JP2014038795A - Lithium ion secondary battery electrode manufacturing method, manufacturing apparatus, and lithium ion secondary battery electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery electrode having excellent and stable performance even when a silicone-based active substance material having a large volume change in charge/discharge cycles is used, and a technique of manufacturing the same.SOLUTION: In the present invention, a stripe-like active material pattern 121 is formed in such a way that, when the pattern width in an uncharged state at a height H2 which is half a peak height H1 from the surface of a current collector 11 is represented by W, the active material pattern width in a charged state is represented by Wc, and an adjacent pattern interval is represented by S, and (Wc/W) is defined as an expansion coefficient n, then the expression S/W≥n/20 is satisfied, whereby a capacity reduction in expansion/contraction cycles can be restrained.

Description

  The present invention relates to a structure of a battery electrode suitable for a lithium ion secondary battery and a technique for manufacturing the same.

  Among the electrodes for lithium ion secondary batteries, in particular, as a negative electrode, a material using a carbon material such as graphite as an active material has been put into practical use because of physical properties such as discharge potential and energy density. In recent years, it has been studied to use silicon or a compound thereof having a charge / discharge capacity per unit mass per unit volume larger than that of a carbon material as an active material. However, silicon-based active materials have a large volume change in the process of occlusion / release of lithium ions, and particularly in secondary battery applications, the lifetime (cycle characteristics) is remarkably shortened, so that they have not been put into practical use.

  For example, Patent Document 1 discloses a configuration example of a secondary battery using a silicon-based active material. Patent Document 1 describes a configuration in which a negative electrode is formed by forming an amorphous silicon thin film having a columnar structure by RF sputtering on the surface of a copper foil functioning as a current collector.

JP 2012-038737 A (for example, paragraph 0071, FIG. 2)

  In Patent Document 1, the stress caused by expansion / contraction in the charge / discharge cycle is alleviated by the cuts formed in the active material film, thereby suppressing the peeling of the active material film, thereby reducing the cycle characteristics of the electrode. It is going to be improved. However, in the above prior art, a columnar structure is obtained by causing a cut in a thin portion appearing in the active material film due to the unevenness on the surface of the current collector film. For this reason, the structure of the obtained active material film depends on the surface state of the current collector film at the time of film formation, and there is a problem that the reproducibility and stability of performance are lacking.

  As described above, a technique for producing a battery electrode that uses an active material having a large volume change in a charge / discharge cycle and has good performance and stability has not been established so far.

  The present invention has been made in view of the above problems, and provides an electrode for a lithium ion secondary battery having good performance and stability even when an active material having a large volume change in a charge / discharge cycle is used, and a manufacturing technique thereof. For the purpose.

  In order to achieve the above object, an electrode for a lithium ion secondary battery according to the present invention includes a base material functioning as a current collector and an active material formed on the base material surface and spaced apart from each other. And a plurality of striped active material patterns protruding from the material surface.

  Moreover, in order to achieve the above object, a method for manufacturing an electrode for a lithium ion secondary battery according to the present invention includes a nozzle body in which a plurality of discharge ports are arranged in a row along a predetermined arrangement direction, and a current collector A substrate that functions as a step of disposing each of the discharge ports in close proximity to the surface of the substrate, and while discharging a coating liquid containing an active material from each of the discharge ports, A plurality of stripe-shaped active material patterns protruding from the substrate surface separated from each other by moving the nozzle body relative to the substrate along the surface of the substrate in a direction intersecting the array direction of the discharge ports Forming on the substrate surface.

  In addition, in order to achieve the above object, the apparatus for manufacturing an electrode for a lithium ion secondary battery according to the present invention has a plurality of discharge ports arranged in a line along a predetermined arrangement direction, and is activated from each of the discharge ports. A nozzle body that continuously discharges a coating liquid containing a material, and a holding unit that holds a base material functioning as a current collector in a state in which each of the discharge ports is in close proximity to the surface of the base material; Moving means for relatively moving the nozzle body and the base material so that the discharge port moves along the surface of the base material, while moving the nozzle body and the base material relatively An active material pattern is formed on the substrate surface by discharging the coating liquid from each of a plurality of discharge ports onto the substrate surface.

In these inventions, the width of the active material pattern at a height half the height of the top of the active material pattern from the surface of the base material is W, and the interval at the height between adjacent active material patterns is S, When an expansion coefficient defined as a ratio of a width after charging to a width before charging of the active material pattern at the height is n, the following formula:
S / W ≧ ⁿ 2/20
So that the relationship is satisfied.

  As will be described in detail later, the inventors of the present application have a very small capacity drop in repeated charge / discharge cycles when a combination of the width W, the interval S, and the expansion coefficient n of the active material pattern is selected so that the above conditions are satisfied. It was found that it can be suppressed. That is, by forming a stripe-shaped active material pattern that satisfies the above relational expression on the substrate surface, the present invention provides good and stable performance even when using an active material having a large volume change in the charge / discharge cycle. It is possible to obtain the lithium ion secondary battery electrode.

  Here, for example, the plurality of active material patterns may be parallel to each other, the widths may be equal to each other, and the interval between adjacent active material patterns may be constant. In this way, a plurality of active material patterns having the same cross-sectional shape can be formed on the substrate surface by arranging them at a constant pitch, and the performance of expansion / contraction of each active material pattern is uniform in the charge / discharge cycle. Can be made more stable.

