JP2018110065A - Active material particle, cathode with active material particle, power storage device with cathode and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent cobalt (Co) and oxygen (O) from being discharged from a surface of a cathode active material particle in order to prevent segregation generation of cobalt to an anode or a separator, and to reduce occurrence of cracking or defect of the cathode active material particle.SOLUTION: An active material particle contains lithium, a metal element M1, a metal element M1 of one of or both II valence and IV valence, and oxygen. The metal element M1 is one or more of cobalt, manganese and nickel. The active material particle contains one or more crystallites. The active material particle includes a first region that is positioned insides, and a second region that is positioned outside of the first region. The active material particle containing more metal elements M2 in the second region than in the first region is used for a secondary battery.SELECTED DRAWING: Figure 1

Description

One embodiment of the present invention relates to an object, a method, or a manufacturing method. Or this invention relates to a process, a machine, a manufacture, or a composition (composition of matter). One embodiment of the present invention relates to a method for manufacturing a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, or an electronic device. In particular, the present invention relates to a positive electrode active material that can be used for a secondary battery, a secondary battery, and an electronic device having the secondary battery.

Note that in this specification, a power storage device refers to all elements and devices having a power storage function. For example, a storage battery (also referred to as a secondary battery) such as a lithium ion secondary battery, a lithium ion capacitor, and an electric double layer capacitor are included.

  Note that in this specification, an electronic device refers to all devices having a power storage device, and an electro-optical device having a power storage device, an information terminal device having a power storage device, and the like are all electronic devices.

Electronic devices carried by users and electronic devices worn by users have been actively developed.

An electronic device carried by the user or an electronic device worn by the user operates using a primary battery or a secondary battery, which is an example of a power storage device, as a power source. An electronic device carried by a user is desired to be used for a long time. For this purpose, a large-capacity secondary battery may be used. When a large-capacity secondary battery is built in an electronic device, the large-capacity secondary battery is large and has a problem of increasing weight. Therefore, development of a small or thin secondary battery having a large capacity that can be built in a portable electronic device is underway.

In particular, since a high voltage of 4V class can be obtained, lithium cobalt composite oxide (LiCoO ₂ ) is widely used as a positive electrode active material for secondary batteries. Patent Document 1 discloses plate-like particles of a positive electrode active material.

High-power, high-capacity lithium-ion secondary batteries can be used for portable information terminals such as mobile phones, smartphones or notebook computers, portable music players, digital cameras, medical devices, hybrid vehicles (HEV), electric vehicles ( EV), or next-generation clean energy vehicles such as plug-in hybrid vehicles (PHEV), and the demand for them rapidly expands with the development of the semiconductor industry, and is essential for the modern information society as a source of rechargeable energy It has become a thing.

Lithium ion secondary batteries have a drawback that they are deteriorated by repeated charge / discharge cycles, and become smaller than the initial battery discharge capacity. Further, depending on the lithium ion secondary battery, there is a risk of ignition during use of a device incorporating the lithium ion secondary battery or rapid charging, and safety is also a problem. If there are many problems that could lead to ignition, not only the secondary battery but also the device equipped with the secondary battery will be collected, leading to enormous collection costs and a decline in the brand. The damage to the manufacturing company is significant.

WO2010 / 074303

Lithium ion secondary batteries and positive electrode active materials used therefor still have room for improvement in various aspects such as cycle characteristics, capacity, charge / discharge characteristics, reliability, safety, or cost.

Observation of particles (lithium cobalt composite oxide (LiCoO ₂ )), which is a positive electrode active material, to identify the cause of deterioration of lithium ion secondary batteries, confirmed multiple cracks (including cracks and cracks) in the particles It was done. In addition to the cracks that can be observed with SEM photographs, it is considered that the particles contain many defects.

The present inventors may release or dissolve cobalt (Co), oxygen (O), or cobalt oxide (Co + O) into the electrolyte from the surface of the particle, mainly from a plurality of cracks and defects in the particle. It is estimated that this is one of the causes of deterioration of lithium ion secondary batteries.

Furthermore, it has also been observed that cobalt released or dissolved into the electrolyte is segregated on the negative electrode and the segregated material is growing. It has also been observed that cobalt is segregated inside the separator.

Based on these circumstances, in order to prevent the occurrence of segregation of cobalt on the negative electrode and separator, it is necessary to prevent the release of cobalt (Co) and oxygen (O) from the surface of the positive electrode active material particles. It is important to reduce the occurrence of cracks and defects.

An object of one embodiment of the present invention is to provide an active material which is not deteriorated in a charge / discharge cycle by being used for a lithium ion secondary battery. Another object of one embodiment of the present invention is to provide a high-capacity secondary battery. Another object of one embodiment of the present invention is to provide a secondary battery with excellent charge and discharge characteristics. Another object of one embodiment of the present invention is to provide a secondary battery with high safety or reliability.

Another object of one embodiment of the present invention is to provide a novel material, an active material, a power storage device, or a manufacturing method thereof.

Note that the description of these problems does not disturb the existence of other problems. Note that one embodiment of the present invention does not have to solve all of these problems. It should be noted that other issues can be extracted from the description, drawings, and claims.

In order to achieve the above object, one embodiment of the present invention includes a current collector and an active material layer over the current collector, and the active material layer includes a plurality of active material particles in contact with the current collector. The active material particles include lithium, metal element M1, one or both of metal elements M2 of II and IV, and oxygen, and metal atom M1 is one or more of cobalt, manganese, and nickel, The particles have one or more crystallites, and the active material particles have a first region located inside and a second region located outside the first region, and the second region Is a positive electrode characterized by containing more metal element M2 than in the first region.

In the above structure, the metal element M2 is one or more of magnesium, calcium, silicon, and titanium. Alternatively, the metal element M2 is magnesium, calcium, and titanium. II-valent and IV-valent metal oxides, specifically magnesium oxide (MgO _x ), calcium oxide (CaO _x ), silicon oxide (SiO _x ), etc. segregate in the vicinity of the surface of the active material particles. Prevents the release of cobalt or oxygen. In this specification and the like, segregation refers to a phenomenon in which a certain element (for example, B) is unevenly distributed in a solid composed of a plurality of elements (for example, A, B, and C). By preventing the elution of cobalt or oxygen into the electrolytic solution, an active material that does not deteriorate in the charge / discharge cycle can be provided.

In the above structure, the second region may further include fluorine. In addition, the presence of fluorine in the positive electrode active material particles may improve the corrosion resistance against hydrofluoric acid generated by the decomposition of the electrolytic solution.

In the above structure, the crystallite size measured by X-ray diffraction (XRD) analysis is 0.5 μm or more, preferably 1 μm or more.

In the above configuration, the size of the active material particles to be measured is 1 μm or more and 50 μm or less. The particle size refers to D50 (also referred to as median diameter).

According to another aspect of the invention, there is provided a secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, the positive electrode having a current collector and an active material layer on the current collector. The active material layer has a plurality of active material particles in contact with the current collector, and the active material particles include lithium, one or both of the metal element M1, the metal element M2, the metal element M2, and the metal element M2, and oxygen. The atom M1 is one or more of cobalt, manganese, and nickel, the active material particles have one or more crystallites, and the active material particles include a first region and a first region located inside. And the second region contains more metal element M2 than the first region, and the secondary battery has a capacity after repeated charging and discharging for 100 cycles. 78% or more of the initial capacity.

According to another aspect of the invention, there is provided a secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, the positive electrode having a current collector and an active material layer on the current collector. The active material layer has a plurality of active material particles in contact with the current collector, and the active material particles include lithium, one or both of the metal element M1, the metal element M2, the metal element M2, and the metal element M2, and oxygen. The atom M1 is one or more of cobalt, manganese, and nickel, the active material particles have one or more crystallites, and the active material particles include a first region and a first region located inside. And the second region contains more metal element M2 than the first region, and the secondary battery is repeatedly charged and discharged in a range of 10 cycles or more and 30 cycles or less. The capacity after carrying out is 98% or more of the initial capacity.

Further, according to another aspect of the invention relating to the manufacturing method, a first active material particle having a defect is coated with one or both of the II-valent and IV-valent metal elements M2 using a sol-gel method. A first step of forming the second active material particles, a second step of heat-treating the second active material particles to obtain the third active material particles, and a slurry containing the third active material particles. And a third step of coating on the current collector, wherein a defect contained in the first active material particles is repaired in the second step.

In the above manufacturing method, the size of the crystallite included in the third active material particle is larger than the crystallite included in the first active material particle.

In the above manufacturing method, the size of the crystallites included in the third active material particles is twice or more that of the crystallites included in the first active material particles.

In the above manufacturing method, the size of the crystallite is measured by XRD analysis.

In the above manufacturing method, the second step is performed in an atmosphere containing oxygen at 600 ° C to 1000 ° C. By heating at 600 ° C. or more and 1000 ° C. or less, cracks and defects of the particles can be reduced, the surface of the particles can be made smooth, and the surface area can be reduced. By reducing the surface area and making it stable in terms of energy, a secondary battery with high safety or reliability can be realized.

In the manufacturing method, the first active material particle contains lithium, the metal element M1, and oxygen, and the metal atom M1 is one or more of cobalt, manganese, and nickel.

In this specification and the like, the layered rock salt type crystal structure of the composite oxide containing lithium and the metal element M1 has a rock salt type ion arrangement in which cations and anions are arranged alternately, and the metal element M1 and This refers to a crystal structure in which lithium can be two-dimensionally diffused because lithium is regularly arranged to form a two-dimensional plane. There may be defects such as cation or anion defects. Strictly speaking, the layered rock salt crystal structure may be a structure in which the lattice of the rock salt crystal is distorted.

In this specification and the like, the rock salt type crystal structure refers to a structure in which cations and anions are alternately arranged. There may be a cation or anion deficiency.

By reducing the size of cracks in the active material particles and reducing the number of cracks and defects so that cobalt and oxygen do not elute into the electrolyte, the stability of the crystal structure in the active material particles can be further improved. And charge / discharge cycle characteristics are further improved.

Further, a secondary battery with high safety or reliability can be provided. In addition, a novel material, an active material, a power storage device, or a manufacturing method thereof can be provided.

Note that the description of these effects does not disturb the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. It should be noted that the effects other than these are naturally obvious from the description of the specification, drawings, claims, etc., and it is possible to extract the other effects from the descriptions of the specification, drawings, claims, etc. It is.

2A and 2B are a perspective view and a cross-sectional view of particles showing one embodiment of the present invention. It is a conceptual diagram which shows the change of the crystallite before and behind the process which shows one aspect | mode of this invention, and a crack. It is a SEM photograph which shows one aspect | mode of this invention. FIG. 6 is a diagram illustrating a material which represents one embodiment of the present invention. FIG. 5 is a diagram illustrating a process illustrating one embodiment of the present invention. It is a figure which shows the process flow which shows 1 aspect of this invention. The figure explaining a coin-type secondary battery. The figure explaining the charging method of a secondary battery. The figure explaining the charging method of a secondary battery. The figure explaining the discharge method of a secondary battery. Sectional drawing of an active material layer at the time of using a graphene compound as a conductive support agent. The figure explaining a cylindrical secondary battery. The figure explaining a secondary battery. The figure explaining a secondary battery. The figure explaining a secondary battery. The figure explaining a secondary battery. 10A and 10B each illustrate an example of an electronic device. 10A and 10B each illustrate an example of an electronic device. 10A and 10B each illustrate an example of an electronic device. The figure explaining the crystal structure of lithium cobaltate. 3 is a graph showing cycle characteristics of a secondary battery using the positive electrode active material of Example 1. 3 is a graph showing rate characteristics of a secondary battery using the positive electrode active material of Example 1. 3 is a graph showing cycle characteristics of a secondary battery using the positive electrode active material of Example 1.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that modes and details can be variously changed. In addition, the present invention is not construed as being limited to the description of the embodiments below.

