JPH06231766A - Negative electrode for non-aqueous secondary battery - Google Patents

Abstract

PURPOSE:To provide a negative electrode, which is good on an output characteristic and a low temperature characteristic, for non-aqueous secondary battery. CONSTITUTION:In a porous negative electrode mainly consisting of carbonaceous material grains, the carbonaceous material grain mainly consists of a graphitic grain whose spacing d002 of a carbon network face is less than 0.337nm. The porous negative electrode whose percentage of the volume occupied by the holes, whose porosity is 10% or more and less than 60% while its hole diameter ranges from 0.1mum to 10mum, to the whole porous volume is 80% or more is used. Therefore, a high capacity non-aqueous secondary battery, which is good on an output characteristic and a low temperature characteristic, can be obtained by employing this porous negative electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode composed mainly of carbonaceous material particles, a negative electrode composed of a chargeable / dischargeable positive electrode and an organic solvent-based electrolytic solution, and particularly graphite particles. Of the negative electrode structure.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of portable electronic devices,
A light-weight, small-sized and high-capacity secondary battery has been demanded as the power source. It is known that high capacity is obtained by using metallic lithium as a negative electrode of a non-aqueous secondary battery using an organic solvent as an electrolytic solution. However, in the metallic lithium negative electrode,
Internal short circuit due to dendritic lithium (lithium dendrite) generated by repeated charging / discharging and reduction in current efficiency are major obstacles to commercialization of high-capacity and long-life batteries. Also, in the case of a battery using metallic lithium, when the battery becomes a high temperature state due to heat generation at the time of a short circuit, because of the high reactivity of metallic lithium, there is a risk of ignition and rupture of the battery can, which is also a great safety point. I have a problem.

For the purpose of improving such drawbacks, as a negative electrode used in a non-aqueous secondary battery using an organic solvent as an electrolytic solution,
Attention has been focused on carbonaceous materials that can electrochemically store and release lithium ions. As a carbonaceous material used for such a negative electrode, various materials have been studied, from a material containing a large amount of amorphous material such as activated carbon to a material having a well-developed crystal represented by graphite.

A carbonaceous material containing a large amount of amorphous material usually has a very large surface area (S _A > 100 m ² / g) and a wide spacing between carbon mesh planes (d ₀₀₂ > 0.337 nm), and crystallization progresses. It is not. Since this type has a large amount of adsorbed on the surface, the amount of lithium absorbed per carbon atom is large, but the current efficiency is low and the cycleability is also low. A carbonaceous material having a so-called pseudo-graphite structure, in which the carbon network surface has grown to some extent but is not completely graphitized, is a lithium-based material that has been conventionally used in metal lithium negative electrodes and lithium alloy negative electrodes. Can store and release.

On the other hand, graphite has a narrow spacing between carbon net planes (d ₀₀₂ <0.337 nm), and is a growth of crystallites in the carbon net plane direction and the laminating direction of the net plane. It is known that such a carbon material intercalates both cations and anions between the carbon network planes to form an intercalation compound, and is considered to be applied as a conductive material, an organic synthesis reaction catalyst or a battery. Has been. The use of such graphite as the negative electrode of a battery is disclosed in JP-A-57-2080.
79, JP-A-58-192266, JP-A-59-143280, JP-A-60-54181, JP-A-60-182670, and JP-A-60-.
221973, JP 61-7567, JP 1-311565, and JP 4-171677.
It is proposed in the Gazette and the like.

In these patents, propylene carbonate (hereinafter abbreviated as PC) as an organic solvent that can be used,
Tetrahydrofuran (hereinafter abbreviated as THF), γ-
Butyrolactone (hereinafter abbreviated as γ-BL), 1,2
-Dimethoxyethane (hereinafter abbreviated as DME), sulfolane, ethylene carbonate (hereinafter abbreviated as EC) and the like are described. Examples include LiCl
PC using O ₄ or LiBF ₄ as a typical solvent
Alternatively, THF is used. In the electrolytic solution using PC as a solvent, J. Electrochem. Soc. , 117
P. 222 (1970), the intercalation compound in which lithium ions are occluded in graphite has a high reactivity with an organic solvent and cannot decompose the electrolytic solution to form a negative electrode, but PC / EC, PC / DME, Or γ
When an electrolytic solution suitable for graphite such as a mixed solvent system containing -BL is used, the negative electrode has a large amount of stored lithium.

