JP2010140793A - Method of manufacturing negative electrode for nonaqueous electrolyte secondary battery, negative electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

The present invention provides a method for producing a negative electrode for a non-aqueous electrolyte secondary battery, in which the amount of lithium preliminarily applied to the negative electrode active material can be quantified by non-destructive in-line inspection, and both improvement in quality and improvement in yield can be achieved. thing.
Before and after a lithium application step of attaching and occluding lithium to a negative electrode active material layer containing a negative electrode active material, the negative electrode active material layer is irradiated with a beta ray from an irradiation source to thereby form a negative electrode active material. The amount of backscattering from the material layer 12b is measured, and then the amount of lithium attached to and stored in the negative electrode active material layer 12b is quantified based on the difference in the amount of backscattering before and after the lithium application step.
[Selection] Figure 3

Description

  The present invention relates to a method for producing a negative electrode for a nonaqueous electrolyte secondary battery, a negative electrode for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery using the same. More specifically, the present invention mainly relates to an improvement in a method for previously applying lithium to a negative electrode active material.

  In recent years, expectations are increasing for non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, as power sources for driving various electronic devices. A lithium ion secondary battery has a high capacity, a high energy density, and can be easily reduced in size and weight. For this reason, it is widely used as a power source for portable small electronic devices such as mobile phones, personal digital assistants (PDAs), notebook personal computers, digital cameras, and portable game machines. In addition, application development as an in-vehicle power source such as an electric vehicle and a hybrid vehicle, an uninterruptible power source, and the like is also in progress.

  In a current typical lithium ion secondary battery, a carbon material such as graphite is used as a negative electrode active material. Further, in recent years, there has been a demand for further increase in capacity and output of lithium ion secondary batteries. As a negative electrode active material for achieving such a demand, an alloy system containing silicon, tin, etc. and alloying with lithium Negative electrode active materials are attracting attention.

  However, in general, the negative electrode active material does not release part of the lithium occluded in the first charge during the discharge. The lithium content that is not released becomes an irreversible capacity that does not participate in the subsequent charge / discharge cycle, and causes a loss of capacity of the lithium ion secondary battery.

  Therefore, in order to reduce the loss due to such irreversible capacity, a method of previously applying lithium to the negative electrode active material has been proposed. Examples of the method for applying lithium to the negative electrode active material include a vacuum deposition method and a method of directly attaching lithium metal to the surface of the negative electrode.

  And since the application amount of lithium to the negative electrode active material directly affects the charge / discharge capacity of the battery, it is important to control the application amount. Also, if the amount of lithium applied to the negative electrode active material is small, the effect of reducing the irreversible capacity will be poor, and conversely, if the amount of lithium applied is too large, the manufacturing cost will increase, so there is no excess or shortage of lithium. It is important to grant.

  In order to inspect how much lithium is applied to the negative electrode active material, for example, the negative electrode before the lithium application step and the negative electrode after the lithium application step are each punched into a predetermined size, and thus obtained samples Using the method for calculating the amount of lithium applied in the lithium application step based on the difference in weight between the negative electrode before the lithium application step and the negative electrode after the lithium application step, each produced a model cell. And a method of calculating the lithium content from the charge / discharge capacity.

In such an inspection, in order to improve the inspection accuracy, it is necessary to increase the number of product samples. In this case, the yield of the product decreases. On the other hand, if the number of samples is reduced, the inspection accuracy is lowered, and the product quality may vary.
Also, with this inspection method, the amount of lithium applied to the negative electrode active material cannot be measured during the negative electrode manufacturing process, that is, a non-destructive in-line inspection cannot be performed.

By the way, Patent Document 1 describes a coating apparatus for continuously coating a paste-like kneaded material mainly composed of a battery active material powder on a continuous strip-shaped metal core. Describes that the weight of the paste applied to the metal core is measured by irradiating the dried paste with β-rays using ⁹⁰ Sr as a radiation source and measuring the radiation dose transmitted through the paste. ing.

Patent Document 2 describes a method for measuring the purity of lithium in a lithium or lithium alloy thin film formed on a substrate.
Japanese Patent No. 3324343 JP 2007-63615 A

In the method of measuring the transmitted dose of beta rays as described in Patent Document 1, in order to transmit all of the lithium applied to the negative electrode current collector, the negative electrode active material layer, and the negative electrode active material layer, a high energy It becomes necessary to use a beta source. However, when irradiated with high-energy beta rays, the beta dose absorbed by lithium in the negative electrode active material layer becomes smaller than the total beta dose transmitted through the negative electrode. The amount of lithium cannot be accurately quantified.
Moreover, in the method of patent document 2, it is premised on destroying a thin film in the case of a measurement.

The object of the present invention is to quantitate the amount of lithium applied in advance to the negative electrode active material layer (hereinafter referred to as “lithium applied amount”) by non-destructive in-line inspection, An object of the present invention is to provide a method for producing a negative electrode for a non-aqueous electrolyte secondary battery that can achieve both improvement in yield.
Another object of the present invention is to provide a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery in which the irreversible capacity and quality variation of the negative electrode active material are reduced.

