JP5095132B2 - Negative electrode for lithium secondary battery and lithium secondary battery including the same - Google Patents

Description

  The present invention relates to a lithium secondary battery, and more particularly to a negative electrode structure.

  In recent years, with the development of portable devices such as personal computers and mobile phones, the demand for batteries as power sources has increased. A battery used for the above applications is required to be used at room temperature, and at the same time, a high energy density and excellent cycle characteristics are required.

  In response to this requirement, high-capacity active materials have been newly developed in each of the positive electrode and the negative electrode. Among them, a simple substance, oxide or alloy of silicon (Si) or tin (Sn) capable of obtaining a very high capacity is considered promising as a negative electrode active material.

  A problem in using silicon as a negative electrode active material is deformation of the negative electrode. At the time of charge and discharge, lithium (Li) is inserted and desorbed, so that the negative electrode active material is greatly expanded and contracted. Therefore, the negative electrode including the current collector is greatly distorted, and wrinkles and cuts are generated. Further, a space is generated between the negative electrode and the separator, and the charge / discharge reaction becomes non-uniform. Therefore, there is a concern that the battery may cause local characteristic deterioration.

  In order to solve such a problem, it has been proposed to provide a space in the negative electrode for relaxing the expansion stress of the active material. This proposal is intended to suppress negative electrode distortion and undulation, and to suppress deterioration of cycle characteristics.

For example, Patent Document 1 proposes forming silicon columnar particles on a current collector.
Patent Document 2 proposes to perform pattern forming in which an active material that forms an alloy with lithium is regularly arranged on a current collector.

  Patent Document 3 proposes that after forming a thin film electrode of silicon, tin or the like on a current collector having unevenness, the unevenness is flattened to form a network-like crack in the thin film.

Patent Document 4 proposes that the columnar particles forming the negative electrode active material are inclined with respect to the normal direction of the current collector surface.
JP 2003-303586 A JP 2004-127561 A JP 2005-108522 A JP-A-2005-196970

  In each of Patent Documents 1 to 3, a negative electrode active material layer made of columnar particles standing upright in the normal direction of the current collector is formed. Since such a negative electrode active material layer has many voids, most of the positive electrode active material does not face the negative electrode active material but faces the exposed portion of the negative electrode current collector. Therefore, lithium supplied from the positive electrode active material 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, during discharging, lithium is not efficiently released from the negative electrode, and charge / discharge efficiency is reduced.

  Since the negative electrode of Patent Document 4 has inclined columnar particles, the utilization ratio of the positive electrode active material and the negative electrode active material is increased, and the capacity retention rate is superior to Patent Documents 1 to 3. However, when the columnar particles are inclined, it is difficult to form a gap in the negative electrode active material layer. Therefore, when the thickness of the columnar particles is increased, the particles are connected to each other, and the negative electrode is greatly distorted during expansion during charging, which may cause wrinkling or cutting of the current collector. Therefore, when the charge / discharge cycle is repeated over a long period of time, the deterioration of the negative electrode tends to proceed.

The present invention is a negative electrode for a lithium secondary battery including a current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes a plurality of columnar particles, and the surface of the current collector includes a plurality of groove portions. When, and a two or more regions defined by a plurality of grooves, two or more regions defined by a plurality of grooves, carries a plurality of columnar particles, a plurality of columnar particles, the current collector The angle α formed by the growth direction parallel to the surface of the current collector of the columnar particles and the plurality of grooves is 0 <α <90. The present invention relates to a negative electrode for a lithium secondary battery that satisfies ° . Furthermore, the present invention provides a negative electrode for a lithium secondary battery including a current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes a plurality of columnar particles, and the surface of the current collector includes a plurality of surfaces. And two or more regions partitioned by a plurality of groove portions, the plurality of groove portions include a plurality of first groove portions and a plurality of second groove portions, and the first groove portion and the second groove portion are different. Two or more regions having a pattern and intersecting each other and defined by a plurality of grooves carry a plurality of columnar particles, and the plurality of columnar particles are in the normal direction of the surface of the current collector. On the other hand, the angle β formed between the growth direction parallel to the surface of the current collector of the columnar particles and the first groove portion satisfies 0 ° <β <90 °, and the columnar particles grow in an oblique direction. The angle γ formed by the growth direction parallel to the surface of the current collector and the second groove satisfies 0 ° <γ <90 °. The present invention relates to a negative electrode for a secondary battery.

The shape of the two or more regions partitioned by the plurality of grooves is, for example, a square, a rectangle, a parallelogram, or a rhombus.

  The active material layer includes, for example, at least one selected from the group consisting of a silicon simple substance, a silicon alloy, a compound containing silicon and oxygen, and a compound containing silicon and nitrogen.

  Here, when the silicon alloy is an alloy of silicon and the metal element M, it is preferable that the metal element M does not form an alloy with lithium. The metal element M is at least one selected from the group consisting of titanium, copper, and nickel, for example.

The compound containing silicon and oxygen preferably has a composition represented by the general formula (1): SiO _x (where 0 <x <2).

  The present invention also relates to a lithium secondary battery comprising the above-described negative electrode for a lithium secondary battery, a positive electrode containing a positive electrode active material capable of occluding and releasing lithium ions, and a lithium ion conductive electrolyte.

