JP2007027102A - Anode for nonaqueous electrolyte solution secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anode for a nonaqueous electrolyte solution secondary battery capable of making an active material uniformly contribute to electrode reaction for a whole area in a thickness direction of an active material layer. <P>SOLUTION: The anode for the nonaqueous electrolyte solution secondary battery is provided with an active material layer containing a silicon-base material. An average peak position of an Si peak of Raman spectrum measured in a thickness direction of the active material layer after charge and discharge are carried out on the anode is 480 to 510 cm<SP>-1</SP>. When the active material layer is virtually divided into two in its thickness direction, an average peak position of one of the divided active material layer and that of the other divided active material layer are preferred to be 480 to 510 cm<SP>-1</SP>, respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a negative electrode used for a non-aqueous electrolyte secondary battery such as a lithium secondary battery, and a non-aqueous electrolyte secondary battery including the negative electrode.

  As a negative electrode of a lithium secondary battery, a material in which a mixture containing a carbon-based material such as graphite is coated on a current collector such as an aluminum foil is widely used. In recent years, the lithium occlusion performance of carbon-based materials has reached a level close to the theoretical value, and development of a new negative electrode active material has been demanded in order to significantly increase the capacity of lithium secondary batteries. A silicon-based material has been proposed as such a negative electrode active material.

  However, since silicon-based materials are poor in electrical conductivity, a conductive aid for imparting electron conductivity to an electrode is generally used in combination. For example, it has been proposed to increase the electron conductivity of an electrode by coating the surface of silicon-based material particles with fine metal particles made of Al, Ti, Fe, Ni, or the like (see Patent Document 1).

  In addition, the present applicant firstly prevented lithium from dropping from the electrode due to the pulverization of the particles of the silicon-based material, and added lithium to the voids between the particles of the silicon-based material for the purpose of imparting electronic conductivity to the electrode. A negative electrode infiltrated with a metal material having a low compound forming ability was proposed (see Patent Document 2).

JP-A-11-250896 Japanese Patent No. 3612669

  By the way, a high-capacity battery is required as a power source for portable electronic devices such as a mobile phone, a video camera, and a notebook personal computer. In order to increase the capacity of the battery, it is necessary to use a high-capacity active material and increase the amount of active material used. However, when the above-described silicon-based material is used as the active material, the thickness of the active material layer is increased in order to increase the amount of the active material. There may be a difference in electrode reaction between the part far from the surface. That is, an electrode reaction is likely to occur at a site near the surface of the active material layer, whereas an electrode reaction is less likely to occur at a site far from the surface. As a result, when charge and discharge are repeated, the capacity retention rate of the battery tends to gradually decrease.

  Accordingly, an object of the present invention is to provide a negative electrode for a non-aqueous electrolyte secondary battery with improved charge / discharge cycle characteristics.

The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery including an active material layer containing a silicon-based material.
The non-aqueous electrolysis, wherein an average peak position of Si peak of Raman spectrum measured in the thickness direction of the active material layer after charging / discharging the negative electrode is 480 to 510 cm ⁻¹ The object is achieved by providing a negative electrode for a liquid secondary battery.

  Further, the present invention includes an active material layer containing particles of a silicon-based material, a metal material having a low lithium compound forming ability penetrates between the particles in the active material layer, and the metal material has a pH of The present invention provides a negative electrode for a non-aqueous electrolyte secondary battery that has been deposited and permeated by electrolytic plating using a plating bath of 7.1 to 11.

  Furthermore, the present invention provides a non-aqueous electrolyte secondary battery provided with the negative electrode.

  According to the present invention, since the active material can be uniformly contributed to the electrode reaction over the entire thickness direction of the active material layer, the charge / discharge cycle characteristics of the battery are improved.

Hereinafter, the present invention will be described based on preferred embodiments thereof. The negative electrode for a nonaqueous electrolyte secondary battery of the present invention includes an active material layer containing a silicon-based material. Silicon-based materials include silicon alone, compounds of silicon and other metal elements, silicon oxides, and the like. These materials can be used alone or in combination. Examples of the metal element include one or more elements selected from the group consisting of Cu, Ag, Ni, Co, Cr, Fe, Ti, Pt, W, Mo, and Au. Of these metal elements, Cu, Ag, Ni, and Co are preferable, and Cu, Ag, and Ni are preferably used from the viewpoint of excellent electronic conductivity and a low ability to form a lithium compound. A particularly preferable silicon-based material is preferably Si or SiO ₂ in view of the high lithium storage capacity.

  There is no restriction | limiting in particular in the form of the silicon-type material in an active material layer. For example, as described in Japanese Patent No. 3612669 related to the previous application of the present applicant, the active material layer may be a layer containing particles of a silicon-based material. Further, a thin film of silicon material formed by various thin film forming means may be used as the active material layer. Examples of such an active material layer include those described in JP-A No. 2003-17040. Alternatively, a sintered body of silicon-based material particles may be used as the active material layer. Examples of such an active material layer include those described in JP-A-2002-260637. In particular, the active material layer is a layer containing particles of a silicon-based material, and even when the active material layer is formed thick, it is likely to have a structure that can be uniformly charged and discharged over the thickness direction of the layer. To preferred.

