JP2017135187A - Negative electrode for nonaqueous lithium type power-storage device, and nonaqueous lithium type power-storage device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for a nonaqueous lithium type power-storage device, which exhibits high input and output characteristics even at a low temperature.SOLUTION: A negative electrode for a nonaqueous lithium type power-storage device comprises: a negative electrode current collector; and a negative electrode active substance layer on one or both faces of the negative electrode current collector, which includes a negative electrode active substance capable of occluding and releasing lithium ions. The negative electrode active substance is a carbon material having a primary particle diameter of 0.005-5 μm. The negative electrode current collector includes a non-smooth region having a geometry selected from concave portions and convex portions on at least part of a face in contact with the negative electrode active substance layer. A ten-point average roughness Rmeasured for a straight line including 10 or more apexes of the geometry selected from concave portions and convex portions in the non-smooth region is 5-100 μm.SELECTED DRAWING: Figure 1

Description

The present invention relates to a negative electrode for a non-aqueous lithium storage element and a non-aqueous lithium storage element using the same.

In recent years, midnight power storage systems, home-use distributed power storage systems based on solar power generation technology, power storage systems for electric vehicles, etc. have attracted attention from the viewpoint of global environment conservation and effective use of energy for resource saving. Yes.
The first requirement in these power storage systems is that the energy density of the power storage elements used is high. As a promising candidate for an energy storage device with high energy density that can meet such demands, development of lithium ion batteries has been energetically advanced.
The second requirement is high input / output characteristics. For example, a combination of a high-efficiency engine and a power storage system (for example, a hybrid electric vehicle) or a combination of a fuel cell and a power storage system (for example, a fuel cell electric vehicle) requires high input / output characteristics in the power storage system during acceleration. ing.

At present, electric double layer capacitors, nickel metal hydride batteries, and the like have been developed as high power storage elements.
Among the electric double layer capacitors, those using activated carbon as electrodes have input / output characteristics of about 0.5 to 1 kW / L. This electric double layer capacitor has high durability (particularly cycle characteristics and high-temperature storage characteristics), and has been considered as an optimum electric storage element in the field where the high output is required. However, for its practical use, the energy density is as low as about 1 to 5 Wh / L and the output duration is short.

On the other hand, nickel-metal hydride batteries currently used in hybrid electric vehicles achieve high output equivalent to electric double layer capacitors and have an energy density of about 160 Wh / L. However, research to increase the energy density and input / output characteristics, further improve the stability at high temperatures, and increase the durability has been energetically advanced.
In addition, research for higher output is also being conducted in lithium ion batteries. For example, a lithium ion battery has been developed that can obtain high input / output characteristics exceeding 3 kW / L at a discharge depth (that is, a value indicating what percentage of the discharge capacity of the device is discharged) 50%. However, the energy density is 100 Wh / L or less, and the high energy density, which is the greatest feature of the lithium ion battery, is intentionally suppressed. Further, its durability (particularly cycle characteristics and high temperature storage characteristics) is inferior to that of an electric double layer capacitor. Therefore, the lithium ion battery can be used only in a range where the depth of discharge is narrower than the range of 0 to 100% in order to have practical durability. Since the capacity that can actually be used is further reduced, research for further improving the durability is being actively pursued.

As described above, there is a strong demand for practical use of a power storage element having high input / output characteristics, energy density, and durability. However, the above-described existing power storage element has advantages and disadvantages. Therefore, a new power storage element that satisfies these technical requirements has been demanded, and development of a power storage element called a lithium ion capacitor has been actively developed as a promising candidate.
A lithium ion capacitor is a kind of power storage element that uses a non-aqueous electrolyte containing an electrolyte containing lithium ions (that is, a non-aqueous lithium-type power storage element),
In the positive electrode, similar to the electric double layer capacitor, non-Faraday reaction by adsorption / desorption of anions,
The negative electrode is a storage element that charges and discharges by a Faraday reaction by insertion and extraction of lithium ions, similar to a lithium ion battery.

An electric double layer capacitor that charges and discharges by a non-Faraday reaction in both the positive electrode and the negative electrode is excellent in input / output characteristics as described above, but has a low energy density. On the other hand, a lithium ion battery that is a secondary battery that charges and discharges by a Faraday reaction in both the positive electrode and the negative electrode is excellent in energy density but inferior in input / output characteristics. The lithium ion capacitor is a new power storage element that aims to achieve both excellent input / output characteristics and high energy density by performing charge and discharge by a non-Faraday reaction at the positive electrode and a Faraday reaction at the negative electrode.
As an example of a lithium ion capacitor, Patent Document 1 proposes a non-aqueous lithium storage element that combines high output characteristics and energy density by using activated carbon as a positive electrode active material and a composite porous material as a negative electrode active material. ing.

  Examples of the use of the lithium ion capacitor include railways, construction machines, and power storage elements for automobiles. These applications are required to exhibit high input / output characteristics over a wide temperature range, particularly at low temperatures. However, at low temperatures, the problem is a decrease in input / output characteristics due to a rapid increase in resistance.

International Publication No. 2014/088074 JP 2001-85016 A JP 2011-222258 A JP 2013-80780 A

  As a factor for increasing the resistance of the electricity storage element at a low temperature, it is conceivable that the diffusion resistance of lithium ions increases in the negative electrode active material layer due to a decrease in ionic conductivity of the non-aqueous electrolyte solution. In order to improve this, the present inventors have proposed a technique for improving output characteristics at low temperatures by using a carbon material as a negative electrode active material and adjusting the primary particle diameter of the carbon material to be small (for example, Patent Document 4). This is presumably because the diffusion of lithium ions in the negative electrode active material layer becomes good due to the presence of gaps formed between the primary particles, and sufficient non-aqueous electrolyte solution can be held in the gaps.

On the other hand, when the primary particle diameter decreases, the interface between particles increases, and the electrical resistance at the interface increases. Moreover, as for most carbon materials, electronic conductivity falls as it becomes low temperature.
Therefore, a non-aqueous lithium storage element using a carbon material having a small primary particle size as a negative electrode active material is low temperature and low voltage region (when the electron density in the negative electrode active material layer is low). When the electron conductivity is lowered and the influence of the electronic resistance at the particle interface becomes significant, it becomes difficult to develop good input characteristics.

In view of the above situation, the problem to be solved by the present invention is to provide a negative electrode for a non-aqueous lithium storage element exhibiting high input / output characteristics even at a low temperature, and a high input / output characteristic at low temperatures using the negative electrode. It is providing the non-aqueous lithium-type electrical storage element shown.
As a method for improving the electronic conductivity of the negative electrode active material layer, Patent Document 2 discloses a technique for forming protrusions on the surface of the negative electrode current collector. Moreover, in patent document 3, the adhesiveness between this electrical power collector and an active material layer is improved by using the negative electrode electrical power collector with the unevenness | _corrugation whose 10-point average roughness _Rzjis is 1.5-7.5 micrometers. A technique for reducing the internal resistance of the negative electrode is disclosed. However, in these patent documents, a preferable primary particle diameter that can sufficiently exhibit the effect of reducing resistance by providing unevenness on the current collector is not studied.

The present inventors have advanced research to solve the above-mentioned problems. As a result, when a carbon material having a small primary particle diameter is used as the negative electrode active material, the negative electrode active material layer has a low voltage state in which the electron density of the negative electrode active material layer is low by providing the negative electrode current collector with a larger uneven shape than before. It was also found that the electron conductivity can be sufficiently ensured and the input characteristics at low temperatures are remarkably improved. And based on this knowledge, this invention was completed.
That is, the present invention is as follows.