  The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to the present invention includes a lithium application step of attaching and occluding lithium to a negative electrode active material layer containing a negative electrode active material, before the lithium application step and after the lithium application step. , Respectively, by irradiating the negative electrode active material layer with beta rays to measure the backscattering amount from the negative electrode active material layer, and then backscattering amount before and after the lithium application step Based on the difference, the amount of lithium deposited and occluded in the negative electrode active material layer is quantified.

  When beta rays are applied to the coating film formed on the metal substrate, most of the beta rays pass through the coating film and reach the surface of the metal substrate, and are scattered back from the surface of the metal substrate. The back scattered beta rays are emitted from the surface of the coating film while being absorbed by the coating film because the energy is low. At this time, the amount of beta rays absorbed by the coating film is proportional to the amount of substance in the coating film. Therefore, when the components and density of the coating film are uniform, the thickness of the coating film can be measured by measuring the beta dose backscattered from the surface of the coating film with a radiation measuring machine. Actually, the beta ray backscattering method is used for measuring a film thickness of a plating film or the like.

On the other hand, the negative electrode for a nonaqueous electrolyte secondary battery has a laminate or a mixture of a negative electrode active material layer and lithium metal applied thereto on the surface of a negative electrode current collector as a metal substrate. Therefore, the beta-ray backscattering method is not originally used for measuring the film thickness.
However, as a result of the study by the present inventors, regardless of the state of lithium in the negative electrode active material layer, that is, whether lithium is attached to the surface of the negative electrode active material layer or occluded inside. It was found that the amount of lithium present in the negative electrode active material layer can be measured by the beta backscattering method. Specifically, the lithium application amount necessary for eliminating the irreversible capacity of the negative electrode active material layer is an amount of 50 μm or less in terms of thickness, and when the lithium application amount is within the above range, The amount of lithium applied to the material layer is proportional to the amount of backscattered beta rays. Therefore, the amount of lithium applied to the negative electrode active material layer can be quantified by the beta ray backscattering method.

  In the above method for producing a negative electrode for a non-aqueous electrolyte secondary battery, the amount of lithium (amount of lithium attached) applied in advance to the negative electrode active material layer can be quantified without destroying the negative electrode active material layer. In addition, the step of measuring the amount of backscattered beta rays from the negative electrode active material layer and the step of imparting lithium to the negative electrode active material layer can be performed subsequently, and the amount of lithium determined by in-line inspection. Is possible.

  That is, according to the above method for producing a negative electrode for a non-aqueous electrolyte secondary battery, the amount of lithium adhesion can be quantified by non-destructive in-line inspection. In addition, this makes it possible to improve the quality of the negative electrode active material layer and reduce the variation in quality, and furthermore, since it is quantified by non-destructive inspection, it is possible to prevent a decrease in yield.

In the method for manufacturing a negative electrode for a non-aqueous electrolyte secondary battery, the amount of lithium is quantified in a predetermined region of the negative electrode active material layer or the surface of the negative electrode current collector, and then lithium is added to another region of the negative electrode active material layer. It is preferable to adjust the amount of lithium to be provided and occluded in the other region based on the result of quantitative determination of the amount of lithium.
In this case, on the line for producing the negative electrode for the non-aqueous electrolyte secondary battery, the quantitative determination result of the lithium amount in the predetermined region of the negative electrode active material layer is sequentially calculated as the amount of lithium applied to the other region of the negative electrode active material layer. It can be reflected in the adjustment. Moreover, the quality of the negative electrode active material layer can be further improved by feedback of such quantitative results.

In the above method for producing a negative electrode for a nonaqueous electrolyte secondary battery, the beta ray source is preferably ¹⁴⁷ Pm, ¹⁴ C, or ²⁰⁴ Tl.
The intensity of the beta rays irradiated from the beta ray source is appropriate for the purpose of measuring the lithium content. For this reason, the precision of the measurement of the amount of backscattering can be improved by using the beta ray source.

A negative electrode for a non-aqueous electrolyte secondary battery according to the present invention includes a negative electrode current collector, a negative electrode active material layer including a negative electrode active material formed on a surface of the negative electrode current collector, and an adhesion and occlusion to the negative electrode active material layer. The lithium is attached and occluded in the negative electrode active material layer by the method for producing a negative electrode for a non-aqueous electrolyte secondary battery of the present invention.
According to the negative electrode for a nonaqueous electrolyte secondary battery, the irreversible capacity of the negative electrode active material can be reduced because the method for producing a negative electrode for a nonaqueous electrolyte secondary battery of the present invention is used for the production of a negative electrode. Furthermore, variation in battery quality can be reduced.

The nonaqueous electrolyte secondary battery of the present invention includes a negative electrode for a nonaqueous electrolyte secondary battery according to the present invention, a positive electrode, a separator interposed between the negative electrode for a nonaqueous electrolyte secondary battery and a positive electrode, And a water electrolyte.
According to the nonaqueous electrolyte secondary battery, the irreversible capacity of the negative electrode active material can be reduced because the method for producing a negative electrode for a nonaqueous electrolyte secondary battery according to the present invention is used for producing a negative electrode, and Variations in battery quality can be reduced.