(Embodiment 1)
FIG. 1A1 illustrates an example of a perspective view of an active material particle 110 having a plurality of cracks 105. Note that FIG. 1A2 is a cross-sectional view in which the cross section is cut along a dotted line 160 in FIG. The active material particles 110 are composite oxide particles containing lithium, the metal element M1, and oxygen. As the metal element M1, one or more of cobalt, manganese, and nickel can be applied.

In the particle 110, a plurality of crystallites can be confirmed in one particle, and the cross section has a crack 105 as illustrated in FIG. Note that an SEM photograph corresponding to FIG. 1A1 is illustrated in FIG. The active material particles 110 shown in FIG. 1 (A1) are untreated, and when the secondary battery is produced as it is for the positive electrode active material layer and the cycle characteristics are measured, the deterioration proceeds and the metal element M1, for example, cobalt Precipitates in the negative electrode and separator.

In order to prevent elution of cobalt or oxygen from the surfaces of active material particles 110 shown in FIG. 1A1, particularly from cracks, a high temperature (600 ° C. or higher) is applied in an oxygen-containing atmosphere. Heat treatment at 1000 ° C. or lower). The heat treatment may be referred to as annealing. As the metal element M2, one or both metals of II value and IV value are applied. Specifically, one or more of magnesium, calcium, silicon, and titanium can be applied. As a coating method, a sol-gel method using an alkoxide of the metal element M2 can be applied.

In the case of applying Ti as the metal element M2, after performing a sol-gel method using a Ti alkoxide, heat treatment is performed at a high temperature (600 ° C. to 1000 ° C.) in an atmosphere containing oxygen. By performing heat treatment together with a sol-gel method using Ti alkoxide, one or both of the metal elements M2 having a valence of II and IV are moved to the vicinity of the surface to prevent elution of cobalt or oxygen. Furthermore, by performing heat treatment after the sol-gel method using Ti, the surface of the active material particles can be smoothed, the surface area can be reduced, and a stable state can be achieved.

In the sol-gel method, an alkoxide of the metal element M2 or the like enters a crack in the active material particle 110, and the crack is repaired by heat treatment. If the temperature of the heat treatment is low, cracks are difficult to repair, and if the temperature is too high, many oxygen vacancies are formed, resulting in a loss of function as the positive electrode active material. Further, if the heating temperature is too high, lithium may be evaporated.

In the case of composite oxide particles containing lithium, the metal element M1, and oxygen, for example, lithium cobalt composite oxide (LiCoO ₂ ), the mass transfer is particularly facilitated because the particles have oxygen vacancies. Therefore, titanium oxide coated by the sol-gel method is easy to repair cracks. A titanium compound obtained by reacting with titanium oxide and LiCoO ₂ is preferable because it has conductivity and does not prevent lithium diffusion. Similarly, coating with a metal alkoxide that becomes a non-stoichiometric oxide or an aqueous metal salt solution of an organic acid is preferable because of electrical conductivity and lithium ion conductivity.

Even a small crack at the end of the particle causes a large crack due to stress concentration. Therefore, the sol-gel method and heat treatment in which the small crack is also repaired are important.

A perspective view of the active material particles 100 after treatment is shown in FIG. Further, FIG. 1B2 shows a cross-sectional view of the processed active material particles when the cross-section is cut along a dotted line 150.

As shown in FIG. 1 (B2), the cracks disappear after the treatment, the crystallites partially grow, and the number of crystallites in the active material particles decreases.

FIG. 2 shows an example of a model diagram of changes in crystallites in the active material particles before and after the treatment. FIG. 2 shows four types of examples.

There are several possible patterns of crystallite changes due to treatment. An example of the change of the crystallite will be described with reference to FIG.

First, FIG. 2A1 illustrates an example in which cracks 105 are generated between different crystallites in the particle 110. FIG. 2A2 illustrates the particle 100 after the above-described treatment is performed on the particle 110 illustrated in FIG. By performing the treatment, the crack 105 is repaired, and different crystallites may become one crystallite.

Next, FIG. 2B1 is an example in which a large number of small cracks 105 are generated in one crystallite in the particle 110. FIG. 2B2 shows the particle 100 after the above-described treatment is performed on the particle 110 in FIG. By performing the treatment, it is conceivable that a large number of cracks 105 are repaired and crystallites without defects are formed.

Next, FIG. 2C1 illustrates an example in which a crack 105 is generated in one crystallite in the particle 110. FIG. 2C2 illustrates the particle 100 after the above-described treatment is performed on the particle 110 illustrated in FIG. By performing the treatment, the crack 105 may be repaired and become a crystallite having no defect.

Next, FIG. 2D1 illustrates an example in which the crystal axes of adjacent crystallites in the particle 110 are different. FIG. 2D2 illustrates the particle 100 after the above-described treatment is performed on the particle 110 illustrated in FIG. It can be considered that adjacent crystallites become one crystallite by performing the treatment. However, it is preferable that adjacent crystallites have the same cubic close-packed structure of oxygen.

In addition, magnesium oxide (MgO _X (0 <X)), calcium oxide (CaO _X (0 <X)), silicon oxide (SiO _X (0 <X)), or the like is formed in the second region outside by heat treatment. Segregate. With such a configuration, cracks are unlikely to occur, and cobalt or oxygen in the active material particles does not flow into the electrolyte.

In addition, the SEM photograph of the several active material particle after a process is shown in FIG.3 (B).

The treated active material particle 100 has a structure in which the number of cracks and defects is reduced so that cobalt and oxygen do not elute into the electrolyte, and the stability of the crystal structure in the active material particle is improved. The characteristics are further improved. Further, the treated active material particles 100 are a new material and can be called a new positive electrode active material.

By using the treated active material particles 100 for the positive electrode active material layer, a secondary battery with high safety or reliability can be provided.

(Embodiment 2)
As a method for coating the active material particles 110 having cracks described in Embodiment 1, a liquid phase method including a sol-gel method, a solid phase method, a sputtering method, a vapor deposition method, a CVD (chemical vapor deposition) method, A method such as a PLD (pulse laser deposition) method can be applied.

In this embodiment mode, a sol-gel method that can be expected to be uniformly coated and can be processed at atmospheric pressure is applied. A manufacturing method thereof will be described with reference to FIGS. 4, 5, and 6.

<Sol-gel method>
First, the alkoxide of the metal element M2 is dissolved in alcohol. As the metal of the alkoxide of the metal element M2, one or both of the above-described II-valent and IV-valent metals, specifically, magnesium, calcium, silicon, and titanium can be used. Furthermore, as M2, various elements such as an alkali metal element, an alkaline earth metal element, an alkali metal element and a typical metal element other than the alkaline earth metal element Italy, and a transition metal element may be used.

Examples of the alkali metal element include Li, Na, K, Rb, Cs, and Fr. Examples of the alkaline earth metal element include Be, Mg, Ca, Sr, Ba, and Ra. The alkali metal element and the alkaline earth element. Typical metal elements other than the similar metal element Italy include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, and Au are listed, and transition metal elements include Al, Zn, Ga, Ge, Cd, In, Sn, Sb, Hg, TI, Pb, Bi, and Po. It is done.

FIG. 4A-1 illustrates a general formula of the alkoxide of the metal element M2. In the formula of FIG. 4A-1, M2 represents an IV valent metal element, and R may be the same or different. Each R independently represents an alkyl group having 1 to 18 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 13 carbon atoms. Examples of the alkyl group having 1 to 18 carbon atoms include a straight chain alkyl group such as a methyl group, an ethyl group, a propyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, an octadecyl group, an isopropyl group, an isobutyl group, t Specific examples of the aryl group having 6 to 13 carbon atoms include a phenyl group, a naphthyl group, a biphenyl group, and a fluorenyl group. Note that R is not limited to the above.

FIG. 4A-2 shows a general formula of titanium alkoxide using titanium as M2 in FIG. 4A-1. Specific examples of titanium alkoxide include tetramethoxy titanium, tetraethoxy titanium, tetra-n-propoxy titanium, tetra-i-propoxy titanium ((A-3) in FIG. 4) (tetraisopropyl orthotitanate, titanium isopropoxide, Titanium). and tetra-n-butoxy titanium, tetra-i-butoxy titanium, tetra-sec-butoxy titanium, tetra-t-butoxy titanium, and the like.

As the solvent for dissolving the alkoxide of the metal element M2, alcohols are preferable, and primary alcohols or secondary alcohols are particularly preferable because of high solubility of the metal alkoxide. For example, methanol, ethanol, propanol, 2-propanol, butanol, 2-butanol and the like can be used.

Next, composite oxide particles (active material particles 110 shown in Embodiment Mode 1) containing lithium and the metal element M1 are added to an alcohol solution of the alkoxide of the metal element M2, and stirred. By adding water (H ₂ O) here, hydrolysis reaction of water and titanium alkoxide occurs as shown in FIG. At the same time, an acid or a base may be added as a catalyst. Further, a similar hydrolysis reaction occurs when an alcohol solution of the alkoxide of the metal element M2 is placed in an atmosphere containing water and stirred.

Further, following the hydrolysis reaction of FIG. 4B, a dehydration condensation reaction of FIG. 4C occurs. By repeating the hydrolysis shown in FIG. 4B and the condensation reaction shown in FIG. 4C, a sol of the oxide of the metal element M2 is generated, and further the reaction proceeds, whereby the oxide of the metal element M2 is produced. Yields a gel.

Here, it is known that a hydroxyl group (OH group) exists on the particle surface of the composite oxide containing lithium and the metal element M1. As shown in FIGS. 4D-1 and 4D-2, the hydroxyl group on the particle surface of the composite oxide containing lithium and the metal element M1 is changed from the alkoxide of the metal element M2 shown in FIG. An oxide of a metal (M2) different from M1 on particles containing the metal (M1) oxide by causing a dehydration condensation reaction shown in FIG. 4C with the hydroxyl group of the metal (M2) generated by hydrolysis. A sol or gel containing is formed.

Thereafter, the particles 111 are collected by filtration and the solvent is removed, whereby the material having the metal element M2 can be coated on the composite oxide particles having the lithium and the metal element M1.

More specifically, a method of coating the particles 111 with titanium oxide using a sol-gel method and then obtaining the active material particles 100 will be described with reference to FIGS.

<Mixing of Metal Alkoxide Solution and Particle 111 (S14 in FIG. 6)>
First, TTIP171 is dissolved in isopropanol 170, and the particles 111 are mixed therein (see FIG. 5A).

