Method for manufacturing electrode for secondary battery

Abstract

To provide a graphene oxide that can be used as a raw material for a conductive additive for forming an active material layer having high electronic conductivity with a small amount of the conductive additive, and a positive electrode for a nonaqueous secondary battery using the graphene oxide as the conductive additive.SOLUTION: A graphene oxide is used as a raw material for a conductive additive for a positive electrode for a non-aqueous secondary battery, and has a weight ratio of oxygen to carbon of 0.405 or more.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.

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 large 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 popular due to their high energy density, are composed of 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 a non-aqueous electrolyte in which a lithium salt such as LiBF4 or LiPF6 is dissolved in an organic solvent such as ethylene carbonate or diethyl carbonate.

[0003] The 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 and lithium ions being inserted into and desorbed from the active materials of the positive and negative electrodes. In the positive electrode or the negative electrode, a binder (also referred to as a binder) is mixed 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).

[0004] ​​​​​​​​​​​Since polymer organic compounds such as these are common, their electron conductivity is extremely low. For this reason, when the ratio of the mixing amount of the binder to the active material amount is increased, the amount of active material in the electrode relatively decreases, so that, as a result, the discharge capacity of the secondary battery decreases.

[0005] Therefore, by mixing conductive aids such as acetylene black (AB) and 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, since 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, it is difficult to achieve surface contact with the active material and is likely to form point contact. For this reason, 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 becomes finer, the cohesive force between particles becomes stronger, so the binder and conductive additive are not uniformly distributed. Therefore, it becomes difficult to mix the active material particles so that they are uniformly dispersed. The active material is not mixed with conductive additives. In the particle agglomeration portion, the active material particles do not contribute to the formation of the discharge capacity of the battery.

[0010] In view of the above problems, in one aspect of the present invention, an active material having high electronic conductivity with a small amount of a conductive additive is provided. One of the objectives of the present invention is to provide graphene oxide, which is a raw material for a conductive additive for forming a porous layer. In addition, a small amount of conductive additive is used to produce a non-aqueous electrolyte containing a highly packed and highly densified positive electrode active material layer. Another object of the present invention is to provide a positive electrode for a secondary battery. One of the objects of the present invention is to provide a non-aqueous secondary battery having a large capacity per electrode volume. Let us assume that. [Means for solving the problem]

[0011] The positive electrode for a non-aqueous secondary battery according to one embodiment of the present invention comprises a conductive assistant contained in a positive electrode active material layer. , using graphene.

[0012] Graphene is a carbon material with a crystalline structure in which the hexagonal skeleton of carbon is extended in a planar fashion. Graphene is an atomic surface of a graphite crystal, and has electrical and mechanical properties. Due to its extraordinary mechanical and chemical properties, graphene is expected to be used for high-mobility field effect transistors, highly sensitive sensors, highly efficient solar cells, and next-generation transparent conductive films It is attracting attention as it is expected to be applied in various fields such as the following.

[0013] In this specification, graphene includes single-layer graphene or multi-layer graphene with 2 to 100 layers. Single-layer graphene refers to a sheet of a one-atom-thick carbon molecule having π bonds. Also, graphene oxide refers to a compound in which the above-mentioned graphene is oxidized. When graphene is formed by reducing graphene oxide, not all of the oxygen contained in the graphene oxide is desorbed, and some oxygen remains in the graphene. When oxygen is contained in the 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. Here, when the graphene is multi-layer graphene, by having 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 for single-layer graphene, 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. 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.

[0014]

[0015]

[0016] The positive electrode active material layer added with graphene as a conductive assistant can be produced 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 mixed 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 of 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 depends directly on the dispersibility of graphene in the positive electrode active material layer. When the dispersibility of graphene is low, graphene aggregates and localizes in the positive electrode active material layer, and thus the network cannot be formed. 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, the inventors of the present application put graphene as a conductive assistant together with the active material and the binder into a dispersion medium and confirmed the positive electrode active material layer thus produced. As a result, it was found that the dispersibility was not sufficient, and as a result a network for electron conduction could not be formed in the positive electrode active material layer. Furthermore instead of graphene as a conductive assistant, graphene oxide-reduced graphene (hereinafter abbreviated as RG O (abbreviation for Reduced Graphene Oxide)) was put into the dispersion medium and the same result was obtained in the positive electrode active material layer thus produced.

[0019] On the other hand, the inventors of the present application used graphene oxide (GO (Graphene O (also abbreviated as xide).) is put into a dispersion medium together with an active material and a binder to form a positive electrode paste After preparation, the dispersed graphene oxide was reduced by heat treatment to obtain graphene, and the positive In the electrode active material layer, an electron conduction network was formed within the active material layer, and it was found that excellent electron conduction conductivity 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 graphene obtained by adding graphene oxide to form a positive electrode paste and then reducing it was found to have high dispersibility.

[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 follows in terms of the difference in dispersibility in the dispersion medium.

[0022] In FIG. 1(A), the structural formula of typical NMP (N-methylpyrrolidone, also referred to as 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 in which a hexagonal skeleton extends in a planar shape, and substantially no functional groups are contained in the structure. Also, RGO has the functional groups it originally had 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. Graphene oxide obtained, having a weight ratio of oxygen to carbon of 0.405 or more, is graphene oxide.

[0027] Here, the weight ratio of oxygen to carbon is an index indicating the degree of oxidation, and is the ratio of the weights of carbon and oxygen among the constituent elements of graphene oxide, with carbon as the reference. Note that the weights of the elements constituting graphene oxide can be measured, for example, by X-ray photoelectron spectroscopy (XPS). X-ray Photoelectron Spectroscopy).

[0028] The fact that the weight ratio of oxygen to carbon in graphene oxide is 0.405 or more means that in a polar solvent, graphene oxide has high dispersibility, indicating that it is a polar substance with sufficient bonding of functional groups such as epoxy groups, carbonyl groups, carboxyl groups, and hydroxyl groups.

[0029] Therefore, by dispersing and kneading graphene oxide having a weight ratio of oxygen to carbon of 0.405 or more together with a positive electrode active material and a binder in a dispersion medium, applying it onto a positive electrode current collector, and heating, a non-aqueous secondary battery positive electrode containing graphene having high dispersibility and an electron conduction network can be formed.

[0030] Graphene oxide preferably has a side length of 50 nm or more and 100 μm or less, more preferably 800 nm or more and 20 μm or less.

