JPH04280068A - Lithium secondary battery - Google Patents

Abstract

PURPOSE:To obtain a lithium battery which has high capacity and excellent cycle life. CONSTITUTION:A lithium secondary battery contains a positive electrode 4 which is made of chalcogen compound, a negative electrode 6, in graphite disordered layers, which is made of carbonaceous material possible to store and release ball lithium ions with fine organization point-oriented, and lithium ion conductive electrolyte.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery with an improved negative electrode.

0002

[Prior Art] In recent years, non-aqueous electrolyte batteries using lithium as a negative electrode active material have attracted attention as high energy density batteries, and manganese dioxide (MnO2) is used as a positive electrode active material.
, fluorocarbon [(CFn)], thionyl chloride (SOC
Primary batteries using batteries such as 12) are already widely used as power sources for calculators and watches, and as backup batteries for memory. Furthermore, in recent years, various electronic devices such as VTRs and communication devices have become smaller and smaller.
With weight reduction, the demand for high energy density secondary batteries as a power source for these devices has increased, and research on lithium secondary batteries using lithium as the negative electrode active material is being actively conducted.

Lithium secondary batteries use lithium for the negative electrode, and propylene carbonate (PC), 1,2-dimethoxyethane (DME), and γ- as the lithium ion conductive electrolyte.
Butyrolactone (γ-BL), tetrahydrofuran (T
LiClO4, LiBF4 in a non-aqueous solvent such as HF)
It is composed of a nonaqueous electrolyte in which lithium salts such as , LiAsF6, and LiPF6 are dissolved, and a lithium ion conductive solid electrolyte, and the positive electrode active materials are mainly TiS2 and Mo.
Compounds that undergo topochemical reactions with lithium, such as S2, V2 O5, and V6 O13, have been studied.

However, the above-mentioned secondary batteries are currently
It has not been put into practical use yet. The main reason for this is that the charging/discharging efficiency is low and the number of charging/discharging cycles (cycles) life is short. This is thought to be largely due to deterioration of lithium due to the reaction between the negative electrode lithium and the non-aqueous electrolyte. That is, lithium dissolved in the nonaqueous electrolyte as lithium ions during discharging reacts with the solvent when precipitated during charging, and its surface is partially inactivated. For this reason,
When charging and discharging are repeated, phenomena such as dendrite-like (dendritic) lithium, precipitation in small spheres, and lithium detachment from the current collector occur.

For this reason, it is possible to absorb lithium by using a carbonaceous material that occludes and releases lithium, such as coke, sintered resin, carbon fiber, and pyrolyzed gas-phase carbon material, as a negative electrode incorporated into a lithium secondary battery. It has been proposed to improve the negative electrode deterioration caused by the reaction between the metal and the non-aqueous electrolyte and dendrite precipitation. However, since such negative electrodes have a small amount of intercalation and desorption of lithium ions, the specific capacity of the negative electrode is small, and when the amount of intercalation of lithium ions is increased (increasing the charging capacity), for example, the structure of the carbonaceous material may deteriorate or Decomposes the solvent in the water electrolyte. Furthermore, when the charging current density is increased, there is a problem that the amount of lithium ions absorbed decreases and lithium metal precipitates. the result,
A lithium secondary battery incorporating the negative electrode has a problem in that it is difficult to improve the cycle life.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and aims to provide a lithium secondary battery with high capacity and excellent cycle life. [Structure of the invention]

[0007]

[Means for Solving the Problems] A lithium secondary battery according to the present invention includes a container, a positive electrode housed in the container,
In a lithium secondary battery that is housed in the container and includes a negative electrode made of a carbonaceous material capable of occluding and releasing lithium ions, and a lithium ion conductive electrolyte, the carbonaceous material has a graphite structure and a turbostratic structure. and is characterized by being spherical particles with a point-oriented microstructure.

The positive electrode is made of various oxides such as manganese dioxide, lithium manganese composite oxide, lithium-containing nickel oxide, lithium-containing cobalt oxide, lithium-containing nickel-cobalt oxide, and amorphous vanadium pentoxide containing lithium. and chalcogen compounds such as titanium disulfide and molybdenum disulfide.

