JP7295984B2 - Secondary battery and module - Google Patents

Description

One aspect of the present invention relates to an article, method, or manufacturing method. Alternatively, the present invention provides a process,
Relating to a machine, manufacture, or 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 generally refers to elements and devices having a power storage function. For example, storage batteries such as lithium ion secondary batteries (also referred to as secondary batteries), lithium ion capacitors, electric double layer capacitors, and the like are included.

In this specification, electronic equipment refers to all devices having a power storage device, and electro-optical devices having a power storage device, information terminal devices 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 a user or an electronic device worn by a user operates using a primary battery or a secondary battery, which are examples of a power storage device, as a power source. Electronic devices carried by users are desired to be used for a long period of time, and for this reason, large-capacity secondary batteries may be used. When a large-capacity secondary battery is incorporated in an electronic device, there is a problem that the large-capacity secondary battery is large and heavy. Therefore, the development of a small or thin secondary battery with a large capacity that can be incorporated in a portable electronic device is underway.

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

High-power, high-capacity lithium-ion secondary batteries are used in portable information terminals such as mobile phones, smartphones, or notebook computers, portable music players, digital cameras, medical equipment, hybrid vehicles (HEV), electric vehicles ( Electric vehicles (EVs) or next-generation clean energy vehicles such as plug-in hybrid vehicles (PHEVs) have rapidly increased in demand along with the development of the semiconductor industry, and are essential to the modern information society as a source of rechargeable energy. It is a thing.

Lithium-ion secondary batteries have the drawback that repeated charge-discharge cycles cause deterioration, resulting in a smaller discharge capacity than the initial battery discharge capacity. In addition, depending on the lithium-ion secondary battery, there is a risk of ignition during use of the device containing the lithium-ion secondary battery, rapid charging, etc., and safety is also a problem. If many problems leading to ignition occur, not only the secondary battery but also the device equipped with the secondary battery will be recalled, resulting in huge collection costs and brand deterioration. The damage to the manufacturing company is great.

WO2010/074303

Cycle characteristics, capacity,
Furthermore, there is still room for improvement in various aspects such as charge/discharge characteristics, reliability, safety, and cost.

In order to identify the cause of deterioration of lithium-ion secondary batteries, particles (lithium-cobalt composite oxide (LiCoO ₂ )), which is a positive electrode active material, were observed, and multiple cracks (including cracks and fissures) were confirmed in the particles. was done. In addition to the cracks that can be observed in the SEM photograph, it is believed that the particles contain a large number of defects.

The inventors have found that cobalt (Co), oxygen (O), or cobalt oxide (Co+O) can be released or dissolved into the electrolyte from the surface of the particles, mainly from multiple cracks and defects in the particles. , is speculated to be one of the causes of deterioration of lithium-ion secondary batteries.

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

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

An object of one embodiment of the present invention is to provide an active material that does not deteriorate in charge-discharge cycles when 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-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 substance, an active material, a power storage device, or a manufacturing method thereof.

The description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Problems other than these can be extracted from the descriptions of the specification, 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 on the current collector, and the active material layer has a plurality of active material particles in contact with the current collector. , the active material particles contain lithium, a metal element M1, one or both of a valence II and a valence IV metal element M2, and oxygen, and the metal atom M1 is one or more of cobalt, manganese, and nickel, and the active material The particle has one or more crystallites, the active material particle has a first region located inside, a second region located outside the first region, and a second region is a positive electrode characterized by containing more metal element M2 than the first region.

In the above configuration, 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, and segregate from the particle surface. It prevents the release of cobalt, or oxygen. In this specification and the like, segregation means that a certain element (for example, B
) is unevenly distributed. By preventing the elution of cobalt or oxygen into the electrolytic solution, it is possible to provide an active material that does not deteriorate during charge-discharge cycles.

In the above structure, the second region may further contain fluorine. In addition, the presence of fluorine in the positive electrode active material particles may improve corrosion resistance to hydrofluoric acid generated by 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. Note that the particle size refers to D50 (also referred to as median diameter).

Another aspect of the invention is a secondary battery having a positive electrode, a negative electrode, an electrolytic solution, and a separator, wherein 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 valence II and a valence IV metal element M2, and oxygen; The atom M1 is one or more of cobalt, manganese, and nickel, the active material particle has one or more crystallites, and the active material particle has a first region located inside and a first region and a second region located outside the
The second region contains more metal element M2 than the first region, and the secondary battery has a capacity of 78% or more of the initial capacity after 100 cycles of repeated charging and discharging.

Another aspect of the invention is a secondary battery having a positive electrode, a negative electrode, an electrolytic solution, and a separator, wherein 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 valence II and a valence IV metal element M2, and oxygen; The atom M1 is one or more of cobalt, manganese, and nickel, the active material particle has one or more crystallites, and the active material particle has a first region located inside and a first region and a second region located outside the
The second region contains more metal element M2 than the first region, and 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. be.

In another aspect of the invention relating to a manufacturing method, the first active material particles having defects are coated with either one or both of the valence II metal element and the metal element M2 of the IV valence using a sol-gel method. A first step of forming second active material particles, a second step of heat-treating the second active material particles to obtain third active material particles, and a slurry containing the third active material particles. The third coating on the current collector
and wherein defects contained in the first active material particles are repaired in the second step.

In the manufacturing method described above, the crystallites contained in the third active material particles are larger in size than the crystallites contained in the first active material particles.

In the manufacturing method described above, the size of the crystallites contained in the third active material particles is at least twice the size of the crystallites contained in the first active material particles.

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

In the above manufacturing method, the second step is performed at 600° C. to 1000° C. in an atmosphere containing oxygen. Heating at 600° C. or higher and 1000° C. or lower can reduce cracks and defects in the particles, make the surface of the particles glossy, and reduce the surface area. A secondary battery with high safety or reliability can be realized by reducing the surface area and creating an energetically stable state.

In the manufacturing method described above, the first active material particles contain 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 alternately arranged, and the metal element M1 and A crystal structure in which lithium can diffuse two-dimensionally because lithium is regularly arranged to form a two-dimensional plane. In addition, there may be defects such as lack of cations or anions.
Strictly speaking, the layered rock salt type crystal structure may be a structure in which the lattice of the rock salt type crystal is distorted.

In this specification and the like, a rock salt crystal structure refers to a structure in which cations and anions are alternately arranged. In addition, there may be a lack of cations or anions.

By reducing the size of cracks in the active material particles and reducing the number of cracks and defects to prevent cobalt and oxygen from eluting into the electrolyte, the stability of the crystal structure in the active material particles can be further enhanced. and the charge/discharge cycle characteristics are further improved.

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

Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Effects other than these are self-evident from the descriptions of the specification, drawings, claims, etc., and it is possible to extract effects other than these from the descriptions of the specification, drawings, claims, etc. is.

1A and 1B are a perspective view and a cross-sectional view of a particle showing one embodiment of the present invention; FIG. FIG. 2 is a conceptual diagram showing changes in crystallites and cracks before and after treatment, showing one embodiment of the present invention. 1 is an SEM photograph showing one embodiment of the present invention. FIG. 1 shows materials illustrating one aspect of the present invention. It is a figure which shows the process which shows one aspect|mode of this invention. It is a figure which shows the process flow which shows one aspect|mode of this invention. 4A and 4B illustrate a coin-type secondary battery; 4A and 4B are diagrams for explaining a charging method of a secondary battery; FIG. 4A and 4B are diagrams for explaining a charging method of a secondary battery; FIG. 4A and 4B are diagrams for explaining a method of discharging a secondary battery; FIG. FIG. 4 is a cross-sectional view of an active material layer in the case of using a graphene compound as a conductive aid; FIG. 3 is a diagram for explaining a cylindrical secondary battery; 4A and 4B are diagrams for explaining a secondary battery; 4A and 4B are diagrams for explaining a secondary battery; 4A and 4B are diagrams for explaining a secondary battery; 4A and 4B are diagrams for explaining a secondary battery; 1A and 1B illustrate examples of electronic devices; 1A and 1B illustrate examples of electronic devices; 1A and 1B illustrate examples of electronic devices; 1A and 1B are diagrams for explaining the crystal structure of lithium cobaltate; FIG. 5 is a graph showing cycle characteristics of a secondary battery using the positive electrode active material of Example 1; 4 is a graph showing rate characteristics of a secondary battery using the positive electrode active material of Example 1. FIG. 5 is a graph showing cycle characteristics of a secondary battery using the positive electrode active material of Example 1;

Embodiments of the present invention will be described in detail below with reference to the drawings. However, those skilled in the art will easily understand that the present invention is not limited to the following description, and that the forms and details thereof can be variously changed. Moreover, the present invention should not be construed as being limited to the description of the embodiments shown below.

