JP4810794B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery including a negative electrode mixture layer including composite particles made of a metal capable of inserting and extracting lithium or a compound thereof and an electron conductive material.

  Non-aqueous electrolyte secondary batteries using organic electrolytes or polymer electrolytes as electrolytes are widely used as power sources for various portable electronic devices because of their high energy density. The use to is expected.

  Among non-aqueous electrolyte secondary batteries, lithium ion secondary batteries using a carbon material capable of occluding and releasing lithium as the negative electrode active material are the most produced, but in order to obtain a higher energy density battery, carbon There is a need for a negative electrode active material that can replace the material.

  As a new negative electrode active material, Patent Document 1 discloses metals such as silicon, aluminum and lead, tin-containing oxides, and silicon oxides. These negative electrode active materials exhibit high discharge capacity, but lithium The volume change during the occlusion / release process is large, and therefore, there is a problem that the discharge capacity is remarkably reduced with the charge / discharge cycle process, and it cannot be practically used as the negative electrode active material.

Further, when the volume of the silicon oxide repeatedly expands and contracts with charge / discharge, the contact area between the conductive material and the silicon oxide decreases, and conduction cannot be obtained, resulting in poor charge / discharge cycle characteristics. In order to improve this, Patent Document 2 discloses a technique for coating the surface of silicon oxide with a conductive material such as carbon. Patent Document 2 exemplifies a negative electrode active material in which SiO _x particles are coated with a conductive material, but there is no description about the thickness of the negative electrode mixture layer.

  Regarding the relationship between the negative electrode active material particles and the thickness of the negative electrode mixture layer, in Patent Document 3, the total sum of the mixture layer is preferably 80 μm or more (the thickness of the single-side coated portion is 40 μm or more). Since generally used electrode materials have a maximum particle size of about 40 μm in terms of particle size distribution, it is mentioned that fading of coating occurs in a portion where large particles exist. Patent Document 4 discloses that the surface of a silicon powder having an average particle diameter of about 1 μm is coated with carbon and a negative electrode having a mixture layer thickness of 150 μm is prepared.

JP 2002-231225 A JP 2002-373653 A JP 2002-203606 A JP 2001-160392 A

  When a metal capable of occluding and releasing lithium or a compound thereof is used as the negative electrode active material of the non-aqueous electrolyte secondary battery, the surface of these metals or the compound thereof may be coated with an electron conductive material such as carbon, The charge / discharge cycle characteristics are greatly improved by mechanically mixing or granulating the compound and the electron conductive material together to form a composite. However, since the swelling of the battery accompanying the charge / discharge cycle is still large, it is difficult to obtain a practical battery.

The cause of the large swelling of the battery is that the particle diameter of the active material particles containing a metal capable of inserting and extracting lithium or a compound thereof and an electron conductive material is too small with respect to the thickness of the negative electrode mixture layer.
When the size of the negative electrode active material particles is small, the number of negative electrode active material particles contained per unit volume in the negative electrode mixture layer increases.

  As a result, the contact area between the active material and the active material and between the active material and the conductive agent is increased. This means that the number of contact failure points between the active material and the active material and between the active material and the conductive agent increases as the negative electrode active material particles expand and contract. This increase in the number of defective portions results in swelling of the negative electrode mixture layer, and consequently swelling of the battery.

  When the volume of the negative electrode active material expands, a force that causes the negative electrode mixture layer to expand in directions parallel to and perpendicular to the electrode plate acts. However, since the length of the electrode plate is determined, even if a force is applied in a direction parallel to the electrode plate, the expansion rate of the negative electrode mixture layer in this direction is limited. When a force exceeding the limit is applied, the force is applied in a direction parallel to the electrode plate and contracting the negative electrode mixture layer, but this force is perpendicular to the electrode plate that easily expands in volume. Will run away in the direction. This means that the swelling of the negative electrode mixture layer in the direction perpendicular to the electrode plate is amplified.

  When a carbon material such as graphite is used as the negative electrode active material, the volume expansion coefficient associated with charge / discharge is small (up to 10%), so the force in the direction parallel to the electrode plate is relatively small. Since the degree to which the vertical force is amplified is small, the swelling of the battery is relatively small. However, when a metal capable of occluding and releasing lithium or a compound thereof is included as the negative electrode active material, the volume expansion associated with charging / discharging of the active material is significantly larger than that of the carbon material, so that the force in the direction parallel to the electrode plate is perpendicular. Combined with the directional force, the swelling of the negative electrode mixture layer in the direction perpendicular to the electrode plate is amplified. As a result, there is a problem that the swelling of the battery is remarkably large.