As indicators for defining the graphite structure of the carbonaceous material, the interplanar spacing (d002) of the (002) plane obtained by X-ray diffraction and the crystallite size in the C-axis direction (Lc
). The graphite structure of the carbonaceous material suitable as the negative electrode material has an average value of the interplanar spacing (d002) of 0.337 to
It is desirable that the average value of the crystallite size (Lc) is 0.380 nm and 1 to 25 nm. d like this
If the values of 002 and Lc deviate from the above ranges, this will lead to a decrease in the amount of lithium ions absorbed and released in the negative electrode made of the carbonaceous material, deterioration of the graphite structure, gas generation due to reductive decomposition of the solvent in the non-aqueous electrolyte, etc. This may cause a decrease in the capacity and cycle life of the secondary battery. More preferable d
002 and Lc are respectively 0.34 to 0.355 nm,
It is in the range of 1 to 10 nm.

As a measure of the ratio of the graphite structure and the turbostratic structure constituting the carbonaceous material, argon laser (wavelength: 51
There is a Raman spectrum of a carbonaceous material measured using 45 nm) as a light source. The measured Raman spectrum is 13
There is a peak originating from the turbostratic structure that appears near 60 cm-1 and a peak originating from the graphite structure appearing near 1580 cm-1, and their peak intensity ratio (for example, the Raman intensity originating from the turbostratic structure is R1, It is effective to use the intensity ratio R1 /R2 ) or the area ratio, where R2 is the Raman intensity derived from the structure. The ratio of graphite structure to turbostratic structure in the carbonaceous material suitable as the negative electrode material is desirably set so that R1/R2 is in the range of 0.5 to 1.5. When the intensity ratio is less than 0.5, decomposition of the solvent in the non-aqueous electrolyte tends to occur, while when the intensity ratio exceeds 1.5, the amount of lithium ions absorbed and released by the negative electrode made of carbonaceous material is reduced. In either case, the charging/discharging efficiency may be reduced. A more preferable intensity ratio (R1/R2) is in the range of 0.7 to 1.3.

The ratio of residual hydrogen due to non-graphitization in the carbonaceous material is defined by the hydrogen/carbon atomic ratio (H/C). The carbonaceous material suitable as the negative electrode material has the H/C of 0.
．． It is desirable that it is 15 or less. Such H/C is 0.
If it exceeds 15, not only will it be difficult to increase the amount of lithium ions inserted into and released from the negative electrode, but there is also a risk that the charging and discharging efficiency will decrease. A more preferable H/C is 0.04 or less.

The point orientation form of the microstructure (aggregation form of crystallites) in the carbonaceous material may be a radial type shown in A in FIG. It can be modeled as a Brooks-Taylor type, which is a combination of layer type and radial type. Regarding the definition of the Brooks-Taylor type, see “Chemical & Physiology”.
cs Carbon” Vol4, 1968, p243
and “Carbon” Vol. 3, 1965, p.
Each of them is described in 185 documents. Also, it is known that the orientation is concentric spheres.

The average particle size of the spherical carbonaceous material particles is desirably in the range of 1 to 100 μm, more preferably 2 to 40 μm. If the average particle size of the carbonaceous material particles is less than 1 μm, the carbonaceous material particles will easily pass through the pores of the separator, which may cause a short circuit between the positive electrode and the negative electrode.
On the other hand, if the average particle size exceeds 100 μm, the specific surface area of the carbonaceous material particles becomes small, which may make it difficult to increase the amount of lithium ions absorbed and released.

[0014] It is desirable that the short axis/long axis of the spherical carbonaceous material particles be 1/10 or more. More preferably, it is desirable to have a shape close to a perfect sphere, with the diameter being 1/2 or more. When such carbonaceous material particles having a nearly perfect spherical shape are used, a uniform lithium ion intercalation/desorption reaction occurs, which improves the structural and mechanical stability of the carbonaceous material, and also increases the packing density. It is possible to improve cycle life and increase capacity.

