JP2010272540A - Anode material and secondary battery using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anode material with high capacity, high initial charge/discharge efficiency, and excellent cycle characteristics, as well as a secondary battery equipped with the anode material. <P>SOLUTION: Of the anode material, a material used for an anode of a rechargeable nonaqueous electrolyte secondary battery equipped with a cathode for doping and dedoping lithium ions, nonaqueous electrolyte solution, and the anode, an anode active material consists of one or more kinds of Li-absorbing particles and one or more kinds of graphite particles of 40 wt.% or more. As to the graphite particles, a (002) face interval d (002) by the X-ray diffraction method is 0.3354 nm or more and 0.338 nm or less, and an area ratio of a G peak to a D peak by the Raman spectrometry is G/D≥9, and the Li-absorbing particles contain at least one out of composite particles of silicon and iron, silicon and titanium, or silicon and nickel. The anode material is used for the secondary battery. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a negative electrode material for a lithium secondary battery and a secondary battery using the same.

  With the recent reduction in size and weight of portable devices, there is a demand for secondary batteries with high capacity and excellent cycle characteristics. On the other hand, the lithium ion secondary battery is expected as a battery having a high voltage and a high energy density.

  Currently, graphite materials are widely used as negative electrode active materials for lithium ion secondary batteries. Graphite has a theoretical electric capacity of 372 mAh / g, but in order to meet the demand for higher capacity in the future, development of a new material that replaces graphite is required. As such a high capacity material, a Li storage alloy such as Si or Sn or a compound thereof is known.

  However, these Li occlusion particles are very large in expansion and contraction during charge and discharge, and when used as a negative electrode active material, separation between particles and separation from the current collector occur, and the initial charge and discharge efficiency decreases, cycle Incurring deterioration of characteristics is a problem.

  In view of this, attempts have been made to relieve stress due to expansion and contraction of particles during charge and discharge by combining Li storage particles and carbon to suppress cycle deterioration.

  For example, Patent Document 1 discloses sintered composite particles having a specific pore volume by sintering graphite particles and carbonaceous particles to Si-containing alloy particles, which can follow volume changes in advance. It is stated that by estimating the pore volume, a liquid junction is ensured in the composite particles and an excellent cycle is exhibited.

  Further, Patent Document 2 discloses composite particles containing a graphite part, an amorphous carbon part and silicon, and a negative electrode for a secondary battery using the same, and reacts with a high graphitic carbon electrolyte. It has been described that it exhibits excellent cycle characteristics while maintaining the characteristics that it is difficult to produce lithium metal on the dendrite and low on the dendrite.

  Patent Document 3 discloses a secondary battery in which a sintered body containing silicon and a carbon material is used as a negative electrode, and the amount of lithium occluded during full charge is 200 to 800 mAh per gram of silicon. It has been described that the collapse of the negative electrode structure is suppressed and the cycle characteristics are improved.

  Further, in Patent Document 4 and Patent Document 5, a method for producing a material in which composite particles containing at least silicon, silicon, and carbon are dispersed and arranged around graphite particles and further coated with an amorphous carbon film. And a secondary battery using the same is disclosed, and improvement of cycle characteristics is proposed.

JP 2001-210323 A JP 2000-203818 A JP 2000-251879 A JP 2002-255529 A JP 2002-255530 A

  However, the prior art has the following problems.

  First, in Patent Document 1, although the pore volume that can follow the volume change is estimated in advance, because of the large number of pores, the particles are easily broken during charge and discharge, the current collection performance is reduced, and the cycle characteristics are deteriorated. End up.

  Moreover, in patent document 3, although the quantity of the lithium occluded by the sintered compact containing a silicon and a carbon material at the time of a full charge is restrict | limited, the expansion / contraction at the time of charging / discharging cannot be avoided, and it is gradually accompanied with a cycle. Current collection is lost, and cycle characteristics deteriorate.

  Patent Document 2, Patent Document 4, and Patent Document 5 describe the improvement of cycle characteristics by combining silicon and carbon and coating with amorphous carbon. However, amorphous carbon is hard and not easily crushed. The stress relaxation effect due to expansion and contraction cannot be obtained, and the cycle characteristics deteriorate.

  The present invention has been made to solve such conventional problems, and its technical problem is to provide a negative electrode material having high capacity, high initial charge / discharge efficiency, and excellent cycle characteristics. Another object of the present invention is to provide a secondary battery having this negative electrode material.

  According to the present invention, in the material used for the negative electrode of the rechargeable non-aqueous electrolyte secondary battery including a positive electrode capable of doping and dedoping lithium ions, a non-aqueous electrolyte, and a negative electrode, the negative electrode active material is 1 type or more of Li occlusion particles and 1 type or more of graphite particles of 40% by weight or more. In the graphite particles, the (002) plane spacing d (002) by X-ray diffraction method is 0.3354 nm or more and 0.338 nm or less, and The area ratio of G peak to D peak by Raman spectroscopic analysis is G / D ≧ 9, and the Li storage particles include at least one of silicon and iron, silicon and titanium, and silicon and nickel composite particles. A characteristic negative electrode material is obtained.

  Further, according to the present invention, there can be obtained a negative electrode material characterized in that in the negative electrode material, the Li storage particles and the graphite particles are mixed to form an electrode.

  According to the present invention, in any one of the negative electrode materials, a layer made of the graphite particles is present on the current collector, and a mixed layer made of the Li storage particles and the graphite particles is further present thereon. A negative electrode material characterized in that is obtained.

  According to the present invention, in any one of the negative electrode materials described above, a mixed layer composed of the Li storage particles and the graphite particles is present on a current collector, and a layer composed of the graphite particles is further formed thereon. A negative electrode material characterized in that it is present is obtained.

  According to the present invention, in the negative electrode material according to any one of the above, by the X-ray diffraction method of graphite in which the Li storage particles form composite particles with graphite and the Li storage particles form composite particles ( 002) A negative electrode material characterized in that an interplanar spacing d (002) is 0.3354 nm or more and 0.338 nm or less and an area ratio of G peak to D peak by Raman spectroscopic analysis is G / D ≧ 9.

  In addition, according to the present invention, in the negative electrode material according to any one of the above, a negative electrode material is obtained in which the Li storage particles have an amorphous structure.

  According to the present invention, in the rechargeable non-aqueous electrolyte secondary battery including a positive electrode capable of doping and dedoping lithium ions, a non-aqueous electrolyte, and a negative electrode, the negative electrode active material is one kind of Li storage particles. In the graphite particles, the (002) plane spacing d (002) by the X-ray diffraction method is 0.3354 nm or more and 0.338 nm or less, and G is obtained by Raman spectroscopic analysis. The area ratio between the peak and the D peak is G / D ≧ 9, and the Li storage particles include at least one kind of composite particles of silicon and iron, silicon and titanium, and silicon and nickel. A secondary battery is obtained.

