JPH09213372A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Abstract] An object of the present invention is to make scaly graphite, which has excellent properties as a negative electrode material in terms of lithium occlusion and desorption ability and carbon powder filling property, into an electrode plate state that facilitates lithium ion occlusion and emission. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery which is free from lithium deposition even in rapid charging and has excellent safety. SOLUTION: The negative electrode active material layer in contact with the current collector contains flake graphite, and the active material layer on the surface of the negative electrode contains spherical graphite. The proportion of spherical graphite is 20% or more by weight.
It is 0% or less. Moreover, 5% or more and 20% or less of fibrous graphite is added to at least one of the active material layers.

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 improvement of its negative electrode.

[0002]

2. Description of the Related Art As electronic devices have become smaller and lighter, there has been an increasing demand for smaller and lighter batteries as power sources. Among them, non-aqueous electrolyte secondary batteries using lithium metal for the negative electrode have been greatly expected because of their large theoretical energy density. However,
When lithium metal is used for the negative electrode, dendritic lithium (dendrites) are generated during charging, and during repeated charging and discharging of the battery, this dendrite grows and penetrates the separator, causing an internal short circuit in the battery. It was.

As a means for solving this problem, various attempts have been made to use not a lithium metal alone but an alloy of a low melting point metal such as aluminum, lead, indium, bismuth and cadmium and a lithium as a negative electrode, but also in this case. With the charge and discharge of the battery, the alloy became finer while repeating the occlusion and release of lithium into the alloy, and this fine alloy penetrated the separator and the battery was internally short-circuited like the lithium metal negative electrode. Is hard to say.

On the other hand, as a solution to the above problem,
A battery using carbon for the negative electrode has been proposed. The battery using carbon as the negative electrode of the non-aqueous electrolyte secondary battery was 1986.
27th Battery Symposium Abstracts P. 97 or 198
7th 28th Battery Symposium Abstracts P. 201, it is said that lithium ion as an active material is supported on carbon of the negative electrode by an electrochemical method outside the battery system, and the positive electrode active material is vanadium pentoxide, manganese dioxide, Alternatively, chromium oxide is used. Above all, batteries using vanadium pentoxide for the positive electrode and carbon for the negative electrode have been put to practical use as coin-type batteries mainly used for memory backup applications and the like. In this battery, as a method of supporting lithium on the negative electrode, a method of electrically contacting lithium metal and carbon in the battery is adopted.

Recently, the summary of the 33rd Battery Symposium in 1992, P.S. At 83, the positive electrode is Li
A cylindrical battery using CoO ₂ and carbon as the negative electrode has been proposed, and it is reported that the capacity of 70% or more of the initial capacity was maintained even after 1200 cycles in deep charge / discharge. At present, this battery system has been put to practical use as a 4V class lithium ion secondary battery. The characteristics of this battery system are
It is said that the charge / discharge reaction of the negative electrode is a reaction of occluding and releasing lithium ions in the carbon of the negative electrode, so that lithium does not deposit on the negative electrode due to charging, and therefore dendrite does not occur, so that good cycle characteristics can be obtained. Another point is that carbon does not cause miniaturization as in a lithium alloy even when lithium ion storage and release reactions are repeated, so that ignition of the battery does not occur. At the same time, another feature of this battery system is that a lithium-containing composite oxide called LiCoO ₂ is used for the positive electrode, and the lithium ions that are the negative electrode active material are supplied from the positive electrode. There is no need to support lithium ions in the.

As the positive electrode active material of the 4V class lithium ion secondary battery, not only LiCoO ₂ but also LiNi
O ₂ , LiMn ₂ O ₄ , LiFeO ₂ , or these C
A material in which o, Ni, Mn, and Fe are partially replaced with another metal element has been studied so far. In addition, as the carbon as the negative electrode material, initially, so-called amorphous carbon, such as coke, pyrolytic carbon, or low-temperature calcined products of various organic substances, has been mainly studied, but occlusion of lithium ions as an active material, Recently, highly crystalline carbon, so-called graphite-based carbon, has been attracting attention from the viewpoint of release ability.