  4 to 6 schematically show changes in the volume of the particles in the negative electrode mixture layer accompanying charge / discharge of a conventional nonaqueous electrolyte secondary battery. 4 to 6, 1 is a negative electrode mixture layer, 2 is a negative electrode current collector, 3 is a negative electrode active material particle, 4 is a conductive agent particle, and 5 is a space in the negative electrode mixture layer. 4 to 6, the shapes of the negative electrode active material particles 3 and the conductive agent particles 4 are shown as circles, but the actual cross-sectional shape of these particles may be an ellipse or a polygon other than a circle. Various shapes including the above can be used. This also applies to FIGS. 1 to 3 described later.

FIG. 4 shows the state of the negative electrode mixture layer in a discharged state before the charge / discharge cycle. The negative electrode active material particles 3 and the conductive agent particles 4 are in contact with each other, and electrical contact between these particles is maintained. At the same time, electrical contact between these particles and the negative electrode current collector 2 is also maintained. The thickness of one surface of the negative electrode mixture layer in this case a T _4.

FIG. 5 shows the state of the negative electrode mixture layer after charging, and the dotted line shows the size of the negative electrode active material particles before charging. The negative electrode active material 3 occludes lithium by charging and expands in volume. In this state, the negative electrode active material particles 3 and the conductive agent particles 4 are in contact with each other, and electrical contact between these particles remains maintained. The volume expansion of the negative electrode active material 3, the thickness of one surface of the negative electrode mixture layer 1 T ₅ becomes, T ₅ is larger than T ₄ in FIG.

FIG. 6 shows the state of the negative electrode mixture layer discharged after the negative electrode has been charged once, and the negative electrode active material particles 3 have returned to a size close to the original FIG. However, since some lithium that is not used for discharge remains in the negative electrode active material, the size of the negative electrode active material particles in FIG. 6 is slightly larger than that in FIG. The thickness of one surface of the negative electrode mixture layer 1 becomes T _6, T ₆ is smaller than T ₅ in FIG. 5, it is greater than T ₄ in FIG. In addition, since the volume change of the negative electrode active material particles is not uniform, the shape of the negative electrode active material particles after charge / discharge often does not return to the original shape.

  As a result, the distances between the negative electrode active material particles and between the negative electrode active material particles 3 and the conductive agent particles 4 are increased, and those that are separated from each other and do not maintain electrical contact are generated. By repeating the charging / discharging cycle, the negative electrode active material particles separating between the particles are increased, and as a result, the swelling of the battery is increased.

  In this case, when the size of the negative electrode active material particles is relatively small compared to the thickness of the negative electrode mixture layer, the small particles have contact points between the negative electrode active materials and between the negative electrode active material and the conductive particles. Therefore, when the volume change of the negative electrode active material particles occurs, the small particles are likely to be separated from each other. Therefore, with the charge / discharge cycle, there is a problem that the number of negative electrode active material particles that are separated from each other increases and the swelling increases.

  Thus, in the charge / discharge cycle, when the negative electrode active material is a particle containing both a metal capable of occluding and releasing lithium or a compound thereof and an electron conductive material, the thickness of the negative electrode mixture layer and the size of the negative electrode active material particle It is understood that this relationship is extremely important.

  Accordingly, an object of the present invention is to provide a thickness of the negative electrode mixture layer in a nonaqueous electrolyte secondary battery including a negative electrode mixture layer including composite particles made of a metal capable of occluding and releasing lithium or a compound thereof and an electron conductive material. By defining the particle diameter of the negative electrode active material relative to the thickness, it is intended to provide a non-aqueous electrolyte secondary battery that suppresses the swelling of the negative electrode mixture layer accompanying the charge / discharge cycle and has a small swelling.

The invention according to claim 1 provides a cumulative distribution of the composite particles in a nonaqueous electrolyte secondary battery including a negative electrode mixture layer including composite particles made of a metal capable of occluding and releasing lithium or a compound thereof and an electron conductive material. In the curve, when the particle diameter of the total number 50% is D ₅₀ (μm) and the thickness of one surface of the negative electrode mixture layer is T (μm) by integrating from the smaller particle diameter, 0.5 <D ₅₀ / T <1. (However, the case where D ₅₀ /T=0.6 and D ′ ₅₀ / D ₅₀ = 1/30 is excluded. Here, in the composite particles, a metal or a compound thereof capable of occluding and releasing lithium. In the cumulative distribution curve, the particle diameter of the total number 50% is D′ 50 (μm) by integrating from the smaller particle diameter)

The invention according to claim 2 is the nonaqueous electrolyte secondary battery according to claim 1, wherein the composite particles are integrated from the smaller particle diameter in the integrated distribution curve of the metal or compound capable of occluding and releasing lithium. When the particle diameter of the total number of 50% is D′ 50 (μm), 0.5 <D′ 50 (μm) and D′ 50 / D50 <0.2.

