JP2000268824A - Lithium battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium battery having a high capacity and long cyclic service life. SOLUTION: This lithium battery is composed of a positive electrode 2, a negative electrode 4 containing an active material capable of storing and releasing lithium ions, and a non-aqueous electrolytic solution or polymer electrolyte. The negative electrode active material contains particles of at least one of elements capable of forming a compound with lithium, having a melting point >=900 deg.C, and having a coefficient of thermal expansion <=9 ppm/K or less at room temp. and such particles are embedded in a carbonaceous substance formed into a plurality of layers and subjected to a mechanical processing so that the partical sizes become smaller than those in the initial period. This battery can be used in an electric automobile as a battery assembly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery having charge / discharge characteristics of high voltage, high energy density, high charge / discharge capacity, long cycle life, and safety. Related to high lithium secondary batteries.

[0002]

2. Description of the Related Art With the reduction in size and weight of portable electronic devices, the development of batteries having a high energy density, particularly secondary batteries, has been required, and lithium secondary batteries have attracted attention as a candidate.

[0003] A lithium secondary battery has a higher voltage, a higher energy density, and is lighter in weight than nickel cadmium batteries, lead storage batteries, and nickel hydrogen batteries. However, in lithium secondary batteries that use lithium metal as the negative electrode active material, lithium dendrites precipitate on the negative electrode surface, causing an internal short circuit with the positive electrode and inactivating the electrolytic solution. Is a problem.

In order to avoid the danger of using lithium metal, a lithium secondary battery using a lithium alloy such as lithium-lead or lithium-aluminum as a negative electrode active material has been developed.

[0005] However, this lithium secondary battery also has a problem of dendrite precipitation and pulverization, and a sufficient battery life has not been obtained.

At present, lithium secondary batteries using graphite as a negative electrode active material have been developed and have been put to practical use. This is because lithium ions are inserted and desorbed from the C plane of graphite by inserting and removing lithium ions, and the lithium ions are inserted and desorbed. The lithium ions are more stable than chemically active metallic lithium. Nor. For this reason, the cycle life was extended and the safety was improved.

[0007]

When graphite is used as the negative electrode active material, the discharge capacity is at most 370 Ah / kg.
In order to increase the capacity of a lithium secondary battery, it is essential to increase the capacity of a negative electrode active material. As a high capacity negative electrode active material,
Elements that can form an intermetallic compound with lithium, such as aluminum and lead, are listed. However, when used alone or mixed with conductive particles as a negative electrode active material, cycle deterioration is fast, and it cannot practically be used as a negative electrode active material. .

There have been various proposals for using a negative electrode active material composed of particles containing an element capable of forming a compound with lithium and a carbonaceous material in a lithium secondary battery (JP-A 5-286763, J.
P-A 6-279112, JP-A 10-3920) have low melting points of Sn (mp 232 ° C), Pb (mp 327 ° C),
Since Zn (mp 419 ° C.), Al (mp 660 ° C.), and the like can be used as elements capable of forming a compound with lithium, when carbonized at 800 ° C. or more, coagulation due to melting occurs. , Coarsening, etc., which may unexpectedly lower the performance of the product. In addition, Sn having a high coefficient of thermal expansion
(22.0 ppm / Kat250 ° C.), Al (23.1 ppm / Kat
at 25 ° C), Mg (24.8ppm / K at 25 ° C), P
Since elements such as b (28.9 ppm / K at 25 ° C.) can also be used, adhesion to carbon cannot be maintained during the carbonization heat treatment and cooling, and the particle shape may not be maintained. Causes a decrease in performance.

Japanese Patent Nos. 2948205 and 2948206 disclose a negative electrode material containing 30 to 90% by weight of silicon.
Since the sintering is only performed at 00-1400 ° C., uniformity of the quality of the negative electrode material and improvement of the quality cannot be expected.

[0010]

The present invention provides a lithium secondary battery comprising: [1] a positive electrode, a negative electrode containing a negative electrode active material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte or a polymer electrolyte. The negative electrode active material is capable of forming a compound with lithium, and contains particles containing at least one element having a melting point of 900 ° C. or higher and a coefficient of thermal expansion at room temperature of 9 ppm / K or lower, A lithium secondary battery is provided because the particles are embedded in a plurality of layers of a carbonaceous material and are mechanically treated so that the fine particles have a size smaller than an initial particle size.

[0011] The carbonaceous material in which the particles are embedded comprises a carbonaceous material (A) and a carbonaceous material (B),
The carbonaceous substance (A) is included in the carbonaceous substance (B), the carbonaceous substance (A) in which the particles are embedded is included in the carbonaceous substance (B), and the carbonaceous substance (A) is included. The distance between the d (002) planes by the X-ray diffraction method is smaller than that of the carbonaceous substance (B).

The carbonaceous material (A) embeds the particles and is included in the carbonaceous material (B), and the carbonaceous material (B) is harder than the carbonaceous material (A). The carbonaceous substance (A) to be buried is included in the carbonaceous substance (B),
And d (00) of the carbonaceous substance (A) by X-ray diffraction.
2) The spacing between the surfaces is 0.335 nm to 0.345 nm.

[0013] The carbonaceous substance (A) in which the particles are embedded is included in the carbonaceous substance (B), and the carbonaceous substance (B) is amorphous carbon.

It is necessary that the element capable of forming a compound with lithium has a melting point of at least 900 ° C. 8 after mixing the carbonization treatment with the carbon precursor
It must be performed at a temperature of at least 00 ° C.
This is for suppressing coarsening and reaction with carbon.

The element capable of forming a compound with lithium must have a coefficient of thermal expansion of 9 ppm / K or less at room temperature (25 ° C.). This is because the coefficient of thermal expansion of graphite near room temperature is 3.1 ppm / K. The coefficient of thermal expansion increases with increasing temperature, and is 3.6 ppm / K at 527 ° C. Carbonization heat treatment,
In order to maintain the particle shape during the cooling process and to maintain the adhesion between the element forming the Li compound and carbon, it is necessary to match the thermal expansion. By satisfying this condition, the charge / discharge cycle characteristics are improved.

The amount of the element capable of forming a compound with lithium is preferably less than 30% by weight based on the total amount of the negative electrode active material. The particle size of the Si particles and the graphite particles is made smaller than the initial particle size by a ball mill.

To reduce the particle size by pulverization,
To form a new surface of Si.
And graphite have good binding properties. S of 1 μm or less from the beginning
If i-particles are used, there is a risk of ignition due to oxidation, and if an oxide film is formed so as not to ignite, the amount of oxides occupying the whole increases, leading to deterioration of charge / discharge characteristics.

The element capable of forming a compound with lithium is preferably at least one element selected from Si, Ge and Pt, preferably an element selected from Si and Ge.

[2] The present invention relates to a method for producing a lithium secondary battery having a positive electrode, a negative electrode containing a negative electrode active material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte or a polymer electrolyte. A step of embedding particles containing at least one element capable of forming a compound with lithium in a carbonaceous material, and, if necessary, a step of mixing with a carbon precursor and carbonizing after the step;
The present invention relates to a method for producing a lithium secondary battery, wherein the particles are a negative electrode active material embedded in the carbonaceous material.

The elements capable of forming a compound with lithium are silicon (Si), germanium (Ge),
Platinum (Pt), preferably one of Si and Ge, and use of the above-mentioned lithium secondary battery in an electric vehicle.

[3] In a lithium secondary battery having a positive electrode, a negative electrode containing a negative electrode active material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte or a polymer electrolyte, the negative electrode active material forms a compound with lithium. Particles containing at least one of the possible elements are embedded in the carbonaceous material, and the carbonaceous material has a distance of 0.335 nm from the d (002) plane determined by X-ray diffraction. 0.3
The present invention relates to a lithium secondary battery containing the carbonaceous material having a thickness of 37 nm.

The particles are embedded in a carbonaceous material, the particles have an average particle size of 20 μm or less, the negative electrode active material has a specific surface area of 1 to 100 m ² / g, and the carbonaceous material has an argon laser. the peak intensity ratio of 1360 cm ^-1 relative to 1580 cm ^-1 by Raman is 0.15 to 1.5, any diffraction peak based on carbides of the lithium with the compound capable of forming elements contained in the particles by X-ray diffractometry The intensity ratio of the background to the background intensity is 5
Must be:

(1) The average particle diameter of the particles is 20 μm
In the following, (2) the intensity ratio of any diffraction peak based on the carbide of an element capable of forming a compound with lithium contained in the particles by X-ray diffraction to the background intensity is 5 or less, and (3) the carbonaceous material peak intensity ratio of 1360 cm ^-1 relative to 1580 cm ^-1 by Raman spectrum using argon laser material is 0.15 to 1.5,
(4) The negative electrode active material preferably has a specific surface area of 1 to 100 m ² / g and preferably satisfies at least two of the above conditions (1) to (4), and the particles are embedded in a carbonaceous material. Has an average particle diameter of 20 μm or less, and the intensity ratio of any diffraction peak based on carbide of an element capable of forming a compound with lithium contained in the particles by X-ray diffraction method to the background intensity is 5 or less; Material 1580 cm ^-1 by Raman spectrum using argon laser
Peak intensity ratio of 1360 cm ^-1 to 0.15 to 1.
5. The specific surface area of the negative electrode active material is 1 to 100 m ² / g.

[4] In a method for manufacturing a lithium secondary battery having a positive electrode, a negative electrode containing a negative electrode active material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte or a polymer electrolyte, the negative electrode active material is made of carbonaceous material. A step of repeating mechanical pressure welding of particles and particles of at least one of the elements capable of forming a compound with lithium, and, if necessary, a step of heat-treating the particles. The present invention relates to a method for producing a lithium secondary battery, characterized by obtaining a negative electrode active material containing an active material embedded in a lithium secondary battery.

The negative electrode active material comprises carbonaceous particles,
At least one of the elements capable of forming a compound with lithium
The particles made of the seed element are produced by a method of repeating mechanical pressing or heat-treating at a temperature of 200 to 1200 ° C., and embedding the particles in the carbonaceous material;
And (1) the average particle size of the particles is 20 μm or less;
The intensity ratio of any diffraction peak based on the carbide of an element capable of forming a compound with lithium contained in the particles by X-ray diffraction to the background intensity is 5 or less,
(3) 1360 cm ^-1 to 1580 cm ^-1 by Raman spectrum of the carbonaceous substance using an argon laser
^-1 peak intensity ratio of 0.15 to 1.5, (4) specific surface area of 1 to 100 m ² / g, preferably at least one or more of the above four conditions, and X
The distance between the d (002) planes by a line diffraction method is 0.335 nm.
A negative electrode active material containing the carbonaceous material having a thickness of about 0.337 nm;

The negative electrode active material is produced by a method of mixing carbonaceous particles and particles comprising at least one element selected from elements capable of forming a compound with lithium with a carbon precursor and carbonizing the mixture. Is a negative electrode active material containing an active material embedded in the carbonaceous material.

The negative electrode active material is manufactured by embedding particles of at least one element among elements capable of forming a compound with lithium in a carbonaceous material, and further mixing the resultant with a carbon precursor and carbonizing the mixture. And the negative electrode active material in which the particles are embedded in the carbonaceous material.

The negative electrode active material is obtained by subjecting the particles composed of carbonaceous particles and at least one of the elements capable of forming a compound with lithium to mechanical compression welding or further heat treatment. After being embedded in the carbonaceous material, it is manufactured by a method of further mixing with a carbon precursor and carbonizing, and the particles are a negative electrode active material embedded in the carbonaceous material.

[5] (a) In manufacturing a lithium secondary battery, it is possible to form a compound with lithium as a negative electrode active material, and has a melting point of 900 ° C. or higher and a coefficient of thermal expansion at room temperature of 9 ppm / K. Mechanically treating the following at least one element and the carbonaceous material (A); (b) mixing the particles obtained by the above-mentioned treatment with the carbonaceous material (B); A) a step of forming a negative electrode active material by subjecting the particles obtained by the above treatment to a carbonization treatment; and
Positive electrode, comprising a negative electrode containing the negative electrode active material and a non-aqueous electrolyte solution or a polymer electrolyte in a container,
Provided is a method for manufacturing a lithium secondary battery.

The element capable of forming a compound with lithium is silicon (Si), germanium (Ge), platinum (Pt), preferably one of Si and Ge.

In the above step (a), “mechanically treating” means repeating mechanical pulverization and pressure contact, and specifically includes a general ball mill, a planetary ball mill, an attritor and the like. Means crushing.

For example, a particle of Si or Ge element and the carbonaceous substance (A) are mixed with a ball mill, and the initial average particle diameter of the Si particles is preferably 以下 or less, more preferably １ ／ or less, particularly preferably. Is performed until it becomes 1/10 or less. In terms of specific particle size, the average particle size is preferably 20 μm or less, more preferably 5 μm or less, and particularly preferably 1 μm or less.
Grinding is performed as follows.

A heat treatment may be performed after the step (a).
It is not necessary to carry out. The temperature for implementation is 200
It is carried out in a non-oxidizing atmosphere at -1200C, preferably 700-1000C.

The carbonaceous substance (B) used in the step (b)
, A carbon precursor such as tar can be used.

The carbonization heat treatment in the step (c) is 800
-1500 ° C, preferably 900-1300 ° C.

The above carbon precursor becomes a carbonaceous substance (B) by a carbonization heat treatment.

Further, by mounting an assembled battery comprising the lithium secondary battery of the present invention on an electric vehicle, it is possible to provide an electric vehicle with a high voltage and a long traveling distance per charge.

The lithium secondary battery of the present invention can also be used as a battery for a hybrid vehicle.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, components of a lithium secondary battery according to the present invention will be described.

FIG. 1 shows an example of a basic structure of a coin-type lithium secondary battery.

In a positive electrode can 1, a positive electrode current collector 2a and a positive electrode mixture 2b
Is installed by welding. In addition, the negative electrode can 3
A negative electrode 4 composed of a negative electrode current collector 4a and a negative electrode mixture 4b is installed by welding. For example, ethylene carbonate (EC) and dimethyl carbonate (D
MC) is impregnated with an electrolyte solution in which an electrolyte (for example, LiPF ₆ ) is dissolved, a separator 5 is inserted, the positive electrode and the negative electrode are opposed to each other, and the positive electrode can and the negative electrode can are pressed with an insulating gasket 6 to form a coin-type lithium Obtain a secondary battery.

FIG. 2 shows an example of the basic structure of a cylindrical lithium secondary battery.

The electrode body is composed of a positive electrode current collector 11 and a positive electrode mixture 12.
The negative electrode mixture 1 is applied to the positive electrode 13 and the negative electrode current collector 14 formed by applying
5, a negative electrode 16 and a separator 17 are applied. The positive electrode 13, the separator 17, the negative electrode 16, and the separator 17 are laminated in this order, and are wound as shown in FIG.

A positive electrode tab 18 and a negative electrode tab 19 are connected to the positive electrode 13 and the negative electrode 16 of the electrode body, respectively. The electrode body is housed in a battery can 20, and the battery can 20 and the negative electrode tab 1
9, the battery lid 21 and the positive electrode tab 18 are connected respectively. The battery cover 21 is fixed to the battery can 20 via an insulating gasket 22 to seal the electrode body and the inside of the battery can 20. In addition, an insulating plate 23 is also provided to prevent the electrode body from contacting the battery can 20 or the battery lid 21. An electrolyte containing lithium ions is injected into the sealed battery can. Both ends of the positive electrode are not coated with the positive electrode mixture and the metal foil is exposed. A negative electrode tab is joined to one of them.

FIGS. 4A and 4B show an example of a prismatic lithium secondary battery. FIG. 4A is a top view and FIG. 4B is a sectional view.

The prismatic lithium secondary battery comprises a separator 3
An electrode body in which a positive electrode 31 and a negative electrode 32 are alternately stacked in 3 is inserted into, for example, an aluminum battery can 34. Positive electrode lead 35 and negative electrode lead 37 welded on top of each electrode
Are connected to a positive terminal 38 and a negative terminal 39, respectively.
The positive terminal 38 and the negative terminal 39 are inserted into the battery cover 41 via the packing 40. The external cable and the battery can be connected by a nut 50 attached to the positive terminal 38 and the negative terminal 39. The battery cover 41 is provided with a safety valve for discharging gas accumulated inside the battery when the pressure inside the battery rises, and an electrolyte injection port. The safety valve includes a gas outlet 42, an O-ring 43, and a sealing bolt 44. The liquid inlet comprises an inlet 45, an O-ring 46, and a sealing bolt 47. After the battery can 34 and the battery lid 41 are laser-welded, an electrolyte is introduced from the inlet 45, and the inlet 45 is sealed with a sealing bolt 47 to obtain a prismatic lithium secondary battery.

FIG. 5 shows an assembled battery in which the above-described prismatic lithium secondary batteries are connected in series.

The battery pack 41 of the above-described prismatic lithium secondary battery 51 is arranged in a line with the battery cover 41 facing upward and the side faces facing each other, and an eight-series connected battery pack is assembled.

The spacers 52 are inserted two by two along the height direction between the opposing surfaces of the batteries 51.

The stainless steel metal plate 53 attached to the side and front and rear of the battery pack and the fixing part 58 are fixed with bolts 59 and tightened so that pressure is applied inward of the battery 51. A rib-shaped projection 60 is formed on a stainless steel metal plate 53. The positive terminal and the negative terminal of each square battery 51 are connected by a current cable so that all the batteries are connected in series, and are connected to the positive terminal 54 and the negative terminal 55 of the assembled battery. Further, the positive terminal and the negative terminal of each battery 51 are connected to a control circuit board 56 via a positive voltage input cable and a negative voltage input cable, respectively, and control the voltage and current of each battery for charge / discharge control of the assembled battery. Can be measured. The control circuit board 56 is equipped with a microcomputer, and when one of the voltage and current of at least one battery 51 goes out of the set range,
It has a function of stopping charging and discharging of the battery pack. A thermocouple 57 is attached to the side of the battery at the fourth position from the end, and a temperature signal is sent to the control circuit board 56 so that charging and discharging are stopped when the battery temperature exceeds a set temperature. In the present invention, the electrode body is a stacked type of strip-shaped electrodes. However, a similar assembled battery can be formed even if the electrode body is a flat and oblong wound type.

In the present invention, the negative electrode active material must contain particles composed of at least one of the elements capable of forming a compound with lithium.

The element capable of forming a compound with lithium is
Specifically, silicon (Si), germanium (Ge),
Platinum (Pt) is preferred. Si and Ge are preferable in terms of handling of powder, manufacturing process, cost, and the like. The particles may be the above-described elemental element, an alloy or an intermetallic compound containing the above-mentioned element, or a mixed particle of particles composed only of the above-mentioned elemental element, and electrochemically insert lithium ions. , Any substance that can be desorbed may be used.

When the average particle diameter of particles of at least one element capable of forming a compound with lithium in the negative electrode active material exceeds 20 μm, the cycle life of the lithium secondary battery is significantly shortened. When the average particle size is small, the characteristics as a negative electrode active material tend to be improved. However, when the average particle size is too small, it is violently oxidized in the air, which is not preferable in handling in the negative electrode preparation step. Therefore, the average particle size of the particles is preferably in the range of 0.1 to 20 μm. Further, the thickness is more preferably 0.5 to 5 μm.

The above-mentioned particles are embedded or included in the carbonaceous material, and there are a particle whose surface is completely covered with the carbonaceous material and a particle partially exposed to the outside of the carbonaceous material. It is preferable that the particle surface is completely covered with the carbonaceous material, but a part of the particle surface may be exposed outside. In addition, one or a plurality of the above-described particles embedded in the carbonaceous material exist in one particle of the negative electrode active material. In particular, even if a large number of the above particles are present, there is no problem in characteristics as long as they are embedded in the carbonaceous material.

The state of the negative electrode active material can be determined by observing the cross section of the negative electrode active material with a scanning electron microscope (SEM).

The particle size of the particles capable of forming a compound with lithium was determined by measuring the particle size distribution of the particles observed in the cross section of the negative electrode active material. At this time, the number of the particles measured was 500 to 1500 for each negative electrode active material.
Was individual. Further, if it is confirmed by observation of a cross section of the negative electrode active material that a carbonaceous material exists around the particles, it can be determined that the particles are embedded in the carbonaceous material.

The content ratio of the particles in the active material in which the particles are embedded in the carbonaceous material is 0.01 to 0.005 by weight.
0.8 is preferable, and 0.05 to 0.7 is more preferable.
It is preferably from 0.1 to 0.5, and particularly preferably from 0.15 to 0.3.

The carbonaceous material (A) in which the particles are embedded must contain a crystalline carbon region. When the carbonaceous substance (A) is amorphous carbon, its charge / discharge characteristics are inferior to crystalline carbon.

The carbonaceous substance (A) preferably has a smaller d (002) than the carbonaceous substance (B). This means that the carbonaceous material (A) has higher crystal perfection than the carbonaceous material (B). D (002) of carbonaceous substance (A)
Is preferably from 0.335 nm to 0.345 nm. Further, the thickness is preferably from 0.335 nm to 0.340 nm, and particularly preferably from 0.335 nm to 0.338 nm.

The X-ray diffraction method according to the present invention includes CuKα ray,
Using X-rays with a tube voltage of 50 kV and a tube current of 250 mA,
It was measured in 0.002-0.01 deg steps. d (00
2) The diffraction curve corresponding to the diffraction from the plane was smoothed, and the background was removed to obtain a substantial d (002) diffraction correction curve. The peak of this correction curve is represented by 2θ, where θ is the diffraction angle of the d (002) plane. From the following equation, d (00
2) was determined.

D (002) = λ / (2 sin θ) λ = 0.15418 nm Depending on the carbonaceous material, the d (002) diffraction peak separates into a plurality, but d (0) corresponding to the peak having the maximum intensity.
The distance between the (02) planes is 0.335 nm to 0.345 nm.