Japanese Patent Application Laid-Open No. 4-115457 states that a graphitic material composed of easily graphitizable spherical particles as a negative electrode exhibits excellent characteristics. C ₆ Li, an intercalation compound of graphite and lithium ions, has been known for a long time. When lithium ions are occluded and released (intercalated, deintercalated) electrochemically, the theoretical capacity is 1 g of carbon. It shows a very large value of 372 mAh. Nevertheless, it was the Journal of E that was not initially adopted as a negative electrode for lithium-ion secondary batteries.
As reported in lectrochemical Society 117, No2 (1970) p.222, when propylene carbonate, which is widely used as one of the solvent components of the electrolytic solution in the non-aqueous electrolytic solution primary battery, is used, the solvent molecule is It was that it decomposed on the surface of graphite and the intercalation reaction of lithium ions into graphite was not carried out smoothly. On the other hand, the abstracts of the 59th Electrochemical Conference of 1992, P.A. In 238, this problem is reported to be solved by using ethylene carbonate as a solvent component of the electrolytic solution as a main component. Since then, natural graphite and various artificial graphites have been studied as negative electrodes of lithium ion secondary batteries, and graphite-based negative electrodes have become the mainstream at present.

On the other hand, as the requirements for the negative electrode of the battery, there is a filling property of how much carbon can be loaded in a limited volume of the battery, in addition to the ability of carbon itself to absorb and release lithium ions. This largely depends on the shape of the powder, not limited to carbon.

When considering the shape of the carbon powder,
It is roughly divided into four types: lump, scale, and fibrous. In a lithium ion battery, usually, a mixed paste of carbon and a binder is applied to both sides or one side of a metal thin film as a current collector, and after the electrode plate is dried, the electrode is formed by appropriately rolling,
Among the above four shapes, flaky carbon is most excellent in the filling property. In other words, in the other three types of carbon, even if the electrode plate is dried and then rolled, the shape of the particles does not change and the particles are merely densely packed, but in the case of flaky carbon, the particles are oriented in the same direction by rolling. Therefore, the filling property becomes larger. Therefore, from the viewpoint of the ability to occlude and release lithium ions and the filling property of carbon powder, it can be said that natural or artificial graphite having a flaky powder shape is the most excellent material as a carbon negative electrode material.

However, in the case of natural graphite, it is necessary to take into account the fact that the material varies due to the difference in the place of production or that the material must be modified by a special treatment to remove a large amount of impurities. It can be said that scaly artificial graphite is the best. Typical scale-like artificial graphite is obtained by graphitizing coal pitch or petroleum pitch, and includes artificial graphite manufactured by Lonza or Nippon Graphite.

[0011]

However, there is a problem to be solved when scale-like artificial graphite is used as a negative electrode material. Certainly, flake graphite is oriented by rolling and the filling property increases, but on the contrary, the filling property increases too much and the pores inside the electrode are limited, and the electrolyte does not penetrate into the electrode when forming the electrode of the battery. Sometimes. For this reason, the intercalation and deintercalation reactions of lithium ions into graphite are performed only on the electrode surface, which causes a problem that it is not suitable for high-rate charging and discharging. When this battery is rapidly charged, the diffusion of lithium ions into the electrode cannot catch up, the concentration of lithium ions on the electrode surface becomes high, and metallic lithium is deposited on the surface of the negative electrode plate rather than intercalating lithium ions in graphite. It becomes easier to precipitate. While such charging and discharging are repeated, lithium may be deposited as dendrites on the surface of the negative electrode. When such a battery is placed at a high temperature, the lithium metal deposited on the negative electrode plate chemically reacts with the electrolytic solution.

The present invention is to solve the above-mentioned problems, and to provide a non-aqueous electrolyte secondary battery using graphite having excellent properties as a negative electrode material in an electrode state suitable for high rate discharge. It is intended.

[0013]

In order to solve these problems, in the present invention, the negative electrode material mixture layer in contact with the current collector contains scaly graphite as a main component, and the negative electrode material mixture layer has a spherical shape. It contains graphite as a main component, and particularly when improving the cycle characteristics of the battery, fibrous graphite is added to at least one of the mixture layers.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Normally, a rolling step is provided during the preparation of a negative electrode plate to bring the active material into an appropriate filled state. However, when flake graphite is used as a mixture, the flake graphite tends to be oriented by rolling. Therefore, it is difficult to control the optimum packing density, that is, the packing density that maintains the optimum pore volume for allowing the liquid to sufficiently penetrate into the electrode plate and reacting the entire mixture. In addition, since the hexagonal mesh plane of graphite, into which lithium ions cannot be inserted and released due to rolling, is oriented parallel to the electrode surface, it is difficult for lithium ions to enter and leave during charging and discharging.