  According to the present invention, there is obtained a secondary battery characterized in that in the secondary battery, the Li storage particles and the graphite particles are mixed to form an electrode.

  According to the present invention, in the secondary battery, a layer made of graphite particles is present on the current collector, and a mixed layer made of Li storage particles and graphite particles is further present thereon. A secondary battery is obtained.

  According to the present invention, in any one of the secondary batteries, a mixed layer composed of the Li storage particles and the graphite particles is present on the current collector, and a layer composed of the graphite particles is further present thereon. A secondary battery characterized by this can be obtained.

  Further, according to the present invention, in any one of the secondary batteries, the Li storage particles form composite particles with graphite, and the (002) plane spacing by graphite X-ray diffraction method that forms composite particles with Li storage particles. A secondary battery is obtained in which d (002) is 0.3354 nm or more and 0.338 nm or less, and the area ratio of G peak to D peak by Raman spectroscopic analysis is G / D ≧ 9.

  Further, according to the present invention, in any one of the secondary batteries, the secondary battery is characterized in that the Li storage particles have an amorphous structure.

  Here, in order to buffer the stress generated by the expansion and contraction of the particles accompanying charging and discharging of the Li storage particles, it is mixed with graphite particles that tend to collapse by pressurization and act as a cushion to relieve the stress caused by the expansion and contraction. It is considered effective to do. Graphite particles having such a function have a (002) plane distance d (002) of 0.3354 nm or more and 0.338 nm or less by X-ray diffraction, and an area ratio of G peak to D peak by Raman spectroscopic analysis is G. It is necessary that / D ≧ 9.

  By mixing such graphite particles and Li occlusion particles, stress due to expansion and contraction of Li occlusion particles is relieved, and electrode peeling between particles causing deterioration of cycle characteristics and from current collectors and underlayers is suppressed. can do. Therefore, according to the present invention, a negative electrode material having a high capacity and excellent cycle characteristics and a secondary battery using the same can be obtained.

  According to the present invention, the negative electrode active material is composed of one or more types of Li storage particles and one or more types of graphite particles, and the (002) plane spacing d (002) of the graphite particles by X-ray diffraction method is 0.3354 nm or more. By providing an area ratio of G peak to D peak of 338 nm or less and Raman spectroscopic analysis to G / D ≧ 9, a negative electrode material having high capacity and excellent cycle characteristics and a secondary battery using the same are provided. it can.

It is an example of sectional drawing which shows the negative electrode structure of the secondary battery by the 1st Embodiment of this invention. It is an example of sectional drawing which shows the negative electrode structure of the secondary battery by the 1st Embodiment of this invention. It shows discharge capacity ratio of the _{(C 100 /} C ₁₎ after initial charge and discharge efficiency and 100 cycles when changing the weight ratio of the graphite particles in the active material in the third embodiment of the present invention. It is an example of sectional drawing which shows the negative electrode structure of the secondary battery by the 4th Embodiment of this invention. It is an example of sectional drawing which shows the high Li occlusion particle by the 4th Embodiment of this invention. It is an example of sectional drawing which shows the negative electrode structure of the secondary battery by the 5th Embodiment of this invention. It is an example of sectional drawing which shows the negative electrode structure of the secondary battery by the 6th Embodiment of this invention. It is an example of sectional drawing which shows the negative electrode structure of the secondary battery by the 7th Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
First, a first embodiment of the present invention will be described in detail with reference to the drawings.

  1 and 2 are cross-sectional views showing a negative electrode of a secondary battery according to the first embodiment of the present invention.

  Referring to FIG. 1, the current collector 6 a is an electrode for taking out an electric current to the outside of the battery and taking in an electric current from the outside into the battery at the time of charging / discharging. The current collector 6a only needs to be a conductive metal foil. For example, aluminum, copper, stainless steel, gold, tungsten, molybdenum, or the like can be used, and the film thickness is 5 to 25 μm.

  The Li occlusion particle 1a is a negative electrode member that occludes or releases lithium during charging and discharging. Examples of the Li storage particles 1a include silicon, tin, germanium, aluminum, lead, indium, calcium, magnesium and composite particles thereof, silicon and carbon, silicon and iron, silicon and titanium, silicon and nickel composite particles, Silicon oxide, tin oxide, boron oxide, phosphorus oxide, germanium oxide, aluminum oxide and their composite oxides, silicon, tin, germanium, aluminum, lead, indium, calcium, magnesium and their composite particles having amorphous structure These are formed from one type or two or more types. The average particle size of the particles is preferably 50 μm or less.

  The graphite particles 2a are negative electrode members that occlude or release lithium during charge and discharge and buffer stress generated by expansion and contraction of the Li occlusion particles 1a. Examples of the graphite particles 2a include graphite particles that are easily crushed by pressurization, that is, highly crystalline. Specifically, the distance between the crystal layers is 0.3354 nm or more and 0.338 nm or less, and the area ratio of G peak to D peak by Raman spectroscopic analysis is graphite particles with G / D ≧ 9. The average particle size is desirably 50 μm or less.

  These active materials are mixed with polyvinylidene fluoride and a conductivity-imparting material, and further added with N-methyl-2-pyrrolidone to form a slurry liquid, which is applied onto the current collector 6a by the doctor blade method.

  Moreover, as shown in FIG. 2, you may apply | coat the mixed layer 4a which mixed Li occlusion particle | grains 1a and the graphite particle | grains 2a on both surfaces of the electrical power collector 6a.

The positive electrode that can be used in the lithium secondary battery according to the present invention is LixMyOz (where M represents at least one transition metal, 0 <x ≦ 2, 0 <y ≦ 2, 0 <z ≦ 4). Composite oxides such as LiCoO ₂ having a layered structure, LiNiO ₂ and LiMnO ₂ , LiMn ₂ O ₄ having a spinel structure, and those obtained by substituting these transition metals and oxygen with other elements, etc. A material, a binder such as polyvinylidene fluoride (PVDF) and the like dispersed and kneaded with a solvent such as N-methyl-2-pyrrolidone (NMP) and applied onto a substrate such as an aluminum foil can be used.

  In addition, as a separator that can be used in the lithium secondary battery in the present invention, a polyolefin such as polypropylene or polyethylene, or a porous film such as a fluororesin can be used.

Examples of the electrolyte solution that can be used in the lithium secondary battery according to the present invention include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), cyclic carbonates such as vinylene carbonate (VC), dimethyl carbonate, and the like. (DMC), chain carbonates such as diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate, ethyl propionate, γ- Γ-lactones such as butyrolactone, chain ethers such as 1,2-ethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1, 3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazo One or two aprotic organic solvents such as lydinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methyl-2-pyrrolidone, etc. A mixture of seeds or more is used to dissolve lithium salts that are dissolved in these organic solvents. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ). ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, imides and the like. Further, a polymer electrolyte may be used instead of the electrolytic solution.

  The shape of the battery in the present invention is not particularly limited, and examples thereof include a cylindrical shape, a square shape, and a coin shape. Moreover, a metal or a metal laminated film can be used as the container.

