JP3302592B2 - Manufacturing method of non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery, and more particularly to a method for manufacturing a non-aqueous electrolyte secondary battery in which an optimal initial charging time is set.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as mobile phones and video cameras and computers and the like have become smaller, lighter, and more sophisticated, secondary batteries serving as power sources for these electronic devices have also become lighter. Therefore, there is an increasing demand for high energy density and repetitive charge / discharge. Recently, in addition to conventionally used lead secondary batteries and nickel cadmium batteries, non-aqueous electrolyte secondary batteries capable of obtaining a voltage higher than the decomposition voltage of water have been developed. Also, secondary batteries using non-aqueous electrolytes, particularly lithium secondary batteries, are expected to have high voltage and high energy density.

[0003] In this type of lithium secondary battery,
Molybdenum, vanadium, titanium,
It is known to use oxides such as niobium, sulfides, selenides and the like. Recently, studies on lithium-containing manganese composite oxides such as spinel-type LiMn ₂ O ₄ , LiCoO ₂ , and LiNiO ₂ with improved and improved cycle characteristics of manganese oxides having high energy density have been actively conducted. I have.

On the other hand, as the negative electrode active material, a lithium alloy, a carbonaceous material capable of occluding and releasing lithium ions, and the like have been studied, including metallic lithium. However, in the case of metallic lithium, there is a problem that dendrite grows with charge / discharge and a short circuit easily occurs.In the case of lithium alloy, collapse of the electrode due to expansion / contraction accompanying charge / discharge is caused. There is a problem that it is easy to perform. Therefore, recently, carbonaceous materials that do not cause these problems are regarded as promising as negative electrode materials for lithium secondary batteries. further,
When lithium metal is used as the negative electrode material,
It is well known that active dendrite generated on the surface of a negative electrode reacts with a non-aqueous solvent, and a part of the solvent causes a decomposition reaction to lower charging efficiency.

In order to avoid such problems, use of a negative electrode having a structure in which a carbonaceous material is bonded to a core made of a metal material has been promoted. That is, in the charging reaction, lithium ions in the electrolytic solution perform a reaction of intercalating between layers of the carbonaceous material, so that not only precipitation of lithium dendrite is prevented but cycle characteristics are improved,
There is an advantage that safety is improved because active metallic lithium is not used. Examples of this type of non-aqueous electrolyte secondary battery include a negative electrode using pitch-based carbon fiber using a rubber-based polymer as a binder, a positive electrode using LiCoO _2, and a battery using a non-aqueous electrolyte. Are known.

In any case, this type of secondary battery is charged with a required electrolyte solution in the manufacturing process, and after assembling the secondary battery in a liquid-tight or air-tight manner, the battery is charged ( In this specification, this is referred to as first charge), and lithium is intercalated into the negative electrode and supplied for practical use.

[0007]

However, after assembling the secondary battery by injecting the non-aqueous electrolyte into the battery (outer can), the initial charge is continuously (without taking too much time). When this is performed, the initial charge / discharge efficiency is poor, and the life of the charge / discharge cycle tends to be shortened accordingly. In other words, if the time until the first charge after assembly is short, the impregnation of the separator and the electrode surface with the nonaqueous electrolyte is insufficient, so that the initial charge / discharge efficiency is poor and the life of the charge / discharge cycle is reduced. I do.

[0008] On the other hand, if the time until the first charging after assembling the secondary battery is too long, there is a problem that the separator is clogged and the battery characteristics are easily hindered. In other words, after assembly, if the time until the first charge is long, the metal forming the electrode core gradually elutes into the electrolytic solution, and during repeated charging and discharging, the eluted metal is deposited on the negative electrode. And clogging of the separator was found to occur.

It has also been found that the temperature at the time of initial charging after assembling a secondary battery by injecting a non-aqueous electrolyte into a battery (outer can) and sealing it tightly is also affected. That is,
It was confirmed that when the temperature at the time of the first charge was low, the mobility of lithium ions in the electrolyte decreased because the viscosity of the nonaqueous electrolyte was higher than that of the aqueous electrolyte. On the other hand, when the temperature at the time of the first charge is high, there is a problem that a decomposition reaction of the electrolytic solution occurs and the battery characteristics are hindered. The present invention has been made in order to solve the above problem, and by selecting an optimum initial charging time and an initial charging temperature, a non-aqueous electrolyte having excellent initial charge / discharge efficiency and cycle characteristics. An object is to provide a method for manufacturing a secondary battery.

