JP2009026676A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery having high energy density and improved high-rate property. <P>SOLUTION: The lithium secondary battery comprises a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a separator arranged between the positive electrode and the negative electrode. At least either the positive electrode or the negative electrode contains mesoporous carbons, and conductive particulates having an average particle size smaller than the average particle size of the mesoporous carbons. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery having an electrode containing mesoporous carbon.

  With the miniaturization of personal computers, video cameras, mobile phones, etc., in the fields of information-related equipment and communication equipment, lithium secondary batteries have been put into practical use because of their high energy density as the power source used for these equipment. It has become widespread. On the other hand, in the field of automobiles, the development of electric vehicles is urgently caused by environmental problems and resource problems, and lithium secondary batteries are also being studied as a power source for electric vehicles. In particular, when a lithium secondary battery is put into practical use as a power source for an electric vehicle, the output of the current lithium secondary battery is low, so that the output of the lithium secondary battery needs to be increased. In order to increase the output of this lithium secondary battery, improvement of the high rate characteristic is an important issue.

  A lithium secondary battery is required to have a high energy density per volume as well as an energy density per mass. In general, the electrode density is improved by pressing the electrodes at a high pressure. By increasing the electrode density, the filling amount in the battery container can be increased, and the energy density per volume as the electrode and the battery can be increased.

However, when the electrode density is increased, voids in the electrode are reduced, resulting in a shortage of electrolytes that are important for electrode reactions existing in the voids, and lithium ions do not move smoothly. Diffusing resistance increases. As a result, there arises a problem that the high rate characteristic is lowered.
On the other hand, in order to improve the high rate characteristics, it is effective to increase the voids in the electrode to facilitate the penetration of the electrolytic solution into the electrode and the movement of lithium ions. The energy density decreases.
As described above, the energy density and the high rate characteristic are in a contradictory relationship, and it has been very difficult to obtain a lithium secondary battery having a high energy density and excellent high rate characteristic.

  Patent Document 1 discloses an electrode in which an electrolyte holding material made of a carbon material having a through hole is arranged in a gap between active materials for the purpose of preventing a decrease in lithium ion concentration during high current discharge. . In this technique, by using a carbon material having a through hole as an electrolyte holding material, the electrolyte holding capacity in the electrode is increased, the decrease in the lithium ion concentration during high current discharge is prevented, and the output is increased.

  Patent Document 2 discloses a lithium secondary battery having an electrode made of mesoporous carbon in which three-dimensional uniform pores are regularly arranged for the purpose of increasing the capacity. In this technique, mesoporous carbon whose pore size and structure are controlled three-dimensionally as a negative electrode active material is used to reduce irreversible capacity and increase capacity.

  Patent Document 3 discloses a lithium secondary battery having a positive electrode containing graphite and acetylene black as a conductive agent for the purpose of improving load characteristics. According to this technology, by using both highly conductive graphite and acetylene black having a high bulk density as a conductive agent for the positive electrode, both the electron conductivity and the ion mobility are improved, and high output is achieved. Yes.

Patent Document 4 discloses a lithium secondary battery having a positive electrode containing expanded graphite and carbon black as a conductive agent for the purpose of increasing capacity and improving cycle characteristics. According to this technology, expanded graphite and carbon black are used in combination as a conductive agent for the positive electrode, the content of expanded graphite is increased, and the content of bulky carbon black is decreased, thereby increasing the capacity and cycle characteristics. We are trying to improve.
Patent Document 5 discloses a lithium secondary battery having an electrode containing active material particles coated with carbon fine particles for the purpose of increasing capacity and improving cycle characteristics. According to this technique, the surface of the active material particles is coated with carbon fine particles, so that a conductive path is formed to increase the capacity and improve the cycle characteristics.

JP 2006-147405 A JP 2005-166325 A Japanese Patent No. 3435731 Japanese Patent No. 3115266 Japanese Patent No. 337351

According to the above-mentioned Patent Document 1, since carbon is generally excellent in electron conductivity, there is no fear of reducing the electron conductivity in the electrode by using the carbon material, but rather the electron conductivity in the electrode is improved. It is said that there is a work to improve. However, the addition of only a carbon material having a through hole can prevent a decrease in the lithium ion concentration during high current discharge, but it cannot secure a sufficient conductive path, and there is a limit to increasing the output.
In addition, none of the lithium secondary batteries described in any of the above documents achieves both energy density and rate characteristics.