  Next, the operation of the negative electrode of the nonaqueous electrolyte secondary battery shown in FIG. 1 will be described in detail. At the time of charging, the negative electrode receives lithium from the positive electrode side through the electrolytic solution. First, lithium ions are occluded in Li occlusion particles 1a and graphite particles 2a present in the negative electrode. At the time of discharging, lithium ions occluded during charging are released from the Li occlusion particles 1a and the graphite particles 2a. During charging, the Li storage particles 1a and the graphite particles 2a expand in volume to store lithium ions. On the other hand, during discharge, the lithium ion is released and contracts to return. In particular, the Li occlusion particle 1a has a larger volume expansion / contraction than the graphite particle 2a, so that it is gradually pulverized by the stress generated at that time, and the electrical contact between the particles or between the current collector and the electrode layer is lost. There is a risk that. However, in the form of the present invention, graphite particles 2a that are easily crushed by pressurization are arranged around the Li storage particles 1a, so that they function as a cushion, and by the expansion and contraction of the Li storage particles 1a during charging and discharging. The generated stress can be relaxed. Therefore, even if charging / discharging is repeated, the current collecting property is maintained, and cycle deterioration can be prevented.

  A specific example of manufacturing a secondary battery according to the first embodiment of the present invention will be described below as Example 1.

  In Example 1 of the present invention, a structure having a mixed layer 4a in which Li storage particles 1a and graphite particles 2a are mixed on a current collector 6a as shown in FIG. It produced and evaluated.

  A rolled copper foil having a thickness of 10 μm is used for the current collector 6a, crystalline Sn particles having an average particle diameter of 2 μm are used for the Li storage particles 1a, and graphite particles 2a having an average particle diameter of 5 μm are used for the graphite particles 2a. These were mixed at a ratio of Li storage particles 1a: graphite particles 2a = 10 wt%: 90 wt% to obtain an active material. As the graphite particles 2a, nine types of graphite particles 2a having different (002) plane distances d (002) by X-ray diffraction method and different G / D peak area ratio G / D by Raman spectroscopic analysis were used.

Polyvinylidene fluoride and a conductivity-imparting material were mixed into the Li storage particles 1a and the graphite particles 2a, and N-methyl-2-pyrrolidone was further added to form a slurry liquid. This slurry liquid was applied onto the current collector 6a by a doctor blade method to produce a mixed layer 4a. After drying, it was compressed using a press machine to obtain a working electrode having a film thickness of 50 μm and an electrode density of 1.6 × 10 ³ kg / m ³ . A coin-type battery was fabricated using metal lithium punched in a circular shape for the counter electrode.

A polypropylene nonwoven fabric was used for the separator. As the electrolyte, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in which LiPF ₆ having a concentration of 1 mol / L was dissolved (mixing volume ratio: EC / DEC = 30/70) was used.

  About the produced battery, the charge / discharge cycle test was done at 20 degreeC. The voltage range of the charge / discharge test was 0 to 2.5V.

Table 1 below shows d (002) and G / D of each graphite particle 2a and the initial charge / discharge efficiency of a coin-type battery produced using the graphite particles 2a. Table 2 below shows the discharge capacity ratio (C ₁₀₀ / C ₁ ).

  From Table 1 and Table 2 below, when graphite particles 2a having d (002) of 0.3354 nm or more and 0.338 nm or less and an area ratio of G peak to D peak by Raman spectroscopic analysis of G / D ≧ 9 are used. It can be seen that both the initial charge / discharge efficiency and the discharge capacity ratio show high values of 90% or more.

  From the evaluation results in Example 1 of the present invention, the negative electrode according to the present invention, that is, d (002) is 0.3354 nm or more and 0.338 nm or less, and the area ratio of G peak to D peak by Raman spectroscopy is G / D ≧ 9. It was proved that the secondary battery including the graphite particles having the high initial charge / discharge efficiency and excellent cycle characteristics.

(Second Embodiment)
Next, a specific example of the secondary battery according to the second embodiment of the present invention will be described in detail as Example 2.

  Example 2 of the present invention has a structure having a mixed layer 4a in which Li storage particles 1a and graphite particles 2a are mixed on a current collector 6a as shown in FIG. The current collector 6a is a rolled copper foil having a thickness of 10 μm, the Li occlusion particles 1a are crystalline Si particles having an average particle size of 5 μm, the graphite particles 2a are average particle size of 10 μm, and the crystal interlayer distance is 0.336 nm. And the graphite particle 2a of G / D = 10 was used. Using these Li occlusion particles 1a and graphite particles 2a as active materials, coin-type batteries were produced in the same manner as in Example 1, and the characteristics of the batteries in which the mixing ratio of Li occlusion particles 1a and graphite particles 2a was changed were compared. . The electrode film thickness was 50 μm.

FIG. 3 shows the initial charge and discharge efficiency and the discharge capacity ratio after 100 cycles when the weight ratio of graphite particles 2a in the active material (graphite particles 2a weight / (graphite particles 2a + Li occlusion particles 1a)%) is changed (C ₁₀₀ / C ₁ ).

FIG. 3 shows that the higher the ratio of the graphite particles 2a, the higher the initial charge / discharge efficiency and the higher the discharge capacity ratio after 100 cycles. In particular, it was found that when the ratio of the graphite particles 2a is 40% by weight or more, the initial charge / discharge effect is 85% or more and the discharge capacity ratio (C ₁₀₀ / C ₁ ) is 80% or more. This is presumably because if the amount is less than 40% by weight (that is, expressed in terms of mass percent, hereinafter referred to as wt%), the mixing amount of the graphite particles 2a is too small and the effect as a buffer material is insufficient.

  From the above results, it became clear that setting the weight ratio of the graphite particles 2a to 40% by weight or more of the negative electrode active material is effective in improving the initial charge / discharge efficiency and the cycle characteristics.

  From the evaluation results in Example 2, the negative electrode according to the present invention, that is, the secondary battery in which the weight ratio of the graphite particles 2a is 40% by weight or more of the negative electrode material active material has high initial charge / discharge efficiency and excellent cycle characteristics. Proved to have

(Third embodiment)
Next, Example 3 as a specific example of the secondary battery according to the third embodiment of the present invention will be described.

Example 3 of the present invention has a structure having a mixed layer 4a in which Li storage particles 1a and graphite particles 2a are mixed on a current collector 6a as shown in FIG. A rolled copper foil having a thickness of 10 μm was used for the current collector 6a. The graphite particles 2a have excellent characteristics in Example 1, and have an average particle diameter of 5 μm, a crystal interlayer distance of 0.336 nm, and an area ratio of G peak to D peak by Raman spectroscopy of G / D = 10. Using the particles 2a and changing the Li storage particles 1a to be mixed as shown in Table 3 below, a coin-type battery was produced in the same manner as in Example 1, and the initial charge / discharge efficiency and the discharge capacity ratio after 100 cycles (C ₁₀₀ / C ₁ ) was evaluated. The mixing ratio was Li storage particles 1a: graphite particles 2a = 20 wt%: 80 wt%.

