DE102013102444B4 - Electrochemical device - Google Patents

Abstract

An electrochemical device comprising: a positive electrode (11) including a positive electrode active material including an activated carbon or an oxide including lithium; a negative electrode (12) having a negative electrode active material including a non-graphitized carbon material which is used for Capable of doping or undoping lithium; an electrolyte (13) comprising a solution in which a lithium salt is dissolved in a solvent; anda lithium ion reference source (19) for doping lithium into the negative electrode (12), the solvent being ethylene carbonate in a range greater than or equal to 0.01 volume percent and less than 5.00 volume percent, propylene carbonate in a range greater than 60 , 00 volume percent and less than or equal to 99.99 volume percent and a linear carbonate in a range greater than or equal to 0 volume percent and less than or equal to 35.00 volume percent.

Description

BACKGROUND OF THE INVENTION

Field of invention

The present invention relates to an electrochemical device such as a lithium ion capacitor, a lithium ion secondary battery and the like.

Description of the prior art

Electrochemical devices that function as rechargeable / discharging batteries include an electric double layer capacitor, a lithium ion secondary battery, and the like. In addition, a hybrid type capacitor such as a lithium-ion capacitor is known which comprises a positive electrode of an electric double-layer capacitor and a negative electrode of a lithium-ion secondary battery.

When such electrochemical devices are used as an energy source and for regenerating energy, the electrochemical devices are required to have higher energy density and lower resistance and be manufactured at a lower cost.

Graphitized carbon or non-graphitized carbon is used for the negative electrode of the above-described electrochemical devices depending on the purpose. Typically, non-graphitized carbon has above-average output characteristics and above-average cycle characteristics.

Conventionally, it is known that in an electrochemical device using non-graphitized carbon for its negative electrode, an electrolyte containing ethylene carbonate is used to form a solid electrolyte interface (SEI) layer on a surface of a negative electrode during initial charging and discharging to build. Such SEI layers mainly contain Li-containing inorganic substances and Li-containing organic substances. The formation of an SEI layer on the surface of a negative electrode prevents the decomposition of an electrolyte and promotes the uniform incorporation of lithium ions (hereinafter referred to as "doping") in the negative electrode and the uniform release of lithium ions from the negative electrode, which causes the Run-off properties are improved.

JP 2001 - 126 760 A1 discloses the formation of a layer on a surface of a negative electrode of a secondary battery using, as an electrolyte, a solution in which LiPF _{6 is dissolved} in a mixed solution of ethylene carbonate, propylene carbonate and dimethyl carbonate.

In an electrochemical device using the in JP 2001 - 126 760 A1 however, an SEI layer tends to grow due to repeated charging and discharging, thereby forming a thick layer. If the thickness of the SEI layer formed on the surface of a negative electrode becomes large, there may arise problems such that the diffusion of lithium ions is inhibited and the internal resistance increases.

US 2009/0 174 986 A1 discloses a lithium-ion capacitor that includes a positive electrode, a negative electrode, and an aprotic organic solvent electrolyte solution of a lithium salt as an electrolyte solution.

Another prior art is the DE 602 13 696 T2 and DE 60 2005 000 013 T2 referenced.

The present invention has been made to solve the problems described above. An object of the present invention is to provide an electrochemical device in which the growth of an SEI layer is inhibited and the resistance is reduced.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, an electrochemical device comprises a positive electrode with an active positive electrode material containing an oxide containing activated carbon or lithium, a negative electrode with an active negative electrode material containing a non- graphitized carbon material capable of doping or undoping lithium, an electrolyte formed by a solution in which a lithium salt is dissolved in a solvent, and a lithium ion reference source for doping the negative electrode with lithium. The solvent contains ethylene carbonate in the range greater than or equal to 0.01 volume percent and less than 5.00 volume percent, propylene carbonate in the range greater than 60.00 volume percent and less than or equal to 99.99 volume percent, and a linear carbonate in one range greater than or equal to 0 volume percent and less than or equal to 35.00 volume percent.

