JP2008123814A - Lithium secondary battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery, and its manufacturing method, excellent in charge and discharge characteristics using active material particles containing silicon as an anode active material and polyimide resin as a binder. <P>SOLUTION: In the lithium secondary battery A1 provided with an anode 4a with a mixture layer containing an active material particles containing silicon and a binder arranged on the surface of a collector made of conductive metal foils, a cathode 3a, and nonaqueous electrolyte, the active material particle consists of an amorphous matter with a half-value width of 4° or more when it has a peak in X-ray diffraction using CuKα, and the binder contains polyimide resin. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a lithium secondary battery excellent in charge / discharge characteristics and a method for producing the same, and in particular, an active material particle containing silicon as a negative electrode active material and a lithium secondary excellent in charge / discharge characteristics using a polyimide resin as a binder. The present invention relates to a battery and a manufacturing method thereof.

  In recent years, a large number of mobile and portable electronic devices such as mobile phones, notebook personal computers, PDAs, and portable digital media players have appeared, and the battery as a driving power source has been improved in function, size and size of these devices. Due to the demand for weight reduction, further increase in capacity is desired. In addition, it is extremely important that these batteries are secondary batteries that can be used repeatedly many times from the viewpoint of economy. In the field of secondary batteries, lithium secondary batteries having a higher energy density than other batteries have attracted attention, and the proportion of the lithium secondary batteries has greatly increased in the secondary battery market.

  Such a lithium secondary battery is generally manufactured as follows. That is, a negative electrode in which a negative electrode mixture containing a negative electrode active material is applied to both sides of a current collector made of a conductive metal foil made of a long sheet-like copper foil, and a positive current collector made of a long, thin sheet-like aluminum foil A separator made of a microporous polyethylene film or the like is placed between the positive electrode coated with a positive electrode mixture containing a positive electrode active material on both sides of the body, and the cylindrical winding is performed with the negative electrode and the positive electrode insulated from each other by the separator. A cylindrical wound electrode body is produced by spirally winding the core. In the case of a rectangular shape, the cylindrical wound electrode body is further crushed with a press machine so as to be inserted into a rectangular battery outer body. Next, these cylindrical wound electrode bodies or rectangular wound electrode bodies are accommodated in the corresponding battery casings, respectively, and a nonaqueous electrolyte is injected into a lithium secondary battery.

As a positive electrode active material in such a non-aqueous electrolyte secondary battery, a compound capable of reversibly occluding and releasing lithium ions, for example, Li _x MO ₂ (where M is Co, Ni, or Mn). A lithium transition metal composite oxide represented by at least one), that is, LiCoO ₂ , LiNiO ₂ , LiNi _y Co _1-y O ₂ (y = 0.01 to 0.99), LiMnO ₂ , LiMn ₂ O ₄ , LiCo _x Mn _y Ni _z O ₂ (x + y + z = 1), LiFePO ₄ or the like is used singly or in combination.

In addition, as a negative electrode active material used for this lithium secondary battery, dendrites can grow while carbonaceous materials such as graphite and amorphous carbon have discharge potentials comparable to lithium metals and lithium alloys. Therefore, it is widely used because it has excellent properties such as high safety, excellent initial efficiency, good potential flatness, and high density. However, when a negative electrode active material made of a carbon material is used, lithium can only be inserted up to the composition of LiC ₆ and the theoretical capacity is 372 mAh / g, which is an obstacle to increasing the capacity of the battery. Yes.

Accordingly, lithium secondary batteries using aluminum, silicon, tin, or the like alloyed with lithium have been developed as negative electrode active materials having high energy density per mass and volume (see Patent Documents 1 to 7 below). In this case, for example, silicon and tin can insert Li up to compositions of Li _4.4 Si and Li _4.4 Sn, respectively, so that the theoretical capacities are 4200 mAh / g and 993 mAh / g, respectively, and a carbon material is used as the negative electrode active material. A much larger capacity can be expected than when it is used. However, particularly when silicon particles, silicon alloy particles, and the like are used as the negative electrode active material, the negative electrode active material expands and contracts with the charge / discharge cycle. As a result of chipping off, there has been a problem that the cycle characteristics of the battery deteriorate.