[0031] Also, 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 graphene, and a binder on a positive electrode current collector, and the graphene is granular positive electrode active ​​​Larger than the average particle size of the substance, 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. Since graphene is a structure having a functional group containing oxygen as described above, graphene oxide is uniformly dispersed in a polar solvent such as NMP without aggregation. 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 a single assembly, 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.

[0032] As already described, since graphene oxide is a structure having a functional group containing oxygen, graphene oxide is uniformly dispersed in a polar solvent such as NMP without aggregation. 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 a single assembly, 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. 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 a single assembly, 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. 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 a single assembly, 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. 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 a single assembly, 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. 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 a single assembly, 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. 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 a single assembly, 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. 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 a single assembly, 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. 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 a single assembly, 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.

[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 of 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 of 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 of 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 of 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 of 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 of 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] Moreover, 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. 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. It is a positive electrode for a non-aqueous secondary battery.

[0036] Also, one aspect of the present invention disperses graphene oxide having a weight ratio of oxygen to carbon of 0.405 or more in a dispersion medium, and adds a positive electrode active material to the dispersion medium in which the graphene oxide is dispersed and kneads to prepare a mixture. A binder is added to the mixture and kneaded to prepare a positive electrode paste. The positive electrode paste is applied to a positive electrode current collector, and after or simultaneously with volatilizing the dispersion medium contained in the applied positive electrode paste, the graphene oxide is reduced to form a positive electrode active material layer containing graphene on the positive electrode current collector. It 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 this, 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] Also, 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. 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.

[0041]

[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, and a positive electrode active material layer containing graphene can be formed. Note that not all of the oxygen contained in graphene oxide needs to be desorbed, and some oxygen may remain in graphene. ​​​​​​​​​​

[0043] When oxygen is contained in graphene, 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 increased, 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 passageways 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 increased, 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 passageways can be formed in graphene. The lower the proportion of oxygen, the higher the conductivity of graphene can be increased, 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 passageways can be formed in graphene. By using the positive electrode, negative electrode, electrolytic solution, and separator manufactured as described above, a non-aqueous secondary battery can be manufactured. By using the positive electrode, negative electrode, electrolytic solution, and separator manufactured as described above, a non-aqueous secondary battery can be manufactured.

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

[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. A non-aqueous secondary battery having a large capacity per electrode volume can be provided.

Brief Description of the Drawings

[0048]

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MODE FOR CARRYING OUT THE INVENTION

[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. FIG. 3(A) shows a perspective view of the positive electrode, FIG. 3(B) shows a plan view of the positive electrode active material layer, and FIGS. 3(C) and 19 show a longitudinal sectional view of the positive electrode active material layer.

[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. Also, 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 regions for connecting to the positive electrode tab are appropriately provided.

[0053] For the positive electrode current collector 201, metals such as stainless steel, gold, platinum, zinc, iron, copper, aluminum, titanium, etc. and alloys thereof, which have high conductivity and do not alloy with carrier ions such as lithium, can be used. Also, an aluminum alloy added with elements such as silicon, titanium, neodymium, scandium, and molybdenum, which improve heat resistance, can be used. Alternatively, it may be formed of a metal element that reacts with silicon to form a silicide. Examples of the metal element that reacts with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, etc. The positive electrode current collector 201 can be appropriately used in shapes such as foil, plate (sheet), net, punching metal, expanded metal, etc. The positive electrode current collector 201 is preferably one with a thickness of 10 μm or more and 30 μm or less.

[0054] Figs. 3(B) and 3(C) are schematic diagrams showing the upper surface and longitudinal cross-section of the positive electrode active material layer 202, respectively. The positive electrode active material layer 202 includes granular positive electrode active material 203, graphite 204 as a conductive assistant, and a binder (also referred to as a binder, not shown).

[0055] The positive electrode active material 203 is a granular positive electrode active material composed of secondary particles having an average particle size and particle size distribution, which are obtained by pulverizing, granulating, and classifying a fired product obtained by mixing raw material compounds in a predetermined ratio and firing them by appropriate means. Therefore, in Figs. 3(B) and 3(C), the positive electrode active material 203 is schematically shown as a sphere, but it is not limited to this shape. As the positive electrode active material 203, a material capable of inserting and desorbing lithium ions can be used.

[0056] ​ and can include, for example, a lithium-containing composite oxide having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. Examples of the lithium-containing composite oxide having an olivine-type structure include composite oxides represented by the general formula LiMPO4 (M is one or more of

[0057] , Fe(II), Mn(II), Co(II), Ni(II)). Typical examples of the general formula LiMPO4 include LiFePO4, LiNi PO4, LiCoPO4, LiMnPO4, LiFe PO4, 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 well balances 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-type crystal structure containing manganese such as LiMn2O4 are preferably mixed with a small amount of lithium nickelate (LiNiO2, LiNi 1-x MO2 (M = Co, Al etc.)) because it has advantages such as suppressing the elution of manganese and suppressing the decomposition of the electrolytic solution.

[0063] In addition, 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) FeSiO4, Li (2-j ) NiSiO4, Li (2-j) CoSiO4, Li (2-j) MnSiO4, Li (2 -j) Fe (2-j) Ni k SiO4, Li l Fe (2-j) Co k SiO4, Li l Fe (2-j) Mn k SiO4, Li l Ni (2-j) Co k SiO l 4, Li Ni (2-j) Mn k SiO4 (k + l is 1 or less, 0 < k < 1, 0 < l < 1) l Fe (2-j) Ni m Co n SiO4, Li q Fe (2-j) Ni m Mn n Si q O4, Li Ni (2-j) Co m ​​n 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. As the NASICON type compound, Fe2(MnO4) 3, Fe2(SO4)3, Li3Fe2(PO4)3, etc. can be mentioned. 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 、LiV3O8 etc.), manganese oxide-based, organic sulfur-based, etc. materials can be used. can be used.

[0065] In addition, when the carrier ion is an alkali metal ion, alkaline earth metal ion, beryllium ion, or magnesium ion other than lithium ion, as the positive electrode active material, in the above lithium compounds and lithium-containing composite oxides, instead of lithium, alkali metal Metals (such as sodium, potassium, etc.), alkaline earth metals (such as calcium, strontium, barium, etc.), beryllium, or magnesium may also be used. Rontium, 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 performing a reduction treatment on graphene oxide having a weight ratio of oxygen to carbon of 0.405 or more. formed by performing a reduction treatment on graphene oxide having a weight ratio of oxygen to carbon of 0.405 or more. 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. formed.