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

A plurality of crystallites can be confirmed in one particle in the particle 110, and a crack 105 is also present in the cross section as shown in FIG. 1(A2). Note that the SEM photograph corresponding to FIG. 1 (A1) is shown in FIG.
(A). The active material particles 110 shown in FIG. 1A1 were untreated, and were used as they were for the positive electrode active material layer to fabricate a secondary battery, and the cycle characteristics were measured. is deposited in the negative electrode and separator.

In order to prevent the elution of cobalt or oxygen from the surface of the active material particles 110 shown in FIG. 1000° C. or lower). The heat treatment may be called annealing. As the metal element M2, one or both of a valence II and a valence IV metal is 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.

When Ti is used as the metal element M2, a sol-gel method using a Ti alkoxide is performed, followed by heat treatment at a high temperature (600° C. or higher and 1000° C. or lower) in an oxygen-containing atmosphere.
By performing heat treatment together with the sol-gel method using Ti alkoxide, one or both of the valence II and valence metal elements M2 are moved to the vicinity of the surface to form a structure that prevents the 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 the active material particles can be in a stable state.

In the sol-gel method, an alkoxide of the metal element M2 or the like penetrates cracks in the active material particles 110, and the cracks are repaired by heat treatment. If the temperature of the heat treatment is too low, the cracks are difficult to be repaired. Also, if the heating temperature is too high, there is a concern that lithium may evaporate.

Composite oxide particles containing lithium, metal element M1, and oxygen, such as lithium-cobalt composite oxide (LiCoO ₂ ), have oxygen vacancies in the particles, so mass transfer is particularly likely to be promoted. Therefore, the titanium oxide coated by the sol-gel method easily repairs the cracks. Titanium compounds obtained by reaction with titanium oxide and LiCoO ₂ are preferred because they are electrically conductive and do not interfere with the diffusion of lithium. Similarly, it is preferable to coat with an alkoxide of a metal that becomes a non-stoichiometric oxide or an aqueous solution of a metal salt of an organic acid, because it has electrical conductivity and lithium ion conductivity.

Even small cracks at the edges of the particles can cause large cracks due to stress concentration, so the sol-gel method and heat treatment, which also repair small cracks, are important.

A perspective view of the active material particles 100 after treatment is shown in FIG. FIG. 1B2 shows a cross-sectional view of the active material particles after treatment taken along the dotted line 150 .

As shown in FIG. 1B2, after the treatment, cracks disappear, 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 active material particles before and after treatment. Figure 2
Here are four examples.

Several patterns are conceivable for changes in crystallites due to treatment. An example of crystallite change will be described with reference to FIG.

First, FIG. 2A1 shows an example in which cracks 105 are generated between different crystallites in a particle 110. FIG. FIG. 2(A2) shows the particle 100 after the particle 110 of FIG. 2(A1) has been subjected to the above-described treatment. It is conceivable that the crack 105 is repaired by the treatment, and the different crystallites become one crystallite.

Next, FIG. 2B1 shows a large number of small cracks 105 in one crystallite in the particle 110.
This is an example where FIG. 2(B2) shows the particle 100 after the particle 110 of FIG. 2(B1) has been subjected to the above-described treatment. It is conceivable that many cracks 105 may be repaired by the treatment, resulting in defect-free crystallites.

Next, FIG. 2(C1) is an example in which a crack 105 is generated in one crystallite in the particle 110 . FIG. 2(C2) shows the particle 1 after performing the above-described treatment on the particle 110 of FIG. 2(C1).
00. It is conceivable that the cracks 105 are repaired by the treatment, resulting in defect-free crystallites.

Next, FIG. 2(D1) is an example in which the crystal axes of adjacent crystallites are different in the particle 110 . FIG. 2D2 shows the particles 100 after the particles 110 in FIG. 2D1 are subjected to the above-described treatment.
is. Adjacent crystallites may become one crystallite by performing the treatment. However, adjacent crystallites preferably have the same cubic closest packing structure of oxygen.

In addition, magnesium oxide (MgO _x (0<X)),
Calcium oxide (CaO _x (0<X)), silicon oxide (SiO _x (0<X)), etc. segregate. With such a structure, cracks are less likely to occur, and cobalt or oxygen in the active material particles does not flow out to the electrolytic solution.

Note that FIG. 3B shows SEM photographs of a plurality of active material particles after treatment.

The active material particles 100 after the treatment have a structure in which the number of cracks and defects is reduced so that cobalt and oxygen are not eluted into the electrolytic solution, and the stability of the crystal structure in the active material particles is improved. Better characteristics. In addition, the active material particles 100 after treatment are novel substances,
It can also be called a novel 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 shown in Embodiment 1, liquid phase methods such as a sol-gel method, solid phase methods, sputtering methods, vapor deposition methods, CVD (chemical vapor deposition) methods, A method such as a PLD (pulse laser deposition) method can be applied.

In the present embodiment, the sol-gel method, which can be expected to provide uniform coating and can be processed at atmospheric pressure, is applied. A manufacturing method thereof will be described with reference to FIGS.

<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-mentioned II- and IV-valent metals, specifically magnesium, calcium, silicon, and titanium can be used. Furthermore, various elements such as alkali metal elements, alkaline earth metal elements, typical metal elements other than alkali metal elements and alkaline earth metal elements, and transition metal elements may be used as M2.

Alkali metal elements include Li, Na, K, Rb, Cs, and Fr, and alkaline earth metal elements include Be, Mg, Ca, Sr, Ba, and Ra. Examples of typical metal elements other than the group metal element I include Sc, Ti, V, Cr, M
n, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag,
Hf, Ta, W, Re, Os, Ir, Pt, and Au, and the transition metal element is A
l, Zn, Ga, Ge, Cd, In, Sn, Sb, Hg, TI, Pb, Bi, Po.

FIG. 4A-1 shows a general formula of the alkoxide of the metal element M2. In the formula of FIG. 4A-1, M2 represents a 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 linear alkyl groups such as methyl group, ethyl group, propyl group, hexyl group, octyl group, decyl group, dodecyl group and octadecyl group, isopropyl group, isobutyl group, t -Branched chain alkyl groups such as butyl group, and examples of the aryl group having 6 to 13 carbon atoms include phenyl group, naphthyl group,
Specific examples include 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 for M2 in FIG. 4A-1. Specific examples of titanium alkoxides include tetramethoxytitanium, tetraethoxytitanium, tetra-n-propoxytitanium, tetra-i-propoxytitanium ((A-
3)) (tetraisopropyl orthotitanate, titanium isopropoxide, Titanium
m tetraisopropoxide, TTIP, etc.), tetra-n-butoxytitanium, tetra-i-butoxytitanium, tetra-sec-butoxytitanium, tetra-t-butoxytitanium, and the like.

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

Next, particles of a composite oxide containing lithium and the metal element M1 (the active material particles 110 described in Embodiment 1) are added to an alcohol solution of the alkoxide of the metal element M2 and stirred. By adding water (H ₂ O) here, a hydrolysis reaction between water and titanium alkoxide occurs as shown in FIG. 4(B). At the same time, an acid or base may be added as a catalyst. A similar hydrolysis reaction also occurs when an alcohol solution of an alkoxide of the metal element M2 is placed in an atmosphere containing water and stirred.

Further, following the hydrolysis reaction of FIG. 4(B), the dehydration condensation reaction of FIG. 4(C) occurs. Figure 4 (
By repeating the hydrolysis shown in B) and the condensation reaction shown in FIG. 4(C), the metal element M2
A sol of the oxide of the metal element M2 is produced by further advancing the reaction.

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. 4(D-1) and 4(D-2), the hydroxyl groups on the surface of the composite oxide particles containing lithium and the metal element M1 are the metal element M shown in FIG. 4(B).
The hydroxyl group of the metal (M2) produced by hydrolysis from the alkoxide of 2, and FIG.
, a sol or gel containing an oxide of a metal (M2) different from M1 is formed on particles containing a metal (M1) oxide.

After that, the particles 111 are collected by filtration and the solvent is removed, so that the composite oxide particles containing lithium and the metal element M1 can be coated with the material containing the metal element M2.

Next, more specifically, a method of coating particles 111 with titanium oxide using a sol-gel method and then obtaining active material particles 100 will be described with reference to FIGS. 5 and 6. FIG.

<Mixing of Metal Alkoxide Solution and Particles 111 (S14 in FIG. 6)>
First, TTIP 171 is dissolved in isopropanol 170, and particles 111 are mixed therein (see FIG. 5(A)).