Table 3 below shows the Li storage particles 1a used in Example 3 and the coin-type battery made using the same, showing the initial charge / discharge efficiency and the discharge capacity ratio after 100 cycles (C ₁₀₀ / C ₁ ). Yes.

From Table 3 below, it can be seen that, when any material is used, the initial charge / discharge efficiency and the discharge capacity ratio (C ₁₀₀ / C ₁ ) show high values of 90% or more. This is presumably because the graphite particles 2a relieve the stress caused by the expansion of the Li storage particles 1a and suppress the crushing of the Li storage particles 1a and the peeling of the electrode from the current collector 6a.

  From the evaluation results in Example 3, it was proved that the secondary battery including the negative electrode according to the present invention has high initial charge / discharge efficiency and excellent cycle characteristics.

(Fourth embodiment)
A fourth embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 4 is a cross-sectional view of a negative electrode according to the fourth embodiment of the present invention.

  As shown in FIG. 4, the current collector 6b has a structure in which a layer composed of high Li storage particles 1b in which Li storage particles 3b and graphite particles 2b are combined is disposed. The current collector 6b is an electrode for taking out a current to the outside of the battery and taking in a current from the outside into the battery at the time of charging / discharging. The current collector 6b only needs to be a conductive metal foil. For example, aluminum, copper, stainless steel, gold, tungsten, molybdenum, or the like can be used, and the film thickness is 5 to 25 μm.

  The high Li occlusion particle 1b that is a composite of the Li occlusion particle 3b and the graphite particle 2b is a negative electrode member that occludes or releases lithium during charge and discharge. Examples of the Li storage particles 3b include silicon, tin, germanium, aluminum, lead, indium, calcium, magnesium and composite particles thereof, silicon and carbon, silicon and iron, silicon and titanium, silicon and nickel composite particles, oxidation Examples include silicon, tin oxide, boron oxide, phosphorus oxide, germanium oxide, aluminum oxide and their composite oxides, silicon, tin, germanium, aluminum, lead, indium, calcium, magnesium and their composite particles having an amorphous structure. Of these, one type or two or more types are formed.

  The graphite particle 2b is a negative electrode member that absorbs or releases lithium during charge and discharge and also buffers stress generated by expansion and contraction of the Li storage particle 3b. Examples of the graphite particles 2b include particles that are easily crushed by pressurization, that is, particles having high crystallinity. Specifically, the graphite particle 2b has a crystal interlayer distance of 0.3354 nm or more and 0.338 nm or less, and an area ratio of G peak to D peak by Raman spectroscopic analysis of G / D ≧ 9.

  5A to 5C are cross-sectional views showing the high Li storage particles 1b shown in FIG. As shown in FIGS. 5 (a) to 5 (c), the high Li storage particles 1b obtained by combining the Li storage particles 3b and the graphite particles 2b are pulverized and mixed with the Li storage particles 3b and the graphite particles 2b. It is a thing.

  In the high Li storage particles 1b, the Li storage particles 3b and the graphite particles 2b are integrated to form particles, and the Li storage particles 3b are uniformly present in the graphite particles 2b. Or the form that the Li occlusion particle 3b exists in the graphite particle 2b surface and the form that the graphite particle 2b exists in the Li occlusion particle 3b surface can be given as examples. The average particle size of the high Li storage particles 1b is preferably 50 μm or less.

  The high Li occlusion particle 1b is used as an active material, polyvinylidene fluoride and a conductivity-imparting material are mixed, and N-methyl-2-pyrrolidone is added to form a slurry liquid, which is applied onto the current collector 6b by the doctor blade method. To do. Moreover, when producing a battery using this electrode, the separator, the positive electrode, the electrolytic solution, the battery shape, and the container as shown in the first embodiment of the present invention can be similarly used.

  Next, the operation of the negative electrode of the nonaqueous electrolyte secondary battery according to the fourth embodiment will be described in detail. At the time of charging, the negative electrode receives lithium from the positive electrode side through the electrolytic solution.

  First, lithium ions are occluded in the high Li occlusion particles 1b, which are a composite of the Li occlusion particles 3b and the graphite particles 2b present in the negative electrode.

  At the time of discharging, lithium ions occluded during charging are released from the high Li occlusion particles 1b obtained by combining the Li occlusion particles 3b and the graphite particles 2b. During charging, the Li storage particles 3b and the graphite particles 2b expand in volume to store lithium ions. On the other hand, during discharge, the lithium ion is released and contracts to return. In particular, the Li occlusion particle 3b has a larger volume expansion / contraction than the graphite particle 2b, so that it is gradually pulverized by the stress generated at that time, and the electrical contact between the particles or between the current collector and the electrode layer is lost. There is a risk that.

  However, in the fourth embodiment of the present invention, since the Li storage particles 3b and the graphite particles 2b that are easily crushed by pressurization are combined, the graphite particles 2b act like a cushion, and charge and discharge. The stress generated by the expansion and contraction of the Li storage particles 3b at the time can be relaxed. Therefore, even if charging / discharging is repeated, the current collecting property is maintained, and cycle deterioration can be prevented.

  Next, a specific example of the secondary battery according to the second embodiment of the present invention will be described in more detail as Example 4.

The fourth example has a structure having a layer 4b composed of high Li occlusion particles 1b in which Li occlusion particles 3b and graphite particles 2b are combined on a current collector 6b as shown in FIG. The current collector 6b is a rolled copper foil having a thickness of 10 μm, the Li occlusion particle 3b is an amorphous Si particle having a particle size of 2 μm, and the graphite particle 2b has an average particle size of 5 μm and a crystal interlayer distance of 0. Particles having a G / D = 10 area ratio between G peak and D peak by .336 nm and Raman spectroscopic analysis were used. These Li occlusion particles 3b and graphite particles 2b are pulverized, mixed at a ratio of Li occlusion particles 3b: graphite particles 2b = 50 wt%: 50 wt% and granulated to obtain high Li occlusion particles 1b having an average particle diameter of 10 μm. It was. Polyvinylidene fluoride and a conductivity-imparting material were mixed with the high Li storage particles 1b obtained by combining the Li storage particles 3b and the graphite particles 2b, and N-methyl-2-pyrrolidone was further added to form a slurry liquid. This slurry was applied onto the current collector 6b by the doctor blade method. After drying, it was compressed using a press machine to obtain a working electrode, and a metal battery punched in a circle was used as a counter electrode to produce a coin-type battery. The film thickness of the electrode composed of the high Li storage particles 1b obtained by combining the Li storage particles 3b and the graphite particles 2b was 50 μm, and the electrode density was 1.6 × 10 ³ kg / m ³ .