  According to the present invention, since the composite particle size including the negative electrode active material relative to the thickness of the negative electrode mixture layer is relatively large, the number of composite particles contained per unit volume in the negative electrode mixture layer can be reduced. As a result, even when the volume of the composite particles changes with the charge / discharge cycle, the number of poor contact points between the composite particles and the composite particles and between the composite particles and the conductive agent is small. A secondary battery can be obtained.

The present invention relates to a cumulative distribution curve of the composite particles in a non-aqueous electrolyte secondary battery including a negative electrode mixture layer including composite particles composed of a metal capable of occluding and releasing lithium or a compound thereof and an electron conductive material. When the particle diameter of the total number 50% is D ₅₀ (μm) and the thickness of one surface of the negative electrode mixture layer is T (μm), the particles are integrated from the smaller particle diameter, and 0.5 <D ₅₀ / T. <1. (However, the case where D ₅₀ /T=0.6 and D ′ ₅₀ / D ₅₀ = 1/30 is excluded. Here, in the composite particles, a metal or a compound thereof capable of occluding and releasing lithium. In the cumulative distribution curve, the particle diameter of the total number 50% is D′ 50 (μm) by integrating from the smaller particle diameter)

  In the present invention, by limiting the relationship between the thickness of one surface of the negative electrode mixture layer and the size of the composite particles containing the negative electrode active material contained therein to the above range, the swelling of the battery accompanying charge / discharge is small. A nonaqueous electrolyte secondary battery can be obtained.

When the number of composite particles larger than T is less than 10% of the total number, the large particles are crushed by a pressurizing step such as a roll press when producing the negative electrode mixture layer. A material having a substantially uniform thickness is obtained. However, when the number of composite particles larger than T is 10% or more of the total number, the obtained negative electrode mixture layer is not preferable because it is not uniform. In this case, since there are a large number of large particles, the volume expansion of the particles significantly increases the thickness of the negative electrode mixture layer and the swelling of the battery increases. Therefore, in the cumulative distribution curve of the composite particles, when the particle diameter of the total number of 90% is D ₉₀ (μm) by integrating from the smaller particle diameter, it is preferable that D ₉₀ / T <1.

In the present invention, by setting 0.5 <D ₅₀ / T <1, the number of composite particles contained per unit volume in the negative electrode mixture layer can be reduced. As a result, the charge / discharge cycle is accompanied. Even when the volume of the composite particles changes, the number of defective contact points between the composite particles and the composite particles and between the composite particles and the conductive agent is small, so that the swelling of the battery can be reduced.

The composite particle comprising a metal capable of occluding and releasing lithium or a compound thereof and an electron conductive material according to the present invention is obtained by simply mixing particles of a metal capable of occluding and releasing lithium or a compound thereof and particles of an electron conductive material. In addition, a single particle includes a metal or a compound thereof capable of occluding and releasing lithium and an electron conductive material, and the composite particles include particles of a metal or a compound thereof capable of occluding and releasing lithium. It is a particle that is clearly present. The composite particles may contain a substance other than a metal capable of occluding and releasing lithium, a compound thereof, or an electron conductive material as long as the characteristics of the battery are not adversely affected.
The volume change accompanying charging / discharging of the composite particle which consists of the metal which can occlude / release lithium, its compound, and an electron conductive material of this invention is typically shown in FIGS. Symbols 1 to 5 in FIGS. 1 to 3 indicate the same components as those in FIGS. 4 to 6. The negative electrode active material particles 3 are composite particles made of the metal of the present invention capable of occluding and releasing lithium or a compound thereof and an electron conductive material.

FIG. 1 shows the state of the negative electrode mixture layer in a discharged state before the charge / discharge cycle. The particle diameter of the negative electrode active material particles 3 is 0.5 with respect to the thickness T of one surface of the negative electrode mixture layer. <D ₅₀ / T <1. That is, half of the number of the negative electrode active material particles 3 has a particle diameter larger than 0.5 times the thickness T of the negative electrode mixture layer. In the battery of the present invention, composite particles containing a relatively large negative electrode active material with respect to the thickness T of the negative electrode mixture layer are used as compared with the conventional batteries shown in FIGS. The thickness of the negative electrode mixture layer and T ₁ in FIG. 1.