  The surface of the negative electrode current collector includes a plurality of groove portions and a region partitioned by the plurality of groove portions, and the region partitioned by the plurality of groove portions carries a plurality of columnar particles. Connection is less likely to occur, and current collectors are prevented from wrinkling and breaking. In addition, since the plurality of columnar particles grow in an oblique direction with respect to the normal direction of the surface of the current collector, the exposed portion of the negative electrode current collector facing the positive electrode active material layer is reduced, and the negative electrode current collector is reduced. Less lithium is deposited on the exposed portion of the electric body. Therefore, charge / discharge efficiency and cycle characteristics are improved.

Hereinafter, the present invention will be described with reference to the drawings, but the present invention is not limited to the following contents.
FIG. 1 is a conceptual cross-sectional view of a negative electrode 10 for a lithium secondary battery according to an embodiment of the present invention parallel to the growth direction of columnar particles.

  The negative electrode 10 includes a current collector 11 and a negative electrode active material layer 12. The negative electrode active material layer 12 includes a plurality of columnar particles 121. The growth direction of the columnar particles 121 forms an angle θ with the normal direction of the surface of the current collector 11. Therefore, the exposed part of the negative electrode current collector facing the positive electrode active material layer is reduced, the charge / discharge efficiency is increased, and the possibility that lithium is deposited on the exposed part of the negative electrode current collector is also reduced. That is, nonuniform electrode reaction is suppressed, and charge / discharge cycle characteristics are also improved. In particular, the rapid deterioration of the cycle characteristics seen when charging / discharging with a large current is remarkably suppressed.

  The angle θ is desirably 10 ° or more and less than 90 °. When θ approaches 90 °, it becomes increasingly difficult to support columnar particles on the current collector. In addition, there are many portions where each columnar particle is shielded by other columnar particles, and the high-rate characteristics may deteriorate. Therefore, the angle θ is more preferably 10 ° or more and 80 ° or less. The angle θ is desirably obtained as an average value of, for example, arbitrary 2 to 10 columnar particles.

  The surface of the current collector 11 has a plurality of grooves 111 and a region 112 partitioned by the plurality of grooves. The plurality of columnar particles 121 are carried in a region 112 partitioned by a plurality of grooves. The plurality of grooves 111 have a function of giving gaps to the negative electrode active material layer, suppressing connection between the columnar particles, and relaxing stress due to expansion of the columnar particles.

  Concavities and convexities exist in the region 112 defined by the plurality of grooves. The columnar particles easily grow on the convex portions on the surface of the current collector, and hardly grow on the plurality of groove portions 111 and the concave portions. However, minute irregularities may exist on the inner wall of the groove 111, and a small amount of active material may be supported on the groove 111.

A groove part and an unevenness | corrugation can be distinguished by the shape.
The groove is, for example, a straight line or a curved line having a length of 1 mm or more, and preferably forms a predetermined pattern.
Concavities and convexities are composed of recesses and projections that are disordered or ordered, and the recesses do not exhibit a linear shape. Such irregularities are inevitably formed when the current collector is an electrolytic copper foil or an electrolytic copper alloy foil, and artificially formed by a plating method, a transfer method, or a cutting method.

  The width of the groove is most preferably about 10 μm, but may be in the range of 1 to 1000 μm, and preferably in the range of 5 to 100 μm. The width of one groove may be uniform or non-uniform. That is, the width may be different depending on the location of the groove.

  The depth of the groove is most preferably about 10 μm, but may be in the range of 1 to 30 μm, and preferably in the range of 1 to 10 μm. In one groove part, the depth may be uniform or non-uniform. That is, the depth may be different depending on the location of the groove.

Examples of a method for forming a plurality of grooves on the surface of the current collector include a transfer method and a cutting method.
The constituent material of the negative electrode current collector is not particularly limited. In general, copper, copper alloy, etc. are suitable for the current collector. The current collector is preferably produced by an electrolytic method. Although the thickness of a collector is not specifically limited, For example, 1-50 micrometers is common.

The surface roughness Ra of the current collector before forming the plurality of grooves is preferably 0.1 to 30 μm, and more preferably 0.3 to 10 μm. When the surface roughness Ra is small, it may be difficult to provide a space between columnar particles adjacent to each other. As the surface roughness Ra increases, the average thickness of the current collector also increases. However, if Ra is 100 μm or less, a sufficiently high capacity lithium secondary battery can be obtained.
Ra is defined in Japanese Industrial Standard (JISB 0601-1994), and can be measured by, for example, a surface roughness meter.

  In the unevenness of the surface of the current collector before forming the plurality of grooves, the distance between the centers of adjacent protrusions is preferably 0.1 μm or more and 200 μm or less, for example, and is 1 μm or more and 20 μm or less. Is more desirable.

  In the present invention, the columnar particles may be particles composed of a single crystal, or may be polycrystalline particles including a plurality of crystallites (crystal grains). The columnar particles may be particles made of microcrystals having a crystallite size of 100 nm or less, or may be amorphous.