However, in a porous negative electrode composed mainly of carbonaceous material particles, the internal resistance increases due to repeated charging / discharging cycles, high rate discharge cannot be performed, and the capacity remarkably decreases due to discharge at low temperature. There was a problem.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention An object of the present invention is to provide a negative electrode having a specific void structure, which has a high utilization factor and a high packing density for a high capacity secondary battery, is excellent in cycleability, and is excellent in output characteristics. Is to provide.

[0009]

In order to solve the above problems, the inventors of the present invention have made extensive studies on the void structure of the carbonaceous material particles and the negative electrode used for the porous negative electrode, and found that the negative electrode having a specific void structure was used. It has been found that, by using it, the secondary battery has a high utilization factor for high capacity, is excellent in cycleability, and is excellent in high-rate discharge characteristics and low-temperature characteristics, and has completed the present invention.

That is, according to the present invention, in a negative electrode for a non-aqueous secondary battery mainly composed of carbonaceous material particles, the carbonaceous material particles are mainly graphite having a carbon mesh plane spacing d ₀₀₂ of less than 0.337 nm. The porosity of the negative electrode for a non-aqueous secondary battery composed of particles is 10 to 60%, and the volume occupied by pores in the pore diameter range of 0.1 to 10 μm is 80% with respect to the total pore volume. The present invention provides a negative electrode for a non-aqueous secondary battery characterized by the above.

The present invention will be described in detail below. The graphite particles having a carbon mesh plane spacing d ₀₀₂ of less than 0.337 nm as referred to in the present invention is a carbonaceous material having a well-developed graphite structure in which carbon mesh plane layers are regularly stacked. The carbonaceous material has various structures depending on its starting material and its treatment (manufacturing) method. However, in any material, the interplanar spacing d ₀₀₂ of the carbon mesh plane becomes small due to the high temperature treatment, and the laminated thickness Lc of the carbon mesh plane is Graphite tends to be large, and graphite has the smallest facet spacing d ₀₀₂ = 0.3354 nm. This d
The decrease of ₀₀₂ and the increase of Lc, that is, the easiness of graphitization greatly depends on the starting material, and the high temperature treatment (up to 300
It is classified into a graphitizable substance that easily graphitizes at 0 ° C. and a non-graphitizable substance that does not easily graphitize (d ₀₀₂ does not easily decrease). When graphitizing this carbonaceous material, in addition to the above d ₀₀₂ and Lc, the true density,
The specific surface area, electric resistance, etc. also change greatly, but the interplanar spacing is particularly important for the formation of intercalation compounds.

D ₀₀₂ used in the present invention is 0.337n
Graphite particles less than m are artificial graphite, naturally occurring graphite,
Any of these may be used, or a mixture of both may be used. Artificial graphite is generally a graphitizable substance typified by petroleum pitch, coal tar pitch, pyrolytic carbon, needle coke, fluid coke, mesophase microbeads, condensed polycyclic hydrocarbon, etc.
It can be obtained by heat treatment at 0 ° C. or higher, more preferably 2800 ° C. or higher.

The carbonaceous material of the present invention has a d ₀₀₂ of 0.337.
Those having a size of less than nm have a high lithium absorption amount (utilization rate) per carbon atom and are particularly effective, and have a d ₀₀₂ of 0.337 nm.
The above is not preferable because the current efficiency is lowered and the utilization rate is lowered. Although the current efficiency may be somewhat lowered, the negative electrode of the present invention can be produced by using the above-mentioned graphite particles and other carbonaceous materials in combination at 50% by weight or less. Examples of such carbonaceous materials include coke, acetylene black, activated carbon, carbide of mesophase microbeads, flue coke, gilsonite coke, needle coke and the like.
Further, so-called milled fiber obtained by crushing carbon fiber or graphite fiber can also be used.

