JP5108355B2 - Negative electrode for lithium secondary battery, lithium secondary battery including the same, and method for producing negative electrode for lithium secondary battery - Google Patents

Description

  The present invention relates to a negative electrode for a lithium secondary battery, a lithium secondary battery including the negative electrode, and a method for producing a negative electrode for a lithium secondary battery.

  Advances in miniaturization and high performance of portable information terminals such as PCs (Personal Computers), mobile phones, and PDAs (Personal Digital Assistants) that use lithium ion secondary batteries, as well as audio-visual devices such as video recorders and memory audio players. It is out. Accordingly, it is desired to increase the capacity of the lithium ion secondary battery. As a negative electrode active material for increasing the capacity, metallic lithium, silicon alloyed with lithium, tin, and the like have been studied.

  However, since these negative electrode active materials are accompanied by a large volume change when reacting with lithium ions, there is a problem that the negative electrode active material is peeled off from the current collector or the negative electrode is deformed by repeated charge and discharge. .

  An electrode structure for solving such a problem is disclosed in Patent Document 1. In the structure disclosed in Patent Document 1, a plurality of columnar bodies made of an active material alloyed with lithium are formed on a current collector made of a material not alloyed with lithium. Such a columnar body is formed, for example, by forming a film of an active material on a current collector and patterning the film by photolithography. Alternatively, it is formed by selectively depositing an active material on a current collector using a plating technique. According to this electrode structure, since the columnar bodies expand so as to fill the gaps between the columnar bodies, it is possible to suppress a decrease in electrode characteristics due to expansion stress.

  In the negative electrode of Patent Document 1, each columnar body stands upright along the normal direction of the current collector. When a lithium secondary battery is configured using such a negative electrode, most of the positive electrode active material layer does not face the columnar body made of the active material, and the portion of the current collector surface that is not covered with the active material ( There is a problem that it faces the “exposed portion of the current collector”. Therefore, lithium supplied from the positive electrode active material layer at the time of charging is not occluded by the negative electrode active material, but tends to be deposited on the exposed portion of the negative electrode current collector. As a result, it becomes difficult to efficiently release lithium from the negative electrode at the time of discharge, so that the charge / discharge efficiency is lowered.

  Moreover, since only the positive electrode active material facing the negative electrode active material is likely to react during discharge, the substantial discharge capacity is reduced. Further, when such a non-uniform reaction proceeds by repeating the charge / discharge cycle, the discharge depth for each particle in the positive electrode, that is, the potential distribution for each particle is expanded. Therefore, the rate of side reactions such as film formation and gas generation due to decomposition of the electrolyte solution at the site in contact with the positive electrode active material in a high potential state increases, the discharge capacity decreases, and the battery progresses further. In particular, when high-rate charging / discharging is performed with a large current value, the cycle characteristics are significantly deteriorated.

  On the other hand, Patent Document 2 by the present applicant proposes to dispose columnar active material particles having a long axis inclined with respect to the normal direction of the current collector surface on the current collector. Yes. According to this configuration, since the ratio of the portion of the positive electrode active material layer facing the exposed portion of the current collector can be reduced, the positive electrode active material and the negative electrode active material can be fully utilized, and the capacity higher than that of Patent Document 1 A maintenance rate can be obtained.

Such active material particles are obtained by depositing silicon particles on the surface of a current collector having minute protrusions on the surface from a direction inclined with respect to the normal direction of the current collector in an oxygen-containing atmosphere. (Oblique deposition). At this time, since the silicon particles are not deposited on the convex portion or the shadowed portion of the silicon oxide grown on the convex portion of the current collector surface (shadowing effect), the current collector surface absorbs the volume expansion. Silicon oxide can be grown while ensuring a gap.
JP 2004-127561 A International Publication No. 2007/015419 Pamphlet

  In Patent Document 2, as described above, the active material particles are formed by oblique vapor deposition using the convex portions on the surface of the current collector. However, when the inventors of the present application examined, the relationship between the shape of the convex portion on the surface of the current collector and the flying direction of the vapor deposition particles (here, silicon particles), the vicinity of the interface with the current collector in each active material particle It has been found that a large distribution of oxygen concentration may occur. The mechanism by which the oxygen concentration is distributed will be described in detail later with reference to the drawings.

  The higher the oxygen ratio (the molar ratio of the oxygen amount to the silicon amount) of silicon oxide, the lower the rate of expansion / contraction associated with lithium occlusion / release, so the active material particles have a distribution of oxygen ratio as described above. When this occurs, there are regions in which the ratio of expansion and contraction of the active material differs in the vicinity of the interface between the active material particles and the current collector. As a result, the active material particles easily peel from the current collector, which may cause a decrease in charge / discharge cycle.

  The present invention has been made in order to solve the above problems, and the object thereof is a negative electrode for a lithium secondary battery in which a negative electrode active material body containing a plurality of silicon oxides is formed on a current collector. By making the oxygen ratio in the vicinity of the interface between each negative electrode active material body and the current collector substantially uniform, the separation of the negative electrode active material body from the current collector surface is suppressed and the charge / discharge cycle characteristics are improved. .

  In order to solve the above-described conventional problems, a negative electrode for a lithium secondary battery according to the present invention is arranged on a current collector and a current collector so as to be spaced apart from each other, and includes a plurality of negative electrode actives containing silicon oxide. A substance. A plurality of first protrusions that support the plurality of negative electrode active material bodies are arranged on the surface of the current collector, and each first protrusion is smaller in height than the first protrusions. A plurality of second convex portions are provided. The average value of the molar ratio of the oxygen amount to the silicon amount of each negative electrode active material body is 0.1 or more and 1.2 or less, and the oxygen amount relative to the silicon amount in the vicinity of the interface between each negative electrode active material body and the current collector is The difference between the maximum value and the minimum value of the molar ratio is 0.4 or less.

  According to the above configuration, the arrangement of the negative electrode active material bodies and the interval between the adjacent negative electrode active material bodies can be controlled by the first protrusions arranged on the surface of the current collector. Can be secured. Further, since the contact area between each negative electrode active material body and the current collector can be increased by the second convex part provided on the surface of the first convex part, the negative electrode active material body and the current collector Can improve the adhesion.

  Further, the average value of the molar ratio of the oxygen amount to the silicon amount of each negative electrode active material body is 0.1 or more and 1.2 or less, thereby suppressing the volume expansion due to lithium occlusion while ensuring a high capacity. it can.

  Furthermore, since the difference between the maximum value and the minimum value of the molar ratio of the oxygen amount to the silicon amount in the vicinity of the interface between each negative electrode active material body and the current collector is suppressed to 0.4 or less, each active material particle Expands and contracts at a substantially uniform rate near the interface with the current collector. Therefore, local stress concentration due to the difference in the expansion and contraction ratios in the vicinity of the interface can be prevented, so that the separation of the active material particles from the current collector due to such stress concentration can be suppressed. The charge / discharge cycle characteristics of the secondary battery can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, in the negative electrode for lithium secondary batteries, peeling of the active material particle resulting from the oxygen concentration distribution of the active material particle in the vicinity of the interface of an active material particle and a collector can be suppressed. Therefore, a lithium secondary battery excellent in charge / discharge cycle characteristics can be provided.

  Hereinafter, embodiments of a negative electrode for a lithium secondary battery according to the present invention will be described with reference to the drawings.

  First, refer to FIG. FIG. 1 is a schematic cross-sectional view of a negative electrode for a lithium secondary battery (hereinafter also referred to as “negative electrode”) of the present embodiment.

The negative electrode 100 includes a current collector 1 and a plurality of negative electrode active material bodies 5 that are arranged on the surface of the current collector 1 at intervals. The negative electrode active material body 5 contains silicon oxide, and the average value of the molar ratio of the oxygen amount to the silicon amount (hereinafter also simply referred to as “oxygen ratio”) is 0.1 or more and 1.2 or less. Further, in the vicinity of the interface between each negative electrode active material body 5 and current collector 1, the difference ΔR between the maximum value Rmax and the minimum value Rmin of the oxygen ratio in each negative electrode active material body 5 is 0.4 or less.

  In addition, the negative electrode active material body 5 may contain impurities such as lithium, Fe, Al, Ca, Mn, and Ti that are supplemented or occluded in the negative electrode active material body 5 in addition to silicon oxide. Moreover, although the some negative electrode active material body 5 is arrange | positioned at intervals, the adjacent negative electrode active material body 5 may partially contact by occluding and expanding lithium at the time of charge. .

  A plurality of first convex portions 2A are arranged on the surface of the current collector 1, and the surface of each first convex portion 2A has a plurality of second projections that are smaller in height than the first convex portions 2A. It has a convex part. A region 4 (also referred to as “groove”) 4 of the current collector 1 where the first convex portion 2A is not formed is substantially flat.

  The first protrusions 2 </ b> A are arranged with a size and a pitch that control the disposition of the negative electrode active material bodies 5 and can ensure appropriate gaps between the negative electrode active material bodies 5. It is preferable that at least a part of the plurality of second protrusions 2B is disposed on a portion of the surface of the first protrusion 2A where the negative electrode active material body 5 is formed, whereby the negative electrode active material body Since the contact area between the current collector 5 and the current collector 1 can be increased, the adhesion between the negative electrode active material body 5 and the current collector 1 can be improved.

  The shape of the first convex portion 2A is not particularly limited, but is, for example, hemispherical, prismatic, or cylindrical. Note that the first protrusion 2A has a 90 ° or less corner (corner) at a portion of the surface of each first protrusion 2A that contacts the negative electrode active material body 5 in a cross section perpendicular to the surface of the current collector 1. ) Is preferably not included. As a result, as will be described in detail later, it is possible to reduce the oxygen ratio distribution width (ΔR) in the vicinity of the interface between the current collector 1 and the negative electrode active material body 5.

  In the negative electrode 100, the second convex portion 2B is formed only on the upper surface of the first convex portion 2A. However, the second convex portion 2B is also formed on the side surface of the first convex portion 2A. May be. Further, the groove 4 of the current collector 1 is substantially flat, but the surface of the groove 4 may be uneven. However, in order to ensure the expansion space of the negative electrode active material body 5, the height of the surface irregularities of the grooves 4 is preferably equal to or smaller than the height of the second convex portions 2 </ b> B.

  As shown in FIG. 1, the negative electrode active material body 5 preferably has a growth direction G inclined with respect to the normal direction N of the current collector 1. With such a configuration, in the lithium secondary battery, the area of the portion of the positive electrode active material layer facing the negative electrode active material body 5 can be increased, so that the charge / discharge efficiency can be increased. In such a negative electrode active material body 5, for example, silicon is incident on the surface of the current collector 1 from a direction inclined with respect to the normal direction N of the current collector 1 in a chamber into which oxygen gas is introduced. Can be formed (oblique deposition).

  The angle formed by the growth direction G of the negative electrode active material body 5 and the normal direction N of the current collector 1 is preferably 10 ° or more. In order to obtain good adhesion, it is better that the contact area between the negative electrode active material body 5 and the current collector 1 is large, that is, the angle may be 0 °. Since no effect is produced, a gap cannot be formed between the adjacent negative electrode active material bodies 5. However, if the angle is 10 ° or more, a sufficient contact area can be obtained while forming a gap between the negative electrode active material bodies 5. On the other hand, the angle may be less than 90 °, but the closer to 90 °, the more difficult it is to form the negative electrode active material body 5, and therefore it is preferably less than 80 °. The negative electrode active material body 5 may have a plurality of portions having different growth directions G. Even in this case, the growth direction of the portion of the negative electrode active material body 5 located near the interface with the current collector 1 G is preferably inclined with respect to the normal direction N of the current collector 1, and a preferable range of the inclination angle is 10 ° or more and less than 90 °.

  The thickness t5 of the negative electrode active material body 5 from the top of the first protrusion is not particularly limited, but is preferably 0.5 μm or more and 50 μm or less from the viewpoint of battery energy density, productivity, reliability, and the like. . If the thickness t5 is 0.5 μm or more, more preferably 5 μm or more, higher battery energy can be obtained. In addition, if the thickness t5 is 50 μm or less, more preferably 30 μm or less, cracks generated when the negative electrode active material body 5 is formed can be reduced, so that the reliability of the negative electrode 100 can be improved.

  The average value of the oxygen ratio in the silicon oxide contained in the negative electrode active material body 5 is 0.1 or more and 1.2 or less as described above. In general, in a negative electrode active material containing silicon, the lower the oxygen ratio, the higher the charge / discharge capacity, but the larger the volume expansion rate due to charging. On the other hand, the higher the oxygen ratio, the smaller the volume expansion rate, but the lower the charge / discharge capacity. In the negative electrode active material body 5 in the present embodiment, the average value of the oxygen ratio is 0.1 or more, and expansion and contraction associated with charge / discharge are suppressed. Can be prevented. Moreover, since the average value of the said oxygen ratio is 1.2 or less, sufficient charge / discharge capacity can be ensured and a high rate charge / discharge characteristic can be maintained. In addition, if the average value of the oxygen ratio is 0.1 or more and 0.6 or less, it is possible to more surely obtain an appropriate charge / discharge cycle characteristic and a high rate charge / discharge characteristic with a good balance. The oxygen concentration profile in the negative electrode active material body 5 is preferably substantially uniform in the thickness direction, but may vary in the thickness direction. The average value of molar ratio should just be in the said range.

Further, in the vicinity of the interface between each negative electrode active material body 5 and current collector 1, the difference ΔR between the maximum value Rmax and the minimum value Rmin of the oxygen ratio in each negative electrode active material body 5 is 0.4 or less. The oxygen ratio in the vicinity of the interface can be measured using a lithium ion wavelength dispersion X-ray microanalyzer.

  Hereinafter, an example of a method for measuring the difference ΔR in the molar ratio of the oxygen amount to the silicon amount in the vicinity of the interface between the negative electrode active material body 5 and the current collector will be described with reference to the drawings.

FIG. 2A is a schematic enlarged view showing a single negative electrode active material body 5, and shows a cross section perpendicular to the current collector 1 and including the growth direction of the negative electrode active material body 5. . Here, in the cross section shown in the figure, a region 7 that is about 2 μm away from the contact surface between the negative electrode active material body 5 and the current collector 1 toward the negative electrode active material body 5 is taken as a measurement region. The measurement region 7 is divided into at least three sub-regions according to the distance y from one end of the measurement region 7. For example, if one end of the measurement region 7 is y = 0 and the opposite end is y = Y, three sub-regions 7a (y / Y: 0 to 1/3), 7b (y / Y: 1/3) 2/3) and 7c (y / Y: 2/3 to 1). Measurement positions are selected one by one from these sub-regions 7a to 7c, and the oxygen ratio at each measurement position is determined using a lithium ion wavelength dispersion X-ray microanalyzer. Subsequently, as shown in FIG. 2B, the difference ΔR between the maximum value Rmax and the minimum value Rmin among the measured values of the oxygen ratio in each of the sub-regions 7a to 7c is calculated. Note that the difference between the maximum value Rmax and the minimum value Rmin may be calculated for each of the plurality of negative electrode active material bodies 5, and the average value thereof may be ΔR.

  In the above measurement method, as the “near the interface” between the current collector 1 and the negative electrode active material body 5, a region of 2 μm from the interface with the surface of the current collector 1 in the negative electrode active material body 5 is defined as the measurement region. However, the measurement region can be arbitrarily selected from a portion within 3 μm from the interface with the surface of the current collector 1 in the negative electrode active material body 5. Even if another layer is provided between the negative electrode active material body 5 and the current collector 1 and the negative electrode active material body 5 is not in contact with the surface of the current collector 1, A measurement region is selected from a portion within 3 μm from the end face of the negative electrode active material body 5 on the side of the electric conductor 1, and ΔR can be obtained by the same method as described above.

As already described, silicon oxide (SiOx, 0 ≦ x ≦ 2) has different amounts of Li storage depending on its oxygen content, and therefore the degree of volume expansion due to storage of Li varies. For example, when the oxygen ratio is zero (Si), lithium can be occluded up to a composition of Li (Li ₂₂ Si ₅ ) per Si atom, but the volume expansion at that time is 4. 4 times. On the other hand, when the oxygen ratio is 2 (SiO ₂ ), lithium cannot be occluded, so that volume expansion does not occur. That is 1 time. Thus, as the oxygen ratio (x value) increases, the volume expansion of silicon oxide (SiO _x ) decreases.

Therefore, the distribution range of the oxygen ratio of SiO _x at the interface between the current collector and each negative electrode active material body is large. For example, if ΔR is greater than 0.4, there is a region where the volume expansion coefficient is significantly different at this interface. However, stress concentration may occur in a part of the interface due to insertion and extraction of lithium accompanying charging and discharging. Therefore, when charging / discharging is repeated, the negative electrode active material body 5 is easily peeled off from the current collector 1, which may cause deterioration in charge / discharge cycle characteristics.

On the other hand, in the present embodiment, the ΔR is suppressed to 0.4 or less, and the distribution width of the oxygen ratio at the interface between the current collector 1 and the negative electrode active material body 5 is small. The ratio of expansion / contraction can be made substantially uniform. Therefore, the stress distribution generated at the interface due to insertion and extraction of lithium becomes substantially uniform and local stress concentration does not occur. Therefore, peeling of the negative electrode active material body 5 can be suppressed, and good charge / discharge cycle characteristics can be obtained.

  When the negative electrode active material body 5 is formed by using oblique deposition as in the present embodiment, in order to suppress the distribution width of the oxygen ratio at the interface between the current collector 1 and each negative electrode active material body 5, It is important to control the relationship between the vapor deposition direction of the active material (for example, Si atoms) with respect to the body 1 and the shapes of the first and second convex portions 2A and 2B formed on the surface of the current collector 1. Become.

  For example, in a cross section perpendicular to the surface of the current collector 1, a portion of the surface of the current collector 1 that is in contact with the negative electrode active material body 5 has a “corner (a protruding portion, an edge portion)” of 90 ° or less. Preferably it is not present. When viewed from the vapor deposition direction, it is preferable that there is no “corner (hereinafter referred to as“ corner ”)” of 90 ° or less on the surface of the current collector 1. Note that “the angle of 90 ° or less does not exist” means that the angle of the first protrusion 2A is 90 ° or less, and the minute unevenness (second protrusion) formed on the first protrusion 2A. The part 2B) may have an angle of 90 ° or less. However, as viewed from the vapor deposition direction, not only the first convex portion 2A but also the second convex portion 2B does not have an angle of 90 ° or less, so the distribution width of the oxygen ratio can be reduced more effectively. . Moreover, it is preferable that the corner | angular of each 1st convex part 2A is roundish, and does not have a clear vertex.

  FIG. 3A shows a case where the cross-sectional shape of the first convex portion 2A has an angle of 90 °, and FIG. 3B shows that the cross-sectional shape of the first convex portion 2A has an angle of 90 ° or less. It is typical sectional drawing for demonstrating the vapor deposition process in the case of not doing.

  As shown in FIG. 3A, in a cross section perpendicular to the surface of the current collector 1, each first protrusion 2 </ b> A has an angle of 90 ° or less on the contact surface with the negative electrode active material body 5 (in the example shown in the figure). 90 °), silicon atoms are incident from the direction of the angle θ with respect to the normal direction N of the current collector 1. At this time, if the flux of silicon atoms (the number of silicon atoms flying per unit area / unit time) is f, the flux of silicon atoms supplied to the region α located on the upper surface of the first convex portion 2A is fcosθ. The flux of silicon atoms supplied to the region β located on the side surface of the first convex portion 2A is represented by fcos (90−θ). Since the growth rate at the time of vapor deposition is determined by the flux, the growth rate is different on the region α and the region β. As a result, the amount of oxygen that reacts during the deposition of silicon atoms is also different. accumulate.

  On the other hand, as shown in FIG. 3B, in the cross section perpendicular to the surface of the current collector 1, the corners of the first protrusions 2A are rounded and have an angle larger than 90 °. In this case, even if silicon atoms are incident from the direction of the angle θ with respect to the normal direction N of the current collector 1, the distribution of the silicon atom flux with respect to the region including such angles is unlikely to occur. Therefore, since the silicon oxide can be grown on the surface of the first convex portion 2A at a substantially uniform rate, the negative electrode active material body 5 having a substantially uniform oxygen ratio can be obtained. In addition, since the effect which suppresses distribution of an oxygen ratio will be acquired if the angle of 90 degrees or less does not exist in the surface where the active material is vapor-deposited among the surfaces of the 1st convex part 2A, since the effect which suppresses distribution of oxygen ratio is acquired, 1st convex part 2A There may be an angle of 90 ° or less on the surface where no active material is deposited. For example, even if the sectional shape of the first convex portion 2A is a triangle having an apex angle of 90 ° or less, oblique deposition is performed at an angle that allows the active material to enter only the side surface of the first convex portion 2A. The oxygen ratio distribution of the negative electrode active material body 5 can be suppressed.

  In Patent Document 2 described above, a commercially available roughened copper foil having a surface roughness Rz of 2 μm to 10 μm is used as a current collector. Various convex portions are randomly arranged on the surface of the copper foil, and active material particles are supported on the convex portions. In such a case, it is considered that some of the active material particles have a non-uniform oxygen concentration distribution depending on the shape of the convex portion. Therefore, it is difficult to suppress the distribution width of the oxygen ratio at the interface between the active material particles and the current collector to 0.4 or less as a whole. On the other hand, in the present embodiment, the shape of the first convex portion 2A for supporting each negative electrode active material body 5 is controlled, and the silicon atom incident surface in the first convex portion 2A has no silicon. Since there is no angle that significantly changes the angle with respect to the incident direction of the atoms, the distribution width of the oxygen ratio at the interface of the negative electrode active material body 5 can be suppressed.

The first convex portions 2A in the present embodiment are preferably arranged regularly, and the arrangement pitch P is, for example, not less than 10 μm and not more than 50 μm. If the arrangement pitch P is 10 μm or more, a high capacity can be secured without increasing the thickness of the negative electrode active material body 5, and if the pitch P is 50 μm or less, between the adjacent negative electrode active material bodies 5, This is because the space for the negative electrode active material body 5 to expand can be more reliably secured. The height h _A of the first convex portion 2A is preferably 5 μm or more. When the height h _A is 5 μm or more, the placement of the negative electrode active material body 5 can be more reliably controlled using the shadowing effect when the negative electrode active material body 5 is formed by oblique deposition. On the other hand, if the height h _A is too large, the current collector 1 becomes thick, and therefore it is preferably 10 μm or less.

The height h _B of the second convex portion 2B is preferably 1 μm or more and 5 μm or less. If the height h _B is within this range, the adhesive force between the current collector 1 and the negative electrode active material body 5 can be sufficiently secured, so that the negative electrode active material body 5 can be prevented from peeling off.

The ratio h _A / h _B of the height h _A of the first protrusion 2A to the height h _B of the second protrusion 2B may be larger than 1, but is preferably 2 or more. If the ratio is too small, that is, if the second convex portion 2B is too high, a shadowing effect is generated by the second convex portion 2B, and the contact area between the negative electrode active material body 5 and the current collector 1 is increased. This is because there is a possibility that it cannot be secured. On the other hand, the ratio h _A / h _B is preferably 25 or less. Thereby, the adhesiveness of 2 A of 1st convex parts and the negative electrode active material body 5 can fully be improved with the 2nd convex part 2B. The ratio h _A / h _B is more preferably 2 or more and 10 or less.

  In the cross section shown in FIG. 1, the width of the first convex portion 2A is preferably 5 μm or more and 30 μm or less. If the width of the first convex portion 2A is less than 5 μm, the contact area between the negative electrode active material body 5 and the first convex portion 2A may not be ensured. Moreover, when larger than 30 micrometers, there exists a possibility that the expansion stress of the negative electrode active material body 5 cannot be relieve | moderated effectively by the groove | channel 4.

  The ratio of the width of the first protrusion 2A to the width of the second protrusion 2B is preferably 2 or more. Thereby, since many 2nd convex parts 2B can be easily formed in the surface of one 1st convex part 2A, the 2nd convex part 2B WHEREIN: Between 1st convex part 2A and the negative electrode active material body 5 Adhesion can be sufficiently enhanced. The ratio is preferably 20 or less. This is because if the ratio is too large, that is, if the width of the second protrusion 2B is too small, it is difficult to ensure a sufficient contact area between the negative electrode active material body 5 and the current collector 1. .

  Next, an outline of a method for manufacturing the negative electrode 100 will be described with reference to the drawings.

  First, a current collector having a plurality of first protrusions on the surface is produced. As a constituent material of the current collector, for example, copper, copper alloy, or the like can be used. The first convex portion has, for example, a hemispherical shape, a cylindrical shape, or a prismatic shape having a diameter or one side of 5 μm to 30 μm and a height of 5 μm to 10 μm. A plurality of second convex portions are arranged on the surface of each first convex portion. The height of the second convex portion is lower than the height of the first convex portion, for example, not less than 1 μm and not more than 5 μm.

  Subsequently, a plurality of negative electrode active material bodies are formed on the surface of the current collector by oblique vapor deposition. Each negative electrode active material body is disposed on the corresponding first convex portion.

  FIG. 4 is a schematic view illustrating the configuration of a vapor deposition apparatus used for forming the negative electrode active material body. In this drawing, only the configuration inside the vacuum chamber of the vapor deposition apparatus is shown, and the configuration outside the vacuum chamber is omitted.

  As shown in the drawing, inside the vacuum chamber, a fixing base 11 for fixing the current collector 1, an oxygen nozzle 14 for introducing oxygen gas into the chamber, and silicon are supplied to the surface of the current collector 1. And a crucible 12 loaded with an evaporation source. For example, silicon can be used as the evaporation source. Further, although not shown, an electron beam heating means for evaporating the material of the evaporation source is provided. The oxygen nozzle 14 is positioned so that the oxygen gas 5 emitted from the oxygen nozzle 14 is supplied near the surface of the current collector 1. The fixed base 11 and the crucible 12 are arranged such that vapor deposition particles (silicon atoms in this case) 16 from the crucible 12 form the current collector 1 from the direction of an angle (deposition angle) θ with respect to the normal direction N of the current collector 1. It arrange | positions so that it may inject into the surface. In this example, the fixed base 11 has a rotation axis. By rotating the fixed base 11 around the rotation axis, the angle of the fixed base 11 with respect to the horizontal plane 18 becomes equal to a predetermined deposition angle θ. Adjusted. Here, the “horizontal plane” refers to a plane perpendicular to the direction in which the material of the evaporation source charged in the crucible 12 is vaporized and faces the fixed base 11.

  The negative electrode active material body 5 is formed by irradiating the crucible 12 with an electron beam (EB) with an electron beam (not shown) while blowing oxygen gas 15 from the oxygen nozzle 14 near the surface of the current collector 1. Then, it is melted and incident on the current collector 1 (EB vapor deposition). On the surface of the current collector 1, silicon atoms 16 and oxygen gas 15 react to grow silicon oxide. At this time, since the silicon atoms 16 are incident on the surface of the current collector 3 from a direction inclined with respect to the normal direction of the current collector 1, the first protrusions on the surface of the current collector 3 (FIG. 1). It is easy to vapor-deposit on the convex part 2A), and silicon oxide grows in a column shape only on the convex part. On the other hand, in the shadowed portion of the silicon oxide that grows in a columnar shape on the surface of the current collector 3, Si atoms do not enter and silicon oxide is not deposited (shadowing effect).

  In this way, a plurality of negative electrode active material bodies are formed on each convex portion of the current collector 1, and the negative electrode 100 is completed. The average value of the oxygen ratio in the negative electrode active material body can be controlled by adjusting the amount of oxygen gas introduced into the vacuum chamber (that is, the oxygen concentration in the atmosphere).

  In the above method, when the negative electrode active material body is formed with the vapor deposition angle θ kept constant, a negative electrode active material body grown along a specific direction is obtained as shown in FIG. Further, during the EB vapor deposition, the vapor deposition angle θ may be changed by rotating the fixed base 11 along the rotation axis to change the installation direction of the current collector 1. In this case, a negative electrode active material body having a plurality of portions with different growth directions is obtained.

  FIG. 5 is a schematic cross-sectional view illustrating another configuration of the negative electrode of the present embodiment, and each negative electrode active material body has a plurality of portions having different growth directions.

  In the illustrated example, each negative electrode active material body 5 is divided into seven portions p1 to p7 according to the growth direction G. Such a negative electrode active material body 5 is obtained by performing a plurality of stages of vapor deposition by changing the vapor deposition direction. The growth directions of the plurality of portions p1 to p7 in each negative electrode active material body 5 may all be different. Moreover, the growth directions of the plurality of portions p1 to p7 may be the same for each negative electrode active material body 5 or may be different.

  Next, referring to the drawings, the configuration of the lithium secondary battery obtained by applying the negative electrode of the present embodiment is taken as an example of a cylindrical lithium secondary battery (hereinafter also simply referred to as “cylindrical battery”). explain.

  FIG. 6 is a schematic cross-sectional view of a cylindrical battery using the negative electrode of this example. In FIG. 6, a cylindrical battery 60 includes a cylindrical electrode group 64 and a battery can 68 that accommodates the electrode group 64. The electrode group 64 is obtained by winding a belt-like positive electrode plate 61 and a belt-like negative electrode plate 62 together with a wide separator 63 disposed therebetween. The electrode group 64 is impregnated with an electrolyte (not shown) that conducts lithium ions. The opening of the battery can 68 is closed by a sealing plate 69 having a positive electrode terminal 65. One end of an aluminum positive electrode lead 61 a is connected to the positive electrode plate 61, and the other end is connected to the back surface of the sealing plate 69. An insulating packing 66 made of polypropylene is disposed on the periphery of the sealing plate 69. One end of a copper negative electrode lead (not shown) is connected to the negative electrode plate 62, and the other end is connected to the battery can 68. An upper insulating ring (not shown) and a lower insulating ring 67 are disposed above and below the electrode group 64, respectively.

  In addition, the structure of the lithium secondary battery provided with the negative electrode of this embodiment is not limited to the structure shown in FIG. The negative electrode of the present embodiment is applicable to lithium secondary batteries having various shapes such as a coin shape, a flat shape, and a square shape in addition to a cylindrical shape. Further, the sealing form of the lithium secondary battery and the material of each element constituting the battery are not particularly limited. It can also be applied to non-aqueous electrolyte secondary batteries other than lithium secondary batteries.

  Further, each component of the lithium secondary battery of the present invention is not particularly limited except that the negative electrode of the present invention is used, and is generally used as a material for a lithium ion battery within a range not impairing the effects of the present invention. It is possible to select various types used in the above.

Example 1
Example 1 of the negative electrode according to the present invention will be described below. Here, as an example, a negative electrode provided with a negative electrode active material body having a plurality of portions having different growth directions was prepared, and the oxygen ratio was measured and the characteristics were evaluated. The method and results will be described.

(I) Production method of negative electrode <Production of current collector>
7A to 7C are cross-sectional process diagrams for explaining a method of manufacturing a current collector in this example. First, as shown in FIG. 7A, a copper foil (thickness: 27 μm) 23 having a surface roughness Rz of 1.5 to 7 μm was prepared. The surface roughness Rz refers to a ten-point average roughness Rz defined in Japanese Industrial Standard (JISB 0601-1994). Here, the roughened copper foil (made by Furukawa Circuit Foil Co., Ltd.) marketed for printed wiring boards was used.

  Next, as shown in FIG. 7 (b), a stainless roller 20 having a plurality of recesses 21 that define the first protrusions, and another roller (not shown) arranged to face the stainless roller 20 In the meantime, the copper foil 23 was passed at a linear pressure of 1.5 t / cm. In this way, a current collector 1 as shown in FIG.

  A plan view and a sectional view of the pattern of the stainless roller 20 are shown in FIGS. As shown in the figure, the stainless steel roller 20 has a plurality of concave portions 21 regularly arranged, and each concave portion 21 has a rhombus shape when viewed from the normal direction of the stainless steel roller 20. The diagonal lengths a and b of the rhombus were 10 μm and 20 μm, respectively. The distance e along the diagonal line a of the adjacent recesses 21 was 20 μm, the distance d along the diagonal line b was 10 μm, and the distance c in the direction parallel to the rhombus sides was 10 μm. Therefore, the arrangement pitch P of the recesses in the direction 25 parallel to the shorter diagonal line a in the rhombus was 30 μm (P = a + e). Moreover, the depth H of each recessed part 21 was 10 micrometers.

Of the copper foil 23 that passed between the rollers, the area that was pressed at a portion other than the recess 21 of the stainless roller 20 was flattened as shown in the figure. On the other hand, the region of the copper foil 23 corresponding to the concave portion 21 entered the concave portion 21 without being flattened, and the first convex portion 2A was formed. The height of the first convex portion 2A was smaller than the depth H of the concave portion 21 of the stainless roller 20, and was about 6 μm. The corners of the obtained first convex portion 2A were rounded. In addition, a second protrusion 2B was formed on the surface of the first protrusion 2A corresponding to the surface unevenness of the copper foil 23, and the height of the second protrusion 2B was about 2 μm. . The shape of the 2nd convex part 2B was roundish rather than each convex part contained in the copper foil 23. FIG.

<Formation of negative electrode active material>
The current collector 1 obtained by the above method (i) is placed on the fixed base 11 in the vacuum chamber shown in FIG. 4, while supplying oxygen gas 5 to the surface of the current collector 1 at 30 sccm, silicon is added. EB vapor deposition was performed as an evaporation source. In the vapor deposition, the fixing base 11 was inclined so as to form an angle of 60 ° with the horizontal plane 18 (θ = 60 °), and vapor deposition was performed in this state for 15 minutes (first vapor deposition step). At this time, the acceleration voltage of the electron beam applied to the evaporation source of silicon alone was set to −9 kV, and the emission was set to 400 mA. The silicon vapor is supplied to the surface of the current collector 1 installed on the fixed base 11 together with the oxygen gas 5 introduced into the vacuum chamber, and as a result, a compound containing silicon and oxygen on the current collector 1. (SiO _x ) was deposited.

  Subsequently, the fixing base 11 is rotated clockwise around the central axis, and an angle of 60 ° is formed with respect to the horizontal plane 18 in a direction opposite to the inclination direction of the fixing base 11 in the first stage vapor deposition step. (Θ = −60 °). In this state, the deposition was performed for 15 minutes under the same conditions as the first-stage deposition process (second-stage deposition process).

  After that, the inclination angle of the fixed base 11 was returned again to the same angle (θ = 60 °) as that in the first stage vapor deposition step, and the same vapor deposition was performed (third vapor deposition step). In this manner, the inclination angle θ of the fixing base 11 was alternately switched between 60 ° and −60 °, and vapor deposition was performed up to the seventh stage to obtain a negative electrode active material body.

(Ii) Analysis <Observation with an electron microscope>
The cross section of the negative electrode active material obtained by the above method was observed with an electron microscope. 9 (a) and 10 (a) are electron micrographs showing the shape of the negative electrode active material body in a cross section perpendicular to the current collector surface, and FIG. 9 (a) is the deposition direction of the negative electrode active material body. FIG. 10A is a cross-sectional view along the direction perpendicular to the vapor deposition direction on the current collector surface.

  FIG. 9A shows that the negative electrode active material body 5 has a zigzag cross-sectional shape due to the deposition direction. Moreover, from FIG. 10A, it was found that the negative electrode active material body 5 had a structure in which a plurality of layers having different vapor deposition directions were stacked. Furthermore, it was confirmed that the cross-sectional shape of the convex portion on the surface of the current collector 1 does not have a clear angle of 90 ° or less.

<Measurement of average value of oxygen ratio in negative electrode active material>
The average value of the oxygen ratio of the negative electrode active material body (molar ratio of the oxygen amount to the silicon amount) was measured by performing fluorescent X-ray measurement from the surface of the current collector 1 on which the negative electrode active material body 5 was formed. As a result, the average value of the oxygen ratio was 0.58.

<Oxygen ratio distribution in the vicinity of the interface between the negative electrode active material body and the current collector>
As described above with reference to FIG. 2, the oxygen ratio at the interface between the current collector 1 and the negative electrode active material body 5 was measured using a wavelength dispersive X-ray microanalyzer (JXA-8900 manufactured by JEOL). Specifically, first, a sample was hardened with a resin and then polished to form a polished cross section corresponding to FIG. Next, carbon coating was performed on the obtained polished cross section. Then, the composition analysis of the negative electrode active material body 5 was performed with the wavelength dispersion type | mold X-ray microanalyzer. The acceleration voltage was 5 kV. In this example, the same composition analysis was performed on the cross section of the negative electrode active material body corresponding to FIG.

  The oxygen map and the silicon map in the polished cross section shown in FIGS. 9A and 10A are shown in FIGS. 9B and 10C, and FIGS. 10B and 10C, respectively. From the X-ray intensity of these maps, the oxygen ratio at the interface between the current collector 1 and the negative electrode active material body 5 was calculated.

  The map shown is a black and white copy of a color image obtained by measurement, and the concentration distribution of each element is represented by brightness. From FIG. 9B and FIG. 10B, it was found that the oxygen concentration distribution in the negative electrode active material body 5 was substantially uniform. Further, as can be seen from FIG. 9C, in the vicinity of the center of the negative electrode active material body 5, a region having a low silicon concentration extends vertically corresponding to the shape of the negative electrode active material body 5 shown in FIG. However, the distribution of the silicon concentration in the vicinity of the interface between the negative electrode active material body 5 and the current collector 1 was substantially uniform. In the cross section shown in FIG. 10C, the silicon concentration in the negative electrode active material body 5 was substantially uniform.

When the six oxygen oxygen ratios m1, m2, and m3 shown in FIG. 9 (a) and m4, m5, and m6 shown in FIG. 10 (a) were measured positions, and the respective oxygen ratios were quantified, the values shown in Table 1 were obtained. Obtained. As can be seen from Table 1, the difference ΔR between the maximum value Rmax and the minimum value Rmin of the oxygen ratio is 0.
38.

(Iii) Production and evaluation of battery <Production of battery>
In this example, a cylindrical battery having the above-described configuration with reference to FIG. 6 was produced as follows.

  First, a negative electrode plate 62 for a cylindrical battery was produced by forming the negative electrode active material body 5 on the current collector 1 by the method (i). Moreover, the positive electrode plate 61 was obtained by coating the active material which has lithium nickelate as a main body on Al foil. Next, the negative electrode plate 62 and the positive electrode plate 61 were wound so as to face each other with a polyethylene separator 63 therebetween, whereby an electrode group 64 was configured. After this electrode group 64 was inserted into the battery can 68 and the electrolyte was injected, a sealing plate 69 was installed. In this way, a 18650 size cylindrical battery was obtained.

<Evaluation method and results>
The battery produced by the method (iii) was repeatedly subjected to a charge / discharge test at a current equivalent to 1C. FIG. 11 is a diagram showing the charge / discharge cycle characteristics obtained as a result of the charge / discharge test. The vertical axis represents the capacity retention rate (%), and the horizontal axis represents the number of cycles (times). From the results shown in FIG. 11, it was confirmed that the battery of this example had excellent charge / discharge cycle characteristics.

  Further, after the charge / discharge test was performed, the battery was disassembled and the negative electrode plate 62 was observed. As a result, it was not observed that the negative electrode active material was peeled off or removed from the current collector 1.

(Comparative Example 1)
Hereinafter, Comparative Example 1 of the negative electrode according to the present invention will be described. Comparative Example 1 differs from Example 1 in that the current collector is produced by a method different from Example 1.

(I) Method for producing negative electrode First, a negative photoresist is applied onto a rolled copper foil (thickness: 27 μm), and the negative photoresist is exposed using a negative mask having a plurality of rhombus patterns. Development was performed. This formed a plurality of openings in the photoresist. Subsequently, after the copper particles were deposited by electrolytic method in these openings, the photoresist was removed. Thus, the columnar convex part which has a rhombus upper surface was formed on copper foil, and the electrical power collector was obtained.

  In the obtained current collector, the height of each convex portion on the surface of the current collector was 10 μm, and the surface roughness Rz of the upper surface of the convex portion was 0.9 μm. In addition, the lengths of the rhombus diagonals on the upper surface of the convex part are 28 μm and 12 μm, the distance along the shorter diagonal line of the adjacent concave part is 18 μm, the distance along the longer diagonal line is 20 μm, and is parallel to the side of the rhombus The interval was 15 μm. Further, in the cross section perpendicular to the current collector surface, the angle formed between the upper surface and the side surface of each convex portion was approximately 90 °.

  Diagonal vapor deposition was performed on the surface of the current collector obtained as described above in the same manner as in Example 1 while changing the incident direction of silicon in seven steps to form a negative electrode active material body.

(Ii) Analysis When the average value of the oxygen ratio of the obtained negative electrode active material body was measured by the same method as in Example 1, it was 0.62. Further, the oxygen ratio at six points located in the vicinity of the interface between the negative electrode active material body and the current collector was measured in the same manner as in Example 1, and the difference ΔR between the maximum value and the minimum value was calculated. .82.

(Iii) Production and Evaluation of Battery Using the negative electrode plate of Comparative Example 1, a cylindrical battery having the configuration shown in FIG. 6 was produced, and a charge / discharge cycle test was performed. The battery fabrication method and test method were the same as those described in Example 1.

  FIG. 12 is a diagram showing charge / discharge cycle characteristics obtained as a result of the charge / discharge cycle test. From the results shown in FIG. 12, it was found that in the battery of Comparative Example 1, the discharge capacity was remarkably reduced from the initial stage and reached about 50% of the maximum capacity after 150 cycles.

  After conducting the charge / discharge test, the battery was disassembled and the negative electrode plate was observed. As a result, it was confirmed that a part of the negative electrode active material was peeled from the current collector. Thus, in Comparative Example 1, it is considered that when charging / discharging is repeated, the negative electrode active material peels from the current collector surface due to the oxygen ratio distribution at the interface of the negative electrode active material body, and as a result, the discharge capacity is reduced. It was.

(Example 2)
Hereinafter, Example 2 of the negative electrode according to the present invention will be described. Here, a negative electrode provided with a negative electrode active material body grown in one direction by oblique vapor deposition was produced using a current collector produced in the same manner as in Example 1, and measurement of oxygen ratio and evaluation of characteristics were performed. The method and result will be described.

(I) Method for Producing Negative Electrode The current collector 1 produced by the same method as in Example 1 was placed on the fixed base 11 in the vacuum chamber shown in FIG. 4, and the surface of the current collector 1 was charged with oxygen gas 5 at 30 sccm. EB deposition using silicon as an evaporation source was performed. In the vapor deposition, the fixing base 11 was inclined so as to form an angle of 60 ° with the horizontal plane 18 (θ = 60 °), and vapor deposition was performed in this state for 50 minutes. At this time, the acceleration voltage of the electron beam applied to the evaporation source of silicon alone was set to −9 kV, and the emission was set to 400 mA. The silicon vapor is supplied to the surface of the current collector 1 installed on the fixed base 11 together with the oxygen gas 5 introduced into the vacuum chamber, and as a result, a compound containing silicon and oxygen on the current collector 1. Has grown. Thus, the negative electrode active material body 5 was formed on the surface of the current collector 1.

(Ii) Analysis <Observation with an electron microscope>
FIG. 13A is an electron micrograph of a single negative electrode active material body in Example 2, showing a cross section perpendicular to the current collector surface and including the vapor deposition direction. From this figure, it was confirmed that each negative electrode active material body 5 had a cross-sectional shape inclined in a specific direction. Moreover, it turned out that the cross-sectional shape of the convex part in the surface of the electrical power collector 1 does not have a clear angle of 90 degrees or less.

<Measurement of average value of oxygen ratio in negative electrode active material>
When the average value of the oxygen ratio (molar ratio of the oxygen amount to the silicon amount) of the negative electrode active material body was determined by fluorescent X-ray measurement in the same manner as in Example 1, it was 0.56.

<Oxygen ratio distribution in the vicinity of the interface between the negative electrode active material body and the current collector>
The oxygen ratio in the vicinity of the interface between the current collector 1 and the negative electrode active material body 5 was measured using a wavelength dispersive X-ray microanalyzer. The measurement was performed in the same manner as in Example 1. However, in Example 1, composition analysis was performed on cross sections in two directions orthogonal to each other. However, in this example, only composition analysis was performed on the cross section illustrated in FIG.

  The oxygen map and silicon map of the cross section shown in FIG. 13 (a) are shown in FIG. 13 (b) and (c). The map shown is a black and white copy of a color image obtained by measurement, and the concentration distribution of each element is represented by brightness. From FIGS. 13B and 13C, although there is a region where the oxygen concentration is slightly low and the silicon concentration is slightly high in the vicinity of the right side surface of the negative electrode active material body 5, a large concentration distribution occurs as a whole. I found out.

  Further, as shown in FIG. 13 (a), the oxygen ratios were quantified from the X-ray intensity by using three points m7, m8, and m9 at the interface between the current collector 1 and the negative electrode active material body 5 as measurement positions. However, values as shown in Table 2 were obtained.

  In Example 2, as can be seen from Table 2, the maximum value Rmax of the oxygen ratio was 0.42, the minimum value Rmin was 0.29, and the difference ΔR was 0.13.

(Iii) Production and Evaluation of Battery Using the negative electrode plate of Example 2, a cylindrical battery having the configuration shown in FIG. 6 was produced, and a charge / discharge cycle test was performed. The battery fabrication method and test method were the same as those described in Example 1.

  FIG. 14 is a diagram showing charge / discharge cycle characteristics obtained as a result of the charge / discharge cycle test. From the results shown in FIG. 14, it was confirmed that the battery of Example 2 had excellent charge / discharge cycle characteristics. Further, after the charge / discharge test was performed, the battery was disassembled and the negative electrode plate was observed. As a result, it was not observed that the negative electrode active material was peeled off or removed from the current collector 1.

(Comparative Example 2)
Hereinafter, Comparative Example 2 of the negative electrode according to the present invention will be described. Comparative Example 2 differs from the negative electrode of Example 2 in that a current collector produced by the same method as Comparative Example 1 is used.

(I) Production of Negative Electrode A negative electrode active material body inclined in a specific direction was formed on the surface of a current collector produced by the same method as in Comparative Example 1. The negative electrode active material body was formed by performing oblique deposition under the same method and conditions as in Example 2. In the vapor deposition step, the upper surface and the side surface of each of the convex portions arranged on the current collector surface with respect to the incident direction of silicon (direction inclined by 60 ° with respect to the normal direction of the current collector surface) are 90. Since the corners at 0 ° face each other, silicon oxide was deposited on both the upper surface and the side surface of each convex portion, and a negative electrode active material body was formed.

(Ii) Analysis <Observation with an electron microscope>
FIG. 15A is an electron micrograph of a single negative electrode active material body in Comparative Example 2, and shows a cross section perpendicular to the current collector surface and including the vapor deposition direction. From this figure, it was confirmed that each negative electrode active material body 5 had a cross-sectional shape inclined in a specific direction. Moreover, it turned out that the cross-sectional shape of the convex part in the surface of the electrical power collector 1 is a rectangle which has an angle of about 90 degrees.

<Measurement of average value of oxygen ratio in negative electrode active material>
When the average value of the oxygen ratio (molar ratio of the oxygen amount to the silicon amount) of the negative electrode active material body was determined by fluorescent X-ray measurement in the same manner as in Example 1, it was 0.61.

<Oxygen ratio distribution in the vicinity of the interface between the negative electrode active material body and the current collector>
The oxygen ratio at the interface between the current collector 1 and the negative electrode active material body 5 was measured using a wavelength dispersive X-ray microanalyzer. The measurement was performed in the same manner as in Example 2.

  The oxygen map and silicon map of the cross section shown in FIG. 15A are shown in FIGS. 15B and 15C, respectively. The map shown is a black and white copy of a color image obtained by measurement, and the concentration distribution of each element is represented by brightness. As can be seen from FIGS. 15B and 15C, in the vicinity of the left side surface of the negative electrode active material body 5, that is, in the region grown on the side surface of the convex portion of the current collector 1, oxygen is larger than other regions. The concentration was significantly reduced and the silicon concentration was significantly increased.

  As shown in FIG. 15 (a), when three points m10, m11, and m12 at the interface between the current collector 1 and the negative electrode active material body 5 were measured, and the respective oxygen ratios were quantified from the X-ray intensity, Values as shown in Table 3 were obtained.

  In Comparative Example 2, as can be seen from Table 3, the maximum value Rmax of the oxygen ratio was 1.12, the minimum value Rmin was 0.19, and the difference ΔR was 0.93.

(Iii) Production and Evaluation of Battery Using the negative electrode plate of Comparative Example 2, a cylindrical battery having the configuration shown in FIG. 6 was produced, and a charge / discharge cycle test was performed. The battery fabrication method and test method were the same as those described in Example 1.

  FIG. 16 is a diagram showing charge / discharge cycle characteristics obtained as a result of the charge / discharge cycle test. From the results shown in FIG. 16, it was found that the discharge capacity of the battery of Comparative Example 2 was significantly reduced from the beginning, and reached about 80% of the maximum capacity after 100 cycles.

  Next, the battery after the charge / discharge cycle test was disassembled, the negative electrode plate was observed with an electron microscope, and compared with the initial negative electrode plate of the charge / discharge cycle test.

  FIGS. 17A and 17B are electron micrographs of the negative electrode plate at the initial stage of the charge / discharge cycle test and the negative electrode plate after the charge / discharge cycle test, respectively. As can be seen from these drawings, in FIG. 17B, a part where the negative electrode active material was peeled off from the current collector was observed particularly on the upper surface of the convex portion formed on the current collector 1. Therefore, in Comparative Example 2, it is considered that the negative electrode active material peels from the current collector surface due to repeated charge and discharge, and as a result, the discharge capacity decreases.

  In addition, the manufacturing method and structure of the current collector of the present invention are not limited to the first and second embodiments described above. The current collector of the present invention has a first convex portion that supports the negative electrode active material body and can control the arrangement thereof, and a second convex portion provided on the surface of the first convex portion, If these protrusions have a shape that can reduce the oxygen concentration distribution at the interface between each negative electrode active material body and the current collector due to the relationship with the vapor deposition direction for forming the negative electrode active material body, Good. Similarly, the configuration, formation method, formation conditions, and the like of the negative electrode active material body of the present invention are not limited to those in Examples 1 and 2 described above. For example, the incident direction (angle θ) of silicon atoms with respect to the normal direction of the current collector is appropriately selected. In Examples 1 and 2, the negative electrode active material layer was formed in a state where the current collector was placed on a fixed base in the vacuum chamber. Instead, in the vacuum chamber, a sheet-like current collector was formed. The negative electrode active material body can also be formed on the traveling current collector by running using a roller.

  The negative electrode for a lithium secondary battery of the present invention can be applied to various lithium secondary batteries such as a coin type, a cylindrical type, a flat type, and a square type. These lithium secondary batteries have a charge / discharge cycle characteristic that is superior to conventional ones while ensuring a high charge / discharge capacity. Therefore, portable information terminals such as PCs, mobile phones, PDAs, video recorders, memory audio players, etc. It can be widely used for audio-visual equipment.

It is typical sectional drawing which shows the negative electrode of embodiment by this invention. (A) is typical sectional drawing for demonstrating the method to measure the oxygen ratio in the interface vicinity of a negative electrode active material body and a collector, (b) is oxygen from the measurement result of (a). It is a figure for demonstrating the method of calculating | requiring the difference of the maximum value and minimum value of a ratio. (A) And (b) is typical for demonstrating the vapor deposition process when the cross-sectional shape of a 1st convex part has an angle | corner of 90 degrees or less, and a case where it does not have such an angle, respectively. It is sectional drawing. It is typical sectional drawing which shows an example of the manufacturing apparatus of the negative electrode of embodiment by this invention. It is typical sectional drawing which shows the other structure of the negative electrode of embodiment by this invention. It is the schematic which illustrates the cylindrical battery using the negative electrode of this invention. (A)-(c) is process sectional drawing for demonstrating the preparation method of the electrical power collector in Example 1. FIG. (A) And (b) is the top view and sectional drawing which illustrate the pattern of the roller used for preparation of the electrical power collector in Example 1, respectively. It is a figure which shows the analysis result of the negative electrode active material body in Example 1, (a) is an electron micrograph which shows the cross section of a negative electrode active material body, (b) and (c) are respectively an oxygen map and It is a silicon map. It is a figure which shows the analysis result of the negative electrode active material body in Example 1, (a) is an electron micrograph which shows the cross section of a negative electrode active material body, (b) and (c) are respectively an oxygen map and It is a silicon map. FIG. 3 is a diagram showing charge / discharge cycle characteristics of the cylindrical battery of Example 1. It is a figure which shows the charging / discharging cycle characteristic of the cylindrical battery of the comparative example 1. It is a figure which shows the analysis result of the negative electrode active material body in Example 2, (a) is an electron micrograph which shows the cross section of a negative electrode active material body, (b) and (c) are respectively an oxygen map and It is a silicon map. It is a figure which shows the charging / discharging cycle characteristic of the cylindrical battery of Example 2. It is a figure which shows the analysis result of the negative electrode active material body in the comparative example 2, (a) is an electron micrograph which shows the cross section of a negative electrode active material body, (b) and (c) are respectively an oxygen map and It is a silicon map. It is a figure which shows the charging / discharging cycle characteristic of the cylindrical battery of the comparative example 2. It is an electron micrograph of the negative electrode plate in the cylindrical battery of Comparative Example 2, and (a) and (b) are views showing the negative electrode plate at the initial stage of the charge / discharge cycle test and after the charge / discharge cycle test, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Current collector 2A 1st convex part 2B 2nd convex part 5 Negative electrode active material body 100 Negative electrode 7 Measurement area 11 Fixing base 12 Crucible 14 Oxygen nozzle 15 Oxygen gas 16 Silicon atom 18 Horizontal surface 20 Roller 21 Recessed part 23 Copper foil 60 Battery 61 Positive electrode 61a Positive electrode lead 62 Negative electrode 63 Separator 64 Electrode group 65 Positive electrode terminal 66 Insulating packing 67 Lower insulating ring 68 Battery can 69 Sealing plate

Claims (8)

A current collector,
A plurality of negative electrode active material bodies that are disposed on the current collector and spaced apart from each other and that contain silicon oxide;
A plurality of first protrusions supporting the plurality of negative electrode active material bodies are arranged on the surface of the current collector,
Each of the first protrusions has a plurality of second protrusions having a height lower than that of the first protrusion.
The average value of the molar ratio of the oxygen amount to the silicon amount of each negative electrode active material body is 0.1 or more and 1.2 or less,
Wherein Ri difference 0.4 der following in the vicinity of the interface between the current collector and the negative electrode active material body, the maximum value and the minimum value of the amount of oxygen to silicon-amount,
The growth direction of each negative electrode active material body is inclined with respect to the normal direction of the current collector,
In the vicinity of the interface between each negative electrode active material body and the current collector, the angle formed by the growth direction of each negative electrode active material body and the normal direction of the current collector is 10 ° or more and 80 ° or less. Negative electrode for secondary battery.   2. The lithium secondary according to claim 1, wherein a contact surface between each of the first protrusions and the negative electrode active material body does not have an angle of 90 ° or less in a cross section perpendicular to the surface of the current collector. Battery negative electrode.   2. The negative electrode for a lithium secondary battery according to claim 1, wherein the plurality of first protrusions are arranged at a pitch of 10 μm or more.   2. The negative electrode for a lithium secondary battery according to claim 1, wherein a height of the plurality of first protrusions is not less than 5 μm and not more than 10 μm.   The negative electrode for a lithium secondary battery according to claim 4, wherein a height of the plurality of second convex portions is 1 μm or more and 5 μm or less.   The negative electrode for a lithium secondary battery according to claim 1, wherein each of the negative electrode active material bodies has a plurality of portions having different growth directions. A positive electrode capable of inserting and extracting lithium ions;
A negative electrode for a lithium secondary battery according to any one of claims 1 to 6 ,
A separator disposed between the positive electrode and the negative electrode for a lithium secondary battery;
A lithium secondary battery comprising an electrolyte having lithium ion conductivity. A step of preparing a current collector in which first protrusions are arranged on the surface, wherein each first protrusion includes a plurality of second protrusions having a height lower than that of the first protrusion; And having the process
Forming a negative electrode active material body containing silicon oxide by oblique vapor deposition on each of the first protrusions on the surface of the current collector,
The average value of the molar ratio of the oxygen amount to the silicon amount of each negative electrode active material body is 0.1 or more and 1.2 or less,
Wherein Ri difference 0.4 der following in the vicinity of the interface between the current collector and the negative electrode active material body, the maximum value and the minimum value of the amount of oxygen to silicon-amount,
The growth direction of each negative electrode active material body is inclined with respect to the normal direction of the current collector,
In the vicinity of the interface between each negative electrode active material body and the current collector, the angle formed by the growth direction of each negative electrode active material body and the normal direction of the current collector is 10 ° or more and 80 ° or less. A method for producing a negative electrode for a secondary battery.