Furthermore, the linear carbonate is preferably at least one selected from the group consisting of diethyl carbonate, ethyl methyl carbonate and dimethyl carbonate.

Furthermore, the lithium salt is preferably at least one selected from the group consisting of LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiSbF ₅ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiCIO ₄ .

According to the present invention, an electrochemical device in which growth of an SEI layer is suppressed and resistance is reduced can be provided.

Figure list

• 1 Fig. 3 is a cross section of an electrochemical device according to the present embodiment.

DETAILED DESCRIPTION OF THE PREFERRED

EMBODIMENTS

An embodiment of the present invention is described in detail below.

An electrochemical device according to the present embodiment includes a positive electrode, a negative electrode, an electrolyte, and a lithium ion reference source. The positive electrode has an active positive electrode material containing an oxide containing activated carbon or lithium. The negative electrode has an active negative electrode material containing a non-graphitized carbon material which is capable of doping or undoping lithium. Further, according to the present embodiment, the electrolyte is formed from a solution in which a lithium salt is dissolved in a solvent. The solvent contains ethylene carbonate in the range greater than or equal to 0.01 volume percent and less than 5.00 volume percent, propylene carbonate in the range greater than 60.00 volume percent and less than or equal to 99.99 volume percent, and a linear carbonate in the range greater as or equal to 0 volume percent and less than or equal to 35.00 volume percent.

1 Figure 13 is a diagram illustrating the electrochemical device of the present invention. In the following description, a lithium ion capacitor will be described as an example of the electrochemical device according to the present embodiment.

With reference to 1 the electrochemical device according to the present embodiment comprises a positive electrode 11 , a negative electrode 12th and an electrolyte 13th . The positive electrode 11 includes a positive electrode current collector 14th and (an) active positive electrode material layer (s) 15th which contain a positive electrode active material and which on one surface or both surfaces of the positive electrode current collector 14th are provided. The negative electrode 12th includes a negative electrode current collector 16 and (an) active negative electrode material layer (s) 17th which contain a negative electrode active material and which on one surface or both surfaces of the negative electrode current collector 16 are provided. There is also a separator 18th between the positive electrode 11 and the negative electrode 12th arranged so that the separator 18th juxtaposes the corresponding electrodes.

The positive electrode 11 and the negative electrode 12th are alternately across the separator 18th laminated. The electrode body 101 consists of the positive electrode 11 , the negative electrode 12th and the separator 18th . In this structure, it is suitable to use the positive electrode 11 and the negative electrode 12th laminate so that the negative electrode 12th on the outermost layer of the electrode body 101 is arranged. The lithium ion reference source 19th is in at least a part of the outside of the electrode body 101 arranged so that the lithium ion reference source 19th the electrode body 101 facing. In 1 is the lithium ion source 19th on the outside of the electrode body 101 arranged so that the lithium ion reference source 19th the negative electrode 12th opposite.

The electrode body 101 and the lithium ion source 19th are in a covering material 20th stored. The electrolyte 13th is in the covering material 20th encapsulated. As a result, both the electrode body 101 also as the lithium ion source 19th with the electrolyte 13th impregnated. In this state, the lithium ions become from the lithium ion source 19th into the negative electrode active material layer 17th endowed. According to the present embodiment, the method is for doping lithium ions into the negative electrode active material layer 17th not particularly restricted. Examples thereof include a method of electrochemically doping lithium ions into the negative electrode active material layer 17th and a method of doping lithium ions by causing a physical short circuit between the negative electrode active material layer 17th and the lithium ion source 19th .

The number of positive electrodes 11 and the negative electrodes 12th , which is the electrode body 101 can be determined according to the desired capacitance and resistance. In addition, the number or amount of lithium ion sources can be used 19th taking into account the amount of lithium ions that are doped and the duration of the doping can be determined accordingly. The location of the lithium ion reference source should also be included 19th not be limited to a particular location. In particular, the lithium ion reference source 19th in the middle of the electrode body 101 as well as at the upper end, at the lower end or the side surface (ie on the outside) of the electrode body 101 be laminated.

