JP5076288B2 - Secondary battery negative electrode and secondary battery using the same - Google Patents

Description

  The present invention relates to a negative electrode for a secondary battery and a secondary battery using the same, and more particularly to a negative electrode for a secondary battery having excellent output characteristics and a higher capacity, and a secondary battery using the same.

  With the spread of mobile terminals such as mobile phones and notebook personal computers, the role of the battery serving as the power source of lithium ion secondary batteries is regarded as important. These batteries are required to have a small size, light weight, high capacity, and performance that does not easily deteriorate even after repeated charge and discharge.

  Moreover, not only small and high capacity but also high output characteristics are required for large lithium ion secondary batteries. In order to realize this, there is a method of reducing the resistance of the battery itself by reducing the thickness of the active material layer as much as possible. However, in this method, the electrode is thinned, so that increasing the battery capacity results in an increase in the number of times the electrode is wound and the number of stacked layers. As a result, the volume and weight of the current collector portion are increased by the increase in the number of wrinkles and the number of layers, making it difficult to increase the capacity.

  Thus, attempts have been made to increase output characteristics by using carbon fiber to lower electrode resistance or increase the specific surface area of particles constituting the electrode.

For example, Patent Document 1 discloses a technique for realizing high output by using graphitic carbon fiber as a negative electrode active material and reducing the resistance of an electrode. Further, a specific surface area in the measurement by the BET method of the negative electrode active material particles in Patent Document 2, is an attempt to improve the output characteristics by the 1.2 m ² or more 6 m ² or less is described.
Japanese Patent Laying-Open No. 2004-117846 (pages 4-5) JP 2004-296305 A

  However, the negative electrode active materials disclosed in Patent Documents 1 and 2 have some problems.

  The first problem is that when graphitic carbon fibers are used for the negative electrode, slurry and electrodes are difficult to produce because the bulk density of the graphitic carbon fibers themselves is small. In addition, these negative electrode active materials have an adverse effect on the presence of an electrolyte component such as propylene carbonate, making it difficult to obtain batteries having stable operating characteristics.

  The second problem is that when the specific surface area of the negative electrode active material particles itself is increased, the negative electrode active material that is not present in the vicinity of the surface in contact with the electrolyte of the negative electrode has little contribution to improving the output characteristics of the battery, and the desired output characteristics, etc. There was a case that could not be obtained. Moreover, a film or the like is formed on the surface of the negative electrode due to decomposition of the electrolytic solution and the apparent specific surface area is reduced, and the effect may be reduced. Further, when a high capacity negative electrode active material such as silicon or tin is used to increase the capacity of the battery, if the expansion / shrinkage due to charge / discharge is large and the specific surface area is increased, the negative electrode active material in the negative electrode during expansion / shrinkage is increased. There was a drawback that internal destruction occurred in the vicinity of the substance.

  Thus, as a result of intensive studies, the present inventor has found that the effect of improving the output characteristics of the battery is greatest when the surface area of the interface of the negative electrode active material layer in contact with the electrolyte is increased. In addition, in order to increase the surface area of the interface, it is not sufficient in terms of controllability of the surface properties, for example, to simply adjust the film formation method of the negative electrode active material layer. I have found that it is only necessary to adjust the range to a predetermined range.

  Furthermore, in order to increase the capacity of the battery, (a) at least one selected from the group consisting of metals, metalloids and their oxides capable of inserting and extracting Li can be used as the negative electrode active material. In order to suppress volume expansion / contraction (of the negative electrode active material layer during charge / discharge) due to the use of the negative electrode active material, (b) an element X that does not occlude Li may be added to the negative electrode active material layer. I discovered that.

  That is, the object of the present invention is to adjust the surface roughness Ra of the current collector to a range of more than 2 μm and 15 μm or less, and the negative electrode active material layer is (a) a metal, a semimetal, and a metal capable of inserting and extracting Li An interface in contact with the electrolyte solution of the negative electrode active material layer formed on the current collector by including at least one negative electrode active material selected from the group consisting of oxides of (b) and (b) an element X that does not occlude Li The surface area of the negative electrode active material layer can be increased, and the negative electrode active material layer can be held at a high surface area by suppressing the volume change of the negative electrode active material layer accompanying charge / discharge (Li storage and release). As a result, the secondary battery having the secondary battery negative electrode can have a high output density and a high capacity.