<Coating of Particle 111 with Titanium Oxide by Sol-Gel Method (S15 in FIG. 6)>
The solution shown in FIG. 5 (A) is stirred for 4 hours under conditions of 25 ° C. and humidity 90% RH. By this treatment, the particles 111 are coated with the TiO _x sol 172 by utilizing hydrolysis and dehydration polycondensation reactions that occur on the surface of the particles 111 with water and TTIP in the atmosphere (see FIG. 5B). The reaction further proceeds to generate a TiO _x gel on the particle surface.

<Recovery of Particle 111 Covered with TiO _x Gel (S16 in FIG. 6)>
In FIG. 6, the mixed solution after the processing of S <b> 15 is filtered to collect the residue.

<Drying of TiOx gel (S17 in FIG. 6)>
In FIG. 6, the residue collected by the process of S16 is vacuum-dried at 70 ° C. for 1 hour to obtain a powder. Here, the particles 111 are covered with a dry gel 173 containing a Ti oxide (see FIG. 5C).

<Drying of TiOx gel (S18 in FIG. 6)>
In FIG. 6, the powder obtained by the process of S17 is heated at 800 ° C. (temperature increase 200 ° C./hour), holding time 2 hours, and the flow rate of the atmosphere containing oxygen is 10 L / min. Obtained (see FIG. 5D).

In this embodiment, an example in which a titanium alkoxide is used as the alkoxide of the metal element M2 has been described, but the present invention is not particularly limited, and another metal alkoxide may be used. Further, the heating conditions are not particularly limited, and a plurality of temperature raising conditions and heat treatment times may be performed. Moreover, the slow cooling conditions after heating are not particularly limited, and the temperature lowering conditions may be adjusted as appropriate.

Note that this embodiment can be freely combined with any of the other embodiments.

(Embodiment 3)
In this embodiment, an example of the shape of a secondary battery including the active material particles 100 functioning as the positive electrode active material described in the above embodiment will be described. The description of the above embodiment can be referred to for materials used for the secondary battery described in this embodiment.

[Coin-type secondary battery]
First, an example of a coin-type secondary battery will be described. FIG. 7A is an external view of a coin-type (single-layer flat type) secondary battery, and FIG. 7B is a cross-sectional view thereof.

In the coin-type secondary battery 300, a positive electrode can 301 also serving as a positive electrode terminal and a negative electrode can 302 also serving as a negative electrode terminal are insulated and sealed with a gasket 303 formed 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 so as to be in contact therewith. The negative electrode 307 is formed of a negative electrode current collector 308 and a negative electrode active material layer 309 provided so as to be in contact therewith.

Note that each of the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 may have an active material layer formed only on one side.

For the positive electrode can 301 and the negative electrode can 302, a metal such as nickel, aluminum, titanium, or the like having corrosion resistance to the electrolytic solution, or an alloy thereof or an alloy of these with another metal (for example, stainless steel) is used. it can. In order to prevent corrosion due to the electrolytic solution, it is preferable to coat nickel, aluminum, or the like. The positive electrode can 301 and the negative electrode can 302 are electrically connected to the positive electrode 304 and the negative electrode 307, respectively.

The negative electrode 307, the positive electrode 304, and the separator 310 are impregnated in an electrolyte, and the positive electrode 304, the separator 310, the negative electrode 307, and the negative electrode can 302 are laminated in this order with the positive electrode can 301 facing down, as shown in FIG. 7B. Then, the positive electrode can 301 and the negative electrode can 302 are pressure-bonded via a gasket 303 to manufacture a coin-shaped secondary battery 300.

By using the active material particles 100 functioning as the positive electrode active material described in the above embodiment for the positive electrode 304, the coin-type secondary battery 300 having excellent cycle characteristics can be obtained.

Here, the flow of current when the secondary battery is charged will be described with reference to FIG. When a secondary battery using lithium is regarded as one closed circuit, the movement of lithium ions and the flow of current are in the same direction. In addition, in the secondary battery using lithium, the anode (anode) and the cathode (cathode) are interchanged by charging and discharging, and the oxidation reaction and the reduction reaction are interchanged. Therefore, the electrode having a high reaction potential is called the positive electrode. An electrode having a low reaction potential is called a negative electrode. Therefore, in the present specification, the positive electrode is referred to as “positive electrode” or “whether the battery is being charged, discharged, a reverse pulse current is applied, or a charge current is applied. The positive electrode is referred to as a “positive electrode”, and the negative electrode is referred to as a “negative electrode” or a “− electrode (negative electrode)”. If the terms anode (anode) and cathode (cathode) related to the oxidation reaction or reduction reaction are used, the charge and discharge are reversed, which may cause confusion. Therefore, the terms anode (anode) and cathode (cathode) are not used in this specification. If the terms anode (anode) or cathode (cathode) are used, specify whether charging or discharging, and indicate whether it corresponds to the positive electrode (positive electrode) or the negative electrode (negative electrode). To do.

A charger is connected to the two terminals illustrated in FIG. 7C, and the secondary battery 300 is charged. As charging of the secondary battery 300 proceeds, the potential difference between the electrodes increases. In FIG. 7F, the secondary battery 300 flows from an external terminal toward the positive electrode 304, and in the secondary battery 300, flows from the positive electrode 304 toward the negative electrode current collector 308, and from the negative electrode to the secondary battery. The direction of current flowing toward the external terminal 300 is a positive direction. That is, the direction in which the charging current flows is the current direction.

[Charging / discharging method]
The secondary battery can be charged and discharged as follows, for example.

≪CC charge≫
First, CC charging will be described as one of charging methods. CC charging is a charging method in which a constant current is supplied to the secondary battery throughout the charging period and charging is stopped when a predetermined voltage is reached. The secondary battery is assumed to be an equivalent circuit of an internal resistance R and a secondary battery capacity C as shown in FIG. In this case, the secondary battery voltage V _B is the sum of the voltage V _C applied to the voltage V _R and the secondary battery capacity C according to the internal resistance R.

During the CC charging, as shown in FIG. 8A, the switch is turned on, and a constant current I flows through the secondary battery. During this time, since a current I is constant, the Ohm's law V R _{= R} × I, a voltage V _R is also constant according to the internal resistance R. On the other hand, the voltage V _C applied to the secondary battery capacity C increases with time. Therefore, the secondary battery voltage V _B increases with time.

And when the secondary battery voltage V _B is has reached a predetermined voltage, for example 4.3 V, to stop the charging. When the CC charging is stopped, as shown in FIG. 8B, the switch is turned off and the current I = 0. Therefore, the voltage _{V R} applied to the internal resistance R becomes 0V. Therefore, the partial voltage drop at the internal resistance R is exhausted, the secondary battery voltage V _B falls.

FIG. 8C shows an example of the secondary battery voltage V _B and the charging current during the CC charging and after the CC charging is stopped. Battery voltage V _B between the had risen doing the CC charging, how to decrease slightly after stopping the CC charging is shown.

≪CCCV charge≫
Next, CCCV charging, which is a charging method different from the above, will be described. CCCV charging is a charging method in which charging is first performed up to a predetermined voltage by CC charging, and then charging is performed until the current flowing through CV (constant voltage) charging is reduced, specifically until the end current value is reached. .

During CC charging, as shown in FIG. 9A, the constant current power source switch is turned on, the constant voltage power source switch is turned off, and a constant current I flows through the secondary battery. During this time, since a current I is constant, the Ohm's law V R _{= R} × I, a voltage V _R is also constant according to the internal resistance R. On the other hand, the voltage V _C applied to the secondary battery capacity C increases with time. Therefore, the secondary battery voltage V _B increases with time.

And when the secondary battery voltage _{V B} is has reached a predetermined voltage, for example 4.3 V, switching from CC charging to CV charging. During the CV charging, as shown in FIG. 9B, the constant voltage power source switch is turned on, the constant current power source switch is turned off, and the secondary battery voltage V _B becomes constant. On the other hand, the voltage V _C applied to the secondary battery capacity C increases with time. Because it is _{V B = V R + V C} , the voltage _{V R} applied to the internal resistance R becomes smaller with time. According voltage V _R becomes smaller according to the internal resistance R, by Ohm's law of V R _{= R} × I, also decreases the current I flowing through the secondary battery.

When the current I flowing through the secondary battery becomes a predetermined current, for example, a current corresponding to 0.01 C, charging is stopped. When the CCCV charging is stopped, as shown in FIG. 9C, all the switches are turned off and the current I = 0. Therefore, the voltage _{V R} applied to the internal resistance R becomes 0V. However, since the voltage V _R applied to the internal resistance R by CV charging is sufficiently small, even run out of the voltage drop at the internal resistance R, the secondary battery voltage V _B is hardly lowered.

FIG. 9D shows an example of the secondary battery voltage V _B and the charging current during the CCCV charging and after the CCCV charging is stopped. It is shown that the secondary battery voltage V _B hardly decreases even when CCCV charging is stopped.

≪CC discharge≫
Next, CC discharge which is one of the discharge methods will be described. CC discharge, constant current in all the discharge period flowed from the secondary battery, a discharge process for stopping the discharge when the secondary battery voltage V _B is has reached a predetermined voltage, for example 2.5V.

An example of the secondary battery voltage V _B and the discharge current during CC discharge is shown in FIG. According discharge proceeds, the secondary battery voltage V _B is shown to continue to drop.

Next, the discharge rate and the charge rate will be described. The discharge rate is the relative ratio of the current during discharge to the battery capacity, and is expressed in units C. In a battery with a rated capacity X (Ah), the current corresponding to 1 C is X (A). When discharged at a current of 2X (A), it is said that it was discharged at 2C, and when discharged at a current of X / 5 (A), it was discharged at 0.2C. The charging rate is also the same. When charging with a current of 2X (A), it is said to be charged at 2C. When charging with a current of X / 5 (A), it is charged at 0.2C. It was said.

(Embodiment 4)
In this embodiment, examples of materials that can be used for the secondary battery including the active material particles 100 functioning as the positive electrode active material described in the above embodiment will be described. In this embodiment, a secondary battery in which a positive electrode, a negative electrode, and an electrolytic solution are wrapped in an exterior body will be described as an example.

[Positive electrode]
The positive electrode has a positive electrode active material layer and a positive electrode current collector.

<Positive electrode active material layer>
The positive electrode active material layer has a positive electrode active material. Moreover, the positive electrode active material layer may have a conductive support agent and a binder.

As the positive electrode active material, the active material particles 100 functioning as the positive electrode active material described in the above embodiment can be used. By using the active material particles 100 functioning as the positive electrode active material described in the above embodiment, a secondary battery with high capacity and excellent cycle characteristics can be obtained.

As the conductive assistant, a carbon material, a metal material, a conductive ceramic material, or the like can be used. Moreover, you may use a fibrous material as a conductive support agent. The content of the conductive additive relative to the total amount of the active material layer is preferably 1 wt% or more and 10 wt% or less, and more preferably 1 wt% or more and 5 wt% or less.

An electrically conductive network can be formed in the active material layer by the conductive assistant. The conductive auxiliary agent can maintain the electric conduction path between the positive electrode active materials. By adding a conductive additive in the active material layer, an active material layer having high electrical conductivity can be realized.