The electrolyte 13th consists according to the present embodiment of a solution in which a lithium salt is dissolved in a solvent. The solvent used in the electrolyte according to the present embodiment contains at least propylene carbonate (PC) and ethylene carbonate (EC), and may further contain a linear carbonate.

According to the present embodiment, the solvent contains ethylene carbonate in the range of more than or equal to 0.01 volume percent and less than 5.00 volume percent, propylene carbonate in the range of more than 60.00 volume percent and less than or equal to 99.99 volume percent and a linear carbonate in the range of greater than or equal to 0 volume percent and less than or equal to 35.00 volume percent. According to the present embodiment, an SEI layer is formed on a surface of the negative electrode by adjusting the amounts of ethylene carbonate, propylene carbonate and the linear carbonate used as solvents in the above-described range and causing the SEI to grow excessively. Shift can be stopped even if charging and discharging are performed repeatedly. As a result, the resistance of the electrochemical device can be reduced.

It is not necessary that the solvent contain a linear carbonate. However, the viscosity of an electrolyte containing ethylene carbonate is generally high. Accordingly, a reduction in the viscosity of such an electrolyte can be achieved when the electrolyte contains a linear carbonate. The linear carbonate is preferably at least one selected from the group consisting of diethyl carbonate (DEC), ethyl methycarbonate (EMC) and dimethyl carbonate (DMC). One chain carbonate alone can be used, or two or more chain carbonates can be mixed for use. Further, since the solvent according to the present embodiment preferably contains a linear carbonate, the solvent preferably contains ethylene carbonate in the range of more than or equal to 0.01 volume percent and less than 5.00 volume percent, propylene carbonate in the range of more than 60.00 volume percent and less as or equal to 99.90 volume percent and a linear carbonate in the range of greater than 0 volume percent and less than or equal to 35.00 volume percent.

Furthermore, the solvent can contain additives such as vinylene carbonate (VC), ethylene sulfite (ES) and fluoroethylene carbonate (FEC) in addition to the compounds described above. By adding the additives described above, the SEI layer can be formed more uniformly, which can improve the sagging properties. One lithium salt alone can be used, and two or more lithium salts can be mixed for use.

In addition, as the lithium salt that is quenched in the solvent, any lithium salt that is ionized to generate lithium ions can be used. For example, the lithium salt is preferably at least one selected from the group consisting of LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiSbF ₅ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiCIO ₄ .

The material of the negative electrode current collector 16 shouldn't be particularly restricted. For example, various materials commonly used in lithium ion secondary batteries and the like, that is, stainless steel, copper, nickel and the like, can be used. In addition, similar materials can be made available to the purchaser of the lithium ion source 19th be used. For the consumer that is used for the electrode or the lithium ion reference source, for example a rolled up foil, an electrolytic foil, a perforated foil with perforations formed through the front and back sides thereof, a reticulated porous carrier foil (English: lath foil), such as an expanded metal, and the like can be used.

The negative electrode active material contained in the negative electrode active material layer 17th contained as the main component contains non-graphitized carbon material, which is a material capable of reversibly doping lithium ions. In terms of properties such as energy density, it is particularly suitable to use an amorphous carbon material among the non-graphitized carbon materials whose d ₀₀₂ value (ie, the distance in the C-axis direction determined by an X-ray diffraction method) im Range of more than or equal to 0.341 nm and less than or equal to 0.339 nm, and its crystal size (Lc) in the C-axis direction is 0.5 to 18 nm. In addition, it is suitable to set the specific surface area of the negative electrode active material layer 17th should be set to about 1 to 40 m ² / g, since the performance properties such as the energy density can be expected to be improved with this structure. According to the present embodiment, the negative electrode active material may contain a material that can reversibly dop lithium ions in addition to the non-graphitized carbon material within the range in which the effects of the present invention can be implemented.

