JP2000323126A - Nonaqueous electrolyte secondary battery and its charging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance discharge capacity and energy density by providing a Li ion conductive porous high polymer electrolyte in a negative electrode mix layer containing a carbon material and having a specific porosity and by including Li in the pores of the electrolyte in a charged state. SOLUTION: The porosity of a negative electrode mix layer is set to 10-50%. Thereby, the safety and the cycle characteristic of this battery are improved. The safety is further improved by setting the volume ratio of a Li ion conductive porous high polymer electrolyte within the pore parts of the negative electrode mix layer to 0.01-0.6. The weight of a positive electrode active material and the weight of a carbon material of a negative electrode are preferably determined so as to satisfy the following relationship: (the reversible capacity of the positive electrode)/(the reversible capacity of the negative electrode + the irreversible capacity of the negative electrode)>1. Thereby, Li is deposited on the negative electrode so that high capacity and high energy density can be accomplished. At that time, the electrically deposited Li is received in the pores inside the negative electrode mix layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery and a method for charging the same.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery using a non-aqueous electrolyte and lithium metal as a negative electrode (hereinafter referred to as a secondary battery)
Can be a high-voltage battery of 3 [V] or more, so that high energy density can be achieved. However, short-circuiting is likely to occur due to dendrite deposition of metallic lithium during charging, and the cycle life is short. There are drawbacks.

For this purpose, a resin film having a shutdown function as a separator using a carbon material such as graphite or carbon, in which dendrites of the metal lithium are unlikely to be deposited, using lithium cobalt oxide as a positive electrode, instead of lithium metal, is used. The so-called lithium-ion batteries used have been put to practical use.

In a lithium ion battery, the positive electrode is activated during charging.
Lithium ions dissolve into the electrolyte from the substance,
Lithium ions in the solution are absorbed by the carbon material that is the negative electrode active material.
Is stored. The opposite reaction occurs in discharge. For example, Kovar
Lithium tomate (LiCoO)_Two) In the positive electrode active material, Li
CoO_TwoFrom CoO_Two+ E^-+ Li⁺Based on the reaction
The theoretical capacity is 274 [mAh / g].
When charged to 00%, the potential becomes noble, and the reversibility
Therefore, in an actual battery, the upper limit voltage of charging is set to 4.1.
Up to 4.2 [V], a highly reversible region, that is,
Reversible capacity (half of theoretical capacity for lithium cobaltate)
Minutes). In addition, metal damage due to overcharging
In order to avoid the deposition of lithium, an excessive amount of
A negative electrode including a carbon material is used. In other words, conventional
In the pond, the active material of the positive electrode is Li _0.5CoO_TwoCharge until
Even if lithium is sucked into the negative electrode as it is,
70-80% of the theoretical capacity of the raw material (Li_aC₆, A <0.
The amounts of the positive and negative electrodes are adjusted so as to satisfy 70). here
The theoretical capacity of a carbon material is, for example, in the case of graphite, C
La LiC₆Capacity when charged to 372 mA
h / g].

[0005]

For this reason, in a lithium ion battery, in a normal use condition, metallic lithium hardly precipitates on the negative electrode, a short circuit does not occur, and a highly safe battery can be obtained. However, since the utilization rate of the carbon material is limited, the energy density of the negative electrode is low, and there is a problem that a battery having a large discharge capacity and a high energy density cannot be manufactured.

[0006]

According to the present invention, there is provided a nonaqueous electrolyte secondary battery comprising a negative electrode mixture layer containing a carbon material and having a porosity of 10% or more and 50% or less. The above problem is solved by providing a conductive polymer electrolyte and allowing metallic lithium to be present in pores of the lithium ion conductive porous polymer electrolyte in the negative electrode mixture layer in a charged state.

[0007] Here, the "charged state" is a state in which the positive electrode active material has released reversible lithium.

Further, the present invention is characterized in that the negative electrode is charged up to the deposition potential of metallic lithium.

Further, the present invention is characterized in that a lithium ion conductive porous polymer electrolyte is provided on the surface or / and in the pores of the positive electrode mixture layer.

The present invention is also characterized in that the lithium ion conductive porous polymer electrolyte occupies 0.1% or more and 60% or less of the pore volume of the negative electrode mixture layer.