As the conductive assistant, for example, artificial graphite such as natural graphite or mesocarbon microbeads, carbon fiber, or the like can be used. As the carbon fibers, for example, carbon fibers such as mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers can be used. Moreover, carbon nanofiber, a carbon nanotube, etc. can be used as carbon fiber. Carbon nanotubes can be produced by, for example, a vapor phase growth method. In addition, as the conductive auxiliary agent, for example, carbon materials such as carbon black (acetylene black (AB), etc.), graphite (graphite) particles, graphene, fullerene can be used. Further, for example, metal powder such as copper, nickel, aluminum, silver, gold, metal fiber, conductive ceramic material, or the like can be used.

Further, a graphene compound may be used as a conductive auxiliary agent.

The graphene compound may have excellent electrical characteristics of having high conductivity and excellent physical characteristics of having high flexibility and high mechanical strength. The graphene compound has a planar shape. The graphene compound enables surface contact with low contact resistance. In addition, even if it is thin, the conductivity may be very high, and a conductive path can be efficiently formed in the active material layer with a small amount. Therefore, it is preferable to use a graphene compound as a conductive auxiliary because the contact area between the active material and the conductive auxiliary can be increased. Moreover, since electrical resistance may be reduced, it is preferable. Here, for example, graphene, multi-graphene, or reduced graphene oxide (hereinafter, RGO) is particularly preferably used as the graphene compound. Here, RGO refers to a compound obtained by reducing graphene oxide (GO), for example.

When an active material having a small particle size, for example, an active material having a size of 1 μm or less is used, the specific surface area of the active material is large, and more conductive paths are required to connect the active materials. Therefore, the amount of the conductive auxiliary agent tends to increase, and the amount of the active material supported tends to decrease relatively. When the carrying amount of the active material is reduced, the capacity of the secondary battery is reduced. In such a case, it is particularly preferable to use a graphene compound as a conductive additive because the graphene compound can efficiently form a conductive path even in a small amount, so that the amount of active material supported is not reduced.

Hereinafter, as an example, a cross-sectional configuration example in the case where a graphene compound is used as the conductive additive for the active material layer 200 will be described.

FIG. 11A shows a vertical cross-sectional view of the active material layer 200. The active material layer 200 includes active material particles 100, a graphene compound 201 as a conductive auxiliary agent, and a binder (not shown). Here, for example, graphene or multi-graphene may be used as the graphene compound 201. Here, the graphene compound 201 preferably has a sheet shape. Further, the graphene compound 201 may have a sheet shape in which a plurality of multi-graphenes or a plurality of graphenes are partially overlapped. Further, the graphene compound 201 may have a sheet shape in which both a plurality of multi-graphenes and a plurality of graphenes are partially overlapped.

In the longitudinal section of the active material layer 200, as shown in FIG. 11A, the sheet-like graphene compound 201 is dispersed substantially uniformly inside the active material layer 200. In FIG. 11A, the graphene compound 201 is schematically represented by a thick line, but is actually a thin film having a thickness of a single layer or multiple layers of carbon molecules. The plurality of graphene compounds 201 are formed so as to cover, cover, or stick to the surfaces of the plurality of active material particles 100, and thus are in surface contact with each other.

Here, a plurality of graphene compounds are bonded to each other, whereby a network graphene compound sheet (hereinafter referred to as graphene compound net or graphene net) can be formed. In the case where the active material is covered with graphene net, the graphene net can also function as a binder for bonding the active materials to each other. Therefore, since the amount of the binder can be reduced or not used, the ratio of the active material to the electrode volume and the electrode weight can be improved. That is, the capacity of the secondary battery can be increased.

Here, it is preferable to use graphene oxide as the graphene compound 201, mix with an active material, and form a layer to be the active material layer 200, followed by reduction. By using graphene oxide having extremely high dispersibility in a polar solvent for the formation of the graphene compound 201, the graphene compound 201 can be dispersed substantially uniformly inside the active material layer 200. In order to volatilize and remove the solvent from the dispersion medium containing the uniformly dispersed graphene oxide and reduce the graphene oxide, the graphene compounds 201 remaining in the active material layer 200 are partially overlapped and dispersed so as to be in surface contact with each other. As a result, a three-dimensional conductive path can be formed. Note that the reduction of graphene oxide may be performed by, for example, heat treatment or may be performed using a reducing agent.

Therefore, unlike a granular conductive auxiliary agent such as acetylene black that makes point contact with the active material, the graphene compound 201 enables surface contact with a low contact resistance. Electric conductivity between the particle 100 and the graphene compound 201 can be improved. Therefore, the ratio of the active material particles 100 in the active material layer 200 can be increased. Thereby, the discharge capacity of the power storage device can be increased.

As the binder, it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer. Further, fluororubber can be used as the binder.

As the binder, for example, a water-soluble polymer is preferably used. For example, polysaccharides can be used as the water-soluble polymer. As the polysaccharide, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, starch, and the like can be used. Further, it is more preferable to use these water-soluble polymers in combination with the rubber material described above.

Or as binder, polystyrene, polymethyl acrylate, polymethyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoro It is preferable to use materials such as ethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose.

A plurality of binders may be used in combination.

For example, you may use combining the material especially excellent in the viscosity adjustment effect, and another material. For example, while rubber materials and the like are excellent in adhesive strength and elastic force, viscosity adjustment may be difficult when mixed with a solvent. In such a case, for example, it is preferable to mix with a material having a particularly excellent viscosity adjusting effect. For example, a water-soluble polymer may be used as a material having a particularly excellent viscosity adjusting effect. Further, as the water-soluble polymer particularly excellent in the viscosity adjusting effect, the aforementioned polysaccharides, for example, carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose, cellulose derivatives such as regenerated cellulose, and starch are used. be able to.

It should be noted that cellulose derivatives such as carboxymethyl cellulose are improved in solubility by being made into a salt such as sodium salt or ammonium salt of carboxymethyl cellulose, and the effect as a viscosity modifier is easily exhibited. When the solubility of the electrode is increased, the dispersibility with the active material and other components can be enhanced when the slurry of the electrode is produced. In the present specification, cellulose and cellulose derivatives used as an electrode binder include salts thereof.

The water-soluble polymer can be dissolved in water to stabilize the viscosity, and other materials combined as an active material and a binder, such as styrene butadiene rubber, can be stably dispersed in an aqueous solution. Moreover, since it has a functional group, it is expected to be easily adsorbed on the surface of the active material. In addition, cellulose derivatives such as carboxymethyl cellulose, for example, have many materials having functional groups such as hydroxyl groups and carboxyl groups, and have functional groups so that polymers interact with each other and widely cover the active material surface. There is expected.

When a binder covers or covers the surface of the active material to form a film, an effect of suppressing the decomposition of the electrolytic solution by acting as a passive film is also expected. Here, the passive film is a film having no electron conductivity or a film having extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, The decomposition of the electrolytic solution can be suppressed. It is further desirable that the passive film suppresses electrical conductivity and can conduct lithium ions.

<Positive electrode current collector>
As the positive electrode current collector, a highly conductive material such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof can be used. The material used for the positive electrode current collector is preferably not eluted at the positive electrode potential. Alternatively, an aluminum alloy to which an element that improves heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, is added can be used. Alternatively, a metal element that forms silicide by reacting with silicon may be used. Examples of metal elements that react with silicon to form silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, and the like. As the current collector, a foil shape, a plate shape (sheet shape), a net shape, a punching metal shape, an expanded metal shape, or the like can be used as appropriate. As the current collector, one having a thickness of 5 μm to 30 μm may be used.

[Negative electrode]
The negative electrode has a negative electrode active material layer and a negative electrode current collector. Moreover, the negative electrode active material layer may have a conductive support agent and a binder.

<Negative electrode active material>
As the negative electrode active material, for example, an alloy-based material or a carbon-based material can be used.

As the negative electrode active material, an element capable of performing a charge / discharge reaction by an alloying / dealloying reaction with lithium can be used. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, and the like can be used. Such an element has a larger capacity than carbon. In particular, silicon has a high theoretical capacity of 4200 mAh / g. For this reason, it is preferable to use silicon for the negative electrode active material. Moreover, you may use the compound which has these elements. For example, SiO, Mg ₂ Si, Mg ₂ Ge, SnO, SnO ₂ , Mg ₂ Sn, SnS ₂ , V ₂ Sn ₃ , FeSn ₂ , CoSn ₂ , Ni ₃ Sn ₂ , Cu ₆ Sn ₅ , Ag ₃ Sn, Ag ₃ Sb, Ni ₂ MnSb, CeSb ₃ , LaSn ₃ , La ₃ Co ₂ Sn ₇ , CoSb ₃ , InSb, SbSn, and the like. Here, an element capable of performing a charge / discharge reaction by an alloying / dealloying reaction with lithium, a compound containing the element, and the like may be referred to as an alloy-based material.

In this specification and the like, SiO refers to, for example, silicon monoxide. Alternatively, SiO can be expressed as SiO _x . Here, x preferably has a value in the vicinity of 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

As the carbon-based material, graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotube, graphene, carbon black, or the like may be used.

Examples of graphite include artificial graphite and natural graphite. Examples of the artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch-based artificial graphite, and the like. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape, which is preferable. MCMB is relatively easy to reduce its surface area, and may be preferable. Examples of natural graphite include flaky graphite and spheroidized natural graphite.

Graphite exhibits a potential as low as lithium metal when lithium ions are inserted into the graphite (when a lithium-graphite intercalation compound is formed) (0.05 V or more and 0.3 V or less vs. Li ^/ Li ⁺ ). Thereby, a lithium ion secondary battery can show a high operating voltage. Further, graphite is preferable because it has advantages such as relatively high capacity per unit volume, relatively small volume expansion, low cost, and high safety compared to lithium metal.

Further, as the negative electrode active material, titanium dioxide (TiO ₂ ), lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ), lithium-graphite intercalation compound (Li _x C ₆ ), niobium pentoxide (Nb ₂ O ₅ ), oxidation An oxide such as tungsten (WO ₂ ) or molybdenum oxide (MoO ₂ ) can be used.

Further, as the anode active material, a double nitride of lithium and a transition metal, Li ₃ with N-type structure _{Li 3-x M x N (} M = Co, Ni, Cu) can be used. For example, Li _2.6 Co _0.4 N ₃ shows a large charge / discharge capacity (900 mAh / g, 1890 mAh / cm ³ ) and is preferable.

When lithium and transition metal double nitride is used, since the negative electrode active material contains lithium ions, it can be combined with materials such as V ₂ O ₅ and Cr ₃ O ₈ that do not contain lithium ions as the positive electrode active material. . Note that even when a material containing lithium ions is used for the positive electrode active material, lithium and transition metal double nitride can be used as the negative electrode active material by previously desorbing lithium ions contained in the positive electrode active material.

A material that causes a conversion reaction can also be used as the negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO), may be used as the negative electrode active material. As a material causing the conversion reaction, oxides such as Fe ₂ O ₃ , CuO, Cu ₂ O, RuO ₂ and Cr ₂ O ₃ , sulfides such as CoS _0.89 , NiS and CuS, Zn ₃ N _{2 are further included.} This also occurs in nitrides such as Cu ₃ N and Ge ₃ N ₄ , phosphides such as NiP ₂ , FeP ₂ and CoP ₃ , and fluorides such as FeF ₃ and BiF ₃ .