  The present invention has been made in view of the above circumstances, and has as its main object to provide a lithium secondary battery having a high energy density and excellent high rate characteristics.

  In order to achieve the above object, the present invention provides a lithium secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a separator disposed between the positive electrode and the negative electrode. A lithium secondary battery, wherein at least one of the positive electrode and the negative electrode contains mesoporous carbon and conductive fine particles having an average particle size smaller than the average particle size of the mesoporous carbon. provide.

  According to the present invention, at least one of the positive electrode and the negative electrode contains mesoporous carbon and conductive fine particles, thereby improving the high energy density by pressing the electrode at a high pressure without impairing the high rate characteristics. It is possible to realize.

  In the said invention, it is preferable that the said electroconductive fine particles are carbon black. This is because carbon black is generally excellent in electron conductivity.

  In the present invention, by including mesoporous carbon and conductive fine particles in at least one of the positive electrode and the negative electrode, a lithium secondary battery having high energy density and excellent high rate characteristics can be obtained. Play.

Hereinafter, the lithium secondary battery of the present invention will be described in detail.
The lithium secondary battery of the present invention is a lithium secondary battery having a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a separator disposed between the positive electrode and the negative electrode, At least one of the positive electrode and the negative electrode contains mesoporous carbon and conductive fine particles having an average particle size smaller than the average particle size of the mesoporous carbon.

  FIG. 1 is a schematic cross-sectional view showing an example of the lithium secondary battery of the present invention. A lithium secondary battery illustrated in FIG. 1 includes a positive electrode current collector 1, a positive electrode 3 containing a positive electrode active material 2, a negative electrode current collector 4, a negative electrode 6 containing a negative electrode active material 5, a positive electrode 3 and A separator 7 disposed between the negative electrodes 6, and the positive electrode 3 contains mesoporous carbon 8 and conductive fine particles 9. In FIG. 1, the mesoporous carbon and the conductive fine particles are contained in the positive electrode. However, the present invention is not limited to this, and it may be contained in at least one of the positive electrode and the negative electrode.

  Since mesoporous carbon has uniform pores, when at least one of the positive electrode and the negative electrode contains mesoporous carbon, the electrolyte can be held in the pores of the mesoporous carbon. The electrolyte can be moved through the pores. Therefore, by pressing the electrode at a high pressure, even if the gap between the active material, the mesoporous carbon and the conductive fine particles is reduced in the electrode, the flow path of the electrolyte solution can be secured by the pores of the mesoporous carbon. Therefore, lithium ions can be diffused and moved smoothly, and lithium ion conductivity can be improved.

In addition, mesoporous carbon is a carbon material and generally has excellent electronic conductivity, and thus is considered to function as a conductive agent. However, since the mesoporous carbon has a relatively large particle size, the contact between the active material and the mesoporous carbon, or the contact between the mesoporous carbons becomes insufficient, and the internal resistance may increase.
On the other hand, conductive fine particles having a particle size of the order of nanometers, for example, fine particles such as carbon black, have a property of being connected in a chain shape. In the present invention, as illustrated in FIG. 1, since the average particle diameter of the conductive fine particles 9 is smaller than the average particle diameter of the mesoporous carbon 8, the conductive fine particles 9 are connected in a chain shape, and the positive electrode active material 2 and A conductive path can be formed by adhering to the surface of the mesoporous carbon 8. Since the conductive fine particles 9 have an average particle size smaller than the average particle size of the mesoporous carbon 8, the arrangement can be relatively freely changed, and the conductive fine particles 9 enter the gap between the positive electrode active material 2 and the mesoporous carbon 8, and the positive electrode active material 2 And it can adhere to the surface of the mesoporous carbon 8. In addition, since the conductive path is composed of conductive fine particles and can be deformed relatively freely while maintaining contact between the conductive fine particles, it is thought that the active material can be prevented from being electrically isolated. . Thereby, an active material and electroconductive fine particles can fully be contacted, and favorable electronic conductivity can be obtained. Furthermore, the active material and mesoporous carbon or between mesoporous carbons can be brought into electrical contact via the conductive fine particles.