[0015] The carbonaceous material particles having the above-mentioned characteristics are produced by using, for example, mesophase spherules, petroleum pitch, coal tar, heavy oil, organic resin, or synthetic polymer materials as raw materials in an inert gas under normal pressure or pressurized conditions. Carbonization (e.g. 800-1
500°C) or graphitization (for example, at 1500°C or higher). In particular, the crystalline phase with optical anisotropy obtained by heat-treating petroleum pitch, coal tar, or heavy oil at temperatures above 350°C produces small spheres (mesophase spherules) in the initial stage of formation, and then separates. Similarly, by carbonizing or graphitizing, it is possible to produce carbonaceous material particles having a nearly perfect spherical shape. .

Examples of the lithium ion conductive electrolyte include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, sulfolane, acetonitrile, 1,2-dimethoxyethane,
Lithium perchlorate (LiClO4), lithium hexafluorophosphate (
LiPF6), lithium borofluoride (LiBF4)
, lithium arsenic hexafluoride (LiAsF6), lithium trifluoromethanesulfonate (LiCF3 SO3
) and other non-aqueous electrolytes in which lithium salts (electrolytes) are dissolved. The amount of the electrolyte dissolved in the nonaqueous solvent is preferably 0.5 to 1.5 mol/l. Moreover, a lithium ion conductive solid electrolyte can be used. For example, a solid polymer electrolyte in which a lithium salt is combined with a polymer compound can be mentioned.

Another lithium secondary battery according to the present invention includes a container, a positive electrode housed in the container, and a carbonaceous material that is housed in the container and is capable of occluding and releasing lithium ions. In a lithium secondary battery comprising a negative electrode consisting of and a lithium ion conductive electrolyte,

0
[018] The carbonaceous material has a graphite structure and a turbostratic structure,
The carbon fiber is characterized in that the microstructure has a lamellar or Brooks-Taylor axial orientation. The graphite structure, the ratio of graphite structure to turbostratic structure, and the hydrogen/carbon atomic ratio in the carbonaceous material are the same as described above.

[0019] The average short axis of the carbon fibers is 1 to 100μ.
m, more preferably in the range of 2 to 40 μm. When the average short diameter of the carbonaceous material fibers is less than 1 μm, the carbonaceous material particles easily pass through the pores of the separator,
There is a risk of short-circuiting between the positive electrode and the negative electrode, and on the other hand, if the average short axis exceeds 100 μm, the specific surface area of the carbonaceous material particles becomes small, and it may become difficult to increase the amount of occlusion and release of lithium ions. It is also effective to bring the average particle size within the above range by means such as pulverizing the carbon fibers.

Furthermore, another lithium secondary battery according to the present invention includes a container, a positive electrode housed in the container, and a carbonaceous material that is housed in the vessel and is capable of occluding and releasing lithium ions. In a lithium secondary battery comprising a negative electrode consisting of a lithium ion conductive electrolyte and a lithium ion conductive electrolyte, the carbonaceous material is a spherical particle with a point-oriented microstructure and has been previously heat-treated in the presence of oxygen. It is characterized by this.

[0021] The heat treatment temperature is preferably in the range of 300 to 800°C, more preferably 400 to 600°C. The reason for this is that when the heat treatment temperature is lower than 300°C, it becomes difficult to effectively oxidize and remove the surface layer of the spherical carbonaceous material particles with a relatively high degree of graphitization. This is because if the temperature exceeds the limit, the spherical carbonaceous material particles may be burned out. The heat treatment is
When the atmosphere is air, it is desirable to carry out the heat treatment for 1 to 10 hours; however, the heat treatment time can be shortened by increasing the oxygen partial pressure of the atmosphere.

[0022] The ratio of the graphite structure to the turbostratic structure in the surface layer of the carbonaceous material after the heat treatment (oxidation treatment) is 0.8 to 1.4 in terms of the intensity ratio (R1/R2) of the Raman spectrum.
It is desirable to set it within the range of .