[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. The 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. The graphite oxide has functional groups such as epoxy groups, carbonyl groups, carboxyl groups, and hydroxyl groups bonded thereto due to the oxidation of the carbon of the graphite. 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, ultrasonic vibration is applied to the dispersion containing graphite oxide to split the graphite oxide having a long interlayer distance and 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 has functional groups such as epoxy groups, carbonyl groups, carboxyl groups, and hydroxyl groups bonded thereto due to the oxidation of the carbon of the graphite. 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, ultrasonic vibration is applied to the dispersion containing graphite oxide to split the graphite oxide having a long interlayer distance and 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 graphite oxide can be obtained. graphite oxide can be obtained. graphite oxide is split, the graphene oxide is separated, 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. 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 g raphene 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 g By increasing the amount of oxidizing agent relative to the graphite powder, the degree of oxidation of graphene oxide (carbon Therefore, the amount of graphene oxide produced can be increased. In addition, the amount of the oxidizing agent relative to the amount of graphite powder used as the raw material may be determined.

[0070] The graphene oxide was prepared using a Hummers method using a sulfuric acid solution of potassium permanganate. The Hummer method uses, for example, nitric acid, potassium chlorate, sodium nitrate, etc. A method for producing graphene oxide other than the s method or the Hummers method may be used as appropriate.

[0071] In addition, graphite oxide can be thinned by adding ultrasonic vibrations, microwaves, radio waves, or This may be achieved by irradiation with thermal plasma or application of physical stress.

[0072] The graphene oxide produced contains epoxy groups, carbonyl groups, carboxyl groups, and hydroxyl groups. In polar solvents such as NMP, graphene oxide has The negatively charged oxygen in the graphene interacts with NMP while interacting with different graphene oxides. Therefore, in polar solvents, graphene oxide disperses uniformly. Firstly, it is easy to disperse.

[0073] In addition, the length of one side of graphene oxide (also called the flake size) is 50 nm or more and 100 nm or less. The flake size is preferably 800 nm to 20 μm. If the particle size is smaller than the average particle size of the positive electrode active material 203, surface contact with multiple positive electrode active materials 203 occurs. Since it becomes difficult to form a connection between the graphenes, the electric potential of the positive electrode active material layer 202 is decreased. It becomes difficult to improve the electrical conductivity.

[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, graphene 2 04 enables surface contact with low contact resistance, so that without increasing the amount of the conductive aid the electron conductivity between the granular positive electrode active material 203 and the graphene 204 can be improved .

[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 surface contact with each other to form an electron conduction path. 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, and 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, and 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. Since it is a very thin film (sheet) composed of a single layer or a stack of these carbon molecules, it traces the surface of each individual granular positive electrode active material 203. 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 is stretched and in a stretched 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 multi-layer thickness 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 to form an electron conduction network by a plurality of graphenes 204. A schematic diagram further enlarged from FIG. 3(C) is FIG. 19. Graphene 204 covers the surface of a plurality of granular positive electrode active materials 203 so as to stick thereto, and the graphenes also contact each other to form a network. formed, so they are in surface contact with each other. Also, the graphenes 204 are in surface contact with each other to form an electron conduction network by a plurality of graphenes 204. FIG. 19 is a schematic diagram further enlarged from FIG. 3(C). Graphene 204 covers the surface of a plurality of granular positive electrode active materials 203 so as to stick thereto, and the graphenes also contact each other to form a network. are 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 these being in 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. Therefore, the bonding between the positive electrode active materials 203 is maintained. From the above, using graphene oxide with an oxygen-to-carbon weight ratio of 0.405 or more as a raw material and reducing it after forming a paste, the graphene formed By using [substance name] as a conductive aid, a positive electrode active material layer 202 having high electronic 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 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 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 or more and 500 nm or less. For the surface contact of a plurality of the granular positive electrode active materials 203, 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, poly ethylene, 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, respectively.

[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 such an extent that they are in surface contact with each other and wrap a part of the surface of the granular positive electrode active material 203. By doing so, 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, applying the positive electrode paste onto a 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). If 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. Further, if 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, causing the positive electrode active material layer 202 to crack or the positive electrode active material layer 202 to peel 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 almost halved so that 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). It is preferable to use lithium iron phosphate having an average particle diameter of the primary particles of 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, and for example, 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, by kneading these mixtures (kneading in a high-viscosity state), aggregation of graphene oxide and lithium iron phosphate can be loosened. Also, since graphene oxide has functional groups, in a polar solvent, the oxygen in the functional groups is negatively charged, so it is difficult for different graphene oxides to aggregate with each other. Also, 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 paste, 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 a positive electrode paste can be produced by kneading (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. This is also acceptable.

[0096] As described in this embodiment, by adding the 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 so as to be 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 manufacturing a battery using the positive electrode, a non-aqueous secondary battery with a high capacity can be manufactured. Furthermore, since the binder can maintain the state where 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. This is also acceptable. This is also acceptable. This is also acceptable. This is also acceptable. This is also acceptable. This is also acceptable. This is also acceptable. This is also acceptable. This is also acceptable.

[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 a cross-sectional view thereof.

[0100] The coin-type secondary battery 300 has 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 means of 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 and precipitation or lithium ion insertion and extraction can be 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, and pitch -based artificial graphite, 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, S b, 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 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 combined with materials such as V2O5 and Cr3O8 that do not contain lithium ions as the positive electrode active material, which is preferable. 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] Also, a material in which a conversion reaction occurs can 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 0.89 , NiS, CuS, etc., nitrides such as Zn3N2, Cu3N, G 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 the 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] Also, 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 associated with the absorption and release of carrier ions during charge and discharge cycles, 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 and 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 during the charge and 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 of forming graphene oxide on the negative electrode active material layer 309 using 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 (hereinafter referred to as graphene oxide dispersion liquid 402) in which graphene oxide is dispersed in the dispersion medium described in Embodiment 1. 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 thus 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 that graphene oxide has, and the object and the substituent are combined to be neutral. ​​​​​​​​​​​​​​It is converted. Note that the voltage applied does not have to be constant. Also, the amount of charge flowing between the anode and the cathode By measuring it, 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, if the voltage applied between the anode and the cathode is 1 V, an oxide film that may be formed by the principle of anodization between the object to be formed and the graphene oxide layer is less likely to be formed.