  In order to solve such problems, a strong polyimide is used to suppress deterioration of cycle characteristics by focusing on the construction of an electrode structure that can be maintained even when the volume of the negative electrode active material made of silicon or silicon alloy is changed. A resin using a resin as a binder (see Patent Document 2 below) or a current collector having a large surface roughness (see Patent Document 3 below) has been developed.

  In addition, a proposal to suppress the reactivity on the new surface of the negative electrode active material made of silicon or silicon alloy by improving the nonaqueous electrolyte (see Patent Document 4 below), silicon or silicon alloy having a small crystallite size, etc. Proposals for improving cycle characteristics by using a negative electrode active material (see Patent Documents 5 and 6 below), and further, an amorphous silicon thin film is formed in a columnar shape on a current collector to change the direction of volume expansion. There has also been proposed a technique (see Patent Document 7 below) for improving the cycle characteristics by controlling.

Japanese Patent Laid-Open No. 10-255768 Japanese Patent Laid-Open No. 2002-260637 JP 2004-235057 A Republished publication WO2004 / 109839 JP 2004-311429 A JP 2004-303593 A JP 2002-313319 A

  Although it is recognized that the lithium secondary battery of the conventional example as described above can achieve a high capacity and has improved the cycle characteristics, the cycle characteristics are still sufficiently improved to meet the user's request. Can not do.

  The inventors have conducted various experiments in order to further improve the cycle characteristics of a lithium secondary battery using silicon or a silicon alloy as the negative electrode active material. As a result, the silicon or silicon alloy as the negative electrode active material has a specific amorphous property. It was found that a lithium secondary battery having a cycle characteristic far superior to that of the conventional example can be obtained by using a polyimide resin as a binder while using it as a powder in the quality state. Has been completed.

  That is, the present invention provides a lithium secondary battery that uses silicon or a silicon alloy as a negative electrode active material and uses a polyimide resin as a binder and has high capacity and excellent long-term cycle characteristics, and a method for manufacturing the same. Objective.

  The above object of the present invention can be achieved by the following configurations. That is, the lithium secondary battery of the present invention includes a negative electrode in which a mixture layer containing active material particles containing silicon and a binder is disposed on the surface of a current collector made of a conductive metal foil, a positive electrode, and a non-aqueous electrolyte. The active material particles are made of an amorphous material having a half width of 4 ° or more when the active material particles have a peak in X-ray diffraction using CuKα, and the binder contains a polyimide resin. It is characterized by.

  Here, “amorphous” is vaguely defined as “a state in which constituent atoms and molecules are not regularly arranged” as being generally different from crystalline. However, in many cases, the constituent atoms and molecules are influenced by other adjacent atoms and molecules, so that it can be said that there is some ordering. In X-ray diffraction, a very wide peak with low intensity is observed, but the three-dimensional arrangement of the amorphous material is orderly, although it cannot be called crystalline. Because.

  In the present invention, “amorphous” is defined as a state having a very broad peak having a half-value width of 4 ° or more when having a peak in X-ray diffraction using CuKα. The above conditions may be satisfied even with particles having very small crystallites in which several atoms are connected, but particles in which such microcrystals are randomly arranged are within the scope of the present invention.

  An active material particle having crystallites has a grain boundary part and a bulk part in which the bonding state of atoms is different. Even if these grain boundary parts, bulk parts, and amorphous parts are composed of the same element, the bonding state of atoms is different, so that the electronic conductivity and reactivity with lithium ions are different. For this reason, inside the active material particles having crystallites, local unevenness is caused in the progress of the chemical reaction during charging and discharging. For example, when the charge / discharge reaction is likely to proceed at the grain interface where cracks are likely to occur, the active material particles crack due to volume expansion and contraction. In addition, when the bulk is more advantageous for charge / discharge reaction, there can be a difference in the volume change between the crystallite that has progressed to the bulk part and the crystallite that has stopped the reaction at the grain interface. Therefore, the active material particles are liable to break or collapse.

  In addition, when the active material particles are single crystals, the inside of the bulk becomes homogeneous, but after charging / discharging, the original state cannot be maintained due to, for example, the bonds in the crystal being displaced, and accompanying the charging / discharging reaction. Will become heterogeneous. In addition, since a silicon single crystal has a (111) plane as a cleavage plane, it breaks along the cleavage plane when the active material expands and contracts due to charge and discharge.