According to the method for producing a negative electrode for a non-aqueous electrolyte secondary battery of the present invention, the amount of lithium previously imparted to the negative electrode active material layer can be quantified by non-destructive in-line inspection. For this reason, both improvement in quality and improvement in yield can be achieved, and a high-quality negative electrode for a non-aqueous electrolyte secondary battery can be provided at low cost.
Moreover, according to the negative electrode for nonaqueous electrolyte secondary batteries and the nonaqueous electrolyte secondary battery of this invention, the irreversible capacity | capacitance of a negative electrode active material and the dispersion | variation in the quality of a battery can be reduced.

  Hereinafter, as a method for producing a negative electrode for a nonaqueous electrolyte secondary battery, a negative electrode for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery of the present invention, a lithium ion secondary battery will be described in detail as an example.

FIG. 1 is a schematic longitudinal sectional view showing an embodiment of a lithium ion secondary battery 10.
Referring to FIG. 1, a lithium ion secondary battery 10 includes a positive electrode 11, a negative electrode 12, a separator 13 that separates the positive electrode 11 and the negative electrode 12, and a positive electrode lead 14 that is electrically connected to the positive electrode 11. And a negative electrode lead 15 electrically connected to the negative electrode 12, an exterior body 16 for housing these, and a gasket 17 for sealing the exterior body 16. In addition, the lithium ion secondary battery 10 includes one single cell including a positive electrode 11, a separator 13, and a negative electrode 12. The lithium ion secondary battery of the present invention is not limited to the above configuration. For example, a plurality of single cells may be overlapped with each other separated by a separator, a positive electrode, a negative electrode Can be made into a strip and wound while being separated by a separator.

The positive electrode 11 includes a positive electrode current collector 11a and a positive electrode active material layer 11b.
As the positive electrode current collector 11a, those commonly used in this field can be used. For example, various positive electrode current collectors used for lithium ion secondary batteries such as a porous conductive substrate and a nonporous conductive substrate. Can be used. Examples of the material for the conductive substrate include metal materials such as stainless steel, titanium, aluminum, and aluminum alloys, and conductive resins.

The positive electrode active material layer 11b is formed on one surface of the positive electrode current collector 11a and includes a positive electrode active material. The positive electrode active material layer 11b may be formed on both surfaces of the positive electrode current collector 11a. The positive electrode active material layer 11b may further include various additives such as a conductive agent and a binder.
As the positive electrode active material, various materials that can occlude and release lithium can be used. Specific examples include lithium-containing composite metal oxides and olivine type lithium phosphate.

The positive electrode active material layer 11b includes, for example, a positive electrode active material and, if necessary, additives such as a conductive agent and a binder dissolved or dispersed in an organic solvent. It can be produced by applying to the surface of the body 11a, drying, and rolling to a predetermined thickness.
The thickness of the positive electrode active material layer 11b is not particularly limited, and can be set as appropriate according to the size of the lithium ion secondary battery, the configuration of the single cell, and the number of stacked layers.

The negative electrode 12 includes a negative electrode current collector 12a and a negative electrode active material layer 12b.
As the negative electrode current collector 12a, for example, various negative electrode current collectors used in lithium ion secondary batteries such as a porous conductive substrate and a non-porous conductive substrate can be used. Examples of the material for the conductive substrate include metal materials such as stainless steel, nickel, copper, and copper alloys, and conductive resins.

  The negative electrode active material layer 12b is formed on one surface of the negative electrode current collector 12a and includes a negative electrode active material. The negative electrode active material layer 12b may be formed on both surfaces of the negative electrode current collector 12a. The negative electrode active material layer 12b may further include various additives such as a conductive agent and a binder.

As the negative electrode active material, various materials that can occlude and release lithium can be used. Specific examples include carbon materials and alloy-based negative electrode active materials.
The alloy-based negative electrode active material is alloyed with lithium during charging and occludes lithium under a negative electrode potential, and releases lithium during discharging. Such an alloy-based negative electrode active material is not particularly limited, and examples thereof include an alloy-based negative electrode active material containing silicon or tin.

  Examples of the alloy-based negative electrode active material containing silicon include silicon, silicon oxide, silicon carbide, silicon nitride, silicon-containing alloy, and solid solutions thereof. Among these, as the silicon-containing alloy, for example, one or more selected from the group consisting of silicon and Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti An alloy containing an element can be given. In addition, silicon oxide, silicon nitride, and silicon-containing alloy, part of the silicon contained in these, B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, It may be substituted with one or more elements selected from the group consisting of Nb, Ta, V, W, Zn, C, N, and Sn.

Examples of the alloy-based negative electrode active material containing tin include tin, tin oxide, tin nitride, tin-containing alloys, solid solutions thereof, SnSiO ₃ , Ni ₂ Sn ₄ , and Mg ₂ Sn. Among these, examples of the tin-containing alloy include a Ni—Sn alloy, a Mg—Sn alloy, a Fe—Sn alloy, a Cu—Sn alloy, and a Ti—Sn alloy.