[0121] When the required thickness of graphene oxide is obtained, the object to be formed 403 is lifted from the graphene oxide dispersion 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. Therefore, 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, since ionized graphene oxide can be electrically moved to the active material, 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. Although it may be good, 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 the 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.

[0126] 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 the 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. As shown in FIG. 6(B), a negative electrode having graphene oxide provided on the negative electrode active material layer 309 is used as the 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. A negative electrode having graphene oxide provided on the negative electrode active material layer 309 is used as the 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. The potential at which the reduction reaction of the graphene oxide occurs or the 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 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 the conductor 407 having graphene oxide and the counter electrode 408 are inserted therein and immersed. Next, the container 405 is filled with the electrolyte 406, and the conductor 407 having graphene oxide and the counter electrode 408 are inserted therein and immersed. Next, the conductor 407 having graphene oxide is used as the working electrode, and at least the counter electrode 408 and the electrolyte 406 are used to assemble an electrochemical cell (open circuit), and the reduction potential of graphene oxide is supplied to the potential of the conductor 407 (working electrode) to reduce the graphene oxide to graphene. Next, the conductor 407 having graphene oxide is used as the working electrode, and at least the counter electrode 408 and the electrolyte 406 are used to assemble an electrochemical cell (open circuit), and the reduction potential of graphene oxide is supplied to the potential of the conductor 407 (working electrode) to reduce the graphene oxide to graphene. Next, the conductor 407 having graphene oxide is used as the working electrode, and at least the counter electrode 408 and the electrolyte 406 are used to assemble an electrochemical cell (open circuit), and 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 respect to the counter electrode 408 or the reduction potential with respect 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.​ 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 , and the state where the reduction current falls below a certain value (the state where the peak corresponding to the reduction current disappears) may be regarded as the state where graphene oxide is reduced (the state where the reduction reaction has ended).

[0128] Moreover, 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 further, such 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 from the low potential side to the high potential side.

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

[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 proportion 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., 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 have low volatility are used , so that even if the internal temperature rises due to an internal short circuit or overcharging of the secondary battery, 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, it is not necessary to install a separator or spacer. Also, since the entire battery can be solidified, the risk of leakage is eliminated 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 these metals, alloys of these metals with other metals (for example, stainless steel, etc.), laminates of these metals, laminates of these metals and the alloys mentioned above (for example, stainless steel / aluminum, etc.), laminates of these metals with 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, 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 of the positive electrode 503, a negative electrode current collector 504 and a negative electrode active material layer 505 of the negative electrode 50 6, a separator 507, an electrolyte solution 508, and an exterior body 509. A separator 507 is installed between the positive electrode 503 and the negative electrode 506 provided inside the exterior body 509. Also the interior of the exterior body 509 is filled with the electrolyte 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 is arranged to be exposed outside from the exterior body 509 as shown.

[0142] In the laminated secondary battery 500, the exterior body 509 is, for example, on a film made of a material such as polyethylene, poly propylene, polycarbonate, ionomer, polyamide, etc., with an a ​A metal thin film with excellent flexibility such as aluminum, stainless steel, copper, nickel, etc. is provided, and further, an insulating synthetic resin film such as a polyamide resin or a polyester resin is provided on the metal thin film as the outer surface of the exterior body. A three-layer laminated 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 electrolytic solution resistance. 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. A three-layer laminated 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 electrolytic solution resistance. It has.

[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. The positive electrode cap and the battery can (outer can) 602 are insulated by a gasket (insulating packing) 610. 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. It is 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. The battery can 602 can be made of a metal such as nickel, aluminum, titanium, etc. that has corrosion resistance against liquids such as electrolytic solution during charging and discharging of the secondary battery, an alloy of the metal, an alloy of the metal and another metal (for example, stainless steel, etc.), a laminate of the metal, a laminate of the metal and the above-mentioned alloy (for example, stainless steel / aluminum, etc.), a laminate of the metal and another metal (for example, nickel / iron / nickel, etc.). Inside the battery can 602, the positive electrode, the negative electrode, and the separator Inside the hollow cylindrical battery can 602, a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 interposed therebetween. A wound battery element is provided. Although not shown, the battery element is wound around a center pin. The battery can 602 has a battery can 602, which has corrosion resistance against liquids such as electrolytic solution during charging and discharging of the secondary battery. A metal such as nickel, aluminum, titanium, etc., an alloy of the metal, an alloy of the metal and another metal (for example, stainless steel, etc.), a laminate of the metal, a laminate of the metal and the above-mentioned alloy (for example, stainless steel / aluminum, etc.), a laminate of the metal and another metal (for example, nickel / iron / nickel, etc.). For example, stainless steel, etc.), a laminate of the metal, a laminate of the metal and the above-mentioned alloy (for example, stainless steel / aluminum, etc.), a laminate of the metal and another metal (for example, nickel / iron / nickel, etc.). For example, stainless steel / aluminum, etc.), a laminate of the metal and another metal (for example, nickel / iron / nickel, etc.). For example, nickel / iron / nickel, etc.). The wound battery element is sandwiched between a pair of opposing insulating plates 608 and 609. Also, 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 value. The PTC element 611 is a thermal resistance 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. A structure in which a plurality of positive electrodes, negative electrodes, and separators are stacked, or a structure in which a positive electrode, a negative electrode, and a separator are wound may also 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 telephone handsets, transceivers, portable radios, mobile phones, car phones, portable game machines, calculators, portable information terminals, electronic notebooks, electronic 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, dehumidifiers and other air conditioning equipment, dishwashers, dish dryers, clothes dryers, futon dryers, electric freezers, refrigerators, refrigerator-freezers, DNA storage freezers, flashlights, chain saws and other power tools, smoke detectors, dialysis machines and other medical equipment, etc. can be mentioned. Furthermore, induction lights, traffic lights, belt conveyors, elevators, escalators, industrial robots, power storage systems, power leveling and energy storage devices for smart grids and other industrial equipment can be mentioned. Also, mobile bodies propelled by electric motors using power from non-aqueous secondary batteries are also included in the category of electrical equipment. As the above mobile bodies, for example, electric vehicles (EVs), hybrid vehicles (HEVs) with both internal combustion engines and electric motors, plug-in hybrid vehicles (PHEVs), tracked vehicles obtained by changing the tires of these vehicles 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. Appliances, electric washing machines, vacuum cleaners, water heaters, fans, hair dryers, air conditioners, humidifiers, dehumidifiers and other air conditioning equipment, dishwashers, dish dryers, clothes dryers, futon dryers, electric freezers, refrigerators, refrigerator-freezers, DNA storage freezers, flashlights, chain saws and other power tools, smoke detectors, dialysis machines and other medical equipment, etc. can be mentioned. Furthermore, induction lights, traffic lights, belt conveyors, elevators, escalators, industrial robots, power storage systems, power leveling and energy storage devices for smart grids and other industrial equipment can be mentioned. Also, mobile bodies propelled by electric motors using power from non-aqueous secondary batteries are also included in the category of electrical equipment. As the above mobile bodies, for example, electric vehicles (EVs), hybrid vehicles (HEVs) with both internal combustion engines and electric motors, plug-in hybrid vehicles (PHEVs), tracked vehicles obtained by changing the tires of these vehicles 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 electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as the main power source for supplying 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 supply for supplying 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 to the electrical equipment from the above main power source or commercial power source. In addition, the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as the main power source for supplying 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 supply for supplying 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 to the electrical equipment from the above main power source or commercial power source. Furthermore, induction lights, traffic lights, belt conveyors, elevators, escalators, industrial robots, power storage systems, power leveling and energy storage devices for smart grids and other industrial equipment can be mentioned.