[1] A negative electrode current collector, and a negative electrode active material layer containing a negative electrode active material capable of inserting and extracting lithium ions on one or both surfaces of the negative electrode current collector,
The negative electrode active material is a carbon material having a primary particle size of 0.005 μm or more and 5 μm or less,
The negative electrode current collector includes a non-smooth region having a shape selected from a concave portion and a convex portion in at least a part of a contact surface with the negative electrode active material layer, and from the concave portion and the convex portion in the non-smooth region. A negative electrode for a non-aqueous lithium storage element, wherein a ten-point average roughness R _zjis measured for a straight line including 10 or more vertices of a selected shape is 5 μm or more and 100 μm or less.

[2] The negative electrode according to [1], wherein a doping amount of lithium ions per unit mass of the negative electrode active material is 530 mAh / g or more and 2500 mAh / g or less.
[3] The negative electrode according to [1] or [2], wherein the specific surface area calculated by the BET method for the negative electrode active material is 100 m ² / g or more and 600 m ² / g or less.
[4] The negative electrode active material is a composite porous carbon material of a porous carbon material having a specific surface area calculated by the BET method of 100 m ² / g or more and a carbonaceous material derived from petroleum pitch or coal pitch. The negative electrode according to any one of [1] to [3].

  [5] It has an electrode laminate composed of the negative electrode, the positive electrode, and the separator according to any one of [1] to [4], and a nonaqueous electrolytic solution containing a lithium ion-containing electrolyte in an outer package. A non-aqueous lithium storage element.

  The non-aqueous lithium storage element using the negative electrode of the present invention can exhibit high input / output characteristics even at low temperatures. Therefore, this non-aqueous lithium storage element can be suitably used particularly as a lithium ion capacitor in the fields of railways, construction machinery, automobiles and the like.

It is the schematic for _{demonstrating} the calculation method of ten-point surface roughness _Rzjis .

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiment.

<Negative electrode>
The negative electrode of the present invention has a negative electrode current collector and a negative electrode active material layer present on one side or both sides thereof.

[Negative electrode current collector]
The material constituting the negative electrode current collector in the present invention is preferably a metal foil that has high electron conductivity and does not deteriorate due to elution into the electrolytic solution and reaction with the electrolyte or ions. There is no restriction | limiting in particular as such metal foil, For example, aluminum foil, copper foil, nickel foil, stainless steel foil, etc. are mentioned. The negative electrode current collector in the non-aqueous lithium storage element of the present embodiment is preferably a copper foil.

The negative electrode current collector in the present invention includes a non-smooth region having a shape selected from a concave portion and a convex portion in at least a part of a contact surface with the negative electrode active material layer. The ten-point average roughness R _zjis measured for a straight line including 10 or more vertices of a shape selected from the concave and convex portions in the non-smooth region is 5 μm or more and 100 μm or less. The value of R _zjis is more preferably 8 μm to 70 μm, and _still more preferably 15 μm to 65 μm. When R _zjis is 5 μm or more, when the primary particle diameter of the negative electrode active material is 5 μm or less, the electron conductivity of the negative electrode active material layer at low temperature can be sufficiently secured, and the input characteristics at low temperature can be improved. On the other hand, if R _zjis is 100 μm or less, the uneven shape of the negative electrode current collector is retained inside the negative electrode active material layer even when the negative electrode active material layer is thinned to obtain a high energy density. There is no concern that the non-smooth region of the negative electrode current collector will break through the opposing positive electrode separator and cause a micro short circuit.

  The “non-smooth region” is a concept including both a case where unevenness is formed on a plane and a case where unevenness is formed on a curved surface. This non-smooth region is preferably 50% or more, more preferably 70% or more, and still more preferably 90% or more of the area of the negative electrode current collector in contact with the negative electrode active material layer. Particularly preferably, the entire area of the negative electrode current collector that is in contact with the negative electrode active material layer is a non-smooth region. The non-smooth region may extend over a portion of the negative electrode current collector that does not contact the negative electrode active material layer.

The shape of each of the concave portion or the convex portion in the non-smooth region is arbitrary. For example, a conical shape, a polygonal pyramid shape, a truncated cone shape, a truncated polygonal pyramid shape and the like can be mentioned, and an indefinite shape may be used. The area of the bottom surface is preferably 25 μm ^{2 to} 400 mm ² , more preferably 30 μm ^{2 to} 225 mm ² , and still more preferably 35 μm ^{2 to} 100 mm ² . The depth of the concave portion or the height of the convex portion is appropriately adjusted so that the ten-point average roughness R _zjis falls within the above range. For example, numerical values of 2.5 μm to 100 μm, preferably 4 μm to 70 μm can be exemplified.

The shape of the concave portion or the convex portion in the non-smooth region may be the same as or different from each other.
In the non-smooth region, only the concave portion may be formed, only the convex portion may be formed, or both the concave portion and the convex portion may be formed. Moreover, these may be formed regularly and may be formed irregularly.
The concave portion and the convex portion in the non-smooth area may be formed so as to contact the adjacent concave portion or convex portion with a part of the bottom surface, or may be formed separately from each other. The distance between the apex of the concave portion or convex portion and the apex of the nearest concave portion or convex portion adjacent to the concave portion or convex portion can be, for example, 5 μm to 20 mm, and preferably 5 μm to 15 mm. In this specification, “the apex of the recess” means the deepest portion of the recess.
When the recessed part and convex part in a non-smooth area | region are formed apart from the adjacent recessed part or convex part, an intermediate | middle flat area shall also be contained in a non-smooth area | region.

The non-smooth region in the present invention is a concept including the following cases, for example.
(1) When having a plurality of convex portions,
(2) When having a plurality of recesses,
(3) When having a plurality of convex portions and a plurality of concave portions, etc. In the above (3), when one or a plurality of convex portions and one or a plurality of concave portions are alternately arranged, only the concave portion Including one or a plurality of small regions having one and a plurality of small regions having only convex portions, a case where convex portions and concave portions are randomly arranged, and a combination thereof.
The surface of the negative electrode current collector that does not contact the negative electrode active material layer may or may not have the non-smooth region as described above.

The ten-point average roughness R _zjis in the present invention is determined by the following method based on JIS B 0601 (2001).
First, a straight line for measuring a cross-sectional curve (roughness curve) is set in the non-smooth region of the negative electrode current collector. It is preferable that ten or more vertices of a shape selected from a concave portion and a convex portion formed on the current collector are included on the straight line to be measured. The number of vertices is more preferably 20-30. The evaluation length should be at least 5 times the average length R _sm of the elements described later, and is preferably about 10 to 15 times the R _sm . When R _sm is unknown, measurement is performed for a provisional evaluation length. When it is determined from the obtained R _sm value that the evaluation length is insufficient, measurement of an appropriate length is performed. A new measurement should be made after resetting the straight line.
The cross-sectional curve can be measured using, for example, a commercially available contact surface shape measuring device.

図１における破線Ｌ_ａｖｅは、断面曲線の平均座標である。 By such measurement, for example, a cross-sectional curve as shown in FIG. 1 is obtained.
An average element length R _sm is calculated from the measured cross section curve, and a reference length (cut-off value λ _c ) is determined using the R _sm . The ten-point average roughness R _zjis is the five coordinates from the top to the fifth in the evaluation length from “L _{+ 1} ” to “L _{+ 5} ”, and the five coordinates from the bottom to the fifth. _Where “L ₋₁ ” to “L ₋₅ ” is a value obtained by the following equation.