  When the active material particles are amorphous, the inside of the particles becomes homogeneous, the chemical reaction associated with charging / discharging occurs uniformly, and even when the charging / discharging reaction proceeds, non-homogenization does not occur. Combined with the use of a strong polyimide resin, it can suppress cracking and collapse of active material particles, and can prevent reaction with the electrolyte accompanying cracking and chipping off from the mixture layer due to collapse. Can be prevented.

  In the present invention, “containing silicon” means containing at least one selected from silicon and silicon alloys. The constituent materials other than the negative electrode, such as the positive electrode and separator electrolyte used in the lithium secondary battery of the present invention, can be appropriately selected and used without particular limitation.

  In the lithium secondary battery of the present invention, the active material particles have a peak in X-ray diffraction using CuKα, and 2θ is in the range of 27 ° to 30 ° and in the range of 50 ° to 54 °. It is preferable that the peak top exists and the full width at half maximum is 4 ° or more.

  The active material particles in the present invention are particles in which atoms and molecular units having different ordering and sizes of bonds are randomly arranged, or particles in which very small crystallites are randomly arranged. In the former case, a substantial peak does not occur in X-ray diffraction, or a halo peak with a very wide half-value width occurs. In this case, there are no bulk boundaries that are grain boundaries or crystalline, and since the electron conductivity in the particles and the reactivity with lithium ions are uniform, the cracking and collapse of the particles can be suppressed, Deterioration of cycle characteristics can be suppressed.

If a broad peak occurs in the X-ray diffraction, the latter is possible. In this case, when the following Scherrer equation is applied, for example, when X-ray diffraction using CuKα has a peak with a peak top 2θ of 28 ° and a half-value width of 4 °, the crystallite size is 20.5 サ イ ズThe calculation with
Scherrer's formula: D _hkl = kλ / βcosθ
(Where D _hkl : crystal size viewed from (hkl) plane, k: proportional constant, λ: X-ray wavelength, β: half-width of diffraction line, θ: diffraction angle)

  In the case of silicon, since the distance between silicon in a single crystal is 2.34 mm, 8 to 9 silicon atoms are arranged in a crystallite having a crystallite size of 20.5 mm. In a crystallite of this size, since the influence of the grain boundary is strongly influenced also in the bulk part, the difference in properties between the grain boundary and the bulk part becomes small. Moreover, since the grain boundary and the bulk part are finely distributed in the active material particles, it does not affect the cracking and collapse caused by the heterogeneity of the active material particles. For this reason, similarly to the former case, it is possible to prevent the reaction with the electrolyte accompanying cracking and the loss from the mixture layer due to the collapse, and the deterioration of the cycle characteristics can be suppressed.

  In the lithium secondary battery of the present invention, the active material particles preferably have an average particle size of 5 μm or more and 25 μm or less.

  By setting the average particle diameter of the active material particles to 5 μm or more, the specific surface area of the original active material can be reduced. As a result, the contact area between the electrolyte and the new active material surface can be reduced, and the effect of improving the cycle characteristics and the effect of suppressing the expansion of the active material are increased. Moreover, the thickness of the active material layer for one side of the negative electrode in a lithium secondary battery using a conventional carbon material such as graphite as the negative electrode active material is about 60 μm to 100 μm. When the same positive electrode as in the conventional example is used, the thickness of the active material layer per side is desirably 40 μm or less in order to increase the capacity of the battery with the configuration of the present invention. However, when an active material layer having a thickness of 40 μm or less is manufactured, the active material layer becomes thick unless the particle size of the active material is 40 μm or less. Further, when many active material particles having a particle size of 25 μm or more are contained, defects such as streaks and blurring occur when the active material mixture is applied to the current collector. Therefore, the average particle diameter of the active material particles is preferably 25 μm or less. The average particle size may be determined from observation with a scanning electron microscope, or may be determined from the particle size reaching 50% of the total particle size when performing particle size distribution measurement and integrating the mass in order of particle size. Also good.

  Moreover, in the lithium secondary battery of this invention, it is preferable that the said active material particle contains 1 mass%-20 mass% oxygen.

  When oxygen is included in the active material, the chemical reaction between the electrolyte and the active material is suppressed, so that the charge / discharge efficiency is stabilized and the cycle characteristics are improved. In order to exhibit this effect, it is preferable that 1 mass% or more of oxygen is included, and 5 mass% or more is more preferable. Moreover, since it will lead to the fall of battery capacity when oxygen concentration is too high, it is preferable that it is 20 mass% or less. This oxygen may be contained not only on the surface of the active material particles but also inside the active material particles.

