JP5186884B2 - Lithium secondary battery electrode and lithium secondary battery - Google Patents

Description

  The present invention relates to an electrode for a lithium secondary battery and a lithium secondary battery.

Conventionally, a lithium secondary battery has carbon particles as a negative electrode active material and metal particles such as silicon and tin that enhance penetration and detachment of lithium ions embedded in the carbon particles, and has a high capacity and a long cycle life. Have been proposed (see, for example, Patent Document 1). Also, a negative electrode in which a thin layer of metal that absorbs and desorbs lithium ions such as silicon and tin is provided on the surface of the negative electrode current collector at a predetermined area ratio, and a carbon material layer is further provided thereon. Therefore, a device with improved discharge capacity and cycle characteristics has been proposed (see, for example, Patent Document 2). Further, in the negative electrode that occludes and releases lithium ions, the first layer containing carbon as a main component and an oxide such as Si or Sn as a component capable of occluding more lithium than the theoretical capacity of lithium occlusion of carbon In order to improve the charge and discharge efficiency and maintain good cycle characteristics by providing a multilayer structure including the second layer, a proposal has been made (for example, see Patent Document 3).
JP 2000-243396 A JP 2005-293960 A JP 2002-358594 A

  However, in the lithium secondary batteries described in Patent Documents 1 to 3, a high capacity and high cycle characteristics are achieved by using silicon or carbon particles in combination, but it is not sufficient. Therefore, the volume expansion when lithium is occluded is larger than the volume expansion of graphite, and the phenomenon such as cracking of the negative electrode active material and peeling from the current collector is likely to be promoted. There is a problem that the electrode characteristics are deteriorated, and further improvement of the electrode characteristics when the charge / discharge cycle is repeated has been desired.

  This invention is made | formed in view of such a subject, and provides the electrode for lithium secondary batteries and lithium secondary battery which can suppress the fall of charging / discharging capacity more when charging / discharging is repeated. With the goal.

  In order to achieve the above-described object, the present inventors use graphite and amorphous silicon, which are carbon materials, as an active material for an electrode for a lithium secondary battery. Charge / discharge was repeated by optimizing the density of crystalline silicon, the relationship between the surface roughness of the current collector and the thickness of the amorphous silicon, and the relationship between the arrangement of the graphite layer and the amorphous silicon layer. At the same time, it was found that the decrease in charge / discharge capacity could be further suppressed, and the present invention was completed.

That is, the electrode for the lithium secondary battery of the present invention is
The peak area intensity ratio between the (002) plane and the (110) plane in the X-ray diffraction measurement of the electrode formed at least on the outermost surface layer and having an active material packing density of 1.2 g / cm ³ or more and 1.7 g / cm ³ or less An active material including a graphite layer having an I110 / I002 of 0.0010 or more and an amorphous silicon layer formed in a layer other than the outermost surface and having a density of 2.0 g / cm ³ or more;
A current collector that is provided in contact with the amorphous silicon layer, has a surface roughness Rz (μm), and has an amorphous silicon thickness t (μm), and satisfies t ≦ Rz / 2;
It is equipped with.

  The lithium secondary battery of the present invention includes a positive electrode including a positive electrode active material containing lithium, a negative electrode using the lithium secondary battery electrode according to any one of the above, the positive electrode, and the negative electrode. And an ion conducting medium that conducts lithium ions.

  In this electrode for a lithium secondary battery, when it is used as a lithium secondary battery and charging and discharging are repeated, a decrease in charge / discharge capacity can be further suppressed. Moreover, the lithium secondary battery provided with this electrode for lithium secondary batteries also has the same effect. The reason why such an effect can be obtained is that, for example, the active material of the electrode is composed of a plurality of different layers, so that the shape and conductivity of the surface in contact with each layer may be different. It is considered that the adhesion and conductivity between the active material and the active material are improved. In addition, for example, each layer of the active material has a different porosity, and it is considered that the retention of an ion conductive medium that conducts lithium ions can be easily maintained by making this porosity appropriate. It is done.

  The electrode for a lithium secondary battery of the present invention can be used as an electrode of a lithium secondary battery such as a lithium ion secondary battery or a lithium air battery. Among these, it is preferable to make it usable for the negative electrode of a lithium ion secondary battery. The electrode for a lithium secondary battery includes an active material having a graphite layer and an amorphous silicon layer, and a current collector.