[0023]

[Operation] According to the lithium secondary battery according to the present invention, the negative electrode is made of a carbonaceous material having a graphite structure and a turbostratic structure, and having a spherical microstructure with point orientation such as a radial type, lamellar type, or Brooks-Taylor type. By forming from particles,
It is possible to increase the amount of intercalation and desorption of lithium ions, suppress deterioration of the structural form during charging and discharging cycles, and further increase the bulk density in terms of shape and increase the specific capacity (mAh/cc) of the negative electrode. In particular, by making the point orientation radial, lamellar, or Brooks-Taylor, the amount of lithium ions absorbed and released can be effectively increased. Therefore, by housing such a negative electrode in a container together with a positive electrode and a non-aqueous electrolyte, a lithium secondary battery with high capacity and long charge/discharge cycle life can be obtained.

In the lithium secondary battery according to the present invention, in addition to the above-mentioned characteristics, the graphite structure has the interplanar spacing (d002) of the (002) plane obtained by X-ray diffraction and the crystallite size in the C-axis direction (Lc). are respectively 0.337 to 0.
380 nm, in the range 1 to 25 nm, the measure of the ratio of graphitic structure to turbostratic structure is the Raman intensity R1 of 1360 cm and 1580 cm measured with an argon laser as the light source.
-1 and the Raman intensity R2 ratio (R1/R2) is 0.
If the negative electrode is formed from carbonaceous material particles having a carbonaceous material particle size in the range of 5 to 1.5, it is possible to further increase the amount of intercalation and release of lithium ions, suppress the deterioration of the structural form during charge and discharge cycles, and furthermore Decomposition of the solvent in the electrolyte can be prevented. Furthermore, the average particle diameter of the spherical carbonaceous material particles is 1 to 100 μm.
By doing so, the amount of lithium ions absorbed and released in the negative electrode can be increased. Therefore, such a negative electrode is used as a positive electrode,
By storing it in a container together with a non-aqueous electrolyte, a lithium secondary battery with even higher capacity and significantly improved charge/discharge cycle life can be obtained.

Further, according to another lithium secondary battery according to the present invention, the negative electrode is formed from carbon fibers having a graphite structure and a turbostratic structure, and having a lamellar or Brooks-Taylor axial microstructure orientation. By doing so, the amount of lithium ions absorbed and released can be increased, and deterioration of the structural form during charging and discharging cycles can be suppressed. Therefore, by housing such a negative electrode in a container together with a positive electrode and a non-aqueous electrolyte, a lithium secondary battery with high capacity and long charge/discharge cycle life can be obtained. Moreover, in addition to the above characteristics, the graphite structure has a lattice spacing (d002) of the (002) plane.
) and the crystallite size in the C-axis direction (Lc) are in the range of 0.337 to 0.380 nm and 1 to 25 nm, respectively,
The scale of the ratio of graphite structure to turbostratic structure is the above (R1 /R2
) If the negative electrode is formed from carbonaceous material particles with a carbonaceous material particle having a carbonaceous material particle size in the range of 0.5 to 1.5, the amount of intercalation and desorption of lithium ions can be further increased as described above, and the structure during charge and discharge cycles can be increased. Deterioration of the morphology can be suppressed, and furthermore, decomposition of the solvent in the non-aqueous electrolyte can be prevented.

Furthermore, according to another lithium secondary battery according to the present invention, the carbonaceous material constituting the negative electrode is made of spherical particles with point-oriented microstructures, which have been previously heat-treated in the presence of oxygen. By doing so, the amount of lithium ions absorbed and released can be increased, and a high capacity can be achieved.

That is, the degree of graphitization of the spherical carbonaceous material particles increases toward the surface, and for example, the peak intensity ratio (R1 /R2) of the Raman spectrum, which is a measure of the ratio of the graphite structure to the turbostratic structure, It has the characteristic of being smaller than the inner side. Since the spherical carbonaceous material particles constituting the negative electrode according to the present invention can be used without being crushed, the graphite structure and turbostratic structure on the particle surface greatly affect the amount and efficiency of lithium ion intercalation and desorption. For this reason, by performing heat treatment in the presence of oxygen in advance, it is possible to oxidize and remove the surface layer of carbonaceous material particles, which have a relatively high degree of graphitization, thereby creating an optimal graphite structure and turbostratic structure. The interior of the particle having the ratio can be exposed to the surface. Moreover, impurities, functional groups, etc. adsorbed on the surface of the spherical carbonaceous material particles can be removed by the heat treatment. Therefore, the amount of lithium ions absorbed and released can be effectively increased, and a high capacity lithium secondary battery can be obtained.