[0010]

According to the first aspect of the present invention, there is provided a step of mounting and disposing a positive electrode, a separator and a negative electrode made of a carbonaceous material capable of occluding and releasing lithium ions in an outer can, A step of injecting a non-aqueous electrolyte into an outer can in which the is mounted and disposed, and a step of liquid-tightly sealing a non-aqueous electrolyte inlet of the outer can into which the non-aqueous electrolyte has been injected to form a secondary battery. And, in the method for producing a non-aqueous electrolyte secondary battery having a step of first charging the secondary battery, after injecting the non-aqueous electrolyte into the outer can, the ambient temperature 25 ~
A method for producing a non-aqueous electrolyte secondary battery, comprising leaving the battery at 45 ° C. for 24-168 hours, sealing the non-aqueous electrolyte inlet in a liquid-tight manner, and performing initial charging.

In the present invention, the ambient temperature is set at 25 to 45 ° C.
And the leaving time is set to 24 to 168 hours, but the range of the ambient temperature and the range of the leaving time are relative. For example, when the ambient temperature is on the low temperature side within the above range, the range is within the above range. Is selected and set to the long time. The reason why the above ambient temperature is set in the range of 25 to 45 ° C. and the leaving time is set in the range of 24 to 168 hours is that the result of many trials and errors, including productivity and reliability, etc. Thus, it is based on the finding that the above range is practically optimal.

According to a second aspect of the present invention, in the method for producing a non-aqueous electrolyte secondary battery according to the first aspect, the carbonaceous material forming the negative electrode has a particle size distribution of pitch-based carbon fibers using mesophase pitch as a raw material. Average particle size D50% = 12-20μm
Characterized by containing pitch-based carbonaceous particles in the range of

According to a third aspect of the present invention, in the method for manufacturing a non-aqueous electrolyte secondary battery according to the first aspect, the carbonaceous material forming the negative electrode has a particle size distribution of pitch-based carbon fibers made from mesophase pitch. Average particle size D50% = 12-20μm
And the optically anisotropic structure contains pitch-based carbonaceous particles developed at random.
According to the first to third aspects of the present invention, in the method for manufacturing a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte is injected into the battery, the injection port is sealed, and the secondary battery is assembled. The time and temperature for performing are set as follows: the ambient temperature is set at 25 to 45 ° C., the leaving time is set at 24 to 170 hours, and then the initial charging is performed. As a result, the impregnation of the separator and the electrode surface with the non-aqueous electrolyte is sufficient, while the elution of the metal forming the electrode core into the non-aqueous electrolyte is reduced and suppressed, so that the first charge is performed in an appropriate state. As a result, the initial charging / discharging efficiency is improved. Further, as the charge / discharge efficiency is improved in the initial stage, the charge / discharge cycle is extended.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment will be described below with reference to FIGS. 1, 2, 3 and 4. FIG.

FIG. 1 is a perspective view showing a main part of a non-aqueous electrolyte secondary battery according to the present invention, and FIG. 2 is a longitudinal sectional view showing a main part of the non-aqueous electrolyte secondary battery. 1 and 2, reference numeral 1 denotes a rectangular cylindrical outer can having a bottom and also serving as a negative electrode terminal made of stainless steel, for example, and reference numeral 2 denotes a battery element portion mounted and arranged in the outer can 1. Here, the battery element part 2
Is formed by spirally winding a laminate of a positive electrode 3, a separator 4, and a negative electrode 5. The battery element portion 2 is temporarily stored in a cage-shaped battery element portion cover 6, and the outer can 1
The non-aqueous electrolyte is injected and accommodated in a region where the battery element portion 2 is attached and arranged.

The opening side of the outer can 1 has a circular hole 7 in the center and a rectangular pressure release hole 8 at a position adjacent to the circular hole 7. 9 is hermetically sealed by laser welding. The stainless steel positive electrode terminal pin 11 is inserted into the circular hole 7 of the sealing body 9 so as to protrude, while being hermetically sealed by the glass-based insulator layer 10. The lead 12 is connected to the positive electrode 3 of the battery element 2.

Further, the opening hole 8 for the pressure of the sealing body 9 is
It is hermetically sealed by a stainless steel rectangular thin plate 13 laser-welded so as to close the inside. Here, the rectangular thin plate 13 has a straight portion and V-shaped cut grooves 14 at both ends thereof. The thinned portions of the cut grooves 14 function as a safety valve, and the pressure is reduced. Elastic polymer material 15 filled in opening 8
It is covered with. The cut groove 14 is formed by pressing the thin plate 13 with a punch or by etching.