In the electrode of the present invention, the graphite layer contained in the active material is a material capable of occluding and releasing lithium, such as natural graphite such as flaky graphite, massive graphite, earthy graphite, artificial graphite, expanded graphite, etc. Graphite may be used, and among these, those having a more spherical outer shape are preferred. Further, this graphite has an active material packing density in the range of 1.2 g / cm ³ or more and 1.7 g / cm ³ or less. When the active material packing density is 1.2 g / cm ³ or more, the adhesion between the active materials such as other layers adjacent to the graphite layer can be improved, and when the active material packing density is 1.7 g / cm ³ or less. In addition, the pressure applied to the electrode can be reduced, and the active material can be prevented from becoming fine particles due to cracking of the active material. The active material packing density is more preferably 1.5 g / cm ³ or less. In addition, as the graphite contained in the active material, the one in which the peak area intensity ratio I110 / I002 between the (002) plane and the (110) plane in the X-ray diffraction measurement using the electrode as a measurement sample is 0.0010 or more is used. . If this peak area intensity ratio I110 / I002 is set to 0.0010 or more, non-uniformity in volume change during charge / discharge can be minimized. When the peak area intensity ratio I110 / I002 is 0.0010 or more, the graphite particles tend to be more spherical. That is, if the graphite raw material is made more spherical, the peak area intensity ratio I110 / I002 can be controlled to be 0.0010 or more. This peak area intensity ratio can be controlled by changing the active material packing density. This graphite is formed at least on the outermost surface layer. In this way, the amorphous silicon layer does not exist on the outermost surface layer, and the retention of the electrolytic solution when the secondary battery is made is higher than that in which the amorphous silicon layer exists on the outermost surface. Get higher. As will be described in detail later, this is an effect caused by the relationship between the surface roughness Rz of the current collector, the unevenness of the amorphous silicon layer, and the size of the graphite particles. Further, since it is formed on the outermost surface layer, it is easy to occlude / release lithium in the graphite layer. The particle diameter d of the graphite is preferably in the range of 10 μm or more and 40 μm or less, and more preferably 20 μm or less. When the particle size is 10 μm or more, the particles are easily bonded to each other, and when the particle size is 40 μm or less, the adhesion between the particles is easily improved. This graphite layer is mixed with a binder, added with a suitable solvent to form a paste, applied to the surface of the amorphous silicon layer formed on the surface of the current collector, dried, and then pressed. Can be formed. As the binder, a fluorine-containing resin such as polyvinylidene fluoride can be used, and as the solvent, an organic solvent such as N-methyl-2-pyrrolidone can be used.

In the electrode of the present invention, the amorphous silicon layer contained in the active material is formed at least on the surface of the current collector and has a density of 2.0 g / cm ³ or more. When the density is 2.0 g / cm ³ or more, the strength of the amorphous silicon layer itself can be further increased. Here, the true density of silicon is 2.34 g / cm ³ , and if the density is about 2.0 g / cm ³ , there will be about 15% voids. Can be increased. This density is preferably 2.1 g / cm ³ or less. By doing so, it is possible to secure the voids in the amorphous silicon layer and to fully exhibit the lithium occlusion / release function. This amorphous silicon layer does not form the outermost surface layer of the active material. For this reason, the amount of occlusion / release of lithium ions in the secondary battery is higher than that in which the amorphous silicon layer is present on the outermost surface. The thickness t of this amorphous silicon layer is preferably 0.5 μm or more and 3.5 μm or less, and more preferably 1.0 μm or more and 3.0 μm or less. When the thickness t is 0.5 μm or more, the lithium occlusion / release function of the amorphous silicon layer itself becomes more prominent. When the thickness t is 3.5 μm or less, separation from the current collector or in the silicon layer occurs. Peeling can be suppressed. This amorphous silicon layer is preferably formed between the graphite layer and the current collector. In this way, since the graphite layer having a higher porosity than the amorphous silicon layer is formed on the surface side, the electrode adhesion, conductivity, and electrolysis are higher than those of the electrode made of amorphous silicon alone. The liquid retention can be maintained, and the effect is shown in improving the discharge capacity at a large current value. This amorphous silicon layer is preferably deposited on the surface of the current collector, for example, by sputtering. In this way, the density can be controlled relatively easily. Note that the amorphous silicon layer and the graphite layer may be alternately formed over a plurality of layers, or a graphite-amorphous silicon two-layer structure in which one layer is formed on the current collector. In the latter, while simplifying a manufacturing process, when charging / discharging is repeated, the fall of charging / discharging capacity | capacitance can be suppressed more.