On the other hand, spherical graphite is relatively difficult to be filled due to its shape, but since the end portion of the hexagonal net surface of graphite has a structure (lamella structure) present on the particle surface, lithium ion due to charging and discharging Getting in and out is relatively smooth.

From the above, scale-like graphite is arranged in the active material layer in contact with the current collector to increase the filling amount of the active material, and spherical graphite is arranged in the active material layer on the surface of the electrode to allow lithium ions to enter and exit. However, a non-aqueous electrolyte secondary battery that is smooth and does not deposit lithium even during rapid charging and has excellent safety can be configured.

Further, the fibrous graphite is lower in filling property than the spherical particles in terms of shape, and good battery characteristics cannot be obtained when used alone, but it is added in a small amount to the scale-like or spherical particles. This ensures an appropriate amount of pores, improves the wettability of the graphite surface with the electrolytic solution, and increases the reaction surface area of the electrode, which is effective in improving the high-rate charge / discharge characteristics. Furthermore, by securing an appropriate amount of holes, it is possible to absorb the volume change due to the expansion and contraction of the carbon particles due to charge and discharge, and it is possible to suppress the collapse of the electrode plate and improve the cycle characteristics.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. In the examples, a cylindrical battery was constructed and evaluated.

Embodiment 1 FIG. 1 is a longitudinal sectional view of a cylindrical battery used in this embodiment. In the figure, 1 indicates a positive electrode,
A mixture of carbon black as a conductive material and an aqueous dispersion of polytetrafluoroethylene as a binder at a weight ratio of 100: 3: 10 was applied to both sides of an aluminum foil, as an active material, LiCoO _2. After being dried, rolled, and then cut into a predetermined size. This is 2
The positive electrode lead plate made of titanium is spot-welded. The mixing ratio of the aqueous dispersion of polytetrafluoroethylene as the binder is calculated by its solid content. Reference numeral 3 denotes a negative electrode, which is composed mainly of a carbonaceous material, which is mixed with an acrylic binder in a weight ratio of 100: 3, is applied on both sides of a nickel foil, dried, and rolled to a predetermined size. It is cut to the size of. A nickel negative electrode lead plate 4 was spot-welded to this. Reference numeral 5 denotes a separator made of a polyethylene microporous film, which is interposed between the positive electrode 1 and the negative electrode 3 and is wholly wound in a spiral to form an electrode plate group. An upper insulating plate 6 and a lower insulating plate 7, which are made of polypropylene, are arranged on the upper and lower chocks of the electrode plate group, and are inserted into a case 8 made of nickel-plated iron. Then, the positive electrode lead plate 2 is spot-welded to the titanium sealing plate 10 and the negative electrode lead plate 4 is spot-welded to the bottom of the case 8, respectively, and then a predetermined amount of electrolytic solution is injected into the case and the battery is sealed via the gasket 9. The plate 10 is sealed to obtain a completed battery. The dimensions of this battery are 14 mm in diameter and 50 mm in height. Note that 11
Is the positive electrode terminal of the battery, and the negative electrode terminal is also served by the battery case 8.

The electrolyte used was a solution in which lithium hexafluorophosphate was dissolved at a concentration of 1 mol / l as a solute in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1.

As the negative electrode material, artificial graphite manufactured by Lonza and 300
Mesophase spherules fired at 0 ° C. were selected as flaky graphite and spheroidal graphite, respectively, and five kinds of negative electrodes shown in (Table 1) were prepared using them, and the batteries were assembled into the cylindrical batteries as batteries A to E. . In the case of the negative electrode having two graphite layers, first, the first layer was applied onto the current collector, and then the second layer was applied thereon.

At that time, when each of the negative electrodes was rolled under the same conditions and produced so as to have the same thickness, the flake graphite had a better packing property than the spherical graphite, and therefore the weight of the active material per electrode plate was large. Has grown.

Since the purpose of this example is to see the difference in characteristics depending on the negative electrode, the amount of the positive electrode mixture is sufficiently larger than the amount of the negative electrode mixture, and 600 mAh under the experimental conditions shown below.
It is configured to output a certain amount of capacity.