FIG. 2 shows the state of the negative electrode mixture layer after charging, and the dotted line shows the size of the negative electrode active material particles 3 before charging. The negative electrode active material particles 3 occlude lithium by charging and expand in volume. Due to this volume expansion, the thickness of the negative electrode mixture layer 1 becomes T ₂ , and T ₂ is larger than T _{1 in} FIG.

FIG. 3 shows the state of the negative electrode mixture layer after charging and discharging the negative electrode. The negative electrode active material particles 3 have returned to a size close to that of FIG. 1 before the charge / discharge cycle, but are completely returned. Absent. The main reason for this is that the negative electrode active material particles 3 contain a metal capable of occluding and releasing lithium or a compound thereof, and once these occlude lithium, the volume expands. It will not return. Then, next is the thickness _{T 3} the negative electrode mixture layer 1, _{T 3} is smaller than _{T 2} of the FIG. 2, it is larger than the _{T 1} of the Figure 1.

In the present invention, composite particles containing a negative electrode active material larger than the thickness T on one side of the negative electrode mixture layer are used as compared with conventional batteries. Further, by setting 0.5 <D ₅₀ / T <1, the number of composite particles having a size of D ₅₀ stacked in the direction perpendicular to the electrode plate is less than two. Therefore, since the number of poor contact points between the composite particles and between the composite particles and between the composite particles and the conductive agent is minimized, the number of composite particles that are separated from each other even when the charge / discharge cycle is repeated is reduced. As a result, the negative electrode mixture layer and the battery Swelling is suppressed.

The particle diameter of the composite particles used in the present invention is such that D ₁₀ > 1 when the particle diameter of the total number of 10% is D ₁₀ (μm) by integrating from the smaller particle diameter in the integrated distribution curve. preferable. In the case of D ₁₀ ≦ 1, there are many small particles, so that the amount of the conductive agent in the electrode mixture has to be increased in order to improve the current collecting property of the particles. Capacity is reduced.

In a composite particle composed of a metal capable of occluding and releasing lithium or a compound thereof and an electron conductive material, the preferred particle size of the metal capable of occluding and releasing lithium or a compound thereof is the cumulative distribution curve of these particles. When the particle diameter of the total number 50% is D′ 50 (μm) by integrating from the smaller one, 0.5 <D′ 50 (μm) and D′ 50 / D50 <0.2. In the case of 0.5 <D′ 50 (μm), the specific surface area of the composite particles can be reduced, and decomposition of the electrolytic solution accompanying charge / discharge can be suppressed. As a result, the cycle life performance of the battery is improved. The specific surface area of the negative electrode active material is preferably 10 m ² g ⁻¹ or less.

In addition, by setting D ′ ₅₀ / D ₅₀ <0.2, in the composite particles, the mixing of the metal capable of occluding and releasing lithium or a compound thereof and the electron conductive material can be made more uniform. Cycle life performance is improved.
The integrated particle size of the composite particles is a value obtained by a laser method after ultrasonically dispersing the composite particles in a solvent.

As a metal capable of occluding and releasing lithium used in the composite particles contained in the negative electrode mixture layer of the present invention or a compound thereof, a metal element such as Si, Sn, Al, In, Bi, Zn, Sb, Ge, Pb, SiO _x (0 <x ≦ 2), SnO _x (0 <x <2), CoO, Co ₂ O ₃ , Co ₃ O ₄ , NiO, MnO, Mn ₂ O ₃ , FeO, Fe ₂ O ₃ , Fe ₃ An oxide such as O ₄ or a mixture of two or more of these can be used. Examples of the shape of the composite particles include plates, thin films, particles, and fibers.

As SiO _x (0 <x <2), a substance having a stoichiometric composition such as SiO _1.5 (Si ₂ O ₃ ), SiO _1.33 (Si ₃ O ₄ ), SiO, and x is 0 or more. Substances of any composition that are largely less than 2 are exemplified. Also, if represented by the composition, it may be a material containing Si and SiO ₂ at an arbitrary ratio.

Examples of SnO _x (0 <x <2) include a substance having a stoichiometric composition such as SnO and SnO ₂ and a substance having an arbitrary composition in which x is greater than 0 and less than 2. Also, if represented by the composition, it may be a material containing Sn and SnO ₂ at an arbitrary ratio.
As the electron conductive material used for the composite particles contained in the negative electrode mixture layer of the present invention, a carbon material or a metal can be used. This metal is preferably not alloyed with lithium.
As a method for synthesizing the composite particles contained in the negative electrode mixture layer of the present invention, a CVD method, a mechanical mixing method, a liquid phase method, a firing method, or the like can be used.