<Coating particles 111 with titanium oxide by sol-gel method (S15 in FIG. 6)>
The solution shown in FIG. 5A is stirred for 4 hours under conditions of 25° C. and 90% RH. This treatment utilizes water in the atmosphere, TTIP, and hydrolysis and dehydration polycondensation reactions that occur on the surface of the particles 111 to coat the particles 111 with TiO _x sol 172 (see FIG. 5B).
Further, the reaction proceeds to generate TiO _x gel on the particle surface.

<Recovery of TiO _x gel-coated particles 111 (S16 in FIG. 6)>
In FIG. 6, the mixed liquid after the process of S15 is filtered to recover the residue.

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

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

In the present embodiment, an example of using titanium alkoxide as the alkoxide of the metal element M2 is shown, but it is not particularly limited, and other metal alkoxides may be used. Moreover, the heating conditions are not particularly limited, and the temperature raising conditions and the number of times of heat treatment may be performed plural times. Also, the conditions for slow cooling after heating are not particularly limited, and the temperature-lowering conditions may be appropriately adjusted.

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

(Embodiment 3)
In this embodiment, the active material particles 10 functioning as the positive electrode active material described in the previous embodiment
An example of the shape of a secondary battery having 0 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. 7(A) is a coin type (single layer flat type)
7B is a cross-sectional view of the secondary battery.

In a coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, are insulated and sealed with a gasket 303 made of polypropylene or the like.
The positive electrode 304 includes a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact therewith.
Formed by Further, 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 the active material layers of the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 may be formed only on one side.

For the positive electrode can 301 and the negative electrode can 302, metals such as nickel, aluminum, and titanium that are corrosion resistant to the electrolyte, alloys thereof, and alloys of these and other metals (for example, stainless steel) can be used. can. Also, in order to prevent corrosion due to the electrolyte, it is preferable to coat with nickel, aluminum, or the like. The positive electrode can 301 is the positive electrode 304, and the negative electrode can 302 is the negative electrode 30.
7 are electrically connected to each other.

The negative electrode 307, the positive electrode 304 and the separator 310 were impregnated with an electrolyte, and
, a positive electrode 304, a separator 310, a negative electrode 307, and a negative electrode can 302 are stacked in this order with the positive electrode can 301 facing down, and the positive electrode can 301 and the negative electrode can 302 are crimped via a gasket 303 to form a coin shape. to manufacture the 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-shaped secondary battery 300 can have excellent cycle characteristics.

Here, the flow of current during charging of the secondary battery 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 secondary batteries using lithium, the anode (anode) and the cathode (cathode) are switched between charging and discharging, and the oxidation reaction and the reduction reaction are switched, so the electrode with a high reaction potential is called a positive electrode. An electrode with a low reaction potential is called a negative electrode. Therefore, in this specification, the positive electrode is the “positive electrode” or “positive electrode” or “positive electrode” during charging, discharging, reverse pulse current, or charging current. A negative electrode is called a “negative electrode” or a “negative electrode”. When using the terms anode and cathode related to oxidation reaction and reduction reaction, during charging and discharging,
It could be the other way around, which can lead to confusion. Accordingly, the terms anode and cathode are not used herein. If the anode (anode)
When using the term "or cathode", specify whether it is during charging or discharging, and also indicate whether it corresponds to the positive electrode (positive electrode) or the negative electrode (negative electrode).

A charger is connected to two terminals shown in FIG. 7C to charge the secondary battery 300 . As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases. In FIG. 7(F), the secondary battery 3
00 to the positive electrode 304 , and in the secondary battery 300 , the positive electrode 30
4 toward the negative electrode current collector 308 and from the negative electrode toward the external terminal of the secondary battery 300 is defined as the positive direction. That is, the direction in which the charging current flows is the direction of the current.

[Charging and discharging method]
Charging and discharging of the secondary battery can be performed, for example, as follows.

≪CC charging≫
First, CC charging will be described as one of charging methods. CC charging is a charging method in which a constant current is passed through the secondary battery throughout the charging period and charging is stopped when a predetermined voltage is reached. A secondary battery is assumed to be an equivalent circuit of internal resistance R and secondary battery capacity C as shown in FIG. 8(A). In this case, the secondary battery voltage _VB is the sum of the voltage V _R across the internal resistance R and the voltage V _C across the secondary battery capacity C.

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

Then, when the secondary battery voltage _VB reaches a predetermined voltage, for example 4.3V, charging is stopped. When CC charging is stopped, the switch is turned off and current I=0, as shown in FIG. 8(B).
becomes. Therefore, the voltage VR applied to the internal resistance _R becomes 0V. Therefore, the voltage drop across the internal resistance R is eliminated, and the secondary battery voltage _VB drops accordingly.

FIG. 8C shows an example of the secondary battery voltage _VB and charging current during CC charging and after CC charging is stopped. The secondary battery voltage _VB , which increased during CC charging,
It shows a slight decrease after the C charging is stopped.

≪CCCV charging≫
Next, CCCV charging, which is a different charging method from the above, will be described. CCCV charging is a charging method in which the battery is first charged to a predetermined voltage by CC charging, and then charged by CV (constant voltage) charging until the flowing current decreases, specifically until the terminal current value is reached. .

During CC charging, as shown in FIG. 9A, the switch of the constant-current power supply is turned on, the switch of the constant-voltage power supply is turned off, and a constant current I flows through the secondary battery. Since the current I is constant during this period, the voltage V _R applied to the internal resistance R is also constant according to Ohm's law of V _R =R×I. On the other hand, the voltage V _C applied to the secondary battery capacity C rises with time. Therefore, the secondary battery voltage _VB increases over time.

Then, when the secondary battery voltage _VB reaches a predetermined voltage, for example 4.3 V, the CC charge is changed to the C charge.
Switch to V charging. During CV charging, as shown in FIG. 9B, the switch of the constant-voltage power supply is turned on, the switch of the constant-current power supply is turned off, and the secondary battery voltage _VB becomes constant. On the other hand, the voltage V _C applied to the secondary battery capacity C rises with time. V _B =V _R
+ _VC , the voltage V _R across the internal resistor R decreases over time. As the voltage V _R applied to the internal resistance R decreases, the current I flowing through the secondary battery also decreases according to Ohm's law of V _R =R×I.

Then, when the current I flowing through the secondary battery reaches a predetermined current, for example, a current corresponding to 0.01C, charging is stopped. When CCCV charging is stopped, all switches are turned off and current I=0 as shown in FIG. 9(C). Therefore, the voltage VR applied to the internal resistance _R becomes 0V. However, since the voltage _VR applied to the internal resistance R is sufficiently reduced by CV charging, the secondary battery voltage _VB hardly drops even if the voltage drop across the internal resistance R disappears.

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

≪CC Discharge≫
Next, CC discharge, which is one of the discharge methods, will be described. CC discharge is a discharge method in which a constant current is supplied from the secondary battery throughout the discharge period, and discharge is stopped when the secondary battery voltage _VB reaches a predetermined voltage, for example, 2.5V.

FIG. 10 shows an example of secondary battery voltage _VB and discharge current during CC discharge. It shows how the secondary battery voltage _VB drops as the discharge progresses.

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

(Embodiment 4)
In this embodiment, the active material particles 10 functioning as the positive electrode active material described in the previous embodiment
Examples of materials that can be used for secondary batteries having 0 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 outer package 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 aid and a binder.

As the positive electrode active material, the active material particles 1 functioning as the positive electrode active material described in the previous embodiment are used.
00 can be used. By using the active material particles 100 functioning as the positive electrode active material described in the above embodiment, the secondary battery can have high capacity and excellent cycle characteristics.

A carbon material, a metal material, a conductive ceramic material, or the like can be used as the conductive aid. A fibrous material may also be used as the conductive aid. The content of the conductive aid with respect to the total amount of the active material layer is preferably 1 wt % or more and 10 wt % or less, more preferably 1 wt % or more and 5 wt % or less.

The conductive aid can form an electrically conductive network in the active material layer. The conductive aid can maintain the path of electrical conduction between the positive electrode active materials. By adding a conductive aid to the active material layer, an active material layer having high electrical conductivity can be realized.

Examples of conductive aids that can be used include natural graphite, artificial graphite such as mesocarbon microbeads, and carbon fiber. As carbon fibers, for example, carbon fibers such as mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers can be used. As the carbon fiber, carbon nanofiber, carbon nanotube, or the like can be used. Carbon nanotubes can be produced, for example, by vapor deposition. Further, as the conductive aid, carbon materials such as carbon black (acetylene black (AB), etc.), graphite (black lead) particles, graphene, fullerene, etc. can be used. Also, for example, powders of metals such as copper, nickel, aluminum, silver, and gold, metal fibers, conductive ceramics materials, and the like can be used.