  In the lithium secondary battery of the present invention, it is preferable that the particle size distribution of the active material particles is such that D10 is 3 μm or more and D90 is 30 μm or less.

  When the particle size distribution of the active material particles is wide, the binder concentrates on the active material particles having a small particle size, and the distribution of the binder becomes uneven. In addition, when large active material particles are mixed, local stress is applied during expansion and contraction, which causes electrode deformation and electrode thickness increase, resulting in a decrease in energy density per volume. When the particle size distribution is within the above range, the binder can be uniformly disposed in the negative electrode mixture layer, and the expansion and contraction of the large active material particles can be suppressed locally. Density reduction can be suppressed.

  Moreover, in the lithium secondary battery of this invention, it is preferable that surface roughness Ra of the electrical power collector which consists of said electroconductive metal foil is 0.2 micrometer or more and 1 micrometer or less.

  When the surface roughness Ra (based on JIS B 0601-1994) of the current collector is 0.2 μm or more, the adhesion between the mixture layer and the current collector becomes strong, and the active material particles expand and contract. Even if it repeats, collapse of an electrode structure can be suppressed and the fall of cycling characteristics can be suppressed. Further, if the surface roughness exceeds 1 μm, the thickness of the current collector increases in proportion thereto, which is not preferable.

  Moreover, in the lithium secondary battery of this invention, it is preferable that the said negative electrode is heat-processed in non-oxidizing atmosphere after arrange | positioning a mixture layer on the electrical power collector which consists of electroconductive metal foil.

  Immobilization of the polyimide resin as a binder proceeds by heat treatment and is sintered densely, and part of the material melts to improve the adhesion between the active material particles and the active material particles and the current collector, Breakage of the current collecting structure in the negative electrode mixture layer due to expansion and contraction of the active material particles due to charge / discharge is suppressed, so that the uniformity of the electrode reaction is improved and the deterioration of the cycle characteristics can be suppressed.

  In the lithium secondary battery of the present invention, the negative electrode preferably has a mixture layer thickness of 40 μm or less and 5 μm or more.

  The thickness of the mixture layer for one side of the negative electrode in a lithium secondary battery using a conventional carbon material such as graphite as the negative electrode active material is about 60 μm to 100 μm. The battery capacity can be increased as compared with the battery. If the thickness of the mixture layer is less than 5 μm, the amount of the mixture layer with respect to the current collector is decreased, and on the contrary, it is not possible to achieve a high capacity.

  In addition, the method for producing a lithium secondary battery of the present invention includes at least one of silicon and a silicon alloy made of an amorphous material having a half width of 4 ° or more when having a peak in X-ray diffraction using CuKα. Active material particles and a binder containing a polyimide resin are dispersed in an organic solvent to produce a mixture slurry or paste, and the mixture slurry or paste is disposed on the surface of a current collector made of a conductive metal foil. After that, dry and roll to a predetermined thickness, then heat-treat in a non-oxidizing atmosphere to sinter the polyimide resin to produce a negative electrode, and a separator is disposed between the negative electrode and the positive electrode The battery outer package is sealed after being inserted into the battery outer package and then injected with a nonaqueous electrolyte.

  In addition to increasing the packing density by placing the mixture slurry or paste on the surface of the current collector made of conductive metal foil and then drying and rolling, the current collector and the active material particles and the binder Since the adhesion is improved, it is easy to maintain the electrode structure, and when it has a peak in X-ray diffraction using CuKα, at least one of silicon and silicon alloy made of an amorphous substance having a half width of 4 ° or more is used. Combined with the use of the active material particles and the binder containing the polyimide resin, a lithium secondary battery capable of obtaining good cycle characteristics can be manufactured.

  Note that the polyimide resin can be sintered in a non-oxidizing atmosphere, for example, in an inert gas atmosphere such as nitrogen or argon, or in a reducing atmosphere such as hydrogen gas. If the precursor layer of polyimide resin is contained in the mixture layer before heat treatment, heat treatment is necessary for imidization, and even when polyimide resin is already used in the mixture before heat treatment Since the polyimide resin can be sintered by performing heat treatment, the adhesion between the binder, the active material particles, and the current collector can be improved.