  Another object of the present invention is to provide a negative electrode material having a long lifetime and high reliability, and a secondary battery using the same.

  In order to solve the above problems, the present invention is characterized by having the following configuration.

1. In a negative electrode for a secondary battery having a current collector and a negative electrode active material layer provided on the current collector,
The negative electrode active material layer side surface of the current collector has a surface roughness (Ra) of more than 2 μm and 15 μm or less,
The negative electrode active material layer comprises (a) at least one negative electrode active material selected from the group consisting of metals, metalloids and their oxides capable of occluding and releasing Li, and (b) element X that does not occlude Li. And a negative electrode for a secondary battery.

  2. 2. The secondary battery according to 1 above, wherein (a) the negative electrode active material contains at least one element M selected from the group consisting of Si, Sn, Al, Pb, Ag, Ge, and Sb. Negative electrode.

  3. 3. The negative electrode for a secondary battery as described in 2 above, wherein (b) the element X that does not occlude Li is at least one element selected from the group consisting of Fe, Ni, Cu, and Ti.

  4). 4. The secondary battery negative electrode according to 3 above, wherein the ratio of the element M to the element X is an atomic ratio of element M: element X = 19: 1 to 1: 9.

  5). 5. The secondary battery negative electrode according to any one of the above 1 to 4, wherein the thickness of the negative electrode active material layer is 0.5 to 5 times the surface roughness (Ra).

  6). 6. A secondary battery comprising the secondary battery negative electrode according to any one of 1 to 5, a secondary battery positive electrode, and an electrolytic solution.

[Action]
In the negative electrode of the present invention, a negative electrode active material layer containing (a) a negative electrode active material and (b) an element X that does not occlude Li is formed on a current collector having a surface roughness (Ra) of more than 2 μm and not more than 15 μm. By forming a film, a negative electrode active material layer having a high surface area reflecting the surface properties of the current collector can be obtained. As a result, the number of sites where Li can be occluded / released on the negative electrode surface (negative electrode active material layer surface) can be increased as compared to conventional secondary batteries, and changes in the surface properties of the negative electrode active material layer associated with charge / discharge can be suppressed. Output characteristics can be improved.

  Further, by using a high-capacity material (at least one kind of negative electrode active material selected from the group consisting of metals, metalloids, and oxides capable of inserting and extracting Li), the surface area of the negative electrode active material layer is increased. Capacitance can be expressed more effectively. Since these negative electrode active materials are excellent in film formability, a negative electrode active material layer having a surface property that accurately reflects the surface property of the current collector can be obtained.

  Furthermore, by using such a negative electrode active material, the thickness of the negative electrode active material layer can be reduced and the resistance in the thickness direction of the negative electrode can be reduced. As a result, the output characteristics of the battery can be improved. In addition, the reliability of the battery can be improved by improving the adhesion between the current collector and the negative electrode active material layer.

  According to the present invention, a negative electrode active material layer containing (a) a negative electrode active material and (b) an element X that does not occlude Li is formed on a current collector having a surface roughness (Ra) of more than 2 μm and not more than 15 μm. By forming the film, it is possible to improve the output characteristics and reliability of the battery.

(1) Negative electrode for secondary battery The negative electrode for a secondary battery of the present invention has a current collector and a negative electrode active material layer. These members will be described below.

(Current collector)
For example, copper, stainless steel, nickel, titanium, or an alloy thereof can be used as the current collector. The surface in contact with at least the negative electrode active material layer of the current collector of the present invention (surface on the negative electrode active material layer side: 21 in FIG. 1) has a surface roughness (Ra) of more than 2 μm and 15 μm or less. There is a need. When the current collector has a surface roughness in such a range, the surface area of the surface of the negative electrode active material layer formed on the current collector can be increased, and the output density can be increased and the capacity can be increased.