[0028]

[Example] Hereinafter, an example in which the present invention is applied to a cylindrical non-aqueous solvent secondary battery will be described in detail with reference to FIG. Example 1

Reference numeral 1 in the figure is a cylindrical stainless steel container with an insulator 2 disposed at the bottom. In this container 1, an electrode group 3 is housed. This electrode group 3 includes a positive electrode 4
, a separator 5 and a negative electrode 6 are laminated in this order, and the strip is spirally wound so that the negative electrode 6 is located on the outside.

The positive electrode 4 is made of lithium cobalt oxide (
It has a shape in which 80% by weight of LiCoO2) powder is mixed with 15% by weight of acetylene black and 5% by weight of polytetrafluoroethylene powder, formed into a sheet, and pressed onto an expanded metal current collector. The separator 5 is made of a polypropylene porous film.

The negative electrode 6 has a microstructure obtained by carbonizing mesophase spherules separated from the pitch by heat treatment, and is point-oriented in a lamellar (thin layer) manner, with an average particle size of 10 μm.
In this example, 98% by weight of spherical carbonaceous material particles of 100% by weight were mixed with 2% by weight of ethylene propylene copolymer, and the mixture was applied to a stainless steel foil as a current collector in an amount of 10mg/cm2. The carbonaceous material particles have various parameters determined by X-ray diffraction: d002=0.3508 nm, Lc
= 2.50nm, Raman intensity R1 of 1360cm-1 measured using an argon laser as a light source and 1580c
The ratio (R1 /R2) of Raman intensity R2 of m-1 is 1
．． It is 1. Further, the carbonaceous material particles have a hydrogen/carbon atomic ratio of 0.003.

In the container 1, 1.0 mol of lithium hexafluorophosphate (LiPF6) was added to a mixed solvent of ethylene carbonate, propylene carbonate, and 1,2-dimethoxyethane (mixed volume ratio 25:25:50). An electrolytic solution having a dissolved composition of /l is contained. An insulating paper 7 with an opening in the center is placed on the electrode group 3. Further, an insulating sealing plate 8 is provided at the upper opening of the container 1 in a fluid-tight manner by caulking the container 1, and a positive electrode terminal 9 is fitted in the center of the insulating sealing plate 8. has been done. This positive electrode terminal 9 is connected to the positive electrode 4 of the electrode group 3 via a positive electrode lead 10. Note that electrode group 3
The negative electrode 6 is connected to the container 1, which is a negative electrode terminal, via a negative electrode lead (not shown). Example 2

[0033] d002 = 0.3452 nm, Lc = 2.50 nm as various parameters by X-ray diffraction
A lithium secondary battery having the same configuration as in Example 1 was assembled, except that a negative electrode having spherical carbonaceous material particles with R1 /R2 of 1.0 was used. Example 3

[0034] d002 = 0.3410 nm, Lc = 5.00 nm as various parameters by X-ray diffraction
, a lithium secondary having the same configuration as in Example 1 except that a negative electrode having spherical carbonaceous material particles with an average particle size of 20 μm and having R1 /R2 of 0.75 and a hydrogen/carbon atomic ratio of 0.001 was used. Assembled the battery. Example 4

Various parameters determined by X-ray diffraction: d002 = 0.347 nm, Lc = 2.00 nm,
A lithium secondary battery having the same configuration as in Example 1 was assembled, except that a negative electrode having spherical carbonaceous material particles with R1 /R2 of 0.95 and an average particle size of 5 μm was used. Example 5

[0036] d002 = 0.3508 nm, Lc = 2.20 nm as various parameters by X-ray diffraction
, Example 1 except that a negative electrode having spherical carbonaceous material particles with R1/R2 of 1.1 and an average particle size of 60 μm was used.
A lithium secondary battery with the same configuration was assembled. Example 6