  In the electrode of the present invention, the current collector is preferably formed of a metal such as aluminum or copper. This current collector is provided with the above-described active material on its surface via an amorphous silicon layer. This current collector is formed so that the relationship between the surface roughness Rz (μm) of the surface provided with the active material and the amorphous silicon thickness t (μm) satisfies t ≦ Rz / 2. . In general, an amorphous silicon layer is said to have a volume change of about 400% due to charge / discharge, and on average, it is considered to change about 1.6 times per side. Considering the porosity (density) of the amorphous silicon layer, it is necessary to satisfy t ≦ (Rz / 1.85), and it is more desirable to satisfy t ≦ Rz / 2. In this way, even when charging / discharging is repeated in the amorphous silicon layer, the volume change is suppressed within the range of the surface roughness Rz of the current collector, thereby separating the current collector from the amorphous silicon layer. Can be suppressed. Moreover, a more uniform electrode can be produced by satisfying this range. Here, the surface roughness Rz is also referred to as a ten-point average roughness, and refers to the surface roughness determined based on JIS-B0601: 2001 Annex 1 (reference). For this current collector, the surface roughness Rz can be controlled by precipitating the metal of the current collector by, for example, an electrolytic method and roughening the surface. The current collector preferably has a surface roughness Rz (μm) satisfying Rz ≦ d <4Rz when the particle diameter of graphite is d (μm). If the surface roughness Rz is equal to or larger than the graphite particle diameter d, it is possible to suppress the graphite particles from fitting into the depressions on the surface of the current collector. Etc. can be suppressed. Moreover, since the particle diameter d of graphite is smaller than 4 times the surface roughness Rz, the amorphous silicon layer deposited so as to satisfy the thickness t ≦ Rz / 2 formed on the surface of the current collector Since sufficient contact can be obtained, adhesion between the graphite layer and the amorphous silicon layer can be improved. Further, the current collector is preferably formed with a surface roughness Rz in the range of 0.4 μm <Rz ≦ 7 μm, and more preferably 4.5 μm or more. When the surface roughness Rz is larger than 0.4 μm, the thickness of the amorphous silicon layer can be secured. In addition, in order to form irregularities with the surface roughness Rz on the surface of the current collector, a current collector thickness corresponding to the surface roughness Rz is required, but when the surface roughness Rz is 7 μm or less, the current collector thickness is reduced. Since it can suppress, the fall of an energy density can be suppressed.

  The lithium secondary battery of the present invention conducts lithium ions by interposing between a positive electrode including a positive electrode active material containing lithium, a negative electrode using the above-described lithium secondary battery electrode, and the positive electrode and the negative electrode. An ion conductive medium. The electrode for a lithium secondary battery described above can be used for the negative electrode of the lithium secondary battery of the present invention. Moreover, as an ion conduction medium, it can be set as the electrolyte solution which melt | dissolved electrolyte.

  The positive electrode of the lithium secondary battery of the present invention is obtained by mixing a positive electrode active material with a conductive material and a binder and adding a suitable solvent to form a paste-like positive electrode mixture. It can be formed by applying and drying on the surface and compressing to increase the electrode density as necessary. Specifically, an aluminum foil, a copper foil, or the like can be used as the current collector. As the positive electrode active material, an oxide containing lithium and a transition metal element or a polyanionic compound can be used. Specifically, for example, lithium cobalt composite oxide, lithium nickel composite oxide, lithium manganese composite oxide, lithium iron composite phosphorus oxide, and the like can be given. The conductive material is for ensuring the electrical conductivity of the positive electrode. For example, one or more carbon material powders such as carbon black, acetylene black, natural graphite, artificial graphite, and coke are mixed. Things can be used. The binder plays a role of connecting the active material particles and the conductive material particles. For example, a fluorine-containing resin such as polytetrafluoroethylene, polyvinylidene fluoride, and fluororubber, or a thermoplastic resin such as polypropylene and polyethylene. Can be used. In addition, an aqueous dispersion of a cellulose-based or styrene-butadiene rubber that is an aqueous binder can also be used. As a solvent for dispersing the positive electrode active material, the conductive material, and the binder, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