A broken line L _ave in FIG. 1 is an average coordinate of the cross-sectional curve.

The ten-point average roughness R _zjis is measured for the negative electrode current collector.
In the case of the negative electrode current collector incorporated in the non-aqueous lithium storage element, the above measurement is performed on the negative electrode body taken out from the non-aqueous lithium storage element.
Removal of the negative electrode body from the storage element can be performed by the same method (described later) as the recovery of the negative electrode active material for measuring the primary particle diameter of the negative electrode active material incorporated in the nonaqueous lithium storage element. it can. That is, the electrolytic solution, lithium salt, binder, and the like are removed from the extracted negative electrode, and the negative electrode current collector after the negative electrode active material is removed may be collected and used for measurement.
As another method, a cross section including a concave portion and / or a convex portion of the negative electrode current collector is cut out from the negative electrode taken out from the non-aqueous lithium storage element, and the cut surface is photographed with a scanning electron microscope, The surface on the negative electrode active material layer side of the negative electrode current collector may be regarded as the measurement cross-sectional curve and calculated by the above calculation method.

The method for forming the non-smooth region of the negative electrode current collector is not particularly limited. For example, a method of preparing a metal foil or the like and applying an appropriate concavo-convex forming means such as embossing, chemical etching, electrolytic deposition, or blasting to the metal foil can be given. Embossing is preferable from the viewpoint of manufacturing cost and shape control of unevenness in the non-smooth region. Embossing can be performed by pressing a metal foil or the like with a press equipped with an embossing roll. The shape of the _unevenness , the interval, and R _zjis can be controlled by the pressing pressure, the surface shape of the embossing roll, and the like.

It is difficult to define the thickness of the negative electrode current collector in the present invention.
However, there is a preferred range for the thickness of the metal foil before forming the non-smooth region. The thickness of the metal foil before the formation of the non-smooth region is preferably 0.1 μm or more in order to maintain the mechanical strength of the current collector during and after the formation of the non-smooth region. In order not to make the electrical resistance of the film excessively large, it is preferable that it is 100 μm or less. The thickness is more preferably 1 μm to 50 μm, still more preferably 5 μm to 30 μm.

[Negative electrode active material layer]
The negative electrode active material layer includes a negative electrode active material capable of inserting and extracting lithium ions. In addition to this, optional components such as a conductive filler and a binder may be included as necessary.

-Negative electrode active material-
The negative electrode active material includes a carbon material that can occlude and release lithium ions. As the negative electrode active material, only this carbon material may be used, or in addition to this carbon material, another material that occludes and releases lithium ions may be used in combination. Examples of the other material include lithium titanium composite oxide and conductive polymer.
In the illustrated embodiment, the content of the carbon material capable of occluding and releasing lithium ions is preferably 50% by mass or more, more preferably 70% by mass or more based on the total amount of the negative electrode active material. Although it can be 100% by mass, it is preferably 90% by mass or less, and may be 80% by mass or less, for example, from the viewpoint of obtaining the effect of the combined use of other materials.

  Examples of carbon materials capable of occluding and releasing lithium ions include non-graphitizable carbon materials; graphitizable carbon materials; carbon black; activated carbon; artificial graphite; natural graphite; graphitized mesophase carbon microspheres; Amorphous carbonaceous materials such as substances; carbonaceous materials obtained by heat treatment of carbon precursors such as petroleum pitch, coal pitch, mesocarbon microbeads, coke, synthetic resin (eg phenol resin); furfuryl Examples include thermal decomposition products of alcohol resins or novolak resins; fullerenes; carbon nanophones; and composite carbon materials thereof.

Among these, a state in which a porous carbon material having a specific surface area (hereinafter also referred to as a BET specific surface area) calculated by the BET method of 100 m ² / g and a petroleum-based pitch or a coal-based pitch coexists. A composite porous carbon material comprising the porous carbon material and the pitch-derived carbonaceous material, which can be obtained by heat treatment in the above, is preferred. Prior to the heat treatment, the porous carbon material and the pitch may be mixed at a temperature higher than the melting point of the pitch. The heat treatment temperature may be a temperature at which a component generated by volatilization or thermal decomposition of the pitch used becomes a carbonaceous material. Preferably they are 400 degreeC or more and 1500 degrees C or less. The obtained carbonaceous material is considered to be mainly composed of polycyclic aromatic hydrocarbons when the heat treatment temperature is 800 ° C. or lower, and low crystalline carbon when the heat treatment temperature is 800 ° C. or higher.
As the atmosphere for performing the heat treatment, a non-oxidizing atmosphere is preferable.

  The primary particle diameter of the negative electrode active material is preferably 0.005 μm or more and 5 μm or less. More preferably, they are 0.020 micrometer or more and 3.5 micrometers or less, More preferably, they are 0.025 micrometer or more and 3 micrometers or less. If the primary particle size is 0.005 μm or more, the negative electrode active material can be easily handled and the amount of solvent in the coating liquid containing the negative electrode active material can be reduced. Cracking of the negative electrode active material layer can be suppressed. On the other hand, if the primary particle diameter is 5 μm or less, the presence of the gap formed by the primary particles can improve the diffusion of lithium ions in the negative electrode active material layer, and sufficient non-aqueous electrolysis can be applied to the gap. Since the liquid can be retained, high output characteristics can be exhibited even at low temperatures.

  In order to adjust the primary particle diameter of the negative electrode active material to the above range, for example, it may be adjusted by changing the raw material and the production method, and the prepared carbon material is pulverized using an appropriate pulverizing means. You may adjust by. The former method is an effective means when using, as the negative electrode active material, for example, a phenol resin carbide, carbon black, a nanocarbon material, a composite carbon material using these as raw materials, or the like. Examples of the pulverizing means in the latter method include a ball mill and a jet mill (wet or dry).

The primary particle diameter of the negative electrode active material in the present invention is determined by the following method.
1) The negative electrode active material powder is photographed with several fields of view with an electron microscope, and the particle size of the particles in these fields of view is measured by using a fully automatic image processing device or the like to measure about 2,000 to 3,000 particles. A value obtained by arithmetically averaging the values of the primary particle diameter.
2) A method in which the surface and / or cross section of the obtained negative electrode is photographed by several fields of view with an electron microscope and arithmetically averaged by the above method.

The primary particle size of the negative electrode active material incorporated in the non-aqueous lithium storage element is
After disassembling the non-aqueous lithium storage element and taking out the negative electrode, by the above method 2), or after removing components other than the negative electrode active material from the taken out negative electrode, by the above method 1),
Can be measured.

The operation of disassembling the negative electrode from the power storage element is preferably performed in an inert atmosphere such as argon.
In order to remove components other than the negative electrode active material from the negative electrode, for example, the following method can be used.
First, the taken-out negative electrode is immersed in ethyl methyl carbonate or dimethyl carbonate, and the electrolytic solution, lithium salt, etc. are removed and air-dried. Next, this is immersed in a mixed solvent of methanol and isopropanol to deactivate lithium ions occluded in the negative electrode active material, and air-dried again. Next, in order to remove the binder contained in the negative electrode active material layer, the negative electrode in which lithium ions are deactivated is immersed in distilled water or NMP. Then, if necessary, the negative electrode active material is peeled off with a spatula or the like, and the negative electrode active material is slid down from the negative electrode current collector by irradiating it with ultrasonic waves, and the negative electrode active material is recovered by suction filtration. Further, if necessary, the obtained negative electrode active material may be again immersed in distilled water or NMP and irradiated with ultrasonic waves, and then suction filtration may be repeated several times. Finally, the obtained negative electrode active material is vacuum-dried at 170 ° C., whereby a powder of the negative electrode active material can be obtained.