Further, the present invention is characterized in that the positive electrode active material and the negative electrode active material satisfy the following relationship. (Reversible capacity of positive electrode active material [mAh]) / (Reversible capacity of carbon material [mAh] + Irreversible capacity of carbon material [mAh])
> 1 Further, the present invention is characterized in that in the charging method, intermittent charging is performed.

[0012]

Next, an embodiment of the present invention will be described with reference to the drawings.

The non-aqueous electrolyte secondary battery according to the present invention comprises a lithium ion conductive porous polymer electrolyte in a negative electrode mixture layer containing a carbon material and having a porosity of 10% or more and 50% or less. In the charged state, lithium metal is present in pores of the lithium ion conductive porous polymer electrolyte in the negative electrode mixture layer.

The negative electrode mixture layer of the nonaqueous electrolyte secondary battery according to the present invention comprises a solid portion containing a negative electrode active material and a binder,
The negative electrode mixture layer has pores, and the pores of the negative electrode mixture layer are provided with a lithium ion conductive porous polymer electrolyte swollen with an electrolytic solution. Therefore, this negative electrode mixture layer
Theoretical calculation of how much metallic lithium can be deposited was performed. The relationship between the volume of each part and the theoretical capacity will be described with reference to FIG.

In the use state of the battery, the porous polymer electrolyte is swollen with the electrolyte and the pores of the porous polymer electrolyte are filled with the electrolyte, but lithium metal can be deposited. The vacancies were vacancies other than all solid portions obtained by summing the negative electrode active material of the negative electrode mixture layer, the binder, and the polymer portion of the porous polymer electrolyte swollen with the electrolytic solution. That is, lithium was able to precipitate also in the pores of the porous polymer electrolyte filled with the electrolytic solution.

However, each symbol is defined as follows.

V: Total volume of negative electrode mixture layer / [cc] 1-x: Volume ratio of solid portion of negative electrode mixture layer, but 0.1%
1 ≦ x ≦ 0.5 x: volume ratio of pore portion of negative electrode mixture layer (therefore, porosity of negative electrode mixture layer is 100 ×%) (1-x) V: solid portion of negative electrode mixture layer X / volume of void portion of negative electrode mixture layer / [cc] a: Volume ratio of carbon material in solid portion of negative electrode mixture layer, provided that 0 <a ≦ 11-a: Volume ratio of binder in solid portion of negative electrode mixture layer a (1-x) V: volume of carbon material of negative electrode mixture layer / [c
c] (1-a) (1-x) V: Volume of binder in negative electrode mixture layer / [cc] b: Volume ratio of porous polymer electrolyte among pores of negative electrode mixture layer, 0 <b <11-b: Volume ratio of pores in which no porous polymer electrolyte is present among pores of negative electrode mixture layer bxV: Porous of pores of negative electrode mixture layer Volume of polymer electrolyte / cc (1-b) xV: Volume of pores where no porous polymer electrolyte is present / [cc] among pores of negative electrode mixture layer c: Vacancy of negative electrode mixture layer The volume ratio of the polymer of the porous polymer electrolyte present in the pore portion, where 0.01 <c <0.6 1-c: the porous polymer electrolyte present in the pore portion of the negative electrode mixture layer Xb (1-c) V: volume of polymer / [cc] xbc of the porous polymer electrolyte present in the pores of the negative electrode mixture layer : A porous polymer electrolyte present vacancy part of the negative electrode mixture layer, the hole portion of the volume / [cc] (1 + bc) xV: Total pore portion of the negative electrode mixture layer volume /
[Cc] y: Theoretical capacity of negative electrode / [mAh] y _Li : Theoretical capacity of lithium deposited in pores of the negative electrode mixture layer / [mAh] y _C : Theoretical capacity of carbon material / [mAh] The theoretical capacity per unit volume of the material is 800
[MAh / cc], and the theoretical capacity per unit volume of lithium is 2062 [mAh / cc].

FIG. 1 shows the relationship between the volume ratio (x) of the solid portion of the negative electrode mixture layer and the theoretical capacity (y) of the negative electrode.

In FIG. 1, a straight line AB indicates the theoretical capacity (y _C ) of the carbon material, and y = −800axV + 800aV.
Is represented by At point A (x = 1, that is, when the negative electrode mixture layer is only empty), the volume of the carbon material is 0 [cc], so the theoretical capacity is 0 [mAh], and at point B (x =
0, ie, when there are no pores in the negative electrode mixture layer), the volume of the carbon material is aVcc, and the theoretical capacity is 800 aV [m
Ah]. That is, the straight line AB indicates the upper limit of the charge amount at which charging is performed by intercalating lithium into the carbon material. In FIG. 1, ABC
The region surrounded by is the portion based on the theoretical capacity of the carbon material, and varies depending on the ratio x of the solid portion of the negative electrode mixture layer and the volume ratio a of the carbon material in the solid portion of the negative electrode mixture layer.

In FIG. 1, a hatched portion 1 and a hatched portion 2
Represented by the sum of the total theoretical capacity of the theoretical capacity (y _C) and the theoretical capacity of the lithium of the carbon material (y _max) is, y _max
= 2062 (1-cb) xV-800axV + 800a
It is represented by V.

In FIG. 1, the area surrounded by ABE is
The theoretical capacity of lithium in the case where lithium is deposited in the void portion where the porous polymer electrolyte does not exist among the void portions of the negative electrode mixture layer is shown. The point E changes depending on the volume ratio b of the porous polymer electrolyte among the pores of the negative electrode mixture layer, and matches B = 0 when b = 0, that is, when the porous polymer electrolyte does not exist, When b = 1, that is, when all the vacancies in the negative electrode mixture layer are filled with the porous polymer electrolyte, the value matches A.

In FIG. 1, the region surrounded by the EBD indicates the porous solid polymer electrolyte present in the pores of the negative electrode mixture layer. Of these, the region surrounded by EBF is the polymer portion of the porous solid polymer electrolyte, and the region surrounded by FBD is the pore portion of the porous solid polymer electrolyte. The position of the point F changes depending on the volume ratio c of the polymer of the porous polymer electrolyte present in the pores of the negative electrode mixture layer. For example, when c = 0.01, the point becomes F1, and c
In the case of = 0.6, it becomes F2.

In the non-aqueous electrolyte secondary battery according to the present invention, the region where lithium can be deposited is the portion shown by hatching in FIG. That is, straight line x = 0.1, straight line x = 0.
5, the region surrounded by the straight line AB and the straight line EB, ie, GH
A region surrounded by LK (a void portion of the negative electrode mixture layer where no porous polymer electrolyte is present) and a straight line x = 0.
1, a region surrounded by a straight line x = 0.5, a straight line AB, and a straight line DB, that is, a region surrounded by IJNM (porous portion 2 of a porous polymer electrolyte). By using this region, the capacity can be increased as compared with the conventional metal lithium secondary battery, and the capacity can be increased as compared with the lithium ion secondary battery.

Various experiments were conducted by changing the porosity of the negative electrode mixture layer (in other words, the volume ratio of the pores in the negative electrode mixture layer). As a result, the porosity of the negative electrode mixture layer was 10% or more. 5
It was found that when the content was 0% or less, excellent safety and cycle characteristics were exhibited. When the porosity was 20% or more and 40% or less, it was found that the cycle characteristics and the safety were further excellent, and in addition, the high rate discharge characteristics were also excellent.

This is because the bond between the graphites was strong and the electric conductivity was sufficient, and the porous polymer electrolyte was sufficiently present in the negative electrode. Was performed easily.

In the nonaqueous electrolyte battery according to the present invention,
By providing the lithium ion conductive porous polymer electrolyte in the pores or on the surface of the positive electrode mixture layer, it is possible to further improve the characteristics of the battery. Also, by charging the negative electrode to the deposition potential of metallic lithium, the capacity of the battery can be further increased.

Further, when the volume ratio of the porous polymer electrolyte in the pores of the negative electrode mixture layer is from 0.01 to 0.6, it is effective for improving the safety of the battery. To 0.
A time of 2 was more effective, more preferably a time of 0.05 to 0.13.