  As the carbon material, at least one carbon material selected from the group consisting of natural graphite, artificial graphite, acetylene black, and vapor grown carbon fiber (VGCF) can be used. Examples of the metal not alloyed with lithium include at least one metal selected from the group consisting of copper, nickel, iron, cobalt, manganese, chromium, titanium, zirconium, vanadium, and niobium, or an alloy composed of two or more metals. Is done.

  Among these electron conductive materials, carbon materials are particularly preferable. Because carbon is different from the above metals and lithium can be inserted and desorbed between the layers, a battery using a negative electrode active material provided with carbon has a negative electrode active material provided with the above metal. This is because the discharge capacity is larger than that of the used battery.

  The composite particles contained in the negative electrode mixture layer of the present invention may have a shape in which the surface of a metal capable of occluding and releasing lithium or a compound thereof is coated with a carbon material, and the shape of the carbon provided on the surface is a thin film or a particle. Either is acceptable.

  As a method of synthesizing the composite particles of the present invention in which a metal capable of occluding and releasing lithium or a compound thereof is coated with a carbon material, an organic compound such as methane, ethane, ethylene, acetylene, butane, benzene, toluene, xylene is used in a gas phase. Decomposing medium and attaching the degradable organisms to the surface of the negative electrode active material particles (CVD method), and thermoplastic resins such as pitch, tar, or furfuryl alcohol, a metal or compound that can occlude and release lithium Examples thereof include a method of baking them after being applied to the surface, and a method of attaching a metal capable of occluding and releasing lithium or a compound thereof and carbon material particles by a mechanical method.

  Examples of the mechanical method include a granulation method, a mechanical milling method, a mechanofusion method, and a hybridization method.

  In the present invention, typical nonmetallic elements such as B, C, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, and Ge are contained in the negative electrode active material. Typical metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu may be included.

The positive electrode active material used in the nonaqueous electrolyte battery of the present invention includes transition metal compounds such as manganese dioxide and vanadium pentoxide, transition metal chalcogen compounds such as iron sulfide and titanium sulfide, lithium-containing olivine compounds, and lithium. Transition metal oxides can be used. As the lithium transition metal oxide, Li _x M1 _y M2 _z O ₂ (M1, M2 represents Ti, V, Cr, Mn, Fe, Co, Ni, Cu, 0.5 ≦ x ≦ 1, y + z = _{1), Li x M3 y Mn} 2-y O 4 (M3 represents Ti, V, Cr, Fe, Co, Ni, and Cu, 0.9 ≦ x ≦ 1.1,0.4 ≦ y ≦ 0 .6) is exemplified.

Furthermore, substances containing Al, P, B, or other typical nonmetallic elements or typical metal elements in these compounds and oxides can be used. Among these positive electrode active materials, composite oxides of lithium, cobalt, and nickel, composite oxides including lithium, cobalt, and nickel, and spinel lithium manganese oxide are preferable. Examples thereof include LiCoO ₂ , LiNiO ₂ , LiNi _x Co _1-x O ₂ (0 <x <1), LiMnO ₂ , LiMn ₂ O _{4 and the} like. The reason is that a battery having a high voltage, a high energy density and good cycle performance can be obtained by using these positive electrode active materials.

  The positive electrode and negative electrode used in the non-aqueous electrolyte secondary battery of the present invention are prepared by mixing an active material or composite particles containing an active material, a conductive agent, and a binder at a predetermined ratio, and adding an appropriate solvent to form a slurry. The slurry can be applied to a current collector and dried.

  As the conductive agent used for the positive electrode or the negative electrode, various carbon materials can be used. Examples of the carbon material include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke.

  Examples of the binder used for the positive electrode or the negative electrode include PVdF (polyvinylidene fluoride), P (VdF / HFP) (polyvinylidene fluoride-hexafluoropropylene copolymer), PTFE (polytetrafluoroethylene), and fluorination. Polyvinylidene fluoride, EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, Or these derivatives can be used individually or in mixture.

  As the solvent or solution used for the positive electrode slurry or the negative electrode slurry, a solvent or solution that dissolves or disperses the binder can be used. As the solvent or solution, a non-aqueous solvent or an aqueous solution can be used. Non-aqueous solvents include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. Can do. On the other hand, as the aqueous solution, water or an aqueous solution to which a dispersant, a thickener, or the like is added can be used. In the latter aqueous solution, latex such as SBR and an active material can be mixed and slurried.

  As the current collector for the positive electrode or the negative electrode, iron, copper, aluminum, stainless steel, or nickel can be used. Examples of the shape include a sheet, a foam, a sintered porous body, and an expanded lattice. Furthermore, as the current collector, a current collector having a hole in an arbitrary shape may be used.