A polypropylene nonwoven fabric was used for the separator. Mixed solvent (mixing volume ratio: EC / DEC = 30/70 ) of ethylene carbonate was dissolved LiPF ₆ at a concentration of 1 mol / L in the electrolyte solution (EC) and diethyl carbonate (DEC) was used.

  About the produced battery, the charge / discharge cycle test was done at 20 degreeC. The voltage range of the charge / discharge test was 0 to 2.5V.

Table 4 below shows the initial charge / discharge efficiency and the discharge capacity ratio after 100 cycles (C ₁₀₀ / C ₁ ). From Table 4 below, a high value of 90% was obtained for both the initial charge / discharge efficiency and the discharge capacity ratio after 100 cycles (C ₁₀₀ / C ₁ ). In this example 4, since the Li occlusion particles 3b and the graphite particles 2b that are easily crushed by pressurization are combined, the stress caused by the expansion and contraction of the Li occlusion particles 3b during charge and discharge is relaxed by the surrounding graphite particles 2b. This is considered to be because the crushing of the Li storage particles 3b and the peeling of the electrode from the current collector 6b were suppressed, and the current collecting property was maintained.

  From the evaluation results in Example 4, the negative battery according to the present invention, that is, a secondary battery having a layer 4b composed of high Li occlusion particles 1b obtained by combining Li occlusion particles 3b and graphite particles 2b on a current collector 6b, It was proved that the initial charge / discharge efficiency was high and the cycle characteristics were excellent.

(Fifth embodiment)
A fifth embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 6 is a cross-sectional view of a negative electrode according to the fifth embodiment of the present invention. As shown in FIG. 6, in the negative electrode according to the fifth embodiment of the present invention, high Li storage particles 1c and graphite particles 2c, which are a composite of Li storage particles 3c and graphite particles 2c ', are mixed on a current collector 6c. The mixed layer 4c is disposed. The current collector 6c is an electrode for taking out an electric current to the outside of the battery or taking an electric current into the battery from the outside during charging and discharging. The current collector 6c only needs to be a conductive metal foil. For example, aluminum, copper, stainless steel, gold, tungsten, molybdenum or the like can be used, and the film thickness is 5 to 25 μm.

  The high Li occlusion particles 1c and the graphite particles 2c, which are a composite of the Li occlusion particles 3c and the graphite particles 2c ', are negative electrode members that occlude or release lithium during charge and discharge. Examples of the Li storage particles 3c include silicon, tin, germanium, aluminum, lead, indium, calcium, magnesium and composite particles thereof, silicon and carbon, silicon and iron, silicon and titanium, silicon and nickel composite particles, Silicon oxide, tin oxide, boron oxide, phosphorus oxide, germanium oxide, aluminum oxide and their composite oxides, silicon, tin, germanium, aluminum, lead, indium, calcium, magnesium and their composite particles having amorphous structure These are formed from one type or two or more types.

  The graphite particles 2c and the graphite particles 2c ′ are negative electrode members that occlude or release lithium during charge and discharge and buffer stress generated by expansion and contraction of the Li occlusion particles 3c. Examples of the graphite particles 2c include particles that are easily crushed by pressurization, that is, particles having high crystallinity. Specifically, the distance between the crystal layers is 0.3354 nm or more and 0.338 nm or less, and the area ratio of G peak to D peak by Raman spectroscopic analysis is graphite particles with G / D ≧ 9. The average particle size of the graphite particles 2c is desirably 50 μm or less. The graphite particle 2c ′ is a crystal that is easily crushed against pressure, in which the distance between layers of the crystal is 0.3354 nm or more and 0.338 nm or less, and the area ratio of G peak to D peak by Raman spectroscopic analysis is G / D ≧ 9. Although highly characteristic graphite particles can also be selected, it is not limited to this range.

  The high Li occlusion particle 1c in which the Li occlusion particle 3c and the graphite particle 2c ′ are combined is obtained by pulverizing, mixing and granulating the Li occlusion particle 3c and the graphite particle 2c ′. As shown in FIG. Li storage particles 3c are present on the surface 2c '. Alternatively, the form in which the graphite particles 2c ′ are present on the surface of the Li storage particles 3c, or the Li storage particles 3c and the graphite particles 2c ′ are integrated to form particles, and the Li storage particles 3c are uniformly present in the graphite particles 2c ′. , Takes the form of The average particle diameter of the high Li occlusion particles 1c is desirably 50 μm or less.

  The high Li storage particles 1c and the graphite particles 2c, which are a composite of these Li storage particles 3c and the graphite particles 2c ', are used as active materials, polyvinylidene fluoride and a conductive material are mixed, and N-methyl-2-pyrrolidone is added. The slurry liquid is applied onto the current collector 6c by the doctor blade method. Moreover, when manufacturing a battery using these negative electrodes, the separator, the positive electrode, the electrolytic solution, the battery shape, and the container as shown in the first embodiment of the invention can be similarly used.

  The operation of the negative electrode of the nonaqueous electrolyte secondary battery shown in FIG. 6 will be described in detail. At the time of charging, the negative electrode receives lithium from the positive electrode side through the electrolytic solution. First, lithium ions are occluded in high Li occlusion particles 1c and graphite particles 2c, which are a composite of Li occlusion particles 3c and graphite particles 2c ′ present in the negative electrode. When discharging, lithium ions occluded during charging are released from the high Li occlusion particles 1c and the graphite particles 2c, which are a composite of the Li occlusion particles 3c and the graphite particles 2c ′. At the time of charging, the Li storage particles 3c, the graphite particles 2c, and the graphite particles 2c ′ expand in volume to store lithium ions. On the other hand, during discharge, the lithium ion is released and contracts to return. In particular, the Li occlusion particle 3c has a larger volume expansion / contraction than the graphite particle 2c and the graphite particle 2c ′, so that it is gradually pulverized by the stress generated at that time, and the electricity between the particles or between the current collector and the electrode layer. May be lost.

  However, in the fifth embodiment of the present invention, the Li storage particles 3c and the graphite particles 2c 'are combined, and further, the graphite particles 2c that are easily crushed by pressurization are disposed around the Li storage particles 3c. And the graphite particles 2c ′ act like a cushion, and can relieve stress generated by expansion and contraction of the Li storage particles 3c during charge and discharge. Therefore, even if charging / discharging is repeated, the current collecting property is maintained, and cycle deterioration can be prevented.

  Next, Example 5 as a specific example of manufacturing a secondary battery according to the fifth embodiment of the present invention will be described.