In the nonaqueous electrolyte battery according to the present invention,
The weight of the positive electrode active material and the weight of the carbon material of the negative electrode were determined so as to satisfy the following equation. (Reversible capacity of positive electrode [mAh]) / (Reversible capacity of negative electrode [m
Ah] + irreversible capacity of the negative electrode [mAh])> 1 Here, the reversible capacity of the positive electrode is not only a capacity in a chargeable / dischargeable area but also a capacity in a good cycle characteristic area. This means that when trying to release all the lithium in the cathode active material, the cathode active material becomes structurally unstable,
The reversibility decreases and the capacity decreases with the cycle. Therefore, it is preferable to use the positive electrode active material in a region (reversible capacity) where reversibility is high and a practical current can be obtained.

Next, the theoretical reversible capacity of the carbon material is C
To LiC ₆ from 372 [mA]
h / g]. Although the irreversible reaction is considered to slightly change depending on the state of the carbon material, it is shown here as the irreversible capacity of the carbon material. This value can be represented by the difference between the amount of charge in the first cycle immediately after the battery is assembled and the amount of charge in the second cycle. However, after charging in the first cycle, the discharge rate was 0.1 C up to a battery voltage of 2.75 [V].
It must be discharged with the following constant current.

A battery provided with a positive electrode and a negative electrode determined by the above formula achieves higher capacity and higher energy density than conventional batteries by depositing metallic lithium on the negative electrode. However, since the deposition of metallic lithium tends to become dendrites, the capacity is reduced due to short-circuiting and cycling. In addition, since the desorption of metallic lithium can be reduced, cycle life characteristics can be improved.

In order to deposit lithium in the pores inside the negative electrode mixture layer, a charging method having two stages, a first stage for performing charging with a constant current and a second stage for intermittent charging, is preferable. . The first stage corresponds to charging for intercalating into carbon, and the second stage corresponds to electrodeposition charging of lithium. In the second stage of depositing lithium, intermittent charging is preferably performed. Here, the intermittent charging is a charging method in which a charging period and a pause period are alternately repeated. This pause period can include a discharge period. In other words, dendrites in the negative electrode can be suppressed by a power outage or discharge during the idle period, and diffusion of lithium ions in the electrode can be promoted, so that metal lithium can be deposited relatively uniformly in the electrode.

The method for forming a porous polymer electrolyte in the pores of the negative electrode mixture layer is as follows. The polymer swelling in the electrolytic solution is dissolved in an organic solvent to prepare a polymer paste, and the polymer paste is impregnated into the negative electrode mixture layer. The polymer paste is not compatible with the polymer and is not compatible with the organic solvent. The organic solvent in the polymer solution was extracted with a soluble liquid. This allowed the porous polymer to fill the pores of the electrode and the electrode surface. Here, as a liquid compatible with the organic solvent,
Water can be used.

Although a porous polymer electrolyte may be present on the surface of the negative electrode mixture layer, lithium dendrite is likely to be generated during charging.

The formation of the porous polymer electrolyte is applicable to the positive electrode, and is preferably performed also for the positive electrode in order to improve safety. The porous polymer becomes a lithium ion conductive porous polymer by swelling with the electrolytic solution, and can exhibit high performance excellent in charge / discharge characteristics at a higher rate than a conventional solid electrolyte.

In addition, the amount of free electrolyte near the active material can be reduced, so that safety can be improved. These positive and negative electrodes can be combined with a conventional separator to form a battery element.However, the conventional separator itself has poor ion conductivity and electron conductivity, and acts to inhibit the movement of lithium ions. Show.
Therefore, it is preferable to use a separator made of a lithium ion conductive porous polymer instead of the conventional separator.

This porous lithium ion conductive polymer separator is produced by applying the above-mentioned polymer paste in the form of a film on a sheet glass, then pouring the sheet glass and the paste into water and extracting an organic solvent. it can. When a battery element is prepared by combining the lithium ion conductive porous polymer separator with the positive and negative electrodes and an electrolyte is added, the lithium ion conductive porous polymer exists between the positive and negative electrode active materials. I can say that. The term “between the positive and negative electrode active materials” includes the inside of the hole of the electrode, the surface of the electrode, and between the positive and negative electrodes.

In the conventional battery, a microporous film made of polyethylene or polypropylene is used as a separator between the positive electrode and the negative electrode. However, in the battery according to the present invention, a porous polymer electrolyte is used between the positive electrode and the negative electrode instead of the separator. Therefore, if a porous polymer electrolyte having a sufficient thickness is provided, a battery that does not require a conventional separator having no electronic conductivity can be manufactured.

It is considered that the shutdown mechanism of the porous polymer electrolyte is activated by an increase in temperature, similarly to the conventional separator. As a result of various experiments, it has been clarified that the ionic conductivity of the porous polymer electrolyte decreases when the temperature rises to a certain temperature, which contributes to the safety of the battery. In addition, the conventional separator itself is an insulator having no ionic conductivity and causes resistance to ionic conduction.However, since the porous polymer electrolyte has excellent ionic conductivity, it has excellent high-rate discharge characteristics. Batteries can be manufactured.

From the above, it is possible to design a battery in which the utilization rate of the conventional carbon material is about 70% of the theoretical capacity and the utilization rate is improved by the present invention. In other words, the conventional battery design was revised, the carbon material of the negative electrode was reduced,
By increasing the amount of the positive electrode active material and using a porous polymer electrolyte, electrodeposition of lithium metal becomes possible.
The portion of the metallic lithium involved in the discharge contributes to an increase in capacity. In addition, by combining the intermittent charging method, the ratio contributing to the discharge of metallic lithium increases, and more favorable results can be obtained.

As the porous polymer to be filled into the surface of the electrode and into the pores, polyvinylidene fluoride (PVd)
F), polyethylene oxide, polyether such as polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride, polyvinylidene chloride, polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinyl pyrrolidone, polyethylene imine, Polybutadiene, polystyrene, polyisoprene and derivatives thereof may be used alone or in combination.
Further, a polymer obtained by copolymerizing various monomers constituting the above polymer may be used.

For preparing the porous polymer, water, an acidic aqueous solution such as phosphoric acid, acetic acid, hydrochloric acid, or nitric acid; an alkaline aqueous solution such as lithium hydroxide or sodium hydroxide; an alcohol such as ethanol or methanol; A mixed solution of alcohol and water may be used.

As the solvent of the non-aqueous electrolyte, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxy Ethane, 1,
Polar solvents such as 2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolan, and methyl acetate, and mixtures thereof may be used.

Examples of the lithium salt dissolved in the solvent of the non-aqueous electrolyte include LiPF ₆ , LiBF ₄ , LiAsF ₆ , and LiCl.
O ₄ , LiSCN, LiI, LiCF ₃ SO ₃ , LiCl, Li
Lithium salts such as Br and LiCF ₃ CO ₂ and mixtures thereof may be used.

[0044] The positive electrode material serving as a lithium as capable of absorbing and releasing compounds, as the inorganic compound, composition formula Li _B M
O ₂ or Li _C M ₂ O ₄ (where M is a transition metal, 0 ≦
B ≦ 1.0 ≦ C ≦ 2), a composite oxide, an oxide having tunnel holes, and a metal chalcogenide having a layered structure can be used. As a specific example, LiC
oO ₂ , LiNiO ₂ , NiOOHLi, LiMn ₂ O ₄ , Li
₂ Mn ₂ O ₄ , MnO ₂ , FeO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , Ti
O ₂ and TiS ₂ are mentioned. Examples of the organic compound include a conductive polymer such as polyaniline. Further, regardless of the inorganic compound or the organic compound, the above-mentioned various active materials may be used as a mixture. The carbon material used for the negative electrode active material may be graphite, graphitizable carbon, non-graphitizable carbon, and low-temperature firing. Carbon materials such as carbon, graphitized MCMB, graphitized mesophase pitch-based carbon, and natural graphite may be used. Moreover, you may use these mixtures.
Further, in addition to the carbon material, an element which forms an alloy with lithium may be added to the negative electrode.

As a material of the battery case, a metal case such as aluminum, magnesium, titanium, iron or the like may be used, or a metal alloy case such as aluminum alloy or titanium alloy may be used. Further, a case using both an aluminum foil and a resin film may be used. Specific examples of the resin film include polyprolylene, polyethylene, and fluororesin, and any resin film can be used as long as it does not easily swell with an electrolytic solution and does not easily react.

[0046]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.

Example 1 Non-aqueous electrolyte secondary batteries (A) and (B) were manufactured according to the following procedure.

First, a battery (A) according to the present invention was manufactured. The positive electrode was prepared by mixing 42.5 wt% of lithium cobaltate, 3 wt% of acetylene black, 4.5 wt% of polyvinylidene fluoride (PVdF), and 50.0 wt% of n-methylpyrrolidone (NMP) with a width of 100%.
[Mm], a length of 550 [mm] and a thickness of 10 [μm] were applied to both surfaces of an aluminum thin film, dried at 150 [° C] and evaporated to produce NMP. The positive electrode was pressed to reduce the thickness of the electrode from 370 [μm] to 180 [μm], and was cut into a size having a width of 20 [mm] and a length of 550 [mm].

The negative electrode was made of 36% by weight of graphite, PVd
F4 wt% and NMP60 wt% mixed active material paste with width 80 [mm], length 550 [mm], thickness 10
It was applied to both sides of a [μm] copper foil, dried at 150 ° C. and evaporated to produce NMP.

Subsequently, the negative electrode was impregnated with a porous polymer. 10% by weight of polyacrylonitrile (PAN) and NM
A polymer solution mixed with 90% by weight of P was applied and allowed to stand for 2 minutes. After allowing the polymer solution to penetrate into the pores of the negative electrode mixture layer, it was immersed in water to extract NMP, and the The PAN is made porous. This negative electrode was dried at 100 ° C. for 25 minutes to remove water. Press this negative electrode to a thickness of 13
0 [μm], the porous polymer impregnated again, the electrode thickness was 165 [μm], width 20 [mm],
It was cut to a size of 550 [mm] in length.

The positive electrode contains an amount of active material that gives a charge of 500 mAh when charged to a battery voltage of 4.15 [V], and the graphite in the negative electrode contains electricity when charged to LiC _6. The coating amount was adjusted so that the amount became 400 [mAh].

After the element was prepared by combining these positive and negative electrodes, the element was inserted into a stainless case having a height of 45 mm, a width of 23 mm, and a thickness of 6 mm. Further, an electrolytic solution in which 1 mol / l of LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate having a volume ratio of 1: 1 was injected, and a nominal capacity of 450 [m
Ah] of the battery (A). Here, the amount of charge of the positive electrode is 500 [mAh], and the nominal capacity is 450 [m
Ah], and this difference, about 50 [mAh], is the irreversible capacity generated in the negative electrode active material.

Next, a battery (B) was manufactured as a comparative example.
The positive electrode used was the same as the battery (A). The negative electrode was manufactured without performing the porous polymer impregnation treatment. That is, graphite 36wt%, PVdF4wt%, NMP60w
The active material paste mixed with t% is applied to a copper foil having a width of 80 [mm], a length of 550 [mm], and a thickness of 10 [μm].
After drying at 50 ° C. to evaporate the NMP,
[Μm], width 20 [mm], length 55
The negative electrode was cut into a size of 0 [mm].

These positive and negative electrodes, a thickness of 25 [μm],
After producing an element by combining with a polyethylene separator having a width of 20 [mm], a height of 45 [mm] and a width of 23 are prepared.
[Mm] and a thickness of 6 [mm]. Further, an electrolytic solution in which 1 mol / l of LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate having a volume ratio of 1: 1 was injected, and a nominal capacity of 450 mol.
[MAh] A battery (B) was manufactured.

The battery (A) was provided with a porous polymer electrolyte in the pores of the negative electrode mixture layer, and employed the following charging method. In the intercalating region of the carbon material, 45
The battery was charged at a constant current of 0 [mA] (corresponding to 1 C). Thereafter, intermittent charging was performed in the metal lithium deposition region. In this intermittent charging, the charging current is 225 [mA] (0.
5 seconds), 2 seconds charging period, blackout (2 seconds), discharging (1 second)
A combination of a pause period and a discharge period constituted by a power outage (2 seconds) is alternately repeated. The discharge current during the discharge period was 100 [mA]. When the amount of charge of the positive electrode active material reached the designed value due to intermittent charging, charging was completed.