Next, the positive electrode 3, the negative electrode 5, and the non-aqueous electrolyte will be described.

Positive Electrode The positive electrode 3 is provided on both surfaces of a current collector 3a such as aluminum foil, aluminum mesh, aluminum punched metal, aluminum lath metal, for example, Li _x MO ₂
(However, M is a transition metal such as Co or Ni, 0.05 ≦ x ≦ 1.10
Of the positive electrode mixture 3b containing the active material represented by the following formula: The active material is LiCoO ₂ , LiNiO ₂ , LiNi
_y Co _(1-y) O ₂ , where 0 <y <1.

The above-mentioned composite oxide is obtained, for example, by using carbonates of lithium, cobalt and nickel as starting materials, mixing these carbonates in predetermined amounts, and calcining the mixture in a temperature range of 600 to 1000 ° C. in an atmosphere containing oxygen. . The starting materials are not limited to carbonates, but can be synthesized from hydroxides and oxides.

Negative Electrode The negative electrode 5 has a structure in which a negative electrode mixture 5b containing a material that absorbs and releases lithium as an active material is formed on both surfaces of a current collector 5a such as a copper foil, a copper mesh, and a copper punched metal. Have. Here, specific examples of the active material include pyrolytic carbons; cokes such as pitch coke, needle coke and petroleum coke; graphites; glassy carbons; and suitable temperatures such as phenolic resins and furan resins. A carbon material such as activated carbon, or a polymer such as lithium metal, lithium alloy such as lithium-aluminum alloy, polyacetylene, or polypyrrole can also be used.

Non-aqueous electrolyte This non-aqueous electrolyte is obtained by dissolving an electrolyte such as a lithium salt in an organic solvent at a ratio of about 0.5 to 1.5 mol / l. Here, as the electrolyte, LiClO ₄ , L
iAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, Li
One or two selected from Br, CH ₃ SO ₃ Li, and CF ₃ SO ₃ Li
More than one lithium salt can be mentioned.

Examples of the organic solvent include propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, γ-butyl lactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan,
Sulfolane, acetonitrile, diethyl carbonate,
One or two selected from dipropyl carbonate and the like
A mixed solvent of more than one kind is exemplified.

Next, a specific example of the present invention will be described.

Example 1 (Preparation of positive electrode) Lithium carbonate and cobalt carbonate were mixed at a molar ratio of Li / Co of 1 and fired in air at 900 ° C. for 5 hours to form a composite oxide as a positive electrode active material. (LiCoO ₂ ) was synthesized. X-ray diffraction measurement was performed on this composite oxide. As a result, it was in good agreement with the LiCoO _{2 of} the JCPDS card. Further, the sample composed of the composite oxide is decomposed with sulfuric acid, the generated carbon dioxide is introduced into barium chloride and sodium hydroxide solution and absorbed, and the carbon dioxide is quantified by titration with a standard sample, The amount of lithium carbonate in the composite oxide was determined by conversion from the amount of carbon dioxide. As a result, lithium carbonate was hardly detected. This composite oxide was pulverized in an automatic mortar to obtain a LiCoO ₂ powder.

91 parts by weight of a mixture of 95% by weight of the LiCoO ₂ powder (positive electrode active material) thus obtained and 5% by weight of lithium carbonate, 6 parts by weight of graphite as a conductive material, and polyhooker as a binder The mixture was mixed with 3 parts by weight of vinylidene and dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode mixture.

This positive electrode mixture was applied to both sides of an aluminum foil, dried, and then subjected to pressure molding with a roller press to produce a sheet-like positive electrode.

(Preparation of Negative Electrode) First, a pitch-based carbon fiber made from mesophase pitch was finely pulverized,
And a carbonaceous powder as an active material was obtained.
As a result of performing X-ray diffraction measurement on the carbon fiber, (0
02) The spacing between the surfaces was 3.76A, and the true specific gravity was 1.58. Furthermore, as a result of measuring the particle size distribution, D50% = 12 to 20
μm range. The particle size distribution was measured using a laser diffraction particle size distribution analyzer (PRO-70 manufactured by Seishin Enterprise Co., Ltd.).
00S) was used.

This carbonaceous powder was mixed at a ratio of 10 parts by weight of polyvinylidene fluoride as a binder per 90 parts by weight to prepare a negative electrode mixture, and this negative electrode mixture was converted into N-methyl-2-pyrrolidone. It was dispersed to form a slurry. This negative electrode mixture slurry was applied to both sides of a strip-shaped copper foil as a negative electrode current collector, dried, and then pressed with a roller press to produce a sheet-shaped negative electrode.