For the positive electrode pantograph 14th For example, aluminum, stainless steel and the like can be used. In terms of lower resistance and lower cost, it is suitable to use an aluminum etching foil which is commonly used for an aluminum electrolytic capacitor and an electric double layer capacitor. An aluminum etching foil has a specific surface area that has been increased by processing the aluminum by etching. Accordingly, the contact area is with the positive electrode active material layer 15th enlarged, resulting in lower resistance and improved performance. Since an aluminum etching foil is a general-purpose item, a reduction in cost can be expected. Either a rolled foil or an electrolytic foil can be used for etching the aluminum etching foil. Furthermore, various types of foils used in lithium ion storage batteries such as a rolled foil, an electrolytic foil and a porous carrier foil (English: lath foil) can be used for the positive electrode current collector.

The positive electrode active material used as the main component in the positive electrode active material layer 15th contains, contains an activated carbon or an oxide containing lithium. For the activated carbon, for example, carbon materials having a polarizing property such as phenolic resin-based activated carbon, coconut shell-based activated carbon, petroleum coke-based activated carbon, or polyacene can be used. Further, a positive electrode material of a lithium ion secondary battery and the like can be used. Examples thereof include lithium cobaltate.

The positive electrode active material layer 15th and the negative electrode active material layer 17th contain a management assistant or a binding agent if required. Examples of the conduction aid include graphite, carbon black, Ketjen black, steam grown carbon, and carbon nanotubes. Of these materials, carbon black and graphite are preferred. For the binder, for example, rubber-based binders such as styrene-butadiene rubber (SBR) and the like, fluorine-containing resins such as polytetrafluoroethylene, polyvinylidene fluoride and the like, and thermoplastic resins such as polypropylene and polyethylene can be used.

For the lithium ion source 19th For example, a material capable of supplying lithium ions such as metallic lithium or a lithium-aluminum alloy can be used. The thickness of the lithium ion reference source 19th can be changed according to the lithium ion doping amount. It is suitable if the thickness is greater than or equal to 5 μm or less than or equal to 400 μm. Will be the thickness of the lithium ion reference source 19th set to a value greater than or equal to 5 µm, the workability can be improved. By the thickness of the lithium ion reference source 19th is set to a value less than or equal to 400 µm, it is also possible to suppress the residues of the lithium ion reference source. The lithium ion reference source 19th can be provided with a collector for the removal of electrical charge.

The present embodiment is described above with reference to the lithium ion capacitor as an example. A lithium ion secondary battery can also be used as the electrochemical device of the present invention.

In general, however, Li transition metal oxides are used for the positive electrode active material of a lithium ion secondary battery, and the initial charge (doping of lithium ions) to the negative electrode is provided by the positive electrode active material. As a result, since it becomes necessary to increase the thickness (weight) of the positive electrode active material layer when a non-graphitized carbon material having a large irreversible capacity is used as the negative electrode active material, the energy density may become low. Therefore, a graphitized carbon material having a small irreversible capacity is often and generally used for the negative electrode active material of a lithium ion secondary battery. However, if the use can tolerate the problems described above, the present invention can be applied to a lithium ion secondary battery using a non-graphitized material for the negative electrode active material. In addition, in a lithium ion secondary battery, the SEI layer is repeatedly broken and is regenerated by charging and discharging, with the exception of a few specific areas. On the other hand, in a lithium-ion capacitor, the SEI layer is not broken. Accordingly, more excellent advantages of the present invention can be realized when a lithium-ion capacitor is used as the electrochemical device.

Examples

(Example 1)

In Example 1, a lithium-ion capacitor was manufactured as an electrochemical device as described above.

3 parts by mass of styrene-butadiene rubber and 3 parts by mass of carboxymethyl cellulose as a binder and 200 parts by mass of water as a solvent were made into a powder of a mixture of 92 parts by mass of a powder made from a phenol-based activated carbon, which is an active positive electrode material and whose specific surface area is 1,500 m ² / g, and 8 parts by mass of graphite is given as a conductive agent. The mixture was kneaded to obtain a positive electrode slurry. Then, using an aluminum foil whose thickness is 20 µm and whose both surfaces are roughened by etching as a positive electrode current collector, the positive electrode slurry was applied to both surfaces of the positive electrode current collector. The applied slurry was dried and the doffer was rolled and pressed. Further, positive electrode active material layers each having a thickness of 30 µm were formed on both surfaces of the positive electrode current collector to obtain a positive electrode. The thickness of the positive electrode was 80 µm. In addition, expanded areas formed by expanding the pickup into a strip-like shape were formed in a portion of an end face of the positive electrode. No positive electrode active material layer was formed on any surface of the stretched area pickup, and the aluminum foil was exposed so that charges can be withdrawn by connecting an external connector. A flat foil without perforations was used for the positive electrode current collector.