  As the active material, for example, silicon or a compound thereof can be used. These silicon-based active material materials are known to have a larger volume change in charge / discharge cycles, although a larger capacity can be obtained than carbon materials such as graphite. By applying the present invention when using a silicon-based active material, it is possible to achieve both high capacity and excellent charge / discharge cycle characteristics.

  For example, the coating liquid may further contain a conductive additive. When a conductive additive is contained together with the active material, the amount of expansion of the active material pattern is reduced by reducing the content of the active material in the active material pattern. In other words, the amount of expansion of the active material pattern can be controlled by controlling the mixing ratio of the active material and the conductive additive. By utilizing this fact, it is possible to manufacture a battery electrode that balances the capacity and cycle characteristics as an electrode.

  In these inventions, for example, the opening shapes of the plurality of discharge ports may be equal to each other and the arrangement pitch of the discharge ports in the arrangement direction may be constant. In this way, a plurality of active material patterns having the same cross-sectional shape can be formed on the substrate surface by arranging them at a constant pitch, and the performance of expansion / contraction of each active material pattern is uniform in the charge / discharge cycle. Can be made more stable.

  Further, for example, the interval in the width direction perpendicular to the extending direction of the active material patterns between adjacent active material patterns may be made smaller than the width of the active material pattern in the width direction. Increasing the interval between the active material patterns increases the margin for expansion of the active material, but decreases the capacity because the amount of active material per area as an electrode decreases. According to the knowledge of the inventors of the present application, since the expansion amount during charging of a typical active material is about twice in the width direction, it is useless to provide an interval larger than the width of the active material pattern. By providing an interval smaller than the pattern width, it is possible to manufacture a battery electrode in which the capacity as the electrode and the cycle characteristics are balanced.

  Further, for example, the coating liquid may be discharged from a discharge port whose opening width in the width direction is smaller than the width of the active material pattern, and the coating liquid may be spread on the substrate surface after the discharge. In order to achieve both high capacity and excellent cycle characteristics, the cross-sectional shape of the active material pattern and the interval between adjacent patterns must be fine. In particular, in order to reduce the pattern interval, it is necessary to reduce the interval between adjacent discharge ports in the nozzle body, and the discharge port peripheral member becomes thin, and its strength can be a problem. By spreading the coating liquid on the surface of the substrate after ejection, the interval between the ejection ports may be larger than the pattern interval after completion, so that such a problem can be avoided.

  Further, for example, the expansion coefficient can be controlled by adjusting the mixing ratio of the active material and the conductive additive. The expansion of the active material pattern during charging is caused by the occlusion of lithium ions by the active material, and the expansion amount depends on the content of the active material in the pattern. It is possible to control the expansion coefficient by adding a conductive aid and changing the ratio of the active material. This can be used to satisfy the above relation. For example, when the dimensions of the active material pattern are limited, the above relationship can be satisfied by adjusting the expansion coefficient of the active material pattern.

  According to the present invention, an active material having a large volume change in the charge / discharge cycle can be obtained by appropriately selecting a combination of the width W of the active material pattern, the interval S, and the expansion coefficient n which is a physical property value of the active material pattern itself. Even when used, it is possible to obtain an electrode for a lithium ion secondary battery having good performance and stability.

It is a figure which shows the structural example of the battery manufactured using this invention. It is a figure which shows typically the manufacturing process of a negative electrode. It is a figure which shows the relationship between the dimension of a discharge outlet and an active material pattern. It is a figure explaining the definition of an expansion coefficient. It is a figure which shows the example of the relationship between a composition of an active material pattern, and an expansion coefficient. It is a figure which shows the example of the change of the discharge capacity in a charging / discharging cycle. It is a figure which shows the example of an experimental result. It is a flowchart which shows the one aspect | mode of an electrode manufacturing process. It is a figure which shows the other structural example of an electrode manufacturing apparatus.

  FIG. 1 is a diagram showing a configuration example of a battery manufactured using the present invention. More specifically, FIG. 1A is a schematic diagram showing a cross-sectional structure of a lithium ion secondary battery module that employs an embodiment of an electrode for a lithium ion secondary battery according to the present invention as a negative electrode, and FIG. b) is a perspective view showing the negative electrode. In this lithium ion secondary battery module 1, the negative electrode active material layer 12, the electrolyte layer 13 having the separator 131 and the electrolytic solution 132, the positive electrode active material layer 14, and the positive electrode current collector 15 are sequentially arranged on the negative electrode current collector 11. It has a laminated structure. In this specification, the X, Y, and Z coordinate directions are defined as shown in FIG.

  FIG. 1B shows the structure of a negative electrode 10 formed by forming a negative electrode active material layer 12 on the surface of the negative electrode current collector 11. As shown in FIG. 1B, the negative electrode active material layer 12 has a line and space structure in which a large number of striped patterns 121 extending along the Y direction are arranged at regular intervals in the X direction.

  On the other hand, the positive electrode has a structure in which the positive electrode active material layer 14 is laminated almost uniformly on the surface of the positive electrode current collector 15. Then, the positive electrode and the negative electrode 10 configured as described above are overlapped through the separator 131 with the respective active material layers facing inward, and the electrolyte solution 132 is impregnated in the gap, whereby the lithium ion secondary A battery module 1 is formed. The lithium ion secondary battery module 1 is appropriately provided with a tab electrode, or a plurality of modules are stacked to form a lithium ion secondary battery.

Here, as the material constituting each layer of the lithium ion secondary battery module 1, for example, an aluminum foil or a copper foil can be used as the positive electrode current collector 15 and the negative electrode current collector 11, respectively. As the positive electrode active material layer 14, known materials as a positive electrode active material may be, for example, LiCoO _2, LiMnO _2, and mixtures thereof. The separator 131 is, for example, a polypropylene (PP) sheet, and the electrolyte solution 132 is, for example, a lithium salt as a supporting salt, for example, a mixture of ethylene carbonate and diethyl carbonate containing lithium hexafluorophosphate (LiPF ₆ ) ( EC / DEC) can be used. The material of each functional layer is not limited to these.

  As the negative electrode active material layer 12, single crystal silicon particles or amorphous silicon particles, or a silicon compound such as SiO or SiOC can be used. Lithium ion secondary batteries have been put into practical use so far, for example, using a carbon material such as graphite as a negative electrode active material, but silicon-based active materials have a higher specific capacity than carbon-based active materials. (Typically, about 4000 mAh / g for single crystal silicon versus about 370 mAh / g for graphite), it is possible to construct a battery with a larger charge / discharge capacity.

  However, in a material that acts as a negative electrode active material by forming an alloy with lithium, such as a silicon-based active material, the volume change of the active material in the lithium ion storage / release cycle accompanying charge / discharge is large. For this reason, due to the repeated expansion and contraction in the charge / discharge cycle, the active material layer is broken or peeled off from the current collector layer, and the capacity gradually decreases. That is, when a material having a large volume change due to charge / discharge is used as an active material, the charge / discharge cycle characteristics of the electrode may become a problem.

  Therefore, in this embodiment, the negative electrode current collector layer 12 having a line-and-space structure is formed as shown in FIG. 1B, and the pattern 121 is formed by the gap space formed between the plurality of stripe-shaped patterns 121. The volume change can be absorbed. That is, by making each active material pattern 121 into a stripe shape extending in a uniaxial direction, each active material pattern 121 is suppressed from expanding in a random direction, and the direction of expansion is perpendicular to the pattern extending direction. It can be limited. Then, by providing a gap in the direction in which the pattern expands, stress applied to the pattern due to expansion can be relaxed, and damage or peeling of the pattern can be prevented.

  As one method for forming such a pattern, there is a method in which a paste-like coating liquid containing an active material is applied to the surface of the negative electrode current collector 11 in a stripe shape and cured. Hereinafter, the manufacturing process of the negative electrode by such a coating technique will be described.

  FIG. 2 is a diagram schematically showing the manufacturing process of the negative electrode. More specifically, FIG. 2A is a diagram showing a main configuration in an example 20 of an electrode manufacturing apparatus for manufacturing the negative electrode 10, and FIG. 2B is a discharge port 211 on the lower surface of the nozzle body 21. It is a figure which shows arrangement | positioning. FIG. 2C is a perspective view showing the process of manufacturing the negative electrode by the electrode manufacturing apparatus 20.

  As shown in FIG. 2A, the negative electrode active material layer 12 having the line-and-space structure as described above has a nozzle body 21 that continuously discharges a coating liquid L containing a negative electrode active material material as a negative electrode current collector 11. It can be manufactured by moving the nozzle body 21 and the negative electrode current collector 11 relatively to each other. More specifically, the electrode manufacturing apparatus 20 has a movable stage 22 whose upper surface is substantially flat and has a mounting surface on which the negative electrode current collector 11 can be mounted. The movable stage 22 is driven by a stage drive mechanism 23 and can move horizontally in the Y direction. Further, above the negative electrode current collector 11 placed on the upper surface of the movable stage 22, as shown in FIG. 2B, a nozzle body 21 having a plurality of discharge ports 211 provided on the lower surface along the X direction. Is placed. At this time, the discharge port 211 provided on the lower surface of the nozzle body 21 is disposed in close proximity to the surface of the negative electrode current collector 11. A paste-like coating liquid containing a negative electrode active material is stored inside the nozzle body 21.

  As the coating solution, the above-described negative electrode active material is kneaded with, for example, polyvinylidene fluoride (PVDF) or polyamideimide as a binder, for example N-methylpyrrolidone (NMP) as a solvent, and the viscosity is appropriately adjusted. What was adjusted to can be used. Further, as will be described later, for example, a conductive additive such as acetylene black or carbon black may be further added.

  When the stage drive mechanism 23 moves the movable stage 22, relative movement between the negative electrode current collector 11 and the nozzle body 21 is realized. That is, when the movable stage 22 is driven in the arrow direction Ds, the nozzle body 21 relatively moves along the surface of the negative electrode current collector 11 in the arrow direction Dn. In this way, the negative electrode current collector 11 and the nozzle body 21 are moved relative to each other, and the coating liquid L discharged from the respective discharge ports 211 is applied to the negative electrode current collector 11, whereby the negative electrode current collector 11. A large number of stripe-shaped active material patterns 121 parallel to each other along the nozzle movement direction Dn are formed on the surface.