In Example 5, a structure having a mixed layer 4c in which high Li storage particles 1c obtained by combining Li storage particles 3c and graphite particles 2c 'and graphite particles 2c are mixed on a current collector 6c as shown in FIG. The current collector 6c is a rolled copper foil having a thickness of 10 μm, the Li storage particles 3c are amorphous Si particles having a particle size of 2 μm, the graphite particles 2c and the graphite particles 2c ′ have an average particle size of 5 μm and a crystalline particle. Particles having an interlayer distance of 0.336 nm and an area ratio of G peak to D peak by Raman spectroscopic analysis of G / D = 10 were used. These Li storage particles 3c and graphite particles 2c ′ are pulverized, mixed and granulated at a ratio of Li storage particles 3c: graphite particles 2c ′ = 50 wt%: 50 wt%, and high Li storage particles 1c having an average particle size of 10 μm. Got. Polyvinylidene fluoride and high Li occlusion particle 1c: graphite particle 2c = 50 wt%: 50 wt% mixed with this Li occlusion particle 3c and graphite particle 2c ′ in a ratio of high Li occlusion particle 1c: graphite particle 2c = 50 wt%: 50 wt% The conductivity imparting material was mixed, and N-methyl-2-pyrrolidone was further added to form a slurry liquid. This slurry liquid is applied onto the current collector 6c by the doctor blade method, dried, and then compressed using a press machine, so that the film thickness is 50 μm and the electrode density is 1.6 × 10 ³ kg / m ^3. It was the pole. A coin-type battery was fabricated using metal lithium punched in a circular shape for the counter electrode.

A polypropylene nonwoven fabric was used for the separator. As the electrolyte, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in which LiPF ₆ having a concentration of 1 mol / L was dissolved (mixing volume ratio: EC / DEC = 30/70) was used.

  About the produced battery, the charge / discharge cycle test was done at 20 degreeC. The voltage range of the charge / discharge test was 0 to 2.5V.

Table 5 below shows the initial charge / discharge efficiency and the discharge capacity ratio after 100 cycles (C ₁₀₀ / C ₁ ). From Table 5 below, high values of 91% for the initial charge / discharge efficiency and 92% for the discharge capacity ratio after 100 cycles (C ₁₀₀ / C ₁ ) were obtained. In this example 5, Li storage particles 3c and graphite particles 2c ′ are combined, and graphite particles 2c that are easily crushed by pressurization are arranged around them. Therefore, the expansion of the Li storage particles 3c during charging and discharging is performed. It is considered that the stress due to the shrinkage was relaxed by the graphite particles 2c and the graphite particles 2c ′, the Li occlusion particles 3c were prevented from being crushed and the electrodes were separated from the current collector 6c, and the current collecting property was maintained.

  From the evaluation results in Example 5, the negative electrode according to the present invention, that is, the current collector 6c has the mixed layer 4c in which the Li storage particles 3c and the graphite particles 2c ′ combined with the high storage particles 1c and the graphite particles 2c are mixed. It has been proved that the secondary battery in the form has high initial charge / discharge efficiency and excellent cycle characteristics.

(Sixth embodiment)
A sixth embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 7 is a cross-sectional view of a negative electrode showing a sixth embodiment of the present invention. As shown in FIG. 7, in the negative electrode showing the sixth embodiment of the present invention, a graphite particle layer 5d is formed on the current collector 6d, and further, a mixed layer in which Li storage particles 1d and graphite particles 2d are mixed. 4d is arranged. The current collector 6d is an electrode for taking out the current to the outside of the battery and taking in the current from the outside into the battery during charging and discharging. The current collector 6d only needs to be a conductive metal foil. For example, aluminum, copper, stainless steel, gold, tungsten, molybdenum, or the like can be used, and the film thickness is 5 to 25 μm.

  The Li storage particles 1d, the graphite particles 2d, and the graphite particles 5d are negative electrode members that store or release lithium during charge and discharge.

  Examples of the Li storage particles 1d include silicon, tin, germanium, aluminum, lead, indium, calcium, magnesium and composite particles thereof, silicon and carbon, silicon and iron, silicon and titanium, silicon and nickel composite particles, Silicon oxide, tin oxide, boron oxide, phosphorus oxide, germanium oxide, aluminum oxide and their composite oxides, silicon, tin, germanium, aluminum, lead, indium, calcium, magnesium and their composite particles having amorphous structure These are formed from one type or two or more types. The average particle size is desirably 50 μm or less.

  The graphite particles 2d and the graphite particles 5d are negative electrode members that occlude or release lithium during charge and discharge and buffer stress generated by expansion and contraction of the Li occlusion particles 1d. Examples of the graphite particles 2d and the graphite particles 5d include particles that are easily crushed by pressurization, that is, particles having high crystallinity. Specifically, the distance between the crystal layers is 0.3354 nm or more and 0.338 nm or less, and the area ratio of G peak to D peak by Raman spectroscopic analysis is graphite particles with G / D ≧ 9. The average particle size is desirably 50 μm or less.

  The graphite particles 5d are mixed with polyvinylidene fluoride and a conductivity-imparting material, and further N-methyl-2-pyrrolidone is added to form a slurry liquid, which is applied onto the current collector 6d by the doctor blade method. Further, on this layer, Li storage particles 1d and graphite particles 2d are mixed to form an active material, polyvinylidene fluoride and a conductive material are mixed, and N-methyl-2-pyrrolidone is further added to form a slurry liquid. Is applied by the doctor blade method. In the present invention, the graphite particle layer 5d and the mixed layer 4d may be either singular or plural, and a multilayered structure can also be adopted.

  When producing a battery using these negative electrodes, the separator, the positive electrode, the electrolytic solution, the battery shape, and the container as shown in the first embodiment of the invention can be used in the same manner.

  Next, the operation of the negative electrode of the nonaqueous electrolyte secondary battery shown in FIG. 7 will be described in detail.

  At the time of charging, the negative electrode receives lithium from the positive electrode side through the electrolytic solution.

  First, lithium ions are occluded in the Li occlusion particles 1d, graphite particles 2d, and graphite particles 5d present in the negative electrode. In discharging, lithium ions occluded during charging are released from the Li occlusion particles 1d and the graphite particles 2d and 5d. During charging, the Li storage particles 1d, the graphite particles 2d, and the graphite particles 5d expand in volume to store lithium ions.

  On the contrary, at the time of discharge, the lithium ion is released and contracts to return to the original state. In particular, the Li occlusion particle 1d has a larger volume expansion / contraction than the graphite particles 2d and 5d, so that it is gradually pulverized by the stress generated at that time, and is in electrical contact between the particles or between the collector and the electrode layer. May be lost.

  However, according to the sixth embodiment of the present invention, the graphite particles 2d that are liable to be crushed by pressurization are arranged around the Li storage particles 1d. Since it is formed, the graphite particles 2d and 5d act like a cushion, and the stress generated by the expansion and contraction of the Li storage particles 1d during charge / discharge can be relieved. Therefore, even if charging / discharging is repeated, the current collecting property is maintained, and cycle deterioration can be prevented.

  A specific example of the secondary battery according to the sixth embodiment of the invention will be described below as Example 6.

  In Example 6, a structure having a graphite particle 5d layer on a current collector 6d and a mixed layer 4d in which Li storage particles 1d and graphite particles 2d are mixed thereon is provided as shown in FIG.

  The current collector 6d is a rolled copper foil having a thickness of 10 μm, the Li storage particles 1d are amorphous Si particles having a particle size of 2 μm, and the graphite particles 2d and 5d have an average particle size of 5 μm and a crystal interlayer. Particles having a distance of 0.336 nm and an area ratio of G peak to D peak by Raman spectroscopic analysis of G / D = 10 were used.

  The graphite particles 5d were mixed with polyvinylidene fluoride and a conductivity-imparting material, and N-methyl-2-pyrrolidone was further added to form a slurry solution, which was applied onto the current collector 6d by the doctor blade method. Further, on this layer, the Li storage particles 1d and the graphite particles 2d are mixed at a ratio of Li storage particles 1d: graphite particles 2d = 50 wt%: 50 wt% to obtain an active material, and the polyvinylidene fluoride and the conductive material are mixed. Further, a slurry obtained by adding N-methyl-2-pyrrolidone was applied by a doctor blade method. After drying, it was compressed using a press machine to obtain a working electrode, and a metal battery punched in a circle was used as a counter electrode to produce a coin-type battery.

The film thickness of the graphite particle layer 5d was 20 μm, the film thickness of the mixed layer 4d of the Li storage particles 1d and the graphite particles 2d was 30 μm, and the electrode density was 1.6 × 10 ³ kg / m ³ .

A polypropylene nonwoven fabric was used for the separator. As the electrolyte, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in which LiPF ₆ having a concentration of 1 mol / L was dissolved (mixing volume ratio: EC / DEC = 30/70) was used.

  About the produced battery, the charge / discharge cycle test was done at 20 degreeC. The voltage range of the charge / discharge test was 0 to 2.5V.

Table 6 below shows the initial charge / discharge efficiency and the discharge capacity ratio after 100 cycles (C ₁₀₀ / C ₁ ).

From Table 6 below, high values of 90% for the initial charge / discharge efficiency and 92% for the discharge capacity ratio after 100 cycles (C ₁₀₀ / C ₁ ) were obtained. In this example 6, graphite particles 2d that are easily crushed by pressurization are disposed around the Li storage particles 1d, and further, a graphite particle layer 5d that is easily crushed by pressurization is formed thereunder. The stress due to the expansion and contraction of the Li occlusion particles 1d is relaxed by the graphite particles 2d and the graphite particles 5d, the crushing of the Li occlusion particles 1d and the peeling of the electrode from the current collector 6d are suppressed, and the current collecting property is maintained. it is conceivable that.

  From the evaluation results in this Example 6, the negative electrode according to the present invention, that is, the secondary electrode having a form having a graphite particle 5d layer on the current collector 6d and a mixed layer 4d in which the Li storage particles 1d and the graphite particles 2d are mixed thereon. The battery was proved to have high initial charge / discharge efficiency and excellent cycle characteristics.

(Seventh embodiment)
A seventh embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 8 is a cross-sectional view of the negative electrode according to the seventh embodiment of the present invention. As shown in FIG. 8, in the negative electrode according to the seventh embodiment of the present invention, a mixed layer 4e obtained by mixing Li storage particles 1e and graphite particles 2e on a current collector 6e, and further a graphite particle layer 5e thereon. It is the structure which arranged. The current collector 6e is an electrode for taking out the current to the outside of the battery and taking in the current from the outside into the battery during charging and discharging. The current collector 6e only needs to be a conductive metal foil. For example, aluminum, copper, stainless steel, gold, tungsten, molybdenum, or the like can be used, and the film thickness is 5 to 25 μm.

  The Li storage particles 1e, the graphite particles 2e, and the graphite particles 5e are negative electrode members that store or release lithium during charge and discharge.

  Examples of the Li storage particles 1e include silicon, tin, germanium, aluminum, lead, indium, calcium, magnesium and composite particles thereof, silicon and carbon, silicon and iron, silicon and titanium, silicon and nickel composite particles, Silicon oxide, tin oxide, boron oxide, phosphorus oxide, germanium oxide, aluminum oxide and their composite oxides, silicon, tin, germanium, aluminum, lead, indium, calcium, magnesium and their composite particles having amorphous structure These are formed from one type or two or more types. The average particle size is desirably 50 μm or less.

  The graphite particles 2e and the graphite particles 5e are negative electrode members that occlude or release lithium during charge and discharge and buffer stress generated by the expansion and contraction of the Li occlusion particles 1e. Examples of the graphite particles 2e and the graphite particles 5e include particles that are easily crushed by pressurization, that is, particles having high crystallinity. Specifically, the distance between the crystal layers is 0.3354 nm or more and 0.338 nm or less, and the area ratio of G peak to D peak by Raman spectroscopic analysis is graphite particles with G / D ≧ 9. The average particle size is desirably 50 μm or less.

  A mixture of these Li occlusion particles 1e and graphite particles 2e is used as an active material, polyvinylidene fluoride and a conductive material are mixed, and N-methyl-2-pyrrolidone is added to form a slurry liquid by a doctor blade method. It coats on the current collector 6e. Further, on this layer, the graphite particles 5e are mixed with polyvinylidene fluoride and a conductivity-imparting material, and further added with N-methyl-2-pyrrolidone to form a slurry liquid is applied by a doctor blade method.

  In the present invention, the mixed layer 4e and the graphite particle layer 5e may be either singular or plural, and a multilayered structure can also be adopted. When producing a battery using these negative electrodes, the separator, the positive electrode, the electrolytic solution, the battery shape, and the container as shown in the first embodiment of the invention can be used in the same manner.

  Next, the operation of the negative electrode of the nonaqueous electrolyte secondary battery shown in FIG. 7 will be described in detail. At the time of charging, the negative electrode receives lithium from the positive electrode side through the electrolytic solution. First, lithium ions are occluded in the Li occlusion particles 1e, graphite particles 2e, and graphite particles 5e present in the negative electrode. In discharging, lithium ions occluded during charging are released from the Li occlusion particles 1e, the graphite particles 2e, and the graphite particles 5e. During charging, the Li storage particles 1e, the graphite particles 2e, and the graphite particles 5e expand in volume in order to store lithium ions. On the other hand, during discharge, the lithium ion is released and contracts to return. In particular, the Li occlusion particle 1e has a larger volume expansion / contraction than the graphite particle 2e and the graphite particle 5e, so that it is gradually pulverized by the stress generated at that time, and is electrically connected between the particles or between the current collector and the electrode layer. Contact may be lost.

  However, in the present invention, graphite particles 2e that are easily crushed by pressurization are arranged around the Li storage particles 1e, and further, a graphite particle layer 5e that is easily crushed by pressurization is formed on the layer. The particles 2e and 5e act like a cushion, and can relieve the stress generated by the expansion and contraction of the Li storage particles 1e during charging and discharging. Therefore, even if charging / discharging is repeated, the current collecting property is maintained, and cycle deterioration can be prevented.