Alternatively, a graphene compound may be used as the conductive aid.

Graphene compounds may have excellent electrical properties of having high electrical conductivity and excellent physical properties of having high flexibility and high mechanical strength. Also, the graphene compound has a planar shape. Graphene compounds enable surface contact with low contact resistance. Moreover, even if it is thin, it may have very high conductivity, and a small amount can efficiently form a conductive path in the active material layer. Therefore, it is preferable to use a graphene compound as a conductive aid because the contact area between the active material and the conductive aid can be increased. Moreover, it is preferable because the electrical resistance can be reduced in some cases. Here, as the graphene compound, for example, graphene or multi-graphene or reduced graphene O
It is particularly preferred to use xide (hereinafter referred to as RGO). Here, RGO refers to a compound obtained by reducing graphene oxide (GO), for example.

When using an active material with a small particle size, for example, an active material with a particle size of 1 μm or less, the specific surface area of the active material is large, and more conductive paths connecting the active materials are required. Therefore, the amount of conductive aid tends to increase, and the amount of supported active material tends to decrease relatively. When the supported 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 aid, since even a small amount of the graphene compound can efficiently form a conductive path, so that the supported amount of the active material does not decrease.

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

FIG. 11A shows a vertical cross-sectional view of the active material layer 200. FIG. Active material layer 200 includes active material particles 10
0, a graphene compound 201 as a conductive aid, 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-like 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 compounds 201 are dispersed substantially uniformly inside the active material layer 200. As shown in FIG. Although the graphene compound 201 is schematically represented by a thick line in FIG. 11A, it is actually a thin film having a thickness of a single layer or multiple layers of carbon molecules. Since the plurality of graphene compounds 201 are formed so as to wrap or cover the plurality of active material particles 100 or stick to the surfaces of the plurality of active material particles 100, they are in surface contact with each other.

Here, a mesh-like graphene compound sheet (hereinafter referred to as graphene compound net or graphene net) can be formed by bonding a plurality of graphene compounds. When the graphene net covers the active material, the graphene net can also function as a binder that binds the active materials together. Therefore, the amount of binder can be reduced or not used, and the ratio of the active material to the electrode volume and electrode weight can be improved. That is, the capacity of the secondary battery can be increased.

Here, it is preferable that graphene oxide be used as the graphene compound 201 and be mixed with an active material to form a layer to be the active material layer 200 and then be reduced. By using graphene oxide, which is highly dispersible in a polar solvent, to form the graphene compound 201 , the graphene compound 201 can be dispersed substantially uniformly inside the active material layer 200 . Since the solvent is removed by volatilization from the dispersion medium containing the uniformly dispersed graphene oxide and the graphene oxide is reduced, the graphene compounds 201 remaining in the active material layer 200 partially overlap and are dispersed to the extent that they are in surface contact with each other. It is possible to form a three-dimensional conductive path.
Note that graphene oxide may be reduced by heat treatment or by using a reducing agent, for example.

Therefore, unlike a granular conductive additive such as acetylene black that is in point contact with the active material, the graphene compound 201 enables surface contact with low contact resistance, so the active material can be obtained with a smaller amount than a normal conductive additive. Electrical conductivity between the particles 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. Fluororubber can also be used as the binder.

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

Alternatively, binders include polystyrene, polymethyl acrylate, polymethyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride,
Materials such as polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, nitrocellulose, etc. are preferably used.

You may use a binder combining two or more among the above.

For example, a material having a particularly excellent viscosity adjusting effect may be used in combination with another material. For example, although rubber materials and the like are excellent in adhesive strength and elasticity, it may be difficult to adjust the viscosity when they are 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 such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose and diacetyl cellulose, cellulose derivatives such as regenerated cellulose, and starch are used. be able to.

In addition, the solubility of cellulose derivatives such as carboxymethyl cellulose is increased by using salts such as sodium salts and ammonium salts of carboxymethyl cellulose.
It becomes easy to exhibit the effect as a viscosity modifier. When the solubility is increased, the dispersibility with the active material and other constituents can be enhanced when the electrode slurry is prepared. In this specification, cellulose and cellulose derivatives used as binders for electrodes also include salts thereof.

The water-soluble polymer stabilizes the viscosity by dissolving in water, and can stably disperse the active material and other materials combined as a binder, such as styrene-butadiene rubber, in the aqueous solution. In addition, since it has a functional group, it is expected to be stably adsorbed on the surface of the active material. Also, cellulose derivatives such as carboxymethyl cellulose,
For example, there are many materials that have functional groups such as hydroxyl groups and carboxyl groups, and it is expected that the polymers will interact with each other due to the functional groups, and that the active material surface will be extensively covered.

When the binder that covers or contacts the surface of the active material forms a film, it is expected to function as a passivation film to suppress the decomposition of the electrolytic solution. Here, the passive film is a film with no electron conductivity or a film with extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, at the battery reaction potential Decomposition of the electrolytic solution can be suppressed. It is further desirable that the passivation film suppresses electrical conductivity and allows lithium ions to conduct.

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

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

As the negative electrode active material, an element capable of performing charge-discharge reaction by alloying/dealloying reaction with lithium can be used. For example, materials containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. Such an element has a larger capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh/g. Therefore, it is preferable to use silicon for the negative electrode active material. Compounds containing these elements may also be used. For example, SiO, _Mg2Si , _Mg2Ge , SnO, _SnO2 , _Mg2Sn , _SnS2 , V
_{2Sn3 , FeSn2 , CoSn2 , Ni3Sn2} , _Cu6Sn5 , _Ag3Sn , _{Ag3
Sb , Ni2MnSb} , _CeSb3 , _LaSn3 , _La3Co2Sn7 , _CoSb3 , I
nSb, SbSn, and the like. Here, elements capable of undergoing charge-discharge reactions by alloying/dealloying reactions with lithium, compounds containing such elements, and the like are sometimes referred to as alloy-based materials.

In this specification and the like, SiO refers to silicon monoxide, for example. Alternatively, SiO is SiO
It can also be expressed as _x . Here x preferably has a value close to one. For example, x is 0
. 2 or more and 1.5 or less are preferable, and 0.3 or more and 1.2 or less are more preferable.

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 artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape and are preferred. MCMB is also relatively easy to reduce its surface area and may be preferred. Examples of natural graphite include:
Flaky graphite, spheroidized natural graphite, and the like can be mentioned.

Graphite exhibits a potential as low as lithium metal when lithium ions are inserted into graphite (at the time of lithium-graphite intercalation compound formation) (0.05 V or more and 0.3 V or less vs. Li/L
i ⁺ ). This allows the lithium ion secondary battery to exhibit a high operating voltage. Furthermore, 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 negative electrode active materials, titanium dioxide (TiO ₂ ), lithium titanium oxide (Li ₄ T
i ₅ O ₁₂ ), lithium-graphite intercalation compound (Li _x C ₆ ), niobium pentoxide (Nb ₂ O ₅ )
, tungsten oxide (WO ₂ ), molybdenum oxide (MoO ₂ ), and the like can be used.

Also, Li _3-x M _x N (M=Co, Ni, Cu) having a Li ₃ N-type structure, which is a composite nitride of lithium and a transition metal, can be used as the negative electrode active material. For example, _Li2.6
Co _0.4 N ₃ exhibits a large charge/discharge capacity (900 mAh/g, 1890 mAh/cm ³ ) and is preferred.

When a composite nitride of lithium and a transition metal is used, lithium ions are included in the negative electrode active material,
It is preferable because 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 as the positive electrode active material, a composite nitride of lithium and a transition metal can be used as the negative electrode active material by preliminarily desorbing the 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, transition metal oxides such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO) that do not form an alloy with lithium may be used as the negative electrode active material. Further, as materials in _which a conversion reaction occurs, oxides such _{as Fe2O3} , CuO, _Cu2O , _RuO2 and _Cr2O3 , sulfides such as _CoS0.89 , NiS and CuS, _{and Zn3N2} , _Cu3N , _Ge3
It also occurs in nitrides such as _N4 , phosphides such as _NiP2 , _FeP2 and _CoP3 , and fluorides such as _FeF3 and _BiF3 .

As the conductive aid and binder that the negative electrode active material layer can have, the same materials as the conductive aid 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. For the negative electrode current collector, it is preferable to use 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, aprotic organic solvents are preferred, such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, and 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-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc., or two or more of these can be used in any combination and ratio.

In addition, by using one or more flame-retardant and non-volatile ionic liquids (room temperature molten salt) as the solvent for the electrolyte, the internal temperature of the power storage device may rise due to internal short circuits, overcharging, etc. Also, it is possible to prevent the power storage device from exploding or igniting. Ionic liquids consist of cations and anions, including organic cations and anions. Organic cations used in the electrolytic solution 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. Anions used in the electrolytic solution include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, and hexafluorophosphate anions. , or perfluoroalkyl phosphate anions.

Further, as electrolytes to be dissolved in the above solvents, for example, LiPF ₆ , LiClO ₄ , LiA
_sF6 , _LiBF4 , _LiAlCl4 , LiSCN, LiBr, LiI, _{Li2SO4 ,
Li2B10Cl10 , Li2B12Cl12 , LiCF3SO3 , LiC4F9SO3 _ _ _ _}
, LiC _{( CF3SO2 ) 3} , LiC( _{C2F5SO2 ) 3} , LiN( _{CF3SO2 ) 2}
, LiN(C ₄ F ₉ SO ₂ )(CF ₃ SO ₂ ), LiN(C ₂ F ₅ SO ₂ ) ₂ or the like, or two or more thereof in any combination and ratio. be able to.

As the electrolytic solution used for the power storage device, it is preferable to use a highly purified electrolytic solution that contains a small amount of particulate matter and elements other than constituent elements of 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.

Vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), LiBOB, and dinitrile compounds such as succinonitrile and adiponitrile may also 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.

A polymer gel electrolyte obtained by swelling a polymer with an electrolytic solution may also be used. By using the polymer gel electrolyte, the safety against leakage and the like is enhanced. Also, the thickness and weight of the secondary battery can be reduced.

Silicone gel, acrylic gel, acrylonitrile gel,
A polyethylene oxide gel, a polypropylene oxide gel, a fluoropolymer gel, or the like can be used. Examples of polymers include polyethylene oxide (PEO
), PVDF, polyacrylonitrile, etc., and copolymers containing them can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous geometry.

Further, instead of the electrolytic solution, a solid electrolyte having an inorganic material such as a sulfide system or an oxide system, or P
A solid electrolyte having a polymeric material such as EO (polyethylene oxide) can be used. When a solid electrolyte is used, installation of separators and spacers becomes unnecessary. In addition, since the entire battery can be made solid, the risk of liquid leakage is eliminated and the safety is dramatically improved.

[Separator]
Also, the secondary battery preferably has a separator. Examples of separators include fibers containing cellulose such as paper, non-woven fabrics, glass fibers, ceramics, synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, and polyurethane. can be used. It is preferable that the separator is processed into an envelope shape and arranged 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, or the like can be used. For example, PVDF, polytetrafluoroethylene, or the like can be used as the fluorine-based material. Examples of polyamide materials that can be used include nylon and aramid (meta-aramid and para-aramid).

Coating with a ceramic-based material improves oxidation resistance, so deterioration of the separator during high-voltage charging and discharging can be suppressed, and the reliability of the secondary battery can be improved. In addition, when coated with a fluorine-based material, the separator and the electrode are more likely to adhere to each other, and the output characteristics can be improved.
Coating with a polyamide-based material, particularly aramid, improves the heat resistance, so that the safety of the secondary battery can be improved.

For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid. Alternatively, a polypropylene film may be coated with a mixed material of aluminum oxide and aramid on the surface thereof in contact with the positive electrode, and coated with a fluorine-based material on the surface thereof 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 unit volume of the secondary battery can be increased.

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

(Embodiment 5)
[Cylindrical secondary battery]
In this embodiment, an example of a cylindrical secondary battery will be described with reference to FIGS. As shown in FIG. 12A, a cylindrical secondary battery 600 has a positive electrode cap (battery cover) 601 on its top surface and battery cans (armor cans) 602 on its side and bottom surfaces. The positive electrode cap and the battery can (outer can) 602 are insulated by a gasket (insulating packing) 610 .

FIG. 12B is a schematic cross-sectional view of a cylindrical secondary battery. A battery element in which a strip-shaped positive electrode 604 and a strip-shaped negative electrode 606 are wound with a separator 605 interposed therebetween is provided inside a hollow columnar battery can 602 . Although not shown, the battery element is wound around a center pin. Battery can 602 is closed at one end and open at the other end. The battery can 602 can be made of a metal such as nickel, aluminum, or titanium that is resistant to corrosion by the electrolyte, an alloy thereof, or an alloy of these and other metals (for example, stainless steel). . Also, in order to prevent corrosion due to the electrolyte, it is preferable to coat with 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 insulating plates 608 and 609 facing each other. A non-aqueous electrolyte (not shown) is filled inside the battery can 602 in which the battery element is provided. The non-aqueous electrolyte is
A battery similar to a coin-type secondary battery can be used.

Since the positive electrode and the negative electrode used in a cylindrical storage battery are wound, it is preferable to form the active material on both sides of the current collector. A positive electrode terminal (positive collector lead) 603 is connected to the positive electrode 604 , and a negative electrode terminal (negative collector lead) 607 is connected to the negative electrode 606 . A metal material such as aluminum can be used for both the positive terminal 603 and the negative terminal 607 . positive terminal 60
3 is resistance welded to the safety valve mechanism 612, and the negative electrode terminal 607 is resistance welded to the bottom of the battery can 602, respectively. The safety valve mechanism 612 is a positive temperature coefficient (PTC) element.
effective) 611 to the positive electrode cap 601 . The safety valve mechanism 612 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermal resistance element whose resistance increases when the temperature rises, and the increase in resistance limits the amount of current to prevent abnormal heat generation. Barium titanate (BaTiO ₃ ) semiconductor ceramics or the like can be used for the PTC element.

Moreover, as shown in FIG.
The module 615 may be constructed by being sandwiched between. The plurality of secondary batteries 600 may be connected in parallel, may be connected in series, or may be connected in series after being connected in parallel. By configuring a module 615 having a plurality of secondary batteries 600,
A large amount of power can be extracted.

FIG. 12D is a top view of the module 615. FIG. The conductive plate 613 is shown in dashed lines for clarity of illustration. As shown in FIG. 12D, the module 615 may have conductors 616 that electrically connect the plurality of secondary batteries 600 . A conductive plate may be provided overlying the conductor 616 . Also, 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 the secondary battery 600
00 can be heated by the temperature control device 617 when it is too cold. 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, the cylindrical secondary battery 600 with high capacity and excellent cycle characteristics can be obtained.

[Structural example of secondary battery]
Another structural example of the secondary battery is described with reference to FIGS.

13(A) and 13(B) are diagrams showing external views of the battery pack. The battery pack
It has a circuit board 900 and a secondary battery 913 . A secondary battery 913 has a terminal 951 and a terminal 952 and is covered with a label 910 . The battery pack may also have an antenna 914 .

The circuit board 900 is fixed with a seal 915 . Circuit board 900 has circuitry 912 . Terminal 911 is electrically connected to terminals 951 and 952 of secondary battery 913 through circuit board 900 . A terminal 911 is electrically connected to an antenna 914 and a 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 used as a control signal input terminal, a power supply terminal, or the like.

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

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

Note that the structure of the battery pack is not limited to that shown in FIG.

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

As shown in FIG. 14A-1, an antenna 914 is provided on one of a pair of surfaces of a secondary battery 913 with a layer 916 interposed therebetween, and as shown in FIG. An antenna 918 is provided with a layer 917 interposed on the other of the pair of surfaces. Layer 917 is, for example, secondary battery 91
It has the function of preventing the influence of 3 on the electromagnetic field. A magnetic material, for example, can be used as the layer 917 .

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

An antenna having a shape applicable to the antenna 914 can be applied to the antenna 918 . Further, the antenna 918 may be a planar conductor. This flat conductor can function as one of conductors for electric field coupling. In other words, the antenna 914 may function as one of the two conductors of the capacitor. As a result, electric power can be exchanged not only by electromagnetic fields and magnetic fields, but also by electric fields.

Alternatively, as shown in FIG. 14B-1, the display device 920 may be provided in the battery packs shown in FIGS. 13A and 13B. The display device 920 is electrically connected to the terminals 911 . Note that the same parts as those of the battery pack shown in FIGS. 13A and 13B are shown in FIG.
The description of the battery packs shown in (A) and FIG. 13(B) can be used as appropriate.