  Further, in the method for producing a lithium secondary battery of the present invention, the active material particles are produced by rapidly cooling at least one raw material of silicon and silicon alloy in a gas phase under reduced pressure to form a solid phase. Preferably there is.

  As a method for producing the active material particles, vacuum deposition, sputtering, CVD, or the like can be used. When at least one raw material of silicon and silicon alloy in a gas phase under reduced pressure is rapidly cooled and solidified, since the arrangement of atoms is disordered in the gas phase, the phase is changed very quickly to form a solid phase. The active material particles in an amorphous state can be efficiently obtained by appropriately pulverizing and classifying them.

  Hereinafter, the best mode for carrying out the present invention will be described in detail based on examples and drawings. However, the following examples illustrate lithium secondary batteries for embodying the technical idea of the present invention, and are not intended to identify the present invention. The invention can be equally applied to various modifications without departing from the technical idea shown in the claims. 1A is a plan view showing the configuration of the electrode body in the middle of manufacturing the battery of Example 1, and FIG. 1B is a plan view of the battery of Example 1. FIG.

[Production of negative electrode active material]
First, an amorphous silicon lump was produced by a vapor phase method. Specifically, a silicon lump was produced by melting metal silicon into a vapor in a vacuum in an electron beam vapor deposition apparatus and depositing it on a cooling part in the electron beam vapor deposition apparatus. Subsequently, the negative electrode active material particle a1 which concerns on Example 1 was produced by grind | pulverizing the obtained silicon lump. This amorphous silicon had a peak top at 2θ of 27.9 ° and 51.8 ° by X-ray diffraction using CuKα, and had broad peaks at half-widths of 6 ° and 9 °, respectively. The average particle diameter of the negative electrode active material a1 was 12.01 μm, D10 in the particle size distribution was 3.91 μm, and D90 was 16.27 μm. Moreover, oxygen content is 14.4 mass%, and it is thought that this oxygen was taken in when producing a silicon lump. This oxygen content was measured with an oxygen analyzer RO416DR (trade name) manufactured by LECO. In addition, the calculation method of the said average particle diameter and particle size distribution is shown below. In Comparative Examples 1 to 3 below, the above oxygen content measurement method and the average particle size and particle size distribution measurement method were similarly employed.

[Calculation method of average particle size and particle size distribution]
The average particle size was calculated by using a laser diffraction particle size distribution measuring device and calculating the average particle size and particle size distribution (D10, D50, D90). In addition, the specific method for calculating the particle size distribution is to integrate the mass of the particles in order from the smallest particle size, and calculate the particle size when the accumulated mass becomes X% of the mass of all particles. Determined by When X is 10, it is expressed as D10, when the value of X is 50, it is expressed as D50, and when the value of X is 90, it is expressed as D90. Among these, D50 represents an average particle diameter. The average particle diameter may be determined by observing the cross section of the electrode with a scanning electron microscope.

[Production of negative electrode]
N-methyl-2-pyrrolidone (NMP) as a dispersion medium is mixed with the above active material particles and a polyimide varnish having a polyimide resin concentration of 20% by mass so that the mass ratio of the active material particles and the polyimide resin is 90:10. To make a negative electrode mixture slurry. This negative electrode mixture slurry was applied to an electrolytic copper foil having a thickness of 35 μm and a surface roughness Ra of 0.27 μm, dried and then rolled, and the obtained product was cut out into a 25 mm × 35 mm rectangular shape, and then in an argon atmosphere. A negative electrode mixture layer was disposed on the surface of the current collector by heat treatment at 400 ° C. for 10 hours and sintering the polyimide resin. The amount of the mixture layer on the current collector was 2.3 mg / cm ² , and the thickness of the mixture layer was 19 μm.

[Production of positive electrode]
NMP as a dispersion medium, LiCoO ₂ powder as a positive electrode active material, carbon material powder as a positive electrode conductive agent, and polyvinylidene fluoride as a positive electrode binder, the mass ratio of the active material, the conductive agent, and the binder is 94. : 3: 3 and then kneaded to obtain a positive electrode mixture slurry. This positive electrode mixture slurry was applied onto an aluminum foil having a thickness of 15 μm, dried and rolled, and the obtained product was cut out into a 20 mm × 20 mm square shape. The amount of the mixture layer on the current collector was 28 mg / cm ² .