  The separator for a non-aqueous electrolyte battery of the present invention can use a microporous polymer membrane, and the material thereof is nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene And polyolefins such as polybutene. Among these, the fineness of polyolefin

A porous membrane is particularly preferred. Alternatively, a microporous film in which polyethylene and polypropylene are laminated may be used.

  As the non-aqueous electrolyte used in the non-aqueous electrolyte battery of the present invention, a non-aqueous electrolyte, a polymer solid electrolyte, a gel electrolyte, and an inorganic solid electrolyte can be used. The electrolyte may have pores. The non-aqueous electrolyte is composed of a non-aqueous solvent and a solute.

  Solvents used in the non-aqueous electrolyte include cyclic carbonates such as ethylene carbonate and propylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, Examples include dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, methyl acetate, methyl acetate, and mixed solvents thereof.

As the solute to be used in the nonaqueous _{electrolyte, LiPF 6, LiBF 4, LiAsF} 6, LiClO 4, LiSCN, LiCF 3 CO 2, LiCF 3 SO 3, LiN (SO 2 CF 3) 2, LiN (SO 2 Examples include salts such as CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ and LiN (COCF ₂ CF ₃ ) ₂ , and mixtures thereof.
As the polymer solid electrolyte, a polymer obtained by adding a solute as described above to a polymer such as polyethylene oxide, polypropylene oxide, polyethylene imide, or a mixture thereof can be used. As the gel electrolyte, a substance obtained by adding the above solvent and solute to the above polymer can be used.
The shape of the battery is not particularly limited, and can be applied to various shapes of non-aqueous electrolyte batteries such as a square, an ellipse, a coin, a button, and a sheet battery.

Hereinafter, the nonaqueous electrolyte battery of the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples.
[Examples 1 to 4 and Comparative Examples 1 to 4]

[Example 1]
By weighing 50% by mass of SiO particles with D ′ ₅₀ = 1 μm and 50% by mass of flaky graphite particles with D ₅₀ = 10 μm, and granulating both, the particle diameter is D ₁₀ = 14 μm, D ₅₀ Composite particles with = 30 μm and D ₉₀ = 47 μm were obtained. The particle size was measured using a particle size analyzer (SALD2000J manufactured by Shimadzu Corporation). The sample was ultrasonically dispersed in an aqueous solvent for 20 minutes. As a refractive index, 2.00-0.05i was used.

  64% by mass of the composite particles, 16% by mass of flake natural graphite powder as a conductive agent, and 20% by mass of PVdF as a binder were mixed, and NMP was added and dispersed to prepare a negative electrode paste. This negative electrode paste was applied onto a copper foil having a thickness of 10 μm, and then dried at 150 ° C. to evaporate NMP. The above operation was performed on both sides of the copper foil, and both sides were compression molded with a roll press. Thus, the sheet-like negative electrode provided with the negative mix layer on both surfaces was manufactured. The thickness T on one side of the negative electrode mixture layer was 50 μm.

Next, 90% by mass of lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material, 3% by mass of acetylene black as a conductive agent, and 4% by mass of PVdF as a binder are mixed and dispersed by adding NMP. A positive electrode paste was prepared. This positive electrode paste was applied onto an aluminum foil having a thickness of 15 μm and then dried at 150 ° C. to evaporate NMP. The above operation was performed on both sides of the aluminum foil, and both sides were compression molded with a roll press. Thus, the sheet-like positive electrode provided with the positive mix layer on both surfaces was manufactured. The thickness of one surface of the positive electrode mixture layer was 110 μm.

The positive electrode and the negative electrode prepared in this way are rolled up with a polyethylene separator, which is a continuous porous body having a thickness of 20 μm and a porosity of 40%, interposed between them, and a container having a height of 48 mm, a width of 30 mm, and a thickness of 4.2 mm The prismatic battery was assembled by inserting it inside. Finally, by injecting a nonaqueous electrolytic solution in which 1 mol / l LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 4: 6, into the inside of the battery, The battery of Example 1 was obtained.
[Example 2]

Example 2 was the same as Example 1 except that the composite particles of SiO and graphite used for the negative electrode were those having particle diameters of D ₁₀ = 20 μm, D ₅₀ = 35 μm, and D ₉₀ = 49 μm. A battery was produced.
[Example 3]

Example 3 was the same as Example 1 except that the composite particles of SiO and graphite used for the negative electrode were those having particle diameters of D ₁₀ = 22 μm, D ₅₀ = 40 μm, and D ₉₀ = 58 μm. A battery was produced.
[Example 4]