As described above, in the present invention, at least one of the positive electrode and the negative electrode contains mesoporous carbon and conductive fine particles, thereby improving the high energy density by pressing the electrode at a high pressure and impairing the high rate characteristics. It is possible to realize without. That is, a lithium secondary battery having a high energy density and excellent high rate characteristics can be obtained.
Hereinafter, the lithium secondary battery of this invention is demonstrated for every structure.

1. Mesoporous carbon The mesoporous carbon used in the present invention is a carbon-based mesoporous material in which uniform pores are regularly arranged. The mesoporous carbon functions as a conductive agent, and the pores function as an electrolyte flow path. is there.

The average pore diameter of the mesoporous carbon is not particularly limited as long as it is a meso region, but it is preferable that the mesoporous carbon has a size that allows the electrolytic solution to easily permeate. Specifically, the average pore diameter of mesoporous carbon is preferably about 2 nm to 50 nm, more preferably in the range of 2 nm to 20 nm, and still more preferably in the range of 2 nm to 6 nm. This is because if the average pore diameter is in the above range, the electrolyte solution can be easily infiltrated, and diffusion and movement of lithium ions can be promoted. If the average pore diameter is too small, lithium ions will easily collide with the pore walls, which may hinder the movement of lithium ions. On the other hand, if the average pore diameter is too large, the strength of the mesoporous carbon decreases, and the pores may be crushed when the electrode is pressed at a high pressure.
The average pore diameter can be determined by adsorption / desorption isotherm measurement by nitrogen adsorption and desorption.

As the specific surface area of the mesoporous carbon, it is preferable that penetration of the electrolytic solution is favorable, preferably specifically is 100 m ² / g or more, more preferably 500m ² / g~2000m ² / g in the range of, more preferably in the range of 1500m ² / g~2000m ² / g.

The shape of mesoporous carbon is not particularly limited, and examples thereof include a spherical shape and an elliptical sphere.
The average particle size of the mesoporous carbon is not particularly limited as long as it is larger than the average particle size of the conductive fine particles. Specifically, although it depends on the thickness of the positive electrode or the negative electrode, the average particle size of the mesoporous carbon is preferably about 0.1 μm to 5 μm, more preferably in the range of 0.1 μm to 2 μm, still more preferably 0. Within the range of 1 μm to 1 μm. This is because if the average particle size is too small, the handleability may deteriorate. On the other hand, if the average particle size is too large, the movement distance of lithium ions becomes long, so that the resistance may increase and it may be difficult to obtain a flat electrode.
The average particle size of the mesoporous carbon is larger than the average particle size of the conductive fine particles by, for example, observing the particle size of the mesoporous carbon and the conductive fine particles in the electrode with a scanning electron microscope (SEM). Can be confirmed. The average particle size of mesoporous carbon can be determined by measuring and averaging the particle size of mesoporous carbon observed with a scanning electron microscope (SEM), for example.

  Although the content of mesoporous carbon contained in the positive electrode or the negative electrode varies depending on the type of the active material, specifically, it is preferably about 1% by weight to 30% by weight, more preferably 1% by weight to 20% by weight. %, More preferably in the range of 1% to 10% by weight. If the mesoporous carbon content is too high, the mesoporous carbon is relatively bulky, so even if the electrode is pressed, the electrode density may be reduced.If the mesoporous carbon content is too low, the mesoporous carbon content is too small. This is because there is a possibility that the voids in the electrode are held by the holes and the effect of improving the lithium ion conductivity cannot be sufficiently obtained.

  The mesoporous carbon may be contained in at least one of the positive electrode and the negative electrode. That is, mesoporous carbon may be contained in the positive electrode, may be contained in the negative electrode, or may be contained in the positive electrode and the negative electrode.

  Further, the mesoporous carbon may be uniformly dispersed throughout the positive electrode or the negative electrode, or may be unevenly distributed. When mesoporous carbon is unevenly distributed, the content of mesoporous carbon may be increased stepwise or continuously from the positive electrode current collector or negative electrode current collector side surface to the separator side surface. Also good.