  There is no restriction | limiting in particular in the thickness of an active material layer. From the viewpoint of improving the energy density, it is advantageous to increase the thickness of the active material layer. However, if the active material layer is too thick, the active material is likely to fall off. From these viewpoints, the thickness of the active material layer is preferably 1 to 200 μm, more preferably 10 to 100, and particularly preferably 15 to 40 μm. In the negative electrode of the present invention, even if the thickness of the active material layer is large, the active material can contribute uniformly to the electrode reaction over the entire thickness direction of the active material layer. From this viewpoint, when the present invention is applied to a negative electrode having a large thickness of the active material layer, the effect becomes remarkable.

  The negative electrode of the present invention is characterized in that the active material can uniformly contribute to the electrode reaction over the entire thickness direction of the active material layer. This feature is expressed by the measurement result of the Raman spectrum of Si measured for the active material layer. The Raman spectrum is a technique for spectroscopically analyzing scattered light due to the Raman effect generated by applying light to a substance. In the case of Si, crystalline silicon and amorphous silicon are both detected as a single element of Si by elemental analysis and cannot be distinguished from each other. On the other hand, in the analysis using the Raman spectrum, it is known that the spectrum is different due to the difference in crystallinity of Si. Therefore, in the present invention, by utilizing the fact that the crystal structure of Si is changed by the electrode reaction, Si crystallinity is measured in the thickness direction of the active material layer from the Si Raman spectrum in the thickness direction of the active material layer. Yes.

FIG. 1 shows Si peaks of Raman spectra measured for crystalline silicon and amorphous silicon. As is clear from this figure, in crystalline silicon, a single sharp peak having a peak position in the vicinity of about 520.5 cm ⁻¹ is observed. On the other hand, in the case of amorphous silicon, a broad peak having a peak position in the vicinity of about 480 cm ⁻¹ is observed. From these peak positions and peak shapes, the difference in crystallinity of Si can be measured.

  In the present invention, the Raman spectrum is measured for the negative electrode after charge / discharge. In this case, the Raman spectrum may be measured for the negative electrode after one cycle of charge / discharge, or it is technically possible to measure the Raman spectrum after performing multiple cycles of charge / discharge. However, if charging and discharging are repeated excessively, the structure of the negative electrode changes due to expansion and contraction of the active material, and it tends to be difficult to improve the reproducibility of measurement. From this viewpoint, it is preferable that the number of times of charging / discharging is small. Specifically, it is preferable to perform charge / discharge of 3 cycles or less, and particularly preferably, measurement is performed on the negative electrode after one cycle of charge / discharge.

  When charging / discharging under the above-described conditions, the structure of the negative electrode after charging / discharging changes depending on the depth of charging / discharging. From the viewpoint of improving the reproducibility of the measurement, the present inventors have found that it is most preferable to measure the Raman spectrum after performing charge / discharge corresponding to 50% of the maximum capacity of the negative electrode with respect to the negative electrode. . It is technically possible to employ other charge / discharge conditions. However, since it has been found that performing recharging and discharging under the above conditions can achieve the highest reproducibility, it is preferable to employ the above conditions.

In contrast to the depth of charge and discharge, the inventors have found that the type of electrolyte used and the type of counter electrode have no substantial effect on the Raman spectrum measurement results. Therefore, there are no particular restrictions on the type of electrolyte or counter electrode when charging / discharging. From the viewpoint of further improving the reproducibility of the measurement, 2% by volume of vinylene carbonate is externally added to a solution obtained by dissolving 1 mol / l LiPF ₆ in a 1: 1 volume% mixed solvent of ethylene carbonate and diethyl carbonate as an electrolytic solution. It is preferable to use LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ as the counter electrode.

  After one cycle of charge and discharge, a sample for measuring Raman spectrum is prepared from the negative electrode. This procedure is as follows. The negative electrode is embedded in an embedding resin such as an epoxy resin, and the resin is cured. After the resin is cured, the negative electrode is cut in the thickness direction to expose the longitudinal section of the active material layer. The exposed cross section is mirror polished with a file and buffing paper. In this way, a measurement sample is obtained. The present inventors have confirmed that there is no substantial difference in measurement results between these operations when performed in the air and when performed in a vacuum or an inert gas atmosphere. Yes.

  A Raman spectrum is measured with respect to the obtained sample at an interval at least equal to the thickness direction of the active material layer (the number of measurements in this case is 11). In the present invention, a laser Raman spectrophotometer “NRS-2100” (trade name) manufactured by JASCO Corporation was used as a measuring apparatus. The excitation wavelength was 514.5 nm. In addition, since the Raman spectrum measuring apparatus generally has high spatial resolution, there is no difficulty in measuring the Raman spectrum at a minute interval that divides the thickness direction of the active material layer at least equally.

In this way, the Raman spectrum is measured at regular intervals over the thickness direction of the active material layer. Next, the peak position of the Si peak in the Raman spectrum measured at each position is measured. An example of the measurement result is shown in FIG. In FIG. 2, the line shown by (1) has shown the measurement result after performing 1 cycle of charging / discharging with respect to the negative electrode of this invention (Example 1 mentioned later). The line shown by (2) has shown the measurement result after charging / discharging 1 cycle with respect to the negative electrode of a comparative product (comparative example 1 mentioned later). The line shown by (3) has shown the measurement result of the negative electrode before charging / discharging. The line indicated by (3) gives the same result regardless of whether the product of the present invention or the comparative product is measured. This is because both the present invention product and the comparative product use silicon-based materials having the same crystal form. In FIG. 2, the horizontal axis represents the thickness of the active material layer. The position of the origin indicates the interface with the current collector. The vertical axis represents the wave number (cm ⁻¹ ) of the peak position of the Si peak in the Raman spectrum. The larger the wave number, the higher the crystallinity of Si, and the smaller the wavenumber, the lower the crystallinity, that is, closer to amorphous.

The sum of the wave numbers (cm ⁻¹ ) of the measured peak positions is calculated, and the calculated value is divided by the number of measurements. Thus, the average peak position is calculated. In the present invention, it is necessary to form the active material layer so that the average peak position is 480 to 510 cm ⁻¹ , preferably 495 to 507 cm ⁻¹ .

The technical significance of the average peak position will be described as follows using silicon as an active material as an example. The silicon contained in the active material layer in the negative electrode of the present invention is in a crystalline state before charging / discharging. The average peak position of the Si peak in the Raman spectrum of the active material layer measured in this state is about 520.5 cm ⁻¹ , which is the Si peak position of the crystalline silicon itself. When one cycle of charging / discharging is performed on this negative electrode, silicon becomes amorphous due to charging / discharging. In this case, when charge / discharge is performed uniformly over the entire thickness direction of the active material layer, silicon is uniformly amorphized, so that the average peak position of the Si peak is about 520.5 cm ⁻ which is the peak position before charge / discharge. ^Less than ¹ . On the other hand, when charge and discharge are performed non-uniformly in the thickness direction of the active material layer, the silicon existing in the deep part of the active material layer has a low degree of amorphization or, in an extreme case, almost amorphous. Do not turn. As a result, the average peak position of the Si peak is not so different from about 520.5 cm ⁻¹ , which is the peak position before charging and discharging. In such a negative electrode (the negative electrode of the comparative product in FIG. 2), only the active material near the active material layer surface contributes to the battery reaction. Therefore, compared with the negative electrode of the present invention, the active material near the active material layer surface. Volume change becomes extremely large. As a result, the active material tends to be pulverized and dropped off, and the negative electrode tends to be short-lived. Thus, the average peak position of the Si peak in the thickness direction of the active material layer is a measure of whether charge / discharge is performed uniformly in the thickness direction of the active material layer.

In the negative electrode of the present invention, when the average peak position of the Si peak exceeds 510 cm ⁻¹ , charge / discharge is not uniformly performed in the thickness direction of the active material layer, and charge / discharge cycle characteristics are deteriorated. The lower limit value of the average peak position of the Si peak is naturally determined in relation to about 480 cm ⁻¹ , which is the Si peak position of amorphous silicon. Currently, 480 cm ⁻¹ is the lower limit value that can be substantially reached.

In the case where charge and discharge are performed uniformly over the entire thickness direction of the active material layer, it is preferable that there is no variation in the Si peak position in the thickness direction. For example, in the graph shown in FIG. 2, in the negative electrode of the present invention (the line indicated by (1) in FIG. 2), the Si peak position is almost the same regardless of the thickness of the active material layer. On the other hand, in the negative electrode of the comparative product (the line indicated by (2) in FIG. 2), the Si peak position gradually increases as it approaches the interface surface with the current collector (that is, it becomes amorphous). Is gone). From this viewpoint, when the active material layer is virtually divided into two in the thickness direction, the average peak position on one side of the active material layer divided into two is preferably 480 to 510 cm ⁻¹ , in 495~507cm ^-1, likewise also preferably mean peak position of the other side 480~510cm ^-1, preferably forming an active material layer such that the 495~507cm ^-1.

  In order for the average peak position of the Si peak of the Raman spectrum measured in the thickness direction of the active material layer to be within the above range, the active material layer may be appropriately formed. A particularly important point is to form the active material layer in such a structure that the non-aqueous electrolyte flows uniformly throughout the thickness direction of the active material layer. In order to form such a structure, for example, when particles of a silicon-based material are used as an active material, an appropriately sized void that allows a non-aqueous electrolyte to flow is formed between the particles. Good. When the active material layer is formed by thin film forming means such as sputtering, the formation conditions of the thin film forming means are controlled so that a minute columnar structure of silicon-based material is formed, and non- What is necessary is just to form the space | gap of a moderate magnitude | size which can distribute | circulate a water electrolyte solution. When using a sintered body of silicon-based material particles as the active material layer, the degree of sintering may be controlled.

  FIG. 3 is a cross-sectional view showing the structure of a preferred embodiment of the negative electrode of the present invention. The negative electrode 20 includes a current collector 10 and an active material layer 11 formed on one surface thereof. In FIG. 3, the active material layer 11 is formed only on one surface of the current collector 10, but it goes without saying that the active material layer may be formed on each surface of the current collector 10. The active material layer 11 includes active material particles 12 and conductive particles 13. The active material layer 11 is continuously covered with a thin surface coating layer 15. In the surface coating layer 15, a large number of micropores 14 communicating with the active material layer 11 are formed.

The particles 12 contained in the active material layer 11 preferably have a maximum particle size of 50 μm or less, particularly 20 μm or less. Moreover, when the particle size of the particle 12 is expressed by a D ₅₀ value, it is preferably 0.1 to 8 μm, particularly 1 to 5 μm. If the maximum particle size is more than 50 μm, the particles 12 may easily fall off. There is no particular limitation on the lower limit of the particle size, and the smaller the better. In view of the method for producing the particles 12, the lower limit is about 0.01 μm. The particle size of the particles 12 is measured by a laser diffraction scattering method and observation with an electron microscope.

  If the amount of the particles 12 with respect to the whole negative electrode is too small, it is difficult to sufficiently improve the charge / discharge capacity. On the other hand, when the amount is too large, the particles 12 easily fall off the negative electrode 20. Considering these, the amount of the particles 12 is preferably 10 to 80% by weight, more preferably 25 to 60% by weight, and further preferably 30 to 50% by weight with respect to the whole negative electrode.

  In the active material layer 11, it is preferable that a metal material having a low lithium compound forming ability penetrates between the particles 12 included in the layer 11. The term “penetration” as used in the present invention means that at least the surface of the particle 12 is coated with a metal material having a low ability to form a lithium compound, and the space between the particles 12 must be filled with the metal material. And not. The metal material does not cover the surface of the particle 12 in such a manner that the non-aqueous electrolyte does not reach the particle 12. That is, the metal material covers the surface of the particle 12 while ensuring a gap that allows the non-aqueous electrolyte to reach the particle 12. The metal material preferably penetrates over the entire thickness direction of the active material layer 11. The particles 12 are preferably present in the permeated metal material. That is, it is preferable that the particles 12 are not substantially exposed on the surface of the negative electrode 20 and are embedded in the active material layer 11. This further prevents the particles 12 from falling off. “Lithium compound forming ability is low” means that lithium does not form an intermetallic compound or solid solution, or even if formed, lithium is in a very small amount or very unstable. Examples of the metal material include copper, nickel, iron, cobalt, and alloys of these metals.

  The metal material having a low ability to form a lithium compound that has penetrated into the active material layer 11 preferably penetrates the active material layer 11 in the thickness direction. Thereby, the particles 12 and the current collector 10 are electrically and reliably conducted through the metal material, and the electron conductivity of the whole negative electrode is further increased. The permeation of the metal material over the entire thickness direction of the active material layer 11 can be confirmed by electron microscope mapping using the metal material as a measurement target. The metal material is preferably deposited by electrolytic plating and penetrates between the particles 12 (hereinafter, this electrolytic plating is also referred to as “penetration plating”). Details of the method of depositing a metal material between the particles 12 by osmotic plating are described in, for example, Japanese Patent No. 3612669 related to the previous application of the present applicant. However, it was not always easy to increase the void ratio described later by depositing a metal material between the particles by the method described in this patent publication. Accordingly, particularly preferred conditions for the penetration plating for increasing the void ratio will be described later.

  It is preferable that the space between the particles 12 in the active material layer 11 is not completely filled with a metal material having a low lithium compound-forming ability, but a space exists between the particles 12. Due to the presence of the voids, the non-aqueous electrolyte can easily circulate over the entire thickness direction of the active material layer 11, and charging / discharging can be performed uniformly. As a result, the average peak position of the Si peak of the Raman spectrum can be easily within the above range. In addition, the presence of the voids relieves the stress generated by the volume change of the active material particles 12 due to charge and discharge. From these viewpoints, the void ratio in the active material layer 11 is preferably about 15 to 45% by volume, particularly about 20 to 40% by volume. The ratio of voids is calculated by the method described later. Since the active material layer 11 is preferably formed by applying a slurry containing the particles 12 and drying it, voids are naturally formed in the active material layer 11. Therefore, in order to set the void ratio within the above range, for example, the particle size of the particles 12, the composition of the slurry, and the application conditions of the slurry may be appropriately selected. Moreover, after apply | coating and drying a slurry and forming a coating film, you may press-process this coating film on suitable conditions, and may adjust the ratio of a space | gap.

[Measurement method of void ratio]
(1) The weight per unit area of the coating film formed by the application of the slurry is measured, and the weight of the particles 12 and the weight of the binder are calculated from the blending ratio of the slurry.
(2) Calculate the weight of the deposited metal species from the change in weight per unit area after penetration plating.
(3) The thickness of the active material layer 11 is calculated | required by carrying out SEM observation of the cross section of a negative electrode after osmosis | permeation plating.
(4) The volume of the active material layer 11 per unit area is calculated from the thickness of the active material layer 11.
(5) The respective volumes are calculated from the weight of the particles 12, the weight of the binder, the weight of the plating metal species, and the respective blending ratios.
(6) From the volume of the active material layer 11 per unit area, the volume of the voids is calculated by subtracting the volume of the particles 12, the volume of the binder, and the volume of the plating metal species.
(7) The void volume thus calculated is divided by the volume of the active material layer 11 per unit area, and a value obtained by multiplying it by 100 is defined as the void ratio (%).

The conditions when the metal material is osmotically plated between the particles 12 are also important from the viewpoint of adjusting the ratio of the voids. The conditions for permeation plating include the composition of the plating bath, the pH of the plating bath, and the current density of electrolysis. Regarding the pH of the plating bath, it is preferable to adjust it to 7.1 to 11 because a negative electrode in which the peak position of the Si peak in the Raman spectrum described above has a suitable value can be easily obtained. Specifically, by setting the pH to 7.1 or more, the surface of the active material silicon particles is cleaned, and plating on the particle surface is promoted, and at the same time, appropriate voids are formed between the active material particles. This is preferable. On the other hand, it is preferable to adjust the pH to 11 or less because significant dissolution of silicon particles can be prevented. The value of pH is measured at the temperature at the time of permeation plating. When copper is used as the metal material for the osmotic plating, it is preferable to use a copper pyrophosphate bath. When nickel is used as the metal material, for example, an alkaline nickel bath is preferably used. In particular, it is preferable to use a copper pyrophosphate bath, even if the active material layer is thickened, because the voids can be easily formed over the entire thickness direction of the layer. When using a copper pyrophosphate bath, the bath composition and pH are preferably as follows.
Copper pyrophosphate trihydrate: 85-120 g / l
-Potassium pyrophosphate: 300-600 g / l
-Potassium nitrate: 15-65 g / l
-Bath temperature: 45-60 ° C
・ Current density: 1 to 7 A / dm ²
PH: Ammonia water and polyphosphoric acid are added to adjust the pH to 7.1 to 9.5.

In particular, when a copper pyrophosphate bath is used, it is preferable to use one having a P ratio defined by a ratio of P ₂ O ₇ weight to Cu weight (P ₂ O ₇ / Cu) of 5 to 12. . If the P ratio is less than 5, the plating layer covering the active material particles tends to be thick, and it may be difficult to obtain a space between the active material particles. Further, when a P ratio exceeding 12 is used, current efficiency is deteriorated, and gas generation is likely to occur, so that production stability may be lowered. When a copper pyrophosphate bath having a P ratio of 6.5 to 10.5 is used as a more preferable copper pyrophosphate bath, the size and number of spaces formed between the particles of the negative electrode active material can be reduced by non-water in the active material layer. This is very advantageous for the flow of the electrolyte.

When an alkaline nickel bath is used, the bath composition and pH are preferably as follows.
Nickel sulfate: 100 to 250 g / l
Ammonium chloride: 15-30 g / l
・ Boric acid: 15-45 g / l
-Bath temperature: 45-60 ° C
・ Current density: 1 to 7 A / dm ²
-PH: 25% by weight ammonia water: Adjust to pH 8-11 within the range of 100-300 g / l.
When this alkaline nickel bath and the above-described copper pyrophosphate bath are compared, there is a tendency that an appropriate space is formed in the active material layer 11 when the copper pyrophosphate bath is used, thereby extending the life of the negative electrode. It is preferable because it is easy to plan.

  The conductive particles 13 included in the active material layer 11 together with the active material particles 12 are made of, for example, a carbon material or a metal material. By containing these particles 13 in the active material layer 11, electron conductivity is further imparted to the active material layer 11. From this viewpoint, the amount of the conductive particles 13 contained in the active material layer 11 is preferably 0.1 to 20% by weight, particularly 1 to 10% by weight. For example, particles such as acetylene black are used as the carbon material. The particle size of the particles 13 is preferably 40 μm or less, and particularly preferably 20 μm or less from the viewpoint of further providing electron conductivity. The lower limit of the particle size of the particle 13 is not particularly limited and is preferably as small as possible. In view of the method for producing the particles 13, the lower limit is about 0.01 μm.

  In the negative electrode 20, the surface of the active material layer 11 may be continuously or discontinuously coated with the thin surface coating layer 15. The main role of the surface coating layer 15 is to prevent the particles 12 contained in the active material layer 11 from being pulverized and dropped by the stress caused by charge / discharge. However, in the negative electrode 20 of the present embodiment, as described above, the metal material having a low lithium compound forming ability penetrates into the active material layer 11, thereby dropping off the particles 12 included in the active material layer 11. Therefore, it is not always necessary to provide the surface coating layer 15. The surface coating layer 15 is preferably made of a metal material having a low lithium compound forming ability. As the metal material, the same metal material that penetrates into the active material layer 11 can be used. The metal material may be the same as or different from the metal material penetrating into the active material layer 11. In the case of the same kind, there exists an advantage that the manufacturing method of the negative electrode 20 does not become complicated. In the case of different types, there is an advantage that an appropriate metal material can be independently selected for each layer.

  When the surface of the active material layer 11 is continuously coated with the surface coating layer 15, the thickness is about 0.3 to 10 μm, particularly about 0.4 to 8 μm, especially about 0.5 to 5 μm. Preferably there is. As a result, the active material layer 11 can be continuously covered almost uniformly with the minimum necessary thickness. As a result, the pulverized particles 12 can be prevented from falling off. Moreover, by setting it as this thin layer, the ratio of the particle | grains 12 to the whole negative electrode becomes relatively high, and can increase the energy density per unit volume and unit weight. On the other hand, when the surface of the active material layer 11 is discontinuously coated with the surface coating layer 15, the thickness is less than 0.3 μm, in particular, 0.25 μm or less, especially 0.1 to 0.25 μm, This is preferable because lithium dendrite can be effectively prevented from being generated on the surface of the negative electrode 20 during charging.

  The surface coating layer 15 has a large number of fine holes 14 that are open at the surface thereof and communicate with the active material layer 11. The micropores 14 exist in the surface coating layer so as to extend in the thickness direction of the surface coating layer 15. By forming the fine holes 14, the nonaqueous electrolytic solution can penetrate into the active material layer 11, and the reaction with the particles 12 occurs sufficiently. The fine holes 14 are fine ones having a width of about 0.1 μm to about 10 μm when the surface coating layer 15 is observed in cross section. Although fine, the micropores 14 have a width that allows the non-aqueous electrolyte to flow. However, since the non-aqueous electrolyte has a smaller surface tension than the aqueous electrolyte, it can sufficiently penetrate even if the width of the micropores 14 is small.

  As the current collector 10 in the negative electrode 20, the same one as conventionally used as the current collector of the negative electrode for the non-aqueous electrolyte secondary battery can be used. The current collector 10 is preferably made of the metal material having a low lithium compound forming ability described above. Examples of such metallic materials are as already described. In particular, it is preferably made of copper, nickel, stainless steel or the like. The thickness of the current collector 10 is not critical in this embodiment. Considering the balance between maintaining the strength of the negative electrode 20 and improving the energy density, the thickness is preferably 10 to 30 μm.

  In the negative electrode 10, it is preferable that holes (not shown) that are open in each surface of the negative electrode 10 and extend in the thickness direction of the active material layer 11 are formed. This hole is distinguished from the fine hole 14 extending in the thickness direction of the surface coating layer 15 in that it extends in the thickness direction of the active material layer 11. Further, this hole is distinguished from the fine hole 14 in that it has a size (diameter) much larger than that of the fine hole 14. In the active material layer 11, the active material layer 11 is exposed on the wall surface of the hole. The role of the hole is as follows.

  One is to supply the non-aqueous electrolyte into the active material layer 11 through the active material layer 11 exposed on the wall surface of the hole. The active material layer 11 is exposed on the wall surface of the hole, but the metal 12 having a low ability to form a lithium compound penetrates between the particles 12 in the active material layer, so that the particles 12 fall off. Is prevented.

  The other is the role of relieving the stress caused by the volume change when the particles 12 in the active material layer 11 change in volume due to charge / discharge. The stress is mainly generated in the planar direction of the negative electrode 20. Therefore, even if the volume of the particles 12 increases due to charging and stress is generated, the stress is absorbed by the pores in the space. As a result, significant deformation of the negative electrode 20 is effectively prevented.

Another role of the hole is that the gas generated in the negative electrode 20 can be released to the outside. Specifically, gas such as H ₂ , CO, and CO ₂ may be generated due to moisture contained in a small amount in the negative electrode 20. When these gases accumulate in the negative electrode 20, the polarization increases and causes charge / discharge loss. By forming the hole, the gas is released to the outside of the negative electrode through this, so that the polarization caused by the gas can be reduced. Furthermore, as another role of the hole, there is a role of heat dissipation of the negative electrode 20. Specifically, since the specific surface area of the negative electrode 20 is increased by the formation of the holes, the heat generated with the occlusion of lithium is efficiently released to the outside of the negative electrode. Further, when stress is generated due to the volume change of the particles 12, heat may be generated due to the stress. Since the stress is relieved by forming the hole, the generation of heat itself is suppressed.

  From the viewpoint of sufficiently supplying the electrolytic solution into the active material layer 11 and from the viewpoint of effectively relieving the stress caused by the volume change of the particles 12, the opening ratio of the holes opened on the surface of the negative electrode 20, that is, A value obtained by dividing the total area of the holes by the apparent area of the surface of the negative electrode 20 and multiplying by 100 is preferably 0.3 to 30%, particularly preferably 2 to 15%. For the same reason, the hole diameter of the hole opened on the surface of the negative electrode 20 is preferably 5 to 500 μm, particularly preferably 20 to 100 μm. Further, by setting the pitch of the holes to preferably 20 to 600 μm, more preferably 45 to 400 μm, the electrolyte can be sufficiently supplied into the active material layer 11, and the stress due to the volume change of the particles 12 can be effectively suppressed. Can be relaxed. Further, when attention is paid to an arbitrary portion on the surface of the negative electrode 20, an average of 100 to 250,000 holes, particularly 1000 to 40000 holes, particularly 5000 to 20000 holes are opened in a 1 cm × 1 cm square observation field. It is preferable.

  The hole may penetrate in the thickness direction of the negative electrode 20. However, in view of the role of the hole that sufficiently supplies the electrolytic solution into the active material layer 11 and relieves the stress caused by the volume change of the particles 12, the hole penetrates in the thickness direction of the negative electrode 20. It is not necessary, and it is sufficient that the surface of the negative electrode 20 is open and extends at least in the active material layer 11 in the thickness direction.

  The hole can be formed by, for example, laser processing. Alternatively, drilling can be performed mechanically with a needle or punch. When both are compared, it is easier to obtain a negative electrode with good cycle characteristics and charge / discharge efficiency when laser processing is used. This is because, in the case of laser processing, since the metal material of the osmosis plating melted and re-solidified by processing covers the surface of the particle 12 existing on the wall surface of the hole, the particle 12 is prevented from being directly exposed, thereby This is because 12 is prevented from falling off the wall surface of the hole. In the case of using laser processing, for example, the laser may be irradiated toward the surface of the negative electrode 20. In addition, as another means for forming the holes, a sandblasting process or a forming method using a photoresist technique can be used. The holes are preferably formed so as to exist at substantially equal intervals. This is because the negative electrode 20 as a whole can react uniformly.

  Details of the manufacturing method of the negative electrode 20 having the above structure are described in, for example, Japanese Patent No. 3612669 related to the previous application of the present applicant.

  As mentioned above, although this invention was demonstrated based on the preferable embodiment, this invention is not restrict | limited to the said embodiment. For example, the negative electrode of the embodiment shown in FIG. 3 was provided with an active material layer formed by applying a slurry containing particles of a silicon-based material. Instead, a silicon-based material was used as a target. Alternatively, an active material layer formed by various thin film forming means or an active material layer made of a sintered body of silicon-based material particles may be used.

  Further, the negative electrode of the embodiment shown in FIG. 3 has an active material layer formed on one or both sides of the current collector, but instead of this, a negative electrode having a structure having no current collector may be used. . In that case, it is preferable to form a pair of surface coating layers on each surface of the active material layer. The negative electrode having such a structure is described in, for example, Japanese Patent No. 3612669 related to the previous application of the present applicant.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[Example 1]
A current collector made of an electrolytic copper foil having a thickness of 18 μm was acid washed at room temperature for 30 seconds. After the treatment, it was washed with pure water for 15 seconds. A slurry containing Si particles was applied on the current collector to a thickness of 15 μm to form a coating film. The average particle size of the particles was D ₅₀ = 2 μm. The composition of the slurry was particle: styrene butadiene rubber (binder) = 100: 1.7 (weight ratio).

The current collector on which the coating film was formed was immersed in a copper pyrophosphate bath having the following bath composition, and copper was permeated to the coating film by electrolysis to form an active material layer. The electrolysis conditions were as follows. DSE was used for the anode. A DC power source was used as the power source. After lifting from the plating bath, it was washed with pure water for 30 seconds and dried in the air. In this way, a target negative electrode was obtained.
Copper pyrophosphate trihydrate: 105 g / l
-Potassium pyrophosphate: 450 g / l
-P ratio: 7.7
・ Potassium nitrate: 30 g / l
・ Bath temperature: 50 ° C
・ Current density: 3 A / dm ²
-PH: Ammonia water and polyphosphoric acid were added to adjust to pH 8.2.