On the other hand, the crystallite size (Lc) in the C-axis direction is obtained from the above correction curve using the following equation.

Lc = K · λ / (β · μCOSθ) K = 0.9 λ = 0.15418 nm β: Half width (radian) Lc obtained from the above correction curve is preferably 0.5 nm or more, and more preferably 1 nm. １００100 nm is preferred, and 5n
m to 80 nm, more preferably 10 nm to 60 nm.
nm is preferred. Particularly, the thickness is preferably from 15 nm to 50 nm.

The carbonaceous substance (B) is preferably harder than the carbonaceous substance (A). In order to maintain the function as a negative electrode active material, particles that can form a compound with lithium by maintaining the shape of the active material by the fact that the carbonaceous material on the outer periphery is hard and by using the softer carbonaceous material inside It is considered necessary to alleviate the strain accompanying the expansion and contraction of.

The hardness of the carbonaceous material was measured using a micro Vickers hardness meter having a nanoindentation function. First, a carbonaceous substance for embedding particles capable of forming a compound with lithium is embedded in a resin, and a smooth cross section is exposed by mechanical polishing. Then, a desired carbonaceous substance position is measured with a micro Vickers hardness tester. Here, a pyramid type indenter was used, and the load was 0.5 to 5 g. The appropriate range of the hardness ratio of the carbonaceous material in the outer peripheral portion to the carbonaceous material in the portion close to particles capable of forming a compound with lithium varies depending on the combination of the carbonaceous materials (A) and (B). The hardness ratio is preferably 1.1 or more. Also, preferably 1.2 to 10.0, more preferably 1.5 to 5.0.
Is preferred.

The crystallinity of the carbonaceous material is determined to be at a wavelength of 0.5145.
It is evaluated by Raman spectrum distribution using an argon laser of nm. Peak around 1580 cm ^-1 corresponds to the crystal structure c plane laminate was formed, 1360 cm ^-1
The nearby peaks correspond to the disordered amorphous structure. 1580
The peak in the vicinity cm ^-1 is a peak in the range of 1570~1620cm ^-1, the peak around 1360 cm ^-1 is a peak in the range of 1350 ^-1. When the proportion of crystalline carbon is higher than that of amorphous carbon,
Peak intensity ratio in the vicinity of 1360 cm ^-1 to the peak intensity near 1580 cm ^-1 in an argon laser Raman spectrum (R value) becomes small, increase the proportion of the amorphous carbon increases. By measuring the argon laser Raman spectrum before and after performing the coating treatment with the carbonaceous substance (B), the crystallinity of the carbonaceous substance (B) can be determined. R before coating with carbonaceous material (B)
If the R value after the coating treatment is larger than the value, the carbonaceous substance (B) is composed of amorphous carbon.

As a method of forming a carbonaceous substance, there is a method of carbonizing a carbon precursor. For example, graphitizable precursors such as petroleum pitch, coal pitch, etc., or isotropic pitch,
Polyacrylonitrile, phenolic resin, furan resin,
And the like are used. For the formation of the carbonaceous substance (A), it is preferable to use a graphitizable precursor.

When the carbonaceous substance (A) is formed from the easily graphitizable precursor, it is preferable to use a non-graphitizable precursor for forming the carbonaceous substance (B). When the carbonization temperature of the carbon precursor is high, the particles capable of forming a compound with lithium form carbides or melt at a high temperature.
0 ° C, particularly 900-1200 ° C, is preferred. The carbonization atmosphere is preferably in an inert gas or a nitrogen gas.

On the other hand, the carbonaceous substance can be formed by mechanical pressure welding of carbon particles so that particles made of at least one element capable of forming a compound with lithium can be in close contact with each other. Crystalline carbon and amorphous carbon are used as the carbonaceous particles at the stage prior to pressure welding, but crystalline carbon is more preferable.

In order to mechanically press the carbonaceous particles and the particles made of at least one element capable of forming a compound with lithium, it is necessary to apply an external force so that the particles adhere to each other. A device that causes such behavior is used. Examples of the above-mentioned device include a device such as a planetary ball mill device capable of mechanically pressing the ball in the event of collision between the ball and the container wall or between the balls, a space between the container set at a predetermined gap and a pressing spatula. For example, a device capable of mechanically applying pressure can be used. By using the above-described apparatus, the carbonaceous particles and the particles made of at least one element capable of forming a compound with lithium can be embedded in the carbonaceous material by repeating mechanical pressure welding.

The carbonaceous substance formed on the particles comprising at least one element capable of forming a compound with lithium by the above method increases the specific surface area, but maintains the physical properties of the previous carbonaceous particles to some extent. I have. In particular, if the carbon particles have a small particle size and a large specific surface area, a negative electrode active material having predetermined physical properties cannot be obtained. Therefore, the specific surface area of the carbon particles is preferably 100 m ² / g or less, and more preferably 0.5 m ² / g. ５０50 m ² / g is preferred. Further, the carbon particles preferably have d (002) of 0.335 nm to 0.345 nm. Furthermore, 0.335 nm to 0.34
0 nm is preferable, and 0.335 nm to 0.337 nm is more preferable. After the mechanical pressing operation, the heat treatment may not be performed, but is performed at 200 to 1200 ° C., particularly 900 to 110 ° C.
Heat treatment at 0 ° C. is preferred. The atmosphere at this time is
As long as the atmosphere can prevent oxidation, any of an inert gas, a nitrogen gas, and a vacuum may be used.

When the carbonaceous substance (A) is formed by this method, a non-graphitizable precursor and a non-graphitizable precursor can be used for forming the carbonaceous substance (B). Particularly, a graphitizable precursor is preferable.

In the negative electrode active material obtained by the above method, the irreversible capacity increases as the specific surface area increases, and the coating performance deteriorates as the specific surface area decreases. Therefore, the specific surface area is 1 to 10
0 m ² / g are preferred, particularly 2~50m ² / g are preferred. Also, the d (002) plane of the carbonaceous material is 0.335 n.
It is preferably from m to 0.345 nm. In addition,
335 nm to 0.340 nm is preferable, and 0.335 nm
~ 0.337 nm is more preferable.

In order to manufacture a lithium secondary battery, various components are required.

As the positive electrode active material, lithium cobalt oxide (Li _x CoO ₂ ), lithium nickel oxide (L
i _x NiO _2), lithium manganese oxide _(Li x Mn
Composite oxides such as ₂ O ₄ , Li _x MnO ₃ ), and lithium nickel cobalt oxide (Li _x Ni _y Co _(1-y) O ₂ ) can be used. Here, 0 ≦ x ≦ 1.2,0
≦ y ≦ 1. That is, they may have a stoichiometric composition, but may also be oxides slightly deviating from the stoichiometric composition. These substances preferably have an average particle size of 3 to 40 μm.

As the electrolytic solution, an organic solvent in which a lithium salt is dissolved as an electrolyte is used.

Examples of the organic solvent include butylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, methyl carbonate, 1,
2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, γ-butyl lactone, γ-valerolactone, dipropyl carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, dimethyl sulfoxide, sulfolane, methyl sulfolane,
Organic solvents such as acetonitrile, methyl acetate, methyl formate and the like, or a mixed solvent of two or more thereof are used.

As the electrolyte, lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ),
Lithium perchlorate (LiClO ₄ ), lithium bistrifluoromethylsulfonylimide (LiN (CF ₂ SO
₂ ) ₂ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluorometasulfonate (LiCF ₂ S)
A lithium salt such as O ₃ ) is used. In particular, lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (L
iBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium bistrifluoromethylsulfonylimide (LiN
(CF ₂ SO ₂ ) ₂ ) is preferred. The amount of the electrolyte dissolved in the organic solvent is preferably 0.5 to 2.0 mol / liter.

As the conductive material for the positive electrode and the negative electrode, graphite, amorphous or carbon containing these materials is used, and the average particle diameter is preferably 30 μm or less, and the specific surface area is preferably 1 to 300 m ² / g. It is preferable to use short carbon fibers having a diameter of 5 to 10 μm and a length of 10 to 30 μm.

On the other hand, metal particles having low reactivity with the electrolytic solution can be used as the conductive material. For example, the negative electrode is nickel, cobalt, iron, copper, titanium, chromium and alloys containing them, and the positive electrode is nickel, cobalt, iron, titanium, chromium, aluminum and alloys containing these. It is difficult for these metal particles to deform the particles by pressing, and as the particle size increases, the applicability deteriorates. Therefore, the average particle size is preferably 30 μm or less.

The binder plays a role of connecting the active material, the conductive material and the current collector. The binder is polyvinylidene fluoride (PV
DF), ethylene-propylene-diene copolymer (EP
Resins such as DM), polytetrafluoroethylene (PTFE), polyethylene, polypropylene, polystyrene, polyvinylpyridine, chlorosulfonated polyethylene, and latex can be used. Further, the binder is preferably 2 to 20% by weight of the mixture of the active material, the conductive material and the binder. In particular, the binder for the positive electrode is 2 to
More preferably, the content of the negative electrode is 10% by weight, and the content of the negative electrode is 5 to 15% by weight.

For the current collector, copper, nickel or stainless steel foil or sponge metal is used for the negative electrode.

For the positive electrode, aluminum, nickel or stainless steel foil or sponge metal is used. Generally, a combination of a negative electrode current collector made of copper and a positive electrode current collector made of aluminum is preferred. These foils are preferably rolled foils because of their higher strength, but may be electrolytic foils. Further, the thickness of the foil is preferably 100 μm or less, particularly preferably 8 to 40 μm.

As the separator, a sheet-like or polymer electrolyte which has low resistance to the ionic conductivity of the electrolytic solution, has no reactivity with the electrolytic solution, and is excellent in the solution holding property is used. As the sheet-like separator, a porous film such as polypropylene, polyethylene, polyolefin, polyester, polytetrafluoroethylene, or polyflon, or a nonwoven fabric made of glass fiber and the above polymer can be used. Particularly, a porous membrane made of polypropylene, polyethylene, or polyolefin is preferable. The polymer electrolyte may be a complex obtained by dissolving the electrolyte in a polymer matrix using polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polyacrylamide, or the like as a polymer matrix, or a gel cross-linked body further containing a solvent, low molecular weight polyethylene oxide, crown ether. For example, a polymer electrolyte in which an ion dissociating group such as described above is grafted to the polymer main chain, and a gel polymer electrolyte in which a high molecular weight polymer contains the above electrolytic solution are used.

The lithium secondary battery of the present invention comprises a positive electrode comprising a positive electrode active material, a positive electrode conductive material, a binder, and a positive electrode current collector, and a negative electrode active material, a binder, a negative electrode current collector, or It is composed of an electrode body, an electrolytic solution, an electrode body and an electrolytic solution, which are laminated by inserting a separator between the negative electrode to which the negative electrode conductive material is added, and a battery container connected to the electrode body.

The electrode body may have a structure in which a positive electrode, a separator, and a negative electrode are stacked and tabs are taken out from each electrode, a structure in which strip-shaped electrodes connected to tabs are stacked and wound, or A structure in which strip-shaped electrodes connected to tabs are stacked, wound, and then deformed flat may be used. That is, any battery having an electrode body in which a separator is inserted between the opposed positive and negative electrodes may be used.

The non-aqueous electrolyte lithium secondary battery to which the present invention is applied has a higher capacity and a higher capacity than a conventional lithium secondary battery.
The service life can be extended.

The lithium secondary battery of the present invention is used for various portable electronic devices. In particular, a notebook personal computer, a notebook word processor, a palmtop (pocket) personal computer, a portable telephone, a PHS, a portable fax, a portable printer, a headphone stereo, It can be used for video cameras, portable televisions, portable CDs, portable MDs, electric shavers, electronic shackles, transceivers, electric tools, radios, tape recorders, digital cameras, portable copiers, portable game machines and the like.

Further, electric vehicles, hybrid vehicles, vending machines, electric carts, power storage systems for load leveling, home storage devices, distributed power storage systems (built-in stationary appliances), emergency power supply systems, etc. Can be used as a secondary battery.

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

[0091]

Example 1 Silicon particles having an average particle size of 10 μm and graphite particles having an average particle size of 20 μm were blended at a weight ratio of 50:50.
This composition was subjected to ball milling for 24 hours by repeating mechanical pressing with a planetary ball mill. The ball mill container and the balls were made of stainless steel, and the powder preparation and the ball mill treatment were performed in an argon atmosphere.

As a result of observing the cross section of the composite material obtained as described above by SEM, the average particle diameter of the silicon particles was 1.2 μm.
It was buried in carbonaceous material (graphite particles). Further, as a result of analysis by X-ray diffraction, peaks indicating diffraction from carbon and silicon were observed. The distance between the d (002) planes of carbon was 0.3359 nm. The R value was 0.3.

The above composite material, petroleum pitch and tetrahydrofuran were mixed at a weight ratio of 100: 50: 500, and
Stirred and refluxed for hours. This was removed with a rotary evaporator to remove tetrahydrofuran and vacuum dried at 150 ° C. for 3 hours to obtain a silicon-carbon composite powder / pitch composite material. The composite material is crushed with a cutter mill to 200 mesh or less and then in air at a rate of 3 ° C./min for 250 minutes.
The temperature was raised to ° C. and maintained for 1 hour. This under nitrogen flow
The temperature was raised to 1000 ° C. at 0 ° C./h and maintained for 1 hour to carbonize the petroleum pitch. This was crushed by a cutter mill to 200 mesh or less to obtain a silicon-carbon composite powder. As a result of analyzing the silicon-carbon composite powder by X-ray diffraction, peaks indicating diffraction from carbon and silicon were observed. The diffraction peaks of carbon existed at intervals of the d (002) plane of 0.3358 nm and 0.3378 nm. Also,
The R value was 0.7, and the specific surface area was 29 m ² / g.

On the other hand, in the cross section of the silicon-carbon composite powder, the hardness of the carbonaceous material at 1 μm and 10 μm from the surface of the powder was measured with a micro Vickers hardness meter, and the ratio of the hardness at 1 μm to the 10 μm was measured. Was 1.7.

Silicon-carbon composite powder: PVDF = 8
The N-methylpyrrolidone solution of PVDF and the silicon-carbon composite powder were kneaded so that the weight ratio was 5:15, and the thickness was 20%.
It was applied to a μm copper foil. After drying at 120 ° C. for 1 hour, the electrode was pressure-formed by a roller press and finally punched out to a diameter of 20 mm to obtain a negative electrode.

As the positive electrode active material, a powder of lithium cobalt oxide LiCoO ₂ having an average particle size of 10 μm was used. Lithium cobalt oxide LiCoO ₂ powder: graphite: PVDF
= 90: 6: 4 to obtain a slurry to form a slurry. At this time, an N-methylpyrrolidone solution was used as in the case of the negative electrode. After sufficiently kneading this slurry, a thickness of 2
It was applied to a 0 μm aluminum foil. After drying at 120 ° C. for 1 hour, the electrode was pressure-formed by a roller press, and finally punched out to a diameter of 20 mm to obtain a positive electrode. Here, since the capacity of the negative electrode was large, the weight ratio of the positive electrode mixture to the negative electrode mixture was set to 15.

Using the negative electrode and the positive electrode produced in the above steps, a coin-type battery shown in FIG. 1 was constructed and its characteristics were evaluated.

The positive electrode current collector 2a is placed on the positive electrode can 1 made of stainless steel.
And the positive electrode 2 composed of the positive electrode mixture 2b was installed by spot welding. Also, the negative electrode current collector 4 is placed on the stainless steel negative electrode can 3.
a and the negative electrode 4 composed of the negative electrode mixture 4b was installed by spot welding. Both the positive electrode and the negative electrode are impregnated with an electrolytic solution obtained by dissolving 1 mol / L of LiPF ₆ in a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at a weight ratio of 1: 2. , The positive electrode and the negative electrode were opposed to each other, and the positive electrode can and the negative electrode can were pressure-bonded with an insulating gasket 6 to obtain a lithium secondary battery.

A charge / discharge cycle test was conducted in which the lithium secondary battery was charged at a charge current of 1 mA and a charge end voltage of 4.2 V, and discharged at a discharge current of 1 mA and a discharge end voltage of 2.7 V. As a result, the initial discharge capacity of the battery was 10.2 mAh.
And the ratio of the irreversible capacity was 12%. Meanwhile, 1
The discharge capacity maintenance ratio at the 100th cycle with respect to the cycle was 94%.

[0100]

Example 2 The silicon-carbon composite powder prepared in Example 1, graphite powder having an average particle size of 15 μm, and PVDF were mixed in a ratio of 30: 7.
A slurry was prepared so as to have a weight ratio of 0:10, kneaded sufficiently, and a negative electrode was prepared in the same manner as in Example 1.

A coin-type battery was manufactured in the same manner as in Example 1. However, LiMn ₂ O ₄ having an average particle size of 10 μm was used as the positive electrode material.

This battery was charged at a charge current of 1 mA and a charge end voltage of 4.3 V, and a discharge current of 1 mA and a discharge end voltage of 2.8.
A charge / discharge cycle test for discharging at V was performed. As a result, the initial discharge capacity of the battery was 4.5 mAh, and the ratio of the irreversible capacity was 10%. On the other hand, the discharge capacity retention ratio at the 100th cycle relative to the first cycle was 97%.

[0103]

Example 3 Germanium particles having an average particle diameter of 1 μm, coal pitch, and tetrahydrofuran were mixed in a ratio of 100: 50: 50.
The mixture was mixed at a weight ratio of 0, and stirred and refluxed for 1 hour. This was removed of tetrahydrofuran using a rotary evaporator and vacuum-dried at 150 ° C. for 3 hours to obtain a germanium-carbon composite powder / pitch composite material. This composite material was pulverized with a cutter mill to 200 mesh or less, then heated to 250 ° C. in air at a rate of 3 ° C./min, and held for 1 hour. This was heated to 1200 ° C. at a rate of 20 ° C./h under nitrogen flow, and held for 1 hour to carbonize the pitch. This was crushed by a cutter mill to 200 mesh or less to obtain a composite material. As a result of analyzing the obtained composite material by a wide-angle X-ray diffraction method, peaks indicating diffraction from carbon and germanium were observed. The distance between the d (002) planes of carbon is 0.345.
It was 0 nm. The average particle size of germanium determined from cross-sectional observation was 3.1 μm. The R value was 1.0. The composite material and the phenol resin were mixed at a weight ratio of 100: 50, and vacuum-dried at 120 ° C. for 3 hours to obtain a composite material / resin composite material.

The composite material is crushed with a cutter mill to a size of 200 mesh or less, and then crushed in air at a rate of 3 ° C./min.
The temperature was raised to 50 ° C. and maintained for one hour. This was heated to 1000 ° C. at a rate of 20 ° C./h under nitrogen flow, and held for 1 hour,
The resin was carbonized. This was crushed by a cutter mill to 200 mesh or less to obtain a germanium-carbon composite powder.
As a result of analysis by X-ray diffraction, peaks indicating diffraction from carbon and germanium were observed. In the diffraction peak of carbon, the distance between the d (002) planes was 0.3395 nm. The R value was 1.6 and the specific surface area was 8 m ² / g.

On the other hand, in the cross section of the germanium-carbon composite powder, the hardness of the carbonaceous material at 1 μm and 10 μm from the surface of the powder was measured by a micro-Vickers hardness meter, and the ratio of the hardness at 1 μm to the 10 μm was measured. Was 1.5.

A battery using the above germanium-carbon composite powder as a negative electrode active material was produced in the same manner as in Example 1.
However, as the electrolytic solution, an electrolytic solution in which 1.5 mol / L of LiPF ₆ was dissolved in a mixed solvent of PC: DMC in a ratio of 2: 3 was used.

The lithium secondary battery obtained above was charged at a charge current of 2 mA and a charge end voltage of 4.2 V, and a discharge current of 2 V was applied.
A charge / discharge cycle test was conducted in which the battery was discharged at a discharge end voltage of 2.7 mA at 2.7 mA. As a result, the initial discharge capacity of the battery was 7.2 mAh, and the ratio of the irreversible capacity was 15%. On the other hand, the discharge capacity retention ratio at the 100th cycle relative to the first cycle was 92%.

Comparative Example 1 Silicon particles having an average particle size of 10 μm and graphite particles having an average particle size of 20 μm were mixed in a weight ratio of 20:80.
And ball-milled for 96 hours. The ball mill container and the balls were made of stainless steel, and the powder preparation and the ball mill were performed in an argon atmosphere. As a result of analyzing the obtained silicon-carbon composite powder by a wide-angle X-ray diffraction method, a peak indicating diffraction from carbon silicon was observed. The spacing between the d (002) planes of carbon was 0.3361 nm. The average particle size of silicon determined from cross-sectional observation was 0.9 μm. The R value was 0.9, and the specific surface area of the silicon-carbon composite powder was 280 m ² / g.

A battery using the above silicon-carbon composite powder as a negative electrode active material was produced in the same manner as in Example 1. However, an electrolytic solution in which 1.5 mol / L of LiPF ₆ was dissolved in a mixed solvent of EC: DMC at a ratio of 1: 2 (weight ratio) was used.

This battery was charged at a charge current of 2 mA and a charge end voltage of 4.2 V, and a discharge current of 2 mA and a discharge end voltage of 2.7.
A charge / discharge cycle test for discharging at V was performed. As a result, the initial discharge capacity of the battery was 13.6 mAh, and the ratio of the irreversible capacity was 53%. On the other hand, the discharge capacity retention ratio at the 100th cycle relative to the first cycle was 23%.

[0111]

Embodiment 4 A cylindrical lithium secondary battery was manufactured as the lithium secondary battery of the present invention. FIG. 2 shows the basic configuration.

The electrode body is composed of a positive electrode current collector 11 and a positive electrode mixture 12.
The negative electrode mixture 1 is applied to the positive electrode 13 and the negative electrode current collector 14 formed by applying
5, a negative electrode 16 and a separator 17 are applied. The positive electrode 13, the separator 17, the negative electrode 16, and the separator 17 are laminated in this order, and are wound as shown in FIG. A positive electrode tab 18 and a negative electrode tab 19 are connected to the positive electrode 13 and the negative electrode 16 of the electrode body, respectively. The electrode body is housed in the battery can 20, and the battery can 20 is connected to the negative electrode tab 1.
9, the battery lid 21 and the positive electrode tab 18 are connected respectively.

The battery cover 21 is fixed to the battery can 20 via an insulating gasket 22 to seal the electrode body and the inside of the battery can 20. In addition, an insulating plate 23 is also provided to prevent the electrode body from contacting the battery can 20 or the battery lid 21. An electrolyte containing lithium ions is injected into the sealed battery can. Battery can 20 and battery lid 21 are SUS
304, SUS316, mild steel or the like with a corrosion-resistant coating.

As the positive electrode active material, lithium cobalt oxide (LiCoO ₂₎ having an average particle size of 10 μm, flaky graphite having an average particle size of 5 μm as a positive electrode conductive material, PVDF as a binder, and 20 μm thick aluminum foil as a positive electrode current collector were used. Using. Lithium cobalt oxide LiCoO ₂ : flaky graphite: PV
The weight ratio of DF was 88: 7: 5, N-methylpyrrolidone was added and mixed to prepare a positive electrode mixture slurry. This was applied to both sides of an aluminum foil, vacuum dried at 120 ° C. for 1 hour, and then an electrode was pressure-formed by a roller press. Thereafter, the positive electrode was cut out to a width of 40 mm and a length of 285 mm. Here, the positive electrode mixture was not applied to the portion of each of the positive electrodes having a length of 10 mm, and the aluminum foil was exposed. A nickel negative electrode tab was pressure-bonded to one of the tabs by ultrasonic bonding.

The negative electrode active material was produced by the following method. Silicon particles having an average particle size of 10 μm and graphite particles having an average particle size of 20 μm were blended at a weight ratio of 80:20, and subjected to ball milling for 48 hours. The ball mill container and the balls were made of stainless steel, and the powder preparation and the ball mill were performed in an argon atmosphere. As a result of analyzing the selected composite material by a wide-angle X-ray diffraction method, the distance between carbon d (002) planes was 0.335.
6 nm. The above composite material: petroleum pitch: tetrahydrofuran is mixed in a weight ratio of 100: 50: 500,
Stirred and refluxed for hours. This was removed with a rotary evaporator to remove tetrahydrofuran and vacuum dried at 150 ° C. for 3 hours to obtain a composite / pitch composite material.

The composite material was crushed with a cutter mill to a size of 200 mesh or less, and then crushed in air at a rate of 3 ° C./min.
The temperature was raised to 50 ° C. and maintained for one hour. This was heated to 1000 ° C. at a rate of 20 ° C./h under nitrogen flow, and held for 1 hour,
The pitch was carbonized. This was crushed by a cutter mill to 200 mesh or less to obtain a silicon-carbon composite powder. The silicon-carbon composite powder was used as a negative electrode active material.

As a result of analyzing the negative electrode active material by a wide-angle X-ray diffraction method, peaks indicating diffraction from carbon and silicon were observed. The distance between the d (002) planes of carbon is 0.3
358 nm. The average particle size of silicon determined from cross-sectional observation was 1.8 μm.

The R value was 1.3 and the specific surface area was 9 m ² /
g. On the other hand, the ratio of the hardness of the carbonaceous material at a position of 1 μm to a position of 10 μm from the powder surface was 1.3.

As the negative electrode active material and the negative electrode conductive material, flaky graphite having an average particle size of 10 μm, PVDF as a binder, and 20 μm thick copper foil as a negative electrode current collector were used. The weight ratio of the negative electrode active material: flaky graphite: PVDF is 60:30:10
Then, N-methylpyrrolidone was added and mixed to prepare a negative electrode mixture slurry. Apply this on both sides of the copper foil,
After vacuum drying at 1 ° C. for 1 hour, the electrode was pressure-formed by a roller press. Thereafter, the negative electrode was cut out to have a width of 40 mm and a length of 290 mm. The application weight ratio between the negative electrode mixture and the positive electrode mixture was 1:10. Here, similarly to the positive electrode, the negative electrode mixture was not applied to the portion having a length of 10 mm at both ends of the negative electrode, and the copper foil was exposed. A nickel negative electrode tab was pressure-bonded to one of the tabs by ultrasonic bonding.

As the separator, a polypropylene porous film having a thickness of 25 μm and a width of 44 mm was used. EC and D
An electrolytic solution obtained by dissolving 1 mol / liter of LiPF ₆ in a mixed solvent having an MC of 1: 2 (weight ratio) was used.

Using the lithium secondary battery obtained above, charging / discharging was repeated at a charge / discharge current of 300 mA, a charge end voltage of 4.2 V, and a discharge end voltage of 2.8 V. As a result, the highest discharge capacity was 1357 mAh. The maintenance ratio of the discharge capacity at the 200th cycle with respect to the highest discharge capacity was 86%.

Comparative Example 2 For comparison, the average particle size was 20 μm.
m of flaky graphite as the negative electrode active material, the negative electrode active material: P
A negative electrode was manufactured by adjusting the weight ratio of VDF to 90:10, and a lithium secondary battery was manufactured in the same manner as in Example 4. However, the weight ratio of the negative electrode mixture: the positive electrode mixture was 1: 2.

Using the lithium secondary battery, a charge / discharge current of 300 mA, a charge end voltage of 4.2 V, and a discharge end voltage of 2.8 were used.
As V, charging and discharging were repeated. As a result, the highest discharge capacity was 734 mAh. The maintenance ratio of the discharge capacity at the 200th cycle with respect to the highest discharge capacity was 85%.

From these results, the lithium secondary battery of the present invention has higher capacity and cycle characteristics equal to or higher than those of the conventional lithium secondary battery.

[0125]

Embodiment 5 A prismatic battery was manufactured as the lithium secondary battery of the present invention.

N-methylpyrrolidone was added to a mixture of lithium cobalt oxide LiCoO ₂ : scale graphite: PVDF having an average particle diameter of 10 μm in a weight ratio of 90: 6: 4, and the mixture was sufficiently kneaded to prepare a slurry. did. The slurry was applied on both sides of a 20 μm-thick aluminum foil by a doctor blade method, and dried at 100 ° C. for 2 hours. The positive electrode is 7
It is a strip of 0 × 120 mm.

The negative electrode active material was produced by the following method. Silicon particles having an average particle size of 1 μm and graphite particles having an average particle size of 10 μm were mixed at a weight ratio of 30:70, and subjected to a ball mill treatment for 24 hours. The ball mill container and the balls were made of stainless steel, and the powder preparation and the ball mill were performed in an argon atmosphere. The composite material: petroleum pitch: tetrahydrofuran was mixed at a weight ratio of 100: 50: 500, and the mixture was stirred and refluxed for 1 hour. This was removed with a rotary evaporator to remove tetrahydrofuran and vacuum dried at 150 ° C. for 3 hours to obtain a silicon-carbon composite powder / pitch composite material. The composite material was crushed with a cutter mill to 200 mesh or less, then heated to 250 ° C. in air at a rate of 3 ° C./min, and held for 1 hour. This is placed under nitrogen at 20 ° C.
/ H, the temperature was raised to 1100 ° C, and the temperature was maintained for 1 hour to carbonize the pitch. This was crushed by a cutter mill to 200 mesh or less to obtain a silicon-carbon composite powder.

The above negative electrode active material, PVDF as a binder,
A copper foil having a thickness of 20 μm was used as a negative electrode current collector. The weight ratio of the negative electrode active material: PVDF was 90:10, and N-methylpyrrolidone was added and mixed to prepare a negative electrode mixture slurry. This was applied to both surfaces of a copper foil by a doctor blade method and dried at 100 ° C. for 2 hours. The negative electrode is 70 × 120
mm.

FIG. 4 shows (a) a top view and (b) a sectional view of a prismatic lithium secondary battery.

The external dimensions of the prismatic lithium secondary battery are height 1
It is 00 mm, width 130 mm and depth 30 mm. The positive electrode 31 is placed in a polyethylene-made separator 33 processed into a bag shape.
The electrode body in which the negative electrodes 32 were alternately laminated was inserted into an aluminum battery can 34. Here, the weight ratio between the positive electrode mixture and the negative electrode mixture was 5: 1. A positive electrode lead 35 and a negative electrode lead 37 welded to the upper part of each electrode are respectively connected to a positive electrode terminal 38,
Connected to negative electrode terminal 39. Positive terminal 38 and negative terminal 39
Is inserted into the battery cover 41 via a packing 40 made of polypropylene. The external cable and battery are connected to the positive terminal 3
8, can be connected by a nut 50 attached to the negative terminal 39. The battery cover 41 was provided with a safety valve for discharging gas accumulated inside the battery when the pressure inside the battery reached 4 to 7 atm, and an electrolyte injection port. The safety valve includes a gas outlet 42, an O-ring 43, and a sealing bolt 44. The liquid inlet comprises an inlet 45, an O-ring 46, and a sealing bolt 47. After the battery can 34 and the battery lid 41 were laser-welded, an electrolytic solution was introduced from the injection port 45, and the injection port 45 was sealed with a sealing bolt 47 to complete a prismatic lithium secondary battery. The electrolytic solution used was a solution obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixed solvent of EC: DMC at a ratio of 1: 2 (weight ratio). The average discharge voltage of the prismatic lithium secondary battery is 3.4 V, the rated capacity is 38 Ah, 130
Wh.

The battery lid 41 of the rectangular lithium secondary battery 51 was oriented upward, and arranged in a line so that the sides of 100 × 130 mm faced each other, thereby assembling an eight-series connected battery shown in FIG. 2 × 10 × 100 between facing surfaces of the battery 51
Two mm spacers 52 made of polytetrafluoroethylene were inserted in the height direction. The stainless steel metal plate 53 attached to the side surface and the front and rear of the assembled battery and the polytetrafluoroethylene fixing part 58 were fixed with bolts 59 and tightened so that pressure was applied to the inside of the battery 51. A rib-shaped projection 60 was formed on a stainless steel metal plate 53. The positive terminal and the negative terminal of each square battery 51 were connected by a current cable so that all the batteries were connected in series, and were connected to the positive terminal 54 and the negative terminal 55 of the assembled battery. Further, the positive terminal and the negative terminal of each battery 51 are connected to a control circuit board 56 via a positive voltage input cable and a negative voltage input cable, respectively, and control the voltage and current of each battery for charge / discharge control of the assembled battery. Measured. The control circuit board 56 is equipped with a microcomputer, and has a function of stopping charging / discharging of the battery pack when at least one of the voltage and current of at least one battery 51 is out of the set range. A thermocouple 57 was attached to the side surface of the battery at the fourth position from the terminal, a temperature signal was sent to the control circuit board 56, and charging and discharging were stopped when the battery temperature exceeded the set temperature. The average discharge voltage of the battery pack is 2
7.2V, rated capacity 38Ah, 1030Wh.

In the present embodiment, the electrode body is a lamination type of strip-shaped electrodes. However, even if the electrode body is a flat and oblong winding type, an assembled battery similar to that of the present embodiment can be constructed. .

Comparative Example 3 In the same manner as in Example 5, a prismatic lithium secondary battery and an assembled battery thereof were produced. However, flaky graphite having an average particle size of 20 μm was used as the negative electrode active material. The weight ratio of the negative electrode mixture: the positive electrode mixture was 1: 2.

The average discharge voltage of the prismatic lithium secondary battery is 3.7 V, the rated capacity is 27 Ah, and 100 Wh. The battery pack had an average discharge voltage of 29.6 V and a rated capacity of 2
7Ah, 800Wh.

[0135]

Embodiment 6 The procedure is the same as that of Embodiment 5, and the length is 5000 m.
m, positive electrode with width 150 mm, length 5100 mm, width 15
A 5 mm negative electrode was prepared. FIG. 6 shows a sectional view of the cylindrical lithium secondary battery of the present invention. The external dimensions of the battery are height 200
mm and a diameter of 60 mm.

The electrode body comprises a separator 63 between a positive electrode 61 composed of a positive electrode current collector 61a and a positive electrode mixture 61b and a negative electrode 62 composed of a negative electrode current collector 62a and a negative electrode mixture 62b.
Has a wound-type structure wound up through. The positive electrode lead 65 and the negative electrode lead 67 welded to the upper part of each electrode are mounted in opposite directions, respectively.
A book strip lead was attached. Next, the positive electrode lead 65
And the negative electrode lead 67 are collectively
It was welded to the negative electrode terminal 69. Positive terminal 68 and negative terminal 69
Was attached to the battery cover 71 while being insulated by a packing 70 made of polypropylene. After the tubular aluminum battery can 64 and the battery lid 71 are laser-welded, the inside of the battery is evacuated with the safety valve 80 having the functions of releasing the internal pressure and sealing the injection port removed from the battery lid 71, The electrolyte was quickly injected into the battery. After that, safety valve 80
Was attached to the battery cover 71, and the battery was sealed. When the pressure inside the battery reaches 3 to 7 atm, gas is released from the safety valve. The average discharge voltage of the cylindrical lithium secondary battery is 3.4 V, the rated capacity is 38 Ah, and 130 Wh.

FIG. 7 shows (a) a top view and (b) a sectional view of the assembled battery of the cylindrical lithium secondary battery described above. This assembled battery has a structure in which four cylindrical batteries are arranged on the upper and lower sides, that is, a total of eight cylindrical batteries. Polyfluoroethylene fixing part 82
Were arranged as shown in FIG. 7, and eight batteries 81 were fixed. The positive terminal 68 and the negative terminal 69 of the cylindrical battery 81 are connected by a current cable 83 so that all batteries are connected in series.
The battery was taken out to the positive terminal 84 and the negative terminal 85 of the assembled battery. In order to shorten the length of the current cable 83 of the cylindrical battery,
The directions of the terminals of the positive electrode and the negative electrode were alternately arranged. Each battery 81
The positive terminal 68 and the negative terminal 69 are connected to a control circuit board 87 via voltage input cables 86, respectively, and the voltage of each battery was measured for charge / discharge control of the assembled battery.

Further, a thermocouple 89 is attached to the inner side surface of the battery arranged in the upper stage, and the temperature signal thereof is transmitted to the control circuit board 8.
7 The control circuit board 87 has a microcomputer, and has a function of stopping charging and discharging of the assembled battery when the voltages of all the batteries and the internal temperature of the assembled battery are out of the set ranges. The average discharge voltage of this assembled battery is 27.2 V, rated capacity 38 Ah, and 1030 Wh. 80 is a safety valve, 88 is a case, 85 is a negative terminal, and 84 is a positive terminal.

[0139]

Example 7 Twelve sets of assembled batteries having the same specifications as those of Example 6 were produced, and an assembled battery module in which these assembled batteries were connected in series was mounted on an electric vehicle. An assembled battery module was installed at the bottom of the body of the electric vehicle. When the driver operates the control device with the steering wheel, the output from the battery module is increased or decreased, and power is transmitted to the converter. Using the electric power supplied from the converter, the electric vehicle was driven by driving the motor and the wheels. When the electric vehicle was operated at 80% of the rated capacity per charge, the capacity reduction rate of the assembled battery after 100 times of running was 2 to 5%.

[0140]

Example 8 Silicon particles having an average particle diameter of 10 μm and graphite particles having an average particle diameter of 20 μm were blended in a weight ratio of 50:50, and mechanical pressing was repeated by a planetary ball mill.
The ball mill treatment was performed for 24 hours. The ball mill container and the balls were made of stainless steel, and the powder preparation and the ball mill were performed in an argon atmosphere.

As a result of analyzing the obtained silicon-carbon composite powder by wide-angle X-ray diffraction, peaks indicating diffraction from carbon and silicon were observed. The d (0
02) The spacing between the planes was 0.3358 nm. Also, L
c was 45 nm. No diffraction peak of silicon carbide was observed. The R value was 0.3. As a result of observing the cross section of the composite powder, the silicon particles were embedded in the carbonaceous substance, and the average particle diameter of silicon was 1.2 μm. The actual average particle size is believed to be greater than 1.2 μm. The silicon - the specific surface area of the carbon composite powder was ^63m 2 / g. Silicon-carbon composite powder: PV
N- of PVDF so that DF = 85: 15 weight ratio
The methylpyrrolidone solution and the silicon-graphite composite powder were kneaded and applied to a copper foil having a thickness of 20 μm. After drying at 120 ° C. for 1 hour, the electrode was pressure-formed by a roller press and finally punched out to a diameter of 20 mm to obtain a negative electrode.

As the positive electrode active material, Li having an average particle size of 10 μm was used.
CoO ₂ powder was used. LiCoO ₂ powder: graphite: PVD
The mixture was mixed at a weight ratio of F = 90: 6: 4 to form a slurry. At this time, an N-methylpyrrolidone solution was used as in the case of the negative electrode. After sufficiently kneading the slurry, a thickness of 2
It was applied to a 0 μm aluminum foil. After drying at 120 ° C. for 1 hour, the electrode was pressure-formed by a roller press, and finally punched out to a diameter of 20 mm to obtain a positive electrode. Here, since the capacity of the negative electrode was large, the weight ratio of the positive electrode mixture to the negative electrode mixture was set to 15.

The negative electrode and the positive electrode produced in the above steps were:
The characteristics of the coin-type battery shown in FIG. 1 were evaluated. A positive electrode 2 composed of a positive electrode current collector 2a and a positive electrode mixture 2b was placed on a stainless steel positive electrode can 1 by spot welding.
Further, the negative electrode 4 composed of the negative electrode current collector 4a and the negative electrode mixture 4b was placed on a stainless steel negative electrode can 3 by spot welding. 1: 2 of ethylene carbonate (EC) and dimethyl carbonate (DMC) for both the positive and negative electrodes
The electrolyte was prepared by dissolving 1 mol / l of LiPF ₆ in a mixed solvent of the above, and a polyethylene separator 5 was inserted so that the positive and negative electrodes faced each other.

This battery was charged at a charge current of 1 mA and a charge end voltage of 4.2 V, and a discharge current of 1 mA and a discharge end voltage of 2.7.
A charge / discharge cycle test for discharging at V was performed. As a result, the initial discharge capacity of the battery was 12.5 mAh, and the ratio of the irreversible capacity was 24%. On the other hand, the discharge capacity retention ratio at the 100th cycle relative to the first cycle was 85%.

[0145]

Example 9 Silicon particles having an average particle diameter of 1 μm and graphite particles having an average particle diameter of 20 μm were blended at a weight ratio of 80:20, and subjected to ball milling for 48 hours using a planetary ball mill, and further treated with the above treated particles. Add the same amount of graphite particles as
The ball mill treatment was performed for 12 hours. The ball mill container and the balls were made of stainless steel, and the powder preparation and the ball mill were performed in an argon atmosphere.

As a result of analyzing the silicon-carbon composite powder obtained as described above by wide-angle X-ray diffraction, peaks indicating diffraction from carbon and silicon were observed. The d (0
02) was 0.3352 nm. Lc is 52
nm. No diffraction peak of silicon carbide was observed. The R value was 0.25. As a result of observing the cross section of the composite powder, the silicon particles were embedded in the carbonaceous material, and the average particle diameter of silicon was 0.7 μm.
The specific surface area of the silicon-carbon composite powder is 49 m ² /
g.

A battery using the above silicon-carbon composite powder as a negative electrode active material was produced in the same manner as in Example 8. Also in this case, a lithium cobalt oxide LiCoO ₂ having an average particle diameter of 10 μm was used as the positive electrode material. However, the electrolyte is EC: D
1 mol / L LiCl in a 1: 2 mixed solvent of MC
An electrolytic solution in which O ₄ was dissolved was used.

A charge / discharge cycle test was performed in which the lithium secondary battery was charged at a charge current of 1 mA and a charge end voltage of 4.2 V, and discharged at a discharge current of 1 mA and a discharge end voltage of 2.7 V. As a result, the initial discharge capacity of the battery was 11.0 mAh.
And the ratio of the irreversible capacity was 20%. Meanwhile, 1
The discharge capacity retention at the 100th cycle relative to the cycle was 88%.

[0149]

Example 10 The silicon-carbon composite powder prepared in Example 8, coal pitch, and tetrahydrofuran were mixed in 100 parts:
The mixture was mixed at a weight ratio of 30: 300, and stirred and refluxed for 1 hour. This was removed with a rotary evaporator to remove tetrahydrofuran and vacuum dried at 150 ° C. for 3 hours to obtain a silicon-carbon composite powder / pitch composite material. This composite material is pulverized with a cutter mill to 200 mesh or less, and then heated to 250 ° C. in air at a rate of 3 ° C./min.
Hold for 1 hour. This is passed at 20 ° C./h for 10
The temperature was raised to 00 ° C. and maintained for 1 hour to carbonize the pitch. This was crushed by a cutter mill to 200 mesh or less to obtain a silicon-carbon composite powder. As a result of analyzing the obtained silicon-carbon composite powder by X-ray diffraction, peaks indicating diffraction from carbon and silicon were observed. The distance between the d (002) planes of carbon is 0.3359 nm and 0.33 nm.
Two peaks at 65 nm were observed. No diffraction peak of silicon carbide was observed. The R value is 0.6.
Met. The specific surface area of the silicon-carbon composite powder was 35 m ² / g.

A battery using the silicon-carbon composite powder as a negative electrode active material was produced in the same manner as in Example 8. However, the cathode material is LiNi _0.8 Co having an average particle size of 10 μm.
_0.2 O ₂ was used. Here, the electrolyte is EC: DMC:
1 mol / L of L in a mixed solvent of DEC of 3: 6: 1
An electrolytic solution in which iPF ₆ was dissolved was used.

This battery was charged at a charging current of 1 mA and a charging end voltage of 4.15 V, and a discharge current of 1 mA and a discharging end voltage of 2.15 V.
A charge / discharge cycle test for discharging at 8 V was performed. As a result, the initial discharge capacity of the battery was 10.2 mAh, and the ratio of the irreversible capacity was 19%.

On the other hand, the discharge capacity retention ratio at the 100th cycle relative to the first cycle was 92%.

[0153]

Example 11 The silicon-carbon composite powder prepared in Example 10, graphite powder having an average particle size of 15 μm, and PVDF
A slurry was prepared so as to have a weight ratio of 0:70:10, kneaded sufficiently, and a negative electrode was prepared in the same manner as in Example 1. Further, a coin-type battery was produced in the same manner as in Example 8. However, LiMn ₂ O ₄ having an average particle size of 10 μm was used as the positive electrode material.

A charge / discharge cycle test was performed in which the lithium secondary battery was charged at a charge current of 1 mA and a charge end voltage of 4.3 V, and discharged at a discharge current of 1 mA and a discharge end voltage of 2.8 V. As a result, the initial discharge capacity of the battery was 4.8 mAh, and the ratio of the irreversible capacity was 12%. On the other hand, the discharge capacity retention ratio at the 100th cycle relative to the first cycle was 96%.

[0155]

Example 12 Germanium particles having an average particle size of 20 μm and graphite particles having an average particle size of 10 μm were blended in a weight ratio of 70:30, and subjected to a ball mill treatment for 6 hours. The ball mill container and the balls were made of stainless steel, and the powder preparation and the ball mill treatment were performed in an argon atmosphere. Further, a heat treatment was performed at 900 ° C. for 5 hours in argon. As a result of analyzing the obtained germanium-carbon composite powder by a wide-angle X-ray diffraction method, peaks indicating diffraction from carbon and germanium were observed. The distance between the d (002) planes of carbon was 0.3355 nm. Lc is 55 nm
Met. No diffraction peak of germanium carbide was observed. The R value was 0.2. As a result of observing the cross section of the composite powder, germanium particles were embedded in the carbonaceous material, and the average particle size of germanium was 2.3 μm. The specific surface area of the germanium-carbon composite powder was 49 m ² / g.

A battery using the above-mentioned germanium-carbon composite powder as a negative electrode active material was produced in the same manner as in Example 8.
However, the cathode material is LiNiO ₂ having an average particle size of 15 μm.
Was used. Further, EPDM was used as a binder, xylene was added to make a slurry, and the slurry was dried by vacuum degassing at room temperature. The electrolytic solution is 1: 1 in a mixed solvent of 1: 2 EC and EMC.
An electrolytic solution in which mol / liter of lithium borofluoride LiBF ₄ was dissolved was used.

The charging current of the lithium secondary battery was 0.5 m.
A, Charged at a charge end voltage of 4.2 V, discharge current 0.5 m
A, A charge / discharge cycle test for discharging at a discharge end voltage of 2.7 V was performed. As a result, the initial discharge capacity of the battery was 1
0.5 mAh, and the ratio of the irreversible capacity was 22%. On the other hand, the discharge capacity retention ratio at the 100th cycle relative to the first cycle was 86%.

[0158]

Example 13 Germanium particles having an average particle diameter of 10 μm and graphite particles having an average particle diameter of 10 μm were blended at a weight ratio of 80:20, and subjected to a ball mill treatment for 72 hours. The ball mill container and the balls were made of stainless steel, and the powder preparation and the ball mill were performed in an argon atmosphere. Further, heat treatment was performed at 1000 ° C. for 1 hour in argon. The germanium-carbon composite powder: coal pitch: tetrahydrofuran was mixed at a weight ratio of 100: 50: 500, and the mixture was stirred and refluxed for 1 hour. This was removed of tetrahydrofuran using a rotary evaporator and vacuum-dried at 150 ° C. for 3 hours to obtain a germanium-carbon composite powder / pitch composite material. The composite material is crushed with a cutter mill to 200 mesh or less and then in air at a rate of 3 ° C./min at 250 ° C.
And kept for 1 hour. This is placed under nitrogen flow for 20 minutes.
The temperature was raised to 1200 ° C. at a rate of ° C./h and maintained for 1 hour to carbonize the coal pitch. This was crushed by a cutter mill to 200 mesh or less to obtain a germanium-carbon composite powder.
As a result of analyzing the obtained germanium-carbon composite powder by a wide-angle X-ray diffraction method, peaks indicating diffraction from carbon and germanium were observed. D (002) of carbon is 0.
Two peaks at 3356 nm and 0.3368 nm were observed. No diffraction peak of germanium carbide was observed. The average particle diameter of germanium determined from cross-sectional observation was 0.8 μm.

The R value was 1.0. The specific surface area of the germanium-carbon composite powder was 14 m ² / g.

A battery using the above-mentioned germanium-carbon composite powder as a negative electrode active material was produced in the same manner as in Example 1.
However, as the electrolytic solution, an electrolytic solution in which 1.5 mol / L of LiPF ₆ was dissolved in a mixed solvent of PC: DMC in a ratio of 2: 3 was used.

This battery was charged at a charge current of 2 mA and a charge end voltage of 4.2 V, and a discharge current of 2 mA and a discharge end voltage of 2.7.
A charge / discharge cycle test for discharging at V was performed. As a result, the initial discharge capacity of the battery was 6.0 mAh, and the ratio of the irreversible capacity was 15%. On the other hand, the discharge capacity retention ratio at the 100th cycle relative to the first cycle was 93%.

[0162]

Example 14 Silicon particles having an average particle size of 10 μm and graphite particles having an average particle size of 20 μm were blended at a weight ratio of 20:80.
The ball mill treatment was performed for 48 hours. The ball mill container and the balls were made of stainless steel, and the powder preparation and the ball mill treatment were performed in an argon atmosphere. The silicon-carbon composite powder: petroleum pitch: tetrahydrofuran 100: 7
The mixture was mixed at a weight ratio of 0: 700, and stirred and refluxed for 1 hour.
This was removed with a rotary evaporator to remove tetrahydrofuran and vacuum dried at 150 ° C. for 3 hours to obtain a silicon-carbon composite powder / pitch composite material. The composite material was pulverized with a cutter mill to 200 mesh or less, then heated to 350 ° C. in air at a rate of 3 ° C./min, and held for 1 hour. This is 1100 ° C at 20 ° C / h under nitrogen flow.
And kept for 1 hour to carbonize the petroleum pitch.
This was crushed by a cutter mill to 200 mesh or less to obtain a silicon-carbon composite powder. The obtained silicon-carbon composite powder was analyzed by a wide-angle X-ray diffraction method.
Peaks indicating diffraction from silicon and silicon carbide were observed. The distance between the d (002) planes of carbon is 0.33.
It was 61 nm and 0.3378 nm, but the distance between the d (002) planes determined from the peak showing the maximum intensity was 0.3.
361 nm. The diffraction peak intensity of silicon carbide at a position where 2θ was about 35 ° was 0.1 with respect to the background. The average particle size of silicon determined from cross-sectional observation was 2.2 μm. The R value was 1.3. The specific surface area of the silicon-carbon composite powder is 20 m
² / g.

A battery using the above silicon-carbon composite powder as a negative electrode active material was produced in the same manner as in Example 1. However, the electrolytic solution was 1.5: 1 in a mixed solvent of EC: DMC of 1: 2.
An electrolytic solution in which mol / liter of lithium hexafluorophosphate LiPF ₆ was dissolved was used.

A charge / discharge cycle test was conducted in which the lithium secondary battery was charged at a charge current of 2 mA and a charge end voltage of 4.2 V, and discharged at a discharge current of 2 mA and a discharge end voltage of 2.7 V. As a result, the initial discharge capacity of the battery was 4.1 mAh, and the ratio of the irreversible capacity was 9%. On the other hand, the discharge capacity maintenance ratio at the 100th cycle with respect to the first cycle is 9
5%.

[0165]

Example 15 Silicon particles having an average particle diameter of 1 μm: petroleum pitch: tetrahydrofuran were mixed at a weight ratio of 100: 70: 700, and the mixture was stirred and refluxed for 1 hour. Using a rotary evaporator to remove tetrahydrofuran,
Vacuum drying was performed at 150 ° C. for 3 hours to obtain a Si / pitch composite material. The composite material is crushed with a cutter mill to 200 mesh or less and then in air at a rate of 3 ° C./min at 250 ° C.
And kept for 1 hour. This is placed under nitrogen flow for 20 minutes.
The temperature was raised to 1100 ° C. at a rate of ° C./h, and maintained for 1 hour to carbonize the pitch. This was crushed by a cutter mill to 200 mesh or less to obtain a silicon-carbon composite powder. As a result of analyzing the obtained silicon-carbon composite powder by a wide-angle X-ray diffraction method, peaks indicating diffraction from carbon, silicon and silicon carbide were observed. At this time, the diffraction peak intensity of the silicon carbide was slight. The carbon d (00
2) was 0.3369 nm. Lc is 15n
m. The diffraction peak intensity of silicon carbide at a position where 2θ was about 35 ° was 0.3 with respect to the background. The R value was 1.4. Also, silicon
The specific surface area of the carbon composite powder was 7 m ² / g.

A battery using the silicon-carbon composite powder as a negative electrode active material was manufactured in the same manner as in Example 1. However, the electrolyte was 1.0 in a 1: 2 mixed solvent of EC: DMC.
An electrolytic solution in which mol / liter of lithium hexafluorophosphate LiPF ₆ was dissolved was used.

A charge / discharge cycle test was performed in which the lithium secondary battery was charged at a charge current of 1 mA and a charge end voltage of 4.2 V, and discharged at a discharge current of 1 mA and a discharge end voltage of 2.7 V. As a result, the initial discharge capacity of the battery was 15.3 mAh.
And the ratio of the irreversible capacity was 23%. Meanwhile, 1
The discharge capacity retention at the 100th cycle relative to the cycle was 81%.

Comparative Example 4 Silicon particles having an average particle size of 3 μm and graphite particles having an average particle size of 20 μm were blended at a weight ratio of 30:70, and subjected to ball milling for 72 hours. The ball mill container and the balls were made of stainless steel, and the powder preparation and the ball mill were performed in an argon atmosphere. The silicon-carbon composite powder: coal pitch: 10 of tetrahydrofuran
The mixture was mixed at a weight ratio of 0: 50: 500, and stirred and refluxed for 1 hour. This was removed with a rotary evaporator to remove tetrahydrofuran and vacuum dried at 150 ° C. for 3 hours to obtain a silicon-carbon composite powder / pitch composite material. The composite material is crushed by a cutter mill to 200 mesh or less, and then heated to 250 ° C. in air at a rate of 3 ° C./min.
Hold for 1 hour. This is cooled to 20 ° C./h for 18
The temperature was raised to 00 ° C. and maintained for 1 hour to carbonize the pitch. This was crushed by a cutter mill to 200 mesh or less to obtain a silicon-carbon composite powder. As a result of analyzing the obtained silicon-carbon composite powder by a wide-angle X-ray diffraction method,
Peaks indicating diffraction from carbon, silicon and silicon carbide were observed. At this time, the diffraction peak intensity of the silicon carbide was slight. The distance between the d (002) planes of carbon was 0.3359 nm. The diffraction peak of silicon carbide at a position where 2θ was about 35 ° showed 6.0 times the intensity of the background. The R value was 0.6. The specific surface area of the silicon-carbon composite powder is 36 m
² / g.

A battery using the above silicon-carbon composite powder as a negative electrode active material was produced in the same manner as in Example 8. However, the electrolyte was 1.0 in a 1: 2 mixed solvent of EC: DMC.
An electrolytic solution in which mol / liter of lithium hexafluorophosphate LiPF ₆ was dissolved was used.

A charge / discharge cycle test was conducted in which the lithium secondary battery was charged at a charge current of 1 mA and a charge end voltage of 4.2 V, and discharged at a discharge current of 1 mA and a discharge end voltage of 2.7 V. As a result, the initial discharge capacity of the battery was 1.6 mAh, and the ratio of the irreversible capacity was 38%. On the other hand, the discharge capacity retention ratio at the 100th cycle relative to the first cycle was 98%.

Comparative Example 5 Silicon particles having an average particle diameter of 1 μm, petroleum pitch, and tetrahydrofuran were mixed in a ratio of 100: 5.
The mixture was mixed at a weight ratio of 0: 500, and stirred and refluxed for 1 hour.
This was removed of tetrahydrofuran using a rotary evaporator and vacuum dried at 150 ° C. for 3 hours to obtain a Si / pitch composite material. The composite material is cut with a cutter mill for 20 minutes.
It was crushed to 0 mesh or less, then heated to 250 ° C. in air at a rate of 3 ° C./min, and kept for 1 hour. This was heated to 700 ° C. at a rate of 20 ° C./h under a nitrogen flow, and held for 1 hour to carbonize the pitch. Use a cutter mill for 20
This was crushed to 0 mesh or less to obtain a silicon-carbon composite powder. As a result of analyzing the obtained silicon-carbon composite powder by a wide-angle X-ray diffraction method, peaks indicating diffraction from carbon, silicon and silicon carbide were observed. At this time,
The diffraction peak intensity of silicon carbide was slight. The distance between the d (002) planes of carbon was 0.359 nm.
The diffraction peak intensity of silicon carbide at a position where 2θ was about 35 ° was 0.1 with respect to the background. Also,
The R value was 1.7. The specific surface area of the silicon-carbon composite powder was 7 m ² / g.

A battery using the above silicon-carbon composite powder as a negative electrode active material was produced in the same manner as in Example 8. However, the electrolyte was 1.0 in a 1: 2 mixed solvent of EC: DMC.
An electrolytic solution in which mol / L of LiPF ₆ was dissolved was used.

A charge / discharge cycle test was conducted in which the lithium secondary battery was charged at a charge current of 1 mA and a charge end voltage of 4.2 V, and discharged at a discharge current of 1 mA and a discharge end voltage of 2.7 V. As a result, the initial discharge capacity of the battery was 16.2 mAh.
And the ratio of the irreversible capacity was 25%. Meanwhile, 1
The discharge capacity maintenance ratio at the 100th cycle relative to the cycle was 2%.

[0174]

According to the present invention, particles containing at least one element capable of forming a compound with lithium are embedded in a carbonaceous substance having a plurality of phases, and d ( 002) The spacing between the planes is 0.3350 nm to 0.3.
By using a negative electrode active material containing a carbonaceous material of 370 nm, a lithium secondary battery that satisfies both excellent cycle characteristics that cannot be obtained with the particles alone and a high capacity that cannot be obtained with a carbonaceous material can be provided. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a coin-type battery of the present invention.

FIG. 2 is a schematic sectional view of a lithium secondary battery of the present invention.

FIG. 3 is an assembly diagram of a positive electrode, a negative electrode, and a separator of the lithium secondary battery of the present invention.

FIG. 4A is a top view of the prismatic lithium secondary battery of the present invention.

FIG. 4B is a schematic sectional view of the prismatic lithium secondary battery of the present invention.

FIG. 5 is a perspective view of the prismatic lithium secondary battery pack battery of the present invention.

FIG. 6 is a schematic sectional view of a cylindrical lithium secondary battery of the present invention.

FIG. 7A is a top view of the cylindrical lithium secondary battery pack battery of the present invention.

FIG. 7B is a cross-sectional view of the cylindrical lithium secondary battery assembly battery of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Positive electrode can, 2a, 11, 61a ... Positive electrode current collector, 2b,
12, 61b ... positive electrode mixture, 2, 13, 31, 61 ... positive electrode, 3 ... negative electrode can, 4a, 14, 62a ... negative electrode current collector, 4
b, 15, 62b ... negative electrode mixture, 4, 16, 32, 62 ...
Negative electrode, 5, 17, 33, 63 ... separator, 6, 22 ...
Gasket, 18 ... Positive electrode tab, 19 ... Negative electrode tab, 20,
34, 64: battery can, 21, 41, 71: battery lid, 23
... Insulating plate, 35,65 ... Positive electrode lead, 37,67 ... Negative electrode lead, 38,54,68,84 ... Positive electrode terminal, 39,5
5, 69, 85 ... negative electrode terminal, 40, 70 ... packing, 4
2 ... gas outlet, 43, 46 ... O-ring, 44, 47 ...
Sealing bolt, 45 injection port, 50 nut, 51 square lithium secondary battery, 52 spacer, 53 metal plate,
56, 87: control circuit board, 57, 89: thermocouple, 5
8, 82 fixed parts, 59 bolts, 60 projecting parts, 8
0: safety valve, 81: battery, 83: current cable, 86:
Voltage input cable, 88 ... case.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Noriyuki Watanabe 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Yasuhisa Aono 7-chome, Omikamachi, Hitachi City, Ibaraki Prefecture No. 1-1 Inside Hitachi, Ltd.Hitachi Research Laboratories (72) Inventor Toroshi Takeuchi 1-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd.Hitachi Research Laboratories (72) Inventor Ren Murakana Ibaraki Prefecture 7-1-1, Omika-cho, Hitachi City Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Koichi Takei 4-1-1, Higashi-cho, Hitachi City, Ibaraki Prefecture F-term in Yamazaki Plant, Hitachi Chemical Co., Ltd. ) 5H003 AA04 BA01 BA03 BA04 BB04 BB15 BD01 BD04 5H014 AA02 BB00 BB01 BB06 EE10 HH01 HH08 5H029 AK03 AL01 AM03 AM04 AM05 AM07 BJ02 BJ03 BJ12 BJ14 CJ01 CJ02 CJ08 HJ 01

Claims (23)

[Claims] 1. A lithium secondary battery having a positive electrode, a negative electrode containing a negative electrode active material capable of inserting and extracting lithium ions, and a lithium secondary battery having a non-aqueous electrolyte or a polymer electrolyte, wherein the negative electrode active material forms a compound with lithium. It is possible to
And has a melting point of 900 ° C. or higher and a coefficient of thermal expansion at room temperature of 9 ppm /
Particles containing at least one element of K or less, the particles being embedded in a plurality of layers of carbonaceous material, and being mechanically treated so that the particles are smaller than the initial particle size. A rechargeable lithium battery. 2. The lithium secondary battery according to claim 1, wherein the element capable of forming a compound with lithium is at least one element selected from silicon and germanium. 3. The carbonaceous material (A) and the carbonaceous material (B) in a plurality of layers, wherein the carbonaceous material (A) is included in the carbonaceous material (B). Lithium secondary battery. 4. The lithium secondary battery according to claim 3, wherein the carbonaceous substance (A) is crystalline carbon, and the carbonaceous substance (B) is amorphous carbon. 5. The lithium secondary battery according to claim 3, wherein the carbonaceous substance (B) is harder than the carbonaceous substance (A). 6. The lithium secondary battery according to claim 1, comprising an element capable of forming a compound with lithium in an amount of less than 30% by weight based on the total amount of the negative electrode active material. 7. A method of using the lithium secondary battery of claim 1 as an assembled battery in an electric vehicle. 8. A method for producing a lithium secondary battery, comprising:
A carbonaceous material (A) is formed by mixing at least one element capable of forming a compound with lithium as a negative electrode active material and having a melting point of 900 ° C. or higher and a coefficient of thermal expansion at room temperature of 9 ppm / K or lower and 9 ppm / K or lower. Mechanically treating, (b) mixing the particles obtained by the above treatment with the carbonaceous substance (B), and (c) carbonizing the particles obtained by the above treatment to produce a negative electrode. A step of forming an active material; and (d) a method of manufacturing a lithium secondary battery, comprising: disposing a positive electrode, a negative electrode containing the negative electrode active material, and a non-aqueous electrolyte or a polymer electrolyte in a container. 9. The method according to claim 8, wherein the element capable of forming a compound with lithium is at least one element selected from silicon and germanium. 10. The method according to claim 8, wherein a heat treatment is performed after the step (a). 11. The method according to claim 8, wherein the step (a) is pulverization using a ball mill. 12. The method according to claim 8, wherein the step (a) is a mechanical pressure welding. 13. A particle containing at least one element capable of forming a compound with lithium and having a melting point of 900 ° C. or more and a coefficient of thermal expansion at room temperature of 9 ppm / K or less, A negative electrode active material for a lithium secondary battery, wherein particles are embedded in a plurality of layers of a carbonaceous material, and are mechanically treated so that the particles have a size smaller than an initial particle size. 14. The negative electrode active material for a lithium secondary battery according to claim 13, wherein the element capable of forming a compound with lithium is at least one element selected from silicon and germanium. 15. The carbonaceous substance (A) comprising a plurality of layers of carbonaceous substance.
14. The negative electrode active material for a lithium secondary battery according to claim 13, wherein the negative electrode active material comprises a carbonaceous material (A) and carbonaceous material (B). 16. The carbonaceous substance (A) is crystalline carbon,
The negative electrode active material for a lithium secondary battery according to claim 15, wherein the carbonaceous material (B) is amorphous carbon. 17. The negative electrode active material for a lithium secondary battery according to claim 15, wherein the carbonaceous substance (B) is harder than the carbonaceous substance (A). 18. The negative electrode active material for a lithium secondary battery according to claim 13, comprising an element capable of forming a compound with lithium in an amount of less than 30% by weight based on the total amount of the negative electrode active material. (A) at least one element capable of forming a compound with lithium and having a melting point of 900 ° C. or more and a coefficient of thermal expansion at room temperature of 9 ppm / K or less and a carbonaceous substance ( A) a step of mechanically treating the above, (b) a step of mixing the particles obtained by the above treatment with a carbonaceous substance (B), and (c) a carbonization of the particles obtained by the above treatment. A method for producing a negative electrode active material for a lithium secondary battery, comprising a step of forming a negative electrode active material by treating. 20. The method according to claim 19, wherein the element capable of forming a compound with lithium is at least one element selected from silicon and germanium. 21. The method according to claim 19, wherein a heat treatment is performed after the step (a). 22. The method according to claim 19, wherein the step (a) is pulverization using a ball mill. 23. The method according to claim 19, wherein the step (a) is a mechanical pressure welding.