5 parts by mass of styrene-butadiene rubber and 4 parts by mass of carboxymethyl cellulose as a binder and 200 parts by mass of water as a solvent were made into a powder of a mixture of 88 parts by mass of a powder of a non-graphitized carbon material, which is a negative electrode active material and whose specific surface area is 20 m ² / g and 6 parts by mass of acetylene black is given as a conductive agent. The mixture was kneaded to obtain a negative electrode slurry. Then, using a copper foil whose thickness is 10 µm as a negative electrode current collector, the negative electrode slurry was uniformly applied to both surfaces of the negative electrode current collector. The applied slurry was dried and the doffer was rolled and pressed. Further, negative electrode active material layers each having a thickness of 20 µm were formed on both surfaces of the negative electrode current collector to obtain a negative electrode. The thickness of the negative electrode was 50 µm. In addition, expanded areas formed by expanding the pickup into a strip-like shape were formed in a portion of the end face of the negative electrode. No negative electrode active material layer was formed on any surface of the expanded portion pickup, and the copper foil was exposed so that electric charges can be extracted by connecting to an external connector. For the negative electrode current collector, a flat foil without preferences was used.

A thin film made of a natural cellulose material and having a thickness of 35 μm was used as the separator. In view of the size and shape of the separator, the separator was configured so that the area of the separator is slightly larger than the corresponding areas of the positive electrode and the negative electrode.

Then, the separator and the negative electrode and the positive electrode were laminated together in the order of separator, negative electrode, separator, positive electrode and separator to obtain an electrode body. A separator was arranged on each of the upper portion and the lower portion of the electrode body. In this example, 4 positive electrodes, 5 negative electrodes and 10 separators were laminated together for each sample. Further, the dimensions of the positive electrode, the negative electrode and the separator were 53 mm × 70 mm, 55 mm × 72 mm and 57 mm × 74 mm, respectively, all excluding the stretched areas. Further, the stretched areas formed on each electrode expanded from the same short side of each electrode. The dimensions of the respective expanded areas were 9 mm × 12 mm.

Then, the stretched portions of the positive electrode and those of the negative electrode extending from the electrode body were each bound together, and each was fixed together on the periphery of the external connector by ultrasonic welding. Further, a lithium ion reference source was made by bonding metallic lithium to a copper foil. The external connection device of the lithium ion reference source was fixed on the stretched area extending from part of the copper foil by ultrasonic welding. The produced lithium ion reference source was arranged on the lower surface of the electrode body in such a way that the metallic lithium is opposite to the electrode body. Then the electrode body was covered with two pieces of cover material, the peripheral areas of 3 sides of the electrode body, including the side on which the positive electrode, the negative electrode and the external connection device of the lithium ion reference source are to be arranged, were thermocompressed, and a thermoplastic layer, which was applied formed on the inner surface of the cover material was bonded thereto to form a bag-like shape. The thermoplastic layer formed on the inner surface of the covering material was made of an acid-modified polyolefin resin. The thickness of the thermoplastic layer was 40 µm.

Further, an electrolyte was filled into the inner portion of the cover material, which had an inflated shape and was provided with the built-in electrode body. In this example, a solution in which LiPF _{6 was} mixed at a concentration of 1.0 mol / l in a mixed solvent containing 0.01 volume percent ethylene carbonate and 99.99 volume percent propylene carbonate was used as the electrolyte.

After the electrolyte was filled, the other side of the two pieces of the covering material was closed by thermocompression under a vacuum atmosphere. Further, lithium ions were doped from the lithium ion reference source into the negative electrode active material of the negative electrode by an electrochemical method. The doping amount was set to 400 mAh / g for the mass of the negative electrode active material.