  Such a coating method is called a so-called nozzle scan method. A technique for applying a coating solution to a substrate by a nozzle scanning method is known, and such a known technique can also be applied to this method, and therefore a detailed description of the apparatus configuration is omitted.

  FIG. 3 is a diagram showing the relationship between the dimensions of the discharge port and the active material pattern. More specifically, FIG. 3A is a diagram showing the relationship between the dimensions of the discharge ports 211 and the cross-sectional shape of the pattern 121. FIGS. 3B to 3D are diagrams showing other examples of the pattern cross-sectional shape. As shown in FIG. 3A, the plurality of discharge ports 211 provided on the lower surface of the nozzle body 21 all have the same opening shape and dimensions. Specifically, each discharge port 211 has a rectangular opening shape having an opening length L1 in the X direction and an opening length L2 in a direction orthogonal to the opening length L1, and they are equally spaced along the X direction ( They are arranged in a line at an arrangement pitch P). As examples of dimensions of each part, for example, L1 = 40 μm, L2 = 30 μm, and P = 60 μm can be set. In this case, the interval D between the ejection ports 211 in the X direction is 20 μm.

  The cross-sectional shape of the active material pattern 121 formed on the surface of the negative electrode current collector 11 by the coating liquid ejected from the ejection port 211 having such dimensions is the ejection port 211 when the coating liquid has a very high viscosity. It is considered that the opening shape is almost the same. However, it is not easy to form a pattern by extruding such a high-viscosity coating solution in order to maintain the cross-sectional shape strictly, and a coating solution having a certain degree of fluidity (that is, a low viscosity) is used. Is more realistic.

  When the coating liquid having such fluidity is discharged from the discharge port 211 and applied to the negative electrode current collector 11, the opening width of the discharge port 211 is formed on the negative electrode current collector 11 as shown in FIG. The active material pattern 121 is formed in a state where the width is wider than L1. In addition, the portion corresponding to the corner of the rectangular shape of the discharge port 211 has a rounded shape. As the width of the active material pattern 121 increases, the interval between adjacent active material patterns 121 is slightly smaller than the interval between adjacent discharge ports 211.

  Considering that the cross-sectional shape of the active material pattern 121 is not necessarily rectangular, the width of each active material pattern 121 and the interval between them are defined as follows. When the height of the top of the active material pattern 121 from the surface of the negative electrode current collector 11 is H1, the height H2 is half of that, that is, the height of 0.5H1 from the surface of the negative electrode current collector 11 is along the X direction. A dimension of the pattern 121 is a pattern width W, and a distance between adjacent patterns along the X direction at the height is a pattern interval W.

  As described above, due to the fluidity of the coating liquid, the width W of the pattern to be formed is wider than the width 211 of the discharge port 211, while the pattern interval S is narrower than the interval D of the discharge port 211. This is advantageous when it is desired to form the active material pattern 121 at a narrow interval. In order to increase the capacity as an electrode, it is necessary to increase the amount of active material supported on the surface of the negative electrode current collector 11, and for this purpose, a large number of stripe patterns must be formed at narrow intervals. preferable. On the other hand, reducing the interval D between the plurality of discharge ports 211 in the nozzle body 21 leads to a decrease in the thickness of the members constituting the side walls of the discharge ports 211, and the strength around the discharge ports 211 is reduced. The problem arises.

  By spreading the coating liquid laterally after ejection and increasing the pattern width W, the interval D between the ejection ports 211 can be made larger than the designed pattern interval S, and such a decrease in strength is avoided. Is possible. In order to set the pattern width W and the interval S to the values as designed, coating such as the viscosity of the coating liquid, the shape of the discharge port 211, the discharge amount of the coating liquid, the relative movement speed between the nozzle body 21 and the negative electrode current collector 11, and the like. Although the conditions need to be managed with high accuracy, the coating technique based on the nozzle scan method has a sufficient track record to meet such demands. For example, it is possible to form an active material pattern having a pattern height H1 = 20 μmm, a pattern width W = 50 μm, and a pattern interval S = 10 μm using the nozzle body 21 having the above-described dimension example. On the other hand, in the above-mentioned Patent Document 1, it is difficult to say that a technique for arranging the voids for absorbing the expansion of the active material in the active material layer systematically and with good controllability is established.

  The cross-sectional shape of the active material pattern is not limited to the above, and various shapes can be considered depending on the opening shape of the discharge port, the viscosity of the coating liquid, and the like. Some examples are shown in FIGS. 3B to 3D. 3B shows an example of an active material pattern having a trapezoidal cross section, FIG. 3C shows an example of an active material pattern having a triangular cross section, and FIG. 3D shows an inverted trapezoidal cross section. Each example of an active material pattern is shown. Further, a shape with rounded corners is also conceivable. For patterns of these arbitrary shapes, as shown in FIGS. 3B to 3D, the pattern width W and the pattern interval S are set as the pattern size and interval at half the pattern height. It is possible to define.