The BET specific surface area of the negative electrode active material is preferably 100 m ² / g or more and 600 m ² / g or less. More preferably 150 meters ² / g or more 550 meters ² / g or less, still more preferably 200 meters ² / g or more 500 meters ² / g or less. If the BET specific surface area is 100 m ² / g or more, the primary particles of the negative electrode active material have pores. Therefore, the interface between the negative electrode active material and the non-aqueous electrolyte can be made sufficiently large, and the non-aqueous electrolyte can be held inside the pores, so that high output characteristics can be expressed even at low temperatures. On the other hand, if it is 600 m < ² > / g or less, since the bulk density of the negative electrode active material layer using this negative electrode active material can be enlarged, the energy density of a non-aqueous lithium electrical storage element using this can be made high.

  The BET specific surface area in the present invention is determined by the BET multipoint method using the adsorption side isotherm obtained by vacuum-drying the sample at 200 ° C. all day and night, and measuring the adsorption and desorption isotherms using nitrogen as an adsorbate. Calculated by the BET 1-point method.

-Optional component-
The negative electrode active material layer in the present invention may contain optional components such as a conductive filler and a binder in addition to the negative electrode active material, as necessary.
The type of the conductive filler is not particularly limited, and examples thereof include acetylene black, ketjen black, and vapor grown carbon fiber. The amount of the conductive filler used is preferably 0 to 30 parts by mass with respect to 100 parts by mass of the negative electrode active material.

  The binder is not particularly limited. For example, PVdF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), styrene-butadiene copolymer, fluororubber, acrylic copolymer, cellulose derivative and the like. Can be used. Among these, PVdF is particularly preferable from the viewpoint of lithium ion permeability. The amount of the binder used is preferably 5 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the negative electrode active material. More preferably, they are 8 mass parts or more and 27 mass parts or less. If the amount of the binder is 5% by mass or more, sufficient electrode strength is exhibited. On the other hand, when the amount of the binder is 30 parts by mass or less, high input / output characteristics are exhibited without inhibiting lithium ions from entering and leaving the negative electrode active material.

[Manufacture of negative electrode]
The negative electrode has a negative electrode active material layer on one side or both sides of a negative electrode current collector. In a typical embodiment, the negative electrode active material layer is fixed to the negative electrode current collector.
The negative electrode can be manufactured by an electrode manufacturing technique in a known lithium ion battery, electric double layer capacitor or the like. For example, various materials including a negative electrode active material are dispersed or dissolved in water or an organic solvent to prepare a slurry-like coating liquid, and this coating liquid is applied to one or both sides of a negative electrode current collector and dried. In addition, the negative electrode active material layer is formed by pressing at room temperature or under heating as necessary. Alternatively, without using a solvent, various materials including a negative electrode active material can be mixed in a dry process, and the resulting mixture can be press-molded and then attached to the negative electrode current collector using a conductive adhesive. is there.

[Pre-doping of negative electrode active material]
The negative electrode active material is preferably doped with lithium ions. In this specification, the lithium ion doped in the negative electrode active material mainly includes three forms.
The first form is lithium ions that are previously occluded as a design value in the negative electrode active material before producing a non-aqueous lithium storage element.
The second form is lithium ions occluded in the negative electrode active material when a non-aqueous lithium electricity storage device is manufactured and shipped.
A third form is lithium ions occluded in the negative electrode active material after using the non-aqueous lithium electricity storage device as a device.

As a method for doping the negative electrode active material with lithium ions, a known method can be used. For example, after forming a negative electrode active material into a negative electrode, the negative electrode is used as a working electrode and metallic lithium is used as a counter electrode, and then an electrochemical cell combining non-aqueous electrolyte is prepared, and then lithium ions are doped electrochemically. how to;
A method of doping the negative electrode with lithium ions by electrically short-circuiting the negative electrode and the metal lithium foil by means such as press-bonding a metal lithium foil to the negative electrode, and then placing it in a non-aqueous electrolyte in this state;
Etc.
By doping lithium ions into the negative electrode active material, it is possible to satisfactorily control the capacity and operating voltage of the obtained non-aqueous lithium storage element.

The doping amount of lithium ions per unit mass of the negative electrode active material of the present embodiment is 530 mAh / g or more and 2500 mAh / g or less.
Doping lithium ions lowers the negative electrode potential. Therefore, when a negative electrode containing a negative electrode active material doped with lithium ions is combined with a positive electrode, the voltage of the non-aqueous lithium storage element increases and the capacity of the positive electrode increases. Therefore, the capacity and energy density of the obtained non-aqueous lithium storage element are increased.
If the doping amount is 530 mAh / g or more, lithium ions are well doped into irreversible sites that cannot be desorbed once the lithium ions in the negative electrode active material are inserted, and the amount of negative electrode active material relative to the desired amount of lithium is further reduced. Can be reduced. Therefore, the negative electrode film thickness can be reduced, and a high energy density can be obtained. The larger the doping amount, the lower the negative electrode potential, and the input / output characteristics, energy density, and durability are improved.
On the other hand, when the doping amount is 2,500 mAh / g or less, there is no possibility that side effects such as precipitation of lithium metal occur.

When a negative electrode active material is preliminarily doped with lithium ions by pressing a metal lithium foil (the first embodiment), a means for attaching lithium metal corresponding to 760 mAh / g or more and 2500 mAh / g or less per unit mass of the negative electrode active material It is preferable to dope by. The amount of lithium metal to be applied is more preferably from 1,050 mAh / g to 2,050 mAh / g, still more preferably from 1,100 mAh / g to 2,000 mAh / g, particularly preferably from 1,200 mAh / g to 1700 mAh / g. An amount corresponding to g or less.
By using the negative electrode current collector in the present invention, macro unevenness is formed on the surface of the formed negative electrode active material layer. As a result, the adhesion between the negative electrode active material layer and the metal lithium foil is improved and the lithium ion doping efficiency is improved, so that the process time can be shortened.

  When the negative electrode active material is doped with lithium ions by metal lithium pressure bonding to the negative electrode, the amount of lithium ions (second form) doped in the negative electrode active material of the non-aqueous lithium storage element at the time of shipment is: It tends to be smaller than the dope amount estimated from the amount of metallic lithium attached. The reason is that a part of the lithium ions doped from the attached metallic lithium is deactivated when the non-aqueous lithium storage element is manufactured. Therefore, it is preferable that the dope amount of lithium ions per unit mass of the negative electrode active material of the non-aqueous lithium storage element at the time of shipment is 620 mAh / g or more and 2,100 mAh / g or less. More preferably, it is 760 mAh / g or more and 1,700 mAh / g or less, More preferably, it is 840 mAh / g or more and 1,500 mAh / g or less.

  The amount of lithium ions (third form) doped in the negative electrode active material of the non-aqueous lithium storage element after use tends to be smaller than the dope amount at the time of shipment. The reason is that the doped lithium ions are further deactivated when the non-aqueous lithium storage element is used. Therefore, it is preferable that the dope amount of lithium ions per unit mass of the negative electrode active material of the non-aqueous lithium storage element after use is 530 mAh / g or more and 1,800 mAh / g or less. More preferably, it is 650 mAh / g or more and 1,400 mAh / g or less, More preferably, it is 730 mAh / g or more and 1,200 mAh / g or less.