(Example 2)

In Example 2, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 0.05 percent by volume of ethylene carbonate and 99.95 percent by volume of propylene carbonate was used as the electrolyte. The structure of Example 2 was the same as that of Example 1 with the exception of the above-described structure of the electrolyte.

(Example 3)

In Example 3, a solution was used as the electrolyte in which LiPF ₆ with a concentration of 1.0 mol / l in a mixed solvent, the 0.10 percent by volume of ethylene carbonate and 99.90 percent by volume Propylene carbonate contained, was dissolved. The structure of Example 3, with the exception of the above-mentioned structure of the electrolyte, was the same as that of Example 1.

(Example 4)

In Example 4, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 0.50 percent by volume of ethylene carbonate and 99.50 percent by volume of propylene carbonate was used as the electrolyte. The structure of Example 4 was the same as that of Example 1, with the exception of the electrolyte structure described above.

(Example 5)

In Example 5, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 1.00 volume percent ethylene carbonate and 99.00 volume percent propylene carbonate was used as an electrolyte. The structure of Example 5 was the same as that of Example 1, with the exception of the electrolyte structure described above.

(Example 6)

In Example 6, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 3.00 percent by volume of ethylene carbonate and 97.00 percent by volume of propylene carbonate was used as the electrolyte. The structure of Example 6 was the same as that of Example 1 with the exception of the above-described structure of the electrolyte.

(Example 7)

In Example 7, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 4.50 percent by volume of ethylene carbonate and 95.50 percent by volume of propylene carbonate was used as the electrolyte. The structure of Example 7 was the same as that of Example 1, with the exception of the electrolyte structure described above.

(Example 8)

In Example 8, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 4.90% by volume of ethylene carbonate and 95.10% by volume of propylene carbonate was used as the electrolyte. The structure of Example 8 was the same as that of Example 1, with the exception of the electrolyte structure described above.

(Comparative example 1)

In Comparative Example 1, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a solvent containing only propylene carbonate (no ethylene carbonate was contained) was used as an electrolyte. The structure of Comparative Example 1 was the same as that of Example 1 except for the structure of the electrolyte described above.

(Comparative example 2)

In Comparative Example 2, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 6.00 percent by volume of ethylene carbonate and 94.00 percent by volume of propylene carbonate was used as the electrolyte. The structure of Comparative Example 2 was the same as that of Example 1 except for the structure of the electrolyte described above.

(Comparative example 3)

In Comparative Example 3, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 40.00% by volume of ethylene carbonate and 60.00% by volume of propylene carbonate was used as the electrolyte. The structure of Comparative Example 3 was the same as that of Example 1 except for the structure of the electrolyte described above.

(Example 9)

In Example 9, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 3.00% by volume of ethylene carbonate, 96.00% by volume of propylene carbonate and 1.00% by volume of diethyl carbonate was used as an electrolyte . The structure of Example 9 was the same as that of Example 1, with the exception of the structure of the electrolyte described above.

(Example 10)

In Example 10, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 3.00 percent by volume of ethylene carbonate, 77.00 percent by volume of propylene carbonate and 20.00 percent by volume of diethyl carbonate was used as an electrolyte . The structure of Example 10 was the same as that of Example 1, with the exception of the electrolyte structure described above.

(Example 11)

In Example 11, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 3.00 percent by volume of ethylene carbonate, 62.00 percent by volume of propylene carbonate and 35.00 percent by volume of diethyl carbonate was used as an electrolyte . The structure of Example 11 was the same as that of Example 1 with the exception of the electrolyte structure described above.

(Comparative example 4)

In Comparative Example 4, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 3.00% by volume of ethylene carbonate, 59.00% by volume of propylene carbonate and 38.00% by volume of diethyl carbonate was used as the electrolyte . The structure of Comparative Example 4 was the same as that of Example 1 except for the structure of the electrolyte described above.

(Example 12)

In Example 12, a lithium ion secondary battery was manufactured as an electrochemical device. Cobalt acid lithium was used as the positive electrode active material, and a polyethylene-based separator was used as the separator.