Example 4 is the same as Example 1 except that the composite particles of SiO and graphite used for the negative electrode were those having particle diameters of D ₁₀ = 25 μm, D ₅₀ = 45 μm, and D ₉₀ = 68 μm. A battery was produced.
[Comparative Example 1]

Comparative Example 1 was the same as Example 1 except that the composite particles of SiO and graphite used for the negative electrode were those having particle diameters of D ₁₀ = 6 μm, D ₅₀ = 20 μm, and D ₉₀ = 32 μm. A battery was produced.
[Comparative Example 2]

Comparative Example 2 was the same as Example 1 except that the composite particles of SiO and graphite used for the negative electrode were those having particle diameters of D ₁₀ = 11 μm, D ₅₀ = 25 μm, and D ₉₀ = 41 μm. A battery was produced.
[Comparative Example 3]

Comparative Example 3 was the same as Example 1 except that the composite particles of SiO and graphite used for the negative electrode were those having particle diameters of D ₁₀ = 28 μm, D ₅₀ = 50 μm, and D ₉₅ = 75 μm. A battery was produced.
[Comparative Example 4]

Comparative Example 4 was the same as Example 1 except that the composite particles of SiO and graphite used for the negative electrode were those having particle diameters of D ₁₀ = 33 μm, D ₅₀ = 55 μm, and D ₉₅ = 83 μm. A battery was produced.

The batteries of Examples 1 to 4 and Comparative Examples 1 to 4 were charged to 4.2 V at a constant current of 400 mA at 25 ° C., and then charged at a constant voltage of 4.2 V for 3 hours. Then, it discharges to 2.5V with a 400 mA constant current, and makes this 1 cycle. The battery thickness after the completion of 50 cycles of charge / discharge was measured, and the battery swelling (%) after the cycle with respect to the battery thickness of 4.2 mm immediately after battery assembly was determined. In all the batteries, a discharge capacity of 400 mAh was obtained in the first cycle.
Table 1 shows the particle diameters and test results of the composite particles of the batteries of Examples 1 to 4 and Comparative Examples 1 to 4.

From Table 1, it was found that the swelling of the battery was small when 0.5 <D ₅₀ / T <1, and the swelling of the battery was particularly small when D ₉₀ / T <1.
In the batteries of Comparative Example 1 and Comparative Example 2 in which D ₅₀ / T is 0.5 or less, the battery swells as a result of an increase in the distance between the composite particles or between the composite particles and the conductive agent during the charge / discharge cycle. It seems that it has grown. Moreover, in the batteries of Comparative Example 3 and Comparative Example 4 in which D ₅₀ / T and D ₉₀ / T were 1.0 or more, the composite particles were too large, and the negative electrode mixture layer swelled significantly due to the volume expansion of the particles. As a result, it is considered that the swelling of the battery has increased.
[Examples 5 to 8 and Comparative Examples 5 to 8]

As particles used for the negative electrode, composite particles containing SnO of D ′ ₅₀ = 1 μm instead of SiO were produced in the same manner as in Example 1. The particle diameter is shown in Table 2. In the same manner as in Example 1, except that this composite particle was used, and the thickness T on one side of the negative electrode mixture layer was 60 μm and the thickness T ′ on one side of the positive electrode mixture layer was 90 μm. Batteries 5 to 8 and Comparative Examples 5 to 8 were produced and tested in the same manner as in Example 1. In both batteries, a discharge capacity of 400 mAh was obtained in the first cycle. The test results of Examples 5 to 8 and Comparative Examples 5 to 8 are shown in Table 2.

Table 2 shows that even when SnO is used, the swelling of the battery can be suppressed by setting the size of the composite particle to 0.5 <D ₅₀ / T <1.
[Examples 9-12 and Comparative Examples 9-12]

As particles used for the negative electrode, composite particles containing Sn of D ′ ₅₀ = 1 μm instead of SiO were produced in the same manner as in Example 1. The particle size is shown in Table 3. In the same manner as in Example 1, except that this composite particle was used, and the thickness T on one side of the negative electrode mixture layer was 55 μm and the thickness T ′ on one side of the positive electrode mixture layer was 75 μm. Batteries 9 to 12 and Comparative Examples 9 to 12 were produced and tested in the same manner as in Example 1. In both batteries, a discharge capacity of 400 mAh was obtained in the first cycle. Table 3 shows the test results of Examples 9-12 and Comparative Examples 9-12.