The display device 920 may display, for example, an image indicating whether or not the battery is being charged, an image indicating the amount of stored electricity, and the like. As the display device 920, electronic paper, a liquid crystal display device, an electroluminescence (also referred to as EL) display device, or the like can be used, for example. For example, by using electronic paper, power consumption of the display device 920 can be reduced.

Alternatively, as shown in FIG. 14(B-2), the secondary battery 9 shown in FIGS. 13(A) and 13(B)
13 may be provided with a sensor 921 . Sensor 921 is connected to terminals 922 and circuit board 900
is electrically connected to the terminal 911 via the . Note that the description of the power storage device illustrated in FIGS. 13A and 13B can be used as appropriate for the same portions as those of the power storage device illustrated in FIGS.

Sensors 921 include, for example, displacement, position, speed, acceleration, angular velocity, number of revolutions, distance, light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate , humidity, gradient, vibration, smell, or infrared rays. By providing the sensor 921 , for example, data (such as temperature) indicating the environment in which the power storage device is placed can be detected and stored in the memory in the circuit 912 .

Further, a structural example of the secondary battery 913 is described with reference to FIGS. 15 and 16. FIG.

A secondary battery 913 illustrated in FIG. 15A includes a wound body 950 provided with a terminal 951 and a terminal 952 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 FIG. 15A illustrates the case 930 separately for convenience, but actually, the wound body 950 is covered with the case 930 and the terminals 951 and 95 are connected.
2 extends outside the housing 930 . As the housing 930, a metal material (such as aluminum) or a resin material can be used.

Note that as shown in FIG. 15B, the housing 930 shown in FIG. 15A may be formed using a plurality of materials. For example, the secondary battery 913 shown in FIG.
30b are bonded together, and the wound body 9 is formed in the region surrounded by the housing 930a and the housing 930b.
50 are provided.

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

Furthermore, the structure of the wound body 950 is shown in FIG. A wound body 950 has 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 laminated with the separator 933 interposed therebetween, and the laminated sheet is wound. Note that the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked more than once.

The negative electrode 931 is connected to the terminal 911 shown in FIG. 13 through one of the terminals 951 and 952 . The positive electrode 932 is connected to the terminal 91 shown in FIG.
1.

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

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

First, as electronic devices to which a secondary battery is applied, for example, television devices (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (mobile phones) Also called a telephone or a mobile phone device), a portable game machine, a personal digital assistant, a sound reproducing device, a large game machine such as a pachinko machine, and the like.

Next, FIGS. 17A and 17B show an example of a tablet terminal that can be folded in two. A tablet terminal 9600 shown in FIGS. 17A and 17B includes a housing 9630
a, a housing 9630b, a movable portion 9640 connecting the housings 9630a and 9630b, a display portion 9631, 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. have. By using a flexible panel for the display portion 9631, the tablet terminal can have a wider display portion. FIG. 17A shows a state in which the tablet terminal 9600 is opened, and FIG. 17B shows a state in which the tablet terminal 9600 is closed.

The tablet terminal 9600 also includes a power storage unit 9635 inside the housings 9630a and 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. A keyboard button can be displayed on the display portion 9631 by touching a position where a keyboard display switching button on the touch panel is displayed with a finger, a stylus, or the like.

A display mode switching switch 9626 can switch the orientation of display such as vertical display or horizontal display, and can select switching between black-and-white display and color display. The power saving mode switching switch 9625 can optimize display luminance according to the amount of external light during use detected by a light sensor incorporated in the tablet terminal 9600 . The tablet terminal may incorporate not only the optical sensor but also other detection devices such as a sensor for detecting inclination such as a gyro and an acceleration sensor.

FIG. 17B shows a closed state, and the tablet terminal includes a housing 9630, a solar battery 96
33 and a charge/discharge control circuit 9634 including a DCDC converter 9636 . As the power storage unit 9635, the secondary battery of one embodiment of the present invention is used.

Note that since the tablet terminal 9600 can be folded in half, it can be folded so that the housings 9630a and 9630b overlap each other when not in use. By folding
Since the display portion 9631 can be protected, the durability of the tablet terminal 9600 can be increased. In addition, since the power storage unit 9635 including 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 terminals shown in FIGS. 17(A) and 17(B) have a function of displaying various information (still images, moving images, text images, etc.), a calendar, a date or time, and the like. It can have a function of displaying on the display unit, a touch input function of performing a touch input operation or editing information displayed on the display unit, a function of controlling processing by various software (programs), and the like.

By the solar cell 9633 attached to the surface of the tablet type terminal, power is
It can be supplied to a display unit, a video signal processing unit, or the like. Note that the solar cell 9633 can be provided on one side or both sides of the housing 9630 so that the power storage unit 9635 can be efficiently charged.

Also, the configuration and operation of the charge/discharge control circuit 9634 shown in FIG.
C) shows a block diagram for explanation. In FIG. 17C, a solar cell 9633 and a power storage body 963
5 shows a DCDC converter 9636, a converter 9637, switches SW1 to SW3, and a display portion 9631. A power storage unit 9635, a DCDC converter 9636, a converter 9637, and switches SW1 to SW3 are the charge/discharge control circuit shown in FIG. 96
34.

First, an example of operation in the case where the solar cell 9633 generates power with external light is described.
Electric power generated by the solar cell is stepped up or down in a DCDC converter 9636 so as to have a voltage for charging the power storage unit 9635 . Then, when the 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 is turned on.
Then, the voltage required for the display portion 9631 is stepped up or stepped down. In addition, the display unit 9631
When the display is not performed, SW1 is turned off and SW2 is turned on to charge the power storage unit 9635 .

Note that although the solar cell 9633 is shown as an example of a power generation means, it is not particularly limited, and the power storage body 9635 is charged by another power generation means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). may be For example, a non-contact power transmission module that transmits and receives power wirelessly (non-contact) for charging may be used in combination with other charging means.

FIG. 18 shows an example of another electronic device. In FIG. 18, a display device 8000 is an example of an electronic device using a secondary battery 8004 of one embodiment of the present invention. Specifically, the display device 800
0 corresponds to a display device for receiving TV broadcast, 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 inside the housing 8001 . The display device 8000 can receive power from a commercial power source or can use power accumulated in the secondary battery 8004 . Therefore, the use of the secondary battery 8004 according to one embodiment of the present invention as an uninterruptible power supply makes it possible to use the display device 8000 even when power cannot be supplied from a commercial power supply due to a power failure or the like.

The display portion 8002 includes a liquid crystal display device, a light emitting device in which each pixel is provided with a light emitting element such as an organic EL element, an electrophoretic display device, a DMD (Digital Micromirror Devi).
ce), PDP (Plasma Display Panel), FED (Field
A semiconductor display device such as an emission display) can be used.

The display device includes all display devices for information display, such as for TV broadcast reception, personal computer, advertisement display, and the like.

In FIG. 18, a stationary lighting device 8100 includes a secondary battery 81 according to one embodiment of the present invention.
03 is an example of electronic equipment. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, and the like. In FIG. 18, the secondary battery 8103 is connected to the housing 81
01 and the light source 8102 are installed inside the ceiling 8104 , but the secondary battery 8103 may be installed inside the housing 8101 . The lighting device 8100 can receive power from a commercial power source or can use power accumulated in the secondary battery 8103 . Therefore, the use of the secondary battery 8103 according to one embodiment of the present invention as an uninterruptible power supply makes it possible to use the lighting device 8100 even when power cannot be supplied from a commercial power supply due to a power failure or the like.

Note that although FIG. 18 illustrates the stationary lighting device 8100 provided on the ceiling 8104 , the secondary battery according to one embodiment of the present invention can be used in places other than the ceiling 8104 , such as the side walls 8105 and the floor 8105 .
106, the window 8107, or the like, or a desk-top lighting device.

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

In FIG. 18, an air conditioner having an indoor unit 8200 and an outdoor unit 8204 is
This is an example of an electronic device using the secondary battery 8203 of one embodiment of the present invention. Specifically, the indoor unit 8200 has a housing 8201, a blower port 8202, a secondary battery 8203, and the like. Although FIG. 18 illustrates the case where the secondary battery 8203 is provided in the indoor unit 8200, the secondary battery 8203 may be provided in the outdoor unit 8204. Alternatively, both the indoor unit 8200 and the outdoor unit 8204 may be provided with the secondary battery 8203 . The air conditioner can receive power from a commercial power source or can use power accumulated in the secondary battery 8203 . In particular, the secondary battery 82 is installed in both the indoor unit 8200 and the outdoor unit 8204.
03, an air conditioner can be used even when power cannot be supplied from a commercial power supply due to a power failure or the like by using the secondary battery 8203 according to one embodiment of the present invention as an uninterruptible power supply. becomes.