As the conductive assistant and binder that the negative electrode active material layer can have, the same materials as the conductive assistant and binder that the positive electrode active material layer can have can be used.

<Negative electrode current collector>
A material similar to that of the positive electrode current collector can be used for the negative electrode current collector. The negative electrode current collector is preferably made of a material that does not alloy with carrier ions such as lithium.

[Electrolyte]
The electrolytic solution has a solvent and an electrolyte. As the solvent for the electrolytic solution, an aprotic organic solvent is preferable, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate. (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4 -One kind of dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, or the like Two or more of these can be used in any combination and ratio.

Also, by using one or more ionic liquids (room temperature molten salts) that are flame retardant and volatile as the electrolyte solvent, the internal temperature rises due to internal short circuit or overcharge of the power storage device. In addition, the storage device can be prevented from rupturing or firing. An ionic liquid consists of a cation and an anion, and contains an organic cation and an anion. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Moreover, as an anion used for electrolyte solution, a monovalent amide type anion, a monovalent metide type anion, a fluorosulfonate anion, a perfluoroalkylsulfonate anion, a tetrafluoroborate anion, a perfluoroalkylborate anion, a hexafluorophosphate anion Or perfluoroalkyl phosphate anions.

Further, as an electrolyte dissolved in the above-described solvents, for example _{LiPF 6, LiClO 4, LiAsF 6} , LiBF 4, LiAlCl 4, LiSCN, LiBr, LiI, Li 2 SO 4, Li 2 B 10 Cl 10, Li 2 B 12 Cl ₁₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₄ F ₉ SO ₂ ) (CF ₃ SO ₂ ), lithium salt such as LiN (C ₂ F ₅ SO ₂ ) ₂ , or two or more of them can be used in any combination and ratio.

As the electrolytic solution used for the power storage device, it is preferable to use a highly purified electrolytic solution having a small content of elements other than the constituent elements of particulate dust and the electrolytic solution (hereinafter, also simply referred to as “impurities”). Specifically, the weight ratio of impurities to the electrolytic solution is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

Further, vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), LiBOB, or dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolytic solution. The concentration of the material to be added may be, for example, 0.1 wt% or more and 5 wt% or less with respect to the entire solvent.

Further, a polymer gel electrolyte obtained by swelling a polymer with an electrolytic solution may be used. By using the polymer gel electrolyte, safety against liquid leakage and the like is increased. Further, the secondary battery can be reduced in thickness and weight.

As the gelled polymer, silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, fluorine polymer gel, or the like can be used. As the polymer, for example, a polymer having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and a copolymer containing them can be used. For example, PVDF-HFP which is a copolymer of PVDF and hexafluoropropylene (HFP) can be used. Further, the formed polymer may have a porous shape.

In place of the electrolytic solution, a solid electrolyte having an inorganic material such as sulfide or oxide, or a solid electrolyte having a polymer material such as PEO (polyethylene oxide) can be used. When a solid electrolyte is used, it is not necessary to install a separator or a spacer. Further, since the entire battery can be solidified, there is no risk of leakage and the safety is greatly improved.

[Separator]
The secondary battery preferably has a separator. As the separator, for example, fibers including cellulose such as paper, nonwoven fabric, glass fiber, ceramics, nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, synthetic fiber using polyurethane, etc. Can be used. The separator is preferably processed into an envelope shape and disposed so as to enclose either the positive electrode or the negative electrode.

The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture thereof. As the ceramic material, for example, aluminum oxide particles, silicon oxide particles and the like can be used. For example, PVDF, polytetrafluoroethylene, or the like can be used as the fluorine-based material. As the polyamide-based material, for example, nylon, aramid (meta-aramid, para-aramid) or the like can be used.

When the ceramic material is coated, the oxidation resistance is improved, so that deterioration of the separator during high voltage charge / discharge can be suppressed, and the reliability of the secondary battery can be improved. In addition, when a fluorine-based material is coated, the separator and the electrode are easily adhered, and the output characteristics can be improved. When a polyamide-based material, particularly aramid, is coated, the heat resistance is improved, so that the safety of the secondary battery can be improved.

For example, a mixed material of aluminum oxide and aramid may be coated on both surfaces of a polypropylene film. In addition, a mixed material of aluminum oxide and aramid may be coated on the surface in contact with the positive electrode of the polypropylene film, and a fluorine-based material may be coated on the surface in contact with the negative electrode.

When a separator having a multilayer structure is used, the safety of the secondary battery can be maintained even if the thickness of the entire separator is thin, so that the capacity per volume of the secondary battery can be increased.

[Exterior body]
As the exterior body included in the secondary battery, for example, a metal material such as aluminum or a resin material can be used. Moreover, a film-shaped exterior body can also be used. As the film, for example, a metal thin film having excellent flexibility such as aluminum, stainless steel, copper, nickel, etc. is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and an exterior is provided on the metal thin film. A film having a three-layer structure provided with an insulating synthetic resin film such as polyamide resin or polyester resin can be used as the outer surface of the body.

(Embodiment 5)
[Cylindrical secondary battery]
In this embodiment, an example of a cylindrical secondary battery is described with reference to FIGS. As shown in FIG. 12A, the cylindrical secondary battery 600 has a positive electrode cap (battery cover) 601 on the top 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.

FIG. 12B is a diagram schematically illustrating a cross section of a cylindrical secondary battery. Inside the hollow cylindrical battery can 602, a battery element in which a strip-like positive electrode 604 and a negative electrode 606 are wound with a separator 605 interposed therebetween is provided. Although not shown, the battery element is wound around a center pin. The battery can 602 has one end closed and the other end open. For the battery can 602, a metal such as nickel, aluminum, titanium, or the like having corrosion resistance to the electrolytic solution, or an alloy thereof or an alloy of these with another metal (for example, stainless steel) can be used. . In order to prevent corrosion due to the electrolytic solution, it is preferable to coat nickel, aluminum, or the like. Inside the battery can 602, the battery element in which the positive electrode, the negative electrode, and the separator are wound is sandwiched between a pair of opposing insulating plates 608 and 609. Further, a non-aqueous electrolyte (not shown) is injected into the inside of the battery can 602 provided with the battery element. As the non-aqueous electrolyte, the same one as a coin-type secondary battery can be used.

Since the positive electrode and the negative electrode used for the cylindrical storage battery are wound, it is preferable to form an active material on both surfaces of the current collector. A positive electrode terminal (positive electrode current collecting lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collecting lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can use a metal material such as aluminum. The positive terminal 603 is resistance-welded to the safety valve mechanism 612, and the negative terminal 607 is resistance-welded to the bottom of the battery can 602. 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 increase in the internal pressure of the battery exceeds a predetermined threshold value. The PTC element 611 is a heat-sensitive resistance element that increases in resistance when the temperature rises, and prevents abnormal heat generation by limiting the amount of current by increasing the resistance. For the PTC element, barium titanate (BaTiO ₃ ) -based semiconductor ceramics or the like can be used.

Alternatively, as illustrated in FIG. 12C, the module 615 may be configured by sandwiching a plurality of secondary batteries 600 between the conductive plate 613 and the conductive plate 614. The plurality of secondary batteries 600 may be connected in parallel, may be connected in series, or may be further connected in series after being connected in parallel. By configuring the module 615 including a plurality of secondary batteries 600, large power can be extracted.

FIG. 12D is a top view of the module 615. In order to clarify the figure, the conductive plate 613 is indicated by a dotted line. As illustrated in FIG. 12D, the module 615 may include a conductive wire 616 that electrically connects the plurality of secondary batteries 600. A conductive plate can be provided so as to overlap with the conductor 616. Further, a temperature control device 617 may be provided between the plurality of secondary batteries 600. When the secondary battery 600 is overheated, it is cooled by the temperature control device 617, and when the secondary battery 600 is too cold, it can be heated by the temperature control device 617. Therefore, the performance of the module 615 is less affected by the outside air temperature.

By using the active material particles 100 functioning as the positive electrode active material described in the above embodiment for the positive electrode 604, a cylindrical secondary battery 600 having high capacity and excellent cycle characteristics can be obtained.

[Example of secondary battery structure]
Another structural example of the secondary battery will be described with reference to FIGS.

FIGS. 13A and 13B are external views of the battery pack. The battery pack includes a circuit board 900 and a secondary battery 913. The secondary battery 913 includes a terminal 951 and a terminal 952 and is covered with a label 910. The battery pack may have an antenna 914.

The circuit board 900 is fixed with a seal 915. The circuit board 900 has a circuit 912. The terminal 911 is electrically connected to the terminal 951 and the terminal 952 included in the secondary battery 913 through the circuit board 900. Further, the terminal 911 is electrically connected to the antenna 914 and the circuit 912 through the circuit board 900. Note that a plurality of terminals 911 may be provided, and each of the plurality of terminals 911 may be a control signal input terminal, a power supply terminal, or the like.

The circuit 912 has a function as a protection circuit that protects the secondary battery 913 from, for example, overcharge, overdischarge, and overcurrent. The circuit 912 may be provided on the back surface of the circuit board 900. The antenna 914 is not limited to a coil shape, and may be a linear shape or a plate shape, for example. An antenna such as a planar antenna, an aperture antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, or a dielectric antenna may be used. The antenna 914 has a function of performing data communication with an external device, for example. As a communication method between the battery pack and other devices via the antenna 914, a response method that can be used between the battery pack and other devices such as NFC can be applied.

The battery pack includes a layer 916 between the antenna 914 and the secondary battery 913. The layer 916 has a function of preventing the influence of the secondary battery 913 on the electromagnetic field, for example. As the layer 916, for example, a magnetic material can be used.

The structure of the battery pack is not limited to FIG.

For example, as shown in FIGS. 14A-1 and 14A-2, an antenna is mounted on another pair of opposing surfaces of the secondary battery 913 shown in FIGS. 13A and 13B. 918 may be provided. 14A-1 is an external view seen from one side direction of the pair of surfaces, and FIG. 14A-2 is an external view seen from the other side direction of the pair of surfaces. Note that the description of the battery pack illustrated in FIGS. 13A and 13B can be used as appropriate for the same portion as the battery pack illustrated in FIGS. 13A and 13B.

As shown in FIG. 14A-1, an antenna 914 is provided on one of a pair of surfaces of the secondary battery 913 with a layer 916 interposed therebetween, and the secondary battery 913 is shown in FIG. 14A-2. An antenna 918 is provided on the other of the pair of surfaces with the layer 917 interposed therebetween. The layer 917 has a function of preventing the influence of the secondary battery 913 on the electromagnetic field, for example. As the layer 917, for example, a magnetic material can be used.

With the above structure, two antennas can be provided in the battery pack, and the sizes of both the antenna 914 and the antenna 918 can be increased.

As the antenna 918, an antenna having a shape applicable to the antenna 914 can be used. Further, the antenna 918 may be a flat conductor. The flat conductor can function as one of electric field coupling conductors. That is, the antenna 914 may function as one of the two conductors of the capacitor. Thereby, not only an electromagnetic field and a magnetic field but power can also be exchanged by an electric field.