  As described above, in an active material material that occludes lithium by forming an alloy, such as a silicon-based active material, the volume change of the active material layer in the charge / discharge cycle is large. Since the active material layer 12 of this embodiment is composed of the stripe-shaped active material pattern 121, the dimensional change in the longitudinal direction is suppressed, and the expansion of the material accompanying charging appears as a bulge of the cross-sectional shape. In particular, since the expansion of the top side of the active material pattern 121 is restricted by the separator 131 and the counter electrode, the cross section mainly expands laterally. Here, an expansion coefficient n is introduced as a parameter that quantitatively represents the degree of expansion of the active material pattern 121, and is defined as follows.

FIG. 4 is a diagram for explaining the definition of the expansion coefficient. In the active material pattern 121 in FIG. 4A, the cross-sectional shape before charging (or discharging state) is indicated by a solid line, and the cross-sectional shape in charging state is indicated by a dotted line. From the above definition, the width W of the pattern 121 in the discharged state can be expressed by the pattern dimension at the height H2 that is half of the pattern height H1. On the other hand, the width Wc of the pattern 121 in the charged state is also expressed by the pattern dimension at the same height H2. And the pattern width of the charged state with respect to the pattern width in the discharged state, that is,
n = Wc / W (Formula 1)
Is defined as the expansion coefficient of the pattern. The expansion coefficient n is a value that depends on the composition of the active material layer.

  The expansion coefficient n can be measured as follows. As shown in FIG. 4B, a metal foil current collector T1, a separator T3, and a lithium metal foil T4 on which a stripe-shaped active material pattern T2 to be measured is laminated, and an electrolytic solution (not shown) is used. A test piece T0 is prepared by impregnation. The separator T3 and the lithium metal foil T4 are respectively provided with observation small holes T31 and T41 at corresponding positions. The silicon-based active material is intended to function as a negative electrode active material in the present embodiment, but acts as a positive electrode when a lithium metal foil is combined as a counter electrode. However, this does not affect experiments aimed at obtaining the expansion coefficient n. This is because there is no change in the process of occlusion / release of lithium ions regardless of whether it is used for positive or negative electrodes.

  As shown in FIG. 4 (c), the test piece T0 thus created is connected to a charge / discharge measuring instrument T5 to perform a charge / discharge operation. For example, the active material pattern T2 is passed through small holes T31 and T41 by a laser microscope. Is observed in-situ and the dimensions are measured. Thus, the pattern width Wc in the charged state and the pattern width W in the discharged state can be obtained, and the expansion coefficient n can be obtained. The method of obtaining the expansion coefficient n is not limited to this, and other methods may be used as long as the pattern width can be compared between the charged state and the discharged state.

  The inventors of the present application conducted an experiment described below for the purpose of finding conditions under which an electrode having excellent charge / discharge cycle characteristics can be formed using an active material having a large volume change due to charge / discharge. In this experiment, a plurality of active material patterns having different compositions (and thus different expansion coefficients n) were prepared with various dimensions, and the charge / discharge cycle characteristics were evaluated.

  FIG. 5 is a diagram showing an example of the relationship between the composition of the active material pattern and the expansion coefficient. Here, a single crystal silicon powder was used as an active material, and a polyamideimide as a binder was added and mixed into an NMP solvent and kneaded to be used as a coating solution. Moreover, the content ratio of the active material in an active material pattern was changed by mixing carbon black as a conductive support agent.

  In the negative electrode material 1 as an example, the solid component excluding the solvent is 90% by weight of single crystal silicon powder, 10% by weight of polyamideimide, and no carbon black is added. The expansion coefficient n at this time was 1.95. This indicates that the pattern width W expands to nearly twice due to charging.

  In the negative electrode material 2, 44% by weight of carbon black was added, and the content of the single crystal silicon powder was 46% by weight. The content of polyamideimide is 10% by weight. The expansion coefficient n is 1.75, which is smaller than that of the negative electrode material 1, because the content of silicon having a large volume change is reduced. Furthermore, in the negative electrode material 3 in which the content of the single crystal silicon powder was reduced to 19% by weight and 71% by weight of carbon black and 10% by weight of polyamideimide were included, the expansion coefficient n was 1.42.

  The carbon-based active material currently in practical use has a silicon content of 0 and functions as an active material in carbon black (more generally, graphite) as shown in FIG. 5 as a “conventional example”. Equivalent to what you have. In this case, the expansion coefficient n is about 1.05, which is sufficiently smaller than the silicon-based active material. Therefore, the charge / discharge cycle characteristics are good.

  Note that when the silicon content in the active material pattern is lowered, the expansion coefficient n is reduced, but the amount of lithium that can be occluded is also reduced, and the capacity as an electrode is reduced. On the other hand, when the silicon content is increased, the charge / discharge capacity is increased, but the expansion coefficient n is increased, and a decrease in capacity over time due to expansion / contraction in the charge / discharge cycle can be a problem. To solve this problem, the active material layer has a line-and-space structure, which can relieve stress and suppress the decrease in capacity. However, if the gap of the active material pattern is increased to absorb the expansion, the active material layer is substantially activated. The amount of material is reduced and the capacity itself is reduced.

  In this way, when using an active material having a large volume change due to charge and discharge, there is a trade-off that if the cycle characteristics are emphasized, the capacity decreases, and if the capacity is increased, the cycle characteristics deteriorate. The conditions for achieving both excellent charge / discharge cycle characteristics have not been established so far.