The negative electrode active material layer 12b is obtained by, for example, dissolving or dispersing a negative electrode active material and, if necessary, a conductive agent, a binder, etc. in an organic solvent, and using the negative electrode mixture slurry thus obtained as the surface of the negative electrode current collector 12a. It can produce by apply | coating to and drying.
Moreover, the negative electrode active material layer 12b made of an alloy-based negative electrode active material can be formed into a thin film by a vapor phase method, for example, on the negative electrode current collector 12a.

  FIG. 2 is a schematic diagram illustrating an example of a vacuum deposition apparatus. This apparatus has an unwinding roll 22 for continuously supplying a strip-like negative electrode current collector 12a into a chamber 20 whose pressure is reduced by a vacuum pump 21, and a negative electrode current collector 12. A pair of film forming rolls 24a and 24b that run so as to face each of the sources 23a and 23b, and a winding roll 25 for winding the negative electrode current collector 12a are provided.

  A negative electrode active material supplied from one vapor deposition source 23a is vapor-deposited on one surface of the negative electrode current collector 12a conveyed to one film forming roll 24a in a region partitioned by a pair of masks 26a. An active material layer (not shown) is formed. Further, the negative electrode active material supplied from the other vapor deposition source 23b is vapor-deposited on the other surface of the negative electrode current collector 12a conveyed to the other film forming roll 24b in a region partitioned by the pair of masks 26b. Then, a negative electrode active material layer (not shown) is formed. Thus, negative electrode active material layers are formed on both surfaces of the negative electrode current collector 12a.

In the case where the alloy-based negative electrode active material layer is formed by the vacuum vapor deposition apparatus shown in FIG. 2, each of the pair of vapor deposition sources 23a and 23b accommodates the negative electrode active material. The vacuum deposition apparatus further includes an electron beam generator or a resistance heating board (not shown). The vapor of the negative electrode active material is generated by irradiating each deposition source 23a, 23b with an electron beam or heating each deposition source 23a, 23b.
When the negative electrode active material is deposited, oxygen is supplied to the vapor of the negative electrode active material from a pair of oxygen nozzles 27a and 27b as necessary. Thereby, the negative electrode active material formed on the surface of the negative electrode current collector 12a can be an oxide.

  In the case where the negative electrode active material layer is formed on the surface of the negative electrode current collector 12a by vacuum deposition, the deposition amount of the negative electrode active material is appropriately set, for example, the acceleration voltage of the electron beam, the current value, the degree of vacuum in the chamber, and the like. Can be adjusted. Specifically, when the acceleration voltage or current value of the electron beam is increased, the deposition amount of the negative electrode active material increases. Further, when the degree of vacuum in the chamber is increased, the amount of evaporation at the same temperature increases, so that the amount of deposition of the negative electrode active material increases.

Further, when the negative electrode active material is deposited by the electron beam, the deposition amount of the negative electrode active material is such that the accelerating voltage of the electron beam, the current value, and the degree of vacuum in the chamber are kept constant while the negative electrode current collector 12a is made negative. It can also be adjusted by changing the time of exposure to the vapor of the active material (specifically, the traveling speed of the negative electrode current collector 12a).
In addition, when the negative electrode active material is deposited by resistance overheating, the deposition amount of the negative electrode active material not only increases the degree of vacuum in the chamber, but also increases the heating temperature by increasing the applied voltage, It can also be increased by increasing the resistance overheating time and increasing the evaporation time.

  The thickness of the negative electrode active material layer 12b is not particularly limited, and can be appropriately set according to the size of the lithium ion secondary battery, the configuration of the single cell, and the number of stacked layers.

  Various separators used for lithium ion secondary batteries can be used as the separator 13. Specifically, a sheet or film having ion permeability and insulating properties and excellent mechanical strength can be used, and more preferably a porous sheet or porous material such as a microporous membrane, a woven fabric, and a non-woven fabric. A film is used.

One end of the positive electrode lead 14 is connected to the positive electrode current collector 11 a, and the other end is led out of the lithium ion secondary battery 10 from one opening 16 a of the outer case 16. One end of the negative electrode lead 15 is connected to the negative electrode current collector 12 a, and the other end is led out of the lithium ion secondary battery 10 from the other opening 16 b of the outer case 16.
As the positive electrode lead 14 and the negative electrode lead 15, various types of leads used in lithium ion secondary batteries can be used. Specifically, the positive electrode lead 14 may be aluminum or the like, and the negative electrode lead 15 may be nickel or the like.

Various exterior bodies used for lithium ion secondary batteries can be used for the exterior body 16. Specific examples include a metal case and a laminated laminate film case.
The gasket 17 is a sealing material for sealing the opening of the exterior body 16. Instead of using the gasket 18, the openings 19a and 19b of the outer case 19 may be directly sealed by welding or the like.