  The method for imparting the mesoporous carbon content gradient to the positive electrode or the negative electrode is not particularly limited as long as it can impart a desired gradient, and specifically, the active material and mesoporous carbon. And a method using a plurality of pastes in which the mesoporous carbon content is changed, a method using the magnetism of the active material, and the like.

  The pore shape of the mesoporous carbon is not particularly limited, and examples of the pore arrangement structure include a 2d-hexagonal structure, a 3d-hexagonal structure, and a cubic structure. The hexagonal structure means that the pores are arranged in a hexagonal structure. The cubic structure means that the pores are arranged in a cubic structure.

Mesoporous carbon, for example, uses mesoporous materials such as mesoporous silica as a template, fills mesoporous silica pores with an organic material as a carbon source, carbonizes in an inert atmosphere, and removes mesoporous silica with hydrofluoric acid, sodium hydroxide, etc. By doing so, it can be manufactured. Specifically, the pore walls of mesoporous silica become the pores of mesoporous carbon.
The pore shape and the like of the mesoporous material used as a template can be changed depending on the type of the surfactant.

2. Conductive fine particles The conductive fine particles used in the present invention have an average particle size smaller than the average particle size of the mesoporous carbon, and function as a conductive agent.

The shape of the conductive fine particles is not particularly limited, and examples thereof include a spherical shape and an elliptical sphere.
The average particle diameter of the conductive fine particles may be smaller than the average particle diameter of the mesoporous carbon, but it is preferable that the conductive fine particles have a size that can enter the gap filled with the active material and the mesoporous carbon. . Specifically, the average particle size of the conductive fine particles is preferably about 5 to 50 times the average particle size of mesoporous carbon. More specifically, the average particle size of the conductive fine particles is preferably about 10 nm to 200 nm, more preferably in the range of 10 nm to 100 nm, and still more preferably in the range of 25 nm to 70 nm. This is because, if the average particle diameter is in the above range, the conductive fine particles are connected in a chain shape and easily adhere to the surface of mesoporous carbon or the active material. Thereby, a conductive path is formed, and electronic conductivity is improved. On the other hand, if the average particle size is too small, the handleability may deteriorate. On the other hand, if the average particle size is too large, it may be difficult for the conductive fine particles to be connected in a chain form or to adhere to the surface of mesoporous carbon or the active material.
Note that the average particle size of the conductive fine particles is smaller than the average particle size of the mesoporous carbon, as described above, for example, by using a scanning electron microscope (SEM) to determine the particle sizes of the mesoporous carbon and the conductive fine particles in the electrode. This can be confirmed by observing. The average particle size of the conductive fine particles can be obtained by measuring and averaging the particle size of the conductive fine particles observed with, for example, a scanning electron microscope (SEM).

  The material of the conductive fine particles is not particularly limited as long as it has conductivity, and materials generally used as a conductive agent can be used. Among them, carbon black is preferably used. This is because carbon black is generally excellent in electron conductivity. Examples of carbon black include acetylene black and ketjen black. In particular, acetylene black is preferable. This is because the versatility is high.

  The content of the conductive fine particles contained in the positive electrode or the negative electrode varies depending on the type of the active material, but is specifically preferably about 0.1 wt% to 10 wt%, more preferably 0.1 It is within the range of 5% by weight to 5% by weight, more preferably within the range of 0.1% to 3% by weight. If the content of the conductive fine particles is too large, the entrance of the pores of the mesoporous carbon may be clogged with the conductive fine particles, and the lithium ion conductivity may not be sufficiently improved. Also, the content of the conductive fine particles This is because if the amount is too small, the electron conductivity may not be sufficiently improved.

  The conductive fine particles may be contained in at least one of the positive electrode and the negative electrode. That is, the conductive fine particles may be contained in the positive electrode, may be contained in the negative electrode, or may be contained in the positive electrode and the negative electrode.

  Further, the conductive fine particles may be uniformly dispersed throughout the positive electrode or the negative electrode, or may be unevenly distributed. When the conductive fine particles are unevenly distributed, the content of the conductive fine particles may be increased stepwise or continuously from the positive electrode current collector or negative electrode current collector side surface toward the separator side surface. It may be.