From Table 3, it was found that even when Sn is used, the swelling of the battery can be suppressed by setting the size of the composite particles to 0.5 <D ₅₀ / T <1.
[Examples 13 to 17]
As particles used for the negative electrode, composite particles containing SiO particles having various D ′ ₅₀ instead of SiO having D ′ ₅₀ = 1 μm were prepared in the same manner as in Example 2. The particle diameter (D ₅₀ ) of the composite particles coincided with the particle diameter of the composite particles used in Example 2. Therefore, in any of the examples, D ₅₀ /T=0.7, and 0.5 <D ₅₀ / T <1 is satisfied.
Table 4 shows the SiO particle diameter (D ′ ₅₀ ), the ratio of the SiO particle diameter (D ′ ₅₀ ) to the composite particle diameter (D ₅₀ ), and the specific surface area of the composite particles. Batteries of Examples 13 to 17 were produced in the same manner as in Example 2 except that the composite particles were used, and the same test as in Example 2 was performed. In both batteries, a discharge capacity of 400 mAh was obtained in the first cycle. The test results are shown in Table 4. Table 4 also shows data of Example 2 for comparison. The discharge capacity at the first cycle was defined as “initial discharge capacity”, and the ratio (%) of the discharge capacity at 100th cycle to the initial discharge capacity was defined as “capacity maintenance ratio”.

From Table 4, it was found that a high capacity retention rate of 85% or more was obtained when 0.5 <D ₅₀ / T <1 and D ′ ₅₀ / D ₅₀ <0.2. In addition, it was found that by setting 0.5 <D ′ ₅₀ , the specific surface area of the composite particles can be reduced to 10 m ² g ⁻¹ or less, and a high capacity retention can be obtained. This is presumably because the decomposition of the electrolyte was suppressed. In addition, the swelling of the batteries of Examples 13 to 17 was 5.0 to 5.3%, which was small.
In the above embodiment, SiO, SnO, or Sn is used as a metal capable of occluding and releasing lithium or a compound thereof. However, in the case where Si, Al, CoO, Mn ₂ O ₃ or the like is used in addition, a composite material is similarly formed. By setting the particle size to 0.5 <D ₅₀ / T <1, it was possible to suppress swelling of the battery. In addition, although scaly graphite was used as the electron conductive material in the composite particles, composite particles can be produced in the same manner even when vapor-grown carbon fibers are used, and the size is defined as the above value. By doing so, it was possible to suppress the swelling of the battery.

The schematic diagram which shows the state of the negative mix layer of the discharge state before the charging / discharging cycle of this invention battery. The schematic diagram which shows the state of the negative mix layer after charge of this invention battery. The schematic diagram which shows the state of the negative mix layer discharged after the negative electrode was once charged of this invention battery. The schematic diagram which shows the state of the negative electrode mixture layer of the discharge state before the charging / discharging cycle of the conventional battery. The schematic diagram which shows the state of the negative mix layer after charge of the conventional battery. The schematic diagram which shows the state of the negative mix layer discharged after the negative electrode of the conventional battery was once charged.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Negative electrode mixture layer 2 Negative electrode collector 3 Negative electrode active material particle 4 Conductive agent particle 5 Space in negative electrode mixture layer

Claims (3)

In a non-aqueous electrolyte secondary battery including a negative electrode mixture layer including composite particles made of a metal capable of occluding and releasing lithium or a compound thereof and an electron conductive material, the particle size in the integrated distribution curve of the composite particles is small. When the particle diameter of the total number 50% is D ₅₀ (μm) and the thickness of one surface of the negative electrode mixture layer is T (μm), the total number is 50 <T ₅₀ / T <1. A non-aqueous electrolyte secondary battery. (However, the case where D ₅₀ /T=0.6 and D ′ ₅₀ / D ₅₀ = 1/30 is excluded. Here, in the composite particles, a metal or a compound thereof capable of occluding and releasing lithium. In the cumulative distribution curve, the particle diameter of the total number 50% is D′ 50 (μm) by integrating from the smaller particle diameter) In the composite particles, when the particle diameter of the total number 50% is D′ 50 (μm) in the integrated distribution curve of the metal capable of occluding and releasing lithium or the compound thereof, the particle diameter of the total particle number is 0. The nonaqueous electrolyte secondary battery according to claim 1, wherein 5 <D ′ ₅₀ (μm) and D ′ ₅₀ / D ₅₀ <0.2. In the composite particles, the total particle diameter of the composite particles accumulated from the smaller particle diameter in the integrated distribution curve of the composite particles is 90%. ₉₀ (Μm), D ₉₀ The nonaqueous electrolyte secondary battery according to claim 1, wherein / T <1.

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