In the lithium secondary battery of the present invention, as the electrolyte, a nonaqueous electrolytic solution containing a supporting salt can be used. The supporting salt is not particularly limited. For example, LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , Li (CF ₃ SO ₂ ) ₂ N, Li (CF ₃ SO ₃ ), LiN (C ₂ ) Known supporting salts such as F ₅ SO ₂ ) can be used. These supporting salts may be used alone or in combination. The concentration of the supporting salt is preferably 0.1 to 2.0M, and more preferably 0.8 to 1.2M. As the electrolytic solution, an aprotic organic solvent can be used. Examples of such an organic solvent include cyclic carbonates, chain carbonates, cyclic esters, cyclic ethers, chain ethers, and the like. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and vinyl carbonate. Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Examples of the cyclic ester carbonate include gamma butyrolactone and gamma valerolactone. Examples of the cyclic ether include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of the chain ether include dimethoxyethane and ethylene glycol dimethyl ether. These may be used alone or in combination.

  The lithium secondary battery of the present invention may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as it has a composition that can withstand the use range of the secondary battery. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a microporous film of an olefin resin such as polyethylene or polypropylene Is mentioned. These may be used alone or in combination.

  The shape of the lithium secondary battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Moreover, you may apply to the large sized thing etc. which are used for an electric vehicle etc. FIG. 1 is a schematic view showing an example of a lithium secondary battery 10 of the present invention. The lithium secondary battery 10 includes a positive electrode 13 in which a positive electrode active material 12 is formed on a current collector 11, a negative electrode 16 in which a negative electrode active material 15 is formed on the surface of the current collector 14, and a positive electrode 13 and a negative electrode 16. And the electrolytic solution 18 filling the space between the positive electrode 13 and the negative electrode 16. In this negative electrode 16, an amorphous silicon layer 20 is formed on the surface of the roughened current collector 14, and a layer of graphite particles 22 fixed by a binder 21 on the surface of the amorphous silicon layer 20. Is provided. This negative electrode 16 is produced by press-molding 22 layers of graphite particles.

The thus formed lithium secondary battery 10 is formed in at least the outermost surface layer and has an active material packing density of 1.2 g / cm ³ or more and 1.7 g / cm ³ or less. ) Plane and (110) plane, a graphite particle 22 layer having a peak area intensity ratio I110 / I002 of 0.0010 or more, and an amorphous layer having a density of 2.0 g / cm ³ or more formed on a layer other than the outermost surface. The negative electrode active material 15 including the porous silicon layer 20 and the amorphous silicon layer 20 are formed to provide the negative electrode active material 15, where the surface roughness Rz and the amorphous silicon thickness t are t ≦ The electrode for lithium secondary batteries provided with the collector 14 which satisfy | fills Rz / 2 is provided as a negative electrode. For this reason, when charging / discharging is repeated, the fall of charging / discharging capacity | capacitance can be suppressed more.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

Below, the example which produced the lithium ion secondary battery concretely is demonstrated as an experiment example. Experimental Examples 1 to 4 and 6 are Examples, Experimental Examples 7 to 10 are Comparative Examples, and Experimental Examples 5 and 11 are Reference Examples.