[Preparation of electrolyte]
LiPF ₆ was dissolved in a solvent in which ethylene carbonate and diethylene carbonate were mixed at a volume ratio of 3: 7 so as to be 1 mol / L, and then 0.4 mass% of carbon dioxide gas was added to prepare an electrolytic solution. did.

[Production of battery]
A lithium secondary battery A1 of Example 1 in which the positive electrode, the negative electrode, and the electrolytic solution were inserted into an aluminum laminate was produced as follows. First, as shown in FIG. 1A, an aluminum positive electrode tab 3b is attached to an end of the positive electrode 3a on the side where the active material layer of the aluminum current collector is not provided, and a copper negative electrode collector of the negative electrode 4a is attached. The negative electrode tab 4b made of nickel is attached to the end of the electric conductor where the active material layer is not provided, and then the surface of the positive electrode 3a and the negative electrode 4a on which the active material layer is provided is attached to the polyethylene porous body separator 5. The electrode body 6 was assembled so as to face each other. After this electrode body 6 is inserted into an aluminum laminate exterior body 1 and heat-sealed except for one surrounding area, a closed portion 2 is formed, and a predetermined amount of electrolyte is injected into the exterior body 1 Then, the remaining one place was sealed by heat sealing to produce a lithium secondary battery A1 of Example 1 as shown in FIG.

[Comparative Example 1]
A battery B1 was produced in the same manner as in Example 1 except that crystalline silicon b1 was used instead of amorphous silicon as the negative electrode active material particles. The crystalline silicon b1 has a purity of 99% or more, and 2θ is 28.4 °, 47.3 °, 56.1 °, 69.2 °, 76.4 ° by X-ray diffraction using CuKα, respectively. Sharp peaks with half widths of 0.22 °, 0.25 °, 0.27 °, 0.32 °, and 0.36 ° appeared. The crystalline silicon particles have a crystallite size of 38.6 nm, an average particle size of 12.18 μm, a particle size distribution with D10 of 5.19 μm, and D90 of 18.41 μm. The crystallite size was determined by the Scherrer equation described above based on the peak where 2θ, which was the strongest in X-ray diffraction, appeared at 28.4 °. This calculation method is the same in Comparative Example 2.

[Comparative Example 2]
A battery B2 was produced in the same manner as in Example 1 except that crystalline silicon b2 was used as the negative electrode active material particles. The crystalline silicon b2 has a purity of 99% or more, and 2θ is 28.4 °, 47.3 °, 56.1 °, 69.1 °, 76.3 ° by X-ray diffraction using CuKα. Extremely sharp peaks with half-widths of 0.13 °, 0.11 °, 0.12 °, 0.11 °, and 0.11 ° respectively appeared. The crystalline silicon particles have a crystallite size of 63.3 nm, an average particle size of 12.08 μm, a particle size distribution with D10 of 4.70 μm, and D90 of 18.68 μm.

[Comparative Example 3]
Instead of disposing a mixture layer containing active material particles made of silicon and a binder on the current collector, the negative electrode was prepared as follows. That is, amorphous silicon a2 was arranged in a columnar shape by electron beam evaporation on a C7025 copper alloy foil having a thickness of 18 μm and a surface roughness Ra of 0.25 μm. The oxygen content was 14.4% by mass. Otherwise, the battery C1 was produced in the same manner as in Example 1.

[Evaluation of charge / discharge cycle characteristics]
About said battery A1, B1, B2, C1, the charging / discharging cycling characteristics were evaluated on the charging / discharging test conditions shown below. In addition, all charging / discharging was performed at 25 degreeC.
(1) Charging conditions in the first cycle The constant current is charged at a constant current of 0.7 mA until it reaches 1 mAh, and then the battery voltage is charged at a constant current of 14 mA until the battery voltage becomes 4.2 V, and then 4.2 V. The battery was charged at a constant voltage until the current reached 0.7 mA.
(2) First cycle discharge conditions Discharge was performed at a constant current of 14 mA until the battery voltage reached 2.75V.
(3) Charging conditions after the second cycle The battery was charged with a constant current of 14 mA until the battery voltage reached 4.2 V, and then charged with a constant voltage of 4.2 V until the current became 0.7 mA.
(4) Discharge conditions after the second cycle The battery was discharged at a constant current of 14 mA until the battery voltage reached 2.75V.