The five types of batteries shown above were subjected to constant current discharge at low current and high current, and the discharge capacities were compared. The test conditions were a charge / discharge current of 100 mA, a charge end voltage of 4.2 V, a discharge end voltage of 3.0 V, and an environmental temperature of 20 ° C. After repeating charge / discharge 5 times, only the discharge current was changed to 500 mA, and the charge / discharge was 100%. I went there. After the above electrical characteristic test is completed, the battery is disassembled in a charged state and the surface state of the electrode plate is observed.
The generation state of the stage structure of lithium in graphite was measured by line diffraction measurement.

Discharge capacity at 5th cycle at low current, discharge capacity at high current, ratio of high current discharge capacity to low current discharge capacity, cycle deterioration represented by (Equation 1) in 100 cycles at high current The ratio and the ratio of the graphite weight per negative electrode of each battery, the peak intensity of the 1st stage, 2nd stage, 3rd stage and graphite by X-ray diffraction measurement are shown in (Table 1).

[0026]

[Equation 1]

[0027]

[Table 1]

Since the battery of this embodiment has a structure having a sufficient positive electrode capacity, the change in potential due to charging and discharging of the positive electrode is similarly small in all batteries, and the charging capacity is limited to the lithium storage capacity of the negative electrode at the end of charging. Reached, and the negative electrode potential dropped sharply.
It is determined by the phenomenon that charging ends when the potential difference of the negative electrode reaches the charging end voltage. On the other hand, the charging and discharging efficiency when discharged at a low current is almost 100% for all batteries.
And the discharge capacity is determined by the charge capacity, and
The charge / discharge efficiency when discharged at a high current is 100% or less, and the discharge capacity is determined by the ease of reaction in which lithium moves in the negative electrode during discharge.

From a comparison of the types of graphite (Table 1), the discharge capacities at low currents showed that battery A using scaly graphite and battery B using spheroidal graphite showed almost the same capacity.
Originally, battery A should have a larger discharge capacity because battery A has a heavier graphite weight than battery B. In actuality, since battery D has a high packing density of graphite and a small pore volume inside the electrode plate, the electrolyte solution does not sufficiently permeate and the reaction does not occur sufficiently. Therefore, charging is uneven in the thickness direction of the electrode plate. It is considered that the discharge capacity was reduced as a result. Further, the discharge capacity at high current is smaller in Battery A than in Battery B. It is considered that in battery A, the reaction in which lithium moves in the negative electrode during strong discharge is not easy, but in battery B, since the lithium in the negative electrode moves easily, a capacity approximately equal to that in low current discharge can be obtained. The cycle deterioration rate showed the same tendency as the high current / low current capacity ratio. According to the decomposition observation, in the battery A, partial deposition of metallic lithium was observed. Looking at the X-ray diffraction peak intensity ratio, Battery A has a strong peak intensity at the 2nd stage, but peaks of 1st, 3rd and graphite are also observed, and uneven charging is performed. Battery B had a strong peak at the 1st stage, but a slight observation at the 2nd stage, but 3r
No peaks of d and graphite were detected, indicating that the charging was relatively uniform. From these facts, it was found that the flake graphite has a large weight that can be filled in the battery, but a uniform reaction does not occur, and particularly the strong discharge characteristics are inferior.

Next, when the mixed systems of the batteries C to E were compared, the discharge capacities at low currents did not show a significant difference, but the batteries C to D were in that order. This was similar to the order of weight of graphite on the negative plate. However, the capacity of the electrode plate was larger than the battery A of scaly graphite alone having a large amount of graphite and the battery B of spheroidal graphite alone, which is not preferable for filling.

On the other hand, the discharge capacity at a high current is battery CE
The order was D, and the difference was particularly remarkable. In the battery C, the spherical graphite that secures an appropriate amount of pores is present on the electrode surface and the reaction to the inside of the electrode plate proceeds smoothly, and the flake graphite having good filling properties is present near the current collector. As a result, a battery having a high capacity and a high ratio of high current / low current capacity was produced. Almost no deterioration was observed in the high current discharge cycle, and there was no change in the battery disassembly observation from the time of battery preparation. In Battery D, scaly graphite, which has few pores and is difficult for electrolyte to permeate and does not easily react with lithium, exists on the surface of the electrode plate, and the lithium transfer reaction inside the electrode plate does not occur smoothly, and at high current. It is considered that the discharge capacity of is reduced. It was confirmed by X-ray diffraction that the mixed stages of 1st, 2nd, 3rd, and graphite were detected and that they were not uniformly charged and discharged. As a result of disassembling and observing the battery, precipitation of lithium was observed on a part of the graphite. Since the flake graphite is distributed throughout the electrode plate in the battery E, it is presumed that the reaction state between the batteries C and D is present. When the battery was disassembled, no change in the electrode plate due to cycles was observed.

From the above results, it was the battery C of the present invention that the discharge capacity was large at both low and high current values as a comprehensive evaluation.

(Example 2) In order to obtain the optimum mixing ratio of spheroidal graphite in the composition of the negative electrode plate of the battery C showing the best characteristics in (Example 1), the six types of negative electrodes shown in (Table 2) are described above. A cylindrical battery was prototyped and evaluated. For evaluation, constant current discharge capacity at low current and high current was measured in the same manner as in (Example 1).

Table 2 shows the evaluation results.

[0035]

[Table 2]

From Table 2, it can be seen that the weight of the mixture per one negative electrode plate becomes the batteries F-G-H-I-J-K in descending order, and becomes smaller as the mixing ratio of the spherical graphite increases. .

In the battery characteristics, batteries I-H-G-J-K-F are in descending order of discharge capacity at low currents, and the capacities of battery F and battery K are low with the minimum and maximum mixing ratios of spherical graphite. It was It is considered that the reason for the small capacity of the battery F is that the ratio of the scaly graphite was large and the packing density was too high, and the reaction inside the electrode plate was insufficient as in the battery A of (Example 1). It is considered that the reason why the capacity of the battery K is small is that the proportion of spheroidal graphite is large and the packing density is low as opposed to the battery F.

Further, the discharge capacities at high currents were batteries I-H-J-K-G-F in descending order, and battery F was particularly small. The ratio of the discharge capacity at high current to the discharge capacity at constant current increased as the mixing ratio of spheroidal graphite increased.
This is also the tendency observed in (Example 1), and it is considered that the spherical graphite is more advantageous in discharging at high current because there are more inlets and outlets of lithium on the surface of the particles.

As a comprehensive evaluation, it was batteries G to J in which the discharge capacities at constant current and high current were well balanced, and the mixing ratio of spherical graphite was 20 to.
The range was 80% (weight ratio).

(Example 3) In order to investigate the effect of adding fibrous graphite in the construction of the negative electrode plate of the battery C showing the best characteristics in (Example 1), the six types of negative electrodes shown in (Table 3) were used. The above cylindrical battery was prototyped and evaluated. As the evaluation method, the discharge capacity at low current and high current was measured in the same manner as in Example 1, charging and discharging were repeated 100 times at a discharge current of 500 mA, and the cycle deterioration rate in 100 cycles was calculated by (Equation 1).

As the fibrous graphite, one obtained by subjecting a vapor-grown carbon fiber manufactured by Showa Denko KK to a high temperature treatment was used.

Table 3 shows the evaluation results.

[0043]

[Table 3]

From Table 3, the fibrous graphite is flake graphite,
Since it is bulkier than spherical graphite, the weight of graphite per electrode plate to which the fibrous graphite is added is smaller than that of the electrode plate to which the fibrous graphite is not added, and becomes smaller as the mixing ratio of the fibrous graphite increases.

In the battery characteristics, the discharge capacities at low currents become larger in the order of battery L-N-M-O-P-Q, which decreases as the mixing ratio of fibrous graphite increases, and the ratio of fibrous graphite of Q is the maximum. The ones had a particularly small capacity. This is because as the content of fibrous graphite increases, the pore volume in the electrode plate increases and the penetration of the electrolytic solution becomes sufficient, and the reaction depth of the active material increases, but on the other hand, the bulk of the fibrous graphite is large. It is considered that this is because the weight of the active material per electrode plate becomes small and the discharge capacity becomes small.

The battery L-
However, the ratio of the discharge capacity at high current to the discharge capacity at low current is higher as the ratio of the fibrous graphite is higher, and the high current discharge characteristics are higher than those of the fibrous graphite. The addition was found to be effective. When fibrous graphite was added to scaly graphite, the weight per electrode plate decreased, and the capacity for low current discharge decreased, but the capacity for high current discharge increased. It is considered that when the fibrous graphite was mixed, it became difficult to fill the scaly graphite, and the reaction came to be carried out smoothly.

