JP3544142B2 - Lithium ion secondary battery - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lithium ion secondary battery used for portable electronic devices, electric vehicles, home power storage and the like. For batteries Related.
[0002]
[Prior art]
In recent years, demand for high-performance secondary batteries has been remarkably increased as a power source for portable electronic devices that support the information-oriented society, and as a key element of electric vehicles and power storage systems to cope with air pollution and global warming. The technology for increasing the capacity of secondary batteries has been remarkable, and the capacity of nickel-metal hydride batteries, which replace conventional NiCad batteries, is increasing every year.
[0003]
On the other hand, unlike these secondary batteries using an aqueous electrolyte, development of a lithium ion secondary battery using a non-aqueous electrolyte and featuring a high electromotive force is also rapidly progressing.
[0004]
Lithium-ion secondary batteries in principle far exceed conventional secondary batteries in capacity per unit weight. However, the non-aqueous electrolyte has a low conductivity, and the electromotive force is high, so that the electrolyte is likely to be decomposed. Therefore, the potential of the non-aqueous electrolyte is not sufficiently utilized, and a further improvement in capacity is required.
[0005]
Further, there has been a problem that the repetition of charge / discharge causes the non-aqueous electrolyte solution to dry out inside the electrode, resulting in capacity deterioration occurring when charge / discharge cycles are repeated.
[0006]
The two major problems of increasing the capacity of the lithium ion secondary battery and extending the cycle life will be described in more detail.
[0007]
First, the expansion of the capacity of the lithium ion secondary battery will be considered.
[0008]
In the case of a lithium ion secondary battery, when a thick electrode is used for the purpose of increasing the energy capacity, the thickness and the current density are not proportional in the normal current density region, unlike the case of the nickel hydride battery. Therefore, it is necessary to increase the effective diffusion coefficient in the electrode in order to increase the battery capacity.
[0009]
Many conventional lithium ion secondary batteries use a positive electrode that uses a layered oxide having a large anisotropic ion diffusion coefficient as an active material, and a carbon-based compound that also has a large anisotropic ion diffusion coefficient as an active material. And a negative electrode. In a practical electrode, powder particles (active material grains) of these active materials are applied on a supporting conductor together with a conductive aid and a binder polymer. Lithium ions in the electrode diffuse by moving in and between the active material grains. That is, the effective ion diffusion coefficient in the electrode is affected not only by the ion diffusion coefficient in the active material grains, which is a material constant, but also by the ion diffusion between the active material grains, which depends on the electrode formation method. It is necessary to improve the ion diffusion between the material grains and to improve the effective ion diffusion coefficient. However, a battery with sufficient improvement in this respect has not been realized.
[0010]
Next, the prolongation of the cycle life of the lithium ion secondary battery will be considered.
[0011]
Similarly to other secondary batteries, the capacity of a lithium ion secondary battery deteriorates when charging and discharging are repeated. The main cause of this is that when charge and discharge are repeated, the electrode repeatedly expands and contracts, causing a non-aqueous electrolyte to be unevenly distributed inside the electrode. This is known as the liquid withdrawal phenomenon, and since the capacity of the lithium ion secondary battery that has caused liquid withdrawal is rapidly deteriorated, a battery that does not cause the liquid withdrawal phenomenon is required but has not been realized yet.
[0012]
On the other hand, safety issues of lithium ion secondary batteries are also regarded as important. Lithium ion secondary batteries have higher electromotive force and use a flammable organic solvent as the solvent for the non-aqueous electrolyte, so they are more resistant to external vibrations and collisions than batteries using aqueous electrolytes. It is necessary to increase the safety by preventing the occurrence of ignition or the like.
[0013]
[Problems to be solved by the invention]
An object of the present invention is to provide a high-capacity lithium-ion secondary battery having a high capacity and having little capacity deterioration when charge / discharge cycles are repeated.
[0014]
Another object of the present invention is to provide a highly safe lithium-ion secondary battery that withstands external impact and is less likely to cause ignition or the like.