The amount of lithium ion doping of the negative electrode active material in the non-aqueous lithium storage element at the time of shipment and after use can be known, for example, as follows.
First, after the negative electrode active material layer in this embodiment is washed with ethyl methyl carbonate or dimethyl carbonate and air-dried, an extract extracted with a mixed solvent composed of methanol and isopropanol and a negative electrode active material layer after extraction are obtained. This extraction is typically performed at an ambient temperature of 23 ° C. in an Ar box.
The amount of lithium contained in the extract obtained as described above and the negative electrode active material layer after extraction is quantified using, for example, an ICP-MS (inductively coupled plasma mass spectrometer), and the like. By obtaining the total, the doping amount of lithium ions in the negative electrode active material can be known. And the numerical value of the said unit should just be calculated by allocating the obtained value by the amount of negative electrode active materials used for extraction.

<Non-aqueous lithium storage element>
The non-aqueous lithium storage element of the present invention comprises an electrode laminate composed of the negative electrode, the positive electrode, and the separator, and a non-aqueous electrolyte solution containing a lithium ion-containing electrolyte in an outer package. The nonaqueous lithium electricity storage element according to the present embodiment can exhibit high input / output characteristics at low temperatures, as will be specifically verified in the examples described later.

<Positive electrode>
The positive electrode in the non-aqueous lithium storage element of the present embodiment includes a positive electrode current collector and a positive electrode active material layer including a positive electrode active material provided on one or both surfaces of the positive electrode current collector.

[Positive electrode current collector]
As the positive electrode current collector, a general current collector usually used in a power storage element can be used. The positive electrode current collector is preferably a metal foil that has high electron conductivity and does not deteriorate due to elution into the electrolytic solution and reaction with the electrolyte or ions. There is no restriction | limiting in particular as such metal foil, For example, aluminum foil, copper foil, nickel foil, stainless steel foil, etc. are mentioned. In the non-aqueous lithium storage element of the present embodiment, the positive electrode current collector is preferably an aluminum foil.
The positive electrode current collector may be a metal foil having no holes, or may be a metal foil having a through hole (for example, a punched metal through hole) or an open part (for example, an expanded metal hole).
The thickness of the positive electrode current collector is not particularly limited, but is preferably 1 to 100 μm. It is preferable that the thickness of the positive electrode current collector is 1 μm or more because the shape and strength of the positive electrode formed by fixing the positive electrode active material layer to the positive electrode current collector can be maintained. On the other hand, when the thickness of the positive electrode current collector is 100 μm or less, the mass and volume of the non-aqueous lithium storage element are appropriate, and the performance per weight and volume tends to be high, which is preferable.

[Positive electrode active material]
The positive electrode active material preferably contains activated carbon. As the positive electrode active material, only activated carbon may be used, or other materials as described later may be used in combination with activated carbon.
There is no restriction | limiting in particular in the kind of activated carbon in a positive electrode active material, and its raw material. However, it is preferable to optimally control the pores of the activated carbon in order to achieve both high input / output characteristics and high energy density.

Specifically, the amount of mesopores derived from pores having a diameter of 20 to 500 mm calculated by the BJH method is V1 (cc / g), and the amount of micropores derived from pores having a diameter of less than 20 mm calculated by the MP method is calculated. When V2 (cc / g)
0.8 <V1 ≦ 2.5 and 0.8 <V2 ≦ 3.0 are satisfied, and
Activated carbon having a specific surface area measured by the BET method of 3,000 m ² / g or more and 4,000 m ² / g or less (hereinafter also referred to as “activated carbon 1”) is preferable from the viewpoint of obtaining a high energy density.

When the BET specific surface area of the activated carbon 1 is 3,000 m ² / g or more, a high energy density is obtained. On the other hand, when the BET specific surface area is 4,000 m ² / g or less, there is no need to add a large amount of binder in order to maintain the strength of the electrode, so that the performance per electrode volume tends to be high. A more preferable value of the BET specific surface area of the activated carbon 1 is 3,200 m ² / g or more and 3,800 m ² / g or less.
The activated carbon 1 having the mesopore volume V1 and the micropore volume V2 described above has a higher BET specific surface area than the activated carbon used for the conventional electric double layer capacitor or lithium ion capacitor.
The micropore amount V2 of the activated carbon 1 is preferably a value larger than 0.8 cc / g in order to increase the specific surface area of the activated carbon and increase the capacity. Moreover, it is preferable that it is 3.0 cc / g or less from a viewpoint of increasing the density as an electrode of activated carbon and increasing the capacity | capacitance per unit volume. V2 is more preferably greater than 1.0 cc / g and not greater than 2.5 cc / g, and still more preferably not less than 1.5 cc / g and not greater than 2.5 cc / g.

The amount of micropores and the amount of mesopores in the present invention are values determined by the following methods, respectively. The sample is vacuum-dried at 200 ° C. all day and night, and adsorption and desorption isotherms are measured using nitrogen as an adsorbate. Using the adsorption-side isotherm obtained here, the micropore volume is calculated by the MP method, and the mesopore volume is calculated by the BJH method.
The MP method uses a “t-plot method” (BC Lippens, JH de Boer, J. Catalysis, 4319 (1965)), and uses a micropore volume, a micropore area, and a micropore. Is a method for obtaining the distribution of M. It is a method devised by Mikhail, Brunauer, Bodor (RS Mikhal, S. Brunauer, EE Bodor, J. Colloid Interface Sci., 26, 45 (1968)).
The BJH method is a calculation method generally used for analysis of mesopores and was proposed by Barrett, Joyner, Halenda et al. (EP Barrett, LG Joyner and P. Halenda, J Am. Chem. Soc., 73, 373 (1951)).

The activated carbon 1 having the above-described characteristics can be obtained using, for example, a raw material (carbon source) and a processing method described below.
The carbon source used as a raw material for the activated carbon 1 is not particularly limited as long as it is a carbon source that is normally used as a raw material for activated carbon. For example, plant-based materials such as wood, wood flour, and coconut shells; fossil-based materials such as petroleum pitch and coke; phenol resin, furan resin, vinyl chloride resin, vinyl acetate resin, melamine resin, urea resin, resorcinol resin, etc. Examples include synthetic resins. Among these raw materials, phenol resin and furan resin are suitable for producing activated carbon 1 having a high specific surface area, and are particularly preferable.

  Examples of a method for carbonizing these carbon sources or a heating method during activation treatment include known methods such as a fixed bed method, a moving bed method, a fluidized bed method, a slurry method, and a rotary kiln method. The atmosphere at the time of heating is an inert gas such as nitrogen, carbon dioxide, helium, or argon; or a gas mixed with other gases containing these inert gases as a main component. A method of firing at a carbonization temperature of about 400 to 700 ° C. and firing for about 0.5 to 10 hours is common.