The graphite particles used in the present invention include 95 particles having a particle diameter in the range of 0.1 to 100 μm.
Particles containing 95% by weight or more of particles contained in the range of 1% to 50 μm are preferably used. 0.
When the particles having a particle size of less than 1 μm are included, the surface area is increased, the amount of side reaction occurring on the surface is increased, the current efficiency is reduced, and the battery capacity is reduced. Also, 100 μm
If coarse particles exceeding the above range are contained, the void structure of the electrode described later becomes unsuitable, and the capacity decreases due to charge / discharge cycles.

The layer thickness Lc on the carbon network surface of the graphite particles used in the present invention is not particularly limited, but Lc is also an important parameter for graphitization and particle shape, and is preferably 30 nm or more, more preferably 50 nm.
The above is good. If it is less than 30 nm, the amount of lithium absorbed and released (utilization rate) becomes low, which is not preferable. The surface area is also not particularly limited, but if the surface area is large, side reactions are more likely to occur, so 50 m ² / g or less is preferable, preferably 25 m ² / g or less, more preferably 1 m ² / g or less.
5 m ² / g is good. However, if it is less than 1 m ² / g, the area of the interface where Li ions come in and out becomes small, and the current density per electrode active material becomes large, which is not preferable.

The porosity and the pore volume of the negative electrode in the present invention are values determined by a mercury porosimetry porosimeter.
From the viewpoint of increasing the packing density of the carbonaceous material and increasing the battery capacity, it is thought that this porosity should be kept low. However, in the negative electrode with carbonaceous material particles having a porosity of 60% or less, low temperature discharge There is a problem that the battery capacity decreases at high time or high rate discharge.

However, the pore diameter of the negative electrode is 0.1 to 10 μm.
When the negative electrode of the present invention in which the percentage of the void volume in the range of m to the total void volume is 80% or more, the void ratio is 6%.
It has been found that even with a negative electrode of 0% or less, the battery capacity does not easily decrease during low temperature discharge or high rate discharge. The reason for this is not clear, but in the electrode where the pore size is small, the products formed by the side reaction during charging in the initial charge / discharge cycle are attached to the surface or in the electrolyte solution near the surface, and there are fine holes. It is presumed that it may be blocking the movement of lithium ions by blocking. Also, the pore diameter is 10 μm
If the number of the above-mentioned portions is large, the capacity may decrease due to charge / discharge cycles, probably because the liquid retaining property of the electrolytic solution deteriorates. From such a viewpoint, the pore diameter is 0.1 to 10.
If the percentage of the volume occupied by the pores in the range of μm to the total volume of the pores is 80% or more and the porosity is 10 to 60% for the negative electrode, the battery capacity will decrease during low temperature discharge or high rate discharge. The secondary battery has a large capacity without causing
Preferably, the volume ratio of the pores in the pore diameter range of 0.5 to 10 μm with respect to the total pore volume is 80% or more and the porosity is 10 to 50%, more preferably the pore diameter is 0.5 to The percentage of the volume occupied by the pores in the range of 10 μm to the total pore volume is 90% or more and the porosity is 25 to
40%.

In a battery in which an electrode is packed in a case with a limited volume, increasing the packing density of the electrode active material by suppressing the porosity of the negative electrode greatly affects the capacity of the battery. When the electrode is mainly composed of the graphite particles of the present invention, a current collector, a composite material, etc. may be used, and the current collector is C
u, Ni, etc. are mixed materials such as Teflon, polyethylene,
Polymers such as nitrile rubber, polybutadiene, butyl rubber, polystyrene, styrene / butadiene rubber, polysulfide rubber, nitrocellulose, cyanoethyl cellulose and acrylonitrile, vinyl fluoride, vinylidene fluoride, chloroprene, etc. are added to the carbonaceous material particles in an amount of 20. weight%
Used in the range of less than.