[0015]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an electrode group including a positive electrode, a negative electrode including a material that absorbs and releases lithium ions, and a separator located between the positive electrode and the negative electrode; and dissolving a lithium salt in a nonaqueous solvent. A non-aqueous electrolyte solution; an inner container for storing the electrode group and the non-aqueous electrolyte solution; an outer container for storing the inner container; and a means for supplying the non-aqueous electrolyte solution from the outer container to the inner container. At least prepared Between the inner container and the electrode group, a material having a high porosity and high liquid retention compared to the separator is inserted. A lithium ion secondary battery characterized in that:
[0017]
No. 2 The present invention provides an electrode group comprising a positive electrode, a negative electrode provided with a material that absorbs and releases lithium ions, and a separator located between the positive electrode and the negative electrode; and dissolving a lithium salt in a non-aqueous solvent. A non-aqueous electrolyte solution; an inner container for storing the electrode group and the non-aqueous electrolyte solution; an outer container for storing the inner container; and a shock absorbing material inserted between the inner container and the outer container. It is a lithium ion secondary battery provided with.
[0018]
As described in the related art, in order to increase the battery capacity, it is necessary to improve the ion diffusion between the active material grains constituting the electrode. Further, the first key point for improving the ion diffusion between the active material grains is that the active material grains are covered with a non-aqueous electrolyte that has permeated into the electrode.
[0019]
In general, the ion diffusion rate at the solid phase interface is reduced due to the disorder of the crystal structure generated on the surface of the fine particles, so that the effective ion diffusion coefficient is significantly lower than the diffusion coefficient in the active material grains.
[0020]
FIG. 1 is a schematic diagram showing lithium ion diffusion in the electrode. As shown in FIG. 1, when the surface of the active material grains is covered with a non-aqueous electrolyte and ion diffusion through the liquid phase occurs, the effective ion diffusion coefficient is greatly improved, thereby increasing the battery capacity. be able to.
[0021]
Further, in order to extend the cycle life of the battery, it is necessary to prevent the non-aqueous electrolyte from withering.
[0022]
If the double container structure as in the first invention is used, even if an organic solvent having a high boiling point and a large viscosity is used as a solvent for the non-aqueous electrolyte, it is possible to sufficiently infiltrate the electrode with the non-aqueous electrolyte, When the active material grain surface is covered with the non-aqueous electrolyte and ion diffusion occurs through the liquid phase, the effective ion diffusion coefficient is greatly improved, and the battery capacity can be increased.
[0023]
Further, since the non-aqueous electrolyte is naturally replenished from the outer container to the electrode group in the inner container, the liquid can be prevented from withering, so that the cycle life is increased.
[0024]
In particular, large lithium-ion rechargeable batteries, which are expected to be applied to electric vehicles, use lithium-ion rechargeable batteries in a much wider range of current than ordinary personal computers. It is considered that the capacity was significantly deteriorated due to the liquid withering. Therefore, the use of the battery of the first aspect of the present invention is very useful because it can prevent liquid withering and can improve cycle life characteristics.
[0025]
Further, according to the first aspect, even when an organic solvent having a high boiling point and a large viscosity is used as a solvent for the non-aqueous electrolyte, the non-aqueous electrolyte can be sufficiently infiltrated into the electrode. As the cycle life characteristics are improved and the non-aqueous electrolyte is less likely to evaporate, the non-aqueous electrolyte is less likely to evaporate even in the event of overcharge or internal short-circuit, etc. Can also be achieved.
[0026]
Also, According to the method for manufacturing a lithium ion battery of the first invention, In addition, it is possible to not only increase the discharge capacity of the lithium ion secondary battery, but also to prevent the deterioration of the discharge capacity due to the withdrawal phenomenon of the non-aqueous electrolyte often caused by repeated charging and discharging.
[0027]
That is, when charging and discharging are repeated after the electrode group and the non-aqueous electrolyte are sealed in a container, the distribution of the electrolyte inside the electrode is biased. This is because the electrodes repeatedly expand and contract due to charge and discharge. Therefore, before the electrode group and the non-aqueous electrolyte are sealed in the container, the electrode group is charged and discharged inside the container in which the electrolyte is immersed, so that the electrolyte is sufficiently infiltrated into the electrode group and the battery is sealed afterwards. In addition to improving the capacity, it is possible to prevent liquid withering occurring at the time of charge and discharge after sealing, and to improve cycle life characteristics.