As the activation method of the carbide after the carbonization treatment, for example, a gas activation method in which firing is performed using an activation gas such as water vapor, carbon dioxide, oxygen, or an alkali metal activation method in which heat treatment is performed after mixing with an alkali metal compound is possible. It is. An alkali metal activation method is preferable for producing activated carbon having a high specific surface area. In this activation method, a carbide and an alkali metal compound such as KOH or NaOH are mixed at a mass ratio of carbide: alkali metal compound of 1: 1 or more (the amount of the alkali metal compound is equal to or more than the amount of the carbide). A large amount), followed by heating in an inert gas atmosphere at a temperature of 600 to 900 ° C. for 0.5 to 5 hours, and then washing and removing the alkali metal compound with acid and water, followed by drying. I do.
In order to increase the amount of micropores and not increase the amount of mesopores, it is preferable to mix with KOH with a larger amount of carbides during activation. In order to increase the amount of any hole, it is preferable to use a large amount of KOH. In order to mainly increase the amount of mesopores, it is preferable to perform water vapor activation after alkali activation treatment.

The average particle diameter of the activated carbon 1 is preferably 1 μm or more and 30 μm or less. More preferably, they are 2 micrometers or more and 20 micrometers or less.
The positive electrode active material may include a material other than activated carbon 1 (for example, activated carbon not having the specific V1 and / or V2, or a material other than activated carbon (for example, a composite oxide of lithium and a transition metal)). Good. In the illustrated embodiment, the content of the activated carbon 1 is preferably more than 50% by mass of the total positive electrode active material, more preferably 70% by mass or more, still more preferably 90% by mass or more, and most preferably 100% by mass. preferable.

  The average particle size in the present invention is the particle size at which the cumulative curve becomes 50% when the particle size distribution is measured using a particle size distribution measuring device and the cumulative curve is determined with the total volume being 100% (that is, the cumulative curve is 50%). , 50% diameter (Median diameter)). This average particle diameter can be measured using a commercially available laser diffraction particle size distribution analyzer. The average particle size and the primary particle size are different values.

[Positive electrode active material layer]
If necessary, the positive electrode active material layer may contain a conductive filler, a binder, and the like in addition to the positive electrode active material.
The type of the conductive filler is not particularly limited, and examples thereof include acetylene black, ketjen black, and vapor grown carbon fiber. The amount of the conductive filler used is preferably 0 part by mass or more and 30 parts by mass or less, and more preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. From the viewpoint of input / output characteristics, it is preferable to use a conductive filler. When the amount used is 30 parts by mass or less, the proportion of the amount of the positive electrode active material in the positive electrode active material layer is high, and the output density per volume tends to increase, which is preferable.

  The binder is not particularly limited. For example, PVdF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), styrene-butadiene copolymer, fluororubber, acrylic copolymer, cellulose derivative and the like. Can be used. The amount of the binder used is preferably 3 parts by mass or more and 20 parts by mass or less, and more preferably 5 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. A binder does not cover the surface of a positive electrode active material as the usage-amount of a binder is 20 mass parts or less. Therefore, ions can enter and exit the positive electrode active material layer quickly, and high input / output characteristics can be obtained. On the other hand, it is preferable that the amount of the binder used is 3 parts by mass or more because the positive electrode active material layer is easily fixed on the positive electrode current collector.

The thickness of the positive electrode active material layer is preferably 15 μm or more and 100 μm or less, more preferably 20 μm or more and 85 μm or less per side. When the thickness is 15 μm or more, a sufficient energy density can be expressed as a non-aqueous lithium storage element. On the other hand, when the thickness is 100 μm or less, high input / output characteristics can be obtained as a non-aqueous lithium storage element. When the positive electrode current collector has holes, the thickness of the positive electrode active material layer means the average value of the thickness per one side of the portion of the positive electrode current collector that does not have holes.
When the bulk density of the positive electrode active material layer is 0.30 g / cm ³ or more, the capacity of the electrode per volume can be increased, and downsizing of the nonaqueous lithium storage element can be achieved. Further, in order to obtain high input output characteristics, further preferable to be 0.70 g / cm ³ or less, and particularly preferably 0.65 g / cm ³ or less.

An anchor layer may be provided between the positive electrode current collector and the positive electrode active material layer. By disposing the anchor layer, the adhesive strength between the positive electrode current collector and the positive electrode active material layer is improved, and as a result, it is possible to obtain a positive electrode in which both conduction is improved and input / output characteristics are excellent. Therefore, it is preferable. Therefore, the conditions required for the anchor layer are: first, the anchor layer itself has high strength, second, the anchor layer itself has high conductivity, and third, the anchor layer and the positive electrode active material. It is mentioned that the interface with the layer has strong adhesive strength.
Therefore, the anchor layer in the present embodiment preferably includes conductive carbon, and particularly preferably includes a mixture of two types of conductive carbon particles having different sizes. Accordingly, the strength of the anchor layer itself can be kept high even if the amount of the binder is small, and the anchor layer itself has high conductivity by decreasing the amount of the binder. Furthermore, the roughness of the anchor layer surface is increased. As a result, the interface between the anchor layer and the positive electrode active material layer has a strong adhesive strength, and can sufficiently satisfy the above three conditions required for the anchor layer.
Examples of the two types of conductive carbon include, for example, first conductive carbon particles having an average particle diameter of 20 nm or more and less than 1 μm;
Second conductive carbon particles having an average particle diameter of 1 μm or more and less than 15 μm;
Is preferred.

[Production of positive electrode]
The positive electrode has a positive electrode active material layer on one side or both sides of a positive electrode current collector. In a typical embodiment, the positive electrode active material layer is fixed to the positive electrode current collector.
The positive electrode can be manufactured by known electrode manufacturing techniques such as a lithium ion battery and an electric double layer capacitor. For example, various materials including a positive electrode active material are prepared in a slurry-like coating solution with water or an organic solvent, and this coating solution is applied to one or both sides on a positive electrode current collector and dried, and if necessary. It is obtained by pressing at room temperature or under heating to form a positive electrode active material layer. It is also possible to mix various materials including the positive electrode active material in a dry process without using a solvent, and press-mold the resulting mixture, and then attach it to the positive electrode current collector using a conductive adhesive. is there.

<Non-aqueous electrolyte>
The non-aqueous electrolyte solution used for the non-aqueous lithium storage element of the present invention may be a non-aqueous liquid containing a lithium ion-containing electrolyte. Such a non-aqueous liquid may contain an organic solvent, an additive, and the like.

Examples of the lithium-ion-containing electrolyte, for _example, can be used _{LiBF 4, LiPF 6, LiN (} SO 2 F) 2, LiN (SO 2 CF 3) 2 lithium salt such. The lithium salt concentration of the non-aqueous electrolyte is preferably in the range of 0.5 to 2.0 mol / L. At 0.5 mol / L or more, sufficient anions are present, and the capacity of the non-aqueous lithium storage element is maintained. On the other hand, at 2.0 mol / L or less, the lithium salt is sufficiently dissolved in the non-aqueous electrolyte solution, and appropriate viscosity and conductivity of the non-aqueous electrolyte solution are maintained.

Examples of the organic solvent include cyclic carbonates represented by ethylene carbonate (EC) and propylene carbonate (PC), chains represented by diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Lactones such as γ-butyrolactone (γBL); and mixed solvents thereof can be used.
Examples of the additive include sultone compounds, cyclic phosphazenes, fluorine-containing cyclic carbonates, cyclic carbonates, cyclic carboxylic acid esters, cyclic acid anhydrides, and mixtures thereof.

<Separator>
The positive electrode and the negative electrode molded as described above are laminated or spirally laminated via a separator to form an electrode laminate including the positive electrode, the negative electrode, and the separator.
The separator is not particularly limited, but for example, a polyethylene microporous film or a polypropylene microporous film used in a lithium ion secondary battery, or a cellulose nonwoven used in an electric double layer capacitor. Paper or the like can be used.
The thickness of the separator is preferably 10 μm or more and 50 μm or less. If the thickness of the separator is 10 μm or more, it is preferable because self-discharge due to an internal micro short circuit tends to be small. On the other hand, if the thickness of the separator is 50 μm or less, the input / output characteristics tend to be high, which is preferable.