The center-to-center distance w ₁ between the columnar particles 121 adjacent to each other can be regarded as the center-to-center distance (that is, the pitch) of the contact portion between the columnar particles and the current collector. The pitch is preferably 0.1 μm or more and 200 μm or less, for example, and more preferably 1 μm or more and 20 μm or less. Although it depends on the diameter of the columnar particles 121, it is considered that a remarkable effect of suppressing deterioration of cycle characteristics can be obtained when the pitch is 0.1 μm or more. If the pitch is 200 μm or less, it is possible to secure a certain energy density and limit the exposed portion of the current collector as viewed from the normal direction. A pitch is calculated | required as an average value of the group of arbitrary 2-10 sets of adjacent columnar particles, for example.

  Although the thickness t of the negative electrode active material layer 12 depends on the diameter of the columnar particles, for example, 0.1 μm ≦ t ≦ 100 μm is preferable, and 1 μm ≦ t ≦ 50 μm is particularly preferable. If the thickness t of the active material layer is 0.1 μm or more, a certain energy density can be secured. If the thickness t of the active material layer is 100 μm or less, the ratio of each columnar particle being shielded by other columnar particles can be kept low, and the current collection resistance from the columnar particles can also be kept low. Therefore, it is advantageous for charge / discharge with a large current (high rate charge / discharge).

  The diameter (the diameter perpendicular to the growth direction of the columnar particles) d of the columnar particles 121 is not particularly limited. The diameter of the columnar particles may vary in the length direction of the columnar particles. However, the diameter d is preferably 100 μm or less, and particularly preferably 1 to 50 μm, from the viewpoint of preventing the columnar particles from cracking or separating from the current collector due to expansion during charging. The diameter of the columnar particles is obtained, for example, as an average value of arbitrary 2 to 10 columnar particles. However, the diameter of the columnar particles is measured by the center height of the columnar particles, that is, the center height of the columnar particles in the normal direction of the current collector.

  A plurality of columnar particles adjacent to each other may coalesce during growth. However, each columnar particle has a different growth starting point. Therefore, the columnar particles combined during the growth are separated in the vicinity of the surface of the current collector, and the crystal growth state is also different. Therefore, it is possible to determine the diameter of each columnar particle.

  The thickness t of the negative electrode active material layer and the diameter d of the columnar particles are measured in a state where the negative electrode active material contains lithium corresponding to the irreversible capacity and does not contain lithium corresponding to the reversible capacity (the reversible capacity is 0). It is desirable to do. The state where the reversible capacity is 0 corresponds to the state where the volume of the negative electrode active material layer in the completed battery is minimum. When lithium is occluded in the columnar particles by charging, the columnar particles expand and the volume of the negative electrode active material layer increases.

  From the viewpoint of securing a large contact area between the electrolyte and the active material and sufficiently relaxing the stress due to expansion of the active material, the negative electrode active material layer is desired to have a predetermined porosity. The porosity P of the active material layer can be measured by, for example, a method using a mercury porosimeter, a method of calculating from the weight and thickness of the active material layer having a certain area and the density of the active material.

  As the negative electrode sample used for measuring the porosity, a sample obtained by cutting out only the current collector portion carrying the active material layer uniformly (uniformly) is used. At that time, the current collector portion carrying the active material layer on both sides may be used for the sample, or the current collector portion carrying the active material layer on one side may be used for the sample.

  In the measurement using a mercury porosimeter, when the volume of mercury that has entered the void of the sample is VH and the true volume of the active material layer is VT, the porosity P is P (%) = 100 {VH / (VT + VH)} Desired. When the current collector portion of the sample has irregularities on the surface, the porosity is calculated by including the volume of mercury that has entered the irregularities of the current collector portion in VH.

  The porosity P using a mercury porosimeter is measured in a state where the active material layer does not contain lithium at all. The porosity P ′ in a state containing lithium corresponding to the irreversible capacity and not including lithium corresponding to the reversible capacity (state where the reversible capacity is 0) can be obtained by correcting the porosity P. An active material layer that contains lithium corresponding to the irreversible capacity and does not contain lithium corresponding to the reversible capacity (state where the reversible capacity is 0) is Va and does not contain lithium at all. Let V0 be the volume. At that time, there is a relationship of P ′ = 100−Va (100−P) / V0.

  The porosity P of the negative electrode is preferably 10% ≦ P ≦ 70%, and more preferably 30% ≦ P ≦ 60%. If the porosity P is 10% or more, it is considered sufficient to relieve stress due to expansion and contraction of the columnar particles. Therefore, an abundant electrolyte in contact with the granular particles can be secured. Even if the porosity P exceeds 70%, it can be suitably used as a negative electrode depending on the use of the battery. However, the energy density of the negative electrode is reduced.

  The porosity P or P ′ can also be calculated from the weight and thickness of the active material layer having a certain area and the density of the active material. When calculating the porosity by calculation, assuming that the thickness of the active material layer having a constant area S in the sample is T, the weight is W, and the density of the active material is D, the porosity P is P (%) = 100 [{ST− (W / D)} / ST].

  FIG. 2 is a top view conceptually showing the relationship between the pattern of the plurality of grooves 211 included in the current collector 21 according to the embodiment of the present invention and the growth direction of the columnar particles.

An arrow D ₁ indicates the growth direction of the columnar particles parallel to the surface of the current collector 21. The arrow D _1, and the groove 211 (the length direction), and an angle alpha. As the height of the columnar particles (the thickness of the negative electrode active material layer) increases, the columnar particles become more easily connected to each other, but when α satisfies 0 ° <α <90 °, the connection between the columnar particles is effectively improved. Can be suppressed. This is because the distance between the columnar particles in the direction perpendicular to and parallel to the arrow D ₁ tends to be long. On the other hand, in the case of alpha = 0 °, since the columnar particles to the bottom of the trench 211 will grow, the distance between columnar particles becomes short easily in the direction parallel to the arrow D _1. Also, in the case of alpha = 90 °, since there is no component of the groove 211 in the direction of arrow D _1, the distance between columnar particles becomes short easily in the direction perpendicular to the arrow D _1. From the viewpoint of sufficiently preventing the connection between the columnar particles, it is preferable to satisfy 20 ° ≦ α ≦ 80 °.

The distance between adjacent grooves 211, that is, the width W1 of the region 212 defined by the plurality of grooves is preferably 10 μm to ₁ cm. If the width W ₁ is too wide, the effect of preventing the connection between the columnar particles becomes too small, and if the width W is too narrow, the effect of preventing the connection between the columnar particles becomes very large, but the capacity of the negative electrode decreases. To do.

  In FIG. 2, the plurality of groove portions 211 are all linear, but the shape of the groove portions is not limited to this. All the grooves may be linear or curved independently. Moreover, when all the groove parts are linear, it is not necessary for all the groove parts to be parallel.

FIG. 3 is a top view conceptually showing the relationship between the pattern of the plurality of grooves 311 included in the current collector 31 according to another embodiment of the present invention and the growth direction of the columnar particles.
Here, the plurality of groove portions 311 includes a plurality of first groove portions 311a and a plurality of second groove portions 311b, and the first groove portions 311a and the second groove portions 311b have different patterns.

Arrow D ₂ indicates the growth direction of columnar particles parallel to the surface of current collector 31. The arrow D ₂ and the first groove 311a (in the length direction) form an angle β, and the arrow D ₂ and the second groove 311b (in the length direction) form an angle γ. From the viewpoint of sufficiently preventing the connection between the columnar particles, it is preferable to satisfy 20 ° ≦ β ≦ 80 ° and 20 ° ≦ γ ≦ 80 °.

For the same reason as in FIG. 1, the distance W ₂ between the adjacent first groove portions 311a is preferably 10 μm to 1 cm, and the distance W ₃ between the adjacent second groove portions 311b is 10 μm to 1 cm. It is preferable.

  As described above, when the plurality of groove portions have two different patterns of groove portions, the area of the groove portions is doubled compared to the case of having only one pattern of groove portions, which is advantageous in terms of suppressing wrinkles. The plurality of groove portions may have three or more different groove portions.

  In the case where the plurality of groove portions have two different patterns of groove portions, the plurality of groove portions preferably form a lattice. The shape of the region in the lattice, that is, the region 312 partitioned by the plurality of grooves is, for example, a square, a rectangle, a parallelogram, or a rhombus. However, the shape of the region partitioned by the plurality of grooves is not limited to a quadrangle, and may be, for example, an ellipse or a circle.

In the case of FIG. 3, if β = γ = 45 °, the shape of the region partitioned by the plurality of grooves is a rectangle, and further, if W ₂ = W ₃ , it is a square. Further, when β and γ are different, the shape of the region defined by the plurality of grooves is a parallelogram, and when W ₂ = W ₃ , it is a rhombus.
1 to 3 do not limit the shape of the columnar particles. The shape of the columnar particles is not particularly limited.

The present invention is particularly effective when the columnar particles contain silicon element.
The columnar particles are made of, for example, at least one selected from the group consisting of a silicon simple substance, a silicon alloy, a compound containing silicon and oxygen, and a compound containing silicon and nitrogen. One of these may constitute an active material layer alone, or a plurality of these may constitute an active material layer. The compound containing silicon and nitrogen may further contain oxygen. As an example in which a plurality of types constitute an active material layer, an active material layer made of a compound containing silicon, oxygen, and nitrogen can be given. In addition, an active material layer formed of a composite of a plurality of silicon oxides having different ratios of silicon and oxygen can be given.

  The metal element M other than silicon contained in the silicon alloy is preferably a metal element that does not form an alloy with lithium. The metal element M may be any chemically stable electronic conductor, but is preferably at least one selected from the group consisting of titanium (Ti), copper (Cu), and nickel (Ni), for example. One kind of metal element M may be contained alone in the silicon alloy, or a plurality of kinds may be contained in the silicon alloy. The molar ratio of silicon to metal element M in the silicon alloy is preferably in the following range.

When the metal element M is Ti, 0 <Ti / Si <2 is preferable, and 0.1 ≦ Ti / Si ≦ 1.0 is particularly preferable.
When the metal element M is Cu, 0 <Cu / Si <4 is preferable, and 0.1 ≦ Cu / Si ≦ 2.0 is particularly preferable.
When the metal element M is Ni, 0 <Ni / Si <2 is preferable, and 0.1 ≦ Ni / Si ≦ 1.0 is particularly preferable.

The compound containing silicon and oxygen desirably has a composition represented by the general formula (1): SiO _x (where 0 <x <2). Here, the x value indicating the content of oxygen element is more preferably 0.01 ≦ x ≦ 1.

The compound containing silicon and nitrogen desirably has a composition represented by the general formula (2): SiN _y (where 0 <y <4/3). Here, the y value indicating the content of nitrogen element is more preferably 0.01 ≦ y ≦ 1.