[0028]
Also, The method for manufacturing a lithium ion battery of the first invention According to this, even if an organic solvent having a high boiling point and a large viscosity is used as the solvent of the non-aqueous electrolyte, the non-aqueous electrolyte can be sufficiently infiltrated into the electrode, and thus the capacity and cycle life characteristics can be improved as described above. Since the non-aqueous electrolyte is unlikely to evaporate, the non-aqueous electrolyte is also unlikely to evaporate even during overcharging or internal short-circuiting, thereby suppressing an increase in battery internal pressure and improving the safety of the battery. be able to.
[0029]
Further, when a lithium ion secondary battery is used in an electric vehicle or the like, safety is the most problematic. No. 2 According to the invention, since the shock absorber is inserted between the inner container and the outer container, it is possible to protect the electrode group inside the inner container even if strong vibration or crushing of the battery container at the time of collision occurs. Is possible, and ignition can be prevented.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the lithium ion secondary battery of the first invention will be described.
[0031]
FIG. 2 is a schematic diagram showing an example of the configuration of the lithium ion secondary battery of the first invention.
[0032]
As shown in FIG. 2A, an inner container 2 houses an electrode group 3 including a positive electrode, a negative electrode, and a separator. It is preferable that the electrode group 3 has a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and a coil shape. The inner container 2 has a lid 1 also serving as an electrode terminal. The inner container 2 has no bottom.
[0033]
The inner container 2 can be a normal metal can or a can made of resin. By using a can made of resin, it is possible to reduce the weight of the entire battery, to prevent corrosion by a non-aqueous electrolyte, and to prevent oxidation.
[0034]
Further, as shown in FIG. 2B, the outer container 4 has a bottom. The outer container 4 can use a can made of resin in addition to a normal metal can. By using a can made of resin, it is possible to reduce the weight of the entire battery, to prevent corrosion by a non-aqueous electrolyte, and to prevent oxidation.
[0035]
As shown in FIG. 2C, the lithium ion secondary battery of the first invention has an inner container 2 in which the above-mentioned electrode group is stored in an outer container 4. The inner container 2 and the outer container 4 are filled with a non-aqueous electrolyte obtained by dissolving a lithium salt in a non-aqueous solvent. Since the inner container 2 does not have a bottom, a conduction path 5 is formed so that the non-aqueous electrolyte can be supplied from the outer container 4 to the inner container 2, and the non-aqueous electrolyte in the outer container can be easily transferred to the inner container 2. It has a structure that can penetrate. The inner container 2 may be provided with a bottom provided with a hole.
[0036]
Since the non-aqueous electrolyte is filled between the inner container and the outer container, it acts as a shock absorber at the same time as replenishment of the electrolyte, causing strong vibration and crushing of the battery container in the event of a collision. Even so, it is possible to protect the electrode group inside the inner container and prevent ignition.
[0037]
In manufacturing the lithium ion secondary battery of the first invention, the nonaqueous electrolyte is sufficiently infiltrated into the electrode group including the positive electrode, the negative electrode, and the separator in the inner container 2 in advance, and then the inner container 2 is inserted into the outer container 4. Further, it is desirable that the outer container is sealed by injecting a non-aqueous electrolyte.
[0038]
In the lithium ion secondary battery of the first invention, in order to thoroughly prevent the liquid withering phenomenon, a method of inserting a more porous liquid retaining layer than the separator between the electrode group and the inner container, A method such as providing a mechanism for re-injecting the non-aqueous electrolyte into the container is desirable.
[0039]
Next 1 Invention lithium ion secondary battery Manufacture The method will be described.
[0040]
Of the above manufacturing method Before sealing the electrode group and the non-aqueous electrolyte in the container, the electrode group is housed in the container containing the non-aqueous electrolyte for a certain period of time, and the electrode group and the non-aqueous electrolyte are repeatedly charged and discharged. Is sealed in a container. As a charging condition, it is desirable to repeat charging and discharging between 4.2V and 3V.
[0041]
Further, if the battery cells are housed in a non-aqueous electrolyte whose viscosity has been reduced by heating the entire container, the time required for infiltration can be reduced, which is more effective.
[0042]
the above In the method of manufacturing a lithium ion secondary battery, if the double container structure as in the first invention is used, this manufacturing process can be facilitated, which is more effective.
[0043]
Next, the lithium ion secondary battery of the third invention will be described.
[0044]
FIG. 2 1 is a schematic diagram illustrating an example of a configuration of a lithium ion secondary battery of the invention.
