JPH04109554A - Manufacture of electrode of secondary battery - Google Patents

Abstract

PURPOSE:To easily and efficiently carry an active material on a carrier by impregnating the inside of a small hole in a carbonaceous material, having a specific physical property value, with the active material in advance. CONSTITUTION:A carbonaceous material whose atomic ratio of hydrogen to carbon is less than 0.15 and whose (002) face has a spacing d002 of more than 3.37A by a wide-angle X-ray diffraction method is brought into contact with an alkali metal serving as an active material melted, preferably lithium, so as to impregnate the inside of an air hole in the carbonaceous material with the active material. The carbonaceous material may contain other atoms, e.g. nitrogen, oxygen, halogen and the like by 7 mole % or less, more preferably 4 mole % or less, most preferably 2 mole % or less. The ratio of hydrogen to carbon is preferably less than 0.10, more preferably less than 0.07, most preferably less than 0.05. The spacing d002 of the (002) face is preferably more than 3.38Angstrom , more preferably 3.39 to 3.75Angstrom , most preferably 3.45 to 3.70Angstrom .

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a secondary battery electrode with high capacity and excellent charge/discharge characteristics. Furthermore, the present invention relates to a method for producing a secondary battery electrode in which the active material is an alkali metal, particularly lithium.

[Prior Art] It has been proposed to use conductive polymers such as polyacetylene as electrodes for lithium secondary batteries. but,
Conductive polymers lack the amount of Li ion doping, that is, electrode capacity and stable charge/discharge characteristics.

Furthermore, attempts have been made to use lithium metal in the negative electrode of lithium secondary batteries, but in this case the charge/discharge cycle characteristics become extremely poor.

In other words, when the battery is discharged, lithium is removed from the negative electrode body.
It becomes ions and moves into the electrolyte, and during charging, this Li
The ions become metallic lithium and are deposited on the negative electrode body again, but when this charging/discharging cycle is repeated, the metallic lithium deposited becomes dendrite-like. Since this dendrite-like metallic lithium is an extremely active substance, it decomposes the electrolyte, resulting in a disadvantage that the charge/discharge cycle characteristics of the battery deteriorate. As this continues to grow, the dendrite-like metal lithium electrodeposit eventually penetrates the separator and reaches the positive electrode body, causing a problem of short-circuiting. In other words, a problem arises in that the charge/discharge cycle life is short.

In order to avoid such problems, attempts have been made to construct a negative electrode by using a carbonaceous material obtained by firing an organic compound as a support and supporting an alkali metal, particularly lithium, as an active material. By using such a negative electrode body, the charge/discharge cycle characteristics of the negative electrode are dramatically improved, but in this case, a step is required in which the necessary active material is supported on the negative electrode carrier or the positive electrode.

[Problems to be Solved by the Invention] Based on the above technical background, an object of the present invention is to provide a method for manufacturing a secondary battery negative electrode in which active materials are combined in advance in a simple and efficient manner. .

[Means for Solving the Problems] In order to solve the above problems, the present inventors have conducted extensive research on an efficient manufacturing method for negative electrodes. The present inventors have discovered that an electrode structure formed by pre-impregnation is extremely effective in achieving the above-mentioned objects, and has thus arrived at the present invention.

That is, the present invention has a hydrogen/carbon atomic ratio of less than 0.15 and a (002) plane spacing d determined by X-ray wide-angle diffraction.
. A carbonaceous substance having an o2 of 3.37 Å or more is brought into contact with an alkali metal, preferably lithium, which is an active material in a molten state, so that the active material is impregnated into the pores of the carbonaceous substance. This invention relates to a method for manufacturing a secondary battery electrode.

The present invention is characterized by the method for manufacturing the negative electrode described above, and other elements can be configured in the same manner as conventional secondary battery electrodes.

In the negative electrode according to the present invention, the active material is an alkali metal, preferably Z notium. This active material moves in and out of the electrode body in response to charging and discharging of the battery.