  The capacity retention rate is a value indicating the ratio of the discharge capacity at the 300th cycle when the discharge capacity at the 15th cycle is 100. Here, the 15th cycle is based on the condition that, in all the batteries A1, B1, B2 and C1, the conductive path is established in the battery and the charge / discharge efficiency is stable. It is. The results are summarized in Table 1.

  From the results shown in Table 1, it can be seen that the battery A1 of Example 1 is superior in cycle characteristics to the batteries B1, B2, and C1 of Comparative Examples 2-3. In this way, in an active material particle having a large volume change such as silicon and a battery using a polyimide resin as a binder for maintaining its electrode structure, when using active material particles made of amorphous silicon without crystallites, It is possible to further suppress the capacity deterioration accompanying the charge / discharge cycle.

  In Example 1, an example in which an electrode body in which a separator is disposed between a pair of positive and negative electrodes is formed and a lithium secondary battery encapsulated in an aluminum laminate outer package is manufactured is shown. These electrode bodies may be combined and connected to each other in series or in parallel, and a metal outer can may be used as the outer body. Furthermore, the positive electrode and the negative electrode are each wound in a spiral shape via a separator to form a wound electrode body, and this wound electrode body is sealed in a cylindrical metal outer can, and a cylindrical lithium secondary battery Furthermore, a flat wound electrode body is formed by crushing a cylindrical wound electrode body, and the flat wound electrode body is enclosed in a square metal outer can. A lithium secondary battery can also be used.

FIG. 1A is a plan view showing a configuration of an electrode body in the middle of manufacture of the battery of Example 1, and FIG. 1B is a plan view of the battery of Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exterior body 2 Closure part 3a Positive electrode 3b Positive electrode tab 4a Negative electrode 4b Negative electrode tab 5 Separator 6 Electrode body

Claims (10)

In a lithium secondary battery comprising a negative electrode in which a mixture layer containing active material particles containing silicon and a binder is disposed on the surface of a current collector made of a conductive metal foil, a positive electrode, and a nonaqueous electrolyte,
When the active material particles have a peak in X-ray diffraction using CuKα, the active material particles are made of an amorphous material having a half width of 4 ° or more,
The lithium secondary battery, wherein the binder includes a polyimide resin.   When the active material particles have a peak in X-ray diffraction using CuKα, the peak top exists in the range of 2θ within the range of 27 ° to 30 ° and the range of 50 ° to 54 °, and the half width is 4 respectively. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is at least °.   The lithium secondary battery according to claim 1, wherein the active material particles have an average particle size of 5 μm or more and 25 μm or less.   The lithium secondary battery according to claim 1, wherein the active material particles contain 1% by mass to 20% by mass of oxygen.   5. The lithium secondary battery according to claim 1, wherein the particle size distribution of the active material particles is such that D10 is 3 μm or more and D90 is 30 μm or less.   The lithium secondary battery according to claim 1, wherein the current collector made of the conductive metal foil has a surface roughness Ra of 0.2 μm to 1 μm.   2. The lithium secondary battery according to claim 1, wherein the negative electrode is obtained by heat-treating a mixture layer on a current collector made of a conductive metal foil in a non-oxidizing atmosphere. 3.   The lithium secondary battery according to claim 1, wherein the negative electrode has a mixture layer thickness of 40 μm or less and 5 μm or more.   When there is a peak in X-ray diffraction using CuKα, an active material particle containing at least one of silicon and a silicon alloy made of an amorphous material having a half width of 4 ° or more, and a binder containing a polyimide resin are organic A mixture slurry or paste is prepared by dispersing in a solvent, and the mixture slurry or paste is placed on the surface of a current collector made of a conductive metal foil, then dried and rolled to a predetermined thickness, and then A negative electrode is manufactured by applying a heat treatment in a non-oxidizing atmosphere to sinter a polyimide resin, a separator is placed between the negative electrode and the positive electrode, inserted into the battery case, and then a non-aqueous electrolyte is injected. A method for producing a lithium secondary battery, wherein the battery outer package is sealed later.   The lithium secondary battery according to claim 9, wherein the active material particles are produced by rapidly cooling at least one raw material of silicon and silicon alloy in a gas phase state under reduced pressure to form a solid phase. Method.

Images