  The inventors of the present application achieve both high capacity and charge / discharge cycle characteristics by appropriately combining the expansion coefficient n of the active material and the pattern dimensions (pattern width W and interval S) through experiments described below. It was found that an electrode can be produced.

  In the experiment, a negative electrode was prepared by the above-described method using a plurality of coating liquids having different compositions, a 2032 type coin battery was made in combination with the separator and the positive electrode, and charge / discharge cycle characteristics were measured. A rolled copper foil having a thickness of 10 μm was used as the negative electrode current collector, and a plurality of types of negative electrode electrodes were produced by changing the composition and dimensions of the coating solution.

As the positive electrode, 20 μm thick rolled aluminum foil was mixed with LiCoO ₂ (LCO) as a positive electrode active material, carbon black as a conductive auxiliary agent, and PVDF as a binder at a weight ratio of 8: 1: 1. A solution obtained by uniformly applying a coating solution obtained by mixing the smelted material in an NMP solvent with a blade coater and drying the coating solution was used. Further, a PP sheet was used as the separator, and an EC / DEC mixture in which 1 mol / dm ³ of LiPF ₆ was dissolved was used as the electrolyte.

The evaluation of the charge / discharge cycle characteristics was carried out by charging / discharging 10 cycles at 25 ° C. at a 0.1 C rate and a cut-off voltage of 0 to 2.0 V (full cell), and measuring the discharge capacity in each cycle. :
(Capacity maintenance ratio) = (Discharge capacity at the 10th cycle) / (Discharge capacity at the 1st cycle) × 100 [%] (Equation 2)
This was done by calculating the capacity retention rate defined in Hereinafter, a part of the result will be described.

  FIG. 6 is a diagram illustrating an example of a change in discharge capacity in a charge / discharge cycle. Here, a sample was used in which the negative electrode material 1 of FIG. 5 was used, the pattern width W was constant (50 μm), and the pattern interval S was changed to produce an active material pattern. FIG. 6 shows the discharge capacity for each charge / discharge cycle with the initial capacity being 100% and the ratio value (S / W) between the pattern interval S and the pattern width W as parameters. The range of the pattern interval S was 6 μm (S / W = 0.12) to 12 μm (S / W = 0.24).

  When the ratio S / W between the pattern interval S and the pattern width W is relatively large, the change in the discharge capacity for each cycle is slight. On the other hand, when the value of this ratio becomes smaller than a certain level, the discharge capacity rapidly increases for each cycle. The tendency to decrease can be seen from FIG. In this experiment, a condition in which the capacity at the 10th cycle maintained 90% or more of the initial capacity was determined as a non-defective product, and the conditions for obtaining a non-defective product were searched.

  FIG. 7 is a diagram showing an example of experimental results. More specifically, FIG. 7A shows the ratio between the pattern interval S and the pattern width W, which was measured by using the negative electrode material 1 and changing the pattern interval S in various ways with the pattern width W being 50 μm and 70 μm. It is a figure which shows the relationship between S / W and the capacity | capacitance maintenance factor after 10 cycles. Moreover, FIG.7 (b) and FIG.7 (c) have shown the result of having conducted the same experiment using the negative electrode material 2 and the negative electrode material 3, respectively.

  From these results, the capacity retention ratio is small in the region where the ratio S / W between the pattern interval S and the pattern width W is small, but when the ratio value is made larger than a certain value, the capacity retention ratio rises sharply and a good charge / discharge cycle is achieved. It can be seen that the characteristics can be obtained. The rising position of the capacity retention rate varies depending on the negative electrode material, and the capacity retention rate rises in a region where the ratio value S / W is smaller as the expansion coefficient n is smaller. That is, if the ratio value S / W is the same, the smaller the expansion coefficient n, the better the cycle characteristics. Therefore, if the pattern width W is the same, the pattern interval S can be reduced as the expansion coefficient n is reduced. This can be seen as an indication that the expansion of the pattern is small, so that the space for absorbing it can be reduced.

  Further, the same material shows the same tendency regardless of the pattern width W, but the smaller the pattern width W, the slightly faster the rise (biased to the left in the figure). This is presumably because when the pattern width W increases, the stress due to expansion in one pattern increases, and it is impossible to absorb this and the pattern is easily damaged.

Thus, there is a correlation among the ratio S / W between the pattern interval S and the pattern width W, the expansion coefficient n, and the capacity retention rate, and based on these correlations, the capacity retention rate after 10 cycles is 90% or more. The conditions for obtaining good products are as follows:
^{S / W ≧ n 2/20} ... ( Equation 3)
Thus, a good approximation can be obtained.

  In Equation 3, if the left side is increased, the gap between patterns increases on the current collector, and the amount of active material contributing to charge / discharge decreases. From the viewpoint of securing the initial capacity, it is preferable that the pattern interval S is at most smaller than the pattern width W, that is, the left side is smaller than 1. On the other hand, if it is attempted to reduce the right side of a single material having a large volume change, it is necessary to reduce the content of the active material by adding a conductive additive or the like, so that the amount of the active material is also reduced. These lead to a decrease in initial capacity. Therefore, in order to achieve both high capacity and excellent charge / discharge cycle characteristics, it can be said that it is preferable to select a condition close to the establishment of an equal sign within a range satisfying (Equation 3).

  From the above, for example, in order to manufacture an electrode for a lithium ion secondary battery having high capacity and excellent cycle characteristics using an active material having a large volume change due to charge and discharge, such as a silicon-based active material, for example, Such a manufacturing process may be executed.

  FIG. 8 is a flowchart showing an aspect of the electrode manufacturing process. Here, the dimensions of the active material pattern are set in advance, and an electrode that satisfies both the design conditions and has both high capacity and good cycle characteristics is manufactured. First, for the active material to be used, the relationship between the mixing ratio of the additive such as the conductive additive and the expansion coefficient n is grasped (step S101). In addition, for example, when the relationship between the composition of the active material and the expansion coefficient n is known from past experiments and literatures, the information may be used. Based on the knowledge, the materials are mixed at a mixing ratio that satisfies the above-mentioned (Equation 3) condition in consideration of the given dimensions and the coating liquid is prepared (step S102). Note that the spread of the coating liquid after ejection depends on the viscosity of the coating liquid, and can be adjusted by the amount of the solvent added to the coating liquid.

  The coating solution thus obtained is applied to, for example, the electrode manufacturing apparatus 20 shown in FIG. 2 to manufacture a negative electrode. Specifically, a metal foil, for example, a copper foil, which becomes the negative electrode current collector 11 is set on the movable stage 22 of the electrode manufacturing apparatus 20 (step S103), and the movable stage 22 is moved by the stage driving mechanism 23 (step S104). . In this state, the coating liquid prepared above is discharged from each of the discharge ports 211 provided in the nozzle body 21 to form an active material pattern (step S105). In this way, it is possible to produce an electrode having both high capacity and good charge / discharge cycle characteristics with excellent productivity.

  In addition, when any of the width W and the interval S of the active material pattern can be freely set, the above (in accordance with the physical properties of the coating liquid containing the active material prepared in advance or appropriately prepared ( By forming a pattern having an active material pattern width W and spacing S that satisfies Equation 3), it is possible to produce an electrode that achieves both high capacity and good charge / discharge cycle characteristics in the same manner. .

  An electrode manufacturing apparatus 20 shown in FIG. 2 is an apparatus that manufactures the negative electrode 10 by applying a coating liquid to the negative electrode current collector 11 that is a sheet-like sheet body, but is more suitable for mass production. As a form, for example, an electrode can be manufactured by a manufacturing apparatus of a so-called roll-to-roll method described below.

  FIG. 9 is a diagram showing another configuration example of the electrode manufacturing apparatus. The electrode manufacturing apparatus 30 holds the long sheet body 3 before forming the active material wound in a roll shape and feeds the sheet body 3 at a constant speed, and after the active material layer is formed. A take-up roller 33 for taking up the sheet S is provided. These are rotationally driven by the roller drive mechanism 36, whereby the sheet body 3 is conveyed at a constant speed in the predetermined conveyance direction Ds. The sheet body 3 functions as a current collector in the completed electrode. For example, a metal foil can be used, but the sheet body 3 may be backed with a resin sheet, for example, to facilitate conveyance.

  On the conveyance path from the supply roller 32 to the take-up roller 33, a nozzle body 31 is provided to face the surface of the sheet body 3. The structure of the nozzle body 31 may be the same as that of the nozzle body 21 described above. The nozzle body 31 is supplied with a coating liquid prepared in an appropriate composition from the coating liquid supply unit 35.

  The nozzle body 31 receives the supply of the coating liquid containing the active material from the coating liquid supply unit 35 and applies the coating liquid to the surface of the sheet body 3. The nozzle facing roller 34 provided on the opposite side of the nozzle body 31 with the sheet body 3 interposed therebetween functions as a backup roller that enables stable application while maintaining the positional relationship between the nozzle body 31 and the sheet body 3 constant. To do.

  Even when the electrode manufacturing apparatus 30 having such a configuration is used, the relationship between the expansion coefficient n of the active material pattern to be formed and its dimensions (pattern width W and interval S) satisfies (Equation 3). By doing so, it is possible to manufacture an electrode that achieves both high capacity and good charge / discharge cycle characteristics.

  As described above, in the above embodiment, the negative electrode current collector 11 corresponds to the “base material” of the present invention. In the electrode manufacturing apparatus 20 of FIG. 2, the movable stage 22 functions as the “holding means” of the present invention, and the stage driving mechanism 23 functions as the “moving means” of the present invention. On the other hand, in the electrode manufacturing apparatus 30 of FIG. 9, the sheet body 3 corresponds to the “base material” of the present invention, the rollers 32 to 34 function as the “holding means” of the present invention, and the roller driving mechanism 36 is the main body. It functions as the “moving means” of the invention.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, although single crystal silicon powder is used as the negative electrode active material in the above embodiment, amorphous silicon or silicon compounds such as SiO and SiOC may be used. The structure of the lithium ion secondary battery electrode described above is not limited to these silicon-based active materials, and even when other active material having a large volume change in charge / discharge is used, both capacity and cycle characteristics are compatible. It is effective in aiming at.