[0037] d002 = 0.3508 nm, Lc = 2.20 nm as various parameters by X-ray diffraction
, except that a negative electrode having R1/R2 of 1.1, a radial point orientation of the microstructure, a hydrogen/carbon atomic ratio of 0.001, and spherical carbonaceous material particles with an average particle size of 3 μm was used. A lithium secondary battery having the same configuration as Example 1 was assembled. Comparative example 1

[0038] 98% by weight of carbonaceous material particles having a non-oriented microstructure and an average particle size of 10 μm obtained by graphitizing phenolic resin powder were mixed with 2% by weight of ethylene propylene copolymer.
Mix this with stainless steel foil as a current collector.
A lithium secondary battery having the same structure as in Example 1 was assembled, except that a negative electrode having a structure coated in an amount of 0 mg/cm2 was used. In addition, various parameters determined by X-ray diffraction of the carbonaceous material are d002 = 0.3500 nm, Lc = 2.30n
m, and the above R1/R2 was 1.1.

[0039]The lithium secondary batteries of Examples 1 to 6 and Comparative Example 1 had a voltage of 4.2V at a charging current of 50mA.
The battery was repeatedly charged and discharged to 2.5 V at a current of 50 mA, and the discharge capacity and cycle life of each battery were measured. The results are shown in FIG.

As is clear from FIG. 3, the lithium secondary batteries of Examples 1 to 6 have increased capacity and significantly improved cycle life compared to the battery of Comparative Example 1. In particular, it can be seen that the capacity and cycle life of the batteries of Examples 1, 4, and 6 are significantly improved. Example 7

[0041] Spherical carbon with a Brooks-Taylor type point orientation in the fine structure obtained by carbonizing mesophase spherules separated by heat treatment from coal tar, with an average particle size of 10 μm and a short axis/long axis of 2/3 or more. Same structure as Example 1, except that a negative electrode having a structure in which 98% by weight of solid particles were mixed with 2% by weight of ethylene propylene copolymer and this was applied to stainless steel foil as a current collector in an amount of 10mg/cm2 was used. assembled a lithium secondary battery. In addition, various parameters determined by X-ray diffraction of the carbonaceous material are d002 = 0.
3500 nm, Lc = 2.20 nm, and the R1/
R2 was 1.1 and the hydrogen/carbon atomic ratio was 0.002. Example 8

[0042] d002 = 0.3452 nm, Lc = 2.50 nm as various parameters by X-ray diffraction
A lithium secondary battery having the same structure as in Example 1 was assembled, except that a negative electrode having spherical carbonaceous material particles with R1 /R2 of 1.0 and an average particle size of 20 μm was used. Example 9

[0043] d002 = 0.3410 nm, Lc = 5.00 nm as various parameters by X-ray diffraction
A lithium secondary battery having the same configuration as in Example 1 was assembled, except that a negative electrode having spherical carbonaceous material particles with R1 /R2 of 0.75 was used. Example 10

[0044] d002 = 0.3560 nm, Lc = 2.00 nm as various parameters by X-ray diffraction
A lithium secondary battery was assembled with the same configuration as in Example 1, except that a negative electrode having spherical carbonaceous material particles with R1 /R2 of 0.95, average particle size of 5 μm, and breadth/major axis of 3/4 or more was used. Ta. Example 11

[0045] d002 = 0.3452 nm, Lc = 2.50 nm as various parameters by X-ray diffraction
, Example 1 except that a negative electrode having spherical carbonaceous material particles with R1/R2 of 1.0 and an average particle size of 100 μm was used.
A lithium secondary battery with the same configuration was assembled.

The lithium secondary batteries of Examples 7 to 11 were repeatedly charged and discharged by charging to 4.2V with a charging current of 50mA and discharging to 2.5V with a current of 50mA, and the cycle life of each battery was determined. and discharge capacity were measured. The results are shown in FIG. Note that FIG. 4 also shows the measurement results of the cycle life and discharge capacity of the battery of Comparative Example 1.