  Hereinafter, Example 7 as a specific example according to the seventh embodiment of the present invention will be described.

  In this example 7, a structure having a mixed layer 4e in which Li storage particles 1e and graphite particles 2e are mixed on a current collector 6e as shown in FIG. 8, and a graphite particle 5e layer thereon is adopted.

  A rolled copper foil having a thickness of 10 μm is used for the current collector 6e, an amorphous Si particle having a particle size of 2 μm is used for the Li-occlusion particles 1e, and an average particle size of 5 μm and the interlayer distance between crystals are used for the graphite particles 2e and 5e Particles having a G / D = 10 area ratio of G peak and D peak by Raman spectroscopic analysis of 0.336 nm.

These Li occlusion particles 1e and graphite particles 2e are mixed at a ratio of Li occlusion particles 1e: graphite particles 2e = 50 wt%: 50 wt% to form an active material, polyvinylidene fluoride and a conductivity-imparting material are mixed, and further N-methyl A slurry obtained by adding -2-pyrrolidone was applied onto the current collector 6e by the doctor blade method. Furthermore, on this layer, graphite particles 5e were mixed with polyvinylidene fluoride and a conductivity-imparting material, and further N-methyl-2-pyrrolidone was added to form a slurry solution, which was applied by a doctor blade method. After drying, it was compressed using a press machine to obtain a working electrode, and a metal battery punched in a circle was used as a counter electrode to produce a coin-type battery. The thickness of the mixed layer 4e of the Li storage particles 1e and the graphite particles 2e was 30 μm, the thickness of the graphite particle 5e layer was 20 μm, and the electrode density was 1.6 × 10 ³ kg / m ³ .

A polypropylene nonwoven fabric was used for the separator. As the electrolyte, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in which LiPF ₆ having a concentration of 1 mol / L was dissolved (mixing volume ratio: EC / DEC = 30/70) was used.

  About the produced battery, the charge / discharge cycle test was done at 20 degreeC. The voltage range of the charge / discharge test was 0 to 2.5V.

Table 7 below shows the initial charge / discharge efficiency and the discharge capacity ratio after 100 cycles (C ₁₀₀ / C ₁ ).

From Table 7 below, the initial charge / discharge efficiency and the discharge capacity ratio after 100 cycles (C ₁₀₀ / C ₁ ) were as high as 90%. In this example 7, since the graphite particles 2e that are easily crushed by pressurization are arranged around the Li occlusion particles 1e, and the graphite particle 5e layer that is easily crushed by pressurization is formed on the graphite particles 2e. The stress due to the expansion and contraction of the Li occlusion particles 1e is relaxed by the graphite particles 2e and the graphite particles 5e, and the crushing of the Li occlusion particles 1e and the peeling of the electrode from the current collector 6e are suppressed, and the current collecting property is maintained. It is thought that it was because of.

  From the evaluation results in this Example 7, the negative electrode according to the present invention, that is, a secondary layer in which a mixed layer 4e in which Li storage particles 1e and graphite particles 2e are mixed on a current collector 6e, and a graphite particle 5e layer on the mixed layer 4e. The battery was proved to have high initial charge / discharge efficiency and excellent cycle characteristics.

  As described above, the negative electrode material for a lithium secondary battery of the present invention is applied to a secondary battery.

1a, 1d, 1e Li occlusion particles 1b, 1c High Li occlusion particles 2a, 2b, 2c, 2c ′, 2d, 2e Graphite particles 3b, 3c Li occlusion particles 4a, 4c, 4d, 4e Mixed layers 5d, 5e Graphite particles 6a , 6b, 6c, 6d, 6e Current collector 10a, 10b, 10c, 10d, 10e Negative electrode 20a Electrode structure

Claims (12)

  In the material used for the negative electrode of the rechargeable non-aqueous electrolyte secondary battery including a positive electrode capable of doping and dedoping lithium ions, a non-aqueous electrolyte, and a negative electrode, the negative electrode active material has one or more Li storage particles. The graphite particles have a (002) plane spacing d (002) of 0.3354 nm or more and 0.338 nm or less by X-ray diffraction, and a G peak by Raman spectroscopy. A negative electrode material, wherein the area ratio of D and D peaks is G / D ≧ 9, and the Li storage particles include at least one of silicon and iron, silicon and titanium, and silicon and nickel composite particles.   2. The negative electrode material according to claim 1, wherein the Li storage particles and the graphite particles are mixed to form an electrode.   3. The negative electrode material according to claim 1, wherein a layer composed of the graphite particles is present on a current collector, and a mixed layer composed of the Li storage particles and the graphite particles is further present thereon. Negative electrode material.   4. The negative electrode material according to claim 1, wherein a mixed layer composed of the Li storage particles and the graphite particles is present on a current collector, and a layer composed of the graphite particles is further formed thereon. A negative electrode material characterized by the presence of   5. The negative electrode material according to claim 1, wherein the Li storage particles form composite particles with graphite, and the X-ray diffraction method of graphite forms composite particles with the Li storage particles. (002) A negative electrode material characterized in that an interplanar spacing d (002) is 0.3354 nm or more and 0.338 nm or less, and an area ratio of G peak to D peak by Raman spectroscopic analysis is G / D ≧ 9.   6. The negative electrode material according to claim 1, wherein the Li storage particles have an amorphous structure.   In a rechargeable non-aqueous electrolyte secondary battery comprising a positive electrode capable of doping and dedoping lithium ions, a non-aqueous electrolyte, and a negative electrode, the negative electrode active material is composed of one or more Li storage particles and 40% by weight or more of graphite. It consists of one or more kinds of particles, and in the graphite particles, the (002) plane spacing d (002) by X-ray diffraction method is 0.3354 nm or more and 0.338 nm or less, and the area ratio of G peak to D peak by Raman spectroscopic analysis is A secondary battery in which G / D ≧ 9 and the Li storage particles include at least one kind of composite particles of silicon and iron, silicon and titanium, and silicon and nickel.   The secondary battery according to claim 7, wherein the Li storage particles and the graphite particles are mixed to form an electrode.   9. The secondary battery according to claim 7, wherein a layer made of graphite particles is present on the current collector, and a mixed layer made of Li occluded particles and graphite particles is further present thereon. Next battery.   10. The secondary battery according to claim 7, wherein a mixed layer composed of the Li storage particles and the graphite particles is present on a current collector, and a layer composed of the graphite particles is further formed thereon. A secondary battery characterized by the presence of   The secondary battery according to any one of claims 7 to 10, wherein the Li storage particles form composite particles with graphite, and the X-ray diffraction method of graphite forms composite particles with Li storage particles (002). (2) A secondary battery characterized in that the interplanar spacing d (002) is 0.3354 nm or more and 0.338 nm or less, and the area ratio of G peak to D peak by Raman spectroscopic analysis is G / D ≧ 9.   The secondary battery according to any one of claims 7 to 11, wherein the Li storage particles have an amorphous structure.

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