The lithium ion secondary battery 1 of the present invention can be manufactured, for example, as follows.
First, the positive electrode 11 and the negative electrode 12 are overlapped via the separator 13 to produce a plate-like electrode group. Next, one end of the positive electrode lead 14 is connected to the positive electrode current collector 11a, and one end of the negative electrode lead 15 is connected to the negative electrode current collector 12a. Then, the flat electrode group is inserted into the outer case 16, and the other ends of the positive electrode lead 14 and the negative electrode lead 15 are led out of the outer case 16, respectively, and a nonaqueous electrolyte is injected into the outer case 16. To do. In this state, the opening is welded via the gasket 17 while the inside of the outer case 16 is vacuum-depressurized.

  The various materials forming the lithium ion secondary battery, the production method of each part, the size of each part, etc. are not limited to the above, and can be set as appropriate.

  In addition, the nonaqueous electrolyte secondary battery of the present invention is not limited to the above embodiment, and can take various forms. Specifically, various forms such as a cylindrical battery, a square battery, a flat battery, a coin battery, and a laminated laminated film battery can be employed.

The manufacturing method of the negative electrode for nonaqueous electrolyte secondary batteries of this invention includes the lithium provision process which makes lithium adhere and occlude with respect to the negative electrode active material layer containing a negative electrode active material.
The lithium application step is a step of attaching and occluding lithium to the negative electrode active material layer of the negative electrode for a non-aqueous electrolyte secondary battery.

Examples of methods for applying lithium to the negative electrode active material layer include vacuum deposition, sputtering, ion plating, laser ablation, chemical vapor deposition (CVD), plasma chemical vapor deposition, and thermal spraying. Is mentioned. Of these, the vacuum deposition method is preferable.
In the case of the vacuum evaporation method, a negative electrode current collector is fixed in a chamber of a vacuum evaporation apparatus, and lithium vapor generated in the target may be attached to the negative electrode active material layer.

The application of lithium to the negative electrode active material by a vacuum vapor deposition method can be performed, for example, using the vapor deposition apparatus shown in FIG. 2 as in the case of forming an alloy-based negative electrode active material by a vapor phase method.
In this case, lithium is accommodated in each of the pair of vapor deposition sources 23a and 23b. In addition, the negative electrode active material layers formed on both surfaces of the negative electrode current collector 12a are vapor-deposited with lithium supplied from the respective vapor deposition sources 23a and 23b in regions partitioned by the pair of masks 26a and 26b, respectively. Further, a gas such as argon inert to lithium is introduced into the chamber 20 as necessary.

  In the case where lithium is applied to the negative electrode active material layer by vacuum deposition, the amount of lithium applied to the negative electrode active material layer is adjusted by appropriately setting, for example, the acceleration voltage of the electron beam, the current value, and the degree of vacuum in the chamber. it can. Specifically, when the acceleration voltage or current value of the electron beam is increased, the amount of applied lithium increases. Further, when the degree of vacuum in the chamber is increased, the amount of lithium applied increases.

Further, in the case of applying lithium by an electron beam, the amount of lithium applied is determined by the time during which the negative electrode active material layer is exposed to lithium vapor while keeping the acceleration voltage of the electron beam, the current value, and the degree of vacuum in the chamber constant ( Specifically, it can also be adjusted by changing the traveling speed of the negative electrode current collector 12a).
In addition, when applying lithium by resistance overheating, the amount of lithium applied not only increases the degree of vacuum in the chamber, but also increases the heating temperature by increasing the applied temperature, or lengthens the resistance overheating time, for example. It can also be increased by lengthening the evaporation time.

  The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to the present invention further includes irradiating the negative electrode active material layer with beta rays before and after the lithium application step, respectively, A measuring step for measuring the amount of scattering, and a quantitative step for quantifying the amount of lithium adhering to and occluded in the negative electrode active material layer based on the difference in the amount of backscattering before and after the lithium application step.

A measurement process is a process of irradiating a beta ray with respect to the negative electrode active material layer of the negative electrode for nonaqueous electrolyte secondary batteries, and measuring the backscattering amount.
For the measurement of the amount of backscattering, for example, a device for measuring the amount of backscattering of beta rays as shown in FIG. 3 can be used.

  The backscattering amount measuring device 40 includes an irradiation source 41 that irradiates beta rays to the negative electrode 12 for a lithium ion secondary battery, a slit 42 that restricts the passage of backscattered beta rays, and a backscattered beta. The detector 43 which collects a line | wire and the fixing stand 44 for affirming the negative electrode 12 are provided. The fixing base 44 fixes the negative electrode 12 so that the negative electrode current collector 12 a faces the irradiation source 41.

Part of the beta rays irradiated from the irradiation source 41 toward the negative electrode current collector 12a is absorbed by the negative electrode active material layer 12b or passes through the negative electrode active material layer 12b, and the negative electrode current collector Backscattered by the body 12a.
Of the beta rays backscattered by the negative electrode active material layer 12 b, those that have passed through the slit 42 are collected by the detector 43 disposed behind the irradiation source 41.

Examples of the source of beta rays irradiated toward the negative electrode current collector 12a include ¹⁴⁷ Pm, ¹⁴ C, and ²⁰⁴ Tl. Of these, ¹⁴⁷ Pm or ¹⁴ C is preferable.
There are various types of beta ray sources in addition to the above-mentioned sources, but the energy of beta rays is generally too large for the other sources. For this reason, when a radiation source other than the above radiation source is used, the beta dose absorbed by lithium in the negative electrode active material layer out of the beta rays backscattered from the negative electrode current collector surface is not absorbed. The beta dose released from the negative electrode active material layer becomes small, and a small amount of lithium on the negative electrode active material layer cannot be accurately quantified. On the other hand, when a beta ray source is selected from the above sources, the amount of lithium applied to the negative electrode active material layer can be accurately quantified because the beta ray energy can be set in an appropriate range. Can do.

  The quantitative step calculates the difference in the amount of backscattering of the beta rays measured in the measurement step before and after the lithium application step, and the amount of lithium attached and occluded in the negative electrode active material layer based on the calculation result Is a step of quantifying

  The amount of back-scattered beta rays reflected by the negative electrode active material layer 12b and collected by the detector 43 is such that the amount of lithium applied to the negative electrode active material layer 12b exceeds 50 μm in terms of film thickness. In the absence, it is proportional to the amount of lithium applied to the negative electrode active material layer 12b. In addition, the amount of lithium applied to the negative electrode active material layer in advance is set according to the irreversible capacity of the negative electrode active material, and the amount is approximately 1 to 20 μm in terms of film thickness. It is.

  For this reason, before and after the above-described lithium application step, the amount of beta rays that are backscattered by the negative electrode active material layer 12b and collected by the detector 43 is measured and compared, whereby the negative electrode active material layer 12b The amount of lithium applied can be quantified.

  In the method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to the present invention, the quantitative measurement is performed in a predetermined region of the negative electrode active material layer, and then lithium is applied to another region of the negative electrode active material layer. At this time, an adjustment step of adjusting the amount of lithium applied to the other region based on the result of the determination may be provided.

Since the amount of lithium attached and occluded in the negative electrode active material layer is quantified by the above quantification step, the lithium application necessary for eliminating the loss due to the irreversible capacity of the negative electrode active material based on the quantification result. It is possible to judge whether the amount is excessive or insufficient. Further, the result of the lithium application amount quantified in the quantification process can be fed back sequentially when the lithium is applied to other regions of the negative electrode active material layer by the adjustment process.
Therefore, when the adjustment step is provided, the accuracy of the lithium application amount can be further improved as a whole of the negative electrode for a nonaqueous electrolyte secondary battery, and the quality of the negative electrode is improved.

In the method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to the present invention, the process of imparting lithium to the negative electrode active material layer 12b and the process of measuring the amount of backscattering of beta rays are performed continuously. Can do.
Therefore, according to the present invention, the amount of lithium attached to the negative electrode active material can be quantified by in-line inspection without destroying the negative electrode active material.

  According to the present invention, as described above, for the negative electrode in a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, the amount of lithium previously imparted to the negative electrode active material can be quantified by non-destructive in-line inspection, It is possible to achieve both improvement in yield and improvement in yield. Accordingly, according to the present invention, a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery with reduced loss and quality variation due to the irreversible capacity of the negative electrode active material are provided at low cost. be able to.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example and a comparative example, these do not limit this invention at all.

<Manufacture of non-aqueous electrolyte secondary batteries>
Example 1
(1) Production of negative electrode As the negative electrode current collector 12a, a strip-shaped copper foil (manufactured by Hitachi Cable Ltd.) having a thickness of 30 μm and a surface roughness (arithmetic average height Ra, JIS B0601 _{: 2001} ) of 0.125 μm is used. It was. Moreover, the apparatus shown in FIG. 2 was used as a vacuum evaporation apparatus. The inside of the chamber 20 of this apparatus was an argon atmosphere with a pressure of 3.5 Pa, and scrap silicon having a purity of 99.999% was used for the pair of vapor deposition sources 23a and 23b. Then, an electron beam from an electron beam generator (not shown) is polarized by a polarization yoke and irradiated to the respective vapor deposition sources 23a and 23b, and the generated Si vapor is formed so that the film formation rate becomes 2 nm / second. The both surfaces of the negative electrode current collector 12a were irradiated from the openings of the masks 26a and 26b. At this time, oxygen was introduced from the pair of oxygen nozzles 27a and 27b, and Si and O ₂ were reacted. As a result, negative electrode active material layers having a composition of SiO _0.6 were formed on both surfaces of the current collector 12a. The total thickness of the negative electrode was 50 μm.

(2) Measurement of backscattering amount (measurement process)
The negative electrode 12 is fixed to a fixed base 44 of a commercially available beta ray backscattering amount measuring device (see FIG. 3), and the negative electrode active material layer 12b is irradiated with beta rays having ¹⁴⁷ Pm as a radiation source, The amount of scattering was measured. The measured value at this time was defined as the amount of backscattering of beta rays in a state where lithium is not applied to the negative electrode active material layer 12b (initial state). The backscattering amount was measured in a dry environment (dew point −40 ° C.), and the distance between the negative electrode and the measuring machine was 10 mm.