As is clear from FIG. 4, Examples 7 to 11
It can be seen that the lithium secondary battery has an increased capacity and a significantly improved cycle life compared to the battery of Comparative Example 1. In particular, it can be seen that the capacity and cycle life of the batteries of Examples 7 and 10 are significantly improved. Example 12

[0048] Carbon fibers obtained by carbonizing mesophase pitch have a Brooks-Taylor microstructure orientation in cross section, and 98% by weight of carbonaceous fibers with an average minor axis of 10 μm are composed of 2% by weight of ethylene propylene copolymer. 10mg/c of this was mixed with stainless steel foil as a current collector.
A lithium secondary battery having the same structure as in Example 1 was assembled, except that a negative electrode having a structure coated in an amount of 2 m2 was used. In addition, various parameters determined by X-ray diffraction of the carbon fiber are d002
= 0.3480 nm, Lc = 3.00 nm, the above R1 /R2 is 0.88, and the hydrogen/carbon atomic ratio is 0.
．． It was 001. Example 13

[0049] d002 = 0.3490 nm, Lc = 2.80 nm as various parameters by X-ray diffraction
A lithium secondary battery having the same configuration as in Example 1 was assembled, except that a negative electrode having carbon fibers with R1 /R2 of 0.90 and an average minor axis of 5 μm was used. Example 14

[0050] d002 = 0.3500 nm, Lc = 2.80 nm as various parameters by X-ray diffraction
A lithium secondary battery having the same configuration as in Example 1 was assembled, except that a negative electrode having carbon fiber with R1 /R2 of 0.91 was used. Example 15

[0051] d002 = 0.3680 nm, Lc = 1.20 nm as various parameters by X-ray diffraction
A lithium secondary battery having the same configuration as in Example 1 was assembled, except that a negative electrode having carbon fibers with R1 /R2 of 1.1 and an average minor axis of 20 μm was used. Comparative example 2

[0052] d002 = 0.3500 nm, Lc = 2.50 nm as various parameters by X-ray diffraction
A lithium secondary battery having the same configuration as in Example 1 was assembled, except that a negative electrode having R1 /R2 of 0.95, a carbon fiber having a random microstructure and selectively non-oriented carbon fibers was used.

For the lithium secondary batteries of Examples 12 to 15 and Comparative Example 2, the charging current was 4.4 mA at a charging current of 50 mA.
The cycle life and discharge capacity of each battery were measured by repeatedly charging and discharging the battery to 2V and discharging to 2.5V at a current of 50 mA. The results are shown in FIG.

As is clear from FIG. 5, Examples 12 to 1
It can be seen that the lithium secondary battery of No. 5 has an increased capacity and a significantly improved cycle life compared to the battery of Comparative Example 2. In particular, it can be seen that the capacity and cycle life of the batteries of Examples 12, 13, and 14 are significantly improved. Example 16

[0055] The fine structure obtained by carbonizing the mesophase small spheres separated by heat treatment from pitch is point-oriented in a lamellar shape (thin layer), and the spherical carbonaceous material particles with an average particle size of 10 μm are heated at 500° C. in air. , heat treated for 5 hours98
% by weight was mixed with 2% by weight of ethylene propylene copolymer, and 10 mg of this was placed on stainless steel foil as a current collector.
A lithium secondary battery having the same structure as in Example 1 was assembled, except that a negative electrode having a structure coated in an amount of /cm2 was used. The carbonaceous material particles before the heat treatment have various parameters determined by X-ray diffraction: d002 = 0.3508 nm, Lc =
Raman intensity R1 of 1360 cm and 1580 cm measured at 2.50 nm using an argon laser as a light source
-1 Raman intensity R2 ratio (R1 /R2) is 1.
It is 1. Further, the carbonaceous material particles have a hydrogen/carbon atomic ratio of 0.003. Moreover, the above R1 / after heat treatment
R2 is 1.2. Example 17

Various parameters determined by X-ray diffraction: d002 = 0.348 nm, Lc = 2.40 nm,
The spherical carbonaceous material particles with R1 /R2 of 1.0 were subjected to the same heat treatment as in Example 16 to obtain R1 /R2 of 1.0.
A lithium secondary battery having the same configuration as in Example 1 was assembled, except that a negative electrode having a ratio of 1.1 was used. Example 18