[Example 2]
Instead of using the copper pyrophosphate bath as the osmotic plating bath, an alkaline nickel bath having the following composition was used. The electrolysis conditions were as follows. A nickel electrode was used as the anode. A DC power source was used as the power source. A negative electrode was obtained in the same manner as Example 1 except for these.
Nickel sulfate: 160 g / l
Ammonium chloride: 22 g / l
・ Boric acid: 30 g / l
・ Bath temperature 50 ℃
・ Current density 5A / dm ²
-PH: It adjusted so that it might become pH 10 using about 210 g / l of 25 weight% ammonia water.

[Comparative Example 1]
Instead of using a copper pyrophosphate bath as the osmotic plating bath, a copper sulfate bath having the following composition was used. The current density was 5 A / dm ² , the bath temperature was 40 ° C., and the pH was 0.4. A DSE electrode was used as the anode. A DC power source was used as the power source. A negative electrode was obtained in the same manner as Example 1 except for these.
・ CuSO ₄ · 5H ₂ 0 250g / l
・ H ₂ SO ₄ 70 g / l

[Evaluation]
The negative electrodes obtained in Examples 1 and 2 and Comparative Example 1 were charged and discharged by the above-described method for one cycle, and then the average peak position of the Si peak in the Raman spectrum was measured. The results are shown in Table 1. Charging / discharging was performed 50% of the maximum capacity of the negative electrode. LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ was used as the counter electrode. As the electrolytic solution, a solution obtained by dissolving 1 mol / l LiPF ₆ in a 1: 1 vol% mixed solvent of ethylene carbonate and diethyl carbonate and adding 2 vol% vinylene carbonate externally was used.

Moreover, about the negative electrode obtained in Example 1 and the comparative example 1, the capacity | capacitance maintenance factor to 100 cycles was measured. The result is shown in FIG. The capacity retention rate was calculated with the discharge capacity at the second cycle (≈3 mAh / cm ² ) being 100. As the positive electrode and the electrolytic solution, the same ones used for the measurement of the average peak position of the Si peak were used.

  As is clear from the results shown in Table 1 and FIG. 4, the average peak position of the Si peak of the Raman spectrum is within a specific range, the negative electrode of each example is compared with the negative electrode of Comparative Example 1, It can be seen that even when charging and discharging are repeated, the decrease in capacity retention rate is low and the cycle characteristics are excellent.

It is a graph which shows the Raman spectrum of silicon. It is a graph which shows Si peak position of the Raman spectrum in the thickness direction of an active material layer. It is a schematic diagram which shows the structure of one Embodiment of the negative electrode of this invention. It is a graph which shows the capacity | capacitance maintenance factor to 100 cycles of the negative electrode obtained in Example 1 and Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Current collector 11 Active material layer 12 Silicon-based material particle 13 Conductive particle 14 Micropore 15 Surface coating layer

Claims (12)

In the negative electrode for a non-aqueous electrolyte secondary battery provided with an active material layer containing a silicon-based material,
The non-aqueous electrolysis, wherein an average peak position of Si peak of Raman spectrum measured in the thickness direction of the active material layer after charging / discharging the negative electrode is 480 to 510 cm ⁻¹ Negative electrode for liquid secondary battery. When the active material layer is virtually divided into two in the thickness direction, the average peak position on one side and the average peak position on the other side of the divided active material layer are 480 to 510 cm ^-1 , respectively. Item 6. The negative electrode for a nonaqueous electrolyte secondary battery according to Item 1.   The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the active material layer has a thickness of 1 to 200 µm.   The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the active material layer includes particles of a silicon-based material.   5. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 4, wherein a metal material having a low ability to form a lithium compound permeates between particles of the silicon-based material in the active material layer.   6. The nonaqueous electrolytic solution according to claim 5, wherein the metal material having a low ability to form a lithium compound is deposited and permeated by electrolytic plating, and the pH of the plating bath used for the electrolytic plating is 7.1 to 11. Negative electrode for secondary battery.   The negative electrode for a non-aqueous electrolyte secondary battery according to claim 5 or 6, wherein the plating bath is a copper pyrophosphate bath or an alkaline nickel bath.   A surface coating layer containing a metal material having a low ability to form a lithium compound is formed on the active material layer, and a plurality of pores leading to the active material layer are formed in the surface coating layer. The negative electrode for a nonaqueous electrolyte secondary battery according to any one of 1 to 7. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 4, wherein the silicon-based material particles are made of Si or SiO ₂ .   An active material layer including particles of a silicon-based material is provided, and a metal material having a low lithium compound forming ability penetrates between the particles in the active material layer, and the metal material has a pH of 7.1 to 11 A negative electrode for a non-aqueous electrolyte secondary battery deposited and permeated by electrolytic plating using a plating bath.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 11, wherein the plating bath is a copper pyrophosphate bath or an alkaline nickel bath. A nonaqueous electrolyte secondary battery comprising the negative electrode for a nonaqueous electrolyte secondary battery according to claim 1.

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