Alternatively, as illustrated in FIG. 14B-1, a display device 920 may be provided in the battery pack illustrated in FIGS. 13A and 13B. The display device 920 is electrically connected to the terminal 911. Note that the description of the battery pack illustrated in FIGS. 13A and 13B can be used as appropriate for the same portion as the battery pack illustrated in FIGS. 13A and 13B.

The display device 920 may display, for example, an image indicating whether charging is being performed, an image indicating the amount of stored power, or the like. As the display device 920, for example, electronic paper, a liquid crystal display device, an electroluminescence (also referred to as EL) display device, or the like can be used. For example, power consumption of the display device 920 can be reduced by using electronic paper.

Alternatively, as illustrated in FIG. 14B-2, the sensor 921 may be provided in the secondary battery 913 illustrated in FIGS. 13A and 13B. The sensor 921 is electrically connected to the terminal 911 through the terminal 922 and the circuit board 900. Note that for the same portion as the power storage device illustrated in FIGS. 13A and 13B, the description of the power storage device illustrated in FIGS. 13A and 13B can be incorporated as appropriate.

Examples of the sensor 921 include displacement, position, velocity, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, and flow rate. It has only to have a function capable of measuring humidity, gradient, vibration, odor, or infrared. By providing the sensor 921, for example, data (such as temperature) indicating an environment where the power storage device is placed can be detected and stored in a memory in the circuit 912.

Further, a structural example of the secondary battery 913 will be described with reference to FIGS.

A secondary battery 913 illustrated in FIG. 15A includes a wound body 950 in which a terminal 951 and a terminal 952 are provided inside a housing 930. The wound body 950 is impregnated with the electrolytic solution inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in FIG. 15A, the housing 930 is illustrated separately for convenience, but in actuality, the wound body 950 is covered with the housing 930, and the terminals 951 and 952 are included in the housing 930. Extends outside. As the housing 930, a metal material (eg, aluminum) or a resin material can be used.

Note that as illustrated in FIG. 15B, the housing 930 illustrated in FIG. 15A may be formed using a plurality of materials. For example, in the secondary battery 913 illustrated in FIG. 15B, a housing 930a and a housing 930b are attached to each other, and a winding body 950 is provided in a region surrounded by the housing 930a and the housing 930b. .

As the housing 930a, an insulating material such as an organic resin can be used. In particular, by using a material such as an organic resin on the surface where the antenna is formed, electric field shielding by the secondary battery 913 can be suppressed. Note that an antenna such as the antenna 914 may be provided inside the housing 930a if the shielding of the electric field by the housing 930a is small. As the housing 930b, for example, a metal material can be used.

Furthermore, the structure of the wound body 950 is shown in FIG. The wound body 950 includes a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked with the separator 933 interposed therebetween, and the laminated sheet is wound. Note that a plurality of stacked layers of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked.

The negative electrode 931 is connected to a terminal 911 illustrated in FIG. 13 through one of a terminal 951 and a terminal 952. The positive electrode 932 is connected to the terminal 911 illustrated in FIG. 13 through the other of the terminal 951 and the terminal 952.

By using the active material particles 100 functioning as the positive electrode active material described in the above embodiment for the positive electrode 932, the secondary battery 913 having high capacity and excellent cycle characteristics can be obtained.

(Embodiment 6)
In this embodiment, an example in which the secondary battery which is one embodiment of the present invention is mounted on an electronic device will be described.

First, as an electronic device to which a secondary battery is applied, for example, a television device (also referred to as a television or a television receiver), a monitor for a computer, a digital camera, a digital video camera, a digital photo frame, a mobile phone (mobile phone) And large game machines such as a portable game machine, a portable information terminal, a sound reproduction device, and a pachinko machine.

Next, FIGS. 17A and 17B illustrate an example of a tablet terminal that can be folded in half. A tablet terminal 9600 illustrated in FIGS. 17A and 17B includes a housing 9630a, a housing 9630b, a movable portion 9640 that connects the housing 9630a and the housing 9630b, a display portion 9631, and a display mode switching switch 9626. , A power switch 9627, a power saving mode switching switch 9625, a fastener 9629, and an operation switch 9628. By using a flexible panel for the display portion 9631, a tablet terminal having a wider display portion can be obtained. FIG. 17A shows a state where the tablet terminal 9600 is opened, and FIG. 17B shows a state where the tablet terminal 9600 is closed.

In addition, the tablet terminal 9600 includes a power storage unit 9635 inside the housing 9630a and the housing 9630b. The power storage unit 9635 is provided across the housing 9630a and the housing 9630b through the movable portion 9640.

Part of the display portion 9631 can be a touch panel region, and data can be input by touching displayed operation keys. Further, a keyboard button can be displayed on the display portion 9631 by touching a position of the keyboard display switching button on the touch panel with a finger or a stylus.

A display mode switching switch 9626 can switch a display direction such as a vertical display or a horizontal display, and can select a monochrome display or a color display. The power saving mode change-over switch 9625 can optimize the display luminance in accordance with the amount of external light in use detected by an optical sensor incorporated in the tablet terminal 9600. The tablet terminal may include not only an optical sensor but also other detection devices such as a gyroscope, an acceleration sensor, and other sensors that detect inclination.

FIG. 17B illustrates a closed state, in which the tablet terminal includes a charge / discharge control circuit 9634 including a housing 9630, a solar battery 9633, and a DCDC converter 9636. Further, as the power storage unit 9635, the secondary battery according to one embodiment of the present invention is used.

Note that since the tablet terminal 9600 can be folded in two, the housing 9630a and the housing 9630b can be folded so as to overlap when not in use. By folding, the display portion 9631 can be protected, so that durability of the tablet terminal 9600 can be improved. Further, since the power storage unit 9635 using the secondary battery of one embodiment of the present invention has high capacity and favorable cycle characteristics, the tablet terminal 9600 that can be used for a long time can be provided.

In addition, the tablet type terminal shown in FIGS. 17A and 17B has a function for displaying various information (still images, moving images, text images, etc.), a calendar, a date or a time. A function for displaying on the display unit, a touch input function for performing touch input operation or editing of information displayed on the display unit, a function for controlling processing by various software (programs), and the like can be provided.

Electric power can be supplied to the touch panel, the display unit, the video signal processing unit, or the like by the solar battery 9633 mounted on the surface of the tablet terminal. Note that the solar battery 9633 can be provided on one or both surfaces of the housing 9630 and the power storage unit 9635 can be charged efficiently.

The structure and operation of the charge / discharge control circuit 9634 illustrated in FIG. 17B are described with reference to a block diagram in FIG. FIG. 17C illustrates the solar battery 9633, the power storage unit 9635, the DCDC converter 9636, the converter 9637, the switches SW1 to SW3, and the display portion 9631. The power storage unit 9635, the DCDC converter 9636, the converter 9637, and the switches SW1 to SW37 are illustrated. SW3 corresponds to the charge / discharge control circuit 9634 shown in FIG.

First, an example of operation in the case where power is generated by the solar battery 9633 using external light is described. The power generated by the solar battery is boosted or lowered by the DCDC converter 9636 so as to be a voltage for charging the power storage unit 9635. When power from the solar cell 9633 is used for the operation of the display portion 9631, the switch SW1 is turned on, and the converter 9637 increases or decreases the voltage required for the display portion 9631. In the case where display on the display portion 9631 is not performed, the power storage unit 9635 may be charged by turning off SW1 and turning on SW2.

Note that the solar battery 9633 is described as an example of the power generation unit, but is not particularly limited, and the power storage unit 9635 is charged by another power generation unit such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). It may be. For example, a non-contact power transmission module that wirelessly (contactlessly) transmits and receives power for charging and other charging means may be combined.

FIG. 18 illustrates an example of another electronic device. In FIG. 18, a display device 8000 is an example of an electronic device using the secondary battery 8004 according to one embodiment of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving TV broadcasts, and includes a housing 8001, a display portion 8002, a speaker portion 8003, a secondary battery 8004, and the like. A secondary battery 8004 according to one embodiment of the present invention is provided in the housing 8001. The display device 8000 can receive power from a commercial power supply. Alternatively, the display device 8000 can use power stored in the secondary battery 8004. Thus, the display device 8000 can be used when the secondary battery 8004 according to one embodiment of the present invention is used as an uninterruptible power supply even when power cannot be supplied from a commercial power supply due to a power failure or the like.

A display portion 8002 includes a liquid crystal display device, a light-emitting device including a light-emitting element such as an organic EL element, an electrophoretic display device, a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), and an FED (Field Emission Display). A semiconductor display device such as) can be used.

The display device includes all information display devices such as a personal computer and an advertisement display in addition to a TV broadcast reception.

In FIG. 18, a stationary lighting device 8100 is an example of an electronic device using the secondary battery 8103 according to one embodiment of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, and the like. FIG. 18 illustrates the case where the secondary battery 8103 is provided inside the ceiling 8104 where the housing 8101 and the light source 8102 are installed, but the secondary battery 8103 is provided inside the housing 8101. It may be done. The lighting device 8100 can receive power from a commercial power supply. Alternatively, the lighting device 8100 can use power stored in the secondary battery 8103. Thus, the lighting device 8100 can be used by using the secondary battery 8103 according to one embodiment of the present invention as an uninterruptible power supply even when power cannot be supplied from a commercial power supply due to a power failure or the like.

Note that FIG. 18 illustrates the installation lighting device 8100 provided on the ceiling 8104; however, the secondary battery according to one embodiment of the present invention is not the ceiling 8104, for example, a sidewall 8105, a floor 8106, a window 8107, or the like. It can also be used for a stationary illumination device provided on the desk, or a desktop illumination device.

The light source 8102 can be an artificial light source that artificially obtains light using electric power. Specifically, discharge lamps such as incandescent bulbs and fluorescent lamps, and light emitting elements such as LEDs and organic EL elements are examples of the artificial light source.

In FIG. 18, an air conditioner including an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using the secondary battery 8203 according to one embodiment of the present invention. Specifically, the indoor unit 8200 includes a housing 8201, an air outlet 8202, a secondary battery 8203, and the like. FIG. 18 illustrates the case where the secondary battery 8203 is provided in the indoor unit 8200, but the secondary battery 8203 may be provided in the outdoor unit 8204. Alternatively, the secondary battery 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive power from a commercial power supply. Alternatively, the air conditioner can use power stored in the secondary battery 8203. In particular, when the secondary battery 8203 is provided in both the indoor unit 8200 and the outdoor unit 8204, the secondary battery 8203 according to one embodiment of the present invention can be used even when electric power cannot be supplied from the commercial power supply due to a power failure or the like. By using as an uninterruptible power supply, an air conditioner can be used.

Note that FIG. 18 illustrates a separate type air conditioner including an indoor unit and an outdoor unit. However, an integrated air conditioner having the functions of the indoor unit and the outdoor unit in one housing is illustrated. The secondary battery according to one embodiment of the present invention can also be used.