Various parameters determined by X-ray diffraction: d002 = 0.345 nm, Lc = 3.00 nm,
The spherical carbonaceous material particles with R1 /R2 of 0.85 were subjected to the same heat treatment as in Example 16 to obtain the R1 /R2 of 0.85.
A lithium secondary battery having the same configuration as in Example 1 was assembled, except that a negative electrode having 1.0 was used. Example 19

Various parameters determined by X-ray diffraction: d002 = 0.342 nm, Lc = 4.20 nm,
The spherical carbonaceous material particles with R1 /R2 of 0.75 were subjected to the same heat treatment as in Example 16 to obtain R1 /R2 of 0.75.
A lithium secondary battery having the same configuration as in Example 1 was assembled, except that a negative electrode having 0.9 was used.

The lithium secondary batteries of Examples 16 to 19 were repeatedly charged and discharged by charging to 4.2V with a charging current of 50mA and discharging to 2.5V with a current of 50mA, and the cycle life of each battery was determined. and discharge capacity were measured. The results are shown in FIG. Note that FIG. 6 also shows the measurement results of the cycle life and discharge capacity of the batteries of Examples 1 and 4.

As is clear from FIG. 6, Examples 16-1
It can be seen that the capacity of the lithium secondary battery No. 9 is significantly increased compared to the batteries of Examples 1 and 4, which were equipped with negative electrodes having spherical carbonaceous particles that were not subjected to heat treatment. In particular, it can be seen that the capacity of the batteries of Examples 16 and 17 is significantly increased.

In Examples 16 to 19, spherical carbonaceous particles with a lamellar dot orientation were used as the negative electrode material, but lithium spherical carbonaceous particles with a radial and Brux-Taylor orientation were used as the negative electrode material. A similar capacity increase was also possible with secondary batteries.

[0062]

As described in detail above, according to the present invention, a lithium secondary battery with high capacity and excellent cycle life can be provided. Further, according to the present invention, a lithium secondary battery with extremely high capacity can be provided.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view showing a cylindrical lithium secondary battery in Example 1 of the present invention.

FIG. 2 is a schematic diagram showing an example of orientation of a microstructure of a carbonaceous material.

FIG. 3 is a characteristic diagram showing the relationship between charge/discharge cycles and discharge capacity in lithium secondary batteries of Examples 1 to 7 and Comparative Example 1.

FIG. 4 is a characteristic diagram showing the relationship between charge/discharge cycles and discharge capacity in lithium secondary batteries of Examples 8 to 11 and Comparative Example 1.

FIG. 5 is a characteristic diagram showing the relationship between charge/discharge cycles and discharge capacity in lithium secondary batteries of Examples 12 to 15 and Comparative Example 2.

FIG. 6 is a characteristic diagram showing the relationship between charge/discharge cycles and discharge capacity in the lithium secondary batteries of Examples 16 to 19 and Examples 1 and 4.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Stainless steel container, 3... Electrode group, 4... Positive electrode, 5... Separator, 6... Negative electrode, 8... Sealing plate, 9... Positive electrode terminal.

Claims (3)

[Claims] 1. A container, a positive electrode housed in the container, a negative electrode housed in the vessel and made of a carbonaceous material capable of intercalating and deintercalating lithium ions, and a lithium ion conductive electrolyte. The lithium secondary battery is characterized in that the carbonaceous material is a spherical particle having a graphite structure and a turbostratic structure and having a point-oriented fine structure. 2. A container, a positive electrode housed in the container, a negative electrode housed in the vessel and made of a carbonaceous material capable of intercalating and deintercalating lithium ions, and a lithium ion conductive electrolyte. The lithium secondary battery is characterized in that the carbonaceous material is carbon fiber having a graphite structure and a turbostratic structure, and having a lamellar or Brooks-Taylor microstructure orientation. 3. A container, a positive electrode housed in the container, a negative electrode housed in the vessel and made of a carbonaceous material capable of intercalating and deintercalating lithium ions, and a lithium ion conductive electrolyte. 1. A lithium secondary battery comprising: the carbonaceous material being spherical particles having a point-oriented microstructure and previously heat-treated in the presence of oxygen.