[0151] Also, mobile bodies propelled by electric motors using power from non-aqueous secondary batteries are also included in the category of electrical equipment. As the above mobile bodies, for example, electric vehicles (EVs), hybrid vehicles (HEVs) with both internal combustion engines and electric motors, plug-in hybrid vehicles (PHEVs), tracked vehicles obtained by changing the tires of these vehicles 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 electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as the main power source for supplying 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 supply for supplying 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 to the electrical equipment from the above main power source or commercial power source. In addition, the above electrical equipment can use the non-aqueous secondary battery according to one aspect of the present invention as the main power source for supplying 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 supply for supplying power to the electrical equipment when the power supply from the above main power source or commercial power source stops.

[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 an 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 70 4 according to an aspect of the present invention is provided inside the housing 701. The display device 700 can receive power supply from a commercial power supply, or can also use the power stored in the non-aqueous secondary battery 704. Therefore, even when the power supply from the commercial power supply cannot be received due to a power outage or the like, by using the non-aqueous secondary battery 704 according to an aspect of the present invention as an uninterruptible power supply, the display device 700 can be used.

[0153] 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 Devic e), a PDP (Plasma Display Panel), an FED (Field E mission Display), etc., and a semiconductor display device can be used.

[0154] In addition to being used for receiving TV broadcasts, the display device includes all display devices for information display, such as for personal computers and for advertising displays.

[0155] In Fig. 9, the installed lighting device 710 is an example of an electrical equipment using a non-aqueous secondary battery 7 13 according to an aspect of the present invention. Specifically, the lighting device 710 includes a housing 711, a light source 7 12, a non-aqueous secondary battery 713, etc. In Fig. 9, the non-aqueous secondary battery 713 is in the housing 71 illustrates the case where it is installed 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 supply, or can use the power stored in the non-aqueous secondary battery 713 Therefore, even when the power supply from the commercial power supply 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, the installed lighting device 710 provided on the ceiling 714 is illustrated, but 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., and can also 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 can be 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 a 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 non-aqueous system secondary battery 723 is illustrated in the case where it is provided in the indoor unit 720, but 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 ​​A non-aqueous secondary battery 723 may be provided in both of 24. 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 illustrated 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 door 732 for the refrigerating compartment, a door 733 for the freezing compartment, a non-aqueous secondary battery 734, etc. 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. Among the above-described electric devices, high-frequency heating devices such as microwave ovens, electric rice cookers, etc.

[0161] ​​​​The machine requires high power in a short time. Therefore, by using a non-aqueous secondary battery according to one 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 electrical equipment is in use. Also, during the time when the electrical equipment is not in use, especially during the time when the ratio of the actually used power to the total power that can be supplied by the commercial power supply (referred to as the power utilization rate) is low, by storing power in the non-aqueous secondary battery, it is possible to suppress the increase in the power utilization 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 utilization 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 electrical equipment, will be described with reference to FIG. 10.

[0165] FIGS. 10(A) and 10(B) show a foldable two-piece tablet terminal 800. FIG. 10(A) shows the open state, and the tablet terminal 800 includes a housing 801, display units 802a and 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 where 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 where 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 made 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 made into 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 may incorporate other detection devices such as sensors for detecting inclination such as a gyro and an acceleration sensor in addition to the optical sensor

[0170] ​​​​​​​​​FIG. 10A shows an example in which the display area of ​​the display unit 802b is the same as that of the display unit 802a. However, there is no particular limitation, and one size may be different from the other size. The quality may also be different. For example, one may be a display panel capable of displaying a higher resolution image than the other. This is also fine.

[0171] FIG. 10B shows the tablet terminal 800 in 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 DC / DC converter 852 In FIG. 10B, a battery 851 and a DCD The configuration shown has a C converter 852, and the battery 851 is the same as the above embodiment. The present invention has a non-aqueous secondary battery as described above.

[0172] In addition, since the tablet terminal 800 can be folded in half, when the housing 801 is closed, Therefore, the display unit 802a and the display unit 802b can be protected, and the display unit 802a and the display unit 802b can be protected. To provide a tablet terminal 800 having excellent durability and excellent reliability from the viewpoint of long-term use. This can be done.

[0173] In addition, the tablet terminals shown in Figs. 10(A) and 10(B) can store various information. Functions for displaying information (still images, videos, text images, etc.), calendars, dates, or times, etc. A function to display information on the display unit, and a function to operate or edit the information displayed on the display unit by touch input. It has the function of inputting information, the function of controlling processing by various software (programs), etc. This can be done.

[0174] The solar cell 811 attached to the surface of the tablet terminal supplies power to the touch panel, display, and It 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 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. Note that when using the non-aqueous secondary battery according to one aspect of the present invention, there are advantages such as being able to achieve miniaturization. Also, regarding the configuration and operation of the charge-discharge control circuit 850 shown in FIG. 10(B), a block diagram is shown and explained in FIG. 10(C).