The negative electrode for a lithium secondary battery of the present invention is produced using, for example, a vapor deposition apparatus 40 as shown in FIG.
The vapor deposition apparatus 40 includes a chamber 41 for realizing a vacuum atmosphere, an electron beam (not shown) as a heating means, a gas introduction pipe 42 for introducing gas into the chamber 41, and a fixing for fixing the current collector. It is equipped with a base 43. The gas introduction pipe 42 includes a nozzle 45 that discharges gas into the chamber 41. A fixing base 43 for fixing the current collector is installed above the nozzle 45. A target 46 that is deposited on the surface of the current collector to form columnar particles is installed below the fixed base 43.

  For example, when columnar particles made of silicon oxide are grown on the surface of the current collector, high-purity oxygen gas is released from the nozzle 45 using silicon alone as the target 46. When the target 46 is irradiated with the electron beam, the target is heated and vaporized. The vaporized silicon passes through the oxygen atmosphere and is deposited on the surface of the current collector as silicon oxide.

  In the vapor deposition apparatus 40, the positional relationship between the current collector and the target 46 can be changed according to the angle of the fixed base 43. That is, the inclination of the columnar particles is controlled by the angle θ formed by the normal direction of the surface of the current collector and the horizontal direction.

FIG. 5 conceptually shows the structure of an example of the lithium secondary battery of the present invention. FIG. 5 is a cross-sectional view of a stacked lithium secondary battery.
The battery 50 includes an electrode plate group including a positive electrode 51, a negative electrode 52, and a separator 53 interposed therebetween. The electrode group and the electrolyte having lithium ion conductivity are accommodated in the exterior case 54. The separator 53 is impregnated with an electrolyte having lithium ion conductivity. The positive electrode 51 includes a positive electrode current collector 51a and a positive electrode active material layer 51b supported on the positive electrode current collector 51a. The negative electrode 52 includes a negative electrode current collector 52a and a negative electrode active material supported on the negative electrode current collector 52a. It consists of a material layer 52b. One end of a positive electrode lead 55 and a negative electrode lead 56 is connected to the positive electrode current collector 51 a and the negative electrode current collector 52 a, respectively, and the other end is led out of the exterior case 54. The opening of the outer case 54 is sealed with a resin material.

  The positive electrode active material layer 51b releases lithium during charging, and occludes lithium during discharging. The negative electrode active material layer 52b occludes lithium during charging and releases lithium during discharging.

  FIG. 5 shows an example of a laminated lithium secondary battery. The negative electrode for a lithium secondary battery of the present invention is a cylindrical battery or a square battery having a spiral (winding) electrode group. Of course, it can also be applied.

  In the stacked battery, the electrodes may be stacked so that the total of the positive electrode and the negative electrode is three or more layers. However, a positive electrode having a positive electrode active material layer on both sides or one side so that all positive electrode active material layers face the negative electrode active material layer and all negative electrode active material layers face the positive electrode active material layer; Alternatively, a negative electrode having a negative electrode active material layer on one side is used. In this case, the inclined state of the columnar particles may be the same for all negative electrode active material layers, or may be different for each negative electrode active material layer. Furthermore, columnar particles having different inclination states may be formed in the same negative electrode. In the case of a negative electrode having negative electrode active material layers on both sides, the inclined state of the columnar particles on both sides may be the same or different.

Since the present invention is characterized by the structure of the negative electrode, the components other than the negative electrode are not particularly limited in the lithium secondary battery.
For example, lithium-containing transition metal oxides such as lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), and lithium manganate (LiMn ₂ O ₄ ) can be used for the positive electrode active material layer. It is not limited to.

  The positive electrode active material layer may be composed of only the positive electrode active material, or may be composed of a mixture containing the positive electrode active material, the binder, and the conductive agent. The positive electrode active material layer may be composed of a plurality of columnar particles in the same manner as the negative electrode active material layer. For the positive electrode current collector, Al, Al alloy, Ni, Ti, or the like can be used.

  Various lithium ion conductive solid electrolytes and non-aqueous electrolytes are used as the lithium ion conductive electrolyte. As the non-aqueous electrolyte, a lithium salt dissolved in a non-aqueous solvent is preferably used. The composition of the nonaqueous electrolyte is not particularly limited.

The separator and the outer case are not particularly limited, and materials used in various forms of lithium secondary batteries can be used.
EXAMPLES Next, although this invention is demonstrated concretely based on an Example, a following example does not limit this invention.

Example 1
A stacked lithium secondary battery as shown in FIG. 5 was produced.
(I) Production of positive electrode 10 g of lithium cobaltate (LiCoO ₂ ) powder having an average particle diameter of about 10 μm as a positive electrode active material, 0.3 g of acetylene black as a conductive agent, and polyvinylidene fluoride powder as a binder. 8 g and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were sufficiently mixed to prepare a positive electrode mixture paste.

  The obtained paste was applied to one side of a positive electrode current collector 51a made of an aluminum foil having a thickness of 20 μm, dried and then rolled to form a positive electrode active material layer 51b. Thereafter, the positive electrode was cut into a predetermined shape. The positive electrode active material layer carried on one side of the aluminum foil had a thickness of 70 μm and a size of 14.5 mm × 14.5 mm. A positive electrode lead 55 was connected to the back surface of the current collector not having the positive electrode active material layer.

(Ii) Production of Negative Electrode A negative electrode was produced using a vapor deposition apparatus (manufactured by ULVAC, Inc.) having an electron beam heating means (not shown) as shown in FIG.
The gas introduction pipe 42 included in the vapor deposition apparatus 40 was connected to an oxygen cylinder via a mass flow controller. From the nozzle 45, oxygen gas with a purity of 99.7% (manufactured by Nippon Oxygen Co., Ltd.) was released at a flow rate of 80 sccm.

  A fixing base 43 for fixing the negative electrode current collector was installed above the nozzle 45. The fixed base 43 was inclined so as to form an angle θ of 63 ° with the horizontal plane. An electrolytic copper foil (manufactured by Furukawa Circuit Foil Co., Ltd.) having a thickness of 35 μm and cut to a size of 80 mm × 15 mm was fixed to the fixing base 43 as a negative electrode current collector. However, a plurality of groove portions 211 having a pattern as shown in FIG. 2 were formed on one surface of the electrolytic copper foil by a cutting method before being fixed to the fixing base.

A target 46 to be deposited on the surface of the negative electrode current collector was installed vertically below the fixed base 43. As the target 46, a simple substance of 99.9999% silicon (manufactured by Kojundo Chemical Laboratory Co., Ltd.) was used.
Here, the surface roughness (Ra) of the electrolytic copper foil used as the negative electrode current collector was 2 μm, and the distance between the centers of the convex portions adjacent to each other was 9 μm.

The plurality of grooves 211 formed on one surface of the electrolytic copper foil had a depth (depth from a reference surface in Ra measurement) of 10 μm and a width of 10 μm. The interval between the plurality of groove portions 211, that is, the width W ₁ of the region 212 defined by the plurality of groove portions was 2 mm. The plurality of groove portions 211 were formed so as to form a 45 ° angle with the longitudinal direction of the electrolytic copper foil. And the electrolytic copper foil was fixed to the fixing stand so that the longitudinal direction of the electrolytic copper foil was parallel to the paper surface of FIG. That is, the angle α formed by the arrow D ₁ and the groove 211 is 45 °.

  In the above state, the negative electrode active material was deposited on the electrolytic copper foil for 30 minutes. At that time, the acceleration voltage of the electron beam applied to the silicon target 46 was set to -8 kV, and the emission was set to 500 mA. Since the vapor of silicon alone passes through the oxygen atmosphere and is deposited on the electrolytic copper foil placed on the fixing base 43, a negative electrode active material layer made of a compound containing silicon and oxygen (silicon oxide) is formed. It was. The negative electrode thus obtained was designated as negative electrode 1A. Thereafter, the negative electrode 1A was cut into a size of 15 mm × 15 mm. A negative electrode lead was connected to the back surface of the current collector having no negative electrode active material layer.

As a result of quantifying the amount of oxygen contained in the obtained negative electrode active material layer by a combustion method, the composition of silicon oxide was SiO _0.5 .
Next, the surface and cross section of the negative electrode 1A were observed with an electron microscope.
As a result of surface observation, the connection between the columnar particles was suppressed, and the angle θ formed by the columnar particles and the normal direction of the surface of the current collector was 45 °. The thickness of the negative electrode active material layer was 20 μm, and the center-to-center distance (pitch) between adjacent columnar particles was 9 μm. The diameter at the center height of the columnar particles was 5 μm.

Next, the porosity P of the negative electrode 1A was measured in the following manner using a mercury porosimeter (Autopore III 9410 manufactured by Shimadzu Corporation).
First, SiO _0.5 columnar particles are uniformly formed on one surface of a 15 mm × 15 mm size electrolytic copper foil (surface roughness Ra = 2 μm, thickness 35 μm) under the same conditions as described above, and a sample of the negative electrode 1A is prepared. Produced. The weight of the active material layer was determined by subtracting the weight of the copper foil from the weight of the obtained sample, and the true volume (VT) of the active material layer was determined from the density of SiO _0.5 . Next, mercury was intruded into the voids of the sample with a mercury porosimeter, and the volume (VH) of the invading mercury was determined. The porosity P was found to be 34% from the true volume (VT) of the active material layer and the volume (VH) of mercury that had entered the voids of the sample.

Hereinafter, the physical properties of the negative electrode 1A are summarized.
(Negative electrode current collector: electrolytic copper foil)
Thickness: 35μm
Surface roughness (Ra): 2 μm
Distance between centers of adjacent convex parts: 9 μm
Groove depth: 10 μm
Groove width: 10 μm
Distance W ₁ between adjacent grooves: 2 mm
Angle α formed by the growth direction (arrow D ₁ ) parallel to the surface of the current collector of the columnar particles and the groove portion: 45 °

(Negative electrode active material layer)
Composition: SiO _0.5
Size: 15mm x 15mm
Angle θ between the columnar particles and the normal direction of the surface of the current collector: 45 °
Thickness t: 20 μm
Distance between centers of adjacent columnar particles: 9 μm
Columnar particle diameter: 5 μm
Porosity P: 34%

(Iii) Production of test battery A positive electrode active material layer and a negative electrode active material layer were opposed to each other through a separator made of a polyethylene microporous film having a thickness of 20 μm manufactured by Asahi Kasei Co., Ltd. to form a thin electrode plate group. This electrode group was inserted into an outer case made of an aluminum laminate sheet together with the electrolyte. As the electrolyte, a nonaqueous electrolyte in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 1 and LiPF ₆ was dissolved at a concentration of 1.0 mol / L was used. The nonaqueous electrolyte was impregnated in the positive electrode active material layer, the negative electrode active material layer, and the separator, respectively. Thereafter, with the positive electrode lead and the negative electrode lead led out to the outside, the inside of the outer case was decompressed and the end of the case was welded with a resin material to complete the test battery. The obtained test battery is referred to as battery 1A.