(3) Lithium application | coating process Based on the result of having produced the model cell by making the counter electrode into Li metal beforehand and measuring the irreversible capacity | capacitance of a negative electrode, the required amount of lithium provision was determined as 10 micrometers in conversion of thickness.
Next, the negative electrode 12 was mounted on the unwinding roll 22 of the vapor deposition apparatus shown in FIG. 2, and the inside of the chamber 20 was set to an argon atmosphere. Li metal (made by Honjo Metal Co., Ltd.) is used as the pair of vapor deposition sources 23a and 23b, which is placed on a tungsten board, Li is evaporated by resistance heating (not shown), and the negative electrode active of the negative electrode 12 is activated. An amount of Li corresponding to 10 μm in terms of thickness was deposited on the material layer 12a. When Li was converted into thickness, the porosity was 0%. Here, the amount of Li evaporation per unit time was controlled by changing the time for heating lithium.

(4) Measurement of backscattering amount (measurement process) and measurement of lithium application amount (quantitative process)
The negative electrode 12 that has undergone the lithium application step is again fixed to a fixed base 44 of a commercially available beta-ray backscattering amount measuring device (see FIG. 3), and beta ¹⁴⁷ Pm is used as a radiation source with respect to the negative electrode active material layer 12b. A line was irradiated and the amount of backscattering was measured. The backscattering amount was measured in a dry environment (dew point −40 ° C.), and the distance between the negative electrode and the measuring machine was 10 mm.

The measured value at this time was defined as the amount of beta ray backscattering in a state where lithium was applied to the negative electrode active material layer 12b (after the lithium application step).
Thus, the difference between the beta ray backscattering amount in the initial state and the beta ray backscattering amount after the lithium application step is obtained, and the lithium application amount to the negative electrode active material layer 12b based on the calibration curve prepared in advance. Was calculated.

(5) Production of positive electrode As the positive electrode active material, a lithium nickel-containing composite metal oxide having an average particle size of secondary particles of 10 μm and a specific surface area by the BET method of 0.45 m ² / g was used. The composition formula of this lithium nickel-containing composite metal oxide was LiNi _0.7 Co _0.2 Al _0.1 O ₂ , and as a result of analysis by powder X-ray diffraction, it had a single-phase hexagonal layered structure.

  100 g of the above positive electrode active material powder, 3 g of acetylene black (conductive agent), 3 g of polyvinylidene fluoride powder (binder) and 50 ml of N-methyl-2-pyrrolidone (NMP) were mixed thoroughly to prepare a positive electrode mixture paste. did. This positive electrode mixture paste was applied to one side of an aluminum foil (positive electrode current collector) having a thickness of 20 μm, dried and rolled to form a positive electrode active material layer. Thereafter, the positive electrode was cut out to a size of 30 mm × 180 mm. The obtained positive electrode plate was cut to prepare a positive electrode having a positive electrode active material layer with a thickness of one side of 50 μm and a size of 30 mm × 200 mm.

(6) Production of wound battery One end of an aluminum positive electrode lead was connected to a portion where the current collector of the obtained positive electrode was exposed. Further, one end of a nickel negative electrode lead was connected to a portion where the current collector of the obtained negative electrode was exposed. The positive electrode, the polyethylene porous membrane, and the negative electrode are placed so that the positive electrode active material layer and the negative electrode active material layer face each other through a polyethylene porous membrane (separator, trade name: hypopore, thickness 20 μm, manufactured by Asahi Kasei Corporation). Superimposed. This was wound and formed into a flat plate shape to produce a flat plate-shaped wound electrode group. The positive electrode lead and the negative electrode lead were connected so as to be parallel to the winding axis direction of the wound electrode group.

This wound electrode group was inserted into an outer case made of an aluminum laminate sheet, and an electrolytic solution was injected. The electrolyte includes a nonaqueous electrolyte in which LiPF ₆ is dissolved at a concentration of 1.0 mol / L in a mixed solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 1: 1. Using. Next, the positive electrode lead and the negative electrode lead are led out from the opening of the outer case to the outside of the outer case, and the opening of the outer case is welded while the inside of the outer case is vacuum-depressurized. An uncharged lithium ion secondary battery was prepared by cutting into lengths.

<Example of creating a calibration curve>
When the amount of lithium applied to the negative electrode active material layer is in a predetermined range in terms of the thickness of lithium, the amount of lithium applied is proportional to the amount of beta ray backscattering in the negative electrode active material layer, and the negative electrode In order to confirm that a calibration curve for quantifying the amount of lithium applied to the active material layer based on the backscattering amount of beta rays in the negative electrode active material layer can be created, the following test was performed.

Test example 1
First, in the same manner as in Example 1, a negative electrode active material having a composition of SiO _0.6 on both surfaces of a negative electrode current collector 12a having a strip-shaped copper foil (thickness 30 μm, surface arithmetic average height (Ra) 0.125 μm). A negative electrode 12 having a thickness of 50 μm and having a layer formed thereon was produced. In this state (initial state), the backscattering amount of beta rays for the negative electrode active material layer 12b of the negative electrode 12 was measured in the same manner as in Example 1.