[0175] 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). First, an example of the operation when power is generated by the solar cell 811 due to external light will be described.

[0176] 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 to the voltage required for the display unit 802. When the display unit 802 is not performing display, SW1 can be turned off and SW2 can be turned on to charge the battery 851. 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 to the voltage required for the display unit 802. When the display unit 802 is not performing display, SW1 can be turned off and SW2 can be turned on to charge the battery 851. 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 to the voltage required for the display unit 802. When the display unit 802 is not performing display, SW1 can be turned off and SW2 can be turned on to charge the battery 851. 811 is used, the switch SW1 is turned on, and the converter 853 steps up or down to the voltage required for the display unit 802. When the display unit 802 is not performing display, SW1 is turned off and SW2 is turned on to charge the battery 851. When the display unit 802 is not performing display, SW1 is turned off and SW2 is turned on to charge the battery 851. When the display unit 802 is not performing display, SW1 is turned off and SW2 is turned on to charge the battery 851.

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

[0178] Also, 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 control battery can be charged by external power supply by plug-in technology or non-contact power feeding. In addition, when 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 operation information (acceleration, deceleration, stop, etc.) of the driver of the electric vehicle 860 and information during driving (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 drive 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 improving 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, thereby improving fuel efficiency.

[0184] Of course, if a 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 the degree of oxidation, expressed as O / C) was 0.547.) was used as a raw material to prepare a cell incorporating a positive electrode having a conductive aid, and the charge-discharge characteristics were compared with those of a cell incorporating a positive electrode having RGO (Reduced Graphene Oxide), which is considered to have a very low degree of oxidation, or graphene as a conductive aid. Furthermore, the charge-discharge characteristics were also compared with those of a cell incorporating a conventional positive electrode using acetylene black (AB) as a conductive aid.

[0188] (Preparation of Positive Electrode with Conductive Aid Using Graphene Oxide as Raw Material) A positive electrode was prepared using graphene oxide with O / C = 0.547. The positive electrode was prepared by mixing positive electrode active material (lithium iron phosphate (LiFePO4) particles), a binder (polyvinylidene fluoride (PVDF), manufactured by Kureha Chemical Co., Ltd.), and graphene oxide as a conductive aid to prepare a positive electrode paste, applying the positive electrode paste to a current collector (aluminum), and drying and reducing it. The mixing ratio of the positive electrode paste during preparation (LiFePO4: conductive aid (graphene oxide) :PVDF) was 93:2:5 (unit wt%).

[0189] (Preparation of Positive Electrode with RGO as Conductive Aid) RGO (Reduced Graphene Oxide) refers to graphene obtained by pre-reducing graphene oxide in this specification, and it has already been reduced at the time of dispersing it in a dispersion medium. Therefore, it is considered that functional groups such as epoxy groups have almost disappeared due to the reduction reaction. RGO was prepared by reducing graphene oxide prepared by the method described in Embodiment 1 by heat treatment in which it was held in a vacuum for 1 hour and then heated to 170 °C and held for 10 hours. It was fabricated. It is considered that in RGO, functional groups such as epoxy groups on the surface 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 of the positive electrode active material layer (LiFePO4: conductive aid (RGO): PVDF) was 94:1 :5. (Fabrication of Positive Electrode with Graphene as Conductive Aid) Graphene used was that manufactured by Graphene Supermarket. The graphene had a specific surface area of 600 m / g, a flake size of about 10 μm, a thickness of 1 nm or less, and an O / C of 0.02. Similar to the above RGO, graphene also has extremely few bonding functional groups 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 aid ( graphene): PVDF) being 94:1:5 and 90:5:5. 2

[0191]

[0192] (Fabrication of Positive Electrode with Acetylene Black as Conductive Aid) Powdery acetylene black (AB) used was that manufactured by Denki Kagaku Kogyo Co., Ltd. It had a specific surface area of 6 8 m 2 / g and an average particle size of 35 nm. The mixing ratio of the positive electrode active material layer (LiFePO4: conductive aid (AB): PVDF) 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 blk 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. The results were obtained.

[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. On the other hand, 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 for the positive electrode, respectively, and incorporated 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 referred to as Cell D, the cell using RGO is referred to as Cell E, the cell using 1% graphene in the mixing ratio is referred to as Cell F, the cell using 5% graphene in the mixing ratio is referred to as Cell G, and the cell using AB is referred to as Cell H. The charging 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 in the 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 in the mixing ratio as the conductive aid and the conventional acetylene black for the positive electrode, the measurement was carried out.

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

[0197] For the positive electrode of, In cell H with acetylene black as the conductive aid, battery characteristics were confirmed. Combined with cell D using a conductive aid made from the oxidized graphene according to the present invention, the charge-discharge characteristics are shown in FIG. 12.

[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 oxidized graphene. In contrast, the thin line is the curve showing the charge-discharge characteristics of cell G with 5% graphene added as the 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 is narrow in the discharge curve 902a and the charge curve 902b, and the discharge capacity is 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 the conductive aid, it does not become a cell with good charge-discharge characteristics. In contrast, in the positive electrode prepared by dispersing oxidized graphene having functional groups bonded by an oxidation reaction in a dispersion medium, it became a cell showing good charge-discharge characteristics. From this, oxidized graphene 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 electron conductivity is formed by the graphene. On the other hand, in the positive electrode active material layer prepared by dispersing RGO or graphene having almost no functional groups in the positive electrode paste, it is considered that an electron conductive network is not sufficiently formed. Therefore, it has been found that using graphene oxide having functional groups as a raw material for the conductive aid is important for expressing high electron conductivity of the positive electrode active material layer. Thus, it is considered that a network with high electron conductivity is formed by the graphene. On the other hand, in the positive electrode active material layer prepared by dispersing RGO or graphene having almost no functional groups in the positive electrode paste, it is considered that an electron conductive network is not sufficiently formed. Therefore, it has been found that using graphene oxide having functional groups as a raw material for the conductive aid is important for expressing high electron conductivity of the positive electrode active material layer. Next, an experiment was conducted to confirm the charge-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). (Fabrication of positive electrode) First, in order to confirm the charge-discharge characteristics of the secondary battery due to differences in the oxidation degree of graphene oxide used, three types of positive electrodes, sample A, sample B, and sample C, were fabricated using graphene oxides with different oxidation degrees. In this example, in order to confirm the differences in the charge-discharge characteristics of the secondary battery due to differences in the oxidation degree of graphene oxide, it was necessary to prepare graphene oxide with varying 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 oxides with different oxidation degrees can be fabricated.