Although FIG. 18 exemplifies a separate type air conditioner composed of an indoor unit and an outdoor unit, an integrated type air conditioner having the function of the indoor unit and the function of the outdoor unit in one housing is used. , 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 a secondary battery 8304 of one embodiment of the present invention. Specifically, the electric refrigerator-freezer 8300 includes a housing 8301, a refrigerator compartment door 8302, a freezer compartment door 8303, a secondary battery 8304, and the like. In FIG. 18, a secondary battery 8304 is provided inside a housing 8301 . The electric refrigerator-freezer 8300
Power can be supplied from a commercial power supply, or power accumulated in the secondary battery 8304 can be used. 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 power cannot be supplied from a commercial power supply due to a power failure or the like.

In addition, during times when electronic equipment is not used, especially during times when the ratio of the amount of power actually used to the total power that can be supplied by commercial power supply sources (called the power usage rate) is low, By storing electric power in the secondary battery, it is possible to suppress an increase in the electric power usage rate during periods other than the above time period. For example, in the case of the electric freezer-refrigerator 8300, the temperature is low and the refrigerator compartment door 830 is closed.
2. Electric power is stored in the secondary battery 8304 at night when the freezer compartment door 8303 is not opened and closed. In the daytime when the temperature rises and the refrigerator compartment door 8302 and the freezer compartment door 8303 are opened and closed, the secondary battery 8304 is used as an auxiliary power supply, so that the power usage rate during the daytime can be kept low.

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

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

By installing a secondary battery in 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 a secondary battery that is one embodiment of the present invention. FIG. 19(A)
A car 8400 shown in is an electric car that uses an electric motor as a power source for running. Alternatively, it is a hybrid vehicle in which an electric motor and an engine can be appropriately selected and used as power sources for running. By using one aspect of the present invention, a vehicle with a long cruising range can be realized. Also, automobile 8400 has a secondary battery. As the secondary battery, many small cylindrical secondary batteries shown in FIG. 12 may be arranged and used on the floor of the vehicle. Also, a battery pack formed by combining a plurality of secondary batteries shown in FIG. 20 may be installed on the floor of the vehicle. The secondary battery can not only drive the electric motor 8406, but also supply power to light emitting devices such as the headlight 8401 and room lights (not shown).

In addition, the secondary battery can supply power to display devices such as a speedometer and a tachometer of the automobile 8400 . In addition, the secondary battery can supply power to a semiconductor device such as a navigation system included in the automobile 8400 .

A vehicle 8500 shown in FIG. 19B can be charged by receiving power from an external charging facility by a plug-in method, a contactless power supply method, or the like to a secondary battery included in the vehicle 8500 . FIG. 19B shows a state in which a charging device 8021 installed on the ground charges a secondary battery 8024 mounted on an automobile 8500 via a cable 8022 . When charging, the charging method, the standard of the connector, etc. may be appropriately performed by a predetermined method such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station provided in a commercial facility, or may be a household power source. For example, plug-in technology can charge the secondary battery 8024 mounted on the automobile 8500 with power supplied from the outside.
Charging can be performed by converting AC power into DC power through a conversion device such as an ACDC converter included in the charging device 8021 . Also, in the case of the automobile 8500 equipped with the charging ACDC converter 8025, charging can be performed even when an AC power supply is connected.

Also, although not shown, the power receiving device can be mounted on a vehicle, and power can be supplied from a power transmission device on the ground in a non-contact manner for charging. In the case of this non-contact power supply system, it is possible to charge the battery not only while the vehicle is stopped but also while the vehicle is running by installing a power transmission device on the road or on the outer wall. In addition, electric power may be transmitted and received between vehicles using this contactless power supply method. Furthermore, a solar battery may be provided on the exterior of the vehicle to charge the secondary battery while the vehicle is stopped or running. An electromagnetic induction method or a magnetic resonance method can be used for such contactless power supply.

FIG. 19C illustrates an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. Figure 19
A scooter 8600 shown in (C) includes a secondary battery 8602 , side mirrors 8601 , and direction indicator lights 8603 . A secondary battery 8602 can supply electricity to the turn signal lights 8603 .

Further, the scooter 8600 shown in FIG.
2 can be stored. The secondary battery 8602 can be stored in the underseat storage 8604 even if the underseat storage 8604 is small. The secondary battery 8602 is removable, and 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 size and weight of the secondary battery itself can be reduced. If the size and weight of the secondary battery itself can be reduced, the cruising distance can be improved because it contributes to the weight reduction of the vehicle. A secondary battery mounted on a 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 during peak power demand. If it is possible to avoid using a commercial power source during peak power demand, it can contribute to energy conservation and reduction of carbon dioxide emissions. Moreover, if the cycle characteristics are good, the secondary battery can be used for a long period of time, so the amount of rare metals such as cobalt used can be reduced.

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

In this example, secondary batteries using positive electrode active material particles having different coating layers were produced, and SEM
and XRD to analyze the characteristics and compare the properties.

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

≪Sample 11≫
Sample 11 was produced by forming a coating layer containing titanium on lithium cobaltate particles containing magnesium and fluorine by a sol-gel method, followed by heating.

In this example, lithium cobalt oxide particles containing magnesium and fluorine, which had been synthesized in advance, were used as the starting material. Specifically, C-20F manufactured by Nippon Kagaku Kogyo Co., Ltd. was used as a starting material.

TTIP was added and dissolved in 2-propanol so that the TTIP per weight of the positive electrode active material was 0.004 ml/g. As TTIP, a reagent with a purity of 99.0% or more manufactured by Kishida Chemical Co., Ltd. was used. To this 2-propanol solution of TTIP was added lithium cobaltate particles with magnesium and fluorine.

The mixed liquid in which the magnesium and lithium cobaltate particles containing fluorine were mixed was stirred with a magnetic stirrer for 70 hours under the conditions of 25° C. and 90% RH. By this treatment, water in the atmosphere and TTIP caused hydrolysis and polycondensation reactions to form a layer containing titanium on the surface of the lithium cobalt oxide particles containing magnesium and fluorine.

The mixed liquid after the above treatment was filtered, and the residue was recovered. 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. (heating rate: 200° C./hour), holding time: 2 hours, and oxygen atmosphere flow rate: 10 L/min.

The heated powder was cooled. Cooling took the same or longer time than heating. It was then sieved. A sieve with an opening of 53 μm was used.

The sieved particles were used as sample 11 of the positive electrode active material.

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

<<Sample 12>>
Sample 12 was produced as a comparative example without heating after forming and drying a layer containing titanium. It was prepared in the same manner as Sample 11, except that it was not heated.

Sample 12 was assumed to be a positive electrode active material having lithium cobalt oxide containing magnesium and fluorine inside and a coating layer containing titanium on the surface, but with no segregation of magnesium 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 no layer containing titanium was formed.

Sample 13 was presumed to be a positive electrode active material that contained lithium cobaltate inside and had a coating layer containing magnesium on the surface but did not contain titanium.

≪Sample 14≫
As a comparative example, Sample 14 did not form a layer containing titanium and was not heated. Specifically, C-20F manufactured by Nippon Kagaku Kogyo Co., Ltd. was used as it was.

Sample 14 is lithium cobalt oxide containing magnesium and fluorine, but is a cathode active material without a coating layer.

≪Sample 21≫
Sample 21 was produced by forming a coating layer containing titanium on lithium cobaltate particles containing magnesium and fluorine by a sol-gel method, followed by heating.

A sample was prepared 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 cobalt oxide inside and a coating layer containing titanium and magnesium on the surface.

≪Sample 22≫
Sample 22 was produced as a comparative example without forming a layer containing titanium. It was produced in the same manner as sample 21, except that no layer containing titanium was formed.

Sample 22 was presumed to be a positive electrode active material that contained lithium cobaltate inside and had a coating layer containing magnesium on the surface but did not contain titanium.

≪Sample 23≫
Sample 23 was produced as a comparative example by forming a layer containing titanium on lithium cobaltate particles containing no magnesium and then heating the layer.

Lithium cobaltate particles used were manufactured by Nippon Kagaku Kogyo Co., Ltd. (product name: C-10N). this is x
These are lithium cobaltate particles in which magnesium is not detected by PS and fluorine is detected in an amount of about 1 atomic %.

It was made in the same manner as sample 21, except that C-10N was used as the starting material.

Sample 23 was presumed to be a positive electrode active material having lithium cobalt oxide inside and a coating layer containing titanium on the surface, but without magnesium segregating on the surface.