In Example 12, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 3.00 percent by volume of ethylene carbonate and 97.00 percent by volume of propylene carbonate was used as the electrolyte.

The constructions of Example 12 were the same as those of Example 1 except for the constructions of the positive electrode active material, the separator, and the electrolyte.

(Example 13)

In Example 13, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 4.50% by volume of ethylene carbonate, 85.50% by volume of propylene carbonate and 10.00% by volume of diethyl carbonate was used as an electrolyte . The construction of Example 13 was the same as that of Example 12 except for the construction of the electrolyte described above.

(Example 14)

In Example 14, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 4.50% by volume of ethylene carbonate, 85.50% by volume of propylene carbonate and 10.00% by volume of ethyl methyl carbonate was used as an electrolyte . The construction of Example 14 was the same as that of Example 12 except for the construction of the electrolyte described above.

(Example 15)

In Example 15, a solution in which LiPF _{6 was dissolved} at a concentration of 1.0 mol / l in a mixed solvent containing 4.50% by volume of ethylene carbonate, 85.50% by volume of propylene carbonate and 10.00% by volume of dimethyl carbonate was used as an electrolyte . The construction of Example 15 was the same as that of Example 12 except for the construction of the electrolyte described above.

(Comparative example 5)

In Comparative Example 5, a solution was used as the electrolyte in which LiPF ₆ at a concentration of 1.0 mol / l in a mixed solvent, the 5.00 percent by volume of ethylene carbonate, 50.00 Volume percent propylene carbonate and 45.00 volume percent diethyl carbonate was dissolved. The structure of Comparative Example 5 was the same as that of Example 12 except for the structure of the electrolyte described above.

Using the procedure described above, twenty electrochemical devices were fabricated for each example. For the manufactured electrochemical device, charging was carried out for 1 hour at 3.8 V at a constant voltage and a constant current. In addition, the electrochemical device was discharged at 80 mV until the voltage was 2.2V. The direct current resistance (DC-R) was calculated based on the voltage drop observed by the discharge, and twenty average values were calculated. As the initial property of the lithium-ion capacitor, a value equal to or less than + 5% of the mean value of Comparative Example 3 (i.e., mean value × 1.05) was considered acceptable ("O") when Comparative Example 3 was used as a reference. In addition, for the lithium ion secondary battery, a value equal to or less than + 5% of the mean value of Comparative Example 5 (i.e., mean value × 1.05) was considered acceptable (“O”) when Comparative Example 5 was used as a reference.

Furthermore, a float test and a cycle test were carried out as endurance tests.

For the circulation test of the lithium ion capacitor, the DC-R was measured at room temperature after 2,000 hours had passed in a state where a voltage of 3.8 V was applied under an environment of 70 ° C. For the circulation test of the lithium ion secondary battery, the DC-R was measured at room temperature after 2,000 hours had passed in a state where a voltage of 4.2 V was applied under an environment of 60 ° C.

For the drain test of the lithium-ion capacitor, charging and discharging were repeated for 5,000 cycles under an environment of 70 ° C. The capacitance and the DC-R were then measured at room temperature. For the drain test of the lithium ion secondary battery, charging and discharging were repeated for 1,000 cycles under an environment of 60 ° C. The capacitance and the DC-R were then measured at room temperature.

In the circulation test and the drainage test, the rate of change of the DC-R was calculated according to the average of the measured values obtained before and after the respective tests. Furthermore, a rate of change of 20% or less was considered acceptable (“O”) in the circulation test. In the drain test, a rate of change of 50% or less was considered acceptable (“O”).

Table 1 illustrates the initial properties and results of determination of the endurance test of the working examples and comparative examples. [Table 1] Type of electrochemical device Cyclic carbonate (volume percent) Linear carbonate (volume percent) Initial property Endurance test (circulation test) Endurance test (expiry test) EC Pc DEC EMC DMC DC-R (mΩ) Assessment result DC-R rate of change (%) Assessment result DC-R rate of change (%) Assessment result Overall assessment result example 1 Lithium-ion capacitor 0.01 99.99 33.0 ◯ 4.9 ◯ 5.2 ◯ ◯ Example 2 0.05 99.95 33.0 ◯ 4.8 ◯ 5.1 ◯ ◯ Example 3 0.10 99.90 32.9 ◯ 4.9 ◯ 5.1 ◯ ◯ Example 4 0.50 99.50 32.8 ◯ 4.9 ◯ 5.2 ◯ ◯ Example 5 1.00 99.00 32.7 ◯ 5.0 ◯ 5.0 ◯ ◯ Example 6 3.00 97.00 32.5 ◯ 6.2 ◯ 6.1 ◯ ◯ Example 7 4.50 95.50 32.4 ◯ 6.5 ◯ 6.6 ◯ ◯ Example 8 4.90 95.10 32.4 ◯ 10.0 ◯ 9.8 ◯ ◯ Comparative example 1 0.00 100.00 35.1 × 5.0 ◯ 5.1 ◯ × Comparative example 2 6:00 am 94.00 32.4 ◯ 22.1 × 23.1 ◯ × Comparative example 3 40.00 60.00 32.0 ◯ 47.8 × 61.1 × × Example 9 3.00 96.00 1.00 32.3 ◯ 6.6 ◯ 6.2 ◯ ◯ Example 10 3.00 77.00 8:00 pm 32.2 ◯ 6.7 ◯ 6.3 ◯ ◯ 1 example 11 3.00 62.00 35.00 32.1 ◯ 6.9 ◯ 6.5 ◯ ◯ Comparative example 4 3.00 59.00 38.00 32.0 ◯ 21.1 × 24.1 ◯ × Example 12 Lithium ion accumulator 3.00 97.00 48.5 ◯ 15.0 ◯ 30.1 ◯ ◯ Example 13 4.50 85.50 10.00 48.3 ◯ 15.2 ◯ 32.1 ◯ ◯ Example 14 4.50 85.50 10.00 48.1 ◯ 15.0 ◯ 33.1 ◯ ◯ Example 15 4.50 85.50 10.00 48.0 ◯ 15.3 ◯ 33.1 ◯ ◯ Comparative example 5 5.00 50.00 45.00 48.0 ◯ 25.0 × 72.1 × ×

As illustrated in Table 1, the initial properties of the working examples of the present invention were as high as those of the comparative examples. In the endurance test, the rate of change of the DC-R improved greatly, whereby an increase in the DC-R can be suppressed. Accordingly, with the constitution of the present invention, there was obtained an electrochemical device in which the growth of the SEI layer was suppressed and lower resistance was obtained.

List of reference symbols

11

positive electrode

12th

negative electrode

13th

electrolyte

14th

Positive electrode pantograph

15th

active positive electrode material layer

16

Negative electrode pantograph

17th

negative electrode active material layer

18th

separator

19th

Lithium ion supply source

20th

Covering material

101

Electrode body

Claims (4)

An electrochemical device comprising: a positive electrode (11) including a positive electrode active material including an activated carbon or an oxide including lithium; a negative electrode (12) with an active negative electrode material, containing a non-graphitized carbon material capable of doping or undoping lithium; an electrolyte (13) comprising a solution in which a lithium salt is dissolved in a solvent; and a lithium ion reference source (19) for doping lithium into the negative electrode (12), the solvent being in a range greater than or equal to 0.01 volume percent and less than 5.00 volume percent, propylene carbonate in a range greater than 60.00 volume percent and less than or equal to 99.99 volume percent and a linear carbonate in a range greater than or equal to 0 volume percent and less than or equal to 35.00 volume percent. Electrochemical device according to Claim 1 wherein the linear carbonate is at least one selected from the group consisting of diethyl carbonate, ethyl methyl carbonate and dimethyl carbonate. Electrochemical device according to Claim 1 or 2 , wherein the lithium salt is at least one selected from the group consisting of LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiSbF ₅ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiCIO ₄ . Electrochemical device according to one of the Claims 1 until 3 wherein the content of ethylene carbonate in the solution is 4.50 volume percent or less.

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