In the present invention, the carbonaceous material used as a support for the active material constituting the electrode body has (a) a hydrogen/carbon atomic ratio (H/C) of less than 015; and (b) an X-ray wide-angle diffraction method. (002) plane spacing (d
o. 2) has a characteristic of 3.37 Å or more. Other atoms such as nitrogen, oxygen, halogen, etc. may be present in this carbonaceous material in a proportion of preferably 7 mol% or less, more preferably 4 mol% or less, particularly preferably 2 mol% or less. good.

1(/C is preferably less than 0.10, more preferably less than 0.07, particularly preferably less than 0.05.

(The spacing (do. 2) of the 0021 plane is preferably 338
Å or more, more preferably 3.39 to 3.75 people, even more preferably 3.40 to 373 people, particularly preferably 34
1 to 370 people, most preferably 345 to 3.70 people.

If any of these parameters, H/C and doo2, deviate from the above range, the overvoltage at the electrode body during charging and discharging will increase, and as a result, gas will be generated from the electrode body, impairing the safety of the battery. Not only the performance is significantly impaired, but also the charge/discharge cycle characteristics are deteriorated.

Furthermore, it is preferable that the carbonaceous material used for the carrier of the electrode body according to the present invention has the following characteristics.

That is, the crystallite size Lc in the C-axis direction is preferably 22 OA or less, more preferably 180 Å or less, still more preferably 5 to 150, particularly preferably 10 to 80, and most preferably 12 to 70.

In addition, in Raman spectrum analysis using argon ion laser light with a wavelength of 5.145, the G value defined by the following formula is preferably less than 25, more preferably less than 20, and particularly preferably 02 It is 03 or more and less than 10, most preferably 03 or more and less than 10.

Here, the G value refers to the wavelength of 5.14 for the carbonaceous material mentioned above.
In the spectral intensity curve recorded on the chart when five people performed Raman spectrum analysis using argon ion laser light, the wave number 1. ．． 580±100cm-
The integral value (area intensity) of the spectral intensity within the range of ' is
It refers to the value divided by the area intensity within the wave number range of 1.360±100 cm-', and corresponds to a measure of the degree of graphitization of the carbonaceous material.

That is, this carbonaceous material has a crystalline portion and an amorphous portion, and the G value can be said to be a parameter indicating the ratio of the crystalline portion in this carbonaceous structure.

Further, it is desirable that the carbonaceous material used for the carrier of the electrode body according to the present invention satisfies the following conditions. That is, the interplanar spacing cL+ of the (110) plane in X-ray wide-angle diffraction analysis. twice the distance a, of2 d zol
is 2.38 to 2.4.7 people, more preferably 239 to
The crystallite size La in the a-axis direction is preferably 10 Å or more, more preferably 15 to 150, particularly preferably 19 to 70.

Furthermore, this carbonaceous material can take any form such as granular or fibrous, but granular or fibrous form is preferable.

In the case of granules, this carbonaceous material preferably has a volume average particle diameter of 30017711 or less, more preferably 02 to 200
F+, more preferably 05 to 150 Jffi, particularly preferably 2 to 100 P, most preferably 5 to 60 Jffi.

Further, the carbonaceous material used in the present invention preferably has a total specific surface area of 1 m27g or more, more preferably 2 m275 or more, still more preferably 3 m2/g or more, particularly preferably 3.5 to 150 m2/g, and most preferably 4 to 150 m2/g. 80m2
/g.

Furthermore, the carbonaceous material used in the present invention preferably has a pore volume measured by a mercury porosimeter of 0. The pore volume measured by a mercury porosimeter is large when it is 1 ml/g or more, more preferably 0.2+J/g or more, still more preferably 0.4 d/g or more, and particularly preferably 0.5 d/g or more, as described below. This is because the active material is likely to be impregnated into the pores of the carbonaceous material in the liquid phase.

Further, it is preferable that the carbonaceous material has a total pore volume of 1.5xlO-3d/g or more as determined from the amount of nitrogen gas adsorbed. More preferably, the total pore volume is 2. OXl 0-
"d/g or more, more preferably 3.0X10-" to 8
xlO-2i/g, particularly preferably 4.0X10-3
~3 x 10-2 pal/g.

The total pore volume and the average pore radius (described below) are determined by measuring the amount of gas adsorbed to the sample (or the amount of desorbed gas) using the constant volume method under several equilibrium pressures. It is determined by measuring the amount of gas present.

The total pore volume is determined from the total amount of gas adsorbed at a relative pressure P/P o "0.995, assuming that the pores are filled with liquid nitrogen.

P: Vapor pressure of the adsorbed gas (mmHg) Po: Saturated vapor pressure of the adsorbed gas at the cooling temperature (mmHg) Further, the amount of nitrogen gas adsorbed (from V, , l, below (1)
The amount of liquid nitrogen filled in the pores (V, ,
, 1 to determine the total pore volume.

T Here, P, and T are the atmospheric pressure (fkgf/cm2) and temperature (K), respectively, and ■, is the molecular volume of the adsorbed gas (for nitrogen, 34 cm, 7 cm”/
mo1).

Further, the average pore radius (γ,) of the carbonaceous material determined from nitrogen gas adsorption is preferably 8 Å or more. More preferably 10 Å or more, still more preferably 10 to 80 people,
Particularly preferably 12 to 60 people, most preferably 14 to 60 people
There are 40 people.

The average pore radius (γ,) is V determined from equation (1) above.
It is obtained by calculating from llq and the BET specific surface area S using the following equation (2).

S Here, it is assumed that the pore is cylindrical.

Such carbonaceous materials can be produced by, for example, heating an organic compound at a temperature of 300 to 3,000°C under a normal inert gas flow.
It can be obtained by decomposition and carbonization.

Examples of starting organic compounds include cellulose:
Phenol resin, polyacrylonitrile, poly(α-
Acrylic resins such as halogenated acrylonitrile;
Halogenated vinyl resins such as polyvinyl chloride, polyvinylidene chloride, and chlorinated polyvinyl chloride; polyamide-imide resins; polyamide resins; arbitrary organic polymer compounds such as conjugated resins such as polyacetylene and poly(ρ-phenylene); naphthalene, phenanthrene, anthracene,
A fused cyclic hydrocarbon compound formed by condensing two or more monocyclic hydrocarbon compounds with three or more members, such as triphenylene, pyrene, chrysene, naphthacene, bicene, perylene, pentaphene, and pentacene, or a carboxylic acid of the above compound. , derivatives like carboxylic acid anhydrides, carboxylic acid imides, various pitches based on mixtures of the above compounds: like indole, isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine, phenanthrene. A fused heterocyclic compound formed by bonding at least two or more 3-membered or more-membered monocyclic compounds to each other, or bonding to one or more 3- or more-membered monocyclic hydrocarbon compounds, and the carboxyl group of each of the above compounds. Acids, carboxylic acid anhydrides, derivatives such as carboxylic acid imides, and also benzene or its derivatives such as carboxylic acids, carboxylic acid anhydrides, carboxylic acid imides, for example 1. ．． Examples include derivatives such as 2.4.5-tetracarboxylic acid, its dianhydride, or its diimide. Furthermore, chain hydrocarbons such as methane, ethane, and propane can also be carbonized by thermal decomposition.

Furthermore, a carbonaceous material such as carbon black or coke may be used as a starting source and further heated to appropriately promote carbonization to form the carbonaceous material constituting the carrier of the electrode body according to the present invention.

The present invention is characterized in that the pores of the above-mentioned carbonaceous material are preliminarily impregnated with an alkali metal, preferably lithium, as an active material before assembling a secondary battery. Lithium is usually used as the active material.