<Exterior body>
A metal can, a laminate film, or the like can be used as the exterior body.
As said metal can, the thing made from aluminum is preferable.
The laminate film is preferably a film in which a metal foil and a resin film are laminated, and an example of a three-layer structure comprising an outer layer resin film / metal foil / interior resin film is exemplified. The outer layer resin film is for preventing the metal foil from being damaged by contact or the like, and a resin such as nylon or polyester can be suitably used. The metal foil is for preventing the permeation of moisture and gas, and foils of copper, aluminum, stainless steel and the like can be suitably used. The interior resin film protects the metal foil from the electrolyte contained in the interior and is used for melting and sealing at the time of heat sealing the exterior body. Polyolefin, acid-modified polyolefin, and the like can be suitably used.

  Examples and comparative examples will be described below to further clarify the features of the present invention. However, the present invention is not limited to the following examples and comparative examples.

<Preparation of negative electrode active material>
[Preparation Example 1a]
Coconut shell activated carbon having a BET specific surface area of 1,780 m ² / g was pulverized with a ball mill and classified to adjust the primary particle diameter to 3.2 μm. 150g of coconut shell activated carbon after pulverization and classification is placed in a stainless steel mesh basket and placed on a stainless steel bat containing 270g of coal-based pitch (softening point: 50 ° C). The composite porous carbon material 1 was obtained by installing in 300mmx300mmx300mm) and performing a thermal reaction. This heat treatment was performed in a nitrogen atmosphere, and the temperature was raised to 600 ° C. in 8 hours and kept at the same temperature for 4 hours. Then, after cooling to 60 degreeC by natural cooling, the composite porous carbon material 1 was taken out from the furnace.
About the obtained composite porous carbon material 1, the primary particle diameter was calculated | required by the method of 1) mentioned above using the scanning electron microscope. Further, by using a pore distribution measuring device (AUTOSORB-1 AS-1-MP) manufactured by Yuasa Ionics, the adsorption and desorption isotherm was measured using nitrogen as an adsorbate, and the BET specific surface area was determined by the method described above. .
The composite porous carbon material 1 had a primary particle size of 3.4 μm and a BET specific surface area of 262 m ² / g.

[Preparation Example 2a]
Coconut shell activated carbon was pulverized with a dry jet mill, classified, and the composite porous carbon material 2 was produced in the same manner as in Preparation Example 1a except that the primary particle diameter was adjusted to 0.65 μm. went. The composite porous carbon material 2 had a primary particle size of 0.68 μm and a BET specific surface area of 271 m ² / g.

[Preparation Example 3a]
The coconut shell activated carbon obtained in Preparation Example 2a after pulverization and classification was further pulverized by a wet jet mill, classified, and used in the same manner as in Adjustment Example 1a except that the primary particle diameter was adjusted to 0.30 μm. The composite porous carbon material 3 was manufactured and evaluated. The composite porous carbon material 3 had a primary particle size of 0.036 μm and a BET specific surface area of 286 m ² / g.

[Preparation Example 4a]
A composite porous carbon material 4 was produced in the same manner as in Preparation Example 3a, except that a coal pitch with a softening point of 90 ° C. was used instead of a coal pitch with a softening point of 50 ° C., and the amount used was 150 g. Evaluation was performed. The composite porous carbon material 4 had a primary particle size of 0.032 μm and a BET specific surface area of 307 m ² / g.

[Preparation Example 5a]
150 g of nanocarbon material containing graphite having a BET specific surface area of 561 m ² / g and a primary particle diameter of 0.46 μm was placed in a stainless steel mesh basket, and 75 g of coal-based pitch (softening point: 38 ° C.) was added. The composite porous carbon material 5 was obtained by placing on a stainless steel bat and placing both in an electric furnace (effective size in the furnace 300 mm × 300 mm × 300 mm) and performing heat treatment. This heat treatment was carried out in a nitrogen atmosphere, and the temperature was raised to 680 ° C. in 10 hours and kept at the same temperature for 4 hours. Then, after cooling to 60 degreeC by natural cooling, the composite porous carbon material 5 was taken out from the furnace. The resulting composite porous carbon material 5 had a primary particle size of 0.51 μm and a BET specific surface area of 405 m ² / g.

[Preparation Example 6a]
A composite porous carbon material 6 was produced and evaluated in the same manner as in Preparation Example 1a except that the primary particle diameter of the coconut shell activated carbon was adjusted to 8.0 μm by pulverization and classification. The composite porous carbon material 6 had a primary particle size of 8.2 μm and a BET specific surface area of 257 m ² / g.

<Preparation of negative electrode current collector>
[Preparation Example 1b]
The ten-point average roughness in the minor axis direction of an electrolytic copper foil having a thickness of 10 μm was measured by the above-described method using a contact surface shape measuring device (DECTAC XT-A). This measurement was performed on a straight line having a length of 25 mm set in an arbitrary direction of the copper foil. As a result, Rzjis of the electrolytic copper foil was 1 μm.
Using this electrolytic copper foil, embossing was performed with a press equipped with an embossing roll to obtain embossed copper foil 1 having unevenness on both sides. The embossed copper foil 1 has an emboss pattern in which concave portions and convex portions are arranged alternately and isotropically in the major axis direction (roll MD direction) and the minor axis direction (TD direction of the roll) of the copper foil. It was. The shape of the bottom surface of the convex part and the concave part was a square, and the distance between the apex of the convex part and the deepest part (vertex) of the nearest concave part adjacent to the convex part was 1 mm.
The resulting ten-point average roughness _{R Zjis} the short axis direction of the embossed foil 1 was measured, _{R zjis} embossed copper foil 1 was 52 .mu.m. At this time, a straight line that continuously passes through the apex of the convex portion at an angle as small as possible with respect to the TD direction of the copper foil was set, and a length of 25 mm on the straight line was set as a measurement target.

[Preparation Examples 2b to 5b]
Embossed copper foils 2 to 5 were obtained by embossing the electrolytic copper foil in the same manner as in Preparation Example 1a _except that the embossing press pressure was adjusted so that R _zjis was the value described in Table 1. It was.

<Example 1>
[Manufacture of negative electrode]
80 parts by mass of composite porous carbon material 1, 5 parts by mass of acetylene black, 15 parts by mass of PVDF (polyvinylidene fluoride), and NMP (N-methylpyrrolidone) were mixed, and the solid content concentration was 20% by mass. A coating solution was obtained. The obtained coating liquid was applied to both surfaces of the embossed copper foil 1, dried and pressed to obtain a negative electrode having a total film thickness of 95 μm. The film thickness of a negative electrode is the value calculated | required from the average value of the thickness measured in arbitrary 10 places of a negative electrode using the Ono Keiki Co., Ltd. film thickness meter (Linear Gauge Sensor GS-551).

[Production of positive electrode]
The phenol resin was carbonized in a baking furnace at 600 ° C. for 2 hours in a nitrogen atmosphere. The fired product obtained was pulverized with a ball mill and classified to obtain a carbide having an average particle size of 7 μm.
This carbide and KOH were mixed at a mass ratio of 1: 5, and activated by heating in a firing furnace at 800 ° C. for 1 hour in a nitrogen atmosphere. Next, after stirring and washing in dilute hydrochloric acid adjusted to a concentration of 2 mol / L for 1 hour, boiling washing was performed in distilled water until it was stable between pH 5 and 6, and then dried to obtain activated carbon 1. .