Subsequently, Li was vapor-deposited with respect to the negative electrode active material layer 12b of the said negative electrode 12 with the vapor deposition apparatus used in Example 1. FIG. The deposition amount of Li was appropriately set in the range of 4 to 6000 μm.
Then, for samples with different Li deposition amounts, the backscattering amount of the beta rays for the negative electrode active material layer 12b was measured in the same manner as in Example 1. Based on the results, the amount of lithium applied converted into thickness and the count number [cps] of beta rays absorbed by lithium in the negative electrode active material layer obtained from the measurement result of the backscattering amount of beta rays The relationship is shown in the graph.

  FIG. 4A is a graph showing the relationship between the lithium application amount [μm] converted to thickness and the number of counts [beta] of beta rays absorbed by lithium in the negative electrode active material layer in Test Example 1 described above. Moreover, FIG. 4B is a graph which expands and shows the range whose lithium application amount is 0-60 micrometers among FIG. 4A.

  As is clear from FIG. 4A, when the amount of applied lithium is several hundred μm or more in terms of the thickness of lithium, even if the amount of applied lithium increases, the number of beta rays absorbed by lithium changes. Is not observed. However, as apparent from FIG. 4B, when the lithium application amount is 60 μm or less in terms of lithium thickness, the increase in lithium application amount is proportional to the number of beta rays absorbed by lithium. You can see that

  On the other hand, as described above, in the field of non-aqueous electrolyte secondary batteries, the amount of lithium applied to the negative electrode active material layer 12b is generally 50 μm or less in terms of lithium thickness. Therefore, in this field, for example, by using FIG. 4B as a calibration curve, the amount of lithium applied to the negative electrode active material layer 12b can be quantified based on the number of beta rays absorbed by lithium. .

  The present invention is extremely useful as, for example, a power source for driving various electronic devices, an in-vehicle power source such as an electric vehicle and a hybrid vehicle, a negative electrode used for an uninterruptible power source and the like, and a manufacturing method thereof, and the various power sources described above. is there.

FIG. 1 is a schematic longitudinal sectional view showing an embodiment of a lithium ion secondary battery. FIG. 2 is a schematic diagram illustrating an example of a vacuum deposition apparatus. FIG. 3 is a schematic configuration diagram illustrating an example of an apparatus for measuring the amount of backscattered beta rays. 4A is a graph showing the relationship between the lithium application amount converted into thickness and the number of beta rays absorbed by lithium in the negative electrode active material layer in Test Example 1. FIG. FIG. 4B is a graph showing, in an enlarged manner, the range of 0-60 μm of lithium applied in FIG. 4A.

Explanation of symbols

  10 lithium ion secondary battery, 11 positive electrode, 11a positive electrode current collector, 11b positive electrode active material layer, 12 negative electrode, 12a negative electrode current collector, 12b negative electrode active material layer, 13 separator, 14 positive electrode lead, 15 negative electrode lead, 16 gasket 17 exterior body, 20 chamber, 21 vacuum pump, 22 unwinding roll, 23a deposition source, 23b deposition source, 24a deposition roll, 24b deposition roll, 25 winding roll, 26a mask, 26b mask, 27a oxygen nozzle, 27b Oxygen nozzle, 40 measuring device, 41 radiation source, 42 slit, 43 detector, 44 fixing base.

Claims (5)

A method for producing a non-aqueous electrolyte secondary battery including a lithium application step of attaching and occluding lithium to a negative electrode active material layer containing a negative electrode active material,
Before the lithium application step and after the lithium application step, the negative electrode active material layer is irradiated with beta rays to measure the amount of backscattering from the negative electrode active material layer, and then the lithium application step A method for producing a negative electrode for a nonaqueous electrolyte secondary battery, wherein the amount of lithium attached to and stored in the negative electrode active material layer is quantified based on a difference in backscattering amount before and after the lithium application step.   When the amount of lithium is quantified in a predetermined region of the negative electrode active material layer and then lithium is applied to the other region of the negative electrode active material layer, it adheres to the other region based on the quantification result of the lithium amount. The method for producing a negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the amount of lithium to be occluded is adjusted. The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the beta ray source is ¹⁴⁷ Pm, ¹⁴ C, or ²⁰⁴ Tl. A negative electrode current collector, a negative electrode active material layer containing a negative electrode active material formed on the surface of the negative electrode current collector, and lithium attached and occluded in the negative electrode active material layer,
A negative electrode for a nonaqueous electrolyte secondary battery, wherein the lithium is attached and occluded in the negative electrode active material layer by the method for producing a negative electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3.   A nonaqueous electrolyte comprising: the negative electrode for a nonaqueous electrolyte secondary battery according to claim 4; a positive electrode; a separator interposed between the negative electrode for the nonaqueous electrolyte secondary battery and the positive electrode; and a nonaqueous electrolyte. Secondary battery.

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