[0045]
As shown in FIG. 3A, the inner container 2 houses an electrode group 3 including a positive electrode, a negative electrode, and a separator. It is preferable that the electrode group 3 has a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and a coil shape. The inner container 2 can be a normal metal can or a can made of resin. By using a can made of resin, it is possible to reduce the weight of the entire battery, to prevent corrosion by a non-aqueous electrolyte, and to prevent oxidation.
[0046]
As shown in FIG. 3B, the outer container 4 has a bottom. The outer container 4 can use a can made of resin in addition to a normal metal can. By using a can made of resin, it is possible to reduce the weight of the entire battery, to prevent corrosion by a non-aqueous electrolyte, and to prevent oxidation.
[0047]
No. 2 As shown in FIG. 3 (c), the inner container 2 containing the above-mentioned electrode group is contained in the outer container 4 of the lithium ion secondary battery of the present invention. The inner container 2 and the outer container 4 are filled with a shock absorbing material. Examples of the shock absorbing material include a method using a rubber-like substance such as SBR (styrene butadiene lavane) as a cushion material, a method of inserting a spring between an inner container and an outer container, and a method of using a gel-like substance. If the non-aqueous electrolyte is filled between the inner container and the outer container, not only can the non-aqueous electrolyte be replenished, but also the interior can be protected.
[0048]
Further, it is desirable that the shock absorbing material is a substance exhibiting flame retardancy or fire extinguishing action. Examples of the substance include a powder fire extinguishing material for an ABC fire extinguisher that is generally widely used.
[0049]
FIG. 2 5 shows another configuration example of the lithium ion secondary battery of the invention. FIG. 4 is a schematic diagram showing an example of a configuration in which a plurality of lithium ion secondary batteries are put in one pack to form a battery pack.
[0050]
In FIG. 4, one lithium ion secondary battery has an inner container 32 in which an electrode group 33 including a positive electrode, a negative electrode, and a separator is housed. It is desirable that the electrode group 33 is formed by laminating a positive electrode and a negative electrode, a separator located between the positive electrode and the negative electrode, and further has a coil shape. The inner container 32 is provided with a lid 31 also serving as an electrode terminal. Further, the inner container 32 in which the electrode group is stored is stored in an outer container 34. An impact absorbing material may be inserted between the inner container and the outer container, or a conductive path may be provided between the inner container and the outer container by filling with an electrolytic solution as in the first invention. Thereby, the battery capacity and the cycle life characteristics can be improved.
[0051]
Such lithium ion secondary batteries are connected in series, placed in a container 35, filled with a shock absorbing material between the container 35 and the lithium ion secondary battery, and further filled with a cooling material, a fire extinguishing material and the like. If it is used as a battery pack, it will be useful for safety.
[0052]
FIG. 2 FIG. 3 is a schematic diagram showing another configuration example of the lithium ion secondary battery of the invention. FIG. 5 is a schematic diagram showing an example of a configuration in which a plurality of lithium ion secondary batteries are put in one pack to form a battery pack. In FIG. 5, one lithium ion secondary battery includes an inner container 42 in which an electrode group 43 including a positive electrode, a negative electrode, and a separator is housed. The electrode group 43 is preferably formed by stacking a positive electrode and a negative electrode, and a separator located between the positive electrode and the negative electrode, and further has a coil shape. Such inner containers 42 are connected in parallel, and are stored in the outer container 44. At this time, the space between the inner container 42 and the outer container 44 is filled with the shock absorbing material. The space between the outer container and the inner container may be filled with a non-aqueous electrolytic solution to serve as both a shock absorber and a replenishing electrolytic solution. Thereby, the battery capacity and the cycle life characteristics can be improved.
[0053]
In addition, the first to the first 2 In the lithium ion secondary battery of the present invention, as the positive electrode active material of the positive electrode, various oxides, for example, manganese dioxide, lithium manganese composite oxide, lithium-containing nickel oxide, lithium-containing cobalt compound, lithium-containing nickel-cobalt oxide, Examples include lithium-containing iron oxides, vanadium oxides containing lithium, and chalcogen compounds such as titanium disulfide and molybdenum disulfide. Among them, lithium-containing cobalt oxides (for example, LiCoO ₂ ), Lithium-containing nickel cobalt oxide (eg, LiNi _0.8 Co _0.2 O ₂ ) And lithium manganese composite oxide (eg, LiMn2O4, LiMnO2) are preferable because a high voltage can be obtained. The positive electrode may contain a conductive agent, a binder, and the like in addition to the positive electrode active material. The positive electrode can be obtained by applying a slurry containing a positive electrode active material, a conductive agent, and a binder to a positive electrode current collector and drying the slurry.
[0054]
1st to 1st 2 In the lithium ion secondary battery of the present invention, examples of the negative electrode material of the negative electrode include carbonaceous materials that occlude and release lithium ions. Examples of the carbonaceous material include graphite materials such as graphite, coke, carbon fiber, and spherical carbon or carbonaceous materials, thermosetting resins, isotropic pitch, mesophase pitch, mesophase pitch-based carbon fiber, mesophase small spheres, and the like (especially, Graphite material or carbonaceous material obtained by subjecting mesophase pitch-based carbon fiber to heat treatment at 500 to 3000C. In particular, it is preferable to use a graphitic material having a graphite crystal having a (002) plane spacing d002 of 0.340 nm or less, which is obtained by setting the heat treatment temperature to 2000 ° C. or higher. A non-aqueous electrolyte secondary battery including a negative electrode containing such a graphite material as a carbonaceous material can significantly improve the battery capacity and large current characteristics. More preferably, the plane distance d002 is 0.336 nm or less.
[0055]
The carbonaceous material is preferably a mesophase pitch-based carbon fiber that has been heat-treated at 2000 ° C. or more. When this is used, the electrode density is 1.3 g / cm. ³ Even at the high density described above, the interface impedance between the negative electrode and the separator is small, so that it is excellent in large current discharge characteristics and rapid charge / discharge cycle performance.
[0056]
As the negative electrode material, in addition to the above-mentioned carbonaceous materials that occlude and release lithium ions, those containing metal oxides, metal sulfides, or metal nitrides, and those made of lithium metal or lithium alloy should be used. Can be.
[0057]
Examples of the metal oxide include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide.
[0058]
Examples of the metal sulfide include tin sulfide and titanium sulfide.
[0059]
Examples of the metal nitride include lithium cobalt nitride, lithium iron nitride, lithium manganese nitride, and the like.
[0060]
Examples of the lithium alloy include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy.
[0061]
The negative electrode may contain a conductive agent, a binder, and the like in addition to the negative electrode material. The negative electrode can be obtained by applying a slurry containing a negative electrode active material, a conductive agent, and a binder to a negative electrode current collector and drying the slurry.
[0062]
In the lithium ion secondary batteries of the first to third inventions, it is desirable to use a porous separator as the separator. As a material of the separator, for example, a porous film containing polyethylene, polypropylene, or polyvinylidene fluoride (PVdF), a synthetic resin nonwoven fabric, or the like can be used. Among them, a porous film made of polyethylene, polypropylene, or both is preferable because the safety of the secondary battery can be improved.
[0063]
In the lithium ion secondary batteries of the first to third inventions, the non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent.
[0064]
As the non-aqueous solvent, a known non-aqueous solvent can be used as a solvent for a lithium ion secondary battery, and is not particularly limited. Propylene carbonate (PC) or ethylene carbonate (EC) has a lower viscosity than PC or EC. It is preferable to use a non-aqueous solvent mainly composed of a mixed solvent with a certain non-aqueous solvent (hereinafter, referred to as a second solvent).
[0065]
As the second solvent, for example, chain carbon is preferable. Among them, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methyl propionate, γ-butyrolactone (BL), acetonitrile ( AN), ethyl acetate (EA), toluene, xylene or methyl acetate (MA). These second solvents can be used alone or in the form of a mixture of two or more.
[0066]
The viscosity of the second solvent at 25 ° C. is preferably 28 mp or less. The amount of ethylene carbonate or propylene carbonate in the mixed solvent is preferably 10 to 80% by volume. A more preferred amount of ethylene carbonate or propylene carbonate is 20 to 75% by volume.
[0067]
As the electrolyte contained in the non-aqueous electrolyte, for example, lithium perchlorate (LiClO ₄ ), Lithium hexafluorophosphate (LiPF) ₆ ), Lithium borofluoride (LiBF ₄ ), Lithium arsenic hexafluoride (LiAsF) ₆ ), Lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), Lithium bistrifluoromethylsulfonylimide [LiN (CF ₃ SO ₂ ) ₂ ] And lithium salts (electrolytes). Among them, LiPF ₆ , LiBF ₄ It is preferable to use
[0068]
The amount of the electrolyte dissolved in the nonaqueous solvent is desirably 0.5 to 2.0 mol / 1.
[0069]
【Example】
(Example 1)
<LiCoO ₂ Preparation of Particles>
Co2O3 is mixed with LiOH and heated at 850 (C, 8 hours) in an oxygen stream to obtain an average particle size of 3 (m LiCoO3). ₂ A powder is prepared and this LiCoO ₂ LiCoO by grinding the powder ₂ Particles were prepared.
<Preparation of positive electrode>
Using a 20 μm thick Al foil as the current collector, ₂ To the active material, 5% by weight of acetylene black having an average particle size of 30 nm as a conductive aid and 5% by weight of polyvinylidene fluoride as a binder polymer were added. A slurry was prepared using N-methylpyrrolidone as a solvent, applied on one side of a current collector, and dried. The thickness of the positive electrode after pressing with a roller (250 kg / cm) was adjusted to 100 μm excluding the current collector.
<Preparation of nitrogen-substituted graphite>
Production of graphite in which part of carbon atoms near the surface was replaced with nitrogen was performed using a commercially available CVD apparatus. First, graphite powder having a particle size of about 15 μm was put in a nickel metal container and set in a CVD reactor. After the vessel was heated to 850 (C) in vacuum, acetonitrile at a partial pressure of 5 mTorr was flowed for 5 minutes using argon as a carrier gas, and about 30% of carbon atoms were nitrogen atoms over a thickness of several nm near the particle surface. Replaced.
<Preparation of negative electrode>
A 12 μm thick Cu foil was used as a current collector. As in the case of the positive electrode 1, 5% by weight of acetylene black having an average particle diameter of 30 nm was added to the above-mentioned negative electrode active material as a conductive aid, and 3% by weight of polyvinylidene fluoride was added as a binder polymer. A slurry was prepared using N-methylpyrrolidone as a solvent, coated on one side of a current collector, and dried. The thickness of the negative electrode after pressing with a roller (300 kg / cm) was adjusted to 100 (m) except for the current collector.
<Infiltration of non-aqueous electrolyte and configuration of secondary battery>
First, a coil formed of a porous polyethylene separator having a thickness of 25 μm having an average diameter of 0.1 micron and the above-described positive electrode and negative electrode was set in an aluminum inner container shown in FIG. Was attached. The non-aqueous electrolyte is lithium hexafluorophosphate (LiPF ₆ ) Was dissolved in a mixed solvent of ethylene carbonate / dimethyl carbonate to a concentration of 1 mol / liter. The inner container was set in a stainless steel container to which electrode terminals were attached, dried, and then introduced into an argon dry box. After the inside of the container was evacuated, the above-mentioned non-aqueous electrolyte was injected, and the container was sealed. Subsequently, the container was heated to 50 (C) to infiltrate the nonaqueous electrolyte into the positive and negative electrodes.
[0070]
After the container was returned to room temperature, a charge / discharge cycle was further performed using the electrode terminals of the container. The latter operation is for infiltrating the non-aqueous electrolyte into minute cracks generated by charging and discharging, and is effective in preventing the battery from draining. Subsequently, the inner container sufficiently infiltrated with the non-aqueous electrolyte was taken out of the container, and inserted into a stainless steel outer container. The outer container was further filled with a non-aqueous electrolyte, and then sealed to complete a secondary battery.
<Charging and discharging characteristics>
The battery obtained by the above method has a capacity of 5 mA / cm per unit area of the electrode. ² The battery was charged at a constant current at a current density of 4.2 V until the battery voltage reached 4.2 V, and then charged at a constant voltage at 4.2 V until the current value became 1/20 of the initial value. Thereafter, the direction of the current was reversed, and discharging was performed until the battery voltage became 3 V. When the battery was charged and discharged, it had a high capacity of 1400 mAh or more in terms of a commercially available 18650 type battery. Further, in order to examine the charge / discharge repetition characteristics, the capacity of these secondary batteries after repeating charge / discharge 100 times under the above conditions was measured, and the decrease in capacity was within 3%. Further, it was found that even if charge / discharge was repeated 500 times, the capacity reduction could be suppressed within 15%.
<Chemical stability>
When the concentration of carbon dioxide contained in the electrolyte of the battery which was repeatedly charged and discharged 100 times for the purpose of confirming the reaction between the electrode active material and the nonaqueous electrolyte was measured, the concentration was 10 ppm for any of the above batteries. It was as follows, and it was found that the electrode active material and the electrolyte hardly reacted.
(Comparative Example 1)
Using the electrode formed in the same manner as in Example 1 and the same non-aqueous electrolyte as in Example 1, a battery was formed by a usual method. That is, the coil including the positive electrode, the negative electrode, and the separator was housed in a stainless steel battery container, and the electrolyte was injected at room temperature in an argon dry box and sealed. The initial capacity of this battery is 5 mA / cm in terms of 18650 type. ² Was 1350 mAh. However, the capacity decreased with the charge / discharge cycle, and the capacity after repeating charge / discharge 100 times decreased by 8%. Further, when the charge and discharge were performed 500 times, the capacity reduction became nearly 25%. When the battery was disassembled and examined, it was found that the electrolyte distribution was uneven, and that a liquid withering phenomenon occurred. From this, it was found that the lithium ion secondary battery using the present invention can not only increase the capacity in the initial state, but also reduce the capacity decrease due to repeated charging and discharging.
(Example 2)
In the same manner as in Example 1, a positive electrode and a negative electrode were prepared, the formed coil was set in an inner container, and lead wires were attached. The inner container was set in a stainless steel container to which electrode terminals were attached, dried, and then introduced into an argon dry box. After evacuation of the inside of the container, a non-aqueous electrolyte was injected, and the container was sealed. Subsequently, the container was heated to 80 (C) to infiltrate the nonaqueous electrolyte into the positive and negative electrodes. After the container was returned to room temperature, a charge / discharge cycle was further performed using the electrode terminals of the container. The inner container impregnated with the non-aqueous electrolyte was taken out and inserted into an outer container made of stainless steel, at which time a mechanism for injecting the non-aqueous electrolyte into the outer container was attached. After that, the battery was sealed to complete the secondary battery, and the non-aqueous electrolyte contained lithium hexafluorophosphate (LiPF) as in Example 1. ₆ ) Was dissolved in a mixed solvent of ethylene carbonate / dimethyl carbonate at a concentration of 1 mol / liter. When the initial discharge capacity was examined in the same manner as in Example 1, it was found to be a high capacity of 1400 mAh in terms of a 18650 type battery. When charging and discharging were repeated 500 times, the capacity was reduced to 1200 mAh (14.3%). Therefore, a non-aqueous electrolyte was injected from a non-aqueous electrolyte injection mechanism provided in the outer container. After the charge and discharge were repeated about 10 times, the capacity was examined, and it was found that the capacity had recovered to 1350 mAh. When charge and discharge were repeated 100 more times, the capacity decreased to about 1280 mAh. It has been proved that the capacity decreases when charging and discharging are repeated because the non-aqueous electrolyte solution withers inside the electrode, and the capacity can be recovered by replenishing the non-aqueous electrolyte solution from the outside. I knew I could do it.
(Example 3)
After the same positive electrode and negative electrode as in Example 1 were prepared, a coil was formed using a 25 μm thick porous polyethylene separator having pores with an average diameter of 0.1 μm. At this time, a polyethylene sheet having a hole having an average diameter of 3 μm was wound around the coil between the coil and the inner container to hold the electrolyte. The coil thus prepared was set in an aluminum inner container, and a lead terminal was attached. The inner container was set in a stainless steel container to which electrode terminals were attached, dried, and then introduced into an argon dry box. After evacuation of the inside of the container, a non-aqueous electrolyte was injected, and the container was sealed. Subsequently, the container was heated to 80 (C) to infiltrate the nonaqueous electrolyte into the positive and negative electrodes. After the container was returned to room temperature, a charge / discharge cycle was further performed using the electrode terminals of the container. The inner container impregnated with the non-aqueous electrolyte was taken out of the container, inserted into a stainless steel outer container, and further filled with the non-aqueous electrolyte and sealed to complete the secondary battery. As in the case of Example 1, lithium hexafluorophosphate (LiPF ₆ ) Was dissolved in a mixed solvent of ethylene carbonate / dimethyl carbonate at a concentration of 1 mol / liter. When the initial discharge capacity of the battery thus prepared was examined, it was found to be a high capacity of 1400 mAh. Next, when charging and discharging were repeated 100 times, the capacity was reduced to 1350 mAh (3.57%). Further, when charging and discharging were performed 500 times, it was found that the capacity was reduced to 1250 mAh (10.7%). As a result, it has been found that the capacity reduction can be further reduced as compared with the case of the first embodiment.