  Further, in the negative electrode material of the above embodiment, the mixing ratio of the active material and the conductive additive is changed variously while the mixing ratio of the binder is constant, but the mixing ratio of the binder may also be changed. . Further, the types of conductive assistant and binder are not limited to those described above.

  Moreover, the cross-sectional shape of the active material pattern in the said embodiment shows the example, Comprising: It is not limited to this, It is possible to use arbitrary cross-sectional shapes. Moreover, the opening shape of the discharge port provided in the nozzle body is not limited to the rectangular shape as in the above embodiment, and various types can be used.

  According to the present invention, it is possible to manufacture a lithium ion secondary battery having both high capacity and excellent cycle characteristics.

1 Lithium ion secondary battery module 3 Sheet body (base material)
10 Negative electrode 11 Negative electrode current collector (base material)
DESCRIPTION OF SYMBOLS 12 Negative electrode active material layer 13 Electrolyte layer 14 Positive electrode active material layer 15 Positive electrode collector 20,30 Electrode manufacturing apparatus 21,31 Nozzle body 22 Movable stage (holding means)
23 Stage drive mechanism (moving means)
32-34 Roller (holding means)
36 Roller drive mechanism (moving means)
121 (Negative electrode) Active material pattern 211 Discharge port S Pattern interval W Pattern width

Claims (12)

A base material that functions as a current collector;
A plurality of stripe-shaped active material patterns formed on the surface of the base material and including active material materials and spaced apart from each other and projecting from the surface of the base material;
The width of the active material pattern at half the height of the top portion of the active material pattern from the surface of the substrate is W, the interval at the height between adjacent active material patterns is S, and the height at the height is When the expansion coefficient defined as the ratio of the width after charging to the width before charging of the active material pattern is n, the following formula:
S / W ≧ ⁿ 2/20
An electrode for a lithium ion secondary battery that satisfies the above relationship.   2. The electrode for a lithium ion secondary battery according to claim 1, wherein the plurality of active material patterns are parallel to each other, have the same width, and have a constant interval between adjacent active material patterns.   The electrode for a lithium ion secondary battery according to claim 1 or 2, wherein the active material is silicon or a compound thereof.   The electrode for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the active material pattern further contains a conductive additive. A state in which each of the discharge ports is close to and opposed to the surface of the substrate, with a nozzle body in which a plurality of discharge ports are arranged in a row along a predetermined arrangement direction and a base material that functions as a current collector A process of arranging in
While discharging a coating liquid containing an active material from each of the discharge ports, the nozzle body is moved relative to the base material along the surface of the base material in a direction intersecting the array direction of the discharge ports. Forming a plurality of stripe-shaped active material patterns on the substrate surface that are separated from each other and protrude from the substrate surface,
The width of the active material pattern at half the height of the top portion of the active material pattern from the surface of the substrate is W, the interval at the height between adjacent active material patterns is S, and the height at the height is When the expansion coefficient defined as the ratio of the width after charging to the width before charging of the active material pattern is n, the following formula:
S / W ≧ ⁿ 2/20
The manufacturing method of the electrode for lithium ion secondary batteries with which the relationship of is satisfy | filled.   The method for manufacturing an electrode for a lithium ion secondary battery according to claim 5, wherein the opening shapes of the plurality of discharge ports are equal to each other, and the arrangement pitch of the discharge ports in the arrangement direction is constant.   7. The lithium ion battery according to claim 5, wherein an interval in the width direction perpendicular to the extending direction of the active material pattern between the adjacent active material patterns is made smaller than a width of the active material pattern in the width direction. The manufacturing method of the electrode for secondary batteries.   The discharge liquid is discharged from the discharge port whose opening width in the width direction is smaller than the width of the active material pattern, and after the discharge, the coating liquid is spread on the surface of the base material. The manufacturing method of the electrode for lithium ion secondary batteries as described in any one of.   The method for producing an electrode for a lithium ion secondary battery according to any one of claims 5 to 8, wherein the coating liquid further contains a conductive additive.   The method for manufacturing an electrode for a lithium ion secondary battery according to claim 9, wherein the expansion coefficient is controlled by adjusting a mixing ratio of the active material and the conductive additive. A plurality of discharge ports are arranged in a row along a predetermined arrangement direction, and a nozzle body that continuously discharges a coating liquid containing an active material from each of the discharge ports;
Holding means for holding the base material functioning as a current collector in a state in which each of the discharge ports is in close proximity to the surface of the base material;
Moving means for relatively moving the nozzle body and the base material so that the discharge port moves along the surface of the base material;
The width of the active material pattern at half the height of the top portion of the active material pattern from the surface of the substrate is W, the interval at the height between adjacent active material patterns is S, and the height at the height is When the expansion coefficient defined as the ratio of the width after charging to the width before charging of the active material pattern is n, the following formula:
S / W ≧ ⁿ 2/20
Lithium ion secondary is formed by discharging the coating liquid from each of the plurality of discharge ports to the substrate surface while relatively moving the nozzle body and the substrate while satisfying the relationship of Battery electrode manufacturing equipment.   The apparatus for manufacturing an electrode for a lithium ion secondary battery according to claim 11, wherein the opening shapes of the plurality of discharge ports are equal to each other, and the arrangement pitch of the discharge ports in the arrangement direction is constant.

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