Impregnation is performed, for example, by bringing the active material into a molten state and bringing it into contact with the above-mentioned carbonaceous material, in which case,
Preferably 3 kg/cm2 or more, more preferably 1
0 kg/cm”, more preferably 20 kg/cm
Impregnation can be carried out by contacting under a pressure of at least 30 kg/cm2, preferably at least 30 kg/cm2.

The amount of active material, preferably lithium, supported on the negative electrode carrier in advance in this manner is preferably 0.02 to 0.25 parts by weight, more preferably 0.03 to 0.20 parts by weight per 1 part by weight of the carrier. Part by weight, more preferably 0.0
4 to 0.15 parts by weight, particularly preferably 0.0
5-0612 parts by weight or less, most preferably 0.06-0
．． It is 10 parts by weight.

In this way, in addition to impregnating and supporting the active material in the carbonaceous material as a carrier in advance, other chemical methods, electrochemical methods, physical methods, such as a predetermined concentration of one ion Alternatively, the active material can be supported by a method such as immersing the support in an electrolytic solution containing alkali metal ions and electrolytically impregnating the support using lithium as a counter electrode and using the support as an anode. The secondary battery electrode is made by impregnating the pores of the above-mentioned carbonaceous material with an active material, and a conductive material and a binder can be added thereto.

As the conductive agent, expanded graphite, metal powder, etc. can be added in an amount usually less than 50% by weight, preferably less than 30% by weight.

In addition, the binder contains 30% by weight of polyolefin, rubber, thermoplastic elastomer, polyester, polyamide, etc.
It can be added in an amount of less than 10% by weight, preferably less than 10% by weight.

The secondary battery electrode obtained by the present invention is usually used as a negative electrode and is opposed to a positive electrode with a separator interposed therebetween.

For example, as shown in Fig. 1, a positive electrode body (1) and a negative electrode body (2) obtained by the present invention are rolled into a spiral shape so as to face each other with a separator (3) interposed therebetween, and this is stored in a cylindrical can. Therefore, a cylindrical secondary battery can be obtained.

The above positive electrode body is not particularly limited, but for example, Li
Preferably, the material is a metal chalcogen compound that releases or acquires alkali metal cations such as ions during charging and discharging reactions. Such metal chalcogen compounds include vanadium oxide, vanadium sulfide, molybdenum oxide, molybdenum sulfide, manganese oxide, chromium oxide, titanium oxide, titanium sulfide, and these. Examples include composite oxides and composite sulfides. Preferably Crx Op+,v,o,,v,o,,,VO
z, Cr2O5, M n O2, T i Oz, Mo
V z O, a, T i S z, Vz Ss
, Mo5t, Mo5s, VS2
, Cr 0.26V o, ts S 2, Cra,
s Vo, ++ SR, etc. Also, LiC○0□
, WO, etc., CuS, Feo2gVo7is
Sulfides such as t, Nao, +Cr52, N i P S
x, phosphorus such as F e P S s,
Selenium compounds such as S e t and N b S e s can also be used.

Further, conductive polymers such as polyaniline and polypyrrole can be used.

The separator that holds the electrolyte is made of a material with excellent liquid retention properties, such as a nonwoven fabric made of polyolefin resin. This separator contains LICI204, LiBF
4. It is impregnated with a non-aqueous electrolyte of a predetermined concentration in which an electrolyte such as L i As F s or L i P F s is dissolved.

Further, a solid electrolyte that is a conductor of alkali metal cations such as Li ions can be interposed between the positive electrode body and the negative electrode body.

[For use] In the secondary battery configured in this way, in the negative electrode, active material ions are supported on the carrier during charging, and active material ions in the carrier are released during discharging. The electrode reaction of discharge progresses.

On the other hand, in the positive electrode, when a metal chalcogen compound is used, active material ions are released into the positive electrode body during charging, and the active material ions are supported during discharging, thereby progressing the electrode reaction of charging and discharging.

Alternatively, when a conductive polymer such as polyaniline is used for the positive electrode, the counter ions of the active material ions are supported on the positive electrode body during charging, and the counter ions of the active material ions are released from the positive electrode body during discharging. The reaction progresses.

A battery reaction accompanying charging and discharging of a battery proceeds by such a combination of electrode reactions of the positive electrode body and the negative electrode body.

[Effects of the Invention] The method for producing a secondary battery electrode of the present invention involves impregnating the pores of the carbonaceous material with the active material in advance before assembling the secondary battery. To easily and efficiently manufacture a secondary battery with high capacity and excellent charge/discharge cycle characteristics.

[Examples] Hereinafter, the present invention will be explained with reference to Examples and Comparative Examples. Note that the present invention is not limited to this example.

In the present invention, elemental analysis and wide-angle X-ray diffraction measurements were carried out by the following methods.

"Elemental Analysis" Samples were dried under reduced pressure at 120°C for approximately 15 hours, then dried on a hot plate in a dry box at 100°C for 1 hour. Then, the sample was collected in an aluminum cup in an argon atmosphere, and the carbon generated by combustion was collected.
The carbon content can be determined from the weight of O2 gas, and the generated Hl
The hydrogen content was determined from the weight of o. In addition, on the actual flow side of the present invention, which will be described later, measurements were performed using a PerkinElmer 240C elemental analyzer.

"X-ray wide-angle diffraction" (1) Interplanar spacing of (002) plane (d QO2) and (11
0) Interplanar spacing (d, □.) If the carbonaceous material is in powder form, it is used as it is, or if it is in the form of minute pieces, it is powdered in an agate mortar, and the amount of high purity for X-ray standards is approximately 15% by weight based on the sample. Silicon powder was added as an internal standard substance and mixed, packed in a sample cell, and a wide-angle X-ray diffraction curve was measured by a single-reflection diffractometer method using a CuXa ray made monochromatic with a graphite monochromator as a radiation source. To correct the curve, the so-called Lorentzian, deflection factor,
No corrections were made for absorption factors, atomic scattering factors, etc., and the following simple method was used. i.e. (002) and (110)
A baseline of the curve corresponding to diffraction was drawn, and the real intensity from the baseline was plotted again to obtain correction curves for the (002) plane and the (110) plane. Find the midpoint of the line segment where a line parallel to the angular axis drawn at two-thirds of the peak height of this curve intersects with the diffraction curve, correct the angle at the midpoint using an internal standard, and calculate this. d oox and d ++ by the following Bragg equation, using the wavelength of the CuKa line.
I found o.

λ: 1.5418 people θ, θ゛: d0゜z, d++. Diffraction angle (2) corresponding to
Crystallite size in C-axis and a-axis directions: Lc; L
a In the corrected diffraction curve obtained in the previous section, the size of the crystallite in the C-axis and a-axis directions was determined from the following equation using the so-called half-width β at a position half the peak height.

β・CO3θ β・cosθ′ There are various discussions about the shape factor K, but K: 0.90
was used. λ, θ, and θ' have the same meanings as in the previous section.

Example 1 (1) Synthetic carbonaceous material Granules of crystalline cellulose (average radius of about 1 mm) were set in an electric heating furnace, heated to 1,000°C at a heating rate of 250°C/hour under nitrogen gas flow, and then heated to 1,000°C. It was held at 1,000°C for 1 hour.

Thereafter, the obtained carbonaceous material particles were set in another electric furnace and heated to 1.800°C at a heating rate of 1.000°C/hour under nitrogen gas flow, and further 1. It was held at 800°C for 1 hour.

The carbonaceous material thus obtained was placed in a 500-mm agate container, and two agate balls with a diameter of 30 mm and a diameter of 25 m were placed.
6 agate balls with a diameter of 20 mm and 16 agate balls with a diameter of 20 mm were added and crushed for 15 minutes.

The obtained carbonaceous material had the following characteristics as a result of elemental analysis, analysis such as X-ray wide-angle diffraction, and measurement of particle size distribution, specific surface area, etc.