About the obtained activated carbon 1, the BET specific surface area, the amount of mesopores, and the amount of micropores were calculated | required by the method mentioned above. The BET specific surface area obtained was 3,627 m ² / g, the mesopore volume was 1.50 cc / g, and the micropore volume was 2.28 cc / g.
80.8 parts by mass of the activated carbon 1, 6.2 parts by mass of ketjen black, 10 parts by mass of PVDF (polyvinylidene fluoride), 3.0 parts by mass of PVP (polyvinylpyrrolidone), and NMP (N-methyl) Pyrrolidone) was mixed to obtain a coating solution having a solid content of 17% by mass. The obtained coating solution is applied to one or both sides of a current collector made of an aluminum foil having a thickness of 15 μm, dried and pressed to obtain a positive electrode having a positive electrode active material layer thickness of 55 μm per side. It was.

[Preparation of electrolyte]
As an organic solvent, a mixed solvent of ethylene carbonate (EC): methyl ethyl carbonate (EMC) = 33: 67 (volume ratio) was used, and the concentration ratio of LiN (SO ₂ F) ₂ and LiPF ₆ was 25:75 (molar ratio). And a solution obtained by dissolving each electrolyte salt so that the sum of the concentrations of LiN (SO ₂ F) ₂ and LiPF ₆ is 1.2 mol / L with respect to the total electrolytic solution. Used as a liquid.
The concentrations of LiN (SO ₂ F) ₂ and LiPF ₆ in the electrolytic solution prepared here were 0.3 mol / L and 0.9 mol / L, respectively.

[Assembly of non-aqueous lithium storage element]
The negative electrode and positive electrode obtained above were cut into 100 mm × 100 mm. An amount of lithium metal foil corresponding to 680 mAh / g per unit mass of the composite porous carbon material 1 was attached to both surfaces of the negative electrode after cutting.
A single-sided positive electrode is used for the top and bottom surfaces, 18 negative electrodes and 17 double-sided positive electrodes are used, and a 15 μm thick polyolefin porous membrane separator (36 sheets in total) is sandwiched between the negative electrode and the positive electrode. did. Thereafter, electrode terminals were connected to the negative electrode and the positive electrode to obtain an electrode laminate. The laminated body was inserted into an outer package made of a laminate film, and the non-aqueous electrolyte solution was injected to seal the outer package, thereby assembling a non-aqueous lithium storage element.

[Capacitance measurement]
The obtained non-aqueous lithium storage element was charged to 3.8 V by constant current and constant voltage charging with a constant voltage charging time of 1 hour at a current value of 1.5 C, and then 1.5 C to 2.2 V. Constant current discharge was applied at the current value. It calculated | required by the calculation according to the electrostatic capacitance F = Q / (3.8-2.2) from the capacity | capacitance Q and voltage change at this time.

[Measurement of low-temperature cell characteristics (input / output resistance at -30 ° C)]
Next, the non-aqueous lithium storage element is charged at a constant current at an environmental temperature of −30 ° C. until reaching 3.8 V at a current value of 1.5 C, and then a constant voltage of 3.8 V is applied. Charging was performed for a total of 2 hours. Subsequently, a constant current was discharged to 2.2 V at a current value of 50C. In the discharge curve (time-voltage) obtained at this time, it is obtained by extrapolating the voltage value at the time of discharge time 2 seconds and 4 seconds by linear approximation, when the voltage at discharge time = 0 seconds is E0. The discharge resistance R _out was obtained by calculation according to R _out = (3.8−E0) / (50C (current value)). Here, the output resistance was obtained by the following formula.
Output resistance (ΩF) = (capacitance F) × (discharge resistance R _out )

Next, similarly, constant current discharge at constant temperature until the voltage reaches 2.2 V at a current value of 1.5 C at an ambient temperature of −30 ° C., and then constant current and constant voltage discharge in which a constant voltage of 2.2 V is applied is 2 in total. Went for hours. Subsequently, constant current charging was performed up to 3.8 V at a current value of 50C. In the charging curve (time-voltage) obtained at this time, when the voltage at charging time = 0 seconds obtained by extrapolating from the voltage values at the time of discharging time 2 seconds and 4 seconds by linear approximation is E0. The charging resistance R _in was obtained by calculation according to R _in = (E0−2.2) / (50C (current value)). Here, the input resistance was obtained by the following equation.
Input resistance (ΩF) = (Capacitance F) × (Charging resistance R _in )

<Examples 2-9 and Comparative Examples 1-3, and Reference Example 1>
Using the negative electrode current collector and negative electrode active material shown in Table 2 and adjusting the amount of lithium metal foil attached to the negative electrode so as to be the dope amount shown in Table 2, the same as in Example 1, Manufacture and evaluation of a negative electrode and a non-aqueous lithium storage element were performed. The results are shown in Table 1.

As understood from Examples 1 to 9, Comparative Examples 1 to 3, and Reference Example 1, the output resistance at low temperatures decreases as the primary particle diameter of the negative electrode active material decreases. In addition, when a negative electrode current collector having a non-smooth region with a primary particle size of 5 μm or less and R _zjis greater than 5 μm is used, the input resistance at low temperatures decreases as the primary particle size of the negative electrode active material decreases. To do. On the other hand, referring to Comparative Example 3 and Reference Example 1, when the primary particle diameter is 5 μm or more, more specifically, 8 μm or more, a negative electrode current collector having a non-smooth region where R _zjis is greater than 5 μm was used. Even in this case, it can be seen that the input resistance is hardly reduced.

  The non-aqueous lithium storage element using the negative electrode of the present invention can be suitably used, for example, in fields such as a hybrid drive system application in automobiles; an assist application for instantaneous power peaks in railways and construction machinery.

Claims (5)

A negative electrode current collector, and a negative electrode active material layer containing a negative electrode active material capable of inserting and extracting lithium ions on one or both surfaces of the negative electrode current collector,
The negative electrode active material is a carbon material having a primary particle size of 0.005 μm or more and 5 μm or less,
The negative electrode current collector includes a non-smooth region having a shape selected from a concave portion and a convex portion in at least a part of a contact surface with the negative electrode active material layer, and from the concave portion and the convex portion in the non-smooth region. A negative electrode for a non-aqueous lithium storage element, wherein a ten-point average roughness R _zjis measured for a straight line including 10 or more vertices of a selected shape is 5 μm or more and 100 μm or less.  2. The negative electrode according to claim 1, wherein a doping amount of lithium ions per unit mass of the negative electrode active material is 530 mAh / g or more and 2,500 mAh / g or less. The negative electrode according to claim 1, wherein the negative electrode active material has a specific surface area calculated by the BET method of 100 m ² / g or more and 600 m ² / g or less. The negative electrode active material is a composite porous carbon material of a porous carbon material having a specific surface area calculated by the BET method of 100 m ² / g or more and a carbonaceous material derived from petroleum-based pitch or coal-based pitch. Item 4. The negative electrode according to any one of Items 1 to 3.  A non-aqueous system comprising: an electrode laminate including the negative electrode, the positive electrode, and the separator according to any one of claims 1 to 4; and a non-aqueous electrolyte solution containing a lithium ion-containing electrolyte. Lithium type storage element.

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