(Preparation of Battery Element Part) The positive electrode in the form of a sheet, a separator made of a microporous polypropylene film having a thickness of 25 μm, and the negative electrode are laminated in this order, and the laminate is placed so that the negative electrode is located outside. Then, the wound product was compressed under a pressure of 10 kgf / cm ² to produce a flat battery element portion.

Next, the battery element portion was housed and placed in a stainless steel bottomed rectangular cylindrical outer can in a state where the battery element portion was covered with a copper electrode cover, and a mixed solvent of propylene carbonate and dimethoxyethane (volume ratio: 50:50), a non-aqueous electrolyte obtained by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a ratio of 1 mol / l was injected.

Subsequently, a positive electrode terminal pin is hermetically sealed in the hole of the rectangular sealing body made of stainless steel having a circular hole in the center and a rectangular pressure release hole in a position adjacent to the hole, respectively, Furthermore, the opening of the outer can is sealed airtight with a 50 μm thick stainless steel thin plate with a V-shaped notch groove formed at a depth of 35 μm and a laser welded to the straight part and both ends to close the pressure release hole. Sealed. This sealing is performed by connecting the lower end of the positive electrode terminal pin of the sealing body to the positive electrode of the battery element part in the outer can via a lead, and then laser welding the sealing body to the opening of the outer can. Thus, a square nonaqueous electrolyte secondary battery (battery dimensions: width 34.0 mm, height: 48.0 mm, thickness: 8.6 mm) having the structure shown in FIGS. 1 and 2 was assembled.

After assembling the non-aqueous electrolyte secondary battery, 25
When the battery was left at 24 ° C. for 24 hours, the battery was initially charged, and a non-aqueous electrolyte secondary battery (Example 1) was manufactured and manufactured.

Examples 2 and 3 After the electrolyte was injected and the injection port was sealed and assembled, each battery was allowed to stand for 120 hours (Example 2) or 168 hours (Example 3) at an ambient temperature of 25 ° C. Thereafter, the same conditions as in Example 1 were used except that the initial charge was performed, and non-aqueous electrolyte secondary batteries were manufactured and manufactured.

Example 4 The same conditions as in Example 1 except that the electrolyte was injected, the injection port was sealed and assembled, the battery was allowed to stand for 120 hours at an ambient temperature of 30 ° C., and then charged for the first time. Then, a non-aqueous electrolyte secondary battery (Example 4) was manufactured and manufactured.

Examples 5 and 6 After the electrolyte was injected and the injection port was sealed and assembled, each battery was left for 24 hours (Example 5) or 120 hours (Example 6) at an ambient temperature of 45 ° C. Thereafter, the same conditions as in Example 1 were used except that the initial charge was performed, and non-aqueous electrolyte secondary batteries were respectively manufactured and manufactured.

COMPARATIVE EXAMPLES 1 AND 2 After injecting the electrolyte, sealing and assembling the injection port, at an ambient temperature of 20 ° C. (Comparative Example 1) or 50 ° C. (Comparative Example 2)
After leaving to stand for 24 hours, the same conditions as in Example 1 were used except that initial charging was performed, and non-aqueous electrolyte secondary batteries were manufactured and manufactured.

Comparative Example 3 The same conditions as in Example 1 except that the electrolyte solution was injected, the injection port was sealed and assembled, the battery was left at an ambient temperature of 25 ° C. for 12 hours, and then charged first. Then, non-aqueous electrolyte secondary batteries were manufactured and manufactured, respectively.

COMPARATIVE EXAMPLES 4 AND 5 After the electrolyte was injected and the injection port was sealed and assembled, at an ambient temperature of 10 ° C. (Comparative Example 4) or 60 ° C. (Comparative Example 5),
After leaving to stand for 24 hours, the same conditions as in Example 1 were used except that initial charging was performed, and non-aqueous electrolyte secondary batteries were manufactured and manufactured.

Comparative Example 6 The same conditions as in Example 1 except that the electrolyte solution was injected, the injection port was sealed and assembled, the battery was left for 192 hours at an ambient temperature of 25 ° C., and then the initial charge was performed. Then, non-aqueous electrolyte secondary batteries were manufactured and manufactured, respectively.