The battery (B) does not contain a porous polymer electrolyte in the pores of the negative electrode mixture layer, and has a polyethylene separator. The charging was performed at the same constant current / constant voltage as before. FIG. 2 shows the relationship between the number of cycles and the discharge capacity of the batteries (A) and (B) having repeated charge / discharge cycles. FIG. 2 shows that the battery (A) having the porous polymer electrolyte in the pores of the negative electrode mixture layer has improved battery cycle characteristics.

The reason for this is that the porous polymer electrolyte suppresses the dendrite conversion of metallic lithium and the elimination of metallic lithium, the fact that the concentration of electric current is less likely to occur, and the relatively low concentration of metallic lithium. It is considered that the reversibility was improved due to the uniform precipitation.

Next, batteries (A) and (B) charged to a voltage of 4.15 V were subjected to a short-circuit test. In the external short-circuit test, the battery was short-circuited via a resistor (200 A / 50 mV). In the internal short-circuit test, the center of the battery placed horizontally on a wooden board
A nail having a diameter of 2.5 [mm] and a length of 70 [mm] was penetrated. In each test (1), the battery was short-circuited at room temperature, and in test (2), the battery was heated to 60 ° C. and then short-circuited. Five short-circuit tests were performed for each of the test conditions. The test results are shown in Table 1.

[0059]

[Table 1]

As a result of Table 1, it was found that the battery (A) according to the present invention did not rupture at all and was highly safe. On the other hand, the conventional battery (B) is particularly dangerous at 60 ° C. This is probably because metallic lithium was precipitated in a dendrite shape. On the other hand, in the battery (A), the precipitation of dendrite was suppressed, and it is considered that the safety was improved.

[0061]

As described above, the nonaqueous electrolyte secondary battery according to the present invention has a higher capacity than the conventional lithium ion battery by the amount of lithium metal involved in charge and discharge. Further, by allowing the porous polymer electrolyte to be present in the pores of the negative electrode mixture layer,
The generation of lithium dendrite can be suppressed, and safety can be improved. Further, the reversibility of metallic lithium can be improved, and the cycle characteristics of the battery can be significantly improved.

In addition to this, by employing the intermittent charging method, the rate of contribution to the discharge of metallic lithium increases, and the capacity of the battery can be increased. According to the present invention, a high-capacity negative electrode using metallic lithium can be manufactured, and a higher-capacity battery than a conventional battery can be manufactured. In addition, by using a porous polymer electrolyte, discharge at a higher rate becomes possible than in the case of using a conventional solid electrolyte having no pores, and a high-performance battery can be manufactured.

[Brief description of the drawings]

FIG. 1 is a view showing the relationship between the volume of each part of a negative electrode mixture layer and the theoretical capacity.

FIG. 2 is a diagram showing the relationship between the number of cycles and the discharge capacity of batteries (A) and (B).

[Explanation of symbols]

1 pores in the negative electrode mixture layer where no porous polymer electrolyte is present 2 pores in the porous polymer electrolyte

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H014 AA02 BB11 EE02 EE05 EE08 EE10 HH01 HH02 HH04 5H029 AJ03 AK03 AL06 AL07 AL08 AM03 AM04 AM05 AM07 AM16 CJ16 HJ09 HJ19

Claims (6)

[Claims] 1. A negative electrode mixture layer containing a carbon material and having a porosity of 10% or more and 50% or less, comprising a lithium ion conductive porous polymer electrolyte, A non-aqueous electrolyte secondary battery comprising lithium metal in pores of a lithium ion conductive porous polymer electrolyte. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode is charged to a deposition potential of metallic lithium. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein a lithium ion conductive porous polymer electrolyte is provided on the surface and / or in the pores of the positive electrode mixture layer. 4. The non-porous lithium ion conductive porous polymer electrolyte as claimed in claim 1, wherein the pore volume of the negative electrode mixture layer is 0.1% or more and 60% or less. Water electrolyte secondary battery. 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material and the negative electrode active material satisfy the following relationship. (Reversible capacity [mAh] of positive electrode active material) / (reversible capacity [mAh] of carbon material + irreversible capacity [mAh] of carbon material)> 1 6. The battery according to claim 1, wherein the battery is intermittently charged.
6. The method for charging a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5.