In FIG. 18, an electric refrigerator-freezer 8300 is an example of an electronic device using the secondary battery 8304 according to one embodiment of the present invention. Specifically, the electric refrigerator-freezer 8300 includes a housing 8301, a refrigerator door 8302, a refrigerator door 8303, a secondary battery 8304, and the like. In FIG. 18, the secondary battery 8304 is provided inside the housing 8301. The electric refrigerator-freezer 8300 can receive power from a commercial power supply. Alternatively, the electric refrigerator-freezer 8300 can use power stored in the secondary battery 8304. Therefore, the electric refrigerator-freezer 8300 can be used by using the secondary battery 8304 according to one embodiment of the present invention as an uninterruptible power supply even when electric power cannot be supplied from the commercial power supply due to a power failure or the like.

In addition, in a time zone when the electronic device is not used, particularly in a time zone where the ratio of the actually used power amount (referred to as the power usage rate) is low in the total power amount that can be supplied by the commercial power supply source. By storing electric power in the secondary battery, it is possible to suppress an increase in the power usage rate outside the above time period. For example, in the case of the electric refrigerator-freezer 8300, electric power is stored in the secondary battery 8304 at night when the temperature is low and the refrigerator door 8302 and the refrigerator door 8303 are not opened and closed. In the daytime when the temperature rises and the refrigerator door 8302 and the freezer door 8303 are opened and closed, the secondary battery 8304 is used as an auxiliary power source, so that the daytime power usage rate can be kept low.

In addition to the above electronic devices, the secondary battery of one embodiment of the present invention can be mounted on any electronic device. According to one embodiment of the present invention, the cycle characteristics of the secondary battery are improved. Further, according to one embodiment of the present invention, a high-capacity secondary battery can be obtained, and thus the secondary battery itself can be reduced in size and weight. Therefore, by mounting the secondary battery which is one embodiment of the present invention on the electronic device described in this embodiment, the electronic device can have a longer lifetime and a lighter weight. This embodiment can be implemented in appropriate combination with any of the other embodiments.

(Embodiment 7)
In this embodiment, an example in which a secondary battery which is one embodiment of the present invention is mounted on a vehicle will be described.

When a secondary battery is mounted on a vehicle, a next-generation clean energy vehicle such as a hybrid vehicle (HEV), an electric vehicle (EV), or a plug-in hybrid vehicle (PHEV) can be realized.

FIG. 19 illustrates a vehicle using the secondary battery which is one embodiment of the present invention. A car 8400 illustrated in FIG. 19A is an electric car that uses an electric motor as a power source for traveling. Or it is a hybrid vehicle which can select and use an electric motor and an engine suitably as a motive power source for driving | running | working. By using one embodiment of the present invention, a vehicle having a long cruising distance can be realized. The automobile 8400 includes a secondary battery. As the secondary battery, a large number of small cylindrical secondary batteries shown in FIG. 12 may be used side by side with respect to the floor portion in the vehicle. Further, a battery pack in which a plurality of secondary batteries shown in FIG. 20 are combined may be installed on the floor portion in the vehicle. The secondary battery not only drives the electric motor 8406 but can supply power to a light-emitting device such as a headlight 8401 or a room light (not shown).

The secondary battery can supply power to a display device such as a speedometer or a tachometer included in the automobile 8400. The secondary battery can supply power to a semiconductor device such as a navigation system included in the automobile 8400.

A car 8500 illustrated in FIG. 19B can charge a secondary battery of the car 8500 by receiving power from an external charging facility by a plug-in method, a non-contact power feeding method, or the like. FIG. 19B illustrates a state where the secondary battery 8024 mounted on the automobile 8500 is charged through the cable 8022 from the ground-installed charging device 8021. When charging, the charging method, connector standard, and the like may be appropriately performed by a predetermined method such as CHAdeMO (registered trademark) or a combo. The charging device 8021 may be a charging station provided in a commercial facility, or may be a household power source. For example, the secondary battery 8024 mounted on the automobile 8500 can be charged by power supply from the outside by plug-in technology. Charging can be performed by converting AC power into DC power via a conversion device such as an ACDC converter included in the charging device 8021. In the case of an automobile 8500 equipped with a charging ACDC converter 8025, charging can be performed even if an AC power supply is connected.

In addition, although not shown, the power receiving device can be mounted on the vehicle, and electric power can be supplied from the ground power transmitting device in a contactless manner and charged. In the case of this non-contact power supply method, charging can be performed not only when the vehicle is stopped but also during traveling by incorporating a power transmission device on a road or an outer wall. In addition, this non-contact power feeding method may be used to transmit and receive power between vehicles. Furthermore, a solar battery may be provided in the exterior part of the vehicle, and the secondary battery may be charged when the vehicle is stopped or traveling. An electromagnetic induction method or a magnetic field resonance method can be used for such non-contact power supply.

FIG. 19C illustrates an example of a motorcycle using the secondary battery of one embodiment of the present invention. A scooter 8600 illustrated in FIG. 19C includes a secondary battery 8602, a side mirror 8601, and a direction indicator lamp 8603. The secondary battery 8602 can supply electricity to the direction indicator lamp 8603.

In addition, the scooter 8600 illustrated in FIG. 19C can store the secondary battery 8602 in the under-seat storage 8604. The secondary battery 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small. The secondary battery 8602 can be removed. When charging, the secondary battery 8602 can be carried indoors, charged, and stored before traveling.

According to one embodiment of the present invention, the cycle characteristics of the secondary battery are improved, and the capacity of the secondary battery can be increased. Therefore, the secondary battery itself can be reduced in size and weight. If the secondary battery itself can be reduced in size and weight, the cruising distance can be improved because it contributes to weight reduction of the vehicle. Moreover, the secondary battery mounted in the vehicle can also be used as a power supply source other than the vehicle. In this case, for example, it is possible to avoid using a commercial power source at the peak of power demand. If it can be avoided to use a commercial power source at the peak of power demand, it can contribute to energy saving and reduction of carbon dioxide emissions. In addition, since the secondary battery can be used for a long period if the cycle characteristics are good, the amount of rare metals such as cobalt can be reduced.

This embodiment can be implemented in appropriate combination with any of the other embodiments.

In this example, a secondary battery using positive electrode active material particles having different coating layers is manufactured, characteristics are analyzed using SEM and XRD, and the results of comparison of characteristics are shown.

<Preparation of positive electrode active material>
In this example, positive electrode active materials of Sample 11 to Sample 14, Sample 21 to Sample 24, and Sample 31 were prepared using cobalt as the metal element M1 and titanium as the metal element M2. The production method of each sample was as follows.

<< Sample 11 >>
Sample 11 was prepared by forming a coating layer containing titanium on lithium cobalt oxide particles containing magnesium and fluorine by a sol-gel method, and then heating.

In this example, lithium cobalt oxide particles having magnesium and fluorine synthesized in advance were used as starting materials. Specifically, a product name manufactured by Nippon Chemical Industry Co., Ltd .; C-20F was used as a starting material.

TTIP was added to 2-propanol and dissolved so that the TTIP per weight of the positive electrode active material was 0.004 ml / g. For TTIP, a reagent having a purity of 99.0% or more manufactured by Kishida Chemical Co., Ltd. was used. Lithium cobaltate particles having magnesium and fluorine were added to the 2-propanol solution of TTIP.

The mixed liquid in which lithium cobaltate particles containing magnesium and fluorine were mixed was stirred with a magnetic stirrer for 70 hours at 25 ° C. and humidity of 90% RH. By this treatment, hydrolysis and polycondensation reaction were caused by water and TTIP in the atmosphere, and a layer containing titanium was formed on the surface of lithium cobaltate particles having magnesium and fluorine.

The mixed solution after the above treatment was filtered to recover the residue. Kiriyama filter paper (No. 4) was used as a filter for filtration.

The collected residue was dried at 70 ° C. for 3 hours.

The dried powder was heated. Heating was performed at 800 ° C. (temperature increase of 200 ° C./hour), a holding time of 2 hours, and an oxygen atmosphere flow rate of 10 L / min.

The heated powder was cooled. The cooling was performed over the same time as the temperature increase or longer. Then it was sifted. A sieve having an opening of 53 μm was used.

The particles after sieving were used as the positive electrode active material of Sample 11.

Sample 11 was presumed to be a positive electrode active material having lithium cobaltate inside and a coating layer containing titanium and magnesium in the surface layer portion.

<< Sample 12 >>
As a comparative example, Sample 12 was formed without heating after forming a layer containing titanium and drying it. A sample 11 was produced except that heating was not performed.

Sample 12 was presumed to be a positive electrode active material having lithium cobaltate containing magnesium and fluorine inside and having a coating layer containing titanium on the surface layer portion, but magnesium was not segregated on the surface.

<< Sample 13 >>
Sample 13 was produced as a comparative example without forming a layer containing titanium. It was produced in the same manner as Sample 11 except that the layer containing titanium was not formed.

Sample 13 was presumed to be a positive electrode active material having lithium cobaltate inside and having a coating layer containing magnesium in the surface layer portion, but not titanium.

«Sample 14»
As a comparative example, Sample 14 did not form a layer containing titanium and was not heated. Specifically, Nippon Chemical Co., Ltd. C-20F was used as it was.

The sample 14 is a lithium cobaltate containing magnesium and fluorine, but is a positive electrode active material having no coating layer.

<< Sample 21 >>
Sample 21 was prepared by forming a coating layer containing titanium on lithium cobalt oxide particles containing magnesium and fluorine by a sol-gel method, and then heating.

It was produced in the same manner as Sample 11 except that the TTIP per positive electrode active material was 0.01 ml / g and the atmosphere during heating was dry air.

Sample 21 was presumed to be a positive electrode active material having lithium cobaltate inside and having a coating layer containing titanium and magnesium in the surface layer portion.

<< Sample 22 >>
Sample 22 was prepared as a comparative example without forming a layer containing titanium. It was produced in the same manner as Sample 21, except that the layer containing titanium was not formed.

The sample 22 was estimated to be a positive electrode active material having lithium cobaltate inside and having a coating layer containing magnesium in the surface layer portion, but not having titanium.

<< Sample 23 >>
As a comparative example, Sample 23 was manufactured by forming a layer containing titanium on lithium cobalt oxide particles not containing magnesium and then heating.

The product made from Nippon Chemical Industry (product name; C-10N) was used for the lithium cobalt oxide particles. This is a lithium cobaltate particle in which magnesium is not detected by XPS and fluorine is detected at about 1 atomic%.

A sample 21 was prepared except that C-10N was used as a starting material.

Sample 23 was estimated to be a positive electrode active material having lithium cobaltate inside and having a coating layer containing titanium in the surface layer portion, but magnesium was not segregated on the surface.

<< Sample 24 >>
As a comparative example, Sample 24 did not form a layer containing titanium on lithium cobalt oxide particles not containing magnesium, and was not heated. Specifically, Nippon Chemical Industry's C-10N was used as it was.

Sample 24 is lithium cobaltate without a coating layer.

<< Sample 31 >>
Sample 31 was prepared by forming a coating layer containing titanium on lithium cobalt oxide particles containing magnesium and fluorine by a sol-gel method, and then heating.

It was produced in the same manner as Sample 11 except that the TTIP per positive electrode active material was 0.01 ml / g.

Sample 31 was presumed to be a positive electrode active material having lithium cobaltate inside and having a coating layer containing titanium and magnesium in the surface layer portion.

Table 1 shows conditions for producing Samples 11 to 14, Samples 21 to 24, and Sample 31. Moreover, the analysis performed about each sample mentioned later is also shown collectively.