The non-aqueous electrolyte secondary batteries of the above Examples and Comparative Examples were initially charged at a constant current and a constant voltage (450 mAh, 4.
Charge at 2V) for 5 hours, then charge at constant current (450mAh, 3.
(0 V cut), and the initial charge / discharge efficiency was measured and evaluated. FIG. 3 is a characteristic diagram showing the discharge efficiency depending on the ambient temperature (vertical axis) set at the time of the first charge and the time (horizontal axis) of being left in the atmosphere. In the above cases, the □ mark indicates that the charge and discharge efficiency is 70%
And less than 85%, and x indicates a case where the charge and discharge efficiency is less than 70%.

As can be seen from FIG. 3, each of the nonaqueous electrolyte secondary batteries of the examples has an initial charge / discharge efficiency of 85% or more and exhibits superior charge / discharge characteristics as compared with the comparative examples. .

Next, the cycle characteristics of the non-aqueous electrolyte secondary batteries of each of the examples and comparative examples were measured and evaluated. That is, at a temperature of 20 ° C, constant current and constant voltage (900mAh, 4.2V)
And charge for 3 hours, then constant current (900mAh, 3.0V cu
The charge / discharge cycle in which the discharge is performed in t) is repeated 500 times, and the cycle characteristics are measured and evaluated. In FIG. 4, the vertical axis shows the discharge capacity (mAh), and the horizontal axis shows the number of cycles (times).

As can be seen from FIG. 4, when the initial charge is carried out, when the electrolyte injection, the standing time after injection sealing and the ambient temperature are appropriately selected and set, the initial charge / discharge efficiency or discharge capacity, the charge / discharge cycle, The characteristics can be easily improved and improved.

[0045]

According to the first to third aspects of the present invention, after the non-aqueous electrolyte is injected and sealed, the initial charge is performed under the conditions of an appropriate ambient temperature and a standing time, so that the separator and the electrode surface can be formed. The electrolyte is sufficiently impregnated into the electrolyte, and the elution of the metal material forming the electrode core into the non-aqueous electrolyte is reduced, so that the initial charging is performed in an optimal state. That is,
The initial charge / discharge efficiency is improved, and the life of the charge / discharge cycle is prolonged with the improvement of the charge / discharge efficiency. Therefore, according to the present invention, an excellent non-aqueous electrolyte secondary battery having a high initial capacity, high charge / discharge efficiency, and a long cycle life can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration example of a main part of a nonaqueous electrolyte secondary battery according to the present invention.

FIG. 2 is a longitudinal sectional view of the non-aqueous electrolyte secondary battery of FIG.

FIG. 3 shows the relationship between the initial charging / discharging efficiency of the nonaqueous electrolyte secondary battery according to the present invention, the ambient temperature until the first charge is performed, and the standing time, as compared with the nonaqueous electrolyte secondary battery of the comparative example. FIG.

FIG. 4 is a characteristic diagram showing a comparison between cycle characteristics of a non-aqueous electrolyte secondary battery according to the present invention and a non-aqueous electrolyte secondary battery of a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Outer can 2 ... Battery element part 3 ... Positive electrode 4 ... Separator 5 ... Negative electrode 8 ... Pressure release hole 9 ... Sealing body 10 ... Positive electrode terminal pin 11 ... Glass insulator layer 12 ...... Positive electrode lead 13 Thin plate (safety valve) 14 Cut groove

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshimi Ueno 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation (56) References JP-A-9-259927 (JP, A) JP Hei 8-162096 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40

Claims (3)

(57) [Claims] 1. A step of mounting and disposing a positive electrode, a separator and a negative electrode made of a carbonaceous material capable of occluding and releasing lithium ions in an outer can. A step of injecting an electrolyte, a step of sealing the nonaqueous electrolyte injection port of the outer can into which the nonaqueous electrolyte is injected to form a secondary battery, and a step of first charging the secondary battery And a method of manufacturing a non-aqueous electrolyte secondary battery having a step, after injecting the non-aqueous electrolyte into the outer can, the ambient temperature 25 ~ 45 ℃
A method for producing a non-aqueous electrolyte secondary battery, comprising leaving the non-aqueous electrolyte injection port liquid-tightly sealed for 24 to 168 hours and then performing initial charging. 2. A carbonaceous material forming a negative electrode contains pitch-based carbonaceous particles having an average particle diameter D50% = 12 to 20 μm according to a particle size distribution of pitch-based carbon fibers using mesophase pitch as a raw material. Claim 1
A method for producing the nonaqueous electrolyte secondary battery according to the above. 3. The carbonaceous material forming the negative electrode has an average particle size D50% = 12 to 20 μm according to a particle size distribution of pitch-based carbon fibers using mesophase pitch as a raw material, and an optically anisotropic structure is random. 2. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery contains pitch-based carbonaceous particles developed in the following manner.