  The surface roughness Ra of the current collector is preferably 3 μm or more and 10 μm or less, more preferably 5 μm or more and 8 μm or less, and further preferably 6 μm or more and 7 μm or less. When the surface roughness is within these ranges, it is possible to more effectively occlude and release Li and achieve high capacity. The surface roughness Ra can be measured by using a surface roughness meter according to JIS B 0601-1994.

  In order to obtain a current collector having such a surface roughness, for example, an electrolytic method can be used. In the case of using an electrolysis method, a collector having a desired surface roughness Ra is obtained by using a mold having a predetermined surface roughness or controlling electrolysis conditions (energization voltage, temperature, time during electrolysis). be able to.

(Negative electrode active material layer)
The negative electrode active material layer of the present invention includes (a) at least one negative electrode active material selected from the group consisting of metals, metalloids, and oxides capable of inserting and extracting Li, and (b) does not absorb Li Element X.

  (A) It is preferable to use at least one element M selected from the group consisting of Si, Sn, Al, Pb, Ag, Ge, and Sb as a metal or metalloid capable of inserting and extracting Li. By using such an element M, the capacity can be increased more effectively, and the film forming property of the negative electrode active material layer can be further improved. Examples of the metal that can occlude and release Li, a compound of a semimetal, a mixture, and an oxide thereof include AlSb, SiOα (0 <α ≦ 2), SnOβ (0 <β ≦ 2), Si—Sn alloy, and SnSiOγ. And so on. Moreover, you may use what can occlude / release an alkali metal or alkaline-earth metal as a negative electrode active material.

  Moreover, in the negative electrode for secondary batteries of the present invention, the negative electrode active material layer contains (b) an element X that does not occlude Li, so that the volume change of the negative electrode active material layer associated with charge and discharge (for Li occlusion and release). Volume expansion and contraction) are suppressed, and the negative electrode active material layer can be held at a high surface area. In addition, this element X may exist in the negative electrode active material layer as a simple substance, or may exist as a compound or a mixture, and the effects of the present invention can be achieved in any state. The element X is an element that does not substantially occlude Li and may be an element that does not alloy with Li.

  (B) The element X that does not occlude Li is preferably at least one element selected from the group consisting of Fe, Ni, Cu, and Ti. By containing these elements X, (a) volume change of the negative electrode active material accompanying charge / discharge is effectively absorbed by (b) element X that does not occlude Li, and volume change of the entire battery is effectively suppressed. can do. The element X that does not occlude (b) Li may be an element that does not occlude alkali metals or alkaline earth metals.

  Further, (a) when the negative electrode active material contains the element M, it is preferable that the ratio of the element M and the element X is an atomic ratio of element M: element X = 19: 1 to 1: 9. If the element X is present at a ratio larger than 1: 9, the ratio of the metal or metalloid involved in charge / discharge decreases, so the volume energy density or weight energy density of the negative electrode decreases. In addition, when the element X is present at a ratio smaller than 19: 1, the effect of adding the element X, that is, the suppression of volume change accompanying charging / discharging of the negative electrode active material and the effect of improving conductivity are reduced. More preferably, the atomic ratio is element M: element X = 14: 1 to 3: 7, and further preferably element M: element X = 9: 1 to 5: 5.

  The thickness of the negative electrode active material layer formed on the current collector is preferably 0.5 to 5 times the surface roughness Ra of the current collector, preferably 1 to 3 times. Is more preferable. When the negative electrode has a thickness within these ranges, optimization can be achieved from the viewpoint of increasing the capacity and reducing the resistance of the negative electrode.

  Further, the negative electrode active material layer can be formed on the current collector by using an appropriate method such as an atomization method, a vacuum deposition method, a sputtering method, a plasma CVD method, a photo CVD method, or a thermal CVD method. it can.

(2) Secondary Battery FIG. 1 shows a schematic structure of an example of a secondary battery having the negative electrode for a secondary battery of the present invention. Positive electrode current collector 11, layer containing positive electrode active material capable of inserting and extracting lithium ions (positive electrode active material layer) 12, layer containing negative electrode active material absorbing and releasing lithium ions (negative electrode active material layer) ) 13, a negative electrode current collector 14, an electrolytic solution 15, and a separator 16 including the same. The surface 21 on the negative electrode active material layer 13 side of the negative electrode current collector 14 has a surface roughness (Ra) of more than 2 μm and 15 μm or less.