<< Comparative Example 1 >>
A negative electrode was produced in the same manner as in Example 1 except that a plurality of grooves were not formed on the electrolytic copper foil. The obtained negative electrode was designated as negative electrode 1B.
Next, the cross section of the negative electrode 1B was observed with an electron microscope, and the porosity P of the negative electrode 1B was determined using a mercury porosimeter.
Hereinafter, the physical properties of the negative electrode 1B are summarized.

(Negative electrode current collector: electrolytic copper foil)
Thickness: 35μm
Surface roughness (Ra): 2 μm
Distance between centers of adjacent convex parts: 9 μm

(Negative electrode active material layer)
Composition: SiO _0.5
Size: 15mm x 15mm
Angle θ between the columnar particles and the normal direction of the surface of the current collector: 45 °
Thickness t: 20 μm
Distance between centers of adjacent columnar particles: 9 μm
Columnar particle diameter: 5 μm
Porosity P: 31%
A test battery 1B was produced in the same manner as in Example 1 except that the negative electrode 1B was used.

[Evaluation method]
(I) Charge / Discharge Characteristics The batteries 1A and 1B were each housed in a constant temperature room at 20 ° C. and charged by a constant current and constant voltage method. Here, the battery is charged at a constant current of 1C rate (1C is a current value that can use up the entire battery capacity in 1 hour) until the battery voltage reaches 4.2V, and after reaching 4.2V, the current value is The battery was charged at a constant voltage until reaching 0.05C.

  After charging, the battery was rested for 20 minutes, and then discharged at a constant rate of 1C rate until the battery voltage reached 2.5V. After discharging at a high rate, re-discharge was performed at a constant current of 0.2 C until the battery voltage reached 2.5V. After the re-discharge, it was paused for 20 minutes.

  The above charging / discharging was repeated 500 cycles. FIG. 6 shows the relationship between the number of cycles and the total discharge capacity (the sum of high-rate discharge and re-discharge).

At the beginning of the cycle, the ratio of the total discharge capacity to the charge capacity was determined as a percentage value as charge / discharge efficiency.
Further, at the beginning of the cycle, the ratio of the discharge capacity in the high rate discharge to the total discharge capacity was obtained as a percentage value as the high rate ratio.
Furthermore, the ratio of the total discharge capacity after 500 cycles to the total discharge capacity at the beginning of the cycle was determined as a percentage value as a capacity retention rate.
The results are shown in Table 1.

  As Table 1 and FIG. 6 show, there was almost no difference between the battery 1A and the battery 1A at the beginning of the cycle. On the other hand, the capacity maintenance rate after 500 cycles was significantly improved in the battery 1A compared to the battery 1B. This is considered to be because the current collector was suppressed from wrinkling and cutting during expansion during charging.

  Therefore, it was confirmed that it is effective in improving the cycle characteristics to form a plurality of grooves with a pattern as shown in FIG. 2 in the current collector. In the present embodiment, the pattern of FIG. 2 is adopted, but the same effect can be expected even if α is an angle other than 45 °.

Example 2
In the same manner as in Example 1, except that a plurality of groove portions 311 including a plurality of first groove portions 311a and a plurality of second groove portions 311b having a pattern as shown in FIG. 3 were formed on one surface of the electrolytic copper foil. Was made. The obtained negative electrode was designated as negative electrode 2A.
Next, the cross section of the negative electrode 2A was observed with an electron microscope, and the porosity P of the negative electrode 1B was determined using a mercury porosimeter.

Hereinafter, the physical properties of the negative electrode 2A are summarized.
(Negative electrode current collector: electrolytic copper foil)
Thickness: 35μm
Surface roughness (Ra): 2 μm
Distance between centers of adjacent convex parts: 9 μm
Depth of first groove: 10 μm
Width of first groove: 10 μm
Second groove depth: 10 μm
Second groove width: 10 μm
Distance W ₂ between adjacent first groove portions: 2 mm
Distance W ₃ between adjacent second groove portions: 2 mm
Angle β formed by the growth direction (arrow D ₂ ) parallel to the surface of the current collector of the columnar particles and the first groove portion: 45 °
Angle γ formed by the growth direction (arrow D ₂ ) parallel to the surface of the current collector of the columnar particles and the second groove portion: 45 °

(Negative electrode active material layer)
Composition: SiO _0.5
Size: 15mm x 15mm
Angle θ between the columnar particles and the normal direction of the surface of the current collector: 45 °
Thickness t: 20 μm
Distance between centers of adjacent columnar particles: 9 μm
Columnar particle diameter: 5 μm
Porosity P: 37%

A test battery 2A was produced in the same manner as in Example 1 except that the negative electrode 2A was used.
Evaluation similar to Example 1 was performed about the battery 2A. Table 2 shows the charge / discharge efficiency, high rate ratio, and capacity retention rate after 500 cycles.