As a method of forming this electrode, a method of mixing an electrode active material and an organic polymer and compression molding, a method of dispersing the electrode active material in a solvent solution of the organic polymer, followed by coating and drying, and an organic polymer After the electrode active material is dispersed in the combined aqueous or oily dispersion, a method of coating and drying is known, but it is not particularly limited, but it is not preferable if the distribution of the binder becomes nonuniform, and thus it is preferable. Is a method of dispersing an electrode active material in an aqueous or oily dispersion of an organic polymer and then coating and drying, more preferably using a non-fluorine-containing organic polymer containing particles of 0.5 μm or less in the organic polymer. Good.

In the method of coating and drying, voids are generated in the part where the dispersion is removed, and the packing density of the electrode active material tends to be low. As a method of eliminating such a drawback, the solid content of the coating liquid is increased and the proportion of the dispersion is reduced to increase the packing density of the electrode active material at the time of coating drying, or if necessary, the coating. The dried electrode may be pressed. However, it is needless to say that proper pressing is important because the pore distribution of the present invention becomes unsuitable if too much pressing is performed.

The electrolytic solution of the present invention cannot be used with a propylene carbonate single solvent type electrolytic solution because it is decomposed by the graphite negative electrode as described above, but is not particularly limited as long as it is used for the graphite negative electrode. Not a thing. For example, carbonates, ethers, ketones,
Examples thereof include nitriles, amides, sulfone compounds, esters, and the like. Further, two or more kinds of these solvents may be mixed and used. Among these, γ-
It is preferable to use a mixed solvent electrolyte containing 10% or more of BL. Examples of the organic solvent to be combined with γ-BL include carbonates, ethers, ketones, nitriles, amides, sulfone compounds, esters, aromatic hydrocarbons and the like. Further, two or more kinds of these solvents may be mixed and used. Among these, carbonates, ethers, ketones, nitriles, esters and the like are preferable, and carbonates are more preferably used.

Specific examples include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, dimethoxyethane, tetrahydrofuran,
2-methyl-tetrahydrofuran, anisole, 1,4
-Dioxane, 4-methyl-2-pentanone, cyclohexanone, acetonitrile, propionitrile, butyronitrile, diethyl carbonate, dimethylformamide, dimethylacetamide, dimethylsulfoxide, sulfolane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, Examples thereof include ethyl propionate, and among these, PC and EC are preferably used.

The electrolyte used in the present invention is not particularly limited, but LiBF ₄ , LiAsF ₆ and LiPF ₄ are used.
₆ , LiClO ₄ , CF ₃ SO ₃ Li, LiI, LiA
_{lCl 4, NaClO 4, NaBF 4} , NaI, (n-
Bu) ₄ NClO ₄ , (n-Bu) ₄ NBF ₄ , KPF
₆ grade is used. Moreover, you may mix and use these electrolytes. LiBF ₄ and LiPF ₆ are preferable from the viewpoints of battery performance, handling safety, toxicity and the like.

The positive electrode to be combined with the negative electrode of the present invention is not particularly limited, but MnO ₂ , MoO ₃ ,
V ₂ O ₅ , V ₆ O ₁₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , lithium-containing transition metal chalcogen compound, TiS ₂ , Mo
Inorganic compounds such as S ₃ , FeS ₂ , CuF ₂ , and NiF ₂ ,
Carbon materials such as carbon fluoride, graphite, vapor-grown carbon fibers and / or pulverized products thereof, pitch-based carbon fibers and / or pulverized products thereof, and conductive polymers such as polyacetylene and poly-p-phenylene. .