  FIG. 2 shows a schematic diagram of the local surface of the negative electrode. In the negative electrode of FIG. 2, there is a current collector 14 having a surface roughness (Ra) of more than 2 μm and not more than 15 μm, and a negative electrode active material layer 13 is formed on the current collector 14. In the present invention, as the constituent material of the negative electrode active material layer 13, (a) a negative electrode active material having good film formability (accurately reflecting the surface state of the current collector) and (b) an element X that does not occlude Li are used. Therefore, a negative electrode active material layer having a surface property reflecting the surface property of the current collector 14 can be obtained. Below, each structural member which comprises a secondary battery is demonstrated.

(Separator)
As the separator 16, a polyolefin such as polypropylene or polyethylene, or a porous film such as a fluororesin is preferably used.

(Positive electrode)
The positive electrode has a positive electrode current collector 11 and a positive electrode active material layer 12. As the positive electrode current collector 11, for example, aluminum, stainless steel, nickel, titanium, or an alloy thereof can be used. As the positive electrode active material layer, for example, a lithium-containing composite oxide that is usually used is used. Specifically, LiMO ₂ (M is selected from Mn, Fe, and Co, and some other cations such as Mg, Al, and Ti are used. And a general-purpose material such as a spinel-type lithium manganese composite material typified by LiMn ₂ O ₄ can be used. The selected positive electrode active material is dispersed and kneaded in a solvent such as N-methyl-2-pyrrolidone (NMP) together with a conductive material such as carbon black and a binder such as polyvinylidene fluoride (PVDF). The positive electrode active material layer 12 can be obtained by a method such as coating on a substrate such as an aluminum foil.

(Electrolyte)
The electrolytic solution 15 includes at least an electrolyte, an aprotic solvent, and an additive.

(Electrolytes)
As the electrolyte, in the case of a lithium secondary battery, a lithium salt is used and dissolved in an aprotic solvent. The lithium salt, lithium imide _{salt, LiPF 6, LiAsF 6, LiAlCl} 4, LiClO 4, LiBF 4, LiSbF 6 , and the like. Of these, LiPF ₆ and LiBF ₄ are particularly preferable. By including these lithium salts, a high energy density can be achieved.

(Aprotic solvent)
The aprotic electrolyte is selected from organic solvents such as cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, γ-lactones, cyclic ethers, chain ethers and their fluorinated derivatives. In addition, at least one organic solvent is used. More specifically,
Cyclic carbonates: propylene carbonate (hereinafter abbreviated as PC), ethylene carbonate (hereinafter abbreviated as EC), butylene carbonate (BC), vinylene carbonate (VC)
Chain carbonates: dimethyl carbonate (DMC), diethyl carbonate (hereinafter abbreviated as DEC), ethyl methyl carbonate (hereinafter abbreviated as EMC), dipropyl carbonate (DPC)
Aliphatic carboxylic acid esters: methyl formate, methyl acetate, ethyl propionate γ-lactones: γ-butyrolactone Cyclic ethers: tetrahydrofuran, 2-methyltetrahydrofuran Chain ethers: 1,2-ethoxyethane (DEE), ethoxy Methoxyethane (EME),
Other: dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1, 3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, fluorinated carboxylic acid ester.
These can be used alone or in combination of two or more.

(Production of battery)
A positive electrode active material and a conductivity-imparting agent described in Tables 1 to 6 were dry-mixed and uniformly dispersed in N-methyl-2-pyrrolidone (NMP) in which PVDF as a binder was dissolved to prepare a slurry. Carbon black was used as the conductivity imparting agent. The slurry was applied on an aluminum metal foil (20 μm for square and cylindrical types, 25 μm for laminated types) serving as a positive electrode current collector, and then NMP was evaporated to obtain a positive electrode sheet. The solid content ratio in the positive electrode was positive electrode active material: conductivity imparting agent: PVDF = 80: 10: 10 (mass%).

  On the other hand, the negative electrode active materials described in Tables 1 to 6 were used. The film thickness of these negative electrodes is set by the capacity ratio with the positive electrode (hereinafter referred to as A / C balance; where A is the capacity per unit surface area of the negative electrode, and C is the capacity per unit surface area of the positive electrode). The coating amount of the positive electrode and the negative electrode was determined so that the A / C balance was 1 or more and 1.7 or less.

As the electrolytic solution, a solvent described in Tables 1 to 6 and 1 mol / L LiPF ₆ dissolved therein as an electrolyte were used.

Then, a negative electrode and a positive electrode are laminated via a separator made of polyethylene, and an aluminum laminated film type secondary battery (Examples 1 to 7 , 23 to 25, Reference Examples 1 to 7 and Comparative Examples 11 to 18), a cylindrical type Secondary batteries (Examples 10 to 16 and Comparative Examples 1 to 8) and square secondary batteries (Examples 17 to 22 , 31 to 33, Reference Examples 8 to 12 and Comparative Examples 9, 10, 19 to 23) Was made. In the case of an aluminum laminate film type secondary battery, the laminate film used has a structure in which a polypropylene resin (sealing layer, thickness 70 μm), polyethylene terephthalate (20 μm), aluminum (50 μm), and polyethylene terephthalate (20 μm) are laminated in this order. Two pieces of this are cut into a predetermined size, and a concave portion having a bottom surface portion and a side surface portion that match the size of the multilayer electrode body is formed in a part thereof, and these are opposed to wrap the multilayer electrode body. Then, the periphery was thermally fused to produce a film-clad battery. Before the last side was heat-sealed and sealed, the electrolyte solution was impregnated with the laminated electrode body.

(Battery evaluation)
The battery manufactured by the above process was evaluated at a temperature of 20 ° C. based on how much the capacity at the time of 50.0C discharge was compared with that at the time of 1C discharge. That is, the closer the 50.0C discharge capacity is to the 1.0C discharge capacity, the higher the output characteristics. The measurement was performed with a discharge start voltage of 4.2 V and a discharge end voltage of 3.0 V. The results are shown in Tables 7-12.

Example 1
The negative electrode active material layer was formed by depositing SiO (negative electrode active material) and Fe (element X) to a thickness of 1.5 μm by binary simultaneous vapor deposition. The atomic ratio of Si and Fe was 9: 1. LiCoO ₂ was used as the positive electrode active material contained in the positive electrode active material layer. To the electrolytic solution, 1 mol / L LiPF ₆ was added as an electrolyte in EC / DEC / EMC = 30/50/20 (mass ratio). A container was made of a member coated with an aluminum foil with a laminate for the battery outer body. The capacity ratio A / C balance between the positive electrode and the negative electrode was 1.05.

(Example 2)
The thickness of the negative electrode active material layer was 3 μm, and other conditions were the same as in Example 1.
(Example 3)
The thickness of the negative electrode active material layer was 5 μm, and other conditions were the same as in Example 1.

Example 4
The thickness of the negative electrode active material layer was 9 μm, and other conditions were the same as in Example 1.
(Example 5)
The thickness of the negative electrode active material layer was 10 μm, and other conditions were the same as in Example 1.

(Example 6)
The thickness of the negative electrode active material layer was 12 μm, and other conditions were the same as in Example 1.
(Example 7)
The thickness of the negative electrode active material layer was 15 μm, and other conditions were the same as in Example 1.

( Reference Example 1 )
The thickness of the negative electrode active material layer was 1 μm, and other conditions were the same as in Example 1.
( Reference Example 2 )
The thickness of the negative electrode active material layer was 18 μm, and other conditions were the same as in Example 1.

(Example 10)
The negative electrode active material layer was formed by simultaneous vapor deposition using two vapor deposition sources of Si (negative electrode active material) and Ni (element X) (Si atom number: Ni atom number = 5: 5). LiMnO ₂ was used as the positive electrode active material contained in the positive electrode active material layer. As the electrolyte, 1 mol / L LiPF ₆ was used as an electrolyte in PC / EC / DEC = 20/20/60 (mass ratio). The Ra on the current collector surface was 5 μm, and the thickness of the negative electrode active material layer was 6 μm. A 18650 cylindrical container was used for the battery outer casing. The capacity ratio A / C balance between the positive electrode and the negative electrode was 1.07.

(Example 11)
The negative electrode active material layer was formed by sputtering using an alloy of Al (corresponding to the negative electrode active material) and Cu (corresponding to the element X) as a target (Al atom number: Cu atom number = 19: 1). The other conditions were the same as in Example 10.

(Example 12)
The negative electrode active material layer was formed by sputtering using an alloy of Si—Sn (corresponding to the negative electrode active material) and Ti (corresponding to the element X) as the negative electrode active material (Si + Sn atom number: Ti atom number). = 14: 1). The other conditions were the same as in Example 10.

(Example 13)
The negative electrode active material layer was formed by simultaneous vapor deposition using two vapor deposition sources of Ag (negative electrode active material) and Fe (element X) (Si atom number: Ni atom number = 1: 9). The other conditions were the same as in Example 10.

(Example 14)
The negative electrode active material layer was formed by simultaneous vapor deposition using two vapor deposition sources of Pb (negative electrode active material) and Ni (element X) (Pb atom number: Ni atom number = 9: 1). The other conditions were the same as in Example 10.

(Example 15)
The negative electrode active material layer was formed by forming a film by simultaneous vapor deposition using two vapor deposition sources of Ge (negative electrode active material) and Cu (element X) (Ge atom number: Cu atom number = 3: 7). The other conditions were the same as in Example 10.

(Example 16)
The negative electrode active material layer was formed by forming a film by simultaneous sputtering using two sputtering sources of SnO (negative electrode active material) and Co (element X) (Sn atom number: Fe atom number = 7: 3). The other conditions were the same as in Example 10.

(Example 17)
The negative electrode active material layer was formed by depositing SnO (negative electrode active material) and Ni (element X) by binary simultaneous vapor deposition. The atomic ratio of SnO and Ni was 7: 3. LiCoO ₂ was used as the positive electrode active material contained in the positive electrode active material layer. As the electrolyte, 1 mol / L LiPF ₆ was used as an electrolyte in EC / DEC / EMC = 30/50/20 (mass ratio). The Ra on the current collector surface was 2.2 μm, and the thickness of the negative electrode active material layer was 2.2 μm. An aluminum square container was used as the battery casing. The capacity ratio A / C balance between the positive electrode and the negative electrode was 1.2.

(Example 18)
The Ra on the current collector surface was 2.5 μm, and the thickness of the negative electrode active material layer was 2.5 μm. The other conditions were the same as in Example 17.
(Example 19)
The Ra on the current collector surface was 3 μm, and the thickness of the negative electrode active material layer was 3 μm. The other conditions were the same as in Example 17.

(Example 20)
Ra of the current collector surface was 5 μm, and the thickness of the negative electrode active material layer was 5 μm. The other conditions were the same as in Example 17.
(Example 21)
The Ra of the current collector surface was 10 μm, and the thickness of the negative electrode active material layer was 10 μm. The other conditions were the same as in Example 17.

(Example 22)
The Ra of the current collector surface was 15 μm, and the thickness of the negative electrode active material layer was 15 μm. The other conditions were the same as in Example 17.
(Examples 23 to 25 and Reference Examples 3 to 7 )
The conditions were the same as in Example 2 except that the surface roughness Ra of the current collector was changed.

(Examples 31-33 and Reference Examples 8-12 )
The conditions were the same as in Example 19 except that the surface roughness Ra of the current collector was changed.
(Comparative Example 1)
The negative electrode active material layer was formed by forming a film by simultaneous vapor deposition using two vapor deposition sources of Si and Ni (the number of Si atoms: the number of Ni atoms = 5: 5). LiMnO ₂ was used as the positive electrode active material contained in the positive electrode active material layer. To the electrolytic solution, 1 mol / L LiPF ₆ was added as an electrolyte in PC / EC / DEC = 20/20/60 (mass ratio). Ra on the current collector surface was 1 μm, and the thickness of the negative electrode active material was 3 μm. A cylindrical container was used as the battery outer package. The capacity ratio A / C balance between the positive electrode and the negative electrode was 1.07.

(Comparative Example 2)
The negative electrode active material layer was formed by sputtering using an alloy of Al and Cu as a target (number of Al atoms: number of Cu atoms = 19: 1). The other conditions were the same as in Comparative Example 1.

(Comparative Example 3)
The negative electrode active material layer was formed by sputtering using an alloy of Si—Sn and Ti as a target (Si + Sn atom number: Ti atom number = 14: 1). The other conditions were the same as in Comparative Example 1.

(Comparative Example 4)
The negative electrode active material layer was formed by forming a film by simultaneous vapor deposition using two vapor deposition sources of Ag and Fe (Si atom number: Ni atom number = 1: 9). The other conditions were the same as in Comparative Example 1.

(Comparative Example 5)
The negative electrode active material layer was formed by forming a film by simultaneous vapor deposition using two vapor deposition sources of Pb and Ni (Pb atom number: Ni atom number = 9: 1). The other conditions were the same as in Comparative Example 1.

(Comparative Example 6)
The negative electrode active material layer was formed by film formation by simultaneous vapor deposition using two vapor deposition sources of Ge and Cu (Ge atom number: Cu atom number = 3: 7). The other conditions were the same as in Comparative Example 1.

(Comparative Example 7)
The negative electrode active material layer was formed by forming a film by simultaneous sputtering using two sputtering sources of SnO and Co (the number of Sn atoms: the number of Fe atoms = 7: 3). The other conditions were the same as in Comparative Example 1.

(Comparative Example 8)
The negative electrode active material layer was produced by forming a film by simultaneous vapor deposition using two vapor deposition sources of Si and Ni as the negative electrode active material (number of Si atoms: number of Ni atoms = 5: 5). The conditions were the same as in Example 10 except that the Ra on the current collector surface was 2 μm.

(Comparative Example 9)
The Ra of the current collector surface was 2 μm, and the thickness of the negative electrode active material was 0.3 μm. The other conditions were the same as in Example 17.
(Comparative Example 10)
Ra on the current collector surface was 17 μm, and the thickness of the negative electrode active material was 17 μm. The other conditions were the same as in Example 17.

(Comparative Examples 11-18)
The conditions were the same as those in Example 2 except that the surface roughness Ra was changed.
(Comparative Examples 19-23)
The conditions were the same as in Example 19 except that the surface roughness Ra was changed.

In addition, when performing simultaneous vapor deposition in the said Example, a reference example, and a comparative example, the vapor deposition source corresponding to a negative electrode active material and the element X was used, respectively. Then, by controlling the composition of this vapor deposition source, the degree of vacuum during vapor deposition, and the temperature and time during vapor deposition, a negative electrode active material layer containing a negative electrode active material and element X at a desired ratio and having a desired thickness Obtained. When sputtering (sputtering using one or two sputtering sources) is performed, the composition of the sputtering source, the temperature at the start of sputtering, the voltage between the sputtering source and the target, etc. are controlled at a desired ratio. A negative electrode active material layer containing the negative electrode active material and element X and having a desired thickness was obtained.

A copper foil having a thickness of 10 μm was used as the negative electrode current collector. The copper foil was obtained by electrodeposition. In each of the examples, reference examples, and comparative examples, the desired surface was obtained by controlling the electrodeposition conditions (the energization voltage, temperature, electrodeposition time, etc. during electrodeposition). A current collector having a roughness Ra was obtained.

上記のようにして作成した二次電池の評価結果を表７〜１２に示す。

The evaluation results of the secondary batteries prepared as described above are shown in Tables 7-12.

（集電体の表面粗さＲａと負極厚さの検討）
集電体の表面粗さＲａを一定とし負極の膜厚を変えた場合、負極厚みが集電体のＲａの０．５倍〜５倍の範囲にあるとき、１Ｃ放電容量に対する５０Ｃ放電容量は、７５％程度と高い出力特性が認められた（実施例１〜７、１０〜２５、３１〜３３）。一方、参考例１〜１２に示されるように、集電体のＲａに対して負極膜厚が薄すぎたり（Ｒａの０．５倍未満）、厚すぎたりする場合（Ｒａの５倍を超える値）、５０Ｃ放電容量は約７０％であった。これは集電体のＲａに対して負極の膜厚が厚くなると、負極表面が滑らかになり比表面積が小さくなってしまうためであると考えられる。また、集電体のＲａに対して負極膜厚が薄すぎる場合は集電体への負極活物質層のカバーレッジが悪く、集電体を完全に負極活物質層で覆うことができないためと思われる。

(Examination of current collector surface roughness Ra and negative electrode thickness)
When the surface roughness Ra of the current collector is constant and the film thickness of the negative electrode is changed, when the negative electrode thickness is in the range of 0.5 to 5 times the Ra of the current collector, the 50C discharge capacity with respect to the 1C discharge capacity is The output characteristics as high as 75% were recognized (Examples 1 to 7, 10 to 25, and 31 to 33). On the other hand, as shown in Reference Examples 1 to 12, when the negative electrode film thickness is too thin (less than 0.5 times Ra) or too thick with respect to Ra of the current collector (more than 5 times Ra) Value), the 50 C discharge capacity was about 70%. This is considered to be because when the film thickness of the negative electrode is increased with respect to Ra of the current collector, the negative electrode surface becomes smooth and the specific surface area decreases. In addition, when the negative electrode film thickness is too thin with respect to Ra of the current collector, the coverage of the negative electrode active material layer on the current collector is poor, and the current collector cannot be completely covered with the negative electrode active material layer. Seem.

(Examination of type of negative electrode active material and Ra of current collector)
Even if the negative electrode active material and the element X are changed to various ones as shown in the examples , reference examples, and comparative examples, high output characteristics can be obtained when the surface roughness Ra exceeds 2 μm and is 15 μm or less. It was. This is considered to be because Li was effectively occluded and released on the negative electrode active material layer surface by setting Ra within the above range.

  Further, when the ratio between the Ra of the current collector and the thickness of the negative electrode is the same, when the Ra of the current collector exceeds 2 μm and is 15 μm or less, 50 C discharge with respect to 1 C discharge capacity as shown in Examples 17 to 22 The capacity was 70% or more. On the other hand, even if the ratio of Ra of the current collector and the thickness of the negative electrode is the same, if the Ra of the current collector is 2 μm or less, or a value exceeding 15 μm or less, it is high as shown in Comparative Example 10. No output was obtained. This is presumably because the smaller the current collector Ra is, the less the specific surface area increases, and the larger current collector Ra is that the electric field distribution is not uniform.

It is a schematic block diagram of the secondary battery which concerns on this invention. It is the schematic of the negative electrode surface vicinity which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Positive electrode collector 12 Positive electrode active material layer 13 Negative electrode active material layer 14 Negative electrode collector 15 Nonaqueous electrolyte solution 16 Porous separator 21 Negative electrode active material layer side surface

Claims (5)

In a negative electrode for a secondary battery having a current collector and a negative electrode active material layer provided on the current collector by an atomization method, a vacuum deposition method, a sputtering method, a plasma CVD method, a photo CVD method, or a thermal CVD method ,
The negative electrode active material layer side surface of the current collector has a surface roughness (Ra) of more than 2 μm and 15 μm or less,
The negative electrode active material layer comprises (a) at least one negative electrode active material selected from the group consisting of metals, metalloids and their oxides capable of occluding and releasing Li, and (b) element X that does not occlude Li. Including
The thickness of the negative electrode active material layer is 0.5 to 5 times the surface roughness (Ra),
The negative electrode for a secondary battery, wherein the negative electrode active material layer has a thickness of 1.5 to 15 µm.   The secondary battery according to claim 1, wherein the negative electrode active material (a) includes at least one element M selected from the group consisting of Si, Sn, Al, Pb, Ag, Ge, and Sb. Negative electrode.   3. The negative electrode for a secondary battery according to claim 2, wherein the element (b) that does not occlude Li is at least one element selected from the group consisting of Fe, Ni, Cu, and Ti.   4. The negative electrode for a secondary battery according to claim 3, wherein a ratio of the element M to the element X is an element number ratio of element M: element X = 19: 1 to 1: 9. 5.   A secondary battery comprising the secondary battery negative electrode according to claim 1, a secondary battery positive electrode, and an electrolytic solution.

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