<SEM>
The results of observing Sample 11 and Sample 14 using SEM are as described in FIG. It was revealed that a positive electrode active material 100 with few cracks and surface area and a relatively smooth surface can be produced by forming a layer containing titanium and heating.

<XRD>
For Samples 11 to 14, the size of the crystallites inside the positive electrode active material particles was analyzed using XRD. The results are shown in Table 2.

As shown in Table 2, Sample 11 in which a layer containing titanium was coated and heated was observed to have a larger crystallite than other samples. The tendency for the crystallites to increase is different depending on the crystal plane, and is prominent on the (003) plane and the like.

It is considered that as the number of cracks increases, the crystallinity decreases, and thus the crystallite size decreases.

Further, it is presumed that defects such as cracks are likely to occur along the (003) plane. FIG. 20 is a model diagram of the crystal structure of lithium cobalt oxide (LiCoO ₂ ). The direction perpendicular to the paper surface is the a-axis direction, the short side of the rectangle in the figure is the b-axis direction, and the long side of the rectangle is the c-axis direction. In the figure, the (003) plane is indicated by a dotted line. As shown in FIG. 20, the (003) plane shows the characteristics of the layer structure. In lithium cobaltate, the bond between lithium and oxygen is weaker than the bond between cobalt and oxygen. For this reason, it is presumed that defects such as cracks are likely to occur in parallel with the (003) plane.

It was speculated that defects such as cracks due to the (003) plane were repaired by covering and heating a layer containing titanium as in this example.

<Cycle characteristics at 25 ° C>
Using the positive electrode active materials of Sample 21 to Sample 24, a CR2032-type (20 mm diameter, 3.2 mm height) coin-type secondary battery was manufactured, and cycle characteristics were evaluated.

For the positive electrode, positive electrode active material (LCO) of sample 21 to sample 24, acetylene black (AB), and polyvinylidene fluoride (PVDF) are LCO: AB: PVDF = 95: 2.5: 2.5 (weight ratio) ) Was applied to an aluminum foil current collector. N-methyl-2-pyrrolidone (NMP) was used as the solvent.

Lithium metal was used for the counter electrode.

1 mol / L lithium hexafluorophosphate (LiPF ₆ ) is used for the electrolyte of the electrolyte, and ethylene carbonate (EC) and diethyl carbonate (DEC) are EC: DEC = 3: 7 ( A mixture obtained by adding 2% by weight of vinylene carbonate (VC) to a mixture by volume ratio) was used.

As the positive electrode can and the negative electrode can, those formed of stainless steel (SUS) were used.

The measurement temperature in the cycle characteristic test was 25 ° C. Charging was performed using CCCV, first, a constant current with a current density of 68.5 mA / g per weight of the active material and an upper limit voltage of 4.6 V, and then a constant voltage charge was performed until the current density reached 1.4 mA / g. The discharge was CC, and was performed at a constant current of 68.5 mA / g current density per active material weight and a lower limit voltage of 2.5V.

In addition, although the conditions of CCCV charge and CC charge in a present Example may differ from the voltage illustrated by description of CCCV charge and CC discharge as described in Embodiment 2, only a voltage differs and it is as charging method and discharge. Are the same. By charging with a high voltage, a high-capacity secondary battery can be obtained.

In FIG. 21, the graph of the discharge capacity maintenance factor at the time of 4.6V charge of the secondary battery using the positive electrode active material of the samples 21-sample 24 and the number of charging / discharging cycles is shown. The discharge capacity retention rate was determined with the initial discharge capacity as 100%.

As can be seen from FIG. 21, sample 22 which is lithium cobaltate particles having magnesium and fluorine is better than sample 24 having no coating layer and sample 23 having only a coating layer containing titanium. The cycle characteristics are shown. This is considered to be an effect that magnesium is segregated on the surface layer portion of the lithium cobalt oxide particles by heating.

Sample 21, which is a positive electrode active material in which a coating layer containing titanium is formed on lithium cobaltate particles containing magnesium and fluorine, showed extremely good cycle characteristics. This was a characteristic superior to that of the sample 22 in which magnesium was segregated in the surface layer portion and the sample 23 in which only the coating layer containing titanium was formed.

In the cycle characteristic measurement, the discharge capacity retention rate at the 10th cycle was 99%. The discharge capacity retention rate at the 30th cycle was 97%.

As described above, it has been clarified that by providing the coating layer having titanium and magnesium, better cycle characteristics can be obtained than when only the coating layer having titanium or only the coating layer having magnesium is provided.

<Initial characteristics, rate characteristics and cycle characteristics at 45 ° C.>
A secondary battery was fabricated using the positive electrode active material of Sample 31, and the initial characteristics and cycle characteristics were evaluated.

For the positive electrode, positive electrode active material (LCO) of sample 31, acetylene black (AB), and polyvinylidene fluoride (PVDF) (manufactured by Solvay, product name: GE51305) are LCO: AB: PVDF = 95: 3: 2. The slurry mixed at (weight ratio) was applied to an aluminum foil current collector. N-methyl-2-pyrrolidone (NMP) was used as the solvent. The amount carried on the positive electrode current collector was about 8.5 mg / cm ² . Others were produced in the same manner as Samples 21-24.

First, initial characteristics and rate characteristics of the secondary battery using the positive electrode active material of Sample 31 were measured.

The initial charge / discharge characteristics were measured by charging with CC / CV, 0.2C, 4.55V, and 0.05C cut-off. Discharging was performed with CC, 0.2C, 3.0V cutoff. Note that 1C = 160 mAh / g. The measurement temperature was 25 ° C.

The rate capacity was measured after the first charge / discharge. The discharge rate was changed, and the conditions other than the discharge rate were the same as the initial charge / discharge, 0.2C charge / 0.2C discharge, 0.2C charge / 0.5C discharge, 0.2C charge / 1.0C discharge, 0. It measured in order of 2C charge / 2.0C discharge. The measurement temperature was 25 ° C.

The results of measuring the initial characteristics and the rate capacity are shown in Table 3 and FIG.

FIG. 22A is a graph of the rate capacity in Table 1. FIG. 22B is a graph showing the rate capacity normalized by the capacity of 0.2C in Table 3.

[Cycle characteristics]
In the cycle characteristics, charging was performed with CC / CV, 1.0C, 4.55V, 0.05C cutoff, and discharging was performed with CC, 1.0C, 3.0V cutoff. The measurement temperature was 45 ° C. FIG. 23 shows a graph of the measured cycle characteristics in terms of discharge capacity retention rate.

In the cycle characteristic measurement, the discharge capacity retention rate at the 10th cycle was 100%. In addition, the discharge capacity retention rate at the 30th cycle was 98%. In addition, the discharge capacity retention rate at the 100th cycle was 79%.

Moreover, the result of measuring the specific surface area of the positive electrode active material of Sample 31 was 0.13 m ² / g.

As a result of measuring the particle size distribution of the positive electrode active material of Sample 31, the average particle size was 25.5 μm, 10% D was 13.5 μm, 50% D was 23.9 μm, and 90% D was 56.4 μm. .

As described above, it has been clarified that the positive electrode active material particles of Sample 31 which is one embodiment of the present invention exhibit extremely good initial charge / discharge capacity, rate capacity, and cycle characteristics.

From the above results, it was revealed that the positive electrode active material particles which are one embodiment of the present invention can obtain extremely good cycle characteristics when used in a secondary battery.

100 Active material particle 105 Crack 110 Active material particle 111 Particle 150 Dotted line 170 Isopropanol 171 TTIP
172 TiOx sol 173 Dry gel 200 Active material layer 201 Graphene compound 300 Secondary battery 301 Positive electrode can 302 Negative electrode can 303 Gasket 304 Positive electrode 305 Positive electrode current collector 306 Positive electrode active material layer 307 Negative electrode 308 Negative electrode current collector 309 Negative electrode active material layer 310 Separator

Claims (13)

A current collector, and an active material layer on the current collector,
The active material layer has a plurality of active material particles in contact with the current collector,
The active material particles include lithium, a metal element M1, a metal element M2 having one or both of II and IV, and oxygen,
The metal atom M1 is one or more of cobalt, manganese, and nickel,
The active material particles have one or more crystallites,
The active material particles have a first region located inside and a second region located outside the first region,
The second region contains more metal element M2 than the first region.
A positive electrode characterized by that. In claim 1,
The metal element M2 is one or more of magnesium, calcium, silicon, and titanium.
A positive electrode characterized by that. In claim 1,
The metal element M2 is magnesium, calcium, and titanium.
A positive electrode characterized by that. In any one of Claims 1 thru | or 3,
The second region further comprises fluorine;
A positive electrode characterized by that. A secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator,
The positive electrode has a current collector and an active material layer on the current collector,
The active material layer has a plurality of active material particles in contact with the current collector,
The active material particles include lithium, a metal element M1, one or both of a metal element M2 having a valence of II and IV, and oxygen,
The metal atom M1 is one or more of cobalt, manganese, and nickel,
The active material particles have one or more crystallites,
The active material particles have a first region located inside and a second region located outside the first region,
The second region contains more metal element M2 than the first region,
The secondary battery has a capacity after repeated charge and discharge of 100 cycles of 78% or more of the initial capacity.
A secondary battery characterized by that. A secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator,
The positive electrode has a current collector and an active material layer on the current collector,
The active material layer has a plurality of active material particles in contact with the current collector,
The active material particles include lithium, a metal element M1, one or both of a metal element M2 having a valence of II and IV, and oxygen,
The metal atom M1 is one or more of cobalt, manganese, and nickel,
The active material particles have one or more crystallites,
The active material particles have a first region located inside and a second region located outside the first region,
The second region contains more metal element M2 than the first region,
The secondary battery has a capacity of 98% or more of the initial capacity after repeated charging and discharging in the range of 10 cycles or more and 30 cycles or less.
A secondary battery characterized by that. A first step of forming second active material particles by coating the first active material particles having defects with one or both of the II and IV metal elements using the sol-gel method. When,
A second step of heat-treating the second active material particles to obtain third active material particles;
Applying a slurry containing the third active material particles on a current collector,
The defect included in the first active material particles is repaired in the second step. In claim 7,
The size of the crystallites contained in the third active material particles is larger than the crystallites contained in the first active material particles;
A manufacturing method of a positive electrode characterized by the above. In Claim 7 or 8, the size of the crystallite contained in the third active material particles is at least twice that of the crystallite contained in the first active material particles.
A manufacturing method of a positive electrode characterized by the above. In any one of Claims 7 thru | or 9,
The method for producing a positive electrode, wherein the size of the crystallite is measured by XRD analysis. In any one of Claims 7 thru | or 10,
The second step is performed in an atmosphere containing oxygen at 600 ° C. or higher and 1000 ° C. or lower.
A manufacturing method of a positive electrode characterized by the above. In any one of Claims 7 thru | or 11,
The metal element M2 is one or more of magnesium, calcium, silicon, and titanium.
A manufacturing method of a positive electrode characterized by the above. In any one of Claims 7 thru | or 12,
The first active material particles include lithium, a metal element M1, and oxygen,
The metal atom M1 is one or more of cobalt, manganese, and nickel.
A manufacturing method of a positive electrode characterized by the above.