For a positive electrode containing no lithium, the negative electrode of the present invention can be used by occluding lithium, or the negative electrode of the present invention can be used by bonding a required amount of metallic lithium to a battery. However, such a battery complicates the assembling process such that it is necessary to assemble under an inert gas at the time of assembling. When a transition metal chalcogen compound containing lithium is used, the battery can be assembled in a stable discharge state in the positive and negative electrodes in the air, there are few restrictions on processing and assembly, and heat generation and explosion due to short circuit of the battery etc. There is no danger of, and it is preferable from the viewpoint of safety.

Examples of such lithium-containing transition metal chalcogen compounds include, for example, Li _{(1- X)} CoO ₂ and Li.
_(1-x) NiO ₂ , Li _(1-x) Co _(1-y) Ni _y O ₂ , L
_{iMn 2 O 4, Li (1} -X) Co (1-Y) M Y O 2 (M is C
o, represents a transition metal other than Ni, Al, In, Sn, _{etc.), Li (1-X)} A Z Co (1-Y) M Y O 2 (A is alkali metal) other than Li.

If necessary, components such as a separator, a terminal and an insulating plate are used as the constituent elements of the battery. The battery structure is not particularly limited, but in order to reduce the capacity decrease during high-rate discharge and low-temperature discharge, use a spiral structure or a laminated structure and increase the electrode area to increase the current per unit electrode area. It is preferable to suppress the density to be small.

[0028]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the invention is not limited thereto. The d ₀₀₂ and Lc of the carbonaceous material were determined from the 002 peak of X-ray diffraction according to the "Japan Society for the Promotion of Science". The current efficiency was calculated as discharge electricity quantity / charge electricity quantity, and the utilization rate was discharge electricity quantity / electric quantity per weight of negative electrode active material (12 g is 96485 coulomb).

[0029]

Example 1 Scale-shaped artificial graphite (d ₀₀₂ = 0.3355n)
m, average particle size 15 μm, particle size range 1 to 50 μm, Lc>
100 nm, BET surface area by N ₂ adsorption = 15 m ² /
g) 100 parts by weight of styrene / butadiene latex (L1571 manufactured by Asahi Kasei Kogyo Co., Ltd.) (solid content 48% by weight) 4.17 parts by weight, carboxymethylcellulose (BSH12 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) aqueous solution as a thickener 130 parts by weight (solid content 1% by weight) and 25 parts by weight of water were added and mixed to obtain a coating liquid. This coating liquid was applied and dried using a 18 μm copper foil as a base material to obtain a negative electrode having a thickness of 110 μm and a coating weight of 90 g / m ² . The porosity and pore size distribution of this negative electrode can be measured by mercury porosimetry (Shimadzu Corporation).
Manufactured by Poisizer 9320), the porosity is 49%, the volume percentage of the pores having a pore diameter of 0.1 to 10 μm is 94%, and the pore diameter is 0.5 to 10 μm. The volume percentage of pores was 88%.

LiCoSn _0.02 O ₂ 1 having an average particle size of 3 μm
A coating liquid prepared by adding 20 parts by weight of graphite (trade name: KS6, manufactured by Lontz Co.) as a conductive filler and 100 parts by weight of a 5% by weight dimethylformamide solution of polyfuccavinylidene as a binder to 100 parts by weight, and using a coating solution of 15 μm Al This coating liquid was applied and dried using a foil as a base material to obtain a positive electrode having a thickness of 120 μm.

The negative electrode and the positive electrode were spirally wound with a polyethylene microporous film interposed therebetween, and 1M LiBF ₄ was added to γ.
The battery shown in FIG. 1 was assembled by impregnating an electrolytic solution dissolved in a mixed solvent of -BL + EC + PC (volume ratio 50:25:25). This battery was repeatedly charged at room temperature with constant current / constant voltage up to 4.2 V at 0.5 A and discharged with constant current up to 2.7 V at 0.5 A. The current efficiency and the negative electrode utilization rate in the first charge / discharge of this battery were 8 each.
It was 7% and 15.2%. The current efficiency after the second cycle exceeds 97%, and the current efficiency after the 10th cycle is 99.
It was 6%. When the current value was raised to 1 A and discharged in the 30th cycle on the way, the discharge capacity was maintained at 80% or more of the initial value. Furthermore, when the charge and discharge cycle at room temperature was repeated and the temperature was lowered to −10 ° C. at the 35th cycle for discharging, the discharge capacity was about 60% of the initial value.