(Example 4)
After the same positive electrode and negative electrode as in Example 1 were prepared, a coil was formed using a 25 μm thick porous polyethylene separator having pores with an average diameter of 0.1 μm. At this time, a porous SBR sheet having a thickness of 1 mm was further wound between the coil and the inner container. The coil thus prepared was set in an aluminum inner container, and a lead terminal was attached. The inner container was set in a stainless steel container to which electrode terminals were attached, dried, and then introduced into an argon dry box. After evacuation of the inside of the container, a non-aqueous electrolyte was injected, and the container was sealed. Subsequently, the container was heated to 80 (C) to infiltrate the nonaqueous electrolyte into the positive and negative electrodes. After the container was returned to room temperature, a charge / discharge cycle was further performed using the electrode terminals of the container. The inner container impregnated with the non-aqueous electrolyte was taken out of the container, inserted into a stainless steel outer container, and further filled with the non-aqueous electrolyte and sealed to complete the secondary battery. As in the case of Example 1, lithium hexafluorophosphate (LiPF ₆ ) Was dissolved in a mixed solvent of ethylene carbonate / dimethyl carbonate at a concentration of 1 mol / liter. The resulting battery had a discharge capacity of 1250 mAh. Since a porous SBR sheet was used, the same discharge capacity as in Example 3 was obtained. Further, when a drop test (dropping 10 times from a height of 1.9 m) was performed on this battery, an internal short circuit occurred with a probability of 3/10 in a battery not wound with an SBR sheet, but the SBR sheet was wound. All batteries did not have internal short circuits. This confirmed that the impact resistance was not good.
[0071]
【The invention's effect】
According to the present invention, it is possible to obtain a high-capacity lithium-ion secondary battery having a high capacity and having little capacity deterioration when charge / discharge cycles are repeated.
[0072]
Further, according to the present invention, a highly safe lithium ion secondary battery can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing lithium ion diffusion in an electrode.
FIG. 2 is a schematic view showing an example of a configuration of a lithium ion secondary battery of the first invention.
FIG. 3 2 1 shows an example of a configuration of a lithium ion secondary battery of the invention. Outline Schematic.
FIG. 4 2 3 shows another configuration example of the lithium ion secondary battery of the invention. Outline Schematic.
FIG. 5 2 3 shows another configuration example of the lithium ion secondary battery of the invention. Outline Schematic.
[Explanation of symbols]
1 ... Lid
2. Inner container
3. Electrode group
4: Outer container
31 ... lid
32 ... Inner container
33 ... electrode group
34 ... outer container
35… Container
42 ... Inner container
43 ... Electrode group
44 ... Outer container.

Claims (3)

Non-aqueous electrolysis comprising a lithium salt dissolved in a non-aqueous solvent; an electrode group including a positive electrode, a negative electrode including a material that absorbs and releases lithium ions, and a separator positioned between the positive electrode and the negative electrode. A liquid; an inner container for storing the electrode group and the non-aqueous electrolyte; an outer container for storing the inner container; and at least means for supplying the non-aqueous electrolyte from the outer container to the inner container ,
A lithium ion secondary battery , wherein a material that is more porous and has higher liquid retention properties than the separator is inserted between the inner container and the electrode group . A non-aqueous electrolysis comprising a lithium salt dissolved in a non-aqueous solvent; an electrode group including a positive electrode, a negative electrode including a material capable of inserting and extracting lithium ions, and a separator positioned between the positive electrode and the negative electrode. A liquid container; an inner container for storing the electrode group and the non-aqueous electrolyte; an outer container for storing the inner container; and a shock absorber inserted between the inner container and the outer container. Lithium ion secondary battery. 3. The lithium ion secondary battery according to claim 2, wherein the shock absorbing material is a substance exhibiting flame retardancy or fire extinguishing action.

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