Examples

[0203] Next, an experiment was conducted to confirm the charge-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). (Fabrication of positive electrode)

[0204] First, in order to confirm the charge-discharge characteristics of the secondary battery due to differences in the oxidation degree of graphene oxide used, three types of positive electrodes, sample A, sample B, and sample C, were fabricated using graphene oxides with different oxidation degrees. In this example, in order to confirm the differences in the charge-discharge characteristics of the secondary battery due to differences in the oxidation degree of graphene oxide, it was necessary to prepare graphene oxide with varying 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 oxides with different oxidation degrees can be fabricated. In this example, in order to confirm the differences in the charge-discharge characteristics of the secondary battery due to differences in the oxidation degree of graphene oxide, it was necessary to prepare graphene oxide with varying 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 oxides with different oxidation degrees can be fabricated. Three types of positive electrodes, sample A, sample B, and sample C, were fabricated using graphene oxides with different oxidation degrees.

[0205] In this example, in order to confirm the differences in the charge-discharge characteristics of the secondary battery due to differences in the oxidation degree of graphene oxide, it was necessary to prepare graphene oxide with varying 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 oxides with different oxidation degrees can be fabricated. In this example, in order to confirm the differences in the charge-discharge characteristics of the secondary battery due to differences in the oxidation degree of graphene oxide, it was necessary to prepare graphene oxide with varying 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 oxides with different oxidation degrees can be fabricated. In this example, in order to confirm the differences in the charge-discharge characteristics of the secondary battery due to differences in the oxidation degree of graphene oxide, it was necessary to prepare graphene oxide with varying 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 oxides with different oxidation degrees can be fabricated. In this example, in order to confirm the differences in the charge-discharge characteristics of the secondary battery due to differences in the oxidation degree of graphene oxide, it was necessary to prepare graphene oxide with varying 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 oxides with different oxidation degrees can be fabricated. In this example, in order to confirm the differences in the charge-discharge characteristics of the secondary battery due to differences in the oxidation degree of graphene oxide, it was necessary to prepare graphene oxide with varying 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 oxides with different oxidation degrees can be fabricated. In this example, in order to confirm the differences in the charge-discharge characteristics of the secondary battery due to differences in the oxidation degree of graphene oxide, it was necessary to prepare graphene oxide with varying 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 oxides with different oxidation degrees can be fabricated.

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

[0207] Regarding 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: X-ray Photoelectron Spectroscopy). The measurement was performed 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 each of Sample A, Sample B, and Sample C, and the weight ratio of oxygen to carbon (or degree of oxidation, expressed 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 according to 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 tended 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 in 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, preliminary firing was carried out 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. After adding PVDF as a binder to the mixture of graphene oxide and lithium iron phosphate, further NMP was added as a dispersion medium and kneaded to prepare a positive electrode paste.

[0216] 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 to 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 approximately lithium iron phosphate: graphene: PVDF = 94:1:5 due to 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, anchor coating was performed on the surface of the current collector for all 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.

[0218] (Charge-discharge characteristics) The positive electrodes of Sample A, Sample B, and Sample C prepared as described above were incorporated into half-cells, and the charge-discharge characteristics of each cell were measured as Cell A , Cell B, and Cell C. 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 with an upper limit voltage of 4.3 V. Discharging was performed by CC for all rates of 0.2C, 1C, 2C, 5C, and 10C, and the lower limit voltage was 2 V.

[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. For each, 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 increased by using graphene oxide having a functional group, the positive electrode active material layer prepared using graphene oxide as a raw material of the conductive assistant Observation was carried out by SEM (Scanning Electron Microscope). In addition, 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 throughout. 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 are aggregated in units of several or dozens. Also, 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 and observing 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. Also, the part of graphene 1002 that is not in contact with the positive electrode active material 1001 is stretched, bent, or forms wrinkles. Moreover, graphene 1002 is not only present 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 of 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 stringy 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, it may be connected by few-layer graphene that is not observed in the SEM image. 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 adhered to the surface of the positive electrode active material. Some of the graphene in the SEM image of FIG. 16(A) are emphasized and shown by thick lines in FIG. 16(B). In both FIGS. 16(B) and 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 graphene 1002 is also in surface contact with each other. Therefore, it is confirmed that inside the positive electrode active material layer, graphene is connected to each other to 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 formulation 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 is also in surface contact with each other. Even with a formulation ratio of 0.6 wt%, it was confirmed that the graphene is 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 formulation of graphene oxide is different, the graphene oxide in the positive electrode active material layer is similarly three-dimensionally dispersed and can form an electron conduction network.

[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 a magnified 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 dark-colored parts confirmed as dot-like 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. For this reason, 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 was performed to confirm the composition of the positive electrode active material layer after fabricating the positive electrode. ​​​​​​​​​​ Analysis was performed.

[0237] The analysis was carried out 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.

[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 washed after being immersed in an electrolyte once. The immersed electrolyte is a mixed solution in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 1:1, and lithium hexafluorophosphate (LiPF6) is dissolved at a concentration of 1 mol / l. Also, the washing for removing lithium salts was performed using DEC. When producing positive electrode GN1, drying for volatilizing the dispersion medium is carried out, but since it is a treatment at 80 °C for 40 minutes in an air atmosphere, graphene oxide is not reduced. in carbonate (DEC) and lithium hexafluorophosphate (LiPF6) dissolved at a concentration of 1 mol / l. The washing for removing lithium salts was performed using DEC. When producing positive electrode GN1, drying for volatilizing the dispersion medium is carried out, but since it is a treatment at 80 °C for 40 minutes in an air atmosphere, graphene oxide is not reduced. lithium hexafluorophosphate (LiPF6) dissolved at a concentration of 1 mol / l. The washing for removing lithium salts was performed using DEC. When producing positive electrode GN1, drying for volatilizing the dispersion medium is carried out, but since it is a treatment at 80 °C for 40 minutes in an air atmosphere, graphene oxide is not reduced. lithium salts was performed using DEC. When producing positive electrode GN1, drying for volatilizing the dispersion medium is carried out, but since it is a treatment at 80 °C for 40 minutes in an air atmosphere, graphene oxide is not reduced. When producing positive electrode GN1, drying for volatilizing the dispersion medium is carried out, but since it is a treatment at 80 °C for 40 minutes in an air atmosphere, graphene oxide is not reduced. in an air atmosphere, graphene oxide is not reduced.

