an active material, a conductive graphene in surface contact with the active material, and a current collector, A secondary battery in which lithium ions are inserted into and removed from the active material during charging and discharging.

2. In claim 1, The secondary battery, wherein the current collector comprises aluminum or copper.

3. A secondary battery having a negative electrode, the negative electrode includes a negative electrode active material containing silicon, conductive graphene in surface contact with the negative electrode active material, and a negative electrode current collector; The secondary battery comprises a negative electrode active material into which lithium ions are inserted and removed during charging and discharging.

4. A secondary battery having a negative electrode, the negative electrode includes a negative electrode active material containing silicon, conductive graphene in surface contact with the negative electrode active material, and a negative electrode current collector; The negative electrode current collector comprises copper, The secondary battery comprises a negative electrode active material into which lithium ions are inserted and removed during charging and discharging.

5. 5. The negative electrode active material according to claim 3, wherein the negative electrode active material is SiO or Mg ２ A secondary battery having Si.

6. In any one of claims 1 to 5, the secondary battery is a non-aqueous secondary battery.

7. In any one of claims 1 to 6, The secondary battery, wherein the conductive graphene is a graphene compound.

Images