  The method for imparting a gradient of the content of the conductive fine particles to the positive electrode or the negative electrode is not particularly limited as long as a desired gradient can be imparted. Specifically, the active material and the conductive material are electrically conductive. Examples include a method using the difference in specific gravity with the conductive fine particles, a method using a plurality of pastes in which the content of the conductive fine particles is changed, and a method using the magnetism of the active material.

3. Positive electrode The positive electrode used in the present invention contains at least a positive electrode active material, and usually further contains a conductive agent and a binder. In the present invention, since the conductive fine particles function as a conductive agent, when the positive electrode contains conductive fine particles and mesoporous carbon, it is not necessary to separately include a conductive agent.

The positive electrode active material is not particularly limited as long as it can occlude and release lithium ions. Examples thereof include LiCoO ₂ , LiCoO ₄ , LiMn ₂ O ₄ , LiNiO ₂ , and LiFePO _4. Can do. Among these, LiNiO ₂ is preferably used.
Examples of the binder include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

  As a method for forming the positive electrode, a general method can be used, but when the positive electrode contains mesoporous carbon and conductive fine particles, it contains a positive electrode active material, mesoporous carbon, conductive fine particles, a binder, and the like. The positive electrode forming paste to be applied is preferably pressed after being applied onto the positive electrode current collector and dried. By pressing, the electrode density can be increased and the energy density can be improved, and since mesoporous carbon is contained, the voids in the positive electrode that becomes the flow path of the electrolyte solution are made to remain in the mesoporous carbon even after pressing. This is because it can be secured by the pores.

4). Negative electrode The negative electrode used in the present invention contains at least a negative electrode active material, and may contain a conductive agent and a binder as necessary. As described above, in the present invention, since the conductive fine particles function as a conductive agent, when the negative electrode contains conductive fine particles and mesoporous carbon, it is not necessary to separately include a conductive agent.

The negative electrode active material is not particularly limited as long as it can occlude and release lithium ions. For example, metal lithium, lithium alloy, metal oxide, metal sulfide, metal nitride, and graphite And the like. Among these, graphite is preferably used. The negative electrode active material may be in the form of a powder or a thin film.
In addition, about the binder used for a negative electrode, the thing similar to the binder used for the said positive electrode can be used.
Moreover, since the formation method of a negative electrode is the same as the formation method of the said positive electrode, description here is abbreviate | omitted.

5). Other Members The lithium secondary battery of the present invention has a separator disposed between the positive electrode and the negative electrode. The separator used in the present invention is not particularly limited as long as it has a function of holding an electrolytic solution. For example, a porous film such as polyethylene and polypropylene, a nonwoven fabric such as a resin nonwoven fabric, and a glass fiber nonwoven fabric can be used. Can be mentioned.

Moreover, as the electrolytic solution used in the present invention, a nonaqueous electrolytic solution having a lithium salt and a nonaqueous solvent is usually used.
The lithium salt is not particularly limited as long as it is a lithium salt used in a general lithium secondary battery. For example, LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , Examples thereof include LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) _3, and LiClO ₄ .
The non-aqueous solvent is not particularly limited as long as it can dissolve the lithium salt. For example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane. 1,2-diethoxyethane, acetonitrile, propionitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone, etc. It is done. These non-aqueous solvents may be used alone or in combination of two or more. Moreover, room temperature molten salt can also be used as a non-aqueous electrolyte.

The positive electrode is usually formed on a positive electrode current collector.
The material for the positive electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include aluminum, SUS, nickel, iron, and titanium. Of these, aluminum and SUS are preferably used.

The negative electrode is usually formed on a negative electrode current collector.
The material of the negative electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include copper, stainless steel, and nickel. Of these, copper is preferably used.

  The shape of the battery case used in the present invention is not particularly limited as long as it can accommodate the positive electrode, the negative electrode, the separator, the positive electrode current collector, the negative electrode current collector and the like described above. , Cylindrical shape, square shape, coin shape, laminate shape and the like. Moreover, the lithium secondary battery of this invention has an electrode body comprised from a positive electrode, a separator, and a negative electrode. The shape of the electrode body is not particularly limited, and specific examples include a flat plate type and a wound type.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Example 1]
7.9 g of n-methylpyrrolidone (NMP) and 0.5 g of polyvinylidene fluoride (PVDF) were stirred with a propeller for 3 minutes. Next, 1.0 g of acetylene black (AB) (average particle size: 40 nm) was added, and the mixture was stirred with a propeller for 10 minutes. Next, 0.5 g of mesoporous carbon (MPC) (average particle diameter: 1 μm) was added, and the mixture was stirred with a propeller for 10 minutes. Next, 8.5 g of LiNiO ₂ was added and the mixture was stirred with a propeller for 10 minutes. In this way, a positive electrode forming paste was prepared.