[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 carried out by discharging at a rate of 1C until a reduction potential of 2.0 V (vs. Li / Li Li Li + ) and maintaining the potential at 2.0 V for 10 hours. was carried out.

[0240] (Positive electrode GN3) Positive electrode GN3 is an electrode that has undergone the same electrochemical reduction as positive electrode GN2, and then charged to 4.3 V at 0.2C Charged by a current and maintained the potential until the current value reached 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 subjecting graphene oxide to a thermal reduction treatment. 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) Regarding the positive electrode active material layers of the above positive electrodes GN1, GN2, GN3, and GN4, the results of X PS analysis 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, which were analyzed by waveform separation of the C1 S spectrum and shown according to the states. 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. 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

[0246] it was quantified. , 24.1 atomic% (40.5% with respect to the total state) and 27.5 atomic% c% (46.0%) and 24.6 atomic% (41.4%) were found to be contained. On the other hand, in the non-reduced positive electrode GN1, while it contains many C-O bonds (17 .1 atomic%), in the reduced positive electrodes GN2, GN3, and GN4, there are fewer (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, it is considered that the functional groups bonded to graphene oxide decreased due to the reduction treatment, so while the C=C bond increased, the C-O bond decreased.

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

[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 2 0% 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 containing the binder. For comparison, the results of XPS analysis of graphene oxide alone in powder form before and after thermal reduction are shown in Table 1. The weight ratio of the carbon bond state of powdered graphene oxide is shown in Tables 6 and 7. Table 6 shows the weight ratio of the carbon bond state of powdered graphene oxide. Table 7 shows the percentage of all binding states.

[0251] [Table 6]

[0252] [Table 7]

[0253] It can be seen that thermal reduction increases the number of C=C bonds while decreasing the number of CO bonds. [Explanation of symbols]

[0254] 100 NMP 101 Graphene or RGO 102 Graphene oxide 200 positive electrode 201 Positive electrode current collector 202 Cathode active material layer 203 Cathode active material 204 Graphene 300 Secondary battery 301 Positive electrode can 302 Anode 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 Object to be formed 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 732 Refrigerator Compartment Door for 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 DC-DC 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 step of impregnating a silicon-containing active material integrated with a current collector into a dispersion liquid in which graphene oxide is dispersed, thereby attaching graphene oxide to the surface; A step of providing conductive graphene by reducing the graphene oxide to give it conductivity; A method for producing an electrode for a secondary battery comprising the steps of:

2. a step of impregnating a silicon-containing active material integrated with a current collector into a dispersion liquid in which graphene oxide is dispersed, thereby attaching graphene oxide to the surface; and providing a sheet-like conductive graphene by reducing the graphene oxide to give it conductivity. The method for manufacturing an electrode for a secondary battery, wherein the sheet-like conductive graphene is provided so as to cover the active material.

3. In claim 1 and claim 2, The method for producing an electrode for a secondary battery, wherein the reduction is carried out by a heat treatment or an electrochemical reduction.

4. In any one of claims 1 to 3, The conductive graphene is sp ２ A method for producing a secondary battery having a carbon-carbon double bond.

5. In any one of claims 1 to 4, The method for producing an electrode for a secondary battery, wherein the conductive graphene is provided so as to be in surface contact with the active material.

6. In any one of claims 1 to 4, The active material is SiO or Mg ２ A method for producing a secondary battery electrode having Si.

7. In any one of claims 1 to 6, The method for producing a secondary battery electrode, wherein the secondary battery electrode is a non-aqueous secondary battery electrode.

8. In any one of claims 1 to 7, The method for producing an electrode for a secondary battery, wherein the conductive graphene has a side length of 50 nm or more and 100 μm or less.

9. In any one of claims 1 to 8, The method for producing an electrode for a secondary battery, wherein the conductive graphene is in surface-to-surface contact with another conductive graphene.

10. In any one of claims 1 to 9, The method for producing an electrode for a secondary battery, wherein the active material is formed on the current collector by a CVD method, a sputtering method, or a coating method.

11. In any one of claims 1 to 10, The method for manufacturing an electrode for a secondary battery, wherein the conductive graphene is formed by performing a reduction treatment on graphene oxide having a weight ratio of oxygen to carbon of 0.405 or more.

12. a step of impregnating a silicon-containing active material integrated with a current collector into a dispersion liquid in which graphene oxide is dispersed, thereby attaching graphene oxide to the surface; A step of providing conductive graphene by reducing the graphene oxide to give it conductivity; The electrode for a secondary battery is produced by the method comprising the steps of:

13. a step of impregnating a silicon-containing active material integrated with a current collector into a dispersion liquid in which graphene oxide is dispersed, thereby attaching graphene oxide to the surface; and providing a sheet-like conductive graphene obtained by reducing the graphene oxide to provide conductivity, The conductive graphene is provided so as to cover the active material.

14. In claim 12 and claim 13, The reduction is carried out by a heat treatment or an electrochemical reduction.

15. In any one of claims 12 to 14, The conductive graphene is sp ２ A secondary battery having a double bond carbon-carbon bond.

16. In any one of claims 12 to 15, The conductive graphene is provided so as to be in surface contact with the active material.

17. In any one of claims 12 to 16, The active material is SiO or Mg ２ An electrode for a secondary battery comprising Si.

18. In any one of claims 12 to 17, The secondary battery electrode is a non-aqueous secondary battery electrode.

19. In any one of claims 12 to 18, The conductive graphene has a side length of 50 nm or more and 100 μm or less.

20. In any one of claims 12 to 19, The conductive graphene is in surface contact with another conductive graphene.

21. In any one of claims 12 to 20, The active material is formed on the current collector by a CVD method, a sputtering method, or a coating method.

22. In any one of claims 12 to 21, The conductive graphene is formed by subjecting the graphene oxide having a weight ratio of oxygen to carbon of 0.405 or more to a reduction treatment.

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