Hydrogen/carbon (atomic ratio) = 0.04 ao,, = 3.59 people, Lc = 14 people ao (2dzo) = 2.41, L a, = 25 Large volume average particle diameter = 21P Specific surface area (BET) =17.3 m''/g The pore distribution measured by a mercury porosimeter is shown in FIG. 2, and the pore volume obtained was 0.702 m''/g.

(2) Impregnation of lithium into the pores of the carbonaceous material The particles of the carbonaceous material described above are immersed in a liquid containing molten lithium.
It was pressurized with argon gas to a pressure of "g/cm". After being left under pressure for 5 minutes, the pressure was returned to normal pressure and the particles of carbonaceous material were taken out. , impregnated with lithium.

The amount of lithium impregnated was 5.2 parts by weight based on 100 parts by weight of the carbonaceous material, including the portion attached to the surface of the particles of the carbonaceous material.

(3) Forming a sheet-like electrode To 100 parts by weight of carbonaceous material particles impregnated with lithium under pressure, 10 parts by weight of synthetic bulbs made of polyethylene with an average fiber length of 0.9 mm were added and mixed mechanically. Thereafter, it was roll-formed into a sheet in an argon gas atmosphere, and then pressure-bonded to a 100-mesh nickel wire mesh at a temperature of 135°C to obtain a 0.2 mm sheet-like electrode body.

(4) Manufacture of positive electrode body 100 parts by weight of M n Oz powder and 10 parts by weight of powdered polytetrafluoroethylene were kneaded, and the resulting mixed material was roll-formed to form a sheet with a thickness of Q and 4 mm. .

(5)! The sheet-like electrode obtained in the cell assembly (3) was used as a negative electrode, a polypropylene nonwoven fabric was interposed as a separator, and the above-mentioned MnO2 sheet-like electrode was laminated as a positive electrode.
This was rolled into a spiral shape as shown in Figure 1 and stored in a stainless steel cylindrical can.

The separator is impregnated with a 1 mol/ρ-propylene carbonate solution of LiCffO4 and the battery is sealed.
A battery as shown in Figure 1 was assembled.

(6) Characteristics of the battery For the battery manufactured in this way, the battery voltage was 1.5 mA at a constant current of 20 mA. The battery was discharged until it reached OV. Then, charge the battery with a constant current of 20mA until the battery voltage reaches 3.3V, and then perform preliminary charging and discharging with a constant current of 20mA for 55 minutes with potential regulation of 3.3V for the upper limit and 1.8V for the lower limit. The cycle was carried out.

Thereafter, charging and discharging were repeated between 3.3 and 1.8 V at a constant current of 20 mA, and cycle evaluation was performed. Table 1 shows the performance at the 7th cycle and the 50th cycle.

Comparative Example 1 A battery was constructed in the same manner as in Example 1 except that a lithium metal sheet was used instead of the negative electrode battery in Example 1.

Table 1 shows the characteristics of the battery.

The Coulombic efficiency at the 50th cycle was significantly reduced in Comparative Example 1, whereas in Example 1 it did not change compared to the 7th cycle.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the structure of a battery according to an embodiment. 1... Positive electrode body 2... Negative electrode body 3... Separator (contains electrolyte) Figure 2 shows the pore distribution of the carbonaceous material synthesized in Example 1. 1 is a chart of a mercury porosimeter shown in FIG. A: Pore volume distribution B: Cumulative pore volume distribution C: Cumulative pore area distribution Figure 1

Claims (1)

[Claims] 1. The hydrogen/carbon atomic ratio is less than 0.15, and the interplanar spacing d_o_o_2 of the (002) plane by X-ray wide-angle diffraction is 3.
．． 1. A method for producing a secondary battery electrode, which comprises bringing a carbonaceous material of 37 Å or more into contact with an alkali metal, which is an active material in a molten state, to pre-impregnate the inside of the pores of the carbonaceous material with the active material.