[Experimental Example 1]
As the negative electrode current collector, an electrolytic foil of 18 μm made of roughened copper was prepared by forming copper on the surface by an electrolytic method to form a surface roughness Rz of 7 μm in an uneven shape. This surface roughness Rz is also referred to as ten-point average roughness, and refers to the surface roughness determined based on JIS-B0601: 2001 Annex 1 (reference). On the negative electrode current collector made of this electrolytic foil, a first negative electrode active material layer made of silicon having a thickness of 1 μm was deposited using a sputtering apparatus (load lock type sputtering film forming apparatus manufactured by Tokki Corporation) (t ≦ Rz / 2). The deposition conditions were a high frequency of 13.56 MHz, a high frequency power of 600 W, an argon flow rate of 40 sccm (1 atm, cc / min at 25 ° C.), a gas pressure of 1 Pa, a sputtering time of 2 hours 43 minutes, and a deposited layer thickness of 1 μm. Specifically, after the inside of the chamber of the sputtering apparatus was evacuated to 5 × 10 ⁻⁵ Pa, argon was introduced into the chamber, and the gas pressure was stabilized so that the gas pressure in the chamber became 1 Pa. A high frequency voltage was applied to a silicon sputtering source by a high frequency power source for a predetermined time while the gas pressure in the chamber was stable, and silicon was deposited on the negative electrode current collector. At this time, the density of silicon was 2.0 g / cm ³ . The silicon density is measured on a small piece of glass (20 mm × 20 mm) under the above-mentioned conditions, and the silicon thickness t is measured. Separately, on a large aluminum foil (100 mmφ) under the same conditions. Sputtering treatment was performed, the weight of the deposited silicon was measured, and the thickness, area and weight were calculated.

Next, graphite particles having a particle diameter of 20 μm (manufactured by Osaka Gas Chemical Co., Ltd.) and polyvinylidene fluoride (PVdF) as a binder are mixed so that the weight ratio is 90/10. ) A dissolved N-methyl 2-pyrrolidone (NMP) solution was added to prepare a negative electrode slurry. This negative electrode slurry was applied onto silicon deposited by sputtering using a doctor blade method to form a second negative electrode active material layer. After drying at 120 ° C. for 3 hours or more, this electrode was pressed using a roll press, the active material packing density of the graphite layer was adjusted to 1.2 g / cm ³ , and punched out to 2.05 cm ^2. The negative electrode of Example 1 was obtained. In addition, the particle diameter of graphite measured using ethanol as a solvent using the laser diffraction type particle size distribution measuring device (SALD-2200 by Shimadzu Corporation), and computed it as a median diameter.

[X-ray diffraction measurement]
X-ray diffraction measurement was performed using the produced negative electrode of Experimental Example 1 before punching, and the peak area intensity ratio I110 / I002 between the (002) plane and the (110) plane of the negative electrode was determined. X-ray diffraction measurement is performed by scanning from 20 ° to 70 ° at 40 kV-30 mA with Cu-Kα ray using an X-ray diffractometer (RINT-2200 manufactured by Rigaku Corporation), and corresponds to the (002) plane and the (110) plane. The peak area was calculated, and the peak area intensity ratio I110 / I002 was calculated using this peak area value. As a result, in Experimental Example 1, I110 / I002 = 0.00116. In addition, this X-ray-diffraction measurement also performed Experimental example 3 and 9 mentioned later.

  Next, non-aqueous electrolyte was prepared by adding lithium hexafluorophosphate to a non-aqueous solution in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 30:70 so as to be 1 mol / L. Using the above negative electrode as a working electrode, a Li foil (thickness 300 μm) as a counter electrode, a separator (Tonen Tapils) is interposed between this working electrode and the counter electrode, and the above non-aqueous electrolyte is filled to produce a two-electrode cell. This was designated as Experimental Example 1.

[Charge / discharge test]
Using the produced bipolar cell of Experimental Example 1, after reducing (charging) to 0.01 V at 0.4 mA, it was oxidized (discharged) to 1.5 V at 0.4 mA to obtain the initial charge capacity, initial discharge capacity, and initial The charge / discharge efficiency was determined. Subsequently, after charging and discharging for 5 cycles at 0.2 C, load characteristics of 0.05 C (0.225 mA), 0.2 C (0.9 mA), and 0.5 C (2.25 mA) were measured. Here, the measured value of 0.05C was taken as 100%, and the ratio with respect to 0.05C at 0.2C and the ratio with respect to 0.05C at 0.5C were calculated. As a result, the initial charge capacity was 4.96 mAh, the initial discharge capacity was 4.51 mAh, and the initial charge efficiency was 91%. For the negative electrode of Experimental Example 1, the initial discharge capacity Qgsi = 4.51 mAh, the mass of coated graphite Cg = 0.01 g, the deposited silicon weight Csi = 0.00042 g, and the discharge capacity Qg = 350 mAh / g of the graphite negative electrode were used. Then, the discharge capacity Qsi of amorphous silicon was calculated using the following equation (1). As a result, it was Qsi = 22404.8 mAh / g. For this reason, the initial discharge capacity was 4.51 mAh, graphite was 3.5 mAh, and amorphous silicon was 1.01 mAh, confirming that the amorphous silicon layer was involved in charge / discharge. The measurement results of Experimental Example 1 are shown in Table 1. Table 1 shows the amorphous silicon layer thickness t (μm), amorphous silicon density (g / cm ³ ), graphite particle size (μm), negative electrode active material packing density (g / cm ³ ), Surface roughness Rz (μm), X-ray diffraction peak area intensity ratio I110 / I002, initial charge capacity (mAh), initial discharge capacity (mAh), initial charge / discharge efficiency (%), discharge capacity (mAh), The capacity (%) with respect to 05C is shown, and the data of Experimental Examples 2 to 12 described later are also shown.
Qsi = (Qgsi−Qg × Cg) / Csi (1)

[Experiment 2]
The negative electrode of Experimental Example 2 and 2 of Experimental Example 2 were the same as Experimental Example 1 except that the gas pressure during sputtering was adjusted to 0.5 Pa and the amorphous silicon layer having a density of 2.1 g / cm ³ was changed to 1 μm. A polar cell was prepared. In Experimental Example 2, as a result of the charge / discharge test, the initial charge capacity was 5.00 mAh, the initial discharge capacity was 4.64 mAh, and the initial charge efficiency was 93%. Further, using initial discharge capacity Qgsi = 4.64 mAh, applied graphite mass Cg = 0.01 g, deposited silicon weight Csi = 0.00042 g, and graphite negative electrode discharge capacity Qg = 350 mAh / g, and When the discharge capacity Qsi of amorphous silicon was determined, it was Qsi = 2714 mAh / g.

[Experiment 3]
The negative electrode of Experimental Example 3 and 2 of Experimental Example 3 were the same as Experimental Example 1 except that the roll press pressure of the electrode coated with graphite was adjusted and the active material packing density of the graphite layer was adjusted to 1.5 g / cm ^3. A polar cell was prepared. In Experimental Example 3, as a result of the charge / discharge test, the initial charge capacity was 4.70 mAh, the initial discharge capacity was 4.28 mAh, and the initial charge efficiency was 91%. Further, using the initial discharge capacity Qgsi = 4.28 mAh, the mass of coated graphite Cg = 0.01 g, the deposited silicon weight Csi = 0.00042 g, and the discharge capacity Qg = 350 mAh / g of the graphite negative electrode, When the discharge capacity Qsi of amorphous silicon was determined, it was Qsi = 1857 mAh / g.

[Experimental Example 4]
The negative electrode of Experimental Example 4 and the bipolar cell of Experimental Example 4 were fabricated in the same manner as in Experimental Example 1 except that the thickness t of the amorphous silicon layer was adjusted to 3 μm by adjusting the sputtering time. In Experimental Example 4, as a result of the charge / discharge test, the initial charge capacity was 5.00 mAh, the initial discharge capacity was 4.64 mAh, and the initial charge efficiency was 93%. Further, using initial discharge capacity Qgsi = 4.64 mAh, applied graphite mass Cg = 0.01 g, deposited silicon weight Csi = 0.00125 g, and graphite negative electrode discharge capacity Qg = 350 mAh / g, using equation (1) When the discharge capacity Qsi of amorphous silicon was determined, it was Qsi = 912 mAh / g.

[Experimental Example 5]
A negative electrode of Experimental Example 5 and a bipolar cell of Experimental Example 5 were produced in the same manner as in Experimental Example 1 except that graphite particles having a particle diameter of 10 μm were used. In Experimental Example 5, as a result of the charge / discharge test, the initial charge capacity was 4.95 mAh, the initial discharge capacity was 4.52 mAh, and the initial charge efficiency was 91%. Further, using initial discharge capacity Qgsi = 4.52 mAh, applied graphite mass Cg = 0.01 g, deposited silicon weight Csi = 0.00042 g, and graphite negative electrode discharge capacity Qg = 350 mAh / g, using equation (1) When the discharge capacity Qsi of amorphous silicon was determined, it was Qsi = 2429 mAh / g.

[Experimental Example 6]
A negative electrode of Experimental Example 6 and a bipolar cell of Experimental Example 6 were fabricated in the same manner as in Experimental Example 1 except that a copper foil having a surface roughness Rz of 4.5 μm was used as a current collector. In Experimental Example 6, as a result of the charge / discharge test, the initial charge capacity was 4.90 mAh, the initial discharge capacity was 4.48 mAh, and the initial charge efficiency was 91%. Further, using initial discharge capacity Qgsi = 4.48 mAh, mass of coated graphite Cg = 0.01 g, deposited silicon weight Csi = 0.00042 g, and discharge capacity Qg = 350 mAh / g of graphite negative electrode, When the discharge capacity Qsi of amorphous silicon was determined, it was Qsi = 2333 mAh / g.

[Experimental Example 7]
Except that a graphite particle having a particle size of 20 μm was applied to a current collector and dried, then sputtering was performed on the graphite particle under the same conditions as in Experimental Example 1, and an amorphous silicon layer was deposited on the graphite particle. Produced the negative electrode of Experimental Example 7 and the bipolar cell of Experimental Example 7 in the same manner as Experimental Example 1. In Experimental Example 7, about the result of the charge / discharge test, after reducing (charging) to 0.5V at 0.01mA, the charge / discharge test was conducted by oxidizing (discharging) to 0.5V at 0.5mA. The initial charge capacity was 6.12 mAh, the initial discharge capacity was 5.63 mAh, and the initial charge efficiency was 92%. Further, using initial discharge capacity Qgsi = 5.63 mAh, applied graphite mass Cg = 0.012 g, deposited silicon weight Csi = 0.00042 g, and graphite negative electrode discharge capacity Qg = 350 mAh / g, according to formula (1) When the discharge capacity Qsi of amorphous silicon was determined, it was Qsi = 3410 mAh / g.

[Experimental Example 8]
The negative electrode of Experimental Example 8 and the bipolar cell of Experimental Example 8 were the same as Experimental Example 1 except that the gas pressure during sputtering was adjusted to 10 Pa and an amorphous silicon layer having a density of 1.95 g / cm ³ was deposited to 1 μm. Was made. In Experimental Example 8, as a result of the charge / discharge test, the initial charge capacity was 4.90 mAh, the initial discharge capacity was 4.50 mAh, and the initial charge efficiency was 92%. Further, using initial discharge capacity Qgsi = 4.50 mAh, applied graphite mass Cg = 0.01 g, deposited silicon weight Csi = 0.00041 g, and negative electrode discharge capacity Qg = 350 mAh / g, according to formula (1) When the discharge capacity Qsi of amorphous silicon was determined, it was Qsi = 2439 mAh / g.

[Experimental Example 9]
The negative electrode of Experimental Example 9 and Experimental Example 9 were the same as Experimental Example 1 except that the roll press pressure of the electrode coated with graphite particles was adjusted to adjust the active material packing density of the graphite layer to 1.8 g / cm ³ . A bipolar cell was produced. In Experimental Example 9, as a result of the charge / discharge test, the initial charge capacity was 4.00 mAh, the initial discharge capacity was 3.53 mAh, and the initial charge efficiency was 88%. Further, using initial discharge capacity Qgsi = 3.53 mAh, mass of coated graphite Cg = 0.01 g, deposited silicon weight Csi = 0.00042 g, and discharge capacity Qg = 350 mAh / g of graphite negative electrode, When the discharge capacity Qsi of amorphous silicon was determined, it was Qsi = 71 mAh / g.

[Experimental Example 10]
The negative electrode of Experimental Example 10 and the bipolar cell of Experimental Example 10 were fabricated in the same manner as in Experimental Example 1 except that the thickness t of the amorphous silicon layer was adjusted to 4 μm by adjusting the sputtering time. In Experimental Example 10, as a result of the charge / discharge test, the initial charge capacity was 4.92 mAh, the initial discharge capacity was 4.03 mAh, and the initial charge efficiency was 82%. Further, using initial discharge capacity Qgsi = 4.03 mAh, applied graphite mass Cg = 0.01 g, deposited silicon weight Csi = 0.007 g, and graphite negative electrode discharge capacity Qg = 350 mAh / g, using equation (1) When the discharge capacity Qsi of amorphous silicon was determined, it was Qsi = 311 mAh / g.

[Experimental Example 11]
A negative electrode of Experimental Example 11 and a bipolar cell of Experimental Example 11 were produced in the same manner as in Experimental Example 1 except that graphite particles having a particle size of 40 μm were used. In Experimental Example 11, as a result of the charge / discharge test, the initial charge capacity was 4.96 mAh, the initial discharge capacity was 4.48 mAh, and the initial charge efficiency was 90%. Further, using initial discharge capacity Qgsi = 4.48 mAh, mass of coated graphite Cg = 0.01 g, deposited silicon weight Csi = 0.00042 g, and discharge capacity Qg = 350 mAh / g of graphite negative electrode, When the discharge capacity Qsi of amorphous silicon was determined, it was Qsi = 2333 mAh / g.

[Experimental example 12]
A negative electrode of Experimental Example 12 and a bipolar cell of Experimental Example 12 were fabricated in the same manner as in Experimental Example 1 except that a copper foil having a surface roughness Rz of 0.25 μm was used as the current collector. In Experimental Example 12, as a result of the charge / discharge test, the initial charge capacity was 4.85 mAh, the initial discharge capacity was 4.33 mAh, and the initial charge efficiency was 89%. Further, using initial discharge capacity Qgsi = 4.33 mAh, applied graphite mass Cg = 0.01 g, deposited silicon weight Csi = 0.00042 g, and graphite negative electrode discharge capacity Qg = 350 mAh / g, using equation (1) When the discharge capacity Qsi of amorphous silicon was determined, it was Qsi = 1976 mAh / g.

[Experimental result]
According to the results of Experimental Examples 1 to 12, a graphite layer is formed on the outermost surface layer, and the active material filling density of the graphite layer is 1.2 g / cm ³ or more and 1.7 g / cm ³ or less, and the X-ray diffraction of the electrode The peak area intensity ratio I110 / I002 between the (002) plane and the (110) plane in the measurement is 0.0010 or more, and an amorphous silicon layer is formed in a layer other than the outermost surface. In Experimental Examples 1 to 6 having a negative electrode satisfying t ≦ Rz / 2, where the density is 2.0 g / cm ³ or more, the surface roughness Rz of the negative electrode current collector, and the thickness t of the amorphous silicon, It was found that the reduction in charge / discharge capacity when charging / discharging was repeated was further suppressed.

It is a schematic diagram which shows an example of the lithium secondary battery 10 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Lithium secondary battery, 11 Current collector, 12 Positive electrode active material, 13 Positive electrode, 14 Current collector, 15 Negative electrode active material, 16 Negative electrode, 17 Separator, 18 Electrolytic solution, 20 Amorphous silicon layer, 21 Binder 22 Graphite particles.

Claims (5)

The peak area intensity ratio between the (002) plane and the (110) plane in the X-ray diffraction measurement of the electrode formed at least on the outermost surface layer and having an active material packing density of 1.2 g / cm ³ or more and 1.7 g / cm ³ or less An active material including a graphite layer having an I110 / I002 of 0.0010 or more and an amorphous silicon layer formed in a layer other than the outermost surface and having a density of 2.0 g / cm ³ or more;
When the active material is provided in contact with the amorphous silicon layer and the surface roughness is Rz (μm) and the amorphous silicon thickness is t (μm), t ≦ Rz / 2 (where 4.5 ≦ Rz ≦ 7.0, 1.0 ≦ t ≦ 3.0) ,
An electrode for a rechargeable lithium battery. The lithium secondary battery electrode according to claim 1, wherein the active material has a density of the amorphous silicon layer of 2.1 g / cm ³ or less. The active material, the active material filling density of the graphite layer is 1.5 g / cm ³ or less, a lithium secondary battery electrode according to claim 1 or 2. The current collector satisfies the Rz ≦ d <4Rz When the particle diameter d of the graphite, lithium secondary battery electrode according to any one of claims 1-3. A positive electrode including a positive electrode active material containing lithium;
A negative electrode using the electrode for a lithium secondary battery according to any one of claims 1 to 4 ,
An ion conductive medium that is interposed between the positive electrode and the negative electrode and conducts lithium ions;
Lithium secondary battery comprising

Images