  As shown in Table 2, a high capacity retention rate was obtained as in the case of the battery 1A even when a plurality of grooves were formed in the current collector in a pattern as shown in FIG. This is presumably because the current collector was sufficiently suppressed from wrinkling and cutting during expansion during charging. In this embodiment, the lattice pattern as shown in FIG. 3 is adopted. However, even if β and γ are angles other than 45 °, the same effect can be expected even if β and γ are different.

  A current collector and a negative electrode active material layer, the negative electrode active material layer includes a plurality of columnar particles, and the plurality of columnar particles grow in an oblique direction with respect to a normal direction of a surface of the current collector. In the negative electrode for a lithium secondary battery, the stress due to the volume change of the active material can be relieved by forming a plurality of grooves on the surface of the current collector. Therefore, wrinkles and breakage of the current collector are reduced, and deterioration of cycle characteristics is suppressed. For this reason, by using the negative electrode of the present invention, it is possible to produce a high-capacity lithium secondary battery excellent in reliability such as cycle characteristics.

1 is a conceptual cross-sectional view parallel to a growth direction of columnar particles of a negative electrode for a lithium secondary battery according to an embodiment of the present invention. It is a top view which shows notionally the relationship between the pattern of the some groove part which the electrical power collector which concerns on one Embodiment of this invention has, and the growth direction of columnar particle | grains. It is a top view which shows notionally the relationship between the pattern of the some groove part which the collector which concerns on another one Embodiment of this invention has, and the growth direction of columnar particle | grains. It is the schematic of the vapor deposition apparatus used for preparation of the negative electrode for lithium secondary batteries of this invention. 1 is a cross-sectional view of a stacked lithium secondary battery according to an embodiment of the present invention. It is a figure which shows the relationship between the charging / discharging cycle number of the lithium secondary battery of Example 1 and Comparative Example 1, and total discharge capacity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Negative electrode 11, 21, 31 Current collector 12 Negative electrode active material layer 111, 211, 311 Groove part 112, 212, 312 Area | region divided by several groove part 121 Columnar particle 311a 1st groove part 311b 2nd groove part 40 Vapor deposition apparatus 41 Chamber 42 Gas introduction pipe 43 Fixing base 45 Nozzle 46 Target 50 Battery 51 Positive electrode 51a Positive electrode current collector 51b Positive electrode active material layer 52 Negative electrode 52a Negative electrode current collector 52b Negative electrode active material layer 53 Separator 54 Exterior case 55 Positive electrode lead 56 Negative electrode lead

Claims (8)

A negative electrode for a lithium secondary battery, comprising: a current collector; and a negative electrode active material layer, wherein the negative electrode active material layer includes a plurality of columnar particles,
The surface of the current collector includes a plurality of grooves, and two or more regions partitioned by the plurality of grooves,
The two or more regions partitioned by the plurality of grooves carry the plurality of columnar particles,
Wherein the plurality of columnar particles with respect to the normal direction of the surface of the current collector, has grown in an oblique direction,
A negative electrode for a lithium secondary battery , wherein an angle α formed by a growth direction of the columnar particles parallel to the surface of the current collector and the plurality of grooves satisfies 0 <α <90 ° . A negative electrode for a lithium secondary battery, comprising: a current collector; and a negative electrode active material layer, wherein the negative electrode active material layer includes a plurality of columnar particles,
The surface of the current collector includes a plurality of grooves, and two or more regions partitioned by the plurality of grooves,
The plurality of groove portions include a plurality of first groove portions and a plurality of second groove portions,
The first groove portion and the second groove portion have different patterns and intersect each other,
The two or more regions partitioned by the plurality of grooves carry the plurality of columnar particles,
The plurality of columnar particles grow in an oblique direction with respect to the normal direction of the surface of the current collector,
An angle β formed by a growth direction of the columnar particles parallel to the surface of the current collector and the first groove satisfies 0 ° <β <90 °,
  An anode for a lithium secondary battery, wherein an angle γ formed by a growth direction of the columnar particles parallel to the surface of the current collector and the second groove satisfies 0 ° <γ <90 °. The negative electrode for a lithium secondary battery according to claim 2 , wherein the shape of the two or more regions partitioned by the plurality of grooves is a square, a rectangle, a parallelogram, or a rhombus. The active material layer includes at least one selected from the group consisting of a silicon simple substance, a silicon alloy, a compound containing silicon and oxygen, and a compound containing silicon and nitrogen . The negative electrode for lithium secondary batteries as described in 2. The negative electrode for a lithium secondary battery according to claim 4 , wherein the silicon alloy is an alloy of silicon and a metal element M, and the metal element M does not form an alloy with lithium. The negative electrode for a lithium secondary battery according to claim 5 , wherein the metal element M is at least one selected from the group consisting of titanium, copper, and nickel. The compound containing silicon and oxygen has the general formula (1): SiOx (where 0 <x <2)
The negative electrode for lithium secondary batteries of Claim 4 which has a composition represented by these. A negative electrode for a lithium secondary battery according to any one of claims 1 7, positive electrode and lithium secondary battery comprising a lithium ion conductive electrolyte, a containing capable of absorbing and desorbing lithium ions positive electrode active material .

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