The obtained positive electrode forming paste was applied onto a 15 μm thick Al current collector with a doctor blade at a basis weight of 12.8 mg / cm ² and dried at 80 ° C. for 30 minutes. Next, it pressed with the roll press machine so that an electrode density might be 2.9 g / cm < ³ >. And it stamped out so that an electrode area might be set to 2 cm < ² >, and the positive electrode was produced.

Using the obtained positive electrode and Li metal prepared as the negative electrode, a 2032 type coin cell was obtained. The separator was a microporous film made of polyethylene (PE) having a thickness of 25 μm. In the electrolytic solution, lithium hexafluorophosphate (LiPF ₆ ) was dissolved as a supporting salt at a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7. Things were used.

[Comparative Examples 1-3]
A coin cell was obtained in the same manner as in Example 1 except that the composition and basis weight of the positive electrode forming paste and the electrode density after pressing were adjusted as shown in Table 1. Table 1 also shows the film thickness of the positive electrode.

[Evaluation]
The energy density and rate characteristics of the coin cells obtained in Example 1 and Comparative Examples 1 to 3 were evaluated. First, the following SOC (state of charge) adjustment was performed, and then the energy amount and the capacity retention rate were measured.
(1) SOC adjustment Conditions for SOC adjustment are shown below.
(A) Charging: 15 mA / g for current-active material, voltage -4.3 V, CC mode (b) Pause: 5 minutes (c) Discharge: 15 mA / g for current-active material, voltage -3 0.0 V, CC mode (d) Pause: 5 minutes This (a) to (d) was performed for 3 cycles. Then, in order to evaluate an energy density and a rate characteristic, charging / discharging (cycle 1 and cycle 2) was performed on the following conditions, respectively.

(2) Measurement of energy (evaluation of energy density)
Cycle 1
(F) Charging: 15 mA / g for current-active material, voltage -4.3 V, CCCV mode, time-24 hours (g) Pause: 2 hours (h) Discharge: 15 mA / g for current-active material g, Voltage -3.0 V, CC mode (i) Pause: 5 minutes The amount of energy was calculated from the discharge curve of cycle 1, and the energy density (mWh / cc) was determined by the following formula. The obtained results are shown in Table 2.

(3) Capacity maintenance rate measurement (rate characteristic evaluation)
Cycle 2
(J) Charging: 15 mA / g for current-active material, voltage -4.3 V, CCCV mode, time -24 hours (k) pause: 2 hours (l) Discharge: 1500 mA / current for current-active material g, Voltage -3.0V, CC mode (m) Pause: 5 minutes

  Using the discharge capacity of cycle 2 and the discharge capacity of cycle 1 described above, the capacity retention rate (%) was obtained by the following formula. The obtained results are shown in Table 2.

  In Comparative Example 1, the rate characteristics were good, but the energy density was small. In Comparative Examples 2 and 3, the energy density was large, but the rate characteristics were lowered. On the other hand, in Example 1, energy density and rate characteristics were compatible.

It is a schematic sectional drawing which shows an example of the lithium secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Positive electrode collector 2 ... Positive electrode active material 3 ... Positive electrode layer 4 ... Negative electrode collector 5 ... Negative electrode active material 6 ... Negative electrode layer 7 ... Separator 8 ... Mesoporous carbon 9 ... Conductive fine particle

Claims (2)

A lithium secondary battery having a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a separator disposed between the positive electrode and the negative electrode,
A lithium secondary battery, wherein at least one of the positive electrode and the negative electrode contains mesoporous carbon and conductive fine particles having an average particle diameter smaller than the average particle diameter of the mesoporous carbon.   The lithium secondary battery according to claim 1, wherein the conductive fine particles are carbon black.

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