On the other hand, the battery Q
-P-O-M-N-L, the cycle life was dramatically extended by the addition of fibrous graphite, and the cycle life became longer as the addition ratio increased. This is because the fibrous graphite is present in the interstices between the particles of the flake graphite or the spherical graphite to prevent the electrode plate from collapsing due to the expansion and contraction of the particles during charge / discharge, and to improve the contact between the particles. It is supposed to be because. Further, the cycle deterioration of the battery M added to the scaly graphite layer was smaller than that of the battery N added to the spherical graphite layer. This is when comparing flake graphite with spheroidal graphite,
Since the flake graphite has a good filling property, the volume of pores in the electrode plate is small, and the expansion and contraction of carbon particles due to charging and discharging cannot be absorbed. Therefore, the volume change of the electrode plate during charging / discharging is large, and when the charging / discharging cycle is repeated, the binding force between the carbon particles gradually decreases and the electrode plate is collapsed. It is presumed that the effect of adding the fibrous graphite to the property of the flake graphite that is easily filled, that is, the effect of suppressing the collapse of the electrode plate due to the cycle is greater than the effect of adding the spherical graphite.

In summary, the addition of fibrous graphite slightly reduces the discharge capacity at low current and high current, but the cycle life characteristics are dramatically improved. Therefore, when the cycle life characteristics are important, a system to which fibrous graphite is added is suitable, and the mixing ratio at that time is preferably in the range of 5 to 20% (weight ratio) of the whole. Further, the effect can be obtained when added to either the scale-like graphite layer or the spherical graphite layer, but the improvement effect was particularly large when added to the scale-like graphite layer.

Summarizing the results of the above three embodiments,
By disposing the spherical graphite layer on the surface of the negative electrode in a weight ratio of 20 to 80% of the whole and by arranging the scaly graphite layer on the surface of the negative electrode in contact with the current collector, discharge characteristics of low current and high current can be obtained. Can be improved. Further, it was found that by adding 5 to 20% of fibrous graphite to at least one of the graphite layers with respect to the total weight of the negative electrode graphite, the discharge capacity is slightly reduced, but the cycle life characteristics can be improved.

Therefore, for applications in which the discharge capacity, that is, energy density is important, among the above-mentioned negative electrode configurations, the configuration in which fibrous graphite is not added is suitable, while for applications in which the cycle life characteristics are important, fibrous graphite is used. A configuration in which is added is suitable.

In this embodiment, a composite oxide of lithium and cobalt was used as the positive electrode active material, but other positive electrode active materials,
For example, lithium-containing oxides such as a composite oxide of lithium and nickel, a composite oxide of lithium and manganese, and a composite oxide of lithium and iron, or cobalt, nickel, manganese, and iron of each of the above composite oxides are converted to other transition metals. Almost the same effect was obtained when using a metal partially substituted.

Although lithium hexafluorophosphate is used as the solute of the electrolytic solution in this embodiment, other lithium-containing salts such as lithium borofluoride, lithium perchlorate, lithium trifluoromethanesulfonate, and hexafluorofluoride are used. Similar effects were obtained even when lithium arsenate was used.

[0053]

As is apparent from the above description, according to the present invention, a spherical graphite layer is formed on the surface of the negative electrode, preferably 2
By disposing at a weight ratio of 0 to 80% and disposing a scaly graphite layer on the surface of the negative electrode that contacts the current collector, excellent discharge capacity characteristics can be obtained at both low current and high current, and at least either By adding 5 to 20% of fibrous graphite to one graphite layer with respect to the total weight of negative electrode graphite, it is possible to provide a non-aqueous electrolyte secondary battery excellent in discharge at high current and cycle life characteristics. it can.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a cylindrical battery of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Positive electrode lead plate 3 Negative electrode 4 Negative electrode lead plate 5 Separator 6 Upper insulating plate 7 Lower insulating plate 8 Case 9 Gasket 10 Sealing plate 11 Positive electrode terminal

Claims (4)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode with a separator interposed therebetween, wherein the negative electrode comprises an active material layer containing graphite as a main material and a current collecting material layer, and the active material layer is a collector. A non-aqueous electrolyte secondary battery in which flake graphite is mainly present in the layer in contact with the electric material, and spherical graphite is mainly present in the surface side layer. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein at least one of spherical graphite and flake graphite contains fibrous graphite. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the proportion of spherical graphite in the entire graphite is in the range of 20% to 80% by weight. 4. The non-aqueous electrolyte secondary battery according to claim 2, wherein the proportion of the fibrous graphite in the whole graphite is in the range of 5% or more and 20% or less by weight.