≪Sample 24≫
Sample 24 was a comparative example in which a titanium-containing layer was not formed on magnesium-free lithium cobalt oxide particles, and heating was not performed. Specifically, C-10N manufactured by Nippon Kagaku Kogyo Co., Ltd. was used as it was.

Sample 24 is lithium cobaltate with no coating layer.

≪Sample 31≫
Sample 31 was produced by forming a coating layer containing titanium on lithium cobalt oxide particles containing magnesium and fluorine by a sol-gel method, followed by 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 cobalt oxide inside and a coating layer containing titanium and magnesium on the surface layer.

Table 1 shows the manufacturing conditions for Samples 11 to 14, Samples 21 to 24, and Sample 31. In addition, analysis performed on each sample, which will be described later, is also shown.

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

<XRD>
For samples 11 to 14, the crystallite size inside the particles of the positive electrode active material was measured by XR
D was used for analysis. Table 2 shows the results.

As shown in Table 2, sample 11, which was coated with a layer containing titanium and was heated, tended to have larger crystallites than the other samples. The tendency for the crystallites to become large differed depending on the crystal plane, and was remarkable for the (003) plane and the like.

It is thought that the larger the number of cracks, the lower the crystallinity and thus the smaller the crystallite size, and the smaller the number of cracks, the higher the crystallinity and the larger the crystallite size.

Further, it is presumed that defects such as cracks are likely to occur along the (003) plane or the like. FIG. 20 is a model diagram of the crystal structure of lithium cobaltate (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 drawing, the (003) plane is indicated by a dotted line. As shown in FIG. 20, the (003) plane exhibits the characteristics of the layered structure. In lithium cobaltate, the bond between lithium and oxygen is weaker than the bond between cobalt and oxygen. Therefore, it is presumed that defects such as cracks are likely to occur parallel to the (003) plane.

It was presumed that defects such as cracks caused by the (003) plane and the like were repaired by coating with a layer containing titanium and heating as in this example.

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

For the positive electrode, the positive electrode active materials (LCO) of Samples 21 to 24, acetylene black (AB), and polyvinylidene fluoride (PVDF) were used in LCO:AB:PVDF=95:2.
An aluminum foil current collector was coated with a slurry mixed at a ratio of 5:2.5 (weight ratio). N-methyl-2-pyrrolidone (NMP) was used as a solvent.

Lithium metal was used as the counter electrode.

1 mol/L of lithium hexafluorophosphate (LiPF ₆ ) is used as the electrolyte in the electrolyte, and ethylene carbonate (EC) and diethyl carbonate (DEC) are added to the electrolyte.
C: DEC = 3: 7 (volume ratio), and 2 vinylene carbonate (VC)
% by weight was added.

The cathode can and the anode can were made of stainless steel (SUS).

The measurement temperature for the cycle characteristics test was set at 25°C. Charging was performed by CCCV, first at a constant current with a current density of 68.5 mA/g per weight of active material, with an upper limit voltage of 4.6 V, and then at a current density of 1.4.
Constant voltage charging was performed until mA/g. Discharge is CC, current density 6 per weight of active material
It was performed at a constant current of 8.5 mA/g and a lower limit voltage of 2.5V.

Note that the conditions for CCCV charging and CC charging in this embodiment are the CC charging described in the second embodiment.
Although the voltages may be different from those exemplified in the description of CV charging and CC discharging, the charging method and discharging are the same except that the voltages are different. By charging with a high voltage, a high-capacity secondary battery can be obtained.

FIG. 21 shows a graph of the discharge capacity retention rate and the number of charge/discharge cycles when charged at 4.6 V for the secondary batteries using the positive electrode active materials of Samples 21 to 24. In FIG. Also, the discharge capacity retention rate was obtained with the initial discharge capacity as 100%.

As is clear from FIG. 21, sample 22, which is lithium cobaltate particles containing magnesium and fluorine, is superior to sample 24 having no coating layer and sample 23 having only a coating layer containing titanium. Cycle characteristics were shown. This is considered to be due to the segregation of magnesium on the surface layer of the lithium cobalt oxide particles due to heating.

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

In the measurement of cycle characteristics, the discharge capacity retention rate at 10 cycles was 99%. Also, the discharge capacity retention rate at the 30th cycle was 97%.

Thus, it was found that by providing a coating layer containing titanium and magnesium, better cycle characteristics can be obtained than when only a coating layer containing titanium or only a coating layer containing magnesium is provided.

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

For the positive electrode, the positive electrode active material (LCO) of Sample 31, acetylene black (AB), and polyvinylidene fluoride (PVDF) (manufactured by Solvay, product name; GE51305) were used as LCO:
A current collector made of aluminum foil was coated with a slurry of AB:PVDF=95:3:2 (weight ratio). N-methyl-2-pyrrolidone (NMP) was used as the solvent. The amount supported on the positive electrode current collector was about 8.5 mg/cm ² . Others were prepared in the same manner as Samples 21-24.

First, the 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 cutoff. Discharge was performed at 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 initial charge and discharge. 0.2C charge/0.2C discharge, 0.2C charge/0.5C discharge, 0.2C charge/0.2C discharge, 0.2C charge/0.5C discharge, 0.2C charge/0.5C discharge under the same conditions as the first charge/discharge except for the discharge rate
Measurement was performed in the order of C charge/1.0C discharge and 0.2C charge/2.0C discharge. Measured temperature is 25
°C.

Table 3 and FIG. 22 show the results of measuring the initial characteristics and rate capacity.

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

[Cycle characteristics]
In cycle characteristics, charge is CC/CV, 1.0C, 4.55V, 0.05C cutoff,
Discharge was performed at 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 the discharge capacity retention rate.

In the measurement of cycle characteristics, the discharge capacity retention rate was 100% after 10 cycles. Also, the discharge capacity retention rate at the 30th cycle was 98%. Also, 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.

Further, 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 was found 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 found that the positive electrode active material particles, which is one embodiment of the present invention, can obtain extremely good cycle characteristics when used in a secondary battery.

100 active material particles 105 cracks 110 active material particles 111 particles 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 (8)

A secondary battery having a positive electrode, a negative electrode, a positive electrode terminal, a negative electrode terminal, a safety valve mechanism, and a PTC element inside a positive electrode cap and a battery can,
the positive electrode is connected to the positive electrode terminal;
The positive electrode terminal is connected to the safety valve mechanism,
The safety valve mechanism is electrically connected to the positive electrode cap via the PTC element,
the negative electrode is connected to the negative electrode terminal;
the negative terminal is connected to the battery can,
The positive electrode has a plurality of active material particles containing magnesium and titanium in the surface layer,
The plurality of active material particles include active material particles having a crystallite size of 1 μm or more in X-ray diffraction analysis.
secondary battery. In claim 1,
The safety valve mechanism has a function of interrupting the electrical connection between the positive electrode cap and the positive electrode when the internal pressure of the storage battery exceeds a predetermined value.
secondary battery. In claim 1 or claim 2,
The PTC element has a function of increasing the resistance when the temperature rises and controlling the amount of current,
secondary battery. In any one of claims 1 to 3,
The PTC element comprises barium titanate,
secondary battery. In a module having a plurality of secondary batteries, a temperature control device, a first conductive plate, and a second conductive plate,
each of the plurality of secondary batteries is electrically connected to a conductor and sandwiched between the first conductive plate and the second conductive plate;
The temperature control device is provided between the plurality of secondary batteries,
The temperature control device has a function of controlling the temperature of the plurality of secondary batteries,
The plurality of secondary batteries have a positive electrode, a negative electrode, a positive electrode terminal, a negative electrode terminal, a safety valve mechanism, and a PTC element inside the positive electrode cap and the battery can,
the positive electrode is connected to the positive electrode terminal;
The positive electrode terminal is connected to the safety valve mechanism,
The safety valve mechanism is electrically connected to the positive electrode cap via the PTC element,
the negative electrode is connected to the negative electrode terminal;
the negative terminal is connected to the battery can,
The positive electrode has a plurality of active material particles containing magnesium and titanium in the surface layer,
The plurality of active material particles include active material particles having a crystallite size of 1 μm or more in X-ray diffraction analysis.
module. In claim 5,
The safety valve mechanism has a function of interrupting the electrical connection between the positive electrode cap and the positive electrode when the internal pressure of the storage battery exceeds a predetermined value.
module. In claim 5 or claim 6,
The PTC element has a function of increasing the resistance when the temperature rises and controlling the amount of current,
module. In any one of claims 5 to 7,
The PTC element comprises barium titanate,
module.

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