[0032]

Comparative Example 1 The negative electrode obtained in Example 1 was operated at a hydraulic pressure of 50 kg /
It was passed through a calender roll set to cm ³ three times and press-molded to obtain a porous negative electrode having a thickness of 70 μm. The porosity of this negative electrode is 14%, the volume percentage of the pores in the range of pore diameter 0.1 to 10 μm is 78%, and the pore diameter is 0.5 to 1.
The volume percentage of pores in the range of 0 μm was 69%. When this negative electrode was used to assemble and charge a battery similar to that of Example 1, the initial current efficiency and negative electrode utilization rate were 75% and 13.3%, respectively. When the battery was discharged at room temperature for 1A for the 10th cycle in the same manner as in Example 1, the discharge capacity was 50% or less of the capacity for the 1st cycle. Further, when discharged at −10 ° C. in the 15th cycle in the same manner as in Example 1, the discharge capacity was 3 times the capacity of the first cycle.
It was less than 0%.

[0033]

Example 2 50 parts by weight of the scaly artificial graphite used in Example 1 was mixed with needle coke (d ₀₀₂ = 0.345 nm, average particle size 10 μm, particle size range 2 to 30 μm, Lc> 5 nm,
Ground product 5 with BET surface area = 5 m ² / g) by N ₂ adsorption
A porous negative electrode was obtained in the same manner as in Example 1 using 0 part by weight of carbonaceous particles. This porous negative electrode has a hydraulic pressure of 50 kg /
It was passed through a calender roll set to cm ³ three times and press-molded to obtain a negative electrode having a thickness of 85 μm and a coating weight of 93 g / m ² . A battery was prepared using this negative electrode in the same manner as in Example 1, and a charge / discharge cycle test was performed. The porosity of this negative electrode was 28%, the volume percentage of the pores in the pore diameter range of 0.1 to 10 μm was 88%, and the pore diameter of 0.5 to 10 μm.
The volume percentage of pores in the range of μm was 81%.
The initial current efficiency and negative electrode utilization rate of this battery are 84
% And 14.3%. Example 1 at the 100th cycle
When discharged at room temperature for 1 A in the same manner as above, the discharge capacity retained 70% or more of the capacity in the first cycle. Also, 15
When discharged at -10 ° C in the 0th cycle in the same manner as in Example 1, the discharge capacity was about 50% of the capacity in the 1st cycle.
Met.

[0034]

The carbonaceous material particles of the present invention are composed mainly of graphite particles having a carbon mesh plane spacing d ₀₀₂ of less than 0.337 nm, and the porosity of the porous negative electrode is 10 to 60.
%, And a porous negative electrode in which the percentage of the volume of pores in the pore diameter range of 0.1 to 10 μm with respect to the total pore volume is 80% or more, the current efficiency and the utilization rate are large, and the cycle is large. A negative electrode for a secondary battery having excellent properties, output characteristics and low temperature characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a configuration example of a battery of the present invention.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode 3 Separator 4 Case (negative electrode) 5 Hermetic pin (positive electrode) 6 Laser sealing

Claims (1)

[Claims] 1. A negative electrode for a non-aqueous secondary battery, which is mainly composed of carbonaceous material particles, wherein the carbonaceous material particles are mainly graphite particles having a carbon mesh plane spacing d ₀₀₂ of less than 0.337 nm, Further, the porosity of the negative electrode for a non-aqueous secondary battery is 10 to 60%, and the volume occupied by pores in the pore diameter range of 0.1 to 10 μm is 80% or more based on the total pore volume. A negative